The reaction of copper(II) hydroxide with 2,2′-bipyridine (bipy) (1 : 1) in alkaline aqueous solution (pH 14) at room temperature affords the alternating carbonate/hydroxo-bridged copper(II) polymeric chain compound {[Cu₃(bipy)₃(µ-OH)₂(µ-CO₃)₂]·11H₂O}_n, 1, as determined by single-crystal X-ray diffraction. The structure of 1 is built up from two similar centro-symmetric dinuclear [(bipy)Cu(µ-OH)]₂ cores which link together via bridging carbonate groups to mononuclear [(bipy)Cu] fragments to form the chain. Interdigitation of adjacent chains through π–π interactions, which involve each bipy ligand, forms sheets that are separated by the water molecules of crystallisation. Variable-temperature magnetic susceptibility measurements have shown that 1 behaves as an isolated spin doublet with two non-interacting spin triplets with the magnetic coupling through the bis-µ-hydroxo bridges being strongly ferromagnetic in nature. The hydrothermal reaction of copper(II) hydroxide, bipy and ammonium hydrogenphosphate (pH 8) yields a dinuclear copper(II) complex of formula {[Cu₂(bipy)₂(µ-OH)₂(HPO₄)(H₂O)]·4H₂O}, 2, as determined by single-crystal X-ray diffraction. The structure of 2 consists of an asymmetric dinuclear bis-µ-hydroxo copper(II) core with a monodentate hydrogenphosphate dianion coordinating to one copper(II) atom (above) and a water molecule to the other (below). Intra- and inter-molecular hydrogen bond interactions involving the hydrogenphosphate, water molecules and bis-µ-hydroxo groups link adjacent dinuclear fragments into chains, which interdigitate to form sheets that are separated by the water molecules of crystallisation. The investigation of the magnetic properties of 2 showed that the strength of the ferromagnetic interaction through the bis-µ-hydroxo bridges is influenced by the significant out-of-plane displacement of the hydrogen atom of the hydroxo groups, brought about through hydrogen bonding to the hydrogenphosphate ligand, and yielded the strongest ferromagnetic coupling yet reported for the bis-µ-hydroxo copper(II) core.