Date: Thu, 14 Oct 1999 13:30:35 -0500 (CDT) Reply-To: CH412F99-L@po.missouri.edu Sender: owner-CH412F99-L@po.missouri.edu Precedence: bulk From: firstname.lastname@example.org To: CH412F99-L@po.missouri.edu Subject: POTW-Club Iiris MIME-Version: 1.0 X-Authentication-Warning: sp2n21.missouri.edu: c762643 owned process doing -bs X-Sender: email@example.com Title: "Isolation and Structure of the OCNCO+ Ion" Authors: Bernhardi, I., Drews, T., Seppelt, K. Reference: Angew. Chem. Int. Ed. 1999, 38(15), 2232-2233. Goals and objectives: The goal was to isolate in substance the ion O=C=N=C=O+ and to establish its structure by experimental and computational methods. Objectives were to generate the ion in the form of a salt by Cl- or F- abstraction with strong Lewis acids AsF5 and SbF5 and to determine its structure and vibrational data experimentally and thereafter also theoretically, the main emphasis being on the central nitrogen atom being the center of the bending of the ion. Methods: Experimental values were obtained by Raman spectroscopy and in part by cristallography. Solution and refinement of the structure was done with the shelx programs. Theoretical values were determined by basis set 6-31G(d,p), in Hartree-Fock (HF) and Moller-Plesset (MP2) approximations and in coupled cluster calculation (CCD) with double substitution of the Hartree-Fock determinant. Discussion: Both, data from experiments and calculations showed bent structure for OCNCO+ with the angle of 130.7 degrees and in the range of 133-138 degrees correspondingly. The calculation of the partial charges according to Mullikan at the MP2 level for the central nitrogen atom gave the value of -0.36. According to the analysis of the natural bond orbitals this was a result of the two nonbonding electron pairs at nitrogen with an occupation of 1.6 and 1.5e-, the former had 23% s character and was responsible for the bending. Regardless of the basis set and method of approximation of the electron correlation, the change in energy between linear and bent arrangements was only a few kJ/mol. Finally similar studies have been made on C3O2 and N5+ ion, which also have been found to be bent at the central atoms according to minimum energy. I liked the paper because it was short and it had a goal quite easy to stay focused at and it enabled to compare three approximations plus the experimental values for the ion. (Although none of them seems to have much regularity in the size or direction of the error compared to the experiment. HF seems to be good for calculating bond lengths and CCD for angles.) It was also quite astonishing to read about the details of synthesis and stabilizing the product. I did not understand what was meant by the term 'potential of the deformation mode' and also the meaning of the vibrational data in Table 1 in terms of the ion. (This is the topic in our current lectures, I believe.) Also the nature of the CCD approximation is not clear to me.