Crystal Chemical Study of Two Scandium(III) Complexes with Pivaloyltrifluoroacetone

Abstract

A scandium(III) tris-(pivaloyltrifluoroacetonate) complex [Sc(ptac)₃] is synthesized, purified, and characterized by the elemental analysis, IR spectroscopy, and the TG/DTA technique. The complex is a highly volatile and low-melting compound that is stable in air and to heat. Slow evaporation of the mother ethanol liquor at room temperature leads to the growth of single crystals of a mixed-ligand complex with an alcohol molecule: [Sc(EtOH)(ptac)₃]. By single crystal X-ray diffraction at a temperature of 150(2) K the [Sc(ptac)₃] and [Sc(EtOH)(ptac)₃] structures are solved. The crystallographic data are: for C₂₄H₃₀F₉O₆Sc space group P-1, a = 9.1565(2) Å, b = 9.6854(3) Å, c = 17.3271(4) Å, β = 79.927(1)°, V = 1465.79(7) ų, Z = 2, d_calc = 1.428 g/cm³, R = 0.041; for C₂₆F₉O₇Sc space group P-1, a = 9.9376(3) Å, b = 13.0243(4) Å, c = 13.2743(4) Å, β = 111.932°, V = 1575.85(8) ų, Z = 2, d_calc = 1.426 g/cm³, R = 0.048. Both structures are composed of neutral molecules; the metal atom coordinates six oxygen atoms of three ligands of β-diketone ([Sc(ptac)₃]) and additionally an oxygen atom of the ethanol molecule ([Sc(EtOH)(ptac)₃]). Tert-butyl and trifluoromethyl substituents in both complexes are oriented so that they create a facial isomer. The Sc-O distances are within 2.07–2.11 Å in [Sc(ptac)₃], and in [Sc(EtOH)(ptac)₃] they are within 2.10–2.24 Å. In the crystals of both compounds, the molecules are linked by only van der Waals interactions, forming a pseudo-layered structure with a hexagonal arrangement inside the layer. Six shortest Sc⋯Sc distances in [Sc(ptac)₃] are within 8.34–10.42 Å. In [Sc(EtOH)(ptac)₃], a distorted hexagonal packing has an average parameter of ~9.5 Å.