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Article

5-Fluoro-1-Methyl-Pyrazol-4-yl-Substituted Nitronyl Nitroxide Radical and Its 3d Metal Complexes: Synthesis, Structure, and Magnetic Properties

by
Ekaterina Kudryavtseva
1,
Andrey Serykh
1,2,
Bogdan Ugrak
1,
Tatyana Dutova
1,
Darina Nasyrova
1,
Dmitrii Aleshin
3,
Nikolay Efimov
3,
Pavel Dorovatovskii
4,
Artem Bogomyakov
5,
Sergey Fokin
5,
Galina Romanenko
5,
Anna Sergeeva
1 and
Evgeny Tretyakov
1,*
1
N. D. Zelinsky Institute of Organic Chemistry, Leninsky Avenue 47, Moscow 119991, Russia
2
D. Mendeleev University of Chemical Technology of Russia, Miusskaya Pl., 9, Moscow 125047, Russia
3
N. S. Kurnakov Institute of General and Inorganic Chemistry, Leninsky Avenue 31, Moscow 119991, Russia
4
NRC Kurchatov Institute, Akademika Kurchatova Pl. 1, Moscow 123182, Russia
5
International Tomography Center, Siberian Branch of Russian Academy of Sciences, Institutskaya Str. 3a, Novosibirsk 630090, Russia
*
Author to whom correspondence should be addressed.
Crystals 2023, 13(12), 1655; https://doi.org/10.3390/cryst13121655
Submission received: 25 October 2023 / Revised: 24 November 2023 / Accepted: 28 November 2023 / Published: 30 November 2023
(This article belongs to the Section Hybrid and Composite Crystalline Materials)
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Versions Notes

Abstract

:
The metal–radical approach is a well-established synthetic way toward multi-spin systems that relies on the coordination of stable radical ligands with transition metal ions. The advantage offered by the use of paramagnetic ligands is that metal–radical magnetic exchange coupling is direct between the magnetic orbitals of the radical and metal ion. With the aim of further exploring this approach, crystals of four heterspin complexes, [M(hfac)2LF]2 {M = Mn, Co, or Ni and hfac = hexafluoroacetylacetonate} and [Cu(hfac)2LF]n, were obtained using a new fluorinated pyrazolyl-substituted nitronyl nitroxide radical, 4,4,5,5-tetramethyl-2-(5-fluoro-1-methyl-1H-pyrazol-4-yl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (LF) as a ligand. The newly synthesized complexes were fully characterized, including X-ray crystallography and magnetometry. XRD analysis revealed that complexes [M(hfac)2LF]2 have similar dimer structures in which a metal ion is in a six-coordinated environment with four O atoms from the two hfac ligands, one radical O atom, and one pyrazole N atom from ligand LF. Nonetheless, the packing patterns of the complexes were found to be considerably different. In [Mn(hfac)2LF]2, there are no magnetically important short contacts between manganese dimers. By contrast, in [Co(hfac)2LF]2 and [Ni(hfac)2LF]2, there are short contacts between non-coordinate O atoms of nitronyl nitroxide moieties. Magnetic behaviors of [M(hfac)2LF]2 showed that the M ions and the directly coordinated radicals are strongly antiferromagnetically coupled (JMn-ON = −84.1 ± 1.5 cm−1, JCo-ON = −134.3 ± 2.6 cm−1, and JNi-ON = −276.2 ± 2.1 cm−1; H ^ = − 2 J S ⃑ ^ M S ⃑ ^ N O ). Notably, the magnetization of [Mn(hfac)2LF]2 having molecular structure proved to be accompanied by hysteresis. The [Cu(hfac)2LF]n complex has a chain-polymer structure with alternating magnetic fragments: three spin exchange clusters {ONO–Cu(II)–ONO} and {Cu(II)} ions. Despite the direct coordination of radicals, its magnetic properties are weakly ferromagnetic (JCu-ON = 14.8 ± 0.3 cm−1).

1. Introduction

Lately, nitronyl nitroxide radicals have been reported to be promising ligands for the construction of molecular-based magnetic materials for potential applications in memory devices, sensors, detectors, actuators, or energy conversion. In addition, these metal-radical systems provide a nice opportunity for studying the role of interactions governing intramolecular electron transfer [1,2,3,4,5,6]. The simplicity of the functionalization of nitronyl nitroxides gives versatility to the development of diverse attractive heterospin complexes [7,8,9,10,11]. These heterospin systems possess uncommon magnetic properties and provide additional opportunities for control over the magnetic behavior of the complexes, and this control is crucial for the design of innovative materials. Moreover, discrete complexes having definite geometry built from paramagnetic metal ions and nitronyl nitroxide radical ligands are appealing candidates for basic investigation on magnetostructural correlations [12,13]. During systematic studies, many metal complexes with nitronyl nitroxide ligands manifesting diverse topological structures, photomagnetic and magnetic properties have been obtained [14,15,16,17,18]. A class of molecular magnets based on metal–nitroxide coordination compounds has been constructed, for instance, cobalt–radical coordination magnets with high coercivity blocking temperatures [19,20,21]. It has been demonstrated that transitions in Cu(II) complexes with nitronyl nitroxides are initiated by temperature changes and via irradiation; photoswitching between low-temperature and high-temperature magnetic states is extremely rapid, occurring within a nanosecond [22,23]. Among complexes of transition metal ions with nitroxides, the highest temperatures of magnetic ordering have been achieved in coordination compounds between Mn(II) and deprotonated benzimidazol-2-yl–substituted nitronyl nitroxides, and in this field, further research is needed to design new paramagnetic ligands for obtaining molecular magnets featuring high TC [24,25]. So far, various nitronyl nitroxides have been created to construct heterospin molecule-based magnetic systems, but a comprehensive series of paramagnetic metal ions’ complexes with fluorinated radicals has not been investigated. Naturally, it is to be expected that the introduction of fluorine into metal–radical systems can have a major effect on their packing in crystals, thus altering intermolecular exchange interaction channels and ultimately the parameters of magnetic materials [26,27,28,29,30,31].
In the last decade, we have focused on pyrazole derivatives because of their interesting coordination chemistry, in particular pyrazol-4-yl–substituted nitroxides, which have given rise to a large family of metal–nitroxide systems with intriguing magnetic properties [32]. To shed light on the influence of a fluorine atom on the magnetism of these magnetic systems, we have initiated research on different complexes of paramagnetic metal ions with fluorinated pyrazolyl-substituted nitronyl nitroxides [33,34]. In this article, we report the synthesis and structure of a novel radical, 4,4,5,5-tetramethyl-2-(5-fluoro-1-methyl-1H-pyrazol-4-yl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (LF). In addition, we describe the synthesis of three four-spin cyclic dimeric [M(hfac)2LF]2 complexes with quadrangle geometry (M = Mn, Co, and Ni) and a [Cu(hfac)2LF]n complex with chain-polymeric structure, their crystal structures, and their magnetic properties. Crystals 13 01655 i001

