Structural characterization of copper(II) complexes based on a new 10-membered binucleating 1,6-diazecine ligand

The three dicopper(II) complexes [Cu2(Lendm)(ClO4)2(H2O)2](ClO4)2·2H2O (1), [Cu2(Lendm)(N3)2(H2O)2](ClO4)2 (2), and [Cu2(Lendm)(C4O4)2(H2O)2]·6H2O (3) (C4O42− = 3,4-dihydroxycyclobut-3-en-1,2-dionate) were synthesized from the novel binucleating ligand 1,6-diazecine, Lendm namely bis{[c,h](2-methylimidazolyl)}-1,6-diazecine-1,6-bis(N,N-dimethylamino-eth-2-yl). The perchlorato, 1 and the squarato complex 3 were structurally characterized by X-ray crystallography. The spectral and structural characterization, and electrochemical properties as well as thermogravimetric analyses of the complexes are reported. The Cu(II) centers in 1 and 3 displayed a distorted square pyramidal environment with the CuN3O2 chromophore. In which the basal sites are occupied by the three nitrogen donors of Lendm: N(1) of the N,N-dimethylamino-eth-2-yl side chain, N(2) of the 10-membered central 1,6-diazecine ring and N(3) of the non-protonated N atom of the imidazolyl, an O(1) of the aqua ligand in 1 or O(1) of the terminal squarato ligand in 3, and an aqua ligand occupying the apical position. In both cases the Lendm behaves as bis-tridentate bridging ligand with the intradinuclear Cu⋯Cu distances are in the range 7.38–7.51 Å. The UV–Vis and IR spectroscopy, elemental and the thermal analyses of the complexes are in complete agreement with the assigned structural formulas. The cyclic voltametric properties of the two complexes 1 and 2 were also studied.