2.3.2. [In(TmtBu)2](InCl4)

A solution of [Tl(TmtBu)]2·2H2O (0.0706 g, 0.050 mmol) in dichloromethane (5 mL) was added to a solution of InCl3·4H2O (0.0294 g, 0.100 mmol) in tetrahydrofuran (5 mL). After allowing the reaction to proceed overnight, the solvent was removed under reduced pressure, and the resulting solid was extracted with dichloromethane (10 mL). Colorless crystals were obtained by slow evaporation from a saturated dichloromethane/toluene (1:1 v/v) solution as [In(TmtBu)2](InCl4) (0.0586 g, 0.044 mmol, yield: 88%). Elemental analysis: Anal. Calcd. for [In(TmtBu)2](InCl4): C 38.03, H 5.17, N 12.67%; Found: C 38.04, H 5.09 N 12.33%. IR (KBr, cm−1): 3181w ν(C–H), 3147 w ν(C–H), 2979 m ν(C–H), 2928 m ν(C–H), 2423 w ν(B–H), 1567 w, 1480 m,1420 s, 1398 m, 1357 s, 1308 m, 1260 w, 1228 m, 1098 s, 1177 s, 1072 w, 822 w, 768 w, 732 m, 687 m, 590 w, 552 w, 496 w, 457 w. Raman (cm−1): 3184 w ν(C–H), 3152 w ν(C–H), 3111 w ν(C–H), 2986 m ν(C–H), 2928 m ν(C–H), 2425 w ν(B–H), 1568 m, 1450 w, 1431 w, 1359 s, 1307 w, 1255 w, 1248 w, 1073 w, 1041 w, 986 w, 932 w, 825 w, 738 w, 637 w, 590 w, 401 w, 320 w. 1H NMR (CDCl3, 298 K): 1.74 (*s*, 9H, C*H*3), 1.79 (*s*, 18H, C*H*3), 6.82 (*d*, 1H, *J* = 2.0 Hz, imidazole *H*), 6.89 (*d*, 2H, *J* = 2.0 Hz, imidazole *H*), 7.08 (*d*, 1H, *J* = 2.0 Hz, imidazole *H*), 7.12 (*d*, 2H, *J* = 2.0 Hz, imidazole *H*). 13C NMR (CDCl3, 298 K): 29.9 (C*C*H3), 30.1 (C*C*H3), 60.1 (*C*CH3), 60.8 (*C*CH3), 118.3 (imidazole *C*<sup>4</sup> or *C*5), 123.9 (imidazole *C*<sup>4</sup> or *C*5), 153.2 (imidazole *C*=S). UV–vis (CH2Cl2, 298 K; λmax, nm (*ε*, M<sup>−</sup>1cm−1)): 268 (17,900), 307 (8000).

#### *2.4. X-ray Crystallography*

Colorless crystals of [Tl(TmtBu)]2·2H2O and [In(TmtBu)2](InCl4) were coated with Paratone-N oil (Hampton Research, Aliso Viejo, CA, USA) and mounted on a Dual-Thickness MicroLoop LD (200 μM) (MiTeGen, New York, NY, USA). X-ray intensity data were measured at T = 178 K on a Rigaku/Oxford Diffraction Rigaku XtaLAB P200 diffractometer (Rigaku Oxford Diffraction, Oxfordshire, UK) fitted with MoKα radiation (λ = 0.71073 Å) so that 100% data completeness was achieved at *θ*max = 25.2◦. Data reduction, including empirical absorption correction, was accomplished with CrysAlisPro (Rigaku Oxford Diffraction, Oxfordshire, UK) [26]. The structures were solved by direct methods [27] and refined (anisotropic displacement parameters and C-bound H atoms in the riding model approximation) on *F*<sup>2</sup> [28]. For **2**, the positions of the water-bound H

