Dimeric Mn(II), Co(II), Ni(II) and Cu(II) complexes of a common carboxylate-appended (2-pyridyl)alkylamine ligand: structure, magnetism and DFT study

Four new complexes of composition [M-2(II)(L-3)(2)(CH3OH)(2)](ClO4)(2) (M = Mn, 1; Co, 2; Ni, 3) and [Cu-2(II)(L-3)(2)](ClO4)(2) (4) (L-3(-) = 3-[2-(((6-methyl)pyridin-2-yl)methyl){(dimethylamino)ethyl}-amino]propionate) have been synthesized and characterized. Structural analysis reveals that 1-4 are discrete syn-anti carboxylate-bridged binuclear coordination complexes with a {M-2(II)(-O-C-O-)(2)}(2+) structural motif. In 1-3 distorted octahedral MN3O3 and in 4 distorted square pyramidal CuN3O2 coordination is satisfied at each M(II) center by three N (a pyridyl and two tertiary aliphatic amines) and a carboxylate O of the ligand, and an O of the carboxylate group. In 1-3 the M(II) center is also coordinated by a CH3OH molecule. Variable-temperature magnetic measurements reveal the presence of weak antiferromagnetic interactions in 1 and weak ferromagnetic interactions in 2-4. The electronic structure of 1-4 has been probed by density functional theory (DFT) calculations at the B3LYP level of theory. In order to gain insight into the origin of the observed electronic transitions, time-dependent (TD)-DFT calculations have been done.