Lanthanide(III) squarates 1. Five families of compounds obtained from aqueous solutions in an open system. Crystal structure and thermal behaviour

Abstract Five families of hydrated lanthanide(III) squarates of respective formulae Ln 2 (H 2 O) 11 (C 4 O 4 ) 3 ·2H 2 O (1-Ln), [Ln(H 2 O) 4 ] 2 (C 4 O 4 ) 3 (2-Ln), H[Ln(H 2 O) x (C 4 O 4 ) 2 ]· y H 2 O ( x + y = 6) (1(H)-Ln), Ln(H 2 O) 6 (C 4 O 4 )(HC 4 O 4 )·H 2 O (2(H)-Ln), H[Ln(H 2 O) 6 (C 4 O 4 ) 2 ] (3(H)-Ln), were prepared by reaction of aqueous solutions of lanthanide salts and squaric acid or squarate anion. The formula of the compound produced depends on the Ln(III) cation radius and conditions of preparation. The crystal structures of the following representative compounds were determined by X-ray single crystal techniques. 1 -Pr: monoclinic, space group P 2/ c , a = 9.687(1), b = 7.632(1), c = 16.423(1) A, β = 89.95(1)°, V = 1214 A 3 , Z = 2. 2-Eu: monoclinic, space group Pc , a = 11.937(2), b = 8.205(1), c = 10.106(2) A, β = 96.04(1)°, V = 984 A 3 , Z = 2. 2(H)-Eu: monoclinic, space group Cc , a = 15.263(2), b = 14.898(1), c = 6.354(1) A, β = 92.24(1)°, V = 1444 A 3 , Z = 4. 3 (H)-Yb: monoclinic, space group C 2/ c , a = 10.272(1), b = 12.450(1), c = 11.760(1) A, β = 110.78(1)°, V = 1406 A 3 , Z = 4. None of the 1 (H)-Ln compounds gave crystals suitable for an X-ray structure determination. The squarate anion behaves like a uni- or a plufimonodentate ligand. 1 -Ln has a double-chained structure; 2 -Ln has a double-layered structure. 2 (H)-Ln and 3 (H)-Ln are made of discrete mononuclear entities. In 2 (H)-Ln, the presence of a monohydrogenosquarate ligand is clearly established, while in 3 (H)-Ln, the proton is likely to be shared by two neighbouring squarate ligands. Both thermal gravimetry and thermal differential analyses were carried out on compounds of the five families in the temperature range 20–800 °C, in a 50% He-50% O 2 atmosphere. The existence of anhydrous squarates stable over wide ranges of temperature was shown. The results are compared with those of the well known lanthanide oxalates and those of another work that do not match ours.