2. Materials and Methods

2.1. Materials and Spectral Measurements

Multistep synthesis of 5-fluoro-1-methyl-1H-pyrazole-4-carbaldehyde (1) will be reported elsewhere (NMR spectra of this aldehyde are given in Supplementary Materials). N,N′-(2,3-dimethylbutane-2,3-diyl)bis(hydroxylamine) was synthesized by a known method [35]. Complexes Mn(hfac)2·3H2O, Co(hfac)2·xH2O, Ni(hfac)2·xH2O and Cu(hfac)2 were prepared as previously reported [36,37,38]. Toluene was distilled under an argon stream and kept in an argon atmosphere.
High-resolution mass spectra were registered on a Bruker micrOTOF II instrument (Bruker Corporation, Billerica, MA, USA) in positive ion electrospray ionization mode. NMR spectra were recorded on Bruker AC-200 or Bruker AV300 spectrometers (Bruker Corporation, Billerica, MA, USA); 1H spectra, 13C spectra with Me4Si as an internal reference, and 19F spectra with CFCl3 as an internal reference were acquired. Fourier transform infrared (FTIR) spectra were registered on a BRUKER Vertex-70 FTIR spectrometer (Bruker Corporation, Billerica, MA, USA). EPR spectrum was acquired in a diluted oxygen-free toluene solution at 295 K at concentrations of ~10−5 M by means of a Jeol JES-FA200 X-band spectrometer (Akishima, Tokyo, Japan) equipped with a TE011 cylindrical resonator having a resonance frequency of 9.4 MHz; isotropic g-factor values were measured experimentally using MgO doped with Mn(II) ions as a standard placed in the resonator simultaneously with the sample solution. Elemental analyses were performed using a Euro EA 3000 elemental analyzer.

2.2. Preparation of Paramagnetic Ligand LF (the Synthetic Procedure Is Similar to That Described Earlier) [33]

2-(5-Fluoro-1-methyl-1H-pyrazol-4-yl)-4,4,5,5-tetramethylimidazolidine-1,3-diol (2). Yield 80%, colorless crystals, mp 120.8–121.2 °С. 1H NMR, δ: 1.05 (s, 12 H, Me), 3.68 (s, 3 H, N-Me), 4.51 (s, 1 H, H-2), 7.31 (d, 1 H, J = 3.07 Hz, H-3′), 7.73 (s, 2 H, N-OH). 13C NMR, δ: 17.30 (s, Me), 23.43 (s, Me), 33.69 (s, N-Me), 65.77 (s, C-4 and C-5), 81.37 (d, J = 4.6 Hz, C-2), 101.04 (d, J = 9.9 Hz, C-4′), 138.07 (d, J = 10.1 Hz, C-3′), 151.44 (d, J = 275.6 Hz, C-5′). 19F NMR, δ: –139.08 (s, 1 F). IR (KBr) ṽmax, cm−1: 3207, 3017, 2983, 2929, 2901, 2863, 2620, 2388, 2351, 2280, 2196, 2058, 1725, 1620, 1542, 1478, 1439, 1414, 1395, 1380, 1361, 1321, 1287, 1265, 1243, 1224, 1203, 1192, 1164, 1138, 1067, 1024, 1000, 948, 917, 860, 829, 804, 762, 735, 700, 680, 657, 638, 601, 577, 537, 515, 503, 429. HRMS calculated for C11H20FN4O2+ 259.1565 [M+H]+, found 259.1526; HRMS calculated for C11H19FN4NaO2+ 281.1384 [M+Na]+, found 281.1341. Anal. calcd. for C11H19FN4O2: C, 51.15; H, 7.41; N, 21.69. Found: C, 51.38; H, 7.36; N, 21.43%.
4,4,5,5-Tetramethyl-2-(5-fluoro-1-methyl-1H-pyrazol-4-yl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (LF). Yield 93%, blue powder, mp 106–107 °С, Rf = 0.45 (ethyl acetate). IR (KBr) ṽmax, cm−1: 3454, 3146, 3044, 2998, 2934, 2361, 2341, 1726, 1621, 1540, 1509, 1490, 1453, 1435, 1415, 1396, 1365, 1320, 1308, 1283, 1225, 1186, 1164, 1143, 1069, 992, 862, 828, 765, 748, 727, 699, 671, 640, 608, 541, 529, 458. ESR (toluene): g = 2.0067, aN (2N) = 0.727 mT, aH (12H) = 0.020 mT. HRMS calculated for C11H17FN4O2+ 256.1330 [M+H]+, found 256.1338; HRMS calculated for C11H16FN4NaO2+ 278.1150 [M+Na]+, found 278.1161. Anal. calcd. for C11H16FN4O2 (%): C, 51.76; H, 6.32; N, 21.95. Found (%): C, 51.52; H, 6.30; N, 21.72. Crystals suitable for XRD analysis were grown from a mixture of acetone and water.

