Leucophosphite, K2[Fe3+4(OH)2(H2O)2(PO4)4].2H2O. possesses an atomic arrangement based on a discrete octahedral tetramnr. The crystal cell criteria are 9.7S2(9), 9.658(9), 9.751(9)Å, β = 102.24(12)°, space group P21/n. The crystal structure was solved by Patterson techniques and includes one K+. two P+, two Fe3+, eight O2−, one (OH)−, and two (H2O) in the asymmetric unit. R(hkl) = 0.074 for 3900 independent F(obs).

The octahedral tetramer involves an edge-sharing dimer which further links at the shared comers to two more octahedra, resulting a center: vertex ratio — 1.5. A topologically identical cluster exists in amarantite, although the two structures differ in the ligand groupings and their relative amounts. In leucophosphite, the tetramer is joined to symmetry equivalent tetramers by bridging (PO4)3− tetrahedra. The K+ ions reside in constricted channels in the structure. Half of the. total water occurs in a structural cavity and probably possesses a tetrahedral grouping of hydrogen bonds.

Average polyhedral interatomic distances are KVI-O 2.927, Fe(l)-O 2.028, Fe(2)-O 2.012, P(l)-O 1.540, and P(2)-O 1.537 A. The (OH)− group is bonded to three Fe3+ cations, resulting in a long Fe3+-(OH)− 2.159 Å average because of extreme cation oversaturation.

The deep red color of amarantite, in contradistinction to the pale-colored leucophosphite and the corner-sharing octahedral chain structures, suggests possible spin coupling on account of the short 2.90 Å Fe-Fe separation in the former compound.

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