A synchrotron single crystal X-ray structure determination of a small crystal: Mo-Mo double bonds in the 3-D microporous molybdenum phosphate NH sub 4 (Mo sub 2 P sub 2 O sub 10 )ter dot H sub 2 O

Black crystals of NH{sub 4}(Mo{sub 2}P{sub 2}O{sub 10}){center dot}H{sub 2}O, (1), can be isolated by reacting MoO{sub 3}, Mo, (NH{sub 4}){sub 2}HPO{sub 4}, H{sub 3}PO{sub 4}, and H{sub 2}O in a mole ratio of 3:1.1:2:4:120 for 16 hr at 360C. The structure of phosphate (1) was determined and refined from single crystal data collected on a 35{times}20{times}10{mu}m{sup 3} crystal at beamline X10A at NSLS, Brookhaven National Laboratory. Compound (1) is monoclinic, space group P2{sub 1}/n with a=9.780(10), b=9.681(5), c=9.884(8) {angstrom}, {beta}=102.17(8), V=915(1) {angstrom}{sup 3} and R(R{sub W})=0.029(0.024) and contains MoO{sub 6} octahedra and PO{sub 4} tetrahedra. The structure is built up from Mo{sub 4} oxo units that have two edge-sharing Mo{sup 4+}O{sub 6} octahedra that contain Mo-Mo double bonds (2.453(2) {angstrom}), with the same two oxygens that bridge the Mo{sup 4+} also serving as a corner for two additional Mo{sup 5+}O{sub 6} octahedra. The Mo{sub 4} units are connected by phosphate groups into a 3-D array which generates several types of tunnel which are filled with NH{sub 4}{sup +} cations and H{sub 2}O. The material is isotypic with the mineral leucophosphite, K(Fe{sub 2}(OH)(H{sub 2}O)(PO{sub 4}){sub 2}){center dot}H{sub 2}O. Water absorption isotherms show that (1) is microporous and has about 10-12 vol% internal void space that can be filled by water.