A new manganese(II) compound [Mn₂(bipy)₄(ta)][ClO₄]₂1(bipy = 2,2′-bipyridme, ta = terephthalate dianion) has been synthesised and its crystal structure determined by single-crystal X-ray diffraction. It crystallizes in the triclinic system, space group P, with a= 9.516(2), b= 11.613(3), c= 11.615(3)Å, α= 70.92(2), β= 80.16(2), γ= 76.64(2)° and Z= 1. The structure consists of canonic terephthalate-bridged [Mn₂(bipy)₄(ta)]²⁺ chains and non-co-ordinated perchlorate anions. Each terephthalate is bound to four manganese atoms through carboxylate oxygens with the sym-sym bridging mode, affording manganese(II) pairs which are linked by the terephthalate group to yield a one-dimensional chain running along the a axis. The intrachain Mn ⋯ Mn separations through the double carboxylate and terephthalate bridges are 4.643(1) and 9.637(2)Å, respectively The manganese(II) ion displays a severely distorted octahedral co-ordination being linked to four nitrogen atoms of two bipy ligands and to two oxygen atoms of two carboxylate groups from two terephthalate ligands. The magnetic susceptibility of 1 as a function of temperature (4.2–290 K) exhibits a sharp maximum at 6.0 K which is consistent with a significant antiferromagnetic coupling between the metal centres. This magnetic behaviour has been interpreted in terms of a dimer with a molecular field approximation, the values obtained for J, g and zJ′ being –1.35 cm^–1,1.97 and –0.04cm^–1, respectively. In the light of the structural data, it can be concluded that the double-carboxylate bridge between the manganese(II) pairs provides a more efficient exchange pathway than that of terephthalate and most likely is responsible for the observed J value.

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).