Local structure and electronic state of a photomagnetic material of CoW cyanide studied by x-ray-absorption fine structure spectroscopy

The local structure and electronic state of a photomagnetic material Cs0.8Co1.1(3-cyanopyridine)(1.9)W(CN)(8).2.1H(2)O have been investigated by means of X-ray-absorption fine structure (XAFS) spectroscopy. The Co K- and W L-edge x-ray-absorption near-edge structure has clarified that upon the transition from the high-temperature (HT) phase to the low-temperature (LT) one, a Co 3d electron is transferred to the W 5d level the electronic state of Co chances from the high-spin divalent state (d(7), spin momentum S = 3/2) to the low-spin trivalent state (d(6),S = 0), while the W state correspondingly varies from the pentavalent state (d(1),S = 1/2) to the tetravalent one (d(2),S = 0). Extended XAFS analysis has revealed that the coordination around W and Co is W(CN)(8)Co-4 and Co(NC)(4)(3-cyanopyridine)(2)W-4, respectively, and that the Co-N distance in the LT phase is decreased by similar to0.17 Angstrom compared to that in the HT one, while the structure around W shows little change. We have also found x-ray-induced phase transition of the present material at 30 K. The x-ray-induced phase was found to be structurally and electronically identical to the HT phase.