Contributions on crystal structures and thermal behaviour of anhydrous phosphates. XXIX - Preparation and structure determination of SrMn2(PO4)(2) and redetermination of beta '-Mn-3(PO4)(2)

Pale rose single crystals of SrMn2(PO4)(2) were obtained from a mixture of SrCl2.6 H2O, Mn(CH3COO)(2), and (NH4)(2)HPO4 after thermal decomposition an d finally melting at 1100 degreesC. The new crystal structure of strontium manganese orthophosphate [P-1, Z=4, a=8.860(6) Angstrom, b = 9.054(6) Angst rom, c = 10.260(7) Angstrom, alpha = 124.27(5)degrees, beta = 90.23(5)degre es, gamma =90.26(6)degrees, 4220 independent reflections, R1 = 0.034, wR2 = 0.046] might be described as hexagonal close-packing of phosphate groups. The octahedral, tetrahedral and trigonal-bipyramidal voids within this [PO4 ] packing provide different positions for 8- and 10-fold [SrOx] and distort ed octahedral [MnO6] coordination according to a formulation (Mn1Mn1Mn2Sr2o ct)-Mn-tbpy-Mn-tet-Sr-oct (PO4)(4). Single crystals of beta'- Mn-3(PO4)(2) (pale rose) were grown by chemical vapour transport (850 degreesC --> 800 d egreesC, P/I mixtures as transport agent). The unit cell of beta'-Mn-3(PO4) (2) [P2(1)/c, Z = 12, a = 8.948(2) Angstrom, b = 10.050(2) Angstrom, c = 24 .084(2) Angstrom, beta = 120.50 degrees, 2953 independent reflections, R1 = 0.0314, wR2 = 0.095] contains 9 independent Mn2+. The reinvestigation of t he crystal structure led to distinctly better agreement factors and signifi cantly reduced standard deviations for the interatomic distances.