Layered zinc hydroxides (LZHs) with the general formula (Zn2+)(x)(OH-)(2x-my ),(A(m-))(y)center dot nH(2)O (A(m-) = Cl- , NO3- , ac(-) , SO42-, etc) are considered as useful precursors for the fabrication of functional ZnO nanostructures. Here, we report the synthesis and structure characterization of the hitherto unknown binary representative of the LZH compound family, Zn-5(OH)(10)center dot 2H(2)O, with A(m-) = OH- , x = 5, y = 2, and n = 2. Zn-5(OH)(10)center dot 2H(2)O was afforded quantitatively by pressurizing mixtures of epsilon-Zn(OH)(2) (wulfingite) and water to 1-2 GPa and applying slightly elevated temperatures, 100-200 degrees C. The monoclinic crystal structure was characterized from powder X-ray diffraction data (space group C2/c, a = 15.342(7) angstrom, b = 6.244(6) angstrom, c = 10.989(7) angstrom, beta = 100.86(1)degrees). It features neutral zinc hydroxide layers, composed of octahedrally and tetrahedrally coordinated Zn ions with a 3:2 ratio, in which H2O is intercalated. The interlayer d(200) distance is 7.53 angstrom. The H-bond structure of Zn-5(OH)(10)center dot 2H(2)O was analyzed by a combination of infrared/Raman spectroscopy, computational modeling, and neutron powder diffraction. Interlayer H2O molecules are strongly H-bonded to five surrounding OH groups and appear orientationally disordered. The decomposition of Zn-5(OH)(10)center dot 2H(2)O, which occurs thermally between 70 and 100 degrees C, was followed in an in situ transmission electron microscopy study and ex situ annealing experiments. It yields initially 5-15 nm sized hexagonal w-ZnO crystals, which, depending on the conditions, may intergrow to several hundred nm-large two-dimensional, flakelike crystals within the boundary of original Zn-5(OH)(10)center dot 2H(2)O particles.