2 CLOSELY-RELATED INTERSECTING TUNNEL STRUCTURES - THE MONOPHOSPHATESK3V1.4W2.6O9(PO4)(2) AND K3NB3WO9(PO4)(2)

Two new monophosphates with original and closely related intersecting tunnel structures have been synthesized. The first one K3V1.4W2.6O9(PO 4)(2) crystallizes in the P2(1)/m space group with a = 7.0392(6) Angst rom, b = 14.332(1) Angstrom, c = 7.5508(7) Angstrom, beta = 106.320(8) degrees, and the second one, K3Nb3WO9(PO4)(2), crystallizes in the Pnm a space group with a = 14.667(2) Angstrom, b = 14.508(3) Angstrom, c = 7.179(1) Angstrom. Their 3D-frameworks [M4P2O17](infinity) are built from the assemblage of octahedral [MO3](infinity) chains interconnecte d through ''MPO9'' units. The two structures differ by the relative or ientation of their [MO3](infinity) chains: in the ''V, W'' phase two s uccessive chains are deduced from each other by a ''(c) over right arr ow'' translation, whereas in the ''Nb, W'' phase one chain out of two is turned by 180 degrees around (a) over right arrow. The analysis of these structures shows also their close relationships with the hexagon al tungsten bronze (HTB): the framework can also be described on the b asis of HTB ribbons running along (b) over right arrow. Another import ant feature deals with the tendency of the transition elements to orde r, especially in the [MO3](infinity), chains. The magnetic study of th e mixed valent monophosphate K3V2W2O9(PO4)(2) evidences electronic loc alization despite the existence of [MO3](infinity) chains.