Table Of ContentSPECTROSCOPY AND STRUCTURE
OF MOLECULAR COMPLEXES
SPECTROSCOPY AND
STRUCTURE OF
MOLECULAR
COMPLEXES
Edited by
1. Yarwood
University 0/ Durham,
Department oj Chemistry,
Science Laboratories,
South Road,
Durham DHl 3LE
England
SPRINGER SCIENCE+BUSINESS MEDIA, LLC 1973
Copyright © 1973 Springer Science+Business Media New York
Originally published by Plenum Publishing Company Ltd in 1973
Softcover reprint of the hardcover 1st edition 1973
All Rights Reserved
No part of this book may be reproduced; stored in a retrieval system,
or transmitted, in any form or by any means, electronic, mechanical,
photocopying, microfilming recording or otherwise, without written
permission from the Publisher
ISBN 978-1-4684-8473-1 ISBN 978-1-4684-8471-7 (eBook)
DOI 10.1007/978-1-4684-8471-7
Library of Congress Catalog Card Number 73-77125
Contributors
D. A. Duddell Chemistry Department, City of Leeds and Carnegie
College, Beckett Park, Leeds LS6 3QS, England.
P. N. Gates Chemistry Department, Royal Holloway College,
Egham, Surrey TW20 OEX, England.
W. B. Person Chemistry Department, University of Florida
Gainesville, Florida 32611, U.S.A.
A. H. Price Edward Davies Chemical Laboratories, Uni
versity College of Wales, Aberystwyth SY23 INE,
Wales.
D. Steele Chemistry Department, Royal Holloway College,
Egham, Surrey TW20 OEX, England.
M. Tamres Chemistry Department, University of Michigan,
Ann Arbor 48104, Michigan, U.S.A.
J. L. Wood Chemistry Department, Imperial College ofScience
and Technology, South Kensington, London SW7
2A Y, England.
J. Yarwood Chemistry Department, University of Durham,
Science Laboratories, South Road, Durham
City DHI 3LE, England.
Preface
This book is intended to be research text aimed principally at
scientists beginning work in the field of molecular complexes. Since,
however, much of the work described is only recently published, it
should be useful also to more experienced workers as a source of the
most recent ideas and interpretations. It should be emphasised that no
attempt has been made to provide an up-to-date review ofthe literature.
Such a review would dearly be impossible in a book ofthis size covering
a wide range of molecular interactions. Rather , the treatment is illustra
tive. We have tried not to ignore the many difficulties (both experi
mental and interpretive) which arise in the process of spectroscopic
study of many (especially weaker) complexes at the same time describ
ing the value of such studies in our attempts to understand how mole
cules interact with one another.
It could be argued that such a text book ought to be written by a
single author and, certainly, this would have had some advantages.
However "production" of a multi-author text, with its inevitable
variations in approach, style and presentation, has the important ad
vantage ofhaving each topic elucidated by an "expert" in that particular
field. It is the editor's task to then ensure that differences of opinion
and style do not destroy the book as an integrated text book. I hope that
I have managed to perform this very difficult task with some degree
of success.
The area of the most controversial difference of opinion among
spectroscopists in the field at the present time should be mentioned
specifically. It will become dear to the reader that the problem of
deciding to what relative extents the various stabilizing forces (for
example, electrostatic polarisation and charge-transfer forces) are
important for any particular dass of complex is a difficult one and is
one which will, no doubt, provoke discussion for a long time to come.
We have tried to indicate how difficult it is, for example, to differ
entiate (either experimentally or theoretically) cases where different
types of forces predominate. This difficulty is severe, even for inter
actions for which the enthalpy change is much greater than RT. For
"weaker" interactions the problem is made worse by the fact that one is
not sure whether one is dealing with a stabilised ground state or with a
system containing only "contacts" (and not "complexes"). Clearly, this
is one ofthe most interesting areas of work, important for all types of
complexes. These problems form achallenge, therefore, to both
chemists and chemical physicists employing many different techniques.
viii PREFACE
We have placed major emphasis in this book on vibrational spec
troscopy although magnetic resonance (and other) techniques are men
tioned where especially appropriate. Only brief mention is made of
electronic spectroscopy since this aspect has been covered fairly com
prehensively in two recent publications (chapter 1, references 1 and 2).
Molecular orbital calculations are rapidly becoming more important
and these have been considered where appropriate. Finally a chapter
has been included on the study of dielectric (microwave) absorption of
molecular complexes and their dipole moments. Such studies have
recently become important in the study of complex lifetimes and for
testing the various complex "models".
We have employed SI units throughout but have retained the
angstrom and wave number (cm-i) for convenience. In order to
minimise confusion during the transition to SI units we have included
in the text the values of severalless familiar parameters (e.g. transition
moments, polarisabilities) in both c.g.s and SI systems. Conversion
factors are included as footnotes to many of the tables and are sum
marised on page xii.
Finally, I should like to thank the contributors for their hard work
and for their support and co-operation during the preparation of this
book. Thanks are also due to Mrs R. Wadge and Mrs D. Armstrong
who have typed (and retyped) various parts of the manuscript, to Miss
L. Hall who helped to eliminate errors from the manuscript, and to Mrs
K. Jones and Mr D. Hartshorn who prepared many of the diagrams.
Grateful thanks are also due to the staff of the Plenum Publishing Co
Ltd. for their helpful co-operation at all times. Individual acknowledge
ments are included, where appropriate, in the separate chapters.
J. Yarwood
Durham City
Sept. 1973
Glossary of Commonly used Symbols
Ai The "true" absolute integrated intensity of the ith
vibrational band (equation 2.5).
