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Synthesis and Structure of Selenolate-Protected Metal Nanoclusters
Published in Yan Zhu, Rongchao Jin, Atomically Precise Nanoclusters, 2021
Except for the Au8 kernel, two Au5Se6 staples (Fig. 3.1), which are linked with the middle of the Au8 kernel, were first observed in the surface protecting structure of Au24(SeC6H5)20. It is worth noting that such Au5Se6 staples were indeed observed experimentally for the first time. Furthermore, two Au3Se4 staple motifs are linked with the ends of the Au8 kernel. In comparison to the Au3S4 observed in Au23(SR)16 nanocluster [69], the bond length of Au-Se (average 2.427 Å) is longer than that of Au-S (average 2.301 Å), which is due to the larger Se atom than the S atom (covalent radius of Se r = 1.20 Å versus S atom r = 1.05 Å). Interestingly, the two Au5Se6 staple motifs are combined by two pairs of Au-Au bonds, and the Au-Au bonds are 3.091 and 3.077 Å. In addition, the Au3Se4 staple motifs are closely linked to the Au5Se6 staple through the Au-Au bond, with the average Au-Au bond length being 2.986 Å. Considering this, the framework of Au24(SeC6H5)20 can be viewed as an interlocked catenane-like construction, which is same as the theoretical structure of Au24(SCH3)20 modeled by Pei et al. [70].
Augmented Cylindrical Waves for Nonchiral Nanotubes and Wires
Published in Pavel N. D’yachkov, Quantum Chemistry of Nanotubes, 2019
A linear chain of carbon atoms with alternating bond lengths 1.34 and 1.20 Å is the simplest nanowire. In this case, the inner cavity is obviously absent; therefore, we analyzed the convergence of the band structure as a function of the radius a of the outer potential barrier. The value a was varied from the covalent radius of carbon up to the a = 2.11 Å (the van der Waals radius of the C atom is equal to 1.7 Å). Physically reasonable band diagrams of carbyne were obtained at a ≥ 1.48 Å. For 1.48 ≤ a ≤ 2.11 Å, only about 3.5–0.2% of the electron density of the system is located beyond the potential cylinder and MT regions occupy 40–27% of the unit cell volume. Because of the rapid decrease in atomic electron density, for the calculation of the electron density distribution in the unit cell, it was sufficient to consider the contributions of atoms located in given and adjacent cells. The contribution of the other atoms of the chain to the QΩ is below 1%.
Impurity Kinetics in Semiconductors
Published in Victor I. Fistul, Impurities in Semiconductors, 2004
The lattice is compressed (σkk < 0) if the covalent radius of an impurity atom is larger than that of the host atom (Ω > 0). By substituting (7.5.14) into (7.5.13) with K=E/3(l-2v), it is easy to obtain a zero effect of elastic fields on one-dimensional diffusion of dilatation centers in an isotropic medium, which is consistent with the conclusion of [38]. It is interesting that the authors of [39,40] thought it necessary to add a drift term to the expression for impurity atom flow to describe the diffusion.
A highly effective halide anion sponge containing tellurium σ-hole
Published in Molecular Physics, 2023
Junjian Miao, Yubi Gao, Xiankai Jiang, Yi Gao
Optimised geometry and electrostatic potential picture of L are shown in Figure 1. The bond lengths of both Te-F bonds are 1.954 and 1.923 Å, which come close to the sum of covalent radii of F and Te elements (1.970 Å) [9], showing both are regular chemical bonds. One Te-F bond is slightly longer than the other Te-F bond, which may be attributed to the formation of the F-Te–Te chalcogen bond along the longer Te-F bond. The Te–Te distance is 3.196 Å, which is significantly shorter than the twice of van der Waals radius of Te atom (4.120 Å) and longer than that of covalent radius of Te atom (2.740 Å) [9]. A relatively strong interaction may exist between them. Figure 1(b) gives the electrostatic potential distribution of species L, only shown were the maxima larger than 20.0 kcal mol−1 with more chemical significance. It is readily to observe that there are two deeper σ-holes around the right Te atom, one is 53.0 kcal mol−1 and the other is 40.0 kcal mol−1. Other maxima are significantly shallower than them in electrostatic potential, ranging from 20.0 to 28.0 kcal mol−1. Calculated electrostatic potential data further show that the positive surface area amounts to 55%, while the negative counterpart does 45%.
Elucidating the underlying mechanism of relatively high T c value of the orthorhombic MoRuP: a first-principles study
Published in Philosophical Magazine, 2021
S. Baǧcı, H. Y. Uzunok, Israa A. Al-Chalabi, H. M. Tütüncü
Using the calculated structural parameters, the TiNiSi crystal structure for MoRuP is sketched in Figure 1(a), while Figure 1(b) shows coordination numbers of Mo, Ru and P atoms, respectively. As can be seen from Figure 1(b), each Mo is in five-fold coordination formed by four Ru and one P atoms, while each Ru atom coordinates to three Mo and two P atoms. Furthermore, each P atom is in three-fold coordination constituted by one Mo and two Ru atoms. The value of bond length between Mo and P atoms amounts to 2.43 Å, being smaller than the sum of the atomic radius of Mo (1.45 Å) and the covalent radius of P (1.07 Å). Additively, the shortest Ru–P distance (2.31 Å) is also smaller than the sum of the atomic radius of Ru (1.34 Å) and the covalent radius of P (1.07 Å). These observations signal that Mo (Ru) and P atoms are bonded not only by ionic interaction but also significantly covalent. We could have expected this situation because the electronegativities of Mo, Ru and P are considerably close to each other. Furthermore, it is worth to mention that the shortest Mo–Ru bond length (2.85 Å) is slightly longer than the sum of atomic radii for these atoms (2.79 Å). This observation implies a significant Mo–Ru bonding in the investigated compound.
A scale of absolute radii derived from electrophilicity index
Published in Molecular Physics, 2021
Hiteshi Tandon, Tanmoy Chakraborty, Vandana Suhag
An in situ property cannot be considered as an atomic property owing to its downsides, viz. non-transferability and bond dependency. It is an accepted fact that covalent radius is one of the in situ properties. Understandably, it cannot be transferred from one chemical moiety to another. Further, some uncertainties based on the magnitude of covalent radius also appear to exist. The nature of a bond and its extent of covalency seem to control the covalent radius. Accordingly, rather than a free atom property, an in situ property is selected if we choose covalent radius as a size descriptor. It is, therefore, believed that such radius is not suitable to be used as a true descriptor for computing any absolute atomic property [36]. To overcome this impediment, we feel that absolute radius, and not covalent radius, should be chosen as radius-dependent property of a free atom.