Specialist Periodical Reports provide systematic and detailed review coverage of progress in the major areas of chemical research. Written by experts in their specialist fields the series creates a unique service for the active research chemist, supplying regular critical in-depth accounts of progress in particular areas of chemistry. For over 80 years the Royal Society of Chemistry and its predecessor, the Chemical Society, have been publishing reports charting developments in chemistry, which originally took the form of Annual Reports. However, by 1967 the whole spectrum of chemistry could no longer be contained within one volume and the series Specialist Periodical Reports was born. The Annual Reports themselves still existed but were divided into two, and subsequently three, volumes covering Inorganic, Organic and Physical Chemistry. For more general coverage of the highlights in chemistry they remain a 'must'. Since that time the SPR series has altered according to the fluctuating degree of activity in various fields of chemistry. Some titles have remained unchanged, while others have altered their emphasis along with their titles; some have been combined under a new name whereas others have had to be discontinued. The current list of Specialist Periodical Reports can be seen on the inside flap of this volume.
Molecular Structure by Diffraction Methods Volume 2
A Review of the Literature Published between Early 1972 and mid-1973
By G. A. Sim, L. E. SuttonThe Royal Society of Chemistry
Copyright © 1974 The Chemical Society
All rights reserved.
ISBN: 978-0-85186-517-1Contents
Part I Electron Diffraction, 1,
Introduction to Part I By L. E. Sutton, 3,
Structures Determined by Gas-phase Electron Diffraction By B. Beagley, 5,
Introduction to Parts II and III By G. A. Sim, 41,
Part II Neutron Diffraction By J. C. Speakman, 43,
1 Introduction, 45,
2 Hydrogen-bonding, the Water Molecule, and Related Topics, 45,
3 An Asymmetric Bifluoride Ion, 52,
4 Constrained Refinement, 53,
5 Amino-acids, Peptides, and Other Molecules Related to Natural Products, 56,
6 Inorganic Crystals, 61,
Part III X-Ray Diffraction, 65,
Chapter 1 Aromatic and other Analogous Compounds By A. F. Cameron, 67,
Chapter 2 Intermolecular Interactions By A. F. Cameron, 89,
Chapter 3 Saturated Hydrocarbons, Heterocyclic Analogues, and Derivatives By A. F. Cameron, 95,
Chapter 4 Natural Products and Small Biological Molecules By G. A. Sim, 131,
Chapter 5 Globular Proteins By T. L. Blundell, 201,
Chapter 6 Titanium, Zirconium, and Hafnium By M. B. Hursthouse, 221,
Chapter 7 Vanadium, Niobium, and Tantalum By M. B. Hursthouse, 226,
Chapter 8 Chromium, Molybdenum, and Tungsten By Lj. Manojlovic-Muir, 231,
Chapter 9 Manganese, Technetium, and Rhenium By Lj. Manojlovic-Muir, 248,
Chapter 10 Iron, Ruthenium, and Osmium By W. S. McDonald, 261,
Chapter 11 Cobalt, Rhodium, and Iridium By Lj. Manojlovic-Muir and K. W. Muir, 297,
Chapter 12 Nickel, Palladium, and Platinum By K. W. Muir, 331,
Chapter 13 Copper, Silver, and Gold By W. S. McDonald, 359,
Chapter 14 Scandium, Yttrium, Lanthanides, and Actinides By M. B. Hursthouse, 394,
Chapter 16 Boron, Aluminium, Gallium, Indium, and Thallium By M. B. Hursthouse, 429,
Chapter 17 Carbon, Silicon, Germanium, Tin, and Lead By M. B. Hursthouse, 446,
Chapter 18 Nitrogen, Phosphorus, Arsenic, Antimony, and Bismuth By M. B. Hursthouse, 459,
Chapter 19 Oxygen, Sulphur, Selenium, and Tellurium By M. B. Hursthouse, 475,
Chapter 20 Fluorine, Chlorine, Bromine, Iodine, and the Noble Gases By M. B. Hursthouse, 483,
Chapter 21 Lithium, Sodium, Potassium, Rubidium, and Caesium By M. B. Hursthouse, 486,
Chapter 22 Beryllium, Magnesium, Calcium, Strontium, and Barium By M. B. Hursthouse, 492,
Author Index, 497,
CHAPTER 1
Part I
ELECTRON DIFFRACTION
Introduction to Part I : Electron Diffraction
BY L. E. SUTTON
This year, the section on electron diffraction is brief. Our intention and hope was that it should be much longer than it is; but the electron diffraction community is a relatively small one, its members are busy with all sorts of tasks and so, being somewhat exhausted, it was unable to repeat the effort made for Volume 1. We do, however, have a very useful chapter on Results, again contributed by Dr. Brian Beagley. Next year we hope to have a more normal-sized section.