2.3. Preparation of Complexes

[Mn(hfac)2LF]2. A solution of 42 mg (0.08 mmol) of Mn(hfac)2·3H2O in 5 mL of dry toluene was heated under reflux for 40 min. After that, the solution was cooled to room temperature, and 21.6 mg (0.08 mmol) of LF dissolved in 1 mL of toluene was added. The reaction mixture was allowed to stand at −15 °C for several days to obtain dark-blue blocks of crystals. They were filtered off, washed with hexane, and air dried, thus giving 45.6 mg of the title product (75.7% based on the Mn ion). IR (KBr, cm–1): 3158(w), 3003(w), 2959(w), 1645(s), 1597(w), 1556(s), 1529(s), 1483(s), 1458(sh), 1443(sh), 1404(m), 1376(s), 1315(m), 1255(s), 1202(s), 1144(s), 1097(m), 1015(m), 948(w), 897(w), 872(m), 827(m), 798(s), 766(m), 741(w), 687(m), 664(s), 643(w), 620(w), 583(s), 539(m), 460(w). Anal. calcd. for C42H36F26Mn2N8O12 (%): C, 34.82; H, 2.50; N, 7.74. Found (%): C, 34.5; H, 2.30; N, 8.02%.
[Co(hfac)2LF]2. A solution of 50.1 mg (0.1 mmol) of Co(hfac)2·xH2O in 5 mL of dry toluene was heated under reflux for 30 min. After that, the solution was cooled to room temperature, and 25.5 mg LF (0.1 mmol) dissolved in 1 mL of toluene was introduced. The resulting mixture was incubated at −15 °C for several days to obtain dark-blue blocks of crystals. They were filtered off, washed with hexane, and air dried, thus giving 45.4 mg of the title product (63.3% based on Co ion). IR (KBr, cm–1): 3158(w), 2999(w), 2948(w), 1644(s), 1590(w), 1555(s), 1526(s), 1495(s), 1462(sh), 1445(sh), 1398(sh), 1373(sh), 1346(s), 1259(s), 1209(s), 1144(s), 1099(m), 1021(m), 971(w), 948(w), 886(w), 868(m), 830(m), 809(w), 793(s), 763(m), 742(w), 690(m), 668(s), 632(w), 616(w), 586(m), 542(m), 468(w). Anal. calcd. for C42H36F26Co2N8O12 (%): C, 34.63; H, 2.49; N, 7.69. Found (%): C, 34.12; H, 2.51; N, 7.81.
[Ni(hfac)2LF]2. A solution of 42 mg (0.08 mmol) of Ni(hfac)2·xH2O in 5 mL of dry toluene was heated under reflux for 30 min. Next, the solution was cooled to room temperature, and 22 mg of LF (0.09 mmol) dissolved in 1 mL of toluene was added. The resultant mixture was allowed to stand at –15 °C for several days, thereby affording dark-blue blocks of crystals. They were filtered off, washed with hexane, and dried in air. Yield 49.8 mg (82.9% based on Ni ion). IR (KBr, cm–1): 3152(w), 3001(w), 2949(w), 1647(s), 1598(w), 1557(s), 1528(s), 1481(s), 1457(sh), 1401(m), 1372(s), 1351(m), 1319(m), 1258(s), 1208(s), 1146(s), 1101(m), 1026(m), 950(w), 867(m), 830(m), 796(s), 765(m), 743(w), 673(s), 640(w), 587(s), 542(m), 465(w). Anal. calcd. for C21H18F13NiN4O6 (%): C, 34.64; H, 2.49; N, 7.70. Found (%): C, 34.81; H, 2.65; N, 7.94.
[Cu(hfac)2LF]n. A mixture of Cu(hfac)2 (46.8 mg, 0.1 mmol) and LF (25 mg, 0.1 mmol) was dissolved in 1 mL of Et2O and then 4 mL of hexane was added. The reaction mixture was kept at room temperature for 10 min, after which it was cooled to −18 °C. The dark brown crystalline aggregates that formed after ~72 h were filtered off, washed with cold hexane, and dried in air. Yield 66 mg (92%). IR (KBr, cm–1): 3139(w), 3006(w), 1642(s), 1598(w), 1557(s), 1527(s), 1486(s), 1437(sh), 1399(m), 1372(s), 1353(m), 1317(m), 1261(s), 1208(s), 1149(s), 1107(m), 1001(m), 869(m), 815(m), 798(s), 763(m), 746(w), 681(s), 596(s), 530(m), 456(w). Anal. calcd. for C21H18CuF13N4O6 (%): C, 34.4; H, 2.5; F, 33.7; N, 7.6. Found (%): C, 34.9; H, 2.8; F, 32.9; N, 7.2.

2.4. X-ray Crystallographic Data and Refinement Details

XRD data for single crystals of LF, [Mn(hfac)2LF]2, [Co(hfac)2LF]2, and [Ni(hfac)2LF] were collected at 100 K on a four-circle Rigaku Synergy S diffractometer equipped with a HyPix600HE area detector using graphite monochromatized Cu Kα-radiation. The intensity data were integrated and corrected for absorption and decay by means of the CrysAlisPro software (Version 1.171.41.106) [39]. The structures were solved by direct methods in SHELXT [40] and refined on F2 using SHELXL-2018 [41] in the OLEX2 software (Windows 2000/XP/Vista) [42]. All nonhydrogen atoms were refined with individual anisotropic displacement parameters. All hydrogen atoms were placed in ideal calculated positions and refined as riding atoms with relative isotropic displacement parameters. A rotating group model was applied to methyl groups.
X-ray diffraction data for single crystals of [Mn(hfac)2LF]2 and [Cu(hfac)2LF]n were collected at 296 K on a three-circle Bruker Smart diffractometer equipped with Apex II area detector using graphite monochromatized Mo Kα-radiation. The intensity data were integrated and corrected for absorption by the SADABS program [43]. The structure was solved by direct methods using SHELXT [40] and refined on F2 using SHELXL-2018 [41] program. All non-hydrogen atoms were refined in anisotropic approximation; the positions of hydrogen atoms were calculated geometrically and included in the refinement as riding groups with relative isotropic displacement parameters.
Detailed data collection and refinement of the compounds are summarized in Table S1 (Supplementary Materials). CCDC 2289354–2289357, 2296169, and 2302426 contain the supplementary crystallographic data for LF, [Mn(hfac)2LF]2, [Co(hfac)2LF]2, [Ni(hfac)2LF]2, and [Cu(hfac)2LF]n. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html (accessed on 1 November 2023) (or from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: +44-1223-336033; E-mail: [email protected]).

2.5. Powder XRD Data

PXRD data were collected on a PowDix 600 (ADANI) diffractometer equipped with a MYTHEN2 R 1D (Dectris) detector at room temperature using Cu Kα radiation at a scanning speed on θ of 0.01 °/s. The samples were placed in an aluminum sample holder. The experimental powder X-ray diffraction pattern agrees with the simulated one from the structures solved by single-crystal XRD data, indicating good crystal phase purity (Supplementary Materials).

2.6. Magnetic Measurements

The magnetic susceptibility of the polycrystalline samples was measured with a Quantum Design PPMS-9 magnetometer in the temperature range of 2–300 K with magnetic field of up to 5 kOe. The measurements were performed on polycrystalline samples placed in polyethylene bags. The magnetic data were corrected for the sample holder and the diamagnetic contribution. Analysis of the experimental magnetic data was performed using PHI program [44].

