Kh. Sugiyarto et al., STRUCTURAL AND ELECTRONIC-PROPERTIES OF IRON(II) AND NICKEL(II) COMPLEXES OF 2,6-BIS(TRIAZOL-3-YL)PYRIDINES, Australian Journal of Chemistry, 46(8), 1993, pp. 1269-1290
Iron(II) and nickel(II) bis(ligand) complexes of 2,6-bis(1,2,4-triazol
-3-yl)pyridine and the substituted derivatives 2,6-bis(1(N)-methyl-1,2
,4-triazol-3-yl)pyridine, 2,6-bis(5-methyl-1,2,4-triazol-3-yl)pyridine
and 2,6-bis(1,5-dimethyl-1,2,4-triazol-3-yl)pyridine have been prepar
ed. Coordination of the unsubstituted ligand through N 4 of the triazo
lyl moieties is confirmed by structure determination of [FeL2][NO3]2.4
H2O and [NiL2]Cl2.3H2O. In both of these complex salts there is an ext
ensive hydrogen-bonded network involving the N 1-H group, the anions a
nd the water molecules. Bis[2,6-bis(1,2,4-triazol-3-yl)pyridine]nickel
(II) dichloride trihydrate: monoclinic, space group C2/c, a 17.971(5),
b 11-433(1), c 14.849(5) angstrom, beta 122.20(1)-degrees, Z 4. Bis[2
,6-bis(1,2,4-triazol-3-yl)pyridine]iron(ii) dinitrate tetrahydrate: te
tragonal, space group I 4(1)/a, a 11.488(2), c 21.055(7) angstrom, Z 4
. [FeL2]Cl2.3H2O is isostructural with the nickel complex and is high-
spin but undergoes a partial transition to low-spin at low temperature
. Conversion to low-spin is complete when the complex is dehydrated, a
nd this change is associated with the effects of the hydrogen bonding.
The solid iron complexes of the N-methyl-substituted ligands in which
the hydrogen-bonding potential is reduced are entirely high-spin down
to 77 K. The complex of the 5-methyl derivative undergoes a continuou
s singlet reversible quintet transition below room temperature.