Isoelectronic systems

Very Short Metal-Actinide Bonds NUIr and Isoelectronic Systems. 

A similar observation was made with the Isoelectronic system... 

So far comparisons of isoelectronic systems of types A, B and C are restricted to few examples, becau especially in type B the kinetic instability of the neutral radicals (SEM) becomes so pronounced that the level RED very often caimot be generated. This low persistency of B may be due to the fact that the odd electron is no longer distributed symmetrically over the molecule. In some cases dimeric products have been identified There are, however, tailor made radicals Rsem. -g-55, which exist as highly coloured, destillable compounds Nonetheless, from the... 

Carbon has one more electron than boron, so the C—H moiety is isoelectronic with the B—H or BH2 moieties. Note that an isoelectronic relationship also exists between C and BH or B. In a formal sense it should be possible to replace a boron atom in a borune with a carbon atom (with an increase of one in positive charge) and retain an isoelectronic system. The best-studied system. C,B DH,2. is isoelectronic with [BI2H, ]3 and may be synthesized readily from decaborane and alkynes and dieihyl sulfide as solvent. 

Here we revisit the VB resonance model in formamide by taking all six resonance structures into account. Such a study allows us to compare the individual contributions from resonance structures 1-6 to the resonance effect in formamide. For comparison, the isoelectronic systems vinylamine and formamidine are also investigated to gain insights into the trends of resonance stabilization. A 6-31G(d) basis set is employed in the calculations, and the orbitals in the VB functions are self-consistently determined for each resonance structure, but restricted to be atomic orbitals. The structural weights of the six resonance structures are listed in Table 2. 

In the following, three comparisons of isoelectronic systems are presented. The first consists of a comparison of the isoelectronic ligands ethyne (HCCH) and phosphaethyne (HCP) for different transition metals and in different states of aggregation. The second compares cyclopenta-dienyl and pentadienyl complexes, while the third relates complexes of benzene and hexaphosphabenzene. Although narrow in terms of breadth of compounds, we hope there is sufficient detail in these systems to convey some appreciation of the systematic variation possible with isoelectronic substitution. 

For these reasons, we present a brief overview of how heteroatoms perturb cluster bonding in strictly isoelectronic systems as well as a com-... 

M. Alfaz Uddin, A.K. Basak, B.C. Saha, Electron impact single ionization cross-sections of helium isoelectronic systems, Int. J. Quantum Chem. 100 (2004) 184. 

The more or less isoelectronic systems CaW04 and CaMo04 show broadband emission with maxima at 410 nm and 530 nm, respectively. Whereas CaW04 is very efficient at room temperature, CaMo04 is partly quenched (96). 

Consequently, isoelectronic substitution may be regarded as a symmetry principle (subject to our broader concept of symmetry given previously) which, when applied to a series of isoelectronic species, allows a systematic treatment of corresponding physical properties of isoelectronic molecules on the basis of algebraic arguments. Thus structural insights into physical phenomena are given not only for one molecular class, but for the whole family of isoelectronic systems. 

Last but not least we mention very recent work on infrared absorption intensities for the isoelectronic systems NHj, and and a... 

The type of vibronic coupling effects displayed in Fig. 1 is unusually weak for conically intersecting PE surfaces. A more generic scenario emerges when we consider the isoelectronic system which is also characterized by an ground and first excited electronic state. . The equilibrium... 

Oxygen has one 2s, three 2p AOs, and six valence electrons. Sulfur has one 3s, three 4p AOs, and six valence electrons. Oxygen and sulfur are isoelectronic. This explains the similarity of the shapes of HOH and HSH (both molecules are bent). By contrast, we say that the very similarity hides a fundamental difference in bonding mechanism due to the fact that S is more electropositive than O. As a result, HOH lies toward the T-delocalization limit, while HSH lies toward the I-delocalization limit. We expect that, in two other isoelectronic systems, the difference in bonding mechanisms will cause them to have radically different shapes. 

Koutselos, A. D. Mason, E. A. (1986). Correlation and prediction of dispersion coefficients for isoelectronic systems. J. Chem. Phys., 85,2154—2160. 

Using the combination of main-frame CDC 6400 and Tektronix computations, a number of phenomena were studied with electron density functions, and especially with projection plots. Particularly useful were plots of difference functions in which the electron distributions of isoelectronic systems were compared directly. In such applications, we noted that a corresponding difference plot of the electron density itself in any given plane is not meaningful since the number of electrons may change that is, from one compound to the next the electron density can shift from one plane to elsewhere. In the projection plot the total number of electrons remains the same for both species and the integral of an isoelectronic difference function must sum to zero. Some examples of the kinds of problems studied are the vm transition of formaldehyde, substituent effects in substituted benzenes, and polarization... 

---