Three new copper(II) diphosphonates, (NH4)(2)Cu-3(hedp)(2)(H2O)(4) (1), [NH3(CH2)(4)NH3]Cu-3(hedp)(2). 2H(2)O (2), and [NH2(C2H4)(2)NH2]Cu-3(hedp)(2) (3), where hedp = 1-hydroxyethylidenediphosphonate, have been synthesized and characterized by single-crystal structural analysis. Crystal data: 1, monoclinic, P2(1)/n, a = 6.2137(13) Angstrom, b = 14.747(2) Angstrom, c = 11.1802(12) Angstrom, beta = 105.83(2)degrees, Z = 2; 2, triclinic, P (1) over bar, a = 7.4840(12) Angstrom, b = 8.032(3) Angstrom, c = 10.007(2) Angstrom, alpha = 111.68(2)degrees, beta = 96.188(14)degrees, gamma = 96.97(2)degrees, Z = 1; 3, triclinic, P (1) over bar, a = 7.0155(6) Angstrom, b = 8.0904(9) Angstrom, c = 9.2644(11) Angstrom, alpha = 112.611(13)degrees, beta = 90.819(8)degrees, gamma = 92.824(7)degrees, Z = 1. The compound 1 is composed of infinite chains with a ladder-type motif. The compounds 2 and 3 adopt a two-dimensional layer structure which contains four-and eight-membered rings assembled from vertex-sharing {CuO4} units and {CPO3} tetrahedra. The magnetic properties of 3 have been investigated.