An ionic nickel(II) phosphate templated by ethylenediamine, (C2H10N2)[Ni(H2O)(6)] (HPO4)(2), has been prepared by hydrothermal synthesis and characterized by single-crystal diffraction data and spectroscopic techniques. The compound crystallizes in the monoclinic space group P2(1)/c with a = 6.226(1), b=16.241(2), and c = 14.778(2) Angstrom, beta = 91.28(1)degrees, V = 1493.9(4) Angstrom (3), and Z = 4. The structure consists of isolated Ni(H2O)(6) octahedra and HPO4 tetrahedra, both of them hydrogen-bonded to ethylenediammonium cations. The compound has been characterized by IR spectroscopy, showing the bands characteristic of the (HPO4)(2-) anions and the ethylenediammonium cation. Diffuse reflectance measurements indicate the presence of octahedrally coordinated Ni(II) ions. The D-q (835 cm(-1)) and Racah (B = 900, C = 4040 cm(-1)) parameters have been calculated for the Ni(II) ions in octahedral sites. (C) 2000 Academic Press.