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Structures and Reactions of Compounds Containing Heavier Main Group Elements
Published in Takayuki Fueno, The Transition State, 2019
The valence ns and np electrons play an essential role in the chemistry of main group atoms, unlike the d electrons of transition metals. It is very helpful to understand the periodic trends of the atomic orbitals. As an example, the atomic radii (r) of maximal electron density calculated for group 14 atoms are shown in Fig. 8.1.10) It may be expected simply that the sizes of the ns and np orbitals increase monotonically going down the periodic table from C to Si, Ge, Sn, and Pb because the principal quantum number (n) increases. However, the size increase is not regular but irregular at Ge and Pb. Such irregularity is not specific to Ge and Pb but common to the fourth and sixth row atoms.
Exploring the potential role of heavy pnictogen elements in ligand design for new metal-ligand cooperative chemistry
Published in Journal of Coordination Chemistry, 2022
W. M. Hollingsworth, E. A. Hill
Given the ever-growing interest in advancing transition metal mediated catalysis, a logical extension of MLC would be to explore heavy main group elements as active ligands. Doing so may lead to greater diversity of chemistry enabled by the combined activity of the transition metal ion and main group partner to perform multi-electron, multi-functional group transformations. This review will focus on discussion of the latest advances in heavy pnictogen atom chemistry with special care taken to highlight examples of MLC. The case will be made for the properties of each element that may yield new ligands and modes of bond activation that have yet to be realized. Establishing this idea leads to the conclusion that using ligands containing heavy pnictogen elements presents an underdeveloped area in the ever-growing field of MLC in inorganic catalysis.
Calculations of atomisation energy and singlet–triplet gap with iterative multireference configuration interaction
Published in Molecular Physics, 2022
Jia-Qi Fan, Wen-Yan Zhang, Qing Ren, Feiwu Chen
Silicon and carbon are in the same main group of the periodic table. For the purpose of comparison, SiH2 is also considered here. The geometries and basis set of SiH2 are consistent with the work of Bauschlicher and Taylor [49]. The FCI result of the singlet–triplet separation of SiH2 in their work was 17.5 kcal/mol. Results of SiH2 calculated with MRCI and IMRCI are presented in Table 3. Niter is from 1 to 2. Regardless of the value of NEC, the singlet–triplet separation ΔE of MRCI remains unchanged at 17.4 kcal/mol, with an error of 0.1 kcal/mol. As for IMRCI, the optimal value 17.5 kcal/mol of ΔE is the same as the FCI result. In comparison with the results of CH2 in Table 2, ΔE of SiH2 converges with NEC more quickly than that of CH2, which indicates that the most important configurations are already included in the reference space when NEC is 20. The best singlet–triplet separation of SiH2 calculated by Chen [48] using perturbation theory and complete active space self-consistent field orbitals is 17.5 kcal/mol. ΔEs calculated with MP2, MP3, CCSD and CCSD(T) are respectively 13.3, 15.8, 17.2 and 17.4 kcal/mol. In comparison with the results of CH2, all calculations demonstrate that SiH2 is much easier to describe from the wavefunction viewpoint.
Structural, electronic, magnetic and thermoelectric properties of inverse Heusler alloys Ti2CoSi, Mn2CoAl and Cr2ZnSi by employing Ab initio calculations
Published in Philosophical Magazine, 2020
D. J. Mokhtari, Inshad Jum’h, H. Baaziz, Z. Charifi, T. Ghellab, Ahmad Telfah, Roland Hergenröder
In general, ternary Heusler alloys have two high ordered structures, namely, the classic Cu2MnAl-type structure and the newly discovered Hg2CuTi-type structure. The inverse Heusler alloys (Hg2CuTi) have composition X2YZ with space group. In Wyckoff positions, X is located at (0,0,0) and (1/4, 1/4, 1/4), Y and Z are located at (1/2, 1/2, 1/2) and (3/4, 3/4, 3/4) respectively [24]. X and Y denote a transition metal, while Z denotes a main group element (Figure 1(b)). Under ambient conditions, the inverse Heusler compounds Ti2CoSi, Mn2CoAl and Cr2ZnSi crystallises in the type Hg2CuTi structure (see Figure 2) and it is demonstrated that the later phase is the most stable. The high-pressure structure is Cu2MnAl type-structure with (225) space group. To find the favourable magnetic state of each alloy we calculated the total energy versus volume for the three magnetic states: the ferromagnetic (FM), Non-magnetic (NM) and antiferromagnetic (AFM) states.