The Divalent Lanthanoid Triflates Ln(CF3SO3)2(CH3CN) (Ln=Sm, Eu): Structure, Luminescence, and Magnetism.

The reaction of the trivalent lanthanoide triflates Ln(OTf)3 (Ln=Sm, Eu; OTf=CF3SO3 -) with the respective metals in acetonitrile leads to the Ln(II)-triflates Eu(OTf)2(CH3CN) (monoclinic, P21/n, Z=4, a=1053.54(1), b=610.28(5), c=1946.92(2) pm, ß =98.611(4)) and Sm(OTf)2(CH3CN) (monoclinic, P21/n, Z=4, a=1054.41(4), b=612.16(2), c=1952.65(7) pm, ß =98.524(2)). The isotypic strontium compound Sr(OTf)2(CH3CN) (monoclinic, P21/n, Z=4, a=1056.39(5), b=610.05(3), c=1950.1(1) pm, ß =98.900(2)°) has been obtained from SrCO3 and triflic acid. The compounds have been investigated by X-ray diffraction, vibrational spectroscopy, luminescence spectroscopy, cyclic voltammetry, thermal analysis, and magnetic measurements.

Stabilization of Pr4+ in Silicates─High-Pressure Synthesis of PrSi3O8 and Pr2Si7O18.

The reaction between PrO2 and SiO2 was investigated at various pressure points up to 29 GPa in a diamond anvil cell using laser heating and in situ single-crystal structure analysis. The pressure points at 5 and 10 GPa produced Pr2III(Si2O7), whereas Pr4IIISi3O12 and Pr2IV(O2)O3 were obtained at 15 GPa. Pr4IIISi3O12 can be interpreted as a high-pressure modification of the still unknown orthosilicate Pr4III(SiO4)3. PrIVSi3O8 and Pr2IVSi7O18 that contain praseodymium in its rare + IV oxidation state were identified at 29 GPa. After the pressure was released from the reaction chamber, the Pr(IV) silicates could be recovered, indicating that they are metastable at ambient pressure. Density functional theory calculations of the electronic structure corroborate the oxidation state of praseodymium in both PrIVSi3O8 and Pr2IVSi7O18. Both silicates are the first structurally characterized representatives of Pr4+-containing salts with oxoanions. All three silicates contain condensed networks of [SiO6] octahedra which is unprecedented in the rich chemistry of lanthanoid silicates.

Stabilization of Guanidinate Anions [CN3 ]5- in Calcite-Type SbCN3.

The stabilization of nitrogen-rich phases presents a significant chemical challenge due to the inherent stability of the dinitrogen molecule. This stabilization can be achieved by utilizing strong covalent bonds in complex anions with carbon, such as cyanide CN- and NCN2- carbodiimide, while more nitrogen-rich carbonitrides are hitherto unknown. Following a rational chemical design approach, we synthesized antimony guanidinate SbCN3 at pressures of 32-38 GPa using various synthetic routes in laser-heated diamond anvil cells. SbCN3 , which is isostructural to calcite CaCO3 , can be recovered under ambient conditions. Its structure contains the previously elusive guanidinate anion [CN3 ]5- , marking a fundamental milestone in carbonitride chemistry. The crystal structure of SbCN3 was solved and refined from synchrotron single-crystal X-ray diffraction data and was fully corroborated by theoretical calculations, which also predict that SbCN3 has a direct band gap with the value of 2.20 eV. This study opens a straightforward route to the entire new family of inorganic nitridocarbonates.

Competition between N and O: use of diazine N-oxides as a test case for the Marcus theory rationale for ambident reactivity.

The preferred site of alkylation of diazine N-oxides by representative hard and soft alkylating agents was established conclusively using the 1H-15N HMBC NMR technique in combination with other NMR spectroscopic methods. Alkylation of pyrazine N-oxides (1 and 2) occurs preferentially on nitrogen regardless of the alkylating agent employed, while O-methylation of pyrimidine N-oxide (3) is favoured in its reaction with MeOTf. As these outcomes cannot be explained in the context of the hard/soft acid/base (HSAB) principle, we have instead turned to Marcus theory to rationalise these results. Marcus intrinsic barriers (ΔG ‡ 0) and Δr G° values were calculated at the DLPNO-CCSD(T)/def2-TZVPPD/SMD//M06-2X-D3/6-311+G(d,p)/SMD level of theory for methylation reactions of 1 and 3 by MeI and MeOTf, and used to derive Gibbs energies of activation (ΔG ‡) for the processes of N- and O-methylation, respectively. These values, as well as those derived directly from the DFT calculations, closely reproduce the observed experimental N- vs. O-alkylation selectivities for methylation reactions of 1 and 3, indicating that Marcus theory can be used in a semi-quantitative manner to understand how the activation barriers for these reactions are constructed. It was found that N-alkylation of 1 is favoured due to the dominant contribution of Δr G° to the activation barrier in this case, while O-alkylation of 3 is favoured due to the dominant contribution of the intrinsic barrier (ΔG ‡ 0) for this process. These results are of profound significance in understanding the outcomes of reactions of ambident reactants in general.