Croconato-containing M(III) (M = Ga, Er) complexes as potential building blocks for mono/multifunctional molecular materials

The one-pot synthesis and structural characterization of two new complexes of the croconato ligand (C₅O₅)^2- with the Ga(III) and Er(III) metal ions are reported. The mononuclear tris-chelated (n-Bu₄N)₃[Ga(C₅O₅)₃], 1, which exhibits an octahedral geometry, is present as Δ and Λ enantiomers in equal amounts; the K₂[Er(C₅O ₅)(μ-SO₄)(OH₂)₄]₂ complex, 2, shows dinuclear erbium moieties with bridging sulfate anions and interposed K(I) cations with a capped trigonal prismatic coordination geometry. 2 shows paramagnetic behavior in the 2-300 K range typical of two isolated Er(III) ions. Vibrational (FT-IR and FT-Raman) and electronic spectroscopies have shown to be a reliable diagnostic tool in distinguishing different molecular arrangements of the croconato ligand in different complexes. The analogies of the gallium complex with the corresponding [M(C₂O ₄)₃]^3- tris-chelated complexes which have been used as chiral building blocks of molecular conductors are pointed out.