Electronic and structural properties of iron(II) and nickel(II) cationic complexes of 2-(pyrazin-2-ylamino)-4-(pyridin-2-yl)thiazole

Complex salts containing the [(FeN6)-N-II](2+) derivative of 2-(pyrazin-2-ylamino)-4-(pyridin-2-yl)thiazole (pzaptH) undergo continuous, temperature-induced singlet ((1)A(1)) reversible arrow quintet (T-5(2)) transitions with the transition temperature being dependent on the nature of the counter anion and the presence of solvate water, the latter tending to stabilize the singlet state. A transition is also observed for the fluoroborate salt in methanol solution. The extent of stabilization of the singlet state for iron(II) in these complexes is somewhat greater than in those derived from the previously studied 2-(pyridin-2-ylamino)-4-(pyridin-2-yl)th The crystal structures of [Fe(pzaptH)(2)] [CF3SO3](2) and [Ni(pzaptH)(2)][BF4](2).2H(2)O have been determined. The average Fe-N distance is 1.985 Angstrom, a value consistent with the essentially low-spin nature of the complex at room temperature, and the average Ni-N distance is 2.089 Angstrom. In both complexes the bridging >NH group is involved in hydrogen bonding to the anions and, in the nickel complex, also to the solvate water. The uncoordinated nitrogen of the pyrazine ring is not hydrogen-bonded. Bis[2-(pyrazin-2-ylamino)-4-(pyridin-2-yl)thiazole]iron(II) triflate: triclinic, space group <P(1)over bar>, a 8.794(5), b 11.082(6), c 17.49(1) Angstrom, alpha 77.59(4), beta 86.80(4), gamma 84.21(4)degrees, Z 2. Bis[2-(pyrazin-2-ylamino)-4-(pyridin-2-yl)thiazole]nickel(II) tetrafluoroborate dihydrate: monoclinic, space group P2(1)/c, a 8.784(3), b 8.795(2), c 41.16(1) Angstrom, beta 94.58(2)degrees, Z 4.