atoms were idealized based on chemically reasonable positions with the O–H and H···H distances initially refined with restraints 0.840 ± 0.001 and 1.30 ± 0.001 Å, respectively, and fixed at these values in the final cycles of refinement. A weighting scheme of the form *w* = 1/[σ2(*Fo* 2)+(*aP*) <sup>2</sup> + *bP*], where *P* = (*F*<sup>o</sup> <sup>2</sup> + 2*Fc* 2)/3), was applied toward the latter stages of each refinement. At the conclusion of each refinement, relatively large residual electron density peaks were noted; details are given in the respective CIFs. The molecular structure diagrams were generated with ORTEP for Windows [29] with 50% displacement ellipsoids, and the packing diagrams were drawn with DIAMOND [30]. Additional data analysis was made with PLATON [31]. Crystal data and refinement details are given in Table 1.


**Table 1.** Crystallographic data and refinement details for [Tl(TmtBu)]2·2H2O and [In(TmtBu)2](InCl4).

#### **3. Results and Discussion**

#### *3.1. Synthesis and Characterization*

The reactions of the ligand K(TmtBu) [22–25] with one equivalent of thallium(I) acetate (TlOAc) were carried out at room temperature, and single crystals of the thallium(I) complex, formulated as [Tl(TmtBu)]2·2H2O, were obtained by slow evaporation of a dichloromethane/ethanol solution at room temperature (Figure 2). The indium(III) complex, [In(TmtBu)2](InCl4), was obtained by the reaction of [Tl(TmtBu)2] with indium(III) chloride InCl3·4H2O. The colorless crystals were obtained from the mixed solution of the saturated dichloromethane/toluene solution (Figure 2).

The expected signals in IR and Raman spectra were obtained for each [Tl(TmtBu)]2 and [In(TmtBu)2](InCl4). Noteworthy were the B–H stretching bands at 2455 cm−<sup>1</sup> for [Tl(TmtBu)]2 and 2423 cm−<sup>1</sup> for [In(TmtBu)2](InCl4), which were clearly evident and redshifted compared to 2480 cm−<sup>1</sup> for K(TmtBu) [25] (Figures S1 and S2 of the Supplementary Materials). The 1H-and 13C NMR spectra of [Tl(TmtBu)]2 in CDCl3 occurred at chemical shifts identical to those of KTmtBu (Figures S3–S5 of the Supplementary Materials). For [In(TmtBu)2](InCl4), all chemical shifts in the 1H-NMR, and all those except for C=S carbon shifts in the 13C-NMR, were clearly split due to the different structural arrangements, i.e., occupying equatorial and axial coordination sites. The UV–Vis absorption spectra of [Tl(TmtBu)]2 and [In(TmtBu)2](InCl4) were also measured (Figure S6 of the Supplementary Materials). Two characteristic absorption bands at 268 and 307 nm were observed for [In(TmtBu)2](InCl4), but for [Tl(TmtBu)]2, only a band at 261 nm was noted. From this observation, the high-energy bands at 260 and 268 nm band were assigned to a ligand TmtBu-based absorption, and the low-energy band for [In(TmtBu)2](InCl4) is metal centered. For more detailed assignments, computational chemistry calculations are required, which are beyond the scope of this study. The 1H-NMR and UV–Vis spectroscopy results indicate that the structures remained intact in the solution state.

