Incorporating Mono- and Trivalent Thallium Cations into Trivalent Lanthanide Squarate and Squarate-Oxalate Complexes

The synthesis and structural characterization of nine new trivalent lanthanide squarate-oxalate complexes, three new trivalent lanthanide squarate complexes containing trivalent thallium, and one new trivalent cerium squarate complex containing monovalent thallium are presented. These new complexes─[Ln 2 (C 4 O 4 )(C 2 O 4 ) 2 (H 2 O) 6 ]·4H 2 O (Ln = Pr, Nd, Sm–Dy, Er, Tm) ( 1 ), Tl[Ln(C 4 O 4 ) 2 (H 2 O) 6 ]·C 4 O 4 (Ln = La, Pr, Nd) ( 2 ), and Tl[Ce(C 4 O 4 ) 2 (H 2 O) 4 ] ( 3 )─all contain the dianionic squarate ligand bound to the lanthanides with varying coordination modes and denticities. Complex 1 expands upon the number of known lanthanide squarate structures that also incorporates oxalate (formed in situ from squarate). Complex 2 expands the members of the known trivalent lanthanide and trivalent thallium (an unusual and challenging oxidation state to stabilize of thallium) squarate complexes known. Complex 3 is a stand-alone compound containing monovalent thallium and trivalent cerium where the squarate is bound via rather atypical coordination modes to the cerium centers. Herein, the synthesis, characterization, and structural descriptions of 1, 2, and 3 are presented.