STRUCTURAL AND ELECTRONIC-PROPERTIES OF IRON(II) AND NICKEL(II) COMPLEXES OF 2-TRIAZOLYL-1,10-PHENANTHROLINE DERIVATIVES

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.