The general remarks about conventions, especially the use of rg and the reporting of error, which were made in the Introduction to Volume 1, still apply.
Structures Determined by Gas-phase Electron Diffraction
BY B. BEAGLEY
1 Introduction
The previous volume (ref. 1, Chapters 2 and 3) reported structure determinations by electron diffraction mostly published before early 1972. The present chapter continues this work, covering the literature to mid-autumn 1973. More precisely, the coverage includes all relevant papers abstracted in Bulletin Signalétique up to and including the October 1973 edition, and all relevant papers found under the keywords ELECTRON DIFFRACTION or MOLECULAR STRUCTURE in Chemical Titles up to and including issue no. 19, 1973. As in ref. 1, parameters quoted are rg values, and error estimates are estimated standard deviations (unless otherwise stated); the Reporter has made subjective estimates where necessary.
The trend reported earlier (ref. 1, Chapter 4) of combining data from rotational spectroscopy with data from electron-diffraction studies, to give increased precision, continues to gain momentum, as many of the papers reported below will confirm. A discussion of the various kinds of structural parameters (rg, rα, rz, etc.) has been given in that chapter, and an extremely useful summary of the way in which they may be obtained and interconverted has been given in Chapter 12 of ref. 2. Other chapters of ref. 2 discuss various aspects of vibrational spectroscopy associated with the calculation of vibrational amplitudes, and review the literature of the subject, including coverage of numerical results. Other important work in this area includes new methods for the calculation of perpendicular amplitudes, which, as well as the better known parallel amplitudes, are required during the interconversions of the structural parameters mentioned above. Both types of amplitude are being used increasingly as fixed parameters in structure determinations, particularly where there are resolution problems. Ref. 2 also includes chapters on the interpretation and precision of gas-phase electron diffraction data, and some experimental results.
Conformational calculations are also being used increasingly in conjunction with electron-diffraction studies, primarily as corroboration of the results, but occasionally as constraints in the refinement (rather as rotational constants are often used). Considerable success in predicting molecular geometry by conformational calculations has been achieved (as comparison with the electron-diffraction results often shows); this is particularly so for molecules which are strained by steric factors or ring formation, i.e. where non-bonded interactions are important. However, conformational calculations are not entirely adequate in their present form, because exact forms of the necessary energy functions are not available.
The traditional wave-mechanically-based methods of rationalizing bond lengths in terms of changes in conjugation and hybridization (ref. 1, p. 64) are still proving of value. Of course, the various kinds of fuller wave-mechanical treatments continue to be applied to predict molecular geometry: e.g. the CNDO and CNDO/2 methods, and the ab initio method, although the latter requires a vast amount of computing time.
Where lone pairs of electrons are present the valence-shell electron-pair repulsion (VSEPR) theory is being increasingly cited to rationalize results. However, in cases where considerable electronegativity differences occur across bonds, there is a growing tendency to invoke electrostatic attraction as well as repulsion to explain their lengths (ref. 1, p. 95). The geometry of molecules having second-row atoms (especially Si, P, and S) adjacent to electron donors continues to be discussed in terms of π-bonding involving d-orbitals
2 Hydrocarbons
A new calculation of zero-point average parameters for ethane gives: for H3C-CH3, r0α = rZ = 1.5323 Å; for D3C-CD3, r0α = rZ = 1.5299 Å; for D3C-CH3, rz = 1.5310 Å. This work employs 'large amplitude theory' to deduce, using electron-diffraction and rotational spectroscopic data, whether D3CCH3 is...
