Unexpected structural complexity of thorium coordination polymers and polyoxo cluster built from simple formate ligands

A simple binary synthetic approach with variable [HCOOH]/[Th(iv)] ratios and the addition of water resulted in the self-assembly of six novel thorium formate complexes with well-controlled structures ranging from 0D clusters and 2D layered networks to 3D frameworks. Specifically, small [HCOOH]/[Th(iv)] promoted the formation of the hexanuclear Th6O4(OH)(4)(HCOO)(12) core, a secondary building unit for the construction of 3D [Th6Na(mu(3)-O)(4)(mu(3)-OH)(4)(HCOO)(14)]center dot[NH2(CH3)(2)]center dot(DMF)(3)(H2O)(5) (Th-SINAP-1), 2D [Th-6(mu(3)-O)(4)(mu(3)-OH)(4)(HCOO)(12)(DMF)(2)]center dot(H2O)(10) (Th-SINAP-2), and 0D [Th-6(mu(3)-O)(4)(mu(3)-OH)(4)(HCOO)(12)(H2O)(6)]center dot G (Th-SINAP-3). The large [HCOOH]/[Th(iv)] inhibited the olation/oxolation reaction, affording 3D frameworks of [Th-2(HCOO)(9)]center dot[NH2(CH3)(2)]center dot(DMF)(H2O)(2) (Th-SINAP-4), [Th-2(HCOO)(9)]center dot[NH2(CH3)(2)]center dot(DMF)(H2O)(4) (Th-SINAP-5), and [Th-2(HCOO)(8)(H2O)(DMF)]center dot(H2O)(3) (Th-SINAP-6) with monomeric Th(iv) cations as the metal nodes. The addition of water not only affected the hydrolysis of Th(iv) to form nucleophilic hydroxo/oxo-aquo Th species, but also influenced the overall solid-state packing via the competition between H2O, HCOO-, OH-/O2-, and DMF for coordination with Th4+ cations. This unexpected structural complexity of thorium formates opens a new avenue for the targeted design and synthesis of atypical coordination polymers, e.g. open-framework materials of actinides, for applications in diverse fields such as radionuclide adsorption.