**Figure 2.** Syntheses of thallium(I) complex, [Tl(TmtBu)]2, and indium(III) complex, [In(TmtBu)2](InCl4).

#### *3.2. Crystal and Molecular Structures*

#### 3.2.1. Molecular Structures

The crystallographic asymmetric unit of [TlI (TmtBu)]2·2H2O comprises one-half of a dimeric complex molecule, being located about a center of inversion and a water molecule of crystallization. The complex molecule is shown in Figure 3a and comprises a central, diamond-shaped core with almost equivalent Tl1–S1, S1i bond lengths (Table 2). The four-coordinate geometry for thallium is completed by the thione-S2 and symmetry-related thione-S3i atoms. An indication of the coordination geometry defined by the S4 donor set is τ4, which is computed from [360 − (α + β)]/141, where α and β are the two widest angles subtended at the thallium(I) atom [32]. In this case, *τ*<sup>4</sup> = 0.63, which corresponds to a seesaw geometry (*τ*<sup>4</sup> = 0.64); the widest angle corresponds to S2–Tl1–S3i , i.e., 156.32(3)◦. The TmtBu ligand is therefore tetra-coordinating, bridging two thallium(I) centers. A curious feature of the molecular structure is a close intramolecular B–H···ring centroid (Tl2S2) separation of 2.17 Å. This is a consequence of the coordination mode of the TmtBu ligand and has been observed in literature analogs, e.g., in the benzene mono-solvate of [Tl(TmtBu)]2 [15] and in [Tl(TmPh)]2, as its chloroform mono-solvate [16], each of which features the same κ<sup>3</sup> coordination mode as described above but with variations in the magnitudes of the Tl–S1 bond lengths.

**Figure 3.** (**a**) Molecular structure of the complex molecule in [Tl(TmtBu)]2·2H2O, showing atom labeling scheme and displacement ellipsoids at the 50% probability level, and (**b**) detail of the supramolecular molecular association (dashed lines) involving the water molecule. Unlabeled atoms in (**a**) are related by the symmetry operation 2 − *x*, 1 − *y*, − *z*.

**Table 2.** Selected geometric parameters (Å, ◦) for [Tl(TmtBu)]2·2H2O.


<sup>a</sup> symmetry operation: 2 − *<sup>x</sup>*, − *<sup>y</sup>*, − *z.*

As highlighted in Figure 3b, the water molecule of crystallization is closely associated with the complex molecule, forming a hydrogen bond to the thione-S2 atom and close contact with the N31-pyrazolyl ring; see Table 3 for the geometric parameters defining these interactions. The H2w···ring centroid separation is 2.47 Å, with the closest contact to a specific atom within the ring being 2.45 Å, i.e., the C19 atom with the next closest interaction, i.e., 2.60 Å with N31, and the longest separation of 2.97 Å with C21. This pattern indicates that the interaction is best described as a localized H2w···π interaction [33].

**Table 3.** Geometric parameters (Å, ◦) characterizing the specified intermolecular contacts operating in the crystal of [Tl(TmtBu)]2·2H2O a.


<sup>a</sup> Cg(1) is the ring centroid of the (N31,N32,C19-C21) ring.

The asymmetric-unit of [InIII(TmtBu)2](InCl4) comprises two independent complex cations, each disposed about a center of inversion, and a InCl4 − anion; the molecular structures are shown in Figure 4a–c. Focusing on the In1-containing molecule, the In1 atom is coordinated by two tripodal TmtBu ligands to define a soft S6 donor set, which defines an octahedral geometry. The geometry is slightly flattened, as the In1–S1 bond length of 2.5682(4) Å is systematically shorter than the In1–S2, S3 bond lengths of 2.6597 (4) and 2.6429(4) Å (Table 4). Despite this difference, the C5–S1 bond lengths are equal within experimental error. Otherwise, the deviations from the ideal octahedral geometry are small, as noted from the relevant angles included in Table 4. As highlighted by the dihedral angles between the pyrazolyl rings listed in Table 4 and the overlay diagram of Figure 4d, there is close agreement between the independent molecules. This observation notwithstanding, there are notable differences in the In–S bond lengths. Thus, in the first independent cation of [InIII(TmtBu)2](InCl4), one In–S bond length is 0.07–0.10 Å shorter than the others, whereas in the second independent cation, the differential between the In–S bond lengths is significantly smaller, i.e., the difference between the shortest and longer bond lengths is now 0.02–0.08 Å.

