Assembly, crystal structures, and luminescent properties of three new thiocyanate-bridging mercury(II) coordination polymers

Abstract

Two ligands, 2-{5,5-dimethyl-3-[2-(pyridin-3-yl)-ethenyl]cyclohex-2-enylidene}propanedinitrile (L1) and 2-{5,5-dimethyl-3-[2-(pyridin-2-yl)-ethenyl]cyclohex-2-enylidene}propanedinitrile (L2), were synthesized. By reaction of mercury thiocyanate with L1 and L2, respectively, coordination polymers [Hg(L1)(μ1,3-SCN)2]n (1), [Hg(L1)2(μ1,3-SCN)2]n (2), and [Hg(L2)(μ1,3-SCN)(SCN)]n (3) with different structures and topologies were obtained. In 1, the thiocyanate shows μ1,3-SCN bridging coordination, and adjacent Hg(II) ions are bridged by two μ1,3-SCN ions to form an infinite chain with the remaining position of five-coordinate Hg(II) occupied by L1. In 2, the thiocyanate has the same coordination as 1. However, Hg(II) has octahedral coordination with two L1 involved in coordination. An unusual feature of 3 is the presence of two types of thiocyanates, one has a S-terminal ligand and the other has a μ1,3-SCN bridge. The mercury(II) in 3 is four-coordinated by L2 and three thiocyanates. Luminescent properties and thermal stabilities of 1–3 were studied.