Cs3Ti5P7O29: a titanium(IV) phosphate containing TiO5 trigonal bipyramids

A new ternary titanium phosphate, Cs3Ti5P7O29, has been synthesized and structurally characterized by single-crystal X-ray diffraction. It crystallizes in the triclinic space group P with a= 6.307(1), b= 10.330(2), c= 20.230(3)Å, α= 88.65(1), β= 84.83(1), γ= 72.37(1)°, Z= 2 and R= 0.0396. The structure consists of tunnels where the caesium cations are located. The framework is composed of two types of corner-sharing dimers of compositions Ti2O11 formed by two octahedra and Ti2O10 by an octahedron and a trigonal bipyramid, discrete TiO6 octahedra, PO4 tetrahedra and P2O7 groups. The structural formula is Cs3Ti(Ti2O)2(PO4)5(P2O7). Five-co-ordinate titanium with trigonal-bipyramidal geometry is unusual in phosphates.