CeP 2 O 7 , a close structural relative of ZrP 2 O 7 , and many other M IV X 2 O 7 (X -P, V, As) phases, forms on heating Ce(HPO 4 ) 2 • xH 2 O between ∼300 and 600 °C and decomposes by oxygen loss at higher temperatures. In-situ X-ray diffraction measurements showed, for some precursor batches, the formation of CeP 2 O 7 in two distinct stages. At room temperature, CeP 2 O 7 is pseudocubic, but probably triclinic, displaying positive thermal expansion below ∼115 °C. Above this temperature, there is a transition to cubic symmetry (Pa3 j ) with the linear coefficient of thermal expansion going to zero at ∼450 °C and becoming negative at higher temperatures. CeP 2 O 7 probably undergoes two phase transitions on compression below ∼10.5 GPa. The phase existing between 0.65 and ∼5 GPa is soft with an average bulk modulus of ∼18 GPa.

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The synthesis and characterization of three new complexes, BiCl 3 (mipit) 2 , BiCl 3 (emit) 2 and BiCl 3 (mnpit) 2 are reported where emit ¼ 1-ethyl-3-methyl-2(3H)-imidazolethione; mnpit ¼ 1-methyl-3-(1-propyl)-2(3H)-imidazolethione;mipit ¼ 1-methyl-3-(2-propyl)-2(3H)-imidazolethione. X-ray crystallographic results are reported for the mnpit and mipit complexes whereas the structure of the emit complex is under reinvestigation because of disorder. BiCl 3 (mnpit) 2 crystallizes in a triclinic space group (P1) with lattice parameters: a ¼ 9.4223(6) Å , b ¼ 10.6275(6) Å , c ¼ 12.8860(8) Å , a ¼ 108.329(1)8, b ¼ 90.388(1)8, g ¼ 115.200(1)8, V ¼ 1093(1) Å 3 , Z ¼ 2. BiCl 3 (mipit) 2 crystallizes in a triclinic space group (P1) with lattice parameters: a ¼ 10.4347(8) Å , b ¼ 11.0018(9) Å , c ¼ 11.2075(9) Å , a ¼ 95.827(1)8, b ¼ 104.890(1)8, g ¼ 117.064(1)8, V ¼ 1071(1) Å 3 , Z ¼ 2. Both complexes show the same pattern with two BiL 2 Cl 4 (L ¼ ligand) octahedra sharing a common edge through bridging chlorine atoms and the ligands occupying trans positions perpendicular to the plane made by the two bismuth atoms and six chlorine atoms. No strong evidence for a hemidirected lone pair is observed in either of the two complexes.

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