CHARACTERIZATION OF NEW LEAD-BASED MONOPHOSPHATE TUNGSTEN BRONZES, PB-X(PO2)(4)(WO3)(2M) -LESS-THAN-OR-EQUAL-TO-M-LESS-THAN-OR-EQUAL-TO-10)

A new series of lead-based monophosphate tungsten bronzes (MPTBh), Pb- x(PO2)(4)(WO3)(2m), was isolated for 6 less than or equal to m less th an or equal to 10 and characterized by X-ray diffraction, electron mic roscopy, and resistivity and magnetic susceptibility measurements. The crystal structure was solved for m = 7 from three-dimensional single- crystal X-ray data [Pb0.66P4W14O50: triclinic, A (1) over bar, a = 6.6 015(3)Angstrom, b=5.3156(4)Angstrom, c=27.039(2)Angstrom, alpha = 90.2 08(6)degrees, beta = 96.757(5)degrees, gamma = 89.867(5)degrees, Z=1, final R = 2.16% for 4462 independent reflections with I> 3.0 sigma(1)] . Lead atoms are distributed in cages bounded by 18 oxygen atoms, in a part that favors a PO4 tetrahedron neighbor Father than a WO6, octahe dron neighbor. Consequently, Ph atoms exhibit an (3+5) eightfold coord ination that takes into account the 6s(2) lone-pair stereoactivity. Re sistivity measurements performed on oriented single crystals reveal qu asi-two-dimensional metallic behavior for the entire temperature range investigated, 4.2 to 300 K. Magnetic susceptibility data indicate Pau li paramagnetic behavior. The results are compared with those of alkal ine-based counterparts, A(x)(PO2)(4) (WO3)(2m) (A = Na, K). (C) 1998 A cademic Press.