**Figure 4.** Molecular structure diagrams for [In(TmtBu)2](InCl4): (**a**) through (**c**) molecular structures of the independent In1- and In2-containing cations, and In3-anion, respectively, showing atom labeling schemes and displacement ellipsoids at the 50% probability level. (**a**) The N32 atom is indicated by an asterisk, and the C15 atom is not labeled. (**b**) The N51 atom is indicated by an asterisk, and the C30 atom is not labeled. The In atoms in (**a**) and (**b**) are located at crystallographic centers of inversion with the unlabeled atoms generated by the application of symmetry operations 1 − *x*, 1 − *y*, − *z* and 1 − *x*, 1 − *y*, 1 − *z*. (**d**) overlay diagram of the In1- and In2-containing cations shown as red and blue images, respectively. The cations have been overlapped so that the S3 faces are coincident.


**Table 4.** Selected geometric parameters (Å, ◦) for [In(TmtBu)2](InCl4).

There are several literature precedents for [In(TmtBu)2](InCl4), including [In(TmtBu)2] + characterized as the Cl− as an acetonitrile tri-solvate [15], and I− as a benzene mono-solvate, salts [15], along with [In(TmMe)2] <sup>+</sup> characterized as the I<sup>−</sup> salt as a diethyl ether monoand dimethylformamide di-solvate [20]. While the indium(III) centers in all three literature

complex cations exist within S6 donor sets, the symmetries of these vary. Thus, in the chloride salt of [In(TmtBu)2] <sup>+</sup>, each indium atom of the two independent molecules sits on an inversion center; in the iodide salt, the indium atom is located on a three-fold inversion center, implying that all In–S lengths are equivalent. The [In(TmMe)2] <sup>+</sup> cation is located on an inversion center.

#### 3.2.2. Molecular Packing

The water molecule of solvation in [Tl(TmtBu)]2·2H2O proves pivotal in assembling the dimeric molecules into a supramolecular chain along the *a*-axis, as shown in Figure 5a. Thus, the water molecule forms O–H···π(pyrazolyl) and O–H···S interactions, as shown in detail in Figure 3b, with the bay region of the TmtBu ligand. At the same time, the water-O atom accepts an interaction from a pyrazolyl-C–H atom; see Table 3 for geometric parameters. Chains pack in the crystal without directional interactions between them, as highlighted in the unit cell diagram of Figure 5b.

**Figure 5.** Molecular packing in the crystal of [Tl(TmtBu)]2·2H2O: (**a**) supramolecular chain aligned along the *a*-axis (non-participating H atoms are omitted) and (**b**) a view of the unit cell contents viewed in projection down the **a**-axis. The O–H···π(pyrazolyl), O–H···S and C–H···O contacts are highlighted as purple, orange and bright-green dashed lines, respectively.

A view of the unit cell contents for [In(TmtBu)2](InCl4) is shown in Figure 6. Globally, when viewed down the *b*-axis, molecules of In1- and In2-containing cations and [InCl4] − anions stack in columns along this axis. The cations align in rows along the *a*-axis, and the rows alternate in an ···ABA··· fashion down the *c*-axis. Interspersed between rows are the [InCl4] − anions, and these are pivotal in providing links between the constituent cations. The primary mode of interaction is via C–H···Cl contacts of the type pyrazolyl-C–H···Cl and methyl-C–H···Cl; for geometric parameters characterizing these interactions, refer to Table 5. The anion also forms an In–Cl···π(pyrazolyl) interaction, which is discussed in more detail in Section 3.3.

**Table 5.** Geometric parameters (Å, ◦) characterizing the specified intermolecular contacts operating in the crystal of [In(TmtBu)2](InCl4) a.


<sup>a</sup> Cg(1) is the ring centroid of the (N21,N22,C12-C14) ring.

**Figure 6.** A view of the unit cell contents for [In(TmtBu)2](InCl4) viewed in projection down the *b*-axis. The In–Cl···π(pyrazolyl) and C–H···Cl contacts are highlighted as purple and orange dashed lines, respectively.

