Synthesis, structural and magnetic characterizations of new complexes of di-2,6-(2-pyridylcarbonyl)pyridine (pyCOpyCOpy) ligand

Using the di-2,6-(2-pyridylcarbonyl)pyridine ligand (L1) as starting framework, five new mononuclear complexes were obtained: [Cu(L1)(MeCN)(ClO4)2] (1) [Co(L1)(MeCN)(Br)2]*MeCN (2), [Fe(L1)2](BF4)2*MeOH*H2O (3), [Cr(L2a)Cl2]*2MeOH (where HL2a is (6-(hydroxyl(methoxy)(pyridin-2-yl)methyl)pyridin-2-yl)(pyridin-2-yl)methanone) (4) and one trinuclear [NiII3] complex, [Ni3(L2b)2(Bz)2(EtOH)2](ClO4)2*2EtOH (where HL2b is (6-(hydroxyl(ethoxy)(pyridin-2-yl)methyl)pyridin-2-yl)(pyridin-2-yl)methanone; Bz = benzoato) (5). Their structural and magnetic characterizations are herein reported. All the metal ions show octahedral coordination geometry, which is slightly unusual for the L1-based Cu(II) complex 1. Formation of complexes 4 and 5 is accompanied by the metal-assisted solvent addition to one carbonyl group of the L1 ligand with methanol or ethanol leading to the deprotonated mono-hemiacetals L2a and L2b ligands respectively. The trinuclear [NiII3] compound 5 shows two different bridging units: two L2b units and two benzoato (Bz) ligands. 5 represents the smallest polynuclear compound in the known {NiII(L1-based)}n (n = 5, 6) series. The magnetic properties of the five complexes have been investigated. While compounds 1-4 show the expected magnetic behavior for mononuclear species, 5 exhibits intramolecular ferromagnetic interactions between the NiII (S = 1) ions stabilizing an ST = 3 ground state