CuII2L based polymeric ladder using dicyanamide bridges: Synthesis, crystal structure and magnetic studies

The reaction in methanol medium of Cu(NO3)2·2.5H2O with H3L1 (H3L1 = 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 [Cu2(L3)(dca)2]n·H2O·1.5MeOH (1). The crystal structure of 1 proves that it is a polymeric complex containing the dianion of the linear hexadentate Schiff base H2L3 (H2L3 = N,N′-bis(5-bromo-salicylidene)-triethylentetramine). Therefore, this demonstrates that the central imidazolidine ring of H3L1 suffered hydrolysis during the reaction, with the consequent cleavage of the central salicylaldehyde residue. The complex so formed shows the linear Schiff base ligand (L3)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-η1:η1 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.