catena-Poly[thorium(IV)-tetrakis(μ(2)-3-carboxyadamantane-1-carboxylato)]: a quadruple helical strand driven by a synergy of coordination and hydrogen bonding.

The title compound, [Th(C(12)H(15)O(4))(4)](n), is the first homoleptic thorium-carboxylate coordination polymer. It has a one-dimensional structure supported by the bidentate bridging coordination of the singly charged 3-carboxyadamantane-1-carboxylate (HADC(-)) anions. The metal ion is situated on a fourfold axis (site symmetry 4) and possesses a square-antiprismatic ThO(8) coordination, including four bonds to anionic carboxylate groups [Th-O = 2.359 (2) Å] and four to neutral carboxyl groups [Th-O = 2.426 (2) Å], while a strong hydrogen bond between these two kinds of O-atom donor [O...O = 2.494 (3) Å] affords planar pseudo-chelated Th{CO(2)...HO(2)C} cycles. This combination of coordination and hydrogen bonding is responsible for the generation of quadruple helical strands of HADC(-) ligands, which are wrapped around a linear chain of Th(IV) ions [Th...Th = 7.5240 (4) Å] defining the helical axis.