A study of paramagnetic transition metal carbonyls and cyanides by electron spin resonance spectroscopy.

Exposure of diamagnetic transition metal carbonyls and cyanides either as the pure compounds or as dilute solutions to ionizing radiation at 77 K results in the formation of electron-loss and electron-capture centres. Working at low temperatures enables unstable complexes to be studied that are not detectable by conventional procedures. The low concentrations produced are ideal for e.s.r. studied since spin-spin broadening is avoided. Four types of complex are studied, each involving a different transition metal-ligand bond. Exposure of dilute solutions of Fe(CO)5 in 2-methyltetrahydrofuran to 60Co ?-rays at 77 K resulted in electron addition to give a 3d9 species, tentatively identified as Fe(CO)5-. The form of the g-tensor components requires a 3d1z2 assignment for the unpaired electron on Fe. A similar study of Mn2 (CO)8 (PR3)2 and M(CO)5X (M = Cr, Mo, W, Re; X = Br, I) shows the excess electron to be accommodated in the metal- metal and metal-halogen o* orbitals respectively. Resolved hyperfine coupling from the 2 axial 31P nuclei in Mn2(CO)8 (PR3)2 reveals information regarding the delocalisation of the excess electron upon the axial ligands. Electron addition to mixed ligand complexes, MCp(CO)nX, (M = Mo, W, Fe; X = C1, I) results in electron capture into the metal-halogen o* orbitals, suggesting this is preferred to association with the organic ligand. The transition metal-hydrogen atom bond was probed in the same way. ?-Radiolysis of Pt(CN)42- ions in aqueous sulphuric acid matrices at 77 K results in the formation of [H-Pt (CN)4]2-, the unpaired electron being in a o* orbital confined to hydrogen and platinum. Finally, it was hoped to form a transition metal-alkyl bond in the same way, using Pt(CN)42- and Ni(CN)42- ions in a variety of solvents known to produce alkyl radicals on radiolysis, but these experiments have so far been inconclusive.