3. Results and Discussion

3.1. Synthesis and Structure of the Organic Radical LF

The route proposed by Ullman and coworkers was used for the preparation of LF (Scheme 1) [45]. On the first stage, 5-fluoro-1-methyl-1H-pyrazole-4-carbaldehyde (1) was condensed with N,N′-(2,3-dimethylbutane-2,3-diyl)bis(hydroxylamine), which led to the formation of the corresponding 4,4,5,5-tetramethylimidazolidine-1,3-diol 2. The latter was next oxidized by manganese dioxide in methanol to form the nitronyl nitroxide derivative LF. The diamagnetic precursor 2 and radical LF were characterized by analytical and various spectroscopic (UV–Vis, FT-IR, 1H and 13C NMR, EPR, and mass) methods.
Attempts to crystallize nitronyl nitroxide LF from a mixture of benzene with hexane, in which a similar radical—LH (ref. [46], CSD refcode: BEMVOF) containing no fluorine atom—gave well-formed crystals, were unsuccessful; paramagnet LF precipitated into the solid phase in the form of solid amorphous droplets. The use of other mixtures of solvents (methylene chloride with heptane or acetone with heptane) led to similar results. Well-shaped crystals of LF suitable for XRD were obtained by crystallization from a mixture of acetone and water. It was revealed that compound LF crystallizes in monoclinic space group P21/c, and the unit cell contains two independent molecules as well as solvate molecules of water (Figure 1). In two independent molecules (A and B), N–O bond lengths range from 1.279(2) to 1.285(2) Å (Table S1), which are typical for nitronyl nitroxides [47]. The dihedral angles between the mean planes of the pyrazole ring and ONCNO moiety are 8.99° and 10.46°, which is slightly greater than that in LH (3.44°). The solvate molecule of water forms two H-bonds with oxygen atoms of the two independent molecules {d(OH⋯ONO) = 2.916 Å, ∠(O–H⋯ONO) = 163°; d(OH⋯ONO) = 2.847 Å, ∠(O–H⋯ONO) = 168°} thereby affording a cluster {LF⋯HOH⋯ LF}. In addition, the cluster is stabilized by short contacts C–H⋯OH2O (2.539 Å) and C–H⋯F (2.604 Å).
The {LFHOH⋯LF} clusters form centrosymmetric dimers {LF⋯HOH⋯LF}2 via two short contacts C–H⋯ONO (2.640 Å) and two short contacts C–H⋯NPz (2.696 Å) (Figure 2). Furthermore, the dimers are stabilized by π–π interactions of aromatic pyrazole systems. The interaction is characterized by a short distance between the centroids of the pyrazole rings (3.401 Å) and short C⋯C contacts (3.352, 3.340, and 3.130 Å). In turn, the dimers are linked into a column via short contacts C–H⋯ONO (2.344 and 2.514 Å) and short contacts C–H⋯NPz (2.570 and 2.651 Å) (Figure S1, Supporting Information). The columns are bound via a set of short contacts C–H⋯ONO and C–H⋯OH2O resulting in the final crystal structure (Figures S2 and S3). From the magnetic point of view, the shortest ONO⋯ONO distances were found to be 4.041 Å inside the dimers and 4.837 Å between nitroxides belonging to adjacent dimers. Additionally, there is a set of hydrogen bonds between the nitroxide O atoms and H atoms of the methyl groups attached to the imidazolyl ring.
Thus, in the case of nonfluorinated nitronyl nitroxide LH, the molecules are packed in a way common for nitronyl nitroxide owing to the most energetically favorable van der Waals interactions of the C–H⋯ONO type, whereas in fluorinated derivative LF, the possibility of additional intermolecular interactions with the participation of a fluorine atom serves as a factor preventing crystallization. Therefore, in the case of nitronyl nitroxide LF, for the formation of a crystal lattice, the participation of additional water molecules is required.

3.2. Synthesis and Structures of Complexes

The interaction of metal hexafluoroacetylacetonates [M(hfac)2] (M = Mn, Co, Ni) with nitronyl nitroxide LF in dry toluene at −15 °C at a 1:1 ratio of the reagents resulted in reproducible synthesis of the polycrystalline phases, whose composition corresponded to the formula [M(hfac)2LF] according to the elemental-analysis data. FT-IR spectra of the complexes showed strong bands in the region 1140–1260 cm–1 due to the presence of hfac-anions. The bands inherent to the paramagnetic ligand LF remained virtually unchanged, with the exception of an absorption band due to vibrations of the N–O group, the intensity of which increased significantly in the Mn, Co, and Ni complexes to give a strong band in the range of 1470–1490 cm−1 (see Supplementary Materials).
XRD analysis revealed that complexes have similar dimer structures [M(hfac)2LF]2 in which a metal ion is in a six-coordinated environment with four O atoms from the two hfac ligands, one radical O atom, and one pyrazole N atom from ligand LF. Figure 3 shows the structure of [Co(hfac)2LF]2 as an example. Selected bond distances, bond angles, and contacts are summarized in Table 1 and Tables S4–S7 (Supplementary Materials).
The structure of [Mn(hfac)2LF]2 results from bridging bidentate ligand coordination via the nitroxide O atom and the N atom of the pyrazole ring. Mn–ONO bond length is 2.126(2) Å, and Mn–N bond length is 2.273(2) Å, which are comparable to those observed in previously reported cyclic manganese–nitroxide dimers [48,49,50]. In the coordinated nitroxide group, the bond length is slightly greater [1.303(3) Å] as compared with the noncoordinated one [1.270(3) Å]. The pyrazole ring is twisted out of the plane of the nitronyl nitroxide moiety with a dihedral angle of ~25.7°. The Mn···Mn distance within the dimer is 6.314 Å, and such interdimer distances exceed 10 Å. Fragments of the crystal structure of [Mn(hfac)2LF]2 are shown in Figures S4–S6. There are short contacts between the O atoms of nitronyl nitroxide (ONO) moieties and H atoms of the N-methyl groups (ONO…H is less than 2.6 Å), between F atoms of the hfac ligands (F⋯F distances are <3 Å), and between F atoms of the hfac ligands and H atoms of the methyl groups of the radical moieties (Figure S6). The packing peculiarity gives no short contacts; ONO⋯ONO exceed 5.5 Å. It is interesting that they become longer when the temperature decreases (5.547(9) Å at room temperature and 5.922(3) at 100 K).
In the [Co(hfac)2LF]2 dimer, which crystallizes in the triclinic P-1 space group, the Co–ONO bond length is 2.032(2) Å, and the Co–N bond length is 2.150(2) Å, which are comparable to those observed in previously described cyclic cobalt–nitroxide cyclic dimers [51,52,53]. In the coordinated nitroxide group, the bond length is slightly greater [1.308(2) Å] as compared with the noncoordinated one [1.266(3) Å]. The pyrazole ring is twisted out of the plane of the nitronyl nitroxide moiety with a dihedral angle of ~38.5°. The Co···Co distance within the dimer is 6.130 Å, which is shorter than the shortest interdimer Co···Co distance of 8.893 Å. Fragments of the crystal structure of [Co(hfac)2LF]2 are shown in Figures S7–S9. It should be noted that in this case, the O atoms of nitronyl nitroxide moieties come into short contact with the H atoms of the methyl groups of the imidazoline moieties (2.603 and 2.656 Å), which may be important magnetically.
Such [Ni(hfac)2LF]2 cyclic dimers, in which a nitronyl nitroxide behaves as a bridging ligand, are rare. Previously, only one such example was described, obtained by the interaction of a [Ni(hfac)2] matrix with 2-(1,5-dimethylpyrazol-4-yl)-4,4,5,5-tetramethyl-2-imidazoline-3-oxide1-oxyl (LMe) [54,55]. In [Ni(hfac)2LF]2, Ni–ONO bond length is 2.034(3) Å, and Mn–N bond length is 2.096(3) Å. In the coordinated nitroxide group, the bond length is also slightly greater [1.302(5) Å] as compared with the noncoordinated one [1.276(6) Å]. The pyrazole ring is twisted out of the plane of the nitronyl nitroxide moiety with a dihedral angle of ~37.8°. The Ni···Ni distance within the dimer is 6.160 Å, and this kind of interdimer distance is 9.478 Å. Fragments of the crystal structure of [Ni(hfac)2LF]2 are shown in Figures S10–S12. From a magnetic standpoint, the shortest interdimer contacts (2.588 Å) between the O atoms of the nitronyl nitroxide moieties and the H atoms of the paramagnetic moieties are important. The ONO⋯ONO distances in this complex are the shortest from [M(hfac)2LF]2 dimers—3.407(6) Å.
The copper complex was obtained by the interaction of Cu(hfac)2 and LF in an ether-hexane mixture as solvent, with subsequent cooling of the reaction mixture to −18 °C. The product was initially formed as a brown resin, which crystallized after a few days. Prolonged exposure to the solution at room temperature led to the decomposition of the product. In contrast to Mn, Co, and Ni complexes, the copper complex has a polymer chain structure [Cu(hfac)2LF)]n with a “head-to-head” motif (Figure 4) resulting from the bridging coordination of LF, with the centrosymmetric coordination of the Cu(II) atom in the Cu(hfac)2 matrices complemented to octahedral by two NPz atoms of the pyrazole rings ([CuO4N2] coordination unit) or by two ONO atoms of the nitroxide groups ([CuO6] coordination unit). Bond distances Cu–ONO and Cu–N in the units [CuO6] and [CuO4N2] are 2.448(2) and 2.469(2) Å, respectively. The angle CuON is equal 131.95(17)°, ONO⋯ONO distance—4.163(7) Å. Early, it was shown that interaction of Cu(hfac)2 with non-fluorinated LH led to a family of complexes with different composition and structure [46], including two chain polymers with the “head-to-head” motif, polymorphs α-[Cu(hfac)2LH)]n and β-[Cu(hfac)2LH)]n. For comparison, Cu–ONO distances are 2.395 and 2.459 Å, and CuON angles are 131.3°and 140.6°, respectively. Note that the α-[Cu(hfac)2LH)]n polymorph is a metastable phase formed uncontrollably and unreproducibly, and the synthesis of β-[Cu(hfac)2LH)]n polymorph is reproducible but accompanied by the formation of a substantial amount of a polymer with the “head-to-tail” motif. Thus, the presence of a fluorine atom in the paramagnetic ligand LF, to some extent, reduces the problem of the stereochemical nonrigidity of the Cu(hfac)2 matrix.

