Kh. Sugiyarto et al., STRUCTURAL AND ELECTRONIC-PROPERTIES OF IRON(II) AND NICKEL(II) COMPLEXES OF 2-TRIAZOLYL-1,10-PHENANTHROLINE DERIVATIVES, Australian Journal of Chemistry, 49(4), 1996, pp. 505-515
Salts of the [FeN6](2+) derivatives of the tridentate systems 2-(triaz
ol-3-yl)-1,10-phenanthroline, 2-(1-methyltriazol-3-yl)-1,10-phenanthro
line, 2-(5-methyltriazol-3-yl)-1,10-phenanthroline and 2-(1,5-dimethyl
triazol-3-yl)-1,10-phenanthroline undergo temperature-induced singlet
((1)A(1)) reversible arrow quintet (T-5(2)) transitions in both the so
lid state and in solution. Both the nature of the associated anion and
the extent of solvation of the salts influence the extent of the tran
sition in solid samples. The solution behaviour has been interpreted i
n terms of a simple thermal equilibrium involving the two spin states.
Electronic spectra of corresponding nickel(II) complexes establish th
at the field strengths for all ligands fall within a narrow range, but
suggest that the order is influenced by electronic effects of the met
hyl substituents. Structural data indicate that a 5-methyl substituent
exerts a small steric barrier to coordination of the triazolyl moiety
. Data were obtained at 298 K for [FeL(2)] [ClO4](2).H2O.C2H5OH (L = 2
-(1-methyltriazol-3-yl)-1,10-phenanthroline) and [FeL(2)] [ClO4](2).3H
(2)O (L = 2-(5-methyltriazol-3-yl)-1,10-phenanthroline). The average F
e-N distance in the former complex is 1 . 96 Angstrom and in the latte
r 1 . 97 Angstrom, indicating that in both instances the metal is esse
ntially in the singlet state in these crystals. The ligands coordinate
in meridional planes of an octahedron and give a distorted environmen
t about the metal atom, the Fe-N-central distances being significantly
shorter than the Fe-N-distal distances in both instances. This distor
tion results in unusually large quadrupole splitting in the Mossbauer
spectra for the complexes in the singlet state. 1-methyltriazol-3-yl)-
1,10-phenanthroline]iron(II) perchlorate monohydrate monoethanolate: t
riclinic, space group P (1) over bar, a 9 . 423(4), b 10 . 536(4), c 1
9 . 402(8) Angstrom, alpha 75 . 59(3), beta 85 . 80(3), gamma 68 . 76(
3)degrees, Z 2. 5-methyltriazol-3-yl)-1,10-phenanthroline]iron(II) per
chlorate trihydrate: tetragonal, space group P4(1)2(1)2, a 14 . 676(3)
, c 16 . 169(3) Angstrom, Z 4.