Search Results (125)

Phenylene-based bis-oxamate polydentate ligands offer a unique opportunity for creating a large variety of coordination compounds, in which paramagnetic metal ions are strongly magnetically coupled. The employment of imino nitroxyl (IN) radicals as supplementary ligands confers numerous benefits, including the strong ferromagnetic interaction between Ni and IN. Furthermore, the chelating IN can act as a capping ligand, thereby impeding the formation of coordination polymers. In this study, we present the molecular and crystal structure and experimental and theoretical magnetic behavior of an exceptional neutral trinuclear complex [Ni(L³⁻)₂(IN)₃]∙5CH₃OH (1) (L is N,N′-1,3-phenylenebis-oxamic acid; IN is [4,4,5,5-tetramethyl-2-(6-methylpyridin-2-yl)-4,5-dihydro-1H-imidazol-1-yl]oxidanyl radical) with a cyclic triangular arrangement. Moreover, in this compound three Ni²⁺ ions are linked by the two bis-oxamate ligands playing a rare tritopic function due to an unprecedented triple deprotonation of the related meta-phenylene-bis(oxamic acid). The main evidence of such a deprotonation of the ligand is the neutrality of the cluster, since there are no anions or cations compensating for its charge in the crystals of the compound. Despite the presence of six possible magnetic couplings in the trinuclear cluster 1, its behavior was reproduced with a high degree of accuracy using a three-J model and ZFS, under the assumption that the three different Ni-IN interactions are equal to each other, whereas only two equivalent-in-value Ni-Ni interactions were taken into account, with the third one being equated to zero. Our study indicates the presence of two opposite-in-nature types of magnetic interactions within the triangular core. DFT and CASSCF/NEVPT2 calculations were completed to support the experimental magnetic data simulation. Full article

Low-loaded copper-exchanged mordenite samples (3 wt.% of copper) were prepared by a solid-state milling method using controlled conditions. The milled samples were then submitted to a calcination process where trimeric copper active species were formed, according to XPS, EPR, IR, and UV–vis recorded spectra. To verify the interaction of the active site with methane at mild conditions, a test experimental design was developed in a batch reactor configuration using mild two-step conditions: (1) activation temperature at 400 °C in an air atmosphere, and (2) isothermal conversion process at 200 °C with 6 bar methane. The analyzed samples were active in methanol conversion in batch conditions, nonetheless less efficient than the usually reported copper mono $\mu$-oxo sites using harder experimental conditions. The herein reported copper active sites are as follows: a trinuclear copper active cluster [Cu₃($\mu$-O)₃]²⁺ and a possible intermediate during methane contact detected as bis($\mu$-oxo) dicopper species were identified and studied on each reaction step. This study revealed that trinuclear copper active sites can be obtained through grinding. Nonetheless, they stabilize after a calcination stage in an air atmosphere. Their stability is then maintained during the whole cyclic experimental test, suggesting their potential use for multicyclic processes. Full article

Organometallic rare-earth complexes have attracted considerable attention in recent years due to their unique structures and exceptional magnetic properties. In this study, we report the synthesis and magnetic characteristics of a family of monopentamethylcyclopentadienyl-coordinated trinuclear rare-earth hepta-chloride clusters [(Li(THF)(Et₂O))(Cp^*RE)₃(μ-Cl)₄(μ₃-Cl)₂(μ₄-Cl)] (RE₃: RE =Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; Cp* = pentamethylcyclopentadienide). These clusters were synthesized by reacting LiCp* with RECl₃ in a 1:1 molar ratio within a mixed solvent system (THF: Et₂O = 1:9), resulting in high solubility in common organic solvents such as DCM, THF, and Et₂O. Magnetic studies conducted on these paramagnetic clusters reveal the coexistence of ferromagnetic and antiferromagnetic superexchange interactions in Gd₃. Additionally, Dy₃ exhibits both ferromagnetic and antiferromagnetic intramolecular dipolar interactions. Notably, slow magnetic relaxation was observed in Dy₃ below 23 K under a zero DC applied field with an energy barrier of 125(6) cm⁻¹. Full article