3.3. Magnetochemical Characterization

The temperature dependence of the magnetic susceptibility of all complexes was measured in the temperature range of 1.8 to 300 K. Figure 5 shows the variation of χM and χMT with temperature for complex [Mn(hfac)2LF]2, where χM is molar magnetic susceptibility and T is absolute temperature. χMT at 300 K is 6.51 cm3·K·mol–1, which is far lower than the spin-only value of 9.50 cm3·K·mol–1 for two nitroxide groups (S = 1/2) and two uncoupled Mn(II) ions (S = 5/2) but is close to the spin-only value (6.00 cm3·K·mol−1) expected for two uncorrelated spin systems with S = 2 and g = 2.00. With a decrease in temperature, χMT diminishes, reaching a plateau at ~6.0 cm3·K·mol–1, and below 25 K, χMT declines rapidly on further cooling.
According to the magnetic measurement data, there are mainly two kinds of magnetic interactions in [Mn(hfac)2LF]2, i.e., the strong antiferromagnetic interaction between the Mn(II) ion and the directly coordinated nitronyl nitroxide moiety, and a weaker magnetic coupling between the Mn(II) ion and a nitroxide group through the pyrazole ring. A tetramer model (spin Hamiltonian H = −2J1·(SMn1SR1 + SMn2SR2) − 2J2·(SMn1SR2 + SMn2SR1)) was used for analysis of the experimental χMT(T) dependence, taking into account intermolecular exchange interactions zJ′. The best fit values of g-factor and exchange interaction parameters are g = 1.97 ± 0.01, J1 = −84.1 ± 1.5 cm−1, J2 = −1.62 ± 0.05 cm−1, and zJ′ = −0.12 ± 0.01 cm−1. The large negative J value is in good agreement with such data reported in the literature [56,57,58,59]. The strong antiferromagnetic interaction is due to an effective overlap between the π-SOMO containing the unpaired electrons of ligand LF and the d orbitals of the Mn(II) ion [60,61]. A very weak intermolecular antiferromagnetic interaction exists at low temperatures, as indicated by negative zJ′.
Field-dependent magnetization of [Mn(hfac)2LF]2 was measured at 2.0 K in the range of −50 to 50 kOe (Figure 6). One can see that the M value gradually changes upon variation of the applied magnetic field and reaches |M| = ~6.6 μB for two {Mn-ON} clusters, which is also in agreement with the finding that two separate {Mn-ON} clusters possess the S = 2 ground state. It is noteworthy that the magnetization of [Mn(hfac)2LF]2 having molecular structure was found to be accompanied by hysteresis, probably due to interactions of the magnetic moments of neighboring molecules. To the best of our knowledge, earlier, such hysteretic behavior was reported only for high-dimensional manganese–radical systems [13,16].
Magnetic susceptibility data on [Co(hfac)2LF]2 as “χMT versus T” plot are displayed in Figure 7. At room temperature, χMT is ~4.75 cm3·K·mol−1 [calculated for two Co(II) ions and two radicals LF]. On cooling, χMT decreases steadily, and at temperatures below 50 K, it drops rapidly. The level of the plateau is close to 3.8 cm3·K·mol−1, which is consistent with a strong antiferromagnetic coupling between spin S = 3/2 of the cobalt ion and spin S = 1/2 of the nitronyl nitroxide moiety, as expected in this type of complex.
A strict analysis of the magnetic data from the [Co(hfac)2LF]2 complex needs to take into account the effects of spin–orbit coupling and zero-field splitting [62]. For [Co(hfac)2LF]2, there are at least two types of spin–spin exchange between the paramagnetic ligands and Co(II) ions: one through the direct bonding of the O atoms of nitronyl nitroxides and Co(II) ions, and the other through the pyrazole ring via the spin-polarization mechanism. In addition, the nitronyl nitroxide’s O atoms form short intermolecular contacts with the H atoms of the methyl groups of the imidazoline moieties. Furthermore, low-temperature magnetic behavior was harder to analyze because octahedral Co(II) energy levels become mostly depopulated until, ultimately, a single Kramers doublet is occupied. At this extreme, antiferromagnetic coupling inside [Co(hfac)2LF]2 may cause the diamagnetic ground state. Such an effect must also contribute to the decrease of χMT at low temperatures. A tetramer model (spin Hamiltonian H = −2J1·(SCo1SR1 + SCo2SR2) − 2J2·(SCo1SR2 + SCo2SR1) − D·S2zCo1 − D·S2zCo2, where D denotes the zero-field splitting parameter for the Co(II) ions) was used for analysis of the experimental χMT(T) dependence, taking into account intermolecular exchange interactions zJ’. The best fit values of parameters are: g = 3.37 ± 0.03, J1 = −134.3 ± 2.6 cm−1, J2 = 0 cm−1 (fixed to avoid overparametrization), D = 20.2 ± 0.5, and zJ’ = −1.2 ± 0.1 cm−1.
The magnetization of [Co(hfac)2LF]2 was measured at 2.0, 4.0, and 6.0 K (Figure 8) and reached only 0.63 μB at 70 kOe, far from being saturated. The results, including the χMT value observed at room temperature and the low M value at 70 kOe, pointed to substantial antiferromagnetic interactions between the Co(II) ion and ligand LF, consistent with the reported Co–nitroxide systems [63,64].
