CRYSTAL STRUCTURE AND THERMAL ANALYSIS OF A 4,4′-BIPY-BRIDGED BINUCLEAR ZINC(II) COMPLEX, 2[R₂NCS₂]₂ · Zn(4,4′-BIPY) (R=PIPERIDYL)

Abstract

The crystal structure of the title complex 2[R2NCS&. Zn(4,4'-bipy) (R = Piperidyl), 1, revealed that it consists of dimers made up from two crystallographically independent molecules. Each zinc atom in 1 forms a Scoordinate pseudo-square-based pyramidal arrangement (with four Zn-S and one Zn-N interactions). Bondlengths to Zn with the coordinating atoms are comparable to those in other Zn(1I) dithiocarbamate complexes. The piperidine ring has a chair conformation. To allow improved packing, the title complex molecules form an approximately linear arrangement extending along both a and 6. TGA showed that 1 is decomposed in two close steps to produce ZnS as identified by residual weight. The complex 1 crystallizes in the monoclinic space group C2 cwithcellparameters: a=22.021(5), 6=22.215(3), c= 17.537(2) A, p=93.49(2)", V = 8563(3) i3 and 2 = 8 . The structure was refined by full-matrix least-squares methods to R = 0.067, Rw = 0.1 14.

Perplexing Coordination Behaviour of Potentially Bridging Bipyridyl-Type Ligands in the Coordination Chemistry of Zinc and Cadmium 1,1-Dithiolate Compounds

“…In [Zn(S2CNEt2)2]2(bpy) (30) [46,47], there are two independent molecules in the asymmetric unit: one where the ZnNNZn vector is coincident with the two-fold axis, and the other where the two-fold axis is perpendicular to the ZnNNZn vector. In a sense, the structure of {Zn[S2CN(CH2)5]2}2(bpy) (36) [52] represents a synthesis of the above in that there are two Thus far, all bipyridyl-type ligands described have had the 4-pyridyl isomer; in the three remaining dithiophosphate structures, isomeric 2-pyridyl and 3-pyridyl species connect zinc atoms. Unlike the polymeric bpe analogue, 11, the structure of Zn[S 2 P(OiPr) 2 ] 2 (2-bpe)} 2 (23) [32], where 2-bpe is the 2-pyridyl isomer of bpe, that is trans-1,2-bis(4-pyridyl)ethylene, is dimeric, no doubt owing to steric congestion, Figure 6b.…”

“…Identical symmetry is found in the R = nPr (31) [44], iPr (32) [48], iBu (33) (30) [46,47], there are two independent molecules in the asymmetric unit: one where the ZnNNZn vector is coincident with the two-fold axis, and the other where the two-fold axis is perpendicular to the ZnNNZn vector. In a sense, the structure of {Zn[S 2 CN(CH 2 ) 5 ] 2 } 2 (bpy) (36) [52] represents a synthesis of the above in that there are two independent molecules, one situated about a centre of inversion and the other molecule having 2-fold symmetry coincident with the ZnNNZn axis. In the non-centrosymmetric molecules, the range of dihedral angles between the pyridyl rings of bpy is 25 to 39 • for the molecule with two-fold axes coincident with the ZnNNZn vector in 30 and the molecule in 222-symmetric 35, respectively.…”

“…With a value of τ = 0.51, the NS 4 donor set is nearly perfectly intermediate between square-pyramidal and trigonal-pyramidal. The remaining structures involving bpy, 29-36 [45][46][47][48][49][50][51][52] have this ligand in the expected bridging mode: see Table 1. The prototype structure of the majority of these [Zn(S 2 CNR 2 ) 2 ] 2 (bpy) structures is the R = Me derivative, 29 [45], shown in Figure 7b.…”