Synthesis and Structural Characterization of [TismPriBenz]ZnX (X = Cl, Br, I) and {[TismPriBenz]Zn}[(THF)ZnX3]: Hypodentate and Atrane Motifs and Their Analysis by the Use of Normalized Continuous Shape Measures

The tris[(1-isopropylbenzimidazol-2-yl)dimethylsilyl]methyl zinc halide compounds [κ3-TismPriBenz]ZnX (X = Cl, Br, I) are obtained via the reactions of [TismPriBenz]Li with ZnX2 (X = Cl, Br, I), while the iodide derivative has also been obtained via the reactions of [κ3-TismPriBenz]ZnH with Me3SnI and MeI. The molecular structures of [κ3-TismPriBenz]ZnX have been determined by X-ray diffraction, thereby demonstrating that the [TismPriBenz] ligand coordinates via a hypodentate L2X κ3-mode. Abstraction of the halide ligand by using ZnX2, nevertheless, affords {[TismPriBenz]Zn}[ZnX3(THF)] derivatives that do adopt the κ4-atrane motif. Analysis of the structures by using normalized continuous shape measures (CShMN or SN) indicates that the hypodentate complexes [κ3-TismPriBenz]ZnX are best described as possessing a distorted tetrahedral geometry, while the atrane complexes {[TismPriBenz]Zn}[Y] (Y = ZnX3(THF), (Zn3I8)0.5, [HB(C6F5)3]) are best described as possessing a distorted trigonal monopyramidal geometry. These descriptions agree well with the visual appearances of the compounds. In contrast, the similarity of the τ4 four-coordinate indices for [κ3-TismPriBenz]ZnX (0.81 to 0.82) and {[TismPriBenz]Zn}[Y] (0.85 to 0.87) does not provide an effective means to distinguish the structures. The use of normalized CShMN values thus affords a useful quantitative method for identifying coordination geometries, especially in situations where the geometries deviate from the idealized structures.