#### *3.3. Hirshfeld Surface Analysis*

To further understand the nature of the contacts between molecules in their respective crystals, an analysis of the calculated Hirshfeld surfaces was conducted employing *Crystal Explorer 17* [34] following established protocols [35]. The analysis shows that there are some close contacts present in each crystal, as evident from the red spots of various intensity observed on the respective *d*norm maps indicating contact distances shorter than the sum of van der Waals radii [36].

For [Tl(TmtBu)]2·2H2O, the *<sup>d</sup>*norm map of the Tl(TmtBu) fragment shows several red spots of moderate to strong intensity (Figure 7), which can be attributed to O1w–H1w···S2, O1w–H2w···C19(π), and C13–H13···O1w close contacts, with the respective contact distances being 2.37, 2.35, and 2.34 Å compared to the respective sums of the van der Waals radii (ΣvdW) of 2.89, 2.79, and 2.61 Å for H···S, H···C, and H···O (Table 6).

**Figure 7.** The two views of the *d*norm Hirshfeld surface mapping for the Tl(TmtBu) fragment of [Tl(TmtBu)]2·2H2O within the range <sup>−</sup>0.1027 to 1.3365 arbitrary units, highlighting close contacts as red regions on the surfaces with their intensity relative to the contact distance.


**Table 6.** *d*norm contact distances (adjusted to neutron values) of intermolecular interactions identified in the crystals of [Tl(TmtBu)]2·2H2O and [In(TmtBu)2](InCl4), as computed through the Hirshfeld surface analysis and in comparison to the corresponding sum of van der Waals radii (ΣvdW).

Hirshfeld surface analysis was also performed for the central thallium atom (Figure 8). The *d*norm map displays several weak to intense red spots indicating additional intramolecular interactions between B1–H1···Tl (*d*norm distance = 2.69 Å vs. ΣvdW = 3.05 Å) and C10–H10a···Tl (*d*norm distance = 3.00 Å vs. ΣvdW = 3.05 Å) on top of S1···Tl, S2···Tl and S3···Tl contacts, as described above.

**Figure 8.** The two views of the *d*norm Hirshfeld surface mapping within the range −0.1027 to 1.3365 arbitrary units for the thallium center in [Tl(TmtBu)]2·2H2O, showing the coordination modes of the metal with two TmtBu ligands of different symmetry: (**a**): *<sup>x</sup>*, *<sup>y</sup>*, *<sup>z</sup>* and (**b**) 2 <sup>−</sup> *<sup>x</sup>*, 1 <sup>−</sup> *<sup>y</sup>*, <sup>−</sup> *<sup>z</sup>*.

The *d*norm analysis was also conducted for each of the In1- or In2-containing cations and In3-anion in [In(TmtBu)2](InCl4) (Figure 9). A number of red spots with moderate intensity are observed for close contacts comprising C41–H41···Cl3, C21–H21···Cl1, and C42–H42···Cl4, in accordance with those interactions identified through the geometric analysis conducted with PLATON [31]. However, additional contacts were noted through the *d*norm map arising from H37c···H30a, with moderate intensity, as well as from C1–H1b···Cl4, C6–H6···Cl4, and C35–H35···C19 with weak intensity. Table 6 summarizes these contacts and compares the separation distances with the respective van der Waals radii.

**Figure 9.** The two views of the *d*norm Hirshfeld surface mapping within the range −0.0195 to 1.7591 arbitrary units for [In(TmtBu)2](InCl4): (**a**) In1-cation, (**b**) In2-cation, and (**c**) In3-anion, with the close contacts indicated by the corresponding red dots on the surfaces with their intensity relative to the contact distance.

In addition to the close contacts as identified through the direct observation of red spots on the Hirshfeld surface of [In(TmtBu)2](InCl4), two other important contacts, specifically In3–Cl1···π(pyrazolyl) and C1–H1b···In3, are detected based on the complementarity of shape as indicated by the hollows and bumps on the shape index mapped over the Hirshfeld surfaces between the independent In1 cation and In3 anion, despite the observation that the contact distances between Cl1 and the closest carbon atom of the five-membered imidazole ring, i.e., Cl1···C14, as well as H1b···In3, are longer than the corresponding ΣvdW, Figure 10.

