Preparation, Molecular and Electronic Structures, and Magnetic Properties of Face-Sharing Bioctahedral Titanium(III) Compounds: [PPh₄][Ti₂(μ-Cl)₃Cl₄(PR₃)₂]

Reduction of TiCl4 with 1 equiv of HSnBu3 followed by addition of [PPh4]Cl and then PR3 leads to two new dinuclear titanium(III) compounds, [PPh4][Ti2(μ-Cl)3Cl4(PR3)2] (R = Et and R3 = Me2Ph), both of which contain an anion with the face-sharing bioctahedral type structure. Their crystal structures are reported. [PPh4][Ti2(μ-Cl)3Cl4(PEt3)2]·2CH2Cl2 crystallized in the triclinic space group P1̄. Cell dimensions: a = 12.461(1) Å, b = 20.301(8) Å, c = 11.507(5) Å, α = 91.44°, β = 113.27(1)°, γ = 104.27(2)°, and Z = 2. The distance between titanium atoms is 3.031(2) Å. [PPh4][Ti2(μ-Cl)3Cl4(PMe2Ph)2]·CH2Cl2 also crystallized in the triclinic space group P1̄ with cell dimensitions a = 11.635(4) Å, b = 19.544(3) Å, c = 11.480(3) Å, α = 100.69(2)°, β = 109.70(1)°, γ = 95.08(2)°, and Z = 2. The distance between titanium atoms in this compound is 2.942(1) Å. Variable temperature magnetic susceptibilities were measured for [PPh4][Ti2(μ-Cl)3Cl4(PEt3)2]. Electronic structure calculations were carried out for a model ion, [Ti2(μ-Cl)3Cl4(PH3)2]-, and another well-known anion, [Ti2(μ-Cl)3Cl6]3-, by employing an ab initio configuration interaction method. The results of the calculations reveal that the metal−metal interaction in these Ti(III) face-sharing compounds can be best described by strong antiferromagnetic coulping that leads to a singlet ground state and a thermally accessible triplet first excited state. Accordingly the measured magnetic data were satisfactorily fitted to a spin-only formula.