Photo-induced magnetization and first-principles calculations of a two-dimensional cyanide-bridged Co-W bimetal assembly.

Abstract

A two-dimensional cyanide-bridged Co-W bimetal assembly, (H5O2+)[Co(4-bromopyridine)2{W(CN)8}], was prepared. A synchrotron radiation (SR) X-ray single-crystal measurement shows that the crystal structure is monoclinic in the P21/c space group. Magnetic and spectroscopic measurements show that this assembly takes Co(S = 0)-WIV(S = 0) in the temperature range of 2-390 K. Such a wide temperature range Co-WIV phase has not been reported so far. First-principles calculations show that the band gap is composed of a WIV valence band and a CoIII conduction band. 785 nm light irradiation causes photo-induced magnetization with a Curie temperature of 27 K and a coercive field of 2000 Oe. The crystal structure of the photo-induced phase was determined to have larger lattice constants in the two-dimensional layer (bc-plane) by 3% compared to the original phase, which is due to the expansion of the distance of Co-N. The photo-induced phase returns to the original phase upon thermal treatment. First-principles calculations, and magnetic, and optical measurements prove that this photomagnetism is caused by the optical charge-transfer-induced spin transition from Co(S = 0)-WIV(S = 0) to Co(S = 3/2)-WV(S = 1/2).