Molecular polarisability ; Orbital exponent for Gaussian
basis functions.
Damping constant for rotational diffusion (equation
2.21).
Vibrational-rotation interaction constant; The electronic
polarisabili ty.
Polarisability derivative - ooc/ OQi or ooc/oR (equation
j
5.1)
The "apparent" (observed) absolute integrated intensity
of the ith vibrational band (equation 2.2).
Rotational constant.
Resonance integrals (equations 1.12)
Damping constant for vibrational relaxation (equation
2.17).
Damping constant for "free" rotation in the liquid
phase.
Concentration, usually in mol dm-3•
Velocity of light in a vacuum.
The equilibrium dissociation energy.
The absolute integrated intensity (equations 2.1 and 2.4)
The reducible representation.
E,e Energy
E Electrical field vector.
Vertical electron affinity of an acceptor (equation
1.10).
e Electronic charge
13 Molar extinction coefficient (equation 3.8).
€ Electrical permittivity of vacuum.
13' Real part of the complex permittivity.
13" Imaginary part of the complex permittivity.
13*( = 13' - ie") Complex permittivity (equation 7.24).
130 Limiting permittivity at low frequency.
e Limiting permittivity (debye) at high frequency.
ro
F Force constant (Urey-Bradley); The weight of the "no
bond" or "dative" states.
f Force constant (valence force field).
f Frequency (chapter 7).
Vibrational degeneracy.
Difference between GI' the stabilization energy of the
"dative" state, and Go, the corresponding stabilization
energy of the "no-bond" state.
x GLOSSARY OF COMMONLY USED SYMBOLS
Standard free energy change.
Rotational and vibrational components of the dipole
autocorrelation function.
H Force constant (Urey-Bradley).
AHa Standard enthalpy change.
'"
:K The Hamiltonian operator.
h The Planck constant.
Microscopic viscosity (equation 7.30).
'fJ
() Molecular quadrupole moment (equation 7.43).
1,1 Incident and transmitted (true) radiation intensities.
0
1 Moment of inertia; spectral intensity (general).
I}) Vertical ionisation potential of a donor (equation 1.10).
J Spin-spin coupling constant.
ij
K Force constant (Urey-Bradley)
k Force constant (valence force field).
k The Boltzmann constant.
Ke, Ka, KDA Equilibrium constant.
k Rate coefficient
k(ii) The absorption coefficient as a function of wave
number (equation 2.10).
Vibrational eigenvector matrix elements (equation 1.52).
Wavelength.
The ith band moment (equation 2.10).
Charge-transfer (vibronic) part of the total dipole
moment derivative for a given vibration al mode
equation 1.60).
Reduced mass.
Observed (i.e. measured) molecular dipole moment.
Dipole moment of the ground state ('Y N) of a complex
(equation 1.27).
/I: The dipole moment derivative (0"#/00) or (ojj/oR) for
a given vibrational mode-usually the total dipole
derivative.
"#' The induced dipole moment (equation 2.7).
m Number of moleeules per unit cello
ro'
Dipole moment derivative for the "electrostatic" inter
actions ("general" solvent-solute interaction) (equation
1.72).
Dipole moment derivative due to electrostatic effects
and due to changes in normal coordinates (equa
tion 1.51).
n Number of atoms in a moleeule.
n Real part of the complex refractive index.
N The Av ogadro constant.
Vibrational mode; vibrational frequency.
'JI
ji Vibrational band position in cm-l•
A-H stretching mode (hydrogen-bonded complexes).
'IIa
GLOSSARY OF COMMONLY USED SYMBOLS xi
In-plane bending mode (hydrogen-bonded complexes).
Out-of-plane bending mode (hydrogen-bonded com
plexes).
Intermolecular stretching mode (hydrogen-bonded com
plexes).
Intermolecular bending modes (hydrogen-bonded com
plexes).
PT Tunnelling mode (hydrogen-bonded complexes)
P Molar polarisation (equation 7.1).
pO
Dipole moment of the "free" molecule.
p Calculated dipole moment (for example, from MO
calculations) .
ap/aQ or Total calculated or observed dipole moment derivative
ap/aR from infrared data, or MO calculations (equation
1.46).
apo/aR
Dipole moment derivative for "free" molecule (in
absence of intermolecular forces).
p Electron density at a particular atom.
p Raman dipolarisation ratio
p Density of a particular solution (equation 7.1).
q,Q Normal vibrational coordinates.
qi Charge density on ith atom.
r, R Internuclear distance; Internal coordinate.
R Molar refraction (equation 7.3).
S, SDA, Overlap integrals (for example, equations 1.3, 1.7 and
Sda-, SOl 1.17).
S Symmetry coordinate.
ßSB Standard entropy change.
(f' Pauling covalent bond character.
To, T Apparent (observed) incident and transmitted radiation
intensities.
Dielectric relaxation time (equation 7.26).
T
U Interaction energy.
v Intermolecular potential (equation 1.6).
v Vibrational quantum number.
v Specific volume.
4>(t) Transition dipole time autocorrelation function (equa
tion 2.14).
4> Wave function of individual atomic or molecular
orbital.
Slater-type or Gaussian basis function.
Unperturbed or modified donor or acceptor wave
function (whoie molecule) (equation 1.2).
Ground or excited electronic wavefunction of complex
(whoie moleeule) (equation l.l).
'Y0 Vibrational wave function.
w Angular frequency (27Tf).
Z Effective nuclear charge (equation 5.3).
