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, (HO)[Co(4-bromopyridine){W(CN)}], was prepared. A synchrotron radiation (SR) X-ray single-crystal measurement shows that the crystal structure is monoclinic in the P2/c space group. Magnetic and spectroscopic measurements show that this assembly takes Co(S = 0)-W(S = 0) in the temperature range of 2-390 K. Such a wide temperature range Co-W phase has not been reported so far. First-principles calculations show that the band gap is composed of a W valence band and a Co 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)-W(S = 0) to Co(S = 3/2)-W(S = 1/2).

Tuning the Optical Properties of Magnetic Materials

“…Adapted from ref. [32] by permission of The Royal Society of Chemistry © 2016. Brpy•HCl, and Na 3 [W V (CN) 8 ]•4H 2 O provides the target compound.…”

“…Adapted from ref. [32] by permission of The Royal Society of Chemistry © 2016. azoline) exclusively in the RR or SS configuration; dmf = N,Ndimethylformamide). [40] These materials can be obtained by slow diffusion of diethyl ether into a solution of Eu- (Figure 7a).…”

“…Further research on bimetallic Co–W assemblies led to the development of another photomagnetic 2D framework (H 5 O 2 )[Co III (4‐Brpy) 2 ][W IV (CN) 8 ] ( 4 ) (4‐Brpy = 4‐bromopyridine) . In contrast to the previous material, 4 exhibits a Co III ls –W IV electronic state in the whole range of its thermal stability 2–390 K. Mixing acidic aqueous solutions of CoCl 2 · 6H 2 O, 4‐Brpy · HCl, and Na 3 [W V (CN) 8 ] · 4H 2 O provides the target compound.…”

“…(c)) Charge density maps for the valence (red) and conduction (blue) bands. Adapted from ref . by permission of The Royal Society of Chemistry © 2016.…”

“…(c) Crystal structure of the PI phase of 4 with marked structural changes in the Co coordination sphere (up) and the crystal packing (down). Adapted from ref . by permission of The Royal Society of Chemistry © 2016.…”