The synthesis and characterization of the tripodal phosphines RSi(CH₂CH₂PPh₂)₃ (R = Me, OMe, OEt) (1–3) is described. The ¹H NMR spectra of all phosphines display virtual coupling patterns. The ligands form the corresponding trinuclear Pd complexes [RSi(CH₂CH₂PPh₂)₃]₂(PdCl₂)₃ (4–6) with three PdCl₂ moieties sandwiched between two tripodal ligands. The complexes 4, 5, and 7 (R = OH) have been analyzed by single crystal X-ray diffraction. The coordination at the Pd center is square planar with the phosphine groups occupying trans positions. The ³¹P{¹H} MAS NMR spectra of polycrystalline 1 are in accordance with the packing motif of the molecules in the unit cell. The tripodal ligand 3 has successfully been immobilized on silica as 3i. It coordinates PdCl₂ on the surface, as demonstrated by ³¹P{¹H} MAS NMR. Hereby, the cis coordination is prevalent when 3i has maximal surface coverage. At low surface coverage, one tripodal linker can accommodate trans coordination at the metal center. A surface-bound trinuclear Pd complex has been generated, as well as a heterobimetallic Pd/Cu complex. All surface species have been characterized by ³¹P{¹H} MAS NMR. Full article

Structural rearrangements in metal–organic supramolecules constructed from the coordination of Cu(II) with m-xpt (m-xylylenebis(pyridyltriazole)) are investigated upon their interaction with 1,4-diazabicyclo[2.2.2]octane (dabco) and carbon dioxide-enriched air. The binuclear [Cu₂(m-xpt)₂]⁴⁺ complexes react with dabco to produce a carbonate-bridged trinuclear complex, [Cu₃(m-xpt)₃(µ-CO₃)]⁴⁺, and an oxalate-bridged binuclear complex, [Cu₂(m-xpt)₂(µ-C₂O₄)]²⁺, where carbonate and oxalate likely originate from CO₂ and dabco, respectively. The trinuclear complex reassembles the original dimer upon the removal of the carbonate ion. Similarly, polymeric [Cu(o-xpt)(PF₆)]_n, formed from Cu(I) and o-xpt (o-xylylenebis(pyridyltriazole)) coordination, undergoes oxidation in CO₂-enriched air to yield a tetranuclear Cu(II) complex, Cu₄(o-xpt)₃(μ₄-CO₃)(μ₂-OH)(μ₂-OCOCH₃)⁴⁺. The reaction progress is monitored by UV-Vis spectroscopy, and the major products are characterized by single-crystal X-ray diffraction. Full article

The oxime group is important in organic and inorganic chemistry. In most cases, this group is part of an organic molecule possessing one or more donor sites capable of forming bonds to metal ions. One family of such compounds is the group of 2-pyridyl (aldo)ketoximes. Metal complexes of 2-pyridyl oximes continue to attract the intense interest of many inorganic chemistry groups around the world for a variety of reasons, including their interesting structures, physical and biological properties, and applications. A unique member of 2-pyridyl ketoximes is di-2-pyridyl ketoxime (dpkoxH), which contains two 2-pyridyl groups and an oxime functionality that can be easily deprotonated giving the deprotonated ligand (dpkox⁻). The extra 2-pyridyl site confers a remarkable flexibility resulting in metal complexes with exciting structural and reactivity features. Our and other research groups have prepared and characterized many metal complexes of dpkoxH and dpkox⁻ over the past 30 years or so. This work is an attempt to build a “periodic table” of dpkoxH, which is near completion. The filled spaces of this “periodic table” contain metal ions whose dpkoxH/dpkox⁻ complexes have been structurally characterized. This work reviews comprehensively the to-date published coordination chemistry of dpkoxH with emphasis on the syntheses, reactivity, relationship to metallacrown chemistry, structures, and properties of the metal complexes; selected unpublished results from our group are also reported. The sixteen coordination modes adopted by dpkoxH and dpkox⁻ have provided access to monomeric and dimeric complexes, trinuclear, tetranuclear, pentanuclear, hexanuclear, heptanuclear, enneanuclear, and decanuclear clusters, as well as to a small number of 1D coordination polymers. With few exceptions ({M^IILn^III₂} and {Ni^II₂Mn^III₂}; M = Ni, Cu, Pd, and Ln = lanthanoid), most complexes are homometallic. The metals whose ions have yielded complexes with dpkoxH and dpkox⁻ are Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Re, Os, Ir, Au, Hg, lanthanoids (mainly Pr and Nd), and U. Most metal complexes are homovalent, but some mixed-valence Mn, Fe, and Co compounds have been studied. Metal ion-assisted/promoted transformations of dpkoxH, i.e., reactivity patterns of the coordinated ligand, are also critically discussed. Some perspectives concerning the coordination chemistry of dpkoxH and research work for the future are outlined. Full article

