Synthesis, structure refinement and characterization of tetrahydrated acid gadolinium diphosphate HGdP{sub 2}O{sub 7}.4H{sub 2}O

Synthesis and single crystal structure are reported for a new gadolinium acid diphosphate tetrahydrate HGdP{sub 2}O{sub 7}.4H{sub 2}O. This salt crystallizes in the monoclinic system, space group P2{sub 1}/n, with the following unit-cell parameters: a=6.6137(2)A, b=11.4954(4)A, c=11.377(4)A, {beta}=87.53(2){sup o} and Z=4. Its crystal structure was refined to R=0.0333 using 1783 reflections. The corresponding atomic arrangement can be described as an alternation of corrugated layers of monohydrogendiphosphate groups and GdO{sub 8} polyhedra parallel to the (1-bar 01) plane. The cohesion between the different diphosphoric groups is provided by strong hydrogen bonding involving the W4 water molecule. IR and Raman spectra of HGdP{sub 2}O{sub 7}.4H{sub 2}O confirm the existence of the characteristic bands of diphosphate group in 980-700cm{sup -1} area. The IR spectrum reveals also the characteristic bands of water molecules vibration (3600-3230cm{sup -1}) and acidic hydrogen ones (2340cm{sup -1}). TG and DTA investigations show that the dehydration of this salt occurs between 79 and 900 deg. C. It decomposes after dehydration into an amorphous phase. Gadolinium diphosphate Gd{sub 4}(P{sub 2}O{sub 7}){sub 3} was obtained by heating HGdP{sub 2}O{sub 7}.4H{sub 2}O in a static air furnace at 850 deg. C for 48h.