The magnetic behavior of the [Ni(hfac)2LF]2 complex in the form of “χMT versus T” plot is depicted in Figure 9. The value of χMT at 300 K is 1.28 cm3·K·mol−1, much smaller than the expected value (3.17 cm3·K·mol−1) for four uncorrelated spins of two high-spin Ni(II) ions (S = 1) with g = 2.2 and two nitroxide spins (S = 1/2). Moreover, when the temperature is reduced, χMT decreases, reaching a plateau at ~1.01 cm3·K·mol−1, and at temperatures below 25 K, it drops rapidly. Such behavior is indicative of a strong antiferromagnetic Ni(II)-nitroxide interaction. The plateau reached below 150 K is a signature of two spins S = 1/2 resulting from the antiferromagnetic interaction in two {Ni(hfac)2LF} spin clusters. These magnetic data were analyzed using a tetramer model (spin Hamiltonian H = −2J1·(SNi1SR1 + SNi2SR2) – 2J2·(SNi1SR2 + SNi2SR1)), taking into account intermolecular exchange interactions zJ’. The best fit values of g-factor and exchange interaction parameters are g = 2.63 ± 0.01, J1 = −276.2 ± 2.1 cm−1, J2 = 1.61 ± 0.04 cm−1, and zJ’ = −0.49 ± 0.02 cm−1. As expected, very strong antiferromagnetic exchange interactions were found in {Ni(hfac)2LF} spin clusters, and this finding is explained by a favorable overlap between the magnetic orbitals of Ni(II) and of the nitronyl nitroxide. The large negative value of J indicates the strong antiferromagnetic interaction between the spins of the Ni(II) ion and the unpaired electron of the nitronyl nitroxide moiety. The J value lies in the range of similar reported complexes [55].
The magnetic behavior of the [Cu(hfac)2LF]n complex in the form of “χMT versus T” plot is depicted in Figure 10. χMT at 300 K is 0.81 cm3·K·mol–1, and close to the expected value of 0.81 cm3·K·mol–1 for two paramagnetic centers—one Cu(II) ion (S = 1/2) with g ~2.15 and nitroxide (S = 1/2, g = 2). χMT increases with lowering temperature to 0.96 cm3·K·mol−1 at 17 K, and then sharply decreases to 0.53 cm3·K·mol−1 at 2 K. Increasing of χMT with lowering temperature is indicative of ferromagnetic exchange interactions between spins of Cu(II) ions and axially coordinated nitroxides in [CuO6] coordination units. These magnetic data were analyzed using the trimer model (spin Hamiltonian H = −2J·(SCuSR1 + SCuSR2) for three-spin exchange clusters and the Curie law for Cu(II) ions of [CuO4N2] coordination units, taking into account intermolecular exchange interactions zJ’. The best fit values of g-factor gCu and exchange interaction parameters are: gCu = 2.10 ± 0.01, J = 14.8 ± 0.3 cm−1, and zJ’ = −0.12 ± 0.01 cm−1. Thus, despite the fact that the values of the Cu–ONO bond length and angle ∠CuON are typical of those in previously studied chain polymer complexes demonstrating a magnetic phase transition with decreasing temperature [34,44], for [Cu(hfac)2LF]n, the phase transition is not observed.
Investigation into metal–nitroxide complexes (where the two or three interacting spin carriers are bonded directly) gives nice examples of a direct exchange. In such systems, the magnetic orbitals are half-occupied orbitals belonging to magnetic centers. For the nitronyl nitroxide, the magnetic orbital is the π* orbital, with its axis being perpendicular to the plane ONCNO [65]; by contrast, the magnetic orbitals of the metal center are the d orbitals that contain only one electron. According to the Kahn–Briat rules [66], the overlap between metal and radical magnetic orbitals causes the emergence of antiferromagnetic interactions.
For the d5 Mn(II) ion, each d orbital should take part in the interaction. Its two magnetic orbitals (dx2−y2, dz2) are orthogonal to the magnetic orbital (π*) of the nitronyl nitroxide and may cause a ferromagnetic interaction, while its magnetic orbitals (one of these: dxy, dyz, and dxz) can overlap with those of the radical, thus causing an antiferromagnetic coupling. The antiferromagnetic coupling observed in [Mn(hfac)2LF]2 may be ascribed to the considerable overlap of the π* magnetic orbital of the equatorial bonded radical with the Mn (II) ion’s magnetic orbital (dyz, dxz).
For the d7 Co(II) ion, such an analysis is problematic owing to spin–orbit coupling. Co2+ possesses three magnetic orbitals (dx2−y2, dz2, and one of these: dxy, dyz, or dxz) [67]. Magnetic coupling J can be written as J = 1/3(Jdx2−y2/π* + Jdz2/π* + Jdxy/π*). The antiferromagnetic coupling registered by us in [Co(hfac)2LF]2 can be explained by the substantial overlap of the π* magnetic orbital of the equatorial bonded radical with the dxy magnetic orbital of Co2+, which can override the ferromagnetic component.
The Ni(II) ion (d8) possesses two magnetic orbitals: dx2−y2 and dz2 [68,69,70]. In complex [Ni(hfac)2LF]2, the conjugated moiety ONCNO is not coplanar with the equatorial plane of the coordination unit; the angle in question is 58°. This large deviation from coplanarity is the cause of the extremely strong nickel–nitroxide antiferromagnetic coupling seen within this compound; the reason is that in the spatial structure, the π* radical orbital is not orthogonal to either the dx2−y2 metal orbital or to the dz2 metal orbital.
Last but not least, the Cu(II) ion has a d9 configuration and is expected to show Jahn-Teller distortion. In complex [Cu(hfac)2LF]n, in the [CuO6] coordination unit, two ONO atoms of the nitroxide groups occupy axial coordination. Such coordination provides the orthogonal arrangement of the spins in the exchange cluster and ferromagnetic exchange interaction with JCu-R values reaching 50 cm−1 [71,72].

