Poly[[aqua-μ(3)-picolinato-μ(2)-picolinato-dipicolinatopotassium(I)terbium(III)] 2.5-hydrate]

In the title compound, [KTb(C(6)H(4)NO(2))(4)(H(2)O)]·2.5H(2)O, each Tb(3+) centre is coordinated by four N and five O atoms from five distinct picolinate ligands in a geometry resembling a highly distorted tricapped trigonal prism. One of the ligands establishes a skew bridge between neighbouring Tb(3+) centres, leading to the formation of one-dimensional anionic polymeric chains, {[(C(6)H(4)NO(2))(4)Tb](−)}(n), running along the direction [010]. Each K(+) cation is seven-coordinated by six O atoms from one anionic polymeric chain and one water mol­ecule [K⋯O 2.676 (3)–3.208 (4) Å]. The uncoordinated water mol­ecules are involved in O—H⋯O hydrogen bonding.