Structural comparison of copper(II) thiocyanate pyridine complexes

Copper(II) thiocyanate forms square planar complexes with substituted pyridines (XPy), trans-[Cu(NCS)2(XPy)2]. Thiocyanate is primarily N-bonded, occasionally producing monomers. But in most cases thiocyanate bridging via long Cu⋯S bonds produces dimers, chains or sheets. Pyridine substituent positions influence the degree of bonding. Bridging ligands L=4,4′-dipyridyl and pyrazine produce [Cu(NCS)2(LL)]. [Display omitted] •Copper(II) thiocyanate form trans square planar complexes with pyridines.•Thiocyanate is always primarily N-bonded.•Long Cu⋯S bonds span weakly bond monomers into chains or sheets.•Pyridine substituent positions influence the degree of bonding. Copper(II) thiocyanate forms a series of closely related complexes when reacted with substituted pyridines (XPy) in methanol. Although these compounds are nominally square planar trans-[Cu(NCS)2(XPy)2], most show N,S-thiocyanate bridging via long Cu–S bonds of ⩾2.7Å. The resulting Jahn-Teller (J-T) distorted octahedra form edge-sharing chains. However, these units can also form sheets or small oligomers. For some 2- or 3-substituted pyridines, isolated square planar trans-[Cu(NCS)2(XPy)2], J-T distorted octahedral trans-[Cu(NCS)2(XPy)2(MeOH)2], or square pyramid trans-[Cu(NCS)2(XPy)2(MeOH)] were isolated. Polymorphism and/or solvento isomers appear to be common, being identified for five of 21 ligands studied. Use of 2-NH2Py produces methoxy-bridged dimers [Cu2(NCS)2(2-NH2Py)2(μ-OMe)2] that are further linked via bridging thiocyanate to form a sheet structure. Unusual aryl bromide metal chelation is noted in the mixed ligand complex trans-[Cu(NCS)2(2-BrPy)(3-BrPy)]. When LL=4,4′-bipyridyl (Bpy) or pyrazine (Pyz) is used, bridging by both the organic and thiocyanate ligands produces sheet networks, trans-[Cu(NCS)2(LL)].