Hetero-metallic trinuclear nickel(II)–cadmium(II) complexes of a salicylaldimine ligand with thiocyanate, cyanate and azide ions: Isolation of a pair of polymorphs with thiocyanate ion

Four new trinuclear hetero-metallic nickel(II)–cadmium(II) complexes [(NiL)2Cd(NCS)2] (1A and 1B), [(NiL)2Cd(NCO)2] (2) and [(NiL)2Cd(N3)2] (3) have been synthesized using [NiL] as a so-called “ligand complex” (where H2L = N,N′-bis(salicylidene)-1,3-propanediamine) and structurally characterized. Crystal structure analyses reveal that all four complexes contain a trinuclear moiety in which two square planar [NiL] units are bonded to a central cadmium(II) ion through double phenoxido bridges. The Cd(II) is in a six-coordinate distorted octahedral environment being bonded additionally to two mutually cis nitrogen atoms of terminal thiocyanate (in 1A and 1B), cyanate (in 2) and azide (in 3). Complexes 1A and 1B have the same molecular formula but crystallize in very different monoclinic unit cells and can be considered as polymorphs. On the other hand, the two isoelectronic complexes 2 and 3 are indeed isomorphous and crystallize only in one form. Their conformation is similar to that observed in 1A.

A pair of polymorphs of hetero-metallic copper(II)–cadmium(II) complex have been synthesized using Cu(II)-salicylaldimine “ligand complex” and SCN−. However, using OCN− and N3− only one form which has the structural similarities with one of the polymorphs is isolated.Figure optionsDownload as PowerPoint slideHighlights
► Trinuclear nickel(II)–cadmium(II) complexes of a salicylaldimine type ligand.
► Isolation of a pair of polymorphs by using thiocyanate as coligand.
► Only one form is obtained with cyanate and azide ion.
► The complexes with cyanate and azide ion are isomorphous to each other.