Group 11 metals form with pyrazolate ligand complexes with a general formula of [MPz]_n. The value of “n” varies depending on the type of substituent in the ligand and the metal atom. Copper(I) and silver(I) ions mainly form cyclic di-, tri-, and tetra-nuclear complexes or polymeric structures. Cyclic trinuclear d¹⁰ metal pyrazolates [MPz^m]₃ (M = Cu(I) and Ag(I); Pz = substituted pyrazolate ligand) are of particular interest because their planar structure allows them to form supramolecular aggregates via noncovalent metal–metal, metal–π, and metal–electron donor interactions. Designing complexes based on these interactions has been a focus of research for the last two decades. The ability of cyclic trinuclear copper(I) and silver(I) pyrazolates to form coordination and supramolecular structures determines their properties and potential applications in catalysis, gas sensing, molecular recognition, and photoluminescence. In this review, we discuss noncovalent interactions between cyclic trinuclear silver(I) and copper(I) complexes with various types of ligands. Full article

In the presented work, titanosilicate with the MWW structure (Ti-MWW) was hydrothermally synthesized using boron and titanium precursors, with piperidine as a structure-directing agent. The resulting layered zeolite precursor, with a Si/Ti molar ratio of 50, was treated in an HNO₃ solution to remove extraframework Ti and B species. The acid-modified zeolite was functionalized with transition metal cations (Cu²⁺, Fe²⁺, Mn²⁺) and trinuclear oligocations (Fe(3) and Mn(3)). The application of this catalytic system is supported by the presence of titanium in the catalytic support structure—similar to a commercial system, V₂O₅–TiO₂. The obtained samples were characterized with respect to their structure (P-XRD, DRIFT), textural parameters (low-temperature N₂ sorption), surface acidity (NH₃-TPD), transition metal content (ICP-OES) and form (UV–vis DRS) as well as catalyst’s reducibility (H₂-TPR). Ti-MWW zeolite samples modified with transition metals were evaluated as catalysts for the selective catalytic reduction of NO with ammonia (NH₃-SCR). The effective temperature range for the NO conversion varied depending on the type of active phase used to functionalize the porous support. The catalytic performance was influenced by transition metal content, its form, and accessibility for reactants as well as interactions between the active phase and titanium-containing support. Among the catalysts tested, the copper-modified Ti-MWW zeolite showed the most promising results, maintaining 90% NO conversion rates across a relatively broad temperature range from 200 to 325 °C. This catalyst meets the requirements of modern NH₃-SCR installations, which aim to operate in the low-temperature region, below 250 °C. Full article

A trinuclear Co(II)-containing complex was assembled using the non-innocent hexahydroxytriphenylene bridging ligand. Cyclovoltammetry and spectroelectrochemistry studies revealed that the central ligand sustained four reversible redox events, leading to different species with diverse optical behavior. Complementary analysis of the molecular structure confirmed by ab initio theoretical calculations were consistent with the bridge in the tris-semiquinone (sq) state for the trinuclear complex. The exchange coupling among the electrons of the bridge resulted in a spin doublet (s = ½) localized close to one of the three Co²⁺ ions, as suggested by the experimental magnetic data. The central doublet underwent one large antiferromagnetic exchange coupling with one Co(II) and almost no coupling with the two other metal ions. Full article

