Anhydrous Yttrium Acetylacetonate and the Course of Thermal “Dehydration” of Y(acac)3·3H2O

Abstract

Hydrocarbon-soluble [Y(acac)3]n (acac = acetylacetonate) is produced in high yield by treatment of Y[N(SiMe3)2]3 with 3 equiv of Hacac in hydrocarbon solvent. Variable-temperature 1H and 89Y NMR studies suggest that the degree of aggregation, n, of this compound is four. Attempted slow crystallization of this compound from hexanes gives, as the least-soluble material, the product of adventitious partial hydrolysis: Y4(OH)2(acac)]10. Its structure was established by X-ray diffraction as Y4(µ3-OH)2(µ-acac)6(acac)4. This centrosymmetric aggregate has a diamond-shaped Y4 core, with µ3-OH groups lying above and below the Y4 plane. The aggregation is further enforced by six acac ligands which have one oxygen terminal and the second bridging two yttrium atoms. Each of the remaining four acac ligands are fully terminal on a different yttrium such that every metal achieves coordination number eight. Various methods to produce this compound in high yield are discussed, including controlled vacuum thermolysis of bulk solid Y(acac)3·3H2O, which gives, after recrystallization from benzene, Y4(OH)2(acac)10·4C6H6. This solid contains the same molecules isolated earlier, packed together in the lattice with benzene molecules. The loss of Hacac on vacuum thermolysis is suggested to be initiated by the hydrogen bonding to acac oxygen which exists in solid Y(acac)3·3H2O. Crystal data for Y4(OH)2(acac)10 (at −174 °C): a = 14.621(4) Å, b = 15.365(4) Å, c = 14.786(5) Å, and β = 116.13(2)° with Z = 2 in space group P21/n. For Y4(OH)2(acac)10·4C6H6 (at −175 °C): a = 13.606(4) Å, b =13.951(5) Å, c = 11.366(4) Å, a = 96.70(2)°, β = 112.39(1)°, and y = 78.57(2)° with Z = 2 in space group P1̄. © 1993, American Chemical Society. All rights reserved.