Trihalogenochalcogenonium-halogenometallates [EX 3 ][MX n ] – Synthesis and crystal structures of [TeX 3 ][MX 6 ] (X=Cl, Br; M=W, Nb, Ta) and a suggestion for a structure designation code for the various structure types in this family of compounds

(TeCl)4(TiCl4) with isolated Te4Cl16 and TiCl4 molecules and second-harmonic-generation

(TeCl4)4(TiCl4) is obtained by reaction of TeCl4 and TiCl4 at 50 °C with quantitative yield. The compound is composed of isolated, molecular (TeCl4)4 heterocubane-type units as well as isolated, molecular TiCl4 tetrahedra. The (TeCl4)4 heterocubane is arranged like a body-centred cubic cell with TiCl4 tetrahedra occupying 4 of 6 octahedral sites. (TeCl4)4(TiCl4) crystallizes in the space group I4̄ with an unidirectional alignment of the tetrahedral building units. The structure of the compound is obtained from single crystal X-ray diffraction and confirmed by Rietveld refinement of powder diffraction data. Thermogravimetry, optical spectroscopy, infrared and Raman spectroscopy are employed to further characterize the title compound. Second harmonic generation (SHG) is observed with a strong intensity (1.6-times higher than potassium dihydrogen phosphate/KDP). The SHG effect is observed in the visible spectral regime as the band gap, derived from a Tauc plot, is 2.8 eV.

Reactive p-block cations stabilized by weakly coordinating anions

The chemistry of the p-block elements is a huge playground for fundamental and applied work. With their bonding from electron deficient to hypercoordinate and formally hypervalent, the p-block elements represent an area to find terra incognita. Often, the formation of cations that contain p-block elements as central ingredient is desired, for example to make a compound more Lewis acidic for an application or simply to prove an idea. This review has collected the reactive p-block cations (rPBC) with a comprehensive focus on those that have been published since the year 2000, but including the milestones and key citations of earlier work. We include an overview on the weakly coordinating anions (WCAs) used to stabilize the rPBC and give an overview to WCA selection, ionization strategies for rPBC-formation and finally list the rPBC ordered in their respective group from 13 to 18. However, typical, often more organic ion classes that constitute for example ionic liquids (imidazolium, ammonium, etc.) were omitted, as were those that do not fulfill the - naturally subjective -"reactive"-criterion of the rPBC. As a rule, we only included rPBC with crystal structure and only rarely refer to important cations published without crystal structure. This collection is intended for those who are simply interested what has been done or what is possible, as well as those who seek advice on preparative issues, up to people having a certain application in mind, where the knowledge on the existence of a rPBC that might play a role as an intermediate or active center may be useful.

DFT-Based Pseudo-Jahn−Teller Coupling Studies on the Steric and Energetic Lone Pair Effect of Four- and Five-Coordinate Halide Molecules and Complexes with Central Ions from the Fifth, Sixth, and Seventh Main Groups

The energetical and stereochemical effect of the s(2) lone pair in the title molecules and complexes is investigated using a pseudo-Jahn-Teller coupling model with parameters adjusted to energies and wave functions from DFT calculations. Vibronic coupling parameters were calculated and compared with those of the coordination number (CN) 3. Inspecting the correlation between the chemical hardness and the vibronic coupling energy (hardness rule), it is found that the tendency to distort decreases with increasing CN. While all considered molecules AX(3) (A(III) = P to Bi; X(-) = F to I) undergo lone pair deformations (D(3h)---> C(3v)), only part of the AX(4)(-) and BX(4) species (B(IV) = S to Po) do so (T(d)---> C(2v)-and even less the ones with CN = 5 (D(3h)---> C(2v) (congruent with C(4v)), AX(5)(2-), BX(5)(-), and CF(5) (C(V); Cl to I). The distorted polyhedra of minimum energy possess usually the butterfly C(2v) shape (CN = 4, tau(2)(zeta) displacement path) and a C(2v) = C(4v)geometry (CN = 5, epsilon' (epsilon) distortion path). A further symmetry lowering to C(s) occurs, if the central ion becomes too small with respect to the ligands (ionic size influence, PCl(Br)(4)(-), PCl(5)(2-)), with the tendency to reduce the CN toward 3 + 1 and 4 + 1, respectively. For CN = 4 the various stationary points of, for example, compressed and elongated C(3v), C(4v), etc. in the multidimensional ground-state potential surface have been characterized. Though of higher energy than the absolute C(2v) minimum, they are shown to govern the dynamics and reactivity of the CN = 4 species to a large extent. To simulate the chemical environment (positively charged counterions, polar solvents), the DFT calculations were performed using the polarizable continuum model COSMO (conductor-like screening model). Though the electronic energy gain upon distortion is not significantly affected by the solvent, the total stabilization energy is distinctly enhanced, frequently leading to lone pair deformations of otherwise electronically stable species. All results obtained by the combined vibronic/DFT approach are well in accord with available experimental data.