4. Conclusions

Thus, investigation of the products of M(hfac)2 (M = Mn, Co, Ni, or Cu) interaction with novel nitronyl nitroxide LF containing a fluorinated pyrazole ring has revealed a family of heterospin complexes with composition 1:1. In all complexes, the radical LF acts as a bridging ligand, connecting two metal ions through the NO unit and pyrazole ring. As a result, a series of cyclic binuclear metal complexes [Mn(hfac)2LF]2, [Co(hfac)2LF]2, and [Ni(hfac)2LF]2 were obtained and completely characterized. In [Mn(hfac)2LF]2, there are no magnetically important short contacts between manganese–nitroxide dimers, whereas in [Co(hfac)2LF]2 and [Ni(hfac)2LF]2, the O atoms of nitronyl nitroxide moieties are engaged in short interdimer contacts with H atoms of the methyl groups of the imidazoline moieties. In these complexes, there is a strong antiferromagnetic interaction between the metal ion and the coordinated nitroxide group. Using the copper matrix led to the formation of the heterospin polymer [Cu(hfac)2LF]n with a “head-to-head” motif and axial coordination of the ONO atoms. Exchange interactions between the odd electrons of Cu(II) and nitronyl nitroxide moieties are ferromagnetic. Therefore, in this paper, we show that the introduction of a fluorine atom into the pyrazole ring linked with the nitronyl nitroxide does not hinder the formation of exchange-coupled metal-nitroxide systems.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/cryst13121655/s1, X-ray crystallographic data and refinement details for LF, [Mn(hfac)2LF]2, [Co(hfac)2LF]2, [Ni(hfac)2LF]2, and [Cu(hfac)2LF]n; selected stereochemical parameters of crystal structures and figures showing fragments of structures; powder XRD data; spectroscopic characterization. Figure S1: The structure of LF. Thermal ellipsoids are set to the 50% probability level; Figure S2: Short C–H⋯ONO contacts and short C–H⋯NPz contacts between the neighboring {LF⋯HOH⋯LF} clusters; Figure S3: Short C–H⋯ONO contacts and short C–H⋯OH2O contacts between neighboring columns consisting of dimers {LF⋯HOH⋯LF}2 (selected column is highlighted with yellow); Figure S4: The structure of [Mn(hfac)2LF]2. Thermal ellipsoids are set to the 50% probability level; Figure S5: Short contacts of type C–H⋯ONO and C–H⋯F between neighboring [Mn(hfac)2LF]2 cyclic dimer molecules; Figure S6: Fragment of crystal structure and short contacts between neighboring [Mn(hfac)2LF]2, the view is parallel to the ac plane; Figure S7: The structure of [Co(hfac)2LF]2. Thermal ellipsoids are set to the 50% probability level; Figure S8: Fragment of crystal structure and short contacts between neighboring [Co(hfac)2LF]2, the view is parallel to the ac plane; Figure S9: Fragment of crystal structure and short C–H⋯ONO contacts between neighboring [Co(hfac)2LF]2 molecules running along the b axis; Figure S10: The structure of [Ni(hfac)2LF]2. Thermal ellipsoids are set to the 50% probability level; Figure S11: Fragment of crystal structure and short C–H⋯ONO contacts between neighboring [Ni(hfac)2LF]2 molecules running along the b axis; Figure S12: Fragment of crystal structure, short C–H⋯ONO and C–H⋯F contacts between neighboring [Ni(hfac)2LF]2, the view is parallel to the ac plane; Figure S13: The structure of [Cu(hfac)2LF]n. Thermal ellipsoids are set to the 50% probability level; Figure S14: Fragment of crystal structure, short F⋯F contacts between neighboring [Cu(hfac)2LF]n chains, view along [100] (a); short ONO⋯ONO contacts between neighboring [Cu(hfac)2LF]n (b). All contacts are shown in yellow; Figure S15: Experimental powder X-ray diffraction (PXRD) pattern of [Mn(hfac)2LF]2 (blue) at room temperature compared with the simulated pattern from the single crystal X-ray data at 100 K (red), and difference curve (grey line); Figure S16: Experimental powder X-ray diffraction (PXRD) pattern of [Cu(hfac)2LF]n (black) at room temperature compared with the simulated pattern from the single crystal X-ray data a (red); Figure S17: 1H NMR spectrum of aldehyde 1 in CDCl3 (Bruker AC-200 spectrometer); Figure S18: 19F NMR spectrum of aldehyde 1 in CDCl3 (Bruker AC-200 spectrometer); Figure S19: 1H NMR spectrum of 2 in DMSO-d6 (Bruker AV300 spectrometer); Figure S20: 13C NMR spectrum of 2 in DMSO-d6 (Bruker AV300 spectrometer); Figure S21: 19F NMR spectrum of 2 in DMSO-d6 (Bruker AV300 spectrometer); Figure S22: FTIR spectrum of 2 in KBr pellet (BRUKER Vertex-70 FTIR spectrometer); Figure S23: FTIR spectrum of LF in KBr pellet (BRUKER Vertex-70 FTIR spectrometer); Figure S24: FTIR spectrum of [Mn(hfac)2LF]2 in KBr pellet (BRUKER Vertex-70 FTIR spectrometer); Figure S25: FTIR spectrum of [Co(hfac)2LF]2 in KBr pellet (BRUKER Vertex-70 FTIR spectrometer); Figure S26: FTIR spectrum of [Ni(hfac)2LF]2 in KBr pellet (BRUKER Vertex-70 FTIR spectrometer); Figure S27: FTIR spectrum of [Cu(hfac)2LF]n in KBr pellet (BRUKER Vector-22 spectrometer); Figure S28: Mass spectrum of 2 (Bruker micrOTOF II instrument in positive ion electrospray ionization (ESI) mode at 4500 V (m/z 50–1600) with internal calibration with the ESI Tuning Mix (Agilent). The carrier gas (N2) flow rate was 3 μL·min–1, and interface temperature 200 °C); Figure S29: Mass spectrum of LF (Bruker micrOTOF II instrument in positive ion electrospray ionization (ESI) mode at 4500 V (m/z 50–1600) with internal calibration with the ESI Tuning Mix (Agilent). The carrier gas (N2) flow rate was 3 μL·min–1, and interface temperature 200 °C); Table S1: Crystal data and structure refinement; Table S2: Selected bond distances in LF (Å); Table S3: Hydrogen bonds for LF [Å and °]; Table S4: Selected bond distances and contacts in [Mn(hfac)2LF]2 (Å); Table S5: Selected bond distances and contacts in [Co(hfac)2LF]2 (Å); Table S6: Selected bond distances in [Ni(hfac)2LF]2 (Å); Table S7: Selected bond distances, contact (d, Å) and angles (ω, deg) in [Cu(hfac)2LF]n.

Author Contributions

Conceptualization, E.T.; methodology, B.U., N.E. and A.B.; validation, P.D., N.E. and A.B.; formal analysis, D.A., P.D. and A.B.; investigation, E.K., A.S.(Andrey Serykh), B.U., T.D., D.N., S.F., G.R. and N.E.; writing—original draft preparation, E.T.; writing—review and editing, A.S.(Anna Sergeeva) and G.R.; supervision, N.E. and E.T.; project administration, E.T. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Russian Science Foundation (project No. 21-73-20079) and the Russian Science Foundation (project No. 23-13-00014) in the part of room temperature SC XRD and magnetochemistry data for [Cu(hfac)2LF]n.

