Ligand Concentration Controlled Supramolecular Isomerism in Two CuSCN Based Coordination Polymers with in Situ Synthesized 4,4‘-Dipyridylsulfide as a Co-Ligand

Abstract

Reactions of CuCl2, 4-pyridylthiol, and NH4SCN in mixed acetonitrile and water solutions at 140 °C and 96 h led to two polymorphs of CuSCN coordination polymers with stoichiometry [Cu2(SCN)2(dps)]∞ (dps = 4,4‘-dipyridyl sulfide). The dps ligand is generated in situ via desulfation coupling of 4-pyridinethiol during the hydrothermal treatment. Polymorph 1 is a two-dimensional (2D) tubular sheet constructed by an unprecedented [CuSCN]∞ column and dps ligand. The [CuSCN]∞ column can be described as two zigzag chains arranged with approximate C2v symmetry, one chain being connected to the other by Cu−S contacts. An alternative description of the [CuSCN]∞ column is the stacking of [CuSCN]2 dimers, alternately rotated by 90° and linked by Cu−N contacts. Polymorph 2 is a 2D planar sheet constructed by [Cu(SCN)]∞ staircase chains and dps ligands. The [CuSCN]∞ staircase can be viewed as an alternating fusion of four-membered Cu−S−Cu−S rings and eight-membered Cu−S−C−N−Cu−S−C−N rings. The two polymorphs are very rare examples of coordination polymers that exhibit a similar local coordination geometry of metal and the same topology but different CuSCN structural motifs. Interestingly, 1 and 2 show quite different photoluminescent properties: the former has emission maxima at 538 nm assigned to a ligand-centered excited state, while the latter shows emission maxima at 636 nm tentatively attributed to both ligand-to-metal and metal-centered transitions.