Isolation of two different Ni₂Zn complexes with an unprecedented cocrystal formed by one of them and a “Coordination Positional Isomer” of the other

Abstract

A new homometallic trinuclear Ni(II) complex [(NiL) ₂Ni(NCS) ₂] (1) and three heterometallic trinuclear Ni(II)–Zn(II)–Ni(II) complexes [(NiL) ₂Zn(NCS) ₂] (2), [(NiL) ₂Zn(NCS)₂(CH₃OH) ₂]•2CH₃OH (3) and {[(NiL) ₂Zn(NCS) ₂(CH₃OH) ₂]} {[(NiL) ₂Zn(NCS) ₂]} (4) have been synthesized by using the “complex as ligand” approach with the “metalloligand” [NiL] (H₂L = N,N′-bis(salicylidene)-1,3-propanediamine) and thiocyanate in different ratios. All the complexes have been structurally and magnetically characterized. In the isomorphous complexes 1 and 2, the two terminal square planar Ni atoms and the central octahedral nickel atom (in 1) or zinc atom (in 2) are arranged in a bent structure where two cis κN-SCN^– thiocyanate ions are coordinated to the central atom. The chemical composition of 3 is very similar to that of 2 but, in 3, the central Zn atom is tetrahedral and the κN-SCN^– thiocyanate ions occupy an axial position of each terminal nickel atom (which now are octahedral with the sixth position occupied by a methanol molecule). Complex 4 consists of two closely related trinuclear units 4A and 4B. In 4A, the coordination environments of the metals are identical to those of 3 whereas 4B is a “coordination position isomer” of complex 2 with the central square pyramidal Zn and one of the terminal square pyramidal Ni atoms coordinated by two κN-SCN^– thiocyanate ions. Complex 4 is a unique example of a cocrystal formed by two similar trinuclear units (4A and 4B) where 4A is identical to an existing complex (3) and 4B is a “coordination position isomer” of another existing complex (2).