Na8[Cr4B12P8O44(OH)4][P2O7].nH2O: a 3D borophosphate framework with spherical cages.

A chromium borophosphate-phosphate (Na(8)[Cr(4)B(12)P(8)O(44)(OH)(4)][P(2)O(7)]nH(2)O, 1), which has an unusual 3D framework structure, was synthesized under hydrothermal conditions. The framework consists of spherical cages composed of CrO(6), PO(4), BO(4), and BO(3) polyhedra. The cages are located at the vertices and the body center of the cubic cell and are interconnected through 12-membered-ring windows along the {111} direction. The actual framework structure is very complex, but the description can be simplified by using the 5-connected fundamental building cluster [CrP(5)B(3)O(24)](11-). In addition, 1 represents the first borate-rich borophosphate that contains a 3D borophosphate partial framework (3(over)infinity[B(3)P(2)O(11)(OH)]) in which the fundamental building unit is an oB dreier single ring (Delta4 square:square square). The cavities of the framework are filled with disengaged water molecules and Na(+) counterions. The former can be reversibly desorbed and reabsorbed and the latter can be exchanged by Li(+) ions, which results in significant shrinkages of the cell volume.