Quantification of the close contacts in each individual component of [TlI (TmtBu)]2·2H2O and [InIII(TmtBu)2](InCl4) was performed through two-dimensional fingerprint plot analysis. The overall and delineated fingerprint plots for the individual components profiled in [Tl(TmtBu)]2·2H2O, namely the TmtBu fragment, the water molecule, the thallium atom as well as the [Tl(TmtBu)]2 dimer, are illustrated in Figure 11. The fingerprint profiles for both TmtBu and [Tl(TmtBu)]2 resemble each other and have the shape of a flying fox, while those for H2O and Tl display a cicada- and pincer-like profile, respectively. The decomposition of the corresponding overall profiles for TmtBu and [Tl(TmtBu)]2 show that their close contacts are dominated by H···H (69.5 and 76.6%, respectively), H···S/S···H (12.8 and 9.8%), <sup>H</sup>···C/C···H (6.2 and 6.6%), H···Tl/Tl···H (3.7 and 3.3%), S···Tl (for TmtBu only, 2.9%), and H···O/O···H (2.3 and 2.6%) as well as by other minor contacts that constitute less than 1.0% of all surface contacts, including H···N/N···H, S···O, and others. Among those contacts, only S···H, C···H, H···Tl/Tl···H, and O···H feature a distinctive tip with *d*<sup>i</sup> + *d*<sup>e</sup> values corresponding to O1w–H1w···S2, O1w–H2w···C19, B1–H1···Tl/C10–H10a···Tl, and C13–H13···O1w, while the rest of the contacts present indistinct profiles.

**Figure 10.** Two views of the shape-index mapped over the Hirshfeld surfaces for [In(TmtBu)2](InCl4) within the property range −1.0 to +1.0 arbitrary units highlighting (**a**) In3–Cl1···π(C14) and (**b**) C1–H1b···In3 contacts, showing the shape complementarity as indicated by the hollow (orange) and bump (blue) on the surfaces.

**Figure 11.** The overall two-dimensional fingerprint and decomposed plots delineated into the major contacts along with the percentage distributions for (**a**) TmtBu, (**b**) H2O molecule, (**c**) thallium center, and (**d**) [Tl(TmtBu)]2 dimer for [Tl(TmtBu)]2·2H2O.

As for the H2O molecule and thallium atom, the major contacts for the former appear in the order H···H (43.8%) > O···H (30.4%) > H···S (10.0%) > H···C (7.2%) > H···N (6.2%) > O···S (2.5%), while the latter is dominated by H···Tl (63.1%) > S···Tl (26.2%) > C···Tl (6.9%) > N···Tl (3.9%). The *d*<sup>i</sup> + *d*<sup>e</sup> distances associated with the significant peaks in these profiles correspond to the reciprocal contacts as identified in the TmtBu and [Tl(TmtBu)]2 profiles.

The overall and selected delineated two-dimensional fingerprint plots for the In1- and In2-cations as well as the In3-anion in [In(TmtBu)2](InCl4) are presented in Figure 12. As a general observation, the In1- and In2-cations exhibit a paw-like overall profile, which can be delineated mainly into H···H, H···Cl, and H···C/C···H contacts that constitute more than 93% of the Hirshfeld surfaces in each case. Specifically, the plots of the H···Cl contacts for the In1- and In2-cations display a distinctive spike in their decomposed fingerprint plots comprising 13–14% of all surface contacts with *d*<sup>i</sup> + *d*<sup>e</sup> tipped at about 2.70 Å, which can be, respectively, attributed to H1b···Cl4 and H42···Cl4. The (inner)-C···H-(outer) and (inner)-H···C-(outer) contacts, represented by the pair of pincer-like profiles in the decomposed H···C/C···H fingerprint plots for the In1- and In2-cations, are due to H35···C19, with both constituting about 5% of the Hirshfeld surfaces with a *d*<sup>i</sup> + *d*<sup>e</sup> distance of 2.76 Å, while the reciprocal (inner)-H···C-(outer) of the In1-cation and (inner)-C···H-(outer) of the In2-cation contribute 4.3 and 5.4%, respectively, to the contact surfaces but with a less significant *d*<sup>i</sup> + *d*<sup>e</sup> distance, being longer than ΣvdW. A distinct feature is observed in the decomposed H···H fingerprint plot for the In2-cation compared to that for the In1-cation, in that for the former, a relatively prominent tip at *d*<sup>i</sup> + *d*<sup>e</sup> = 1.93 Å is assignable to H37c···H30a.

