Doubly-hydrated hexafluoroacetylacetone as a tetradentate ligand: synthesis, magnetochemistry, and thermal transformations of a dimanganese(III) complex

Abstract

A convenient synthesis of the doubly-hydrated form of hexafluoroacetylacetone (hfacH) is reported, viz. 1,1,1,5,5,5-hexafluoropentane-2,2,4,4-tetraol (hfptH[sub 4]; 1), together with the initial employment of the latter as a ligand. A reaction system in CH[sub 2]Cl[sub 2] comprising [Mn[sub 3]O(OAc)[sub 6](py)[sub 3]](ClO[sub 4]), hfacH, hfptH[sub 4], and py (py = pyridine) in a 1:6:1.5:9 ratio leads to a 58% yield of (pyH)[sub 2][Mn[sub 2](hfpt)(hfac)[sub 4]]. The structure of 1 confirms a bis(gem-diol) structure with an extended-chain conformation. The anion of 2 consists of two Mn(hfac)[sub 2] fragments bridged by the hfpt[sup 4[minus]] group; the latter functions as a bidentate chelate ligand to each Mn[sup III], employing one alkoxide oxygen atom from each gem-diolate pair. Variable-temperature magnetochemical studies have been performed on powdered samples of 2 in the range 5-320 K. The Mn[sup III] centers are weakly interacting; the exchange interaction is ferromagnetic, and fitting of the data leads to the following values for the variables: J = +0.21 cm[sup [minus]1] (employing the [minus]2JS[sub 1][center dot]S[sub 2] convention), D = 0.9 cm[sup [minus]1], g = 1.99. Vacuum thermolysis of 2 in the range 111-150[degrees]C yields (py)Mn(hfac)[sub 3] and lesser amounts of cis-Mn(py)[sub 2](hfac)[sub 2], Mn(hfac)[sub 3], the tetraol, and a manganese ([ge]IV) oxide.more » All but the oxide are volatile and have been characterized in part by single-crystal X-ray diffraction. The mechanism of thermolysis is proposed to be initiated by proton transfer from pyH[sup +] to the tetraolate oxygen to which it is hydrogen bonded; this process facilitates the electrophilic cleavage of C/O bonds, which furnishes hfac[sup [minus]] as well as oxide for the manganese oxide product.« less