Synthesis and structure of the n=4 member of the framework aluminium alkylenediphosphonate series Al2[O3PCnH2nPO3](H2O)2F2

We report here the solvothermal synthesis and crystal structure of the hybrid inorganic-organic framework material Al-2[O3PC4H8PO3](H2O)(2)F-2 center dot 2H2O (monoclinic, P2(1)/m, a = 4.961(2) angstrom, b = 11.930(5) angstrom, c = 10.727(5) angstrom, beta = 93.972(6)degrees, Z = 2, R(F, F-2 > 2 sigma) = 0.094, R-w(F-2, all data) = 0.262), the third member of the Al-2[O3PCnH2nPO3](H2O)(2)F-2 framework series. The structure is formed from corrugated chains of corner-sharing AlO4F2 octahedra in which alternating AlO4F2 octahedra contain two fluorine atoms in a trans or a cis configuration. The diphosphonate groups link the chains together through Al-O-P-O-Al bridges and through the butyl groups to form a three-dimensional framework structure containing a one-dimensional channel system consisting of one type of channel only. The channels contain four extra-framework water molecules per unit cell. The formation of this member of the series shows that the form of the alkyl chain can successfully define the number of channel types and the channel length in this hybrid framework system.