Syntheses, structures and magnetism of alpha-Mn(dca)(2), [Mn(dca)(2)(H2O)(2)]center dot H2O, [Mn(dca)(2)(C2H5OH)(2)]center dot(CH3)(2)CO, [Fe(dca)(2)(CH3OH)(2)] and [Mn(dca)(2)(L)(2)], where L = pyridine, CH3OH or DMF and dca(-) = dicyanamide, N(CN)(2)(-)
Sr. Batten et al., Syntheses, structures and magnetism of alpha-Mn(dca)(2), [Mn(dca)(2)(H2O)(2)]center dot H2O, [Mn(dca)(2)(C2H5OH)(2)]center dot(CH3)(2)CO, [Fe(dca)(2)(CH3OH)(2)] and [Mn(dca)(2)(L)(2)], where L = pyridine, CH3OH or DMF and dca(-) = dicyanamide, N(CN)(2)(-), J CHEM S DA, (17), 1999, pp. 2987-2997
Citations number
35
Categorie Soggetti
Inorganic & Nuclear Chemistry
Journal title
JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS
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(d
ca)(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 molecula
r 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)M
n ..., similar to that found for the isomorphous analogues of Co, Ni, Fe an
d Cu. Magnetisation measurements confirmed a high spin manganese d(5) syste
m displaying antiferromagnetic coupling (theta = -25 K) above 25 K and unde
rgoing long range magnetic ordering (T-N = 16 K) to a spin-canted antiferro
magnet (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 hy
steresis data at 2 K (remnant magnetisation of 29 cm(3) Oe mol(-1) and coer
cive 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 divers
ity are given on the basis of the nature of exchange coupling pathways with
in the rutile structure and a mechanism for the long range magnetic orderin
g is proposed. A range of 1-D chain complexes of type [Mn(dca)(2)(L)(2)], c
ontaining 'ribbons' of doubly bridged Mn(N=C-N-C=N)(2)Mn have been structur
ally characterised. The complex [Fe(dca)(2)(CH3OH)(2)] is isostructural wit
h 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 di
splaying, in addition, penetration of ribbons of trans-Mn(dca)(2)(H2O)(2) t
hrough the grids. Dehydration or desolvation results in formation of the al
pha-Mn(dca)(2) phase. The Lewis-base adducts all display very weak antiferr
omagnetic coupling (J approximate to -0.12 cm(-1)) and no magnetic long-ran
ge 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-o
rdinating solvents.