Azide bridged dicopper(II), dicobalt(II) complexes and a rare double μ-chloride bridged ferromagnetic dicobalt(II) complex of a pyrazolyl-pyrimidine ligand: Synthesis, crystal structures, magnetic and DFT studies

Two new dinuclear copper(II) complexes [Cu-2(PymPz)(2)(N-3)(2)Cl-2] (1), [Cu-2(PymPz)(2)(N-3)(4)] (2) and two new dinuclear cobalt(II) complexes [Co-2(PymPz)(2)Cl-4] (3), [Co-2(PymPz)(2)(N-3)(4)] (4) [PymPz = 2-(3,5-dimethyl-1H-pyrazol-1-yl)-4,6-dimethylpyrimidine] have been synthesized and characterized crystallographically and spectroscopically. In each of the complexes 1,2 and 4 the two adjacent metal centers are bridged by a pair of mu-1,1 azide groups whereas in 3 the metal centers are bridged by a pair of chloride ions. In the complexes, all the metal centers are pentacoordinated. In 1 and 2 the copper(II) centers have distorted square pyramidal geometry (tau = 0.18 for 1 and 0.091 for 2) but in 3 and 4 cobalt(II) centers have distorted trigonal bipyramidal geometry (tau = 0.619 for 3 and 0.557 for 4). Complexes 1 and 2 show antiferromagnetic interaction (J = -7.09 cm(-1) for 1 and J = -17.00 cm(-1) for 2) whereas 3 and 4 show ferromagnetic interaction (J = 7.44 cm(-1) for 3 and J = 10.45 cm(-1) for 4). Complex 3 displays an unprecedented ferromagnetic interaction over double mu-chloro bridges in the observed angle range (94.87 degrees). The exchange path-ways parameters for all the complexes have also been evaluated from density functional theoretical calculations to corroborate the bridging signatures with experimental findings. (C) 2012 Elsevier Ltd. All rights reserved.