Inspired by the reported crystal structure of compound 1, we aimed to synthesize and determine the structure of compound 2, where two imidazolium (H₂im⁺) ions serve as diamagnetic countercations. Here, we report the thermal stabilities, FT–IR, visible, and RSE spectra, as well as the magnetic properties of both compounds. In these structures, µ-EDTA acts as a pentadentate chelator for both terminal Cu centers within the centrosymmetric linear trinuclear anion. The Cu(µ-EDTA) chelates bind to the central Cu(Him)₄ unit in subtly different ways: in compound 1, µ-EDTA has a free acetate arm and binds the central Cu(II) center through a syn,anti-carboxylate group. In contrast, in compound 2, the non-chelating acetate arm serves as a monodentate O-donor to the central Cu(II) atom, increasing the Cu(terminal)···Cu(central) distance from 6.08 Å in 1 to 6.80 Å in 2. Additionally, pairs of H₂im⁺ ions in compound 2 display antiparallel π-stacking interactions. We conclude that the H₂im⁺ counterions in compound 2 enable the magnetic isolation of the nearly identical trinuclear anion present in both compounds. DFT calculations further support the role of different interactions in stabilizing each crystal structure. In compound 2, dominant contributions from N–H···O hydrogen bonds and π-stacking interactions are accompanied by other, less conventional interactions, such as multiple C–H···O contacts and an O···CO(π-hole) interaction within the trinuclear anion. Full article

The synthesis, structural, and magnetic characterization of a novel neutral copper(II) hexanuclear complex [Cu₆(en)₄(OCH₂CH₂O)₂(pyox)₄]·3eg·en·12H₂O (1) was investigated [en = ethylenediamine, eg = ethylene glycol, and H₂pyox = 4-(1H-pyrazole-4-yl)phenylene-N-oxamic acid]. The crystal structure of 1, obtained by the single-crystal X-ray diffraction technique, revealed that the hexacopper(II) complex is built from two linear tricopper(II) complex subunits. Each subunit contains two [Cu(en)]²⁺ moieties connected to a [Cu(OCH₂CH₂O)] unit by two pyox²⁻ ligands acting as μ-κN:κN′ bridges, as well as a [OCH₂CH₂O]²⁻ ligand, which is ultimately found in the μ₃-κO,O′:κO:κO′ coordination form. The subunits are connected via the amide portion of the pyox²⁻ ligand, linked to copper atoms in the other subunit. They occupy the apical coordination positions, leading the trinuclear copper(II) segments to be almost perpendicular. The structural, chemical, and spectroscopic characterizations evidenced that ethylene glycol acted both as a solvent and a reactant upon deprotonation, forming the –OCH₂CH₂O– ligand due to the basic crystallization environment. DC magnetic studies revealed a strong antiferromagnetic interaction between the copper atoms within the trinuclear subunits, influenced by alkoxide and pyrazolate bridging ligands. Our findings offer new insights into the structural and magnetic properties of copper(II) complexes, enhancing the understanding of metal–ligand interactions in supramolecular chemistry. Full article

The reaction of manganese halides with polydentate Schiff bases obtained by the condensation of 3-ethoxysalicylaldehyde and different amino alcohols, resulting in a NO₃ set of donors, yielded a series of manganese clusters with {Mn^III₆Mn^IINa₂}, {Mn^III₃Mn^IINa}, and {Mn^III₃} metallic cores. The influence of the ligand substituents and the halide on the final nuclearity has been studied. Analysis of their static magnetic behaviour confirms the ground states of 19/2 for the {Mn^III₆Mn^IINa₂} complexes, 7/2 for the {Mn^III₃Mn^IINa} clusters, and 12/2 for the triangular {Mn^III₃} systems, and a weak field induced a slow relaxation of the magnetization for the trinuclear complexes. Full article

