MAGNETOSTRUCTURAL CORRELATION IN A SERIES OF IODIDE SALTS OF P-N-ALKYLPYRIDINIUM NITRONYL NITROXIDES - DEPENDENCE OF THE IODIDE-PYRIDINIUM RING INTERACTION ON THE LENGTH OF THE N-ALKYL CHAIN
K. Awaga et al., MAGNETOSTRUCTURAL CORRELATION IN A SERIES OF IODIDE SALTS OF P-N-ALKYLPYRIDINIUM NITRONYL NITROXIDES - DEPENDENCE OF THE IODIDE-PYRIDINIUM RING INTERACTION ON THE LENGTH OF THE N-ALKYL CHAIN, Journal of materials chemistry, 4(9), 1994, pp. 1377-1385
Magnetic measurements and X-ray crystal analyses were carried out on i
odide salts of p-N-alkylpyridinium a-nitronyl nitroxides oxyl-4,5-dihy
dro-3H-imidazol-2'yl)-1-R-pyridinium, with R = methyl (1(+)), ethyl (2
(+)), n-propyl (3(+)) and n-butyl (4(+))]. The strongly antiferromagne
tic crystal of 1(+).l(-) consists of a radical dimer and the iodide io
n is out of the plane of the pyridinium ring. 2(+).l(-), which is weak
ly antiferromagnetic, includes two crystallographically independent mo
lecules, 2A(+) and 2B(+), each of which forms a centrosymmetric dimer.
in the pyridinium ring of 2A(+) the iodides are 'out-of-plane' while
for 2B(+) they are 'in-plane'. The ferromagnetic 3(+).l(-) and 4(+).l(
-) have similar structures: the crystal consists of a two-dimensional
(2D) layer formed by a contact between the pyridinium ring and in-plan
e iodides. In this series, the iodide ion changes position from out-of
-plane to in-plane and the magnetism varies from antiferromagnetic to
ferromagnetic. It is found that the nitronyl nitroxide with an out-of-
plane iodide has a short intermolecular contact between the NO groups
(type I), while that with an in-plane iodide forms a contact between t
he NO group and the pyridinium ring (type II). The observed magnetic b
ehaviour can be interpreted in terms of an antiferromagnetic interacti
on for the type I contact and a ferromagnetic interaction for type II.