Structures of strontium diformate and strontium fumarate. A synchrotron powder diffraction study

Abstract

The crystal structures of strontium diformate in space groups P212121 (α form, 295 K), P41212 (β form, 334 and 540 K) and I41/amd (δ form, 605 K), and strontium fumarate in space groups Fddd (β form, 105 K) and I41/amd (α form, 293 K) have been determined from synchrotron X-ray powder diffraction data. Except for the α-strontium diformate, all the structures are based on a diamond-like Sr-ion arrangement, as in strontium acetylene dicarboxylate. The formate ions are disordered in the δ phase owing to steric hindrance. The fumarate ions are disordered over four (α) or two (β) symmetry-equivalent orientations. α-Strontium fumarate crystallizes with a unique 90° carboxylate dihedral angle, and is stable up to 773 K.