A synthetic phase formed in the Cu3(P04)2-phosphoric acid system at 55,000 psi and 400°C has been found to be an interesting polymorph of pseudomalachite, Cu5(P04)2(0H)4. This new phase crystallizes in the space group P21/a with a = 9.186(2), b = 10.684(2), c = 4.461(1) Å, and β = 92.31(1)°. The structure was solved by direct methods. Full-matrix least-squares refinement of the automatic diffractometer data converged to a residual R = 0.056 (Rw = 0.067). The unit cell has a volume essentially identical to that of pseudomalachite and one essentially equal axial length which, in both structures, represents the stacking distance between two-dimensional copper-containing sheets. The coordination polyhedra about the copper ions are similar in the two structures; the copper ions occupy two six-coordinated sites in the synthetic structure characterized by four short and two long bonds; the third copper ion is in a distorted square pyramidal coordination (four short and one long bond) with a sixth oxygen atom just outside the coordination sphere. The difference between the two structures is in the polyhedral linkages within these sheets; pseudomalachite is based on a three-connected two-dimensional net, while the synthetic phase is based on a four-connected net.

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