Tl2MoO4-Pr-2(MoO4)(3) system and new molybdates Tl(5)Ln(MoO4)(4)

The first study of the Tl2MoO4-Pr-2(MoO4)(3) system is reported. The system was studied by X-ray powder diffraction, differential thermal analysis, an d visual polythermal analysis. Its phase diagram was mapped. Intermediate p hase of compositions 1:1 and 5:1 with incongruent melting points of 910 and 620 degreesC were found in the system. A new polymorph of TlPr(MoO4)(2) wa s obtained. Tl5Pr(MoO4)(4) was prepared for the first time. Double molybdat es Tl(5)Ln(MoO4)(4) were found to exist for all lanthanides from lanthanum to lutetium, including yttrium. Tl5La(MoO4)(4) is isostructural to its isof ormula analogues, potassium lanthanum and rubidium lanthanum molybdates; it has a monoclinically distorted palmierite structure with a = 10.534(8) Ang strom, b = 18.22(1)Angstrom, c = 14.84(1) Angstrom, beta = 103.79(4)degrees , presumed space group P2/m, P2, or Pm, Tl5Ce(MoO4)(4) seems to have a simi lar structure. The Tl(5)Ln(MoO4)(4) compounds for Pr-Lu or Y are isostructu ral to one another. Their crystals are monoclinic with a = 18.214-18.009 An gstrom, b = 6.233-6.171 A, c = 16.867-16.658 Angstrom, beta = 101.22 degree s -100.78 degrees, Z=4, presumed space group P2(1)/n.