Lanthanide Squarate Complexes Containing Mono- and Trivalent Thallium

The synthesis and structural characterizationof 16 new thalliumlanthanide squarate complexes and 1 new cerium squarate oxalate complexare presented. These new complexes-Tl[Ln(C4O4)(H2O)(5)]center dot C4O4 (Ln = La-Nd) (1), Tl-3[Ln(3)(C4O4)(6)(H2O)(6)]center dot 8H(2)O (Ln = Sm-Lu, Y) (2), Tl[Ce(C4O4)(2)(H2O)(6)]center dot C4O4 (3), and [Ce-2(C4O4)(2)(C2O4)(H2O)(8)]center dot 2H(2)O (4)-all contain the squarate ligand bound to the trivalent lanthanides withvarying coordination modes and denticities. Of the four new groupsof complexes prepared in this work, two groupings contain monovalentthallium and trivalent lanthanides, the most common oxidation statesfor these metals. One complex (3), however, containstrivalent thallium, which is an unusual and challenging oxidationstate to stabilize. The Tl3+ cation is formed from in situ oxidation by way of tetravalent cerium (Ce4+/Ce3+, E degrees = 1.72 V; Tl3+/Tl+ = 1.252 V), leading to the formation of a Tl3+-Ce3+-squarate complex. Additionally, one complex(4) is unique in this work in that it contains both thesquarate and oxalate ligands, the latter of which was formed in situ from squarate. Single-crystal X-ray diffractionanalysis reveals that 1 and 2 have a 2Dstructure constructed from either LnO(4)(H2O)(5) monocapped square antiprismatic (CN = 9) metal centers (for 1) or LnO(4)(H2O)(4) square antiprismatic (CN = 8) metal centers (for 2), 3 is a 1Dchain structure constructed from CeO3(H2O)(6) monocapped square antiprismatic (CN = 9) cerium centers,and 4 is a 3D framework structure constructed from CeO5(H2O)(4) monocapped square antiprismatic (CN = 9) cerium centers. 2 and 4 displayrare coordination modes for the squarate ligand. Herein, the synthesis, characterization, and structural descriptions of these new complexesare presented.

Automated summary

The paper presents the synthesis and structural characterization of 16 new thallium lanthanide squarate complexes and 1 new cerium squarate oxalate complex. These complexes exhibit different coordination modes and denticities between the trivalent lanthanides and squarate ligands. The study also discusses the unusual presence of trivalent thallium and the rare coordination modes of certain complexes.