Carbon, isoelectronic series

Such a peculiarity has also been observed in many other compounds with metal-carbon bonds, especially cobalt-carbon. As part of a study (using the above-mentioned extended CNDO method) of the AM(CO)3 isoelectronic series (AM from 772-C2H4Ni to rj6-C6H6Cr) it was shown that, in the t 3-C3HsCo derivative, the allyl group was linked to cobalt by means of the two C(H2) carbons and not predominantly by the C(H) carbon atom, despite the fact that Co—C(H2) = 2.10 A as compared with Co—C(H) = 1.98 A (55). 

Fig. 1 The ground state of the carbon-like isoelectronic series, calculated in the large-Z approximation. The energies divided by Z2 are shown as functions of Z. Experimental values are indicates by dots, while the energies calculated from (51) are shown as curves. The lower (solid) curve, which approaches the experimental values with increasing Z, has been corrected for relativistic effects. The upper (dashed) curve is uncorrected...

Two theoretical analyses of the electronic structures of carbonates and related species have been published. - Russian workers have reported the results of MO calculations of the isoelectronic series of oxy-anions BO , CO ", and NOj. The derived data, when compared to the results of Jf-ray spectral investigations, accurately describe the principal characteristics of the spectra. Perkins has studied the electronic structure of inter alia H2CS3, CS ", and CS4 using a self-consistent MO method. Perhaps the most interesting conclusion to come from the investigations is the fact that the molecule H2CS3 is shown to be quite stable. 

Figure 19 Relations of infrared frequencies of the asymmetric X = Y = Z vibrations to nuclear charges of the terminal carbon atoms of isoelectronic series.

Pyykko, R, andRuneberg, N. (1991). Ab initio studies of bonding trends. Rart 9. The dicyanamide-carbon suboxide-dicyanoether-cyanogen azide isoelectronic series A=B=0=Et=E, J. Mol. Struct. (Theochem) 234,279. 

Ethyne, ethene and ethane contain 10. 12 and 14 valence electrons, respectively. They are isoelectronic with N2, 02 and F., respectively. Along both series of molecules the central link becomes progressively weaker and the bond lengths increase. The carbon-carbon bond length increases from 121 pm in ethyne to 133 pm in ethene and to 155 pm in ethane. The corresponding bond enthalpy terms are 837, 612 and 348 kJ mol Data for the diatomic molecules is contained in the text. Discuss these data in terms of the VSEPR and MO treatments of the molecules. 

The cyanide ion is isoelectronic with CO, and binds to platinum and other metal ions by a donation of a pair of electrons in an sp hybrid orbital on the carbon atom, along with a complementary jt back-donation from filled metal orbitals to empty jt orbitals on CN. The anion is a poorer it acceptor than CO, but stable complexes are formed with platinum(II) and platinum(IV), and the ligand is high in the spectrochemical series. 

Our group has devoted two articles for the study of systems where the chiral subunits are bonded to a boron or to a metallic atom (Scheme 3.28). In both cases, the weakness of the bonds formed can be easily broken. In the first case, a series of bisdiphenylborates and the effect of the fluoro substitution on the relative stability of the homo vs. heterochiral complexes have been studied by means of DFT calculations (B3LYP/6-31G ) [29]. In addition, the corresponding isoelectronic structures, in which the boron has been substituted by a carbon or a positively charged nitrogen, have been considered. In all the cases, the homo and heterochiral complexes present D2 and S4 symmetries, respectively. 

K. D. Berlin u. D. M. Hellwege, Carbon-Phosphorus Heterocycles, Topics in Phosphorus Chemistry 6, 1 (1969). H. Schmidbaur, Isoelectronic Species in Organophosphorus, Organosilicon and Organoaluminium Series, Advances in Organometallic Chemistry 9, 260 (1970). 

A separate series of closo-carboranes, isoelectronic with the BnH2 dianions and the neutral QB 2H compounds, consists of the monocarbon anions CB iH (Table 5-3). The preparative routes to these species vary widely, but a commonly used method for incorporating a single carbon atom into a borane cage involves the conversion of cyanoboranes to amino derivatives the cyano carbon atom satisfies its valence requirements via absorption into the cluster framework. 

An interesting series is provided by (53)-(55). In (53), replacement of the Os(CO)4 fragments with isolobal CH2 and Sn with isoelectronic carbon yields spiropentane (54). Replacement of two CH2 units in spiropentane with isolobal... 

The closo-carboranes of the CrtBn 2H series are isoelectronic with corresponding [B H ]2- ions and have the same closed polyhedral structures with one hydrogen atom bonded to each carbon and boron. 

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