2,2′-bipyrimidine- and 2,3-bis(2-pyridyl)pyrazine-containing manganese(II) compounds:: structural and magnetic properties

The preparation, crystal structures and magnetic properties of four different manganese(II) compounds of formula [Mn(bipym)Cl-2](n).2nH(2)O (1), [Mn-2(dpp)(2)(H2O)(2)Cl-4].2H(2)O (2), [Mn(dpp)(H2O)(2)](n)(ClO4)(2n).1.5nH(2)O (3) and [Mn(dpp)(dca)(2)](n) (4) [bipym = 2,2'-bipyrimidine, dpp = 2,3-bis(2-pyridyl)pyrazine and dca = dicyanamide anion] are reported. Compounds I and 3 are uniform chains of six-coordinated manganese(II) ions bridged by bis(bidentate) bipym (1) and dpp (3) ligands with two chloride groups (1) and two water molecules (3) in cis position, The electroneutrality in 3 is achieved by uncoordinated perchlorate anions. The manganese atom in I and 3 exhibits a distorted octahedral environment mainly due to the short bite angle at the bis(chelating) bipym [70.9(1)degrees] and dpp [72.6(2)degrees] ligands. The intrachain Mn ... Mn separations are 6.164(1) Angstrom in 1 and 7.289(2) Angstrom in 3. Complex 2 is binuclear with a pair of chlorine atoms bridging the manganese atoms in a central Mn2Cl2 plane, the intramolecular Mn ... Mn separation being 3.805(2) Angstrom. Each manganese atom in 2 is six-coordinated with two nitrogen atoms from a bidentate dpp, a water molecule and three chlorine atoms (one terminal and two bridging) building a distorted octahedral environment. Compound 4 is a rhombic layered compound where the manganese atoms of each sheet are linked by single mu-1,5-dca bridges with Mn ... Mn separations of 6.909(1) and 7.674(1) Angstrom. Each manganese atom in 4 is in a distorted octahedral environment, being coordinated to six nitrogen atoms, four from dca ligands and two from a bidentate dpp molecule. Magnetic susceptibility measurements for 1-4 in the temperature range 1.9-290 K show the occurrence of significant magnetic interactions between the local high spin manganese(n) ions which are antiferromagnetic across bridging bipym (J = -1.19 cm(-1), 1), dpp (J = -0.25 cm(-1), 3) and dca (J = -0.26 cm(-1), 4) and ferromagnetic through the double-mu-chloro bridge (J = +0.11 cm(-1), 2).