A V(IV) tetraphosphate with a tunnel structure K-2(VO)(2)P4O13

A V(IV) tetraphosphate K-2(VO)(2)P4O13 has been synthesized for the first time, and crystals of this new phase can be grown in air. It crystallizes in the space group Pbca with a = 22.181(2)Angstrom, b = 11.564(1)Angstrom, c = 9.948(1)Angstrom. The original structure of this phase consists of corner sharing P4O13 tetraphosphate groups and VO6 octahedra forming a tridimensional framework [V2P4O15](infinity). The latter delimits large tunnels running along c and small tunnels running along b and [101], where two kinds of sites K(1) and K(2) are occupied by potassium. The horseshoe conformation of the P4O13 group is different from those observed previously which are principally S shaped, The magnetic susceptibility investigation shows a paramagnetic behavior, with a C parameter of 1.55 mu(B). The thermogravimetric study shows the exceptional stability of V(IV) in this phosphate matrix, whatever the atmosphere air or oxygen up to 750 degrees C. (C) 1997 Academic Press.