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The crystal and molecular structure of the title compound ( I ) has been determined by three-dimensional X-ray analysis from 750 non-zero reflexions measured photographically. The compound crystallizes in the orthorhombic system, space group P212,21 with a = 7-00 f 0.02, b = 18.93 f 0.03, and c = 5.38 f 0.01 A, Z = 4. The crystal structure has been solved by the symbolic addition procedure applied to non-centrosymmetric crystals, and refined by least-squares calculations to R 0.087. The compound has the exo-conformation. The introduction of an oxygen atom in position 7 of the norbornene skeleton produces interesting modifications in some bond distances and angles.

This paper reports a thermal and spectroscopic study of Pr(HCOO) 3 crystal in the range 300-10 K. Room temperature Raman phonons are assigned based on group theory analysis and correlations with other rare earth formates. Differential scanning calorimetric (DSC) measurements show that there is a slight anomaly in the behavior of the heat capacity at around 140 K. Temperature-dependent Raman spectra were recorded and the changes observed are discussed. These results suggest that Pr(HCOO) 3 undergoes a second-order phase transformation at temperatures lower than 140 K. Based on the group-to-subgroup relations, we propose a possible low-temperature structure and discuss the driving mechanism of the phase transformation.

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