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

Abstract

The preparation, crystal structures and magnetic properties of four different manganese(II) compounds of formula [Mn(bipym)Cl₂]_n·2nH₂O (1), [Mn₂(dpp)₂(H₂O)₂Cl₄]·2H₂O (2), [Mn(dpp)(H₂O)₂]_n(ClO₄)_2n·1.5nH₂O (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 1 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 1 and 3 exhibits a distorted octahedral environment mainly due to the short bite angle at the bis(chelating) bipym [70.9(1)°] and dpp [72.6(2)°] ligands. The intrachain Mn⋯Mn separations are 6.164(1) Å in 1 and 7.289(2) Å 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) Å. 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 μ-1,5-dca bridges with Mn⋯Mn separations of 6.909(1) and 7.674(1) Å. 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(II) 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-μ-chloro bridge (J = +0.11 cm⁻¹, 2).