A New Inorganic-Organic Hybrid Zinc Phosphate Prepared with L-Histidine with an Unusual Stability in Water

A new layered zinc phosphate (Mu-39) has been synthesized by hydrothermal treatment with biomolecules as original templates. It was synthesized with the L-histidine amino acid (C6H9N3O2). The structure was determined by a single crystal X-ray diffraction study combined with exhaustive solid-state NMR experiments. These last ones [H-1 -> C-13 HETCOR, H-1 single quantum/double quantum (DQ), P-31, H-1 -> P-31 CPMAS, H-1 -> P-31 HETCOR] ascertained the formulation of Mu-39 as {[C6H10N3O2+][Zn-2(HPO4)(PO4)(-)]center dot H2O}(n) with a hydrogen phosphate and phosphate ligands, and ruled out partial protonation such as (H1-xPO4)(HxPO4). A P-31 magic angle spinning (MAS) NMR study supported the almost complete racemization of L-histidine during the hydrothermal synthesis with only a small enantiomeric excess of 25% remaining. The compound crystallizes in the triclinic symmetry (space group P (1) over bar) with a = 8.6109(6) angstrom, b = 9.0319(6) angstrom, c = 9.9523(7) angstrom, and alpha = 84.481(2)degrees, beta = 83.279(2)degrees, gamma = 74.652(2)degrees, V = 739.56(9) angstrom(3), Z = 2. The inorganic layer is built up from four-membered rings sharing T-O-T bonds (T = Zn and P) and connected to each other in order to form ladders which are joined together via a Zn-O-P bond for creating eight-membered rings. The interest and the originality of this new zinc phosphate come especially from its unusual stability in aqueous solution.