Unligated Diruthenium(II,II) Tetra(trifluoroacetate):  The First X-ray Structural Study, Thermal Compressibility, Lewis Acidity, and Magnetism

The title compound, [Ru2(O2CCF3)4] (1), has been obtained without any exogenous ligands and crystallized by deposition from the gas phase at 170 °C. Its crystal structure has been determined for the first time to confirm an infinite chain motif built on axial Ru···O interactions of the diruthenium(II,II) units. The X-ray diffraction studies at variable temperatures showed no phase transitions in the range of 295−100 K but revealed a significant decrease in the volume per atom from 14.2 to 13.3 Å3. This noticeable thermal compressibility effect is discussed in connection with the solid-state packing of the [Ru2(O2CCF3)4]∞ chains. The highly electrophilic character of the diruthenium(II,II) units has been shown by the gas-phase deposition reaction of [Ru2(O2CCF3)4] with an aromatic donor substrate, namely [2.2]paracyclophane (C16H16). As a result of the above reaction, a new arene adduct [Ru2(O2CCF3)4·C16H16] (2) has been isolated in crystalline form. It has an extended one-dimensional (1D) chain structure comprised of alternating building units and based on the rare bridging mode of [2.2]paracyclophane, [Ru2(O2CCF3)4·(μ2-η2:η2-C16H16)]∞. The magnetic susceptibility of 1 and 2 has been measured and compared in the range of 1.8−300 K. In addition, in the course of synthesis of 1 by the carboxylate exchange reactions, a new mixed-carboxylate diruthenium(II,II) core complex [Ru2(O2CCF3)3(O2CC2H5)] (3), bearing no exogenous ligands, has also been isolated and structurally characterized. It exhibits an interesting polymeric structure in which the ruthenium(II) centers selectively form axial interdimer contacts with the O-atoms of the propionate groups only.