The preparation of the tridentate chelating agents 2-(1,10- phenanthrolin-2-yl)thiazole, 2-(1,10-phenanthrolin-2-yl)-4-(2- pyridyl)thiazole 2-(1,10-phenanthrolin-2-yl)thiazolidine and 2-(1,10- phenanthrolin-2-yl)benzothiazole is described. Data from the spectra of the bis-ligand nickel complexes indicate that the ligands all have field strengths in the iron(II) crossover region. The temperature dependence of the magnetism of the bis-ligand iron(II) complexes reveals that, except for the complexes of the pyridylthiazole, a smooth, temperature-induced 5T2 ↔ 1A1 transition occurs in these compounds. For no complex is the transition complete within the experimental temperature range (83-363 K). The complex of the pyridylthiazole is high-spin throughout the range, the uncoordinated pyridyl group hindering the close approach of ligand and metal atom necessary for spin-pairing. The ability of the other ligands to induce a spin transition is primarily a consequence of distortions in the environment about the metal atom arising from coordination of the five- membered thiazole or related ring.

Goodwin, H., Mather, D., & Smith, F. (1975). Metal complexes of 1,10-phenanthroline derivatives. IX. 5T2 ↔ 1A1 spin transitions in iron(II) complexes of 2-(1,10-phenanthrolin-2-yl)thiazole derivatives. Australian Journal of Chemistry, 28(1), 33.