Novel ternary Ag II Co III F 5 fluoride: synthesis, structure and magnetic characteristics.

We present a new compound in the silver-cobalt-fluoride system, featuring paramagnetic silver (d 9 ) and high-spin cobalt (d 6 ), synthesized by solid-state method in an autoclave under F 2 overpressure. Based on powder X-ray diffraction, we determined that Ag II Co III F 5 crystallizes in a monoclinic system with space group C 2/ c . The calculated fundamental band-gap falls in the visible range of the electromagnetic spectrum, and the compound has the character of charge-transfer insulator. AgCoF 5 is likely a ferrimagnet with one predominant superexchange magnetic interaction constant between mixed spin cations (Ag-Co) of -62 meV (SCAN result). Magnetometric measurements conducted on a powdered sample allowed the identification of a transition at 128 K, which could indicate magnetic ordering.