A novel organic-inorganic hybrid based on diphosphopentamolybdate cluster, {Cu(DETA)}(2)[{Cu(DETA)(H2O)}Mo-5-P2O23]center dot 4.5H(2)O [DETA: diethylenetriamine] (1), has been synthesized by hydrothermal method and characterized by X-ray crystallography, showing that the [Mo5P2O23](6-) cluster, which supported by the {Cu(DETA)(H2O)}(2+) unit, is linked through two {Cu(DETA)}(2+) bridging units to construct a 1D chain-like infinitely extended structure. Each chain is further linked to two adjacent chains by hydrogen bonds to yield a 2D layer parallel to the ac plane.