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

Abstract

Four new complexes of composition [M^II₂(L³)₂(CH₃OH)₂](ClO₄)₂ (M = Mn, 1; Co, 2; Ni, 3) and [Cu^II₂(L³)₂](ClO₄)₂ (4) (L³(−) = 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^II₂(–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.