Steric Control over Supramolecular Polymer Formation in trans-1,2-Bis(4-pyridyl)ethylene Adducts of Zinc Xanthates: Implications for Luminescence

Abstract

Steric control over supramolecular aggregation is demonstrated for a series of adducts formed between Zn(S 2 COR) 2 and trans-1,2-bis(4-pyridyl)ethylene, whereby supramolecular zigzag polymers are found when R is small, that is, Et (1) and n-Bu (2), but only bimetallic aggregates could be formed when R = Cy (3). This results in different coordination geometries: fourcoordinate N 2 S 2 zinc in 1 and 2, and five-coordinate NS 4 zinc in 3, a feature which greatly influences photophysical responses in the solid state. When excited in the UV region, {Zn(S 2 COEt) 2 L} ¥ (1) and {[Zn(S 2 COCy) 2 ] 2 L} (3) produce broad luminescence in the visible region. Five-coordinate 3 produces more broad and intense luminescence than four-coordinate 1. The configuration interaction singles (CIS) and post-Hartree-Fock (HF) calculations for 1 and 3 indicate the A-band excited state is responsible for the observed luminescence which is strongly associated with charge transfer from S and Zn.

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

“…When the steric bulk of the R group in the xanthate ligand is increased, a new aggregation pattern in observed. In [Zn(S 2 COCy) 2 ] 2 (bpe) (6) [31], isolated from analogous 1:1 solutions that yielded 4 and 5, the xanthate ligands revert to S,S-coordination modes and a binuclear aggregate is formed, similar to that shown in Figure 1b. Such steric effects in the coordination chemistry of metal 1,1-thiolates is well documented [25,68,70].…”

“…There are six structures in this category, 1-6 [28][29][30][31], and general features of these are summarised in Table 1 along with the other zinc structures, 1-57 , included in this survey. The first structure to be described contains the smallest bipyridyl-type ligand, namely pyrazine (pyr), and is a one-dimensional coordination polymer formulated as [Zn(S 2 COEt) 2 (pyr)] n (1) [28].…”

“…A difference in the conformation of the bpy ligand in the structures of 2 and 3 is noted, namely the dihedral angle between the pyridyl rings in 2 is 13.9 • compared with 29.0 • in 3, indicating conformational flexibility. The three remaining structures in this section contain the trans-1,2-bis(4-pyridyl)ethylene (bpe) ligand in a bridging mode [31]. In [Zn(S 2 COR) 2 (bpe)] n , for R = Et (4) and nBu (5), both xanthate ligands are S,O-chelating resulting in N 2 O 2 S 2 donor sets which are best described as being skew-trapezoidal bipyramidal in which the pyridyl-N atoms lie over the relatively long Zn-O bonds.…”

“…With τ = 0.51, the NS 4 coordination geometry in 6 is almost exactly intermediate between the two ideal five-coordinate geometries. The influence of aggregation patterns in 4-6-that is, polymeric versus dimeric-was shown to have a distinct influence upon the solid-state luminescence responses [31].…”

Exploring the Topological Landscape Exhibited by Binary Zinc-triad 1,1-dithiolates

“…In short, the bulkier the R substituent, the less likely it is that supramolecular aggregation will occur. This concept is now well established in the structural chemistry of main group element 1,1-dithiolates [17,[40][41][42] and in the structural chemistry of related organotin carboxylates [43][44][45], where bulky groups can disrupt [18,[46][47][48]. Further, it should be stressed that the nature of R, at least that present in the overwhelming majority of zinc-triad xanthate structures, does not exert a significant influence upon the electronic structure of the xanthate anion [49].…”