**Figure 12.** The overall two-dimensional fingerprint and decomposed plots delineated into the major contacts along with the percentage distributions for (**a**) In1-cation, (**b**) In2-cation, and (**c**) In3-anion for [In(TmtBu)2](InCl4).

On the other hand, the decomposition of the squid-like overall fingerprint plot for the In3-anion shows that about 94.4% of the contact surfaces are dominated by Cl···H with a *d*<sup>i</sup> + *d*<sup>e</sup> distance tipped at 2.66 Å ascribed to the close C41–H41···Cl3 contact, while other minor contacts include Cl···C and In···H, which contribute about 3.1 and 2.0%, respectively, to the total surface, both with *d*<sup>i</sup> + *d*<sup>e</sup> tips arising from the In3–Cl1···π(C14) and C1–H1b···In3 contacts as discussed above.

#### **4. Conclusions**

The synthesis, spectroscopic and X-ray crystallographic characterizations of two main group element complexes of a soft S3-tripod-type ligand have been described. S4-seesaw and S6-flatenened octahedral geometries were found for the central atoms in Tl(TmtBu)]2·2H2O and [In(TmtBu)2](InCl4), respectively. The analyses of the calculated Hirshfeld surfaces confirmed the geometric analysis of the molecular packing. These results suggest soft S3-tripod-type ligands related to that discussed herein are a potentially useful class of ligands for coordination to *p*-block elements. The coordination of sulfur atoms gives rise to distinct electronic characteristics compared with the well-known hard N3-type ligands. Therefore, the present chemistry paves the way for new coordination chemistry based on soft S3-tripod-type ligands.

**Supplementary Materials:** The following supporting information can be downloaded at: https:// www.mdpi.com/article/10.3390/cryst13050745/s1. Figure S1: IR spectra for [Tl(TmtBu)]2·2H2O and [In(TmtBu)2](InCl4); Figure S2: FT-Raman spectra for [Tl(TmtBu)]2·2H2O and [In(TmtBu)2](InCl4); Figure S3: 1H-NMRspectrum of [TlI (TmtBu)]2·2H2O; Figure S4: 1H-NMR spectrum for [InIII(TmtBu)2](InCl4); Figure S5: 13C-NMR spectrum of [InIII(TmtBu)2](InCl4); Figure S6: UV–Vis spectra for [Tl(TmtBu)]2·2H2O and [In(TmtBu)2](InCl4).

**Author Contributions:** Investigation, formal analysis, A.K. Investigation, formal analysis, writing—original draft preparation, writing—review and editing, K.F., S.L.T. and E.R.T.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by an Ibaraki University Priority Research Grant and by the Joint Usage/Research Center for Catalysis (proposals 22DS0143 and 23DS0198).

**Data Availability Statement:** Crystallographic datasets for the structures [Tl(TmtBu)]2·2H2O and [In(TmtBu)2](InCl4) are available through the Cambridge Structural Database with deposition numbers CCDC 2253015 ([Tl(TmtBu)]2·2H2O) and 2253016 ([In(TmtBu)2](InCl4)). These data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/ (accessed on 31 March 2023).

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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