A new layered divalent metal monohydrogenphosphate [Co-(H 2O)(HPO 4)]·H 2O (1) was hydrothermally synthesized from the reaction of CoCl 2·6H 2O with H 3PO 4 in the presence of cis-Pt(NH 3) 2Cl 2 and ethylenediamine. The structure features extensive intra- and inter-layer hydrongen bonding among the hydrogenphosphate anoin, the coordinated water and the crystallization water. X-ray crystallographic parameters for 1 are orthorhombic Pnma (#62), a=1.7528(2), b=0.56158(7), c=0.47867(6) nm, V=0.47116(9) nm 3, Z=4