Designing a heterotrinuclear CuII—NiII—CuIIcomplex from a mononuclear CuIISchiff base precursor with dicyanamide as a coligand: synthesis, crystal structure, thermal and photoluminescence properties

Schiff bases are considered `versatile ligands' in coordination chemistry. The design of polynuclear complexes has become of interest due to their facile preparations and varied synthetic, structural and magnetic properties. The reaction of the `ligand complex' [CuL] {H2Lis 2,2′-[propane-1,3-diylbis(nitrilomethanylylidene)]diphenol} with Ni(OAc)2·4H2O (OAc is acetate) in the presence of dicyanamide (dca) leads to the formation of bis(dicyanamido-1κN1)bis(dimethyl sulfoxide)-2κO,3κO-bis{μ-2,2′-[propane-1,3-diylbis(nitrilomethanylylidene)]diphenolato}-1:2κ6O,O′:O,N,N′,O′;1:3κ6O,O′:O,N,N′,O′-dicopper(II)nickel(II), [Cu2Ni(C17H16N2O2)2(C2N3)2(C2H6OS)2]. The complex shows strong absorption bands in the frequency region 2155–2269 cm−1, which clearly proves the presence of terminal bonding dca groups. A single-crystal X-ray study revealed that two [CuL] units coordinate to an NiIIatom through the phenolate O atoms, with double phenolate bridges between CuIIand NiIIatoms. Two terminal dca groups complete the distorted octahedral geometry around the central NiIIatom. According to differential thermal analysis–thermogravimetric analysis (DTA–TGA), the title complex is stable up to 423 K and thermal decomposition starts with the release of two coordinated dimethyl sulfoxide molecules. Free H2Lexhibits photoluminescence properties originating from intraligand (π–π*) transitions and fluorescence quenching is observed on complexation of H2Lwith CuII.