Designing a heterotrinuclear Cu~II—N~III—Cu~II complex from a mononuclear Cu~II Schiff base precursor with dicyanamide as a coligand: synthesis, crystal structure, thermal and photo-luminescence properties

摘要

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] {H_2L is 2,2'-[propane-1,3-diylbis(nitrilo-methanylylidene)]diphenol} with Ni(OAc)_2-4H_2O (OAc is acetate) in the presence of dicyanamide (dca) leads to the formation of bis(dicyanamido-1κN~1)bis(dimethyl sulfoxide)-2κO,3κO-bis{μ-2,2'-[propane-1,3-diylbis(nitrilo-methanylylidene)]diphenolato}-1:2κ~6O,O':O,N,N',O';1:3κ~6O,O':O,N,N',O'-dicop-per(II)nickel(II), [Cu_2Ni(C_17H_16N_2O_2)_2(C_2N_3)_2(C_2H_6OS)_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 Ni~II atom through the phenolate O atoms, with double phenolate bridges between Cu~II and Ni~II atoms. Two terminal dca groups complete the distorted octahedral geometry around the central Ni~II atom. According to differential thermal analysis-thermogravi-metric 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 H_2L exhibits photoluminescence properties originating from intraligand (π-π*) transitions and fluorescence quenching is observed on complexation of H_2L with Cu~II.