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

The crystal structures of strontium diformate in space groups P2 ₁2₁2₁ ( form, 295 K), P4₁2 ₁2 (Β form, 334 and 540 K) and I41/amd ( form, 605 K), and strontium fumarate in space groups Fddd (Β form, 105 K) and I41/amd ( form, 293 K) have been determined from synchrotron X-ray powder diffraction data. Except for the -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 phase owing to steric hindrance. The fumarate ions are disordered over four (α) or two (Β) symmetry-equivalent orientations. -Strontium fumarate crystallizes with a unique 90° carboxylate dihedral angle, and is stable up to 773 K.