Cu II2L based polymeric ladder using dicyanamide bridges: Synthesis, crystal structure and magnetic studies

Abstract

The reaction in methanol medium of Cu(NO 3) 2·2.5H 2O with H 3L 1 (H 3L 1 = 2-(5-bromo-2-hydroxyphenyl)-1,3-bis[4-(5-bromo-2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) and sodium dicyanamide, Na(dca), in 2:1:1 molar ratio, afforded [Cu 2(L 3)(dca) 2] n ·H 2O·1.5MeOH ( 1). The crystal structure of 1 proves that it is a polymeric complex containing the dianion of the linear hexadentate Schiff base H 2L 3 (H 2L 3 = N, N′-bis(5-bromo-salicylidene)-triethylentetramine). Therefore, this demonstrates that the central imidazolidine ring of H 3L 1 suffered hydrolysis during the reaction, with the consequent cleavage of the central salicylaldehyde residue. The complex so formed shows the linear Schiff base ligand (L 3) 2− with an unusual dinucleating ONN + NNO bistridentate donor behaviour, where both tridentate compartments are anti positioned, and each dca anion is μ-1,5-η 1:η 1 coordinated. This combination results in a ladder-like polymer based on dinuclear blocks. The voids formed between ladders in the crystalline structure trap some methanol and water solvates by means of H bonds. In addition, the magnetic characterisation of 1 demonstrated that the copper(II) ions are weakly coupled, showing an overall antiferromagnetic behaviour.