A Combined Experimental and Computational Study on Supramolecular Assemblies in Hetero-tetranuclear Nickel(ii)-cadmium(ii) Complexes with NO-donor Compartmental Schiff Bases

Two new hetero-tetranuclear nickel(ii)/cadmium(ii) complexes, a cubane [(CHCO)Ni(L)Cd(NCS)] (1) and a linear tetramer [(DMSO)NiLCd(NCS)(μ-SCN)Ni(DMSO)LCd(NCS)] (2) {where HL = N,N'-bis(3-methoxysalicylidene)propane-1,3-diamine and HL = N,N'-bis(3-ethoxysalicylidene)propane-1,3-diamine are potential octadentate compartmental Schiff bases}, were synthesized and characterized. The structures of both complexes were confirmed by single crystal X-ray diffraction studies. Complex 1 contained a NiCdO cubane core, whereas complex 2 featured an end-to-end thiocyanate-bridged tetranuclear moiety. Furthermore, complex 1 showed C-HH-C interactions, whereas a unique Sπ interaction was observed in complex 2. Theoretical studies were performed using several computational tools such as NBO and AIM analyses. Both complexes showed photoluminescence in DMSO medium at room temperature upon irradiation with ultraviolet light. The lifetimes of the excited states were ∼27 ns.