Bis[μ-2-(4-hy-droxy-phen-yl)acetato]-κO,O':O;κO:O,O'-bis-{aqua-(4,4'-bi-pyridine-κN)[2-(4-hy-droxy-phen-yl)acetato-κO,O']erbium(III)} monohydrate.

The title dinuclear complex, [Er(2)(C(8)H(7)O(3))(6)(C(10)H(8)N(2))(2)(H(2)O)(2)]·H(2)O, contains two Er(III) atoms in the asymmetric unit, six 2-(4-hy-droxy-phen-yl)acetate (PAA) anions, two 4,4'-bipyridine (bipy) mol-ecules, two coordinated water mol-ecules and one solvent water mol-ecule. The central Er(III) atoms are nine-coordinated. The coordination environment includes six O atoms from three PAA anions, one bridging O atom from a PAA anion, one O atom from a water mol-ecule and an N atom from a bipy ligand in a distorted tricapped trigonal-prismatic geometry. The occurrence of numerous O-H⋯O and O-H⋯N hydrogen bonds involving coordinated and noncoordinated water as well as bipy groups builds up an intricate three-dimensional network.