Cyclic trinuclear homo-metal complexes, [{Fe(L³⁺²Br)py}₃] (1) and [{Mn(L³⁺²Br)}₃(py)₂ MeOH] (2), along with a hetero-metal complex, [FeMn₂(L³⁺²H)₃(DMF)₃] (3), were synthesized using asymmetric ditopic ligands (H₃L³⁺²H: 2-(2-hydroxyphenyl)-6-ol-5-(salicylideneamino)benzoxazole, H₃L³⁺²Br: 2-(2-hydrox-5-bromoyphenyl)-6-ol-5-(5-bromosalicylideneamino)benzoxazole). The molecular structure of 1 is characterized by a tripod structure with three-fold symmetry, where an enantiomer pair forms a dimeric capsule with dimensions of approximately 3 × 1.6 × 1.6 nm³. Complexes 2 and 3, which lack three-fold symmetry, exhibit similar molecular structures to previously reported complexes with these ligands, but do not form a capsule structure. Magnetic measurements of 1–3 reveal the presence of significantly weak antiferromagnetic interactions between the metal ions. Full article

Trinuclear and tetranuclear ruthenium carbonyls of the types Ru₃(CO)_n(NO)₂, Ru₃(N)(CO)_n(NO), Ru₃(N)₂(CO)_n, Ru₃(N)(CO)_n(NCO), Ru₃(CO)_n(NCO)(NO), Ru₄(N)(CO)_n(NO), Ru₄(N)(CO)_n(NCO), and Ru₄(N)₂(CO)_n related to species observed experimentally in the chemistry of Ru₃(CO)₁₀(µ-NO)₂ have been investigated using density functional theory. In all cases, the experimentally observed structures have been found to be low-energy structures. The low-energy trinuclear structures typically have a central strongly bent Ru–Ru–Ru chain with terminal CO groups and bridging nitrosyl, isocyanate, and/or nitride ligands across the end of the chain. The low-energy tetranuclear structures typically have a central Ru₄N unit with terminal CO groups and a non-bonded pair of ruthenium atoms bridged by a nitrosyl or isocyanate group. Full article

The reaction of Mn(II) salts in the air with different R-salicylaldehyde oximes and the sodium or cesium salts of 9-anthracenecarboxylato (9-AC) allows for the isolation of new six polynuclear compounds: [Mn₃NaO(salox)₃(9-AC)₂(EtOH)₃H₂O]_n·2EtOH (1), [Mn₃NaO(3-Me-salox)₃(9-AC)₂(EtOH)₃H₂O]_n·EtOH (2), [Mn₆O₂(salox)₆(9-AC)₂(EtOH)₂(H₂O)₂]·3EtOH (3), [Mn₃O(3-Me-salox)₃(9-AC)(EtOH)₃(H₂O)]·1.8EtOH·3H₂O (4), [Mn₆O₂(Me-salox)₆(9-AC)₂(EtOH)₄(H₂O)₂]·0.5H₂O (5), and [Mn₆O₂(Et-salox)₆(9-AC)₂(EtOH)₄(H₂O)₂]·3EtOH (6). H₂salox is a salicylaldehyde oxime, H₂(3-Me-salox) is a 3-methyl-salicylaldehyde oxime, H₂Me-salox is a 1-(2-hydroxyphenyl)ethan-1-one oxime and a H₂-Et-salox is 1-(2-hydroxyphenyl)propan-1-one oxime. Structurally, compounds 1 and 2 consist of chains of trinuclear {Mn^III₃(μ₃-O)(salox)₃}⁺ units connected by Na⁺ ions. Compounds 3, 5, and 6 are hexanuclear units formed by two parallel trinuclear units {Mn^III₃(μ₃-O)(salox)₃}⁺ or {Mn^III₃(μ₃-O)(Me-salox)₃}⁺ planes related through an inversion center. Compound 4 consists of two isolated [Mn₃O(3-Me-salox)₃(9-AC)(EtOH)₃(H₂O)] trinuclear molecules in the unit cell showing crystallographic differences. Magnetic studies reveal a set of antiferromagnetic interactions in compounds 1 and 2 and a combination of antiferromagnetic and ferromagnetic interactions in compounds 3, 5, and 6. In all cases, the magneto-structural correlation between the intramolecular Mn^III-N-O-Mn^III torsion angle and the magnetic exchange within these units have been confirmed. For compounds 5 and 6, ac magnetic measurements reveal the slow relaxation of magnetization with moderate energy barriers of 19.9 cm⁻¹ and 31.1 cm⁻¹, respectively. Absorbance and fluorescence measurements in solution show the transitions of the 9-anthracenecarboxylate chromophore for all the compounds. Full article