Data Availability Statement

The data that support the findings of this study are available upon reasonable request from the authors.

Acknowledgments

Crystal structure determination was performed in the Department of Structural Studies at Zelinsky Institute of Organic Chemistry, Moscow.

Conflicts of Interest

The authors declare no conflict of interest.

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Crystals 13 01655 sch001
Scheme 1. Preparation of nitronyl nitroxide derivative LF.
Scheme 1. Preparation of nitronyl nitroxide derivative LF.
Crystals 13 01655 sch001
Crystals 13 01655 g001
Figure 1. H-bonds and short contacts in cluster {LF⋯HOH⋯LF} (colour code: N: blue, O: red, F: greenish, C: gray, H: white).
Figure 1. H-bonds and short contacts in cluster {LF⋯HOH⋯LF} (colour code: N: blue, O: red, F: greenish, C: gray, H: white).
Crystals 13 01655 g001
Crystals 13 01655 g002
Figure 2. Binding of clusters {LF⋯HOH⋯ LF} into a centrosymmetric dimer (colour code: N: blue, O: red, F: greenish, C: gray, H: white).
Figure 2. Binding of clusters {LF⋯HOH⋯ LF} into a centrosymmetric dimer (colour code: N: blue, O: red, F: greenish, C: gray, H: white).
Crystals 13 01655 g002
Crystals 13 01655 g003
Figure 3. Molecular structure of complex [Co(hfac)2LF]2 (colour code: Co: violet, N: blue, O: red, F: greenish, C: grey, H: white).
Figure 3. Molecular structure of complex [Co(hfac)2LF]2 (colour code: Co: violet, N: blue, O: red, F: greenish, C: grey, H: white).
Crystals 13 01655 g003
Crystals 13 01655 g004
Figure 4. The fragment of chain in [Cu(hfac)2LF]n structure (colour code: Cu: cyan, N: blue, O: red, F: greenish, C: grey, H: white).
Figure 4. The fragment of chain in [Cu(hfac)2LF]n structure (colour code: Cu: cyan, N: blue, O: red, F: greenish, C: grey, H: white).
Crystals 13 01655 g004
Crystals 13 01655 g005
Figure 5. The plot of χM and χMT vs temperature for complex [Mn(hfac)2LF]2. The solid line is a theoretical curve.
Figure 5. The plot of χM and χMT vs temperature for complex [Mn(hfac)2LF]2. The solid line is a theoretical curve.
Crystals 13 01655 g005
Crystals 13 01655 g006
Figure 6. The field dependence of magnetization of [Mn(hfac)2LF]2 at 2.0 K.
Figure 6. The field dependence of magnetization of [Mn(hfac)2LF]2 at 2.0 K.
Crystals 13 01655 g006
Crystals 13 01655 g007
Figure 7. A plot of χM and χMT vs. temperature for complex [Co(hfac)2LF]2. The solid line is a theoretical curve.
Figure 7. A plot of χM and χMT vs. temperature for complex [Co(hfac)2LF]2. The solid line is a theoretical curve.
Crystals 13 01655 g007
Crystals 13 01655 g008
Figure 8. The field dependence of magnetization for [Co(hfac)2LF]2 at 2.0, 4.0, and 6.0 K.
Figure 8. The field dependence of magnetization for [Co(hfac)2LF]2 at 2.0, 4.0, and 6.0 K.
Crystals 13 01655 g008
Crystals 13 01655 g009
Figure 9. A plot of χM and χMT vs. temperature for complex [Ni(hfac)2LF]2. The solid line is a theoretical curve.
Figure 9. A plot of χM and χMT vs. temperature for complex [Ni(hfac)2LF]2. The solid line is a theoretical curve.
Crystals 13 01655 g009
Crystals 13 01655 g010
Figure 10. A plot of χM and χMT vs temperature for complex [Cu(hfac)2LF]n. The solid line is a theoretical curve.
Figure 10. A plot of χM and χMT vs temperature for complex [Cu(hfac)2LF]n. The solid line is a theoretical curve.
Crystals 13 01655 g010
Table 1. Selected bond distances, contact (Å), and angles (deg) in complexes.
Table 1. Selected bond distances, contact (Å), and angles (deg) in complexes.
ComplexM–ONOM–NM–Ohfac∠MONONN–OM
N–O		ONO⋯ONO
[Mn(hfac)2LF]2
296 K		2.127(4)2.289(5)2.137(5)–
2.166(5)		129.4(4)1.315(6)
1.263(7)		5.547(9)
[Mn(hfac)2LF]2
100 K		2.126(2)2.273(2)2.148(2)–
2.174(2)		125.3(1)1.303(3)
1.270(3)		5.922(3)
[Co(hfac)2LF]22.032(2)2.150(2)2.038(2)–
2.109(2)		121.8(1)1.308(2)
1.266(3)		3.715(3)
[Ni(hfac)2LF]22.034(3)2.097(4)2.011(3)–
2.051(3)		122.3(3)1.303(5)
1.276(5)		3.407(6)
[Cu(hfac)2LF]n2.448(2)2.469(2)1.933(2)–
1.968(2)		131.9(2)1.292(3)
1.269(3)		4.163(7)
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Kudryavtseva, E.; Serykh, A.; Ugrak, B.; Dutova, T.; Nasyrova, D.; Aleshin, D.; Efimov, N.; Dorovatovskii, P.; Bogomyakov, A.; Fokin, S.; et al. 5-Fluoro-1-Methyl-Pyrazol-4-yl-Substituted Nitronyl Nitroxide Radical and Its 3d Metal Complexes: Synthesis, Structure, and Magnetic Properties. Crystals 2023, 13, 1655. https://doi.org/10.3390/cryst13121655

AMA Style

Kudryavtseva E, Serykh A, Ugrak B, Dutova T, Nasyrova D, Aleshin D, Efimov N, Dorovatovskii P, Bogomyakov A, Fokin S, et al. 5-Fluoro-1-Methyl-Pyrazol-4-yl-Substituted Nitronyl Nitroxide Radical and Its 3d Metal Complexes: Synthesis, Structure, and Magnetic Properties. Crystals. 2023; 13(12):1655. https://doi.org/10.3390/cryst13121655

Chicago/Turabian Style

Kudryavtseva, Ekaterina, Andrey Serykh, Bogdan Ugrak, Tatyana Dutova, Darina Nasyrova, Dmitrii Aleshin, Nikolay Efimov, Pavel Dorovatovskii, Artem Bogomyakov, Sergey Fokin, and et al. 2023. "5-Fluoro-1-Methyl-Pyrazol-4-yl-Substituted Nitronyl Nitroxide Radical and Its 3d Metal Complexes: Synthesis, Structure, and Magnetic Properties" Crystals 13, no. 12: 1655. https://doi.org/10.3390/cryst13121655

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