Structural and physicochemical study of erbium and holmium complexes with proline

The synthesis method for erbium and holmium complexes with proline, [Er(Pro)₂(H₂O)₅]Cl₃ and [Ho₂(Pro)₂(H₂O)₁₂]Cl₆, is described. The compounds were obtained as monoclinic single crystals with space groups P2₁ and C2, respectively (unit cell parameters: for the erbium complex a = 8.28448(8) Å, b = 10.98673(10) Å, c = 11.80654(13) Å, α = γ = 90°, β = 106.8425(11)°, V = 1028.528(18) ų; for the holmium complex a = 22.7640(4) Å, b = 7.94201(10) Å, c = 20.7638(3) Å, α = γ = 90°, β = 15.8591(19)°, V = 3378.04(10) ų). The coordination polyhedron of erbium and holmium are square antiprisms. The erbium compound forms an infinite chain, while the holmium crystal contains isolated dimers involving twelve coordinated water molecules and an extensive hydrogen-bond network stabilizing the structure. The thermal behavior of the complexes was studied over a wide temperature range using DSC and TGA techniques.