catena-Poly[[[tetra­kis(μ-2-butenoato)dicopper(II)]-μ-2-butenoato-[diaqua­(2-butenoato)holmium(III)]-di-μ-2-butenoato-[diaqua­(2-butenoato)holmium(III)]-μ-2-butenoato] trihydrate]

The title compound {[Cu(2)Ho(2)(C(4)H(5)O(2))(10)(H(2)O)(4)]·3H(2)O}(n), is a one-dimensional 3d/4f organic–inorganic hybrid complex, the Ho(III) member of the isotypic lanthanoid series with Ln = Gd(III), Er(III) and Y(III). The structure shows an alternation of Cu(2) and Ho(2) dinuclear units bridged by the ligands and hydrogen bonds only. The chains are composed of Cu(2) classical dinuclear η(1):η(1):μ(2) fourfold bridges [Cu⋯Cu = 2.6417 (9) Å] and of Ho(2) units bridged by two η(2):η(1):μ(2) carboxyl­ate units. This results in distorted square-based pyramidal CuO(5) units and irregular HoO(9) units. The alternating Cu(2) and Ho(2) units are bridged into linear arrays along the a axis by a set of one η(2):η(1):μ(2) carboxyl­ate O atom and two hydrogen bonds with Cu⋯Ho separations of 4.4883 (10) and 4.5086 (10) Å. The distance between adjacent chains, as calculated by the closest and furthest distances between two chains, covers the range 10–14 Å. The H atoms of the water mol­ecules could not be located, but the O⋯O separations for these species suggest the presence of O—H⋯O hydrogen bonds.