A new copper(II) acetate, [Na2Cu(CH3COO)(4)(H2O)].H2O (1), has been crystallized from an aqueous solution containing sodium acetate and copper(II) acetate monohydrate in a 4:1 ratio and the structure determined by X-ray crystallography. 1 crystallizes in the monoclinic space group P2(1)/c, with a = 16.638(3) Angstrom, b = 11.781(2) Angstrom, c = 15.668(3) Angstrom, beta = 90.11(3)degrees, V = 3071.0(11) Angstrom(3), and Z = 4. In the asymmetric unit, sodium ions bridge two crystallographically unique square planar [Cu(CH3COO)(4)](2-) units to their symmetry-generated neighbors to form corrugated 2D sheets of Na2Cu(CH3COO)(4), which are held together by H-bonding interactions involving the waters of crystallization. In contrast, the structures of known sodium copper acetates are better described as 3D frameworks. The metal centers are bridged by a number of acetates in novel coordination modes. The square planar Cu(II) geometry generated by oxygen atoms from four different acetates is an unexpected feature given the weak ligand field provided by the acetate ligands.