New thallium diphosphate Tl2Me(H2P2O7)2• 2 H2O, Me = Mg, Mn, Co, Ni and Zn.: Synthesis, single crystal X-ray structures and powder X-ray structure of the Mg phase

Crystals of thallium dihydrogendiphosphate Tl2Me(H2P2O7)(2)center dot 2 H2O (Me = Mg (1), Mn (2), Co (3), Ni (4) and Zn (5)), have been synthesized and analyzed by powder X-ray diffractometry (Mg phase) and single crystal X-ray diffractometry (other phases). They resulted to be isostructural within triclinic group P (1) over bar, with the following unit-cell parameters: a = 6.9620(1), b = 7.3635(1), c = 7.7713(1) angstrom, alpha = 81.8014(5), beta = 70.8597(6), gamma = 86.1373(7)degrees, V = 372.44(8) angstrom(3) (1); a = 6.9577(6), b = 7.4745(6), c = 7.8248(7) angstrom, alpha = 80.723(2) beta = 71.912(1), gamma = 85.661(1)degrees, V = 381.62(6) angstrom(3) (2); a = 6.9767(7), b = 7.3634(7), c = 7.7690(7) angstrom, alpha = 81.421(2), beta = 71.114(2), gamma = 86.424(2)degrees, V = 373.36(6) angstrom(3) (3); a = 6.9658(7), b = 7.3079(7), c = 7.7016(7) angstrom, alpha = 81.801(2), beta = 71.185(2), gamma = 86.528(2)degrees, V = 367.27(6) angstrom(3) (4) and a = 6.9628(7), b = 7.3625(7), c = 7.7401(8) angstrom, alpha = 81.590(2), beta = 71.441(2), gamma = 86.323(2)degrees, V = 372.04(6) angstrom(3) (5). Me is octahedrally coordinated by two water molecules and four oxygen atoms belonging to two different diphosphate groups. Thallium cations make up interactions with oxygen atoms within Van der Waals coordination sphere, making up irregular coordination polyhedra. The frarmework of the present compounds can be described as a three-dimensional framework made from vertex-sharing polyhedra. The basic unit is the [Me(H2P2O7)(2)center dot 2 H2O] moiety, which displays a crystallographic Ci symmetry, with the Me cation on the inversion centre. Such units are held together by an intricate scheme of Tl...O interactions; hydrogen bonds complete the network.