Quasilinear structure

The microwave spectra of gaseous CsOH have been studied in a high temperature spectrometer by Kuczkowski et al. (9) and Lide et al. (10). The spectroscopic data were more consistent with patterns expected from a linear molecule, although a "quasilinear" structure could not be completely eliminated. Acquista et al. ( ) observed the infrared spectra of CsOH and... 

Most of the (W,W)-carbenes are predicted to be linear and this substitution pattern results in a polarized two-electron three-center n system. Here also, the C—W bonds have some multiple bond character these (W,W)-carbenes are best described by the superposition of two ylidic structures featuring a positive charge at the carbene carbon atom. The most studied carbenes of this type are the transient dicarbomethoxycarbenes and the masked diborylcarbenes. Since no carbenes of the latter type have yet been isolated, they are not included in this chapter. Lastly, the quasilinear (D,W)-carbenes combine both types of electronic interaction. The D substituent lone pair interacts with the py orbital, while the W substituent vacant orbital interacts with the px orbital. These two interactions result in a polarized allene-type system with DC and CW multiple bonds. Good examples of this type of carbene are given by the transient halogenocarboethoxycarbenes and by the stable (phosphino)(silyl)- and (phosphino)(phosphonio)carbenes (see below). 

See, e.g., M. Hargittai, I. Hargittai, Linear, bent, and quasilinear molecules. In Structures and Conformations of Non-rigid Molecules, J. Laane, M. Dakkouri, B. van der Veken, and H. Oberhammer, eds., NATO ASI Series C. Mathematical and Physical Sciences, Vol. 410, pp. 465-489, Kluwer Academic Publishers, Dordrecht, Boston, London, 1993. 

Z. Varga, G. Lanza, C. Minichino, M. Hargittai, Quasilinear Molecule par Excellence, SrCl2 Structure from High-Temperature Gas-Phase Electron Diffraction and Quantum Chemical Calculations Computed Structures of SrCl2-Argon Complexes. Chem. Eur J. 2006, 12, 8345-8357. 

Difficulties arise in the band structure treatment for quasilinear periodic chains because the scalar dipole interaction potential is neither periodic nor bounded. These difficulties are overcome in the approach presented in [115] by using the time-dependent vector potential, A, instead of the scalar potential. In that formulation the momentum operator p is replaced by tt =p + (e/c A while the corresponding quasi-momentum Ic becomes k = lc + (e/c)A. Then, a proper treatment of the time-dependence of k, leads to the time-dependent self-consistent field Hartree-Fock (TDHF) equation [115] ... 

Table 11.2 Structures of the monomeric group 2 metal dihalides, MX2. The term quasilinear is explained in the text.

Some recent studies of free radicals are given in Table XL Here, we give the ground electronic state, pertinent comments, and structural parameters for some of the radicals. The reader is directed to the references of the table for a more detailed discussion of the experimental methods and analysis of the rotational spectrum. A number of interesting radicals are given in the table, such as cyclic C3 H, C O, C3 H, C H, and HC3 O. Also, we note that the shorter OH distance in MgOH as compared to CaOH and other alkaline earth hydroxide radicals indicates the quasilinear nature of this molecule. 

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