Dinuclear, star-shaped tetranuclear and trinuclear-based two-dimensional metal complexes derived from a less investigated Schiff base ligand: Syntheses, crystal structures and spectroscopic correlation

The work in this paper deals with five new complexes of composition [CuII(MeCN)L(UVIO2)(NO3)2]⋅MeCN (1), [(CuIIL)3CdII](ClO4)2 (2) and [(CuIIL)2MII(μ1,5-dicyanamide)2]n (M = Co (3), M = Ni (4) and M = Zn (5)) derived from a single-compartment Schiff base ligand H2L, which is the [2 + 1] condensation product of salicylaldehyde and 1,4-diaminobutane. Single crystal X-ray structures of all the five complexes have been determined. Compound 1 is a diphenoxo-bridged CuII(UVIO2) system, compound 2 is a star-shaped tetranuclear system where the cadmium(II) center is encapsulated in between three [CuIIL] moieties and the three isomorphous compounds 3–5 are trinuclear CuIIMIICuII-based (M = Co, Ni, Zn) two-dimensional, square-grid systems where the trinuclear units are bridged by μ1,5-dicyanamide ligands. In addition to the exploration of much less investigated Schiff base ligand family having four carbon atoms between the two imine nitrogen atoms, the types of structures presented here either have some novelties or are new examples and therefore deserves importance. The d–d spectra of copper(II)-diamagnetic metal ion complexes (1, 2 and 5) and the corresponding mononuclear copper(II) compound have been recorded with the aim to shed light on the correlation of d–d band position with the displacement of copper(II) from the least-squares basal plane, revealing excellent correlation.