Isoreticular Tp*–W–Cu–S cluster-based one-dimensional coordination polymers with an uncommon [Tp*WS3Cu2] + [Cu] combination and their third-order nonlinear optical properties

Abstract

We herein report three isoreticular Tp*–W–Cu–S cluster-based one-dimensional coordination polymers, namely, [Tp*WS₃Cu₂(CN)₂Cu](pz)_0.5 (2), [Tp*WS₃Cu₂(CN)₂Cu](bipy)_0.5·0.5DMF (3), and [Tp*WS₃Cu₂(CN)₂Cu](bpb)_0.5·DMF (4), from the reaction of [Et₄N][Tp*WS₃] (1) with CuCN in the presence of bridging ligands pyrazine (pz), 4,4′-bipyridine (bipy), and 1,4-bis(4-pyridyl)benzene (bpb) under solvothermal conditions. In 2–4, a pair of butterfly-shaped [Tp*WS₃Cu₂]⁺ clusters are connected by two [Cu(CN)₂]⁻ units to give a macrocyclic unit, which is further strung by pz/bipy/bpb to give linear chains. Besides their rare isoreticular nature, 2–4 are also unique in that they contain a [Tp*WS₃Cu₂] + [Cu] combination instead of the widely acknowledged nest-shaped [Tp*WS₃Cu₃]²⁺ or cuboidal [Tp*WS₃Cu₃X]⁺ (X = Cl, Br, I) cluster skeleton. Compounds 2–4 are also characterized by FT-IR, elemental analysis, UV-vis and ESI-MS. The ESI-MS results also indicate that the pz/bipy/bpb coordination is labile in solution under harsh ionization conditions, yielding CN-ligated anionic species which are assumed as the key contributors to the enhanced NLO performance of 2–4 compared to that of the starting material 1.