Syntheses, structures and magnetism of α-Mn(dca)2, [Mn(dca)2(H2O)2]•H2O, [Mn(dca)2(C2H5OH)2]•(CH3)2CO, [Fe(dca)2(CH3OH)2] and [Mn(dca)2(L)2], where L = pyridine, CH3OH or DMF and dca- = dicyanamide, N(CN)2-

The dicyanamide anion has been observed to adopt two bridging co-ordination modes (mu and mu(3)) in alpha-Mn(dca)(2), [Mn(dca)(2)(H2O)(2)]. H2O, [Mn(dca)(2)(C2H5OH)(2)].(CH3)(2)CO, [Fe(dca)(2)(CH3OH)(2)] and [Mn(dca)(2)(L)(2)] [L = py, CH3OH or DMF; dca = dycanamide N(CN)(2)(-)], and generates weak ligand fields thus stabilising high spin configurations. The N- or O-bonded ligands L play an important role in the stabilisation of both the molecular structures and the three dimensional structure, via hydrogen bonding. The unsolvated alpha-Mn(dca)(2) adopts a rutile-like single network structure, based on the near orthogonal packing of 'ribbons' of ... Mn(N=C-N-C=N)(2)Mn ..., similar to that found for the isomorphous analogues of Co, Ni, Fe and Cu. Magnetisation measurements confirmed a high spin manganese d(5) system displaying antiferromagnetic coupling (theta = -25 K) above 25 K and undergoing long range magnetic ordering (T-N = 16 K) to a spin-canted antiferromagnet (weak ferromagnet). Magnetisation and heat capacity measurements on some samples of alpha-Mn(dca)(2) indicated a possible second transition at approximate to 6 K, the nature of which is under investigation. From the hysteresis data at 2 K (remnant magnetisation of 29 cm(3) Oe mol(-1) and coercive field of 406 Oe) a canting angle of 0.05 degrees is estimated for this soft magnet. Other samples gave a higher value for the coercive field. The alpha-M(dca)(2) series has a diverse range of ground states; Cu-II (d(9)) is a paramagnet, Ni-II (d(8)) and Co-II (d(7)) are ferromagnets and Fe-II (d(6)) and Mn-II (d(5)) are canted antiferromagnets. Reasons for this diversity are given on the basis of the nature of exchange coupling pathways within the rutile structure and a mechanism for the long range magnetic ordering is proposed. A range of 1-D chain complexes of type [Mn(dca)(2)(L)(2)], containing 'ribbons' of doubly bridged Mn(N=C-N-C=N)(2)Mn have been structurally characterised. The complex [Fe(dca)(2)(CH3OH)(2)] is isostructural with the manganese analogue. 2-D Square grids are found in crystals of [Mn(dca)(2)(C2H5OH)(2)].(CH3)(2)CO and in [Mn(dca)(2)(H2O)(2)]. H2O, the latter displaying, in addition, penetration of ribbons of trans-Mn(dca)(2)(H2O)(2) through the grids. Dehydration or desolvation results in formation of the alpha-Mn(dca)(2) phase. The Lewis-base adducts all display very weak antiferromagnetic coupling (J approximate to -0.12 cm(-1)) and no magnetic long-range order. Dissolution of the compounds in protic solvents leads to complete dissociation of the dicyanamide, and the axially co-ordinated ligands, L, can readily be exchanged by reaction or recrystallisation in different co-ordinating solvents.