Electronic and Vibronic Spectra of Transition Metal Complexes I

213 Pages·1994·3.819 MB·English

by  G. Blasse (auth.), H. Yersin (eds.)

7 1 scipoT ni tnerruC yrtsimehC
Electronic and Vibronic
Spectra of Transition
Metal Complexes I
Editor: H. Yersin
With contributions by
G. Blasse, A. Ceulemans, M. ,3( Colombo,
H. U. Gtidel, A. Hauser, .P E. Hoggard,
C. Reber, H.-H. Schmidtke, D. Wexler,
J. I. Zink
htiW 67 serugiF dna 42 selbaT
galreV-regnirpS
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Guest Editor
Prof. .rD Hartmut Yersin
Institut for Physikalische dnu
Theoretische Chemie
ti~tisrevinU Regensburg
eSfartsstiitisrevinU 13
93053 Regensburg, FRG
Editorial Board
.forP ,rD Jack D. Dunitz Laboratorium fur Chemie Organische
Hochschule Eidgentissischen der
elfartsstiitisrevinU CH-8006 6/8, hcirUZ
.forP .rD Klaus Hafner der Chemie Organische Institut fiir ,HT
eBartsnesreteP ,51 Darmstadt, 64287 GRF
.forP .rD Sho Ito Faculty of Sciences, Pharmaceutical
Bunri Tokushima ,ytisrevinU
Japan 770, Tokushima
.forP .rD Jean-Marie Lehn Institut ed Universit6 Chimie, ed Strasbourg,
rue Blaise Pascal, 1 .B .P 296/R8, Z F-67008 Strasbourg-Cedex
.forP .rD Kenneth N. Raymond Department of University Chemistry, of California,
,yelekreB AC 94720, ASU
.forP .rD Charles (41 Rees Professor Hofmann of Department Chemistry, Organic
of College Imperial Chemistry, of Science dna Technology,
London Kensington, South 7WS ,YA2 England
.forP .rD Joachim Thiem Institut fur Hamburg, Universitiit Chemie, Organische
Martin-Luther-King-Platz ,6 Hamburg, 20146 GRF
.forP .rD Fritz VOgtle der Biochemie und Chemie Organische fiir Institut ,t~itisrevinU
e3lartS-kgamoD-drahreG ,1 12135 Bonn, GRF
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Preface
In recent years there has been a considerable amount of research on
transition metal complexes due to the large number of potential or
already realized technical applications such as solar energy
conversion throughp hoto-redox processes, optical information and
storage systems, photolithographic processes, etc. Moreover, metal
complexes are also of considerable importance in biology and
medicine. Most of these applications are directly related to the
electronic and vibronic properties of the ground and lowest excited
states.
There is substantial practical and also scientific interest in
developing a better understanding of the important electronic and
vibronic structures of transition metal complexes than is presently
available. Such knowledge is required for a more successful tailoring
of complexes with specific, user-defined properties (e,g. extinction
coefficients, emission wavelengths, lifetimes and quantum yields,
spatial charge redistributions in excited states compared to ground
states, photo-redox properties, etc.). For example, this appears
feasible for transition metal complexes with organic ligands, for
which the lowest excited electronic states can often be chemically
tuned to possess mainly metal-centered (MC), metal-to-ligand-
charge-transfer (MLCT), ligand-to-metal-charge-transfer (LMCT),
ligand-to-ligand-charge-transfer (LL'CT), or ligand-centered (LC)
character. Such controllable chemical variations can thereby lead to
complexes with quite different properties.
Spectroscopic methods can yield the required understanding of
the complexes. Especially optiscpaelc troscopy provides very detailed
information about electronic and vibronic structures, in particular,
when highly resolved spectra are available. However, without the
development of suitable models, which are usually based on
perturbation theory, group theory, and recently also on ab-initio
calculations, a thorough understanding of the complexes is very
difficult to achieve. In this volume and in a subsequent one some
leading researchers will show that such a detailed description of
transition metal complexes can indeed be successfully achieved.
This volume provides a survey of modern developments for the
description of electronic and vibronic structures of transition metal
complexes. Since this research area is investigated by both chemists
and physicists, who work theoretically as well as experimentally, it
is clear that building a bridge between these groups is difficult.
Nevertheless, it would be highly desirable to accomplish this aim at
least partially. Thus, in a theoretical contribution A. Ceulemans
discusses, in a shell-theoretical view, the still fascinating properties
of the low-lying electronic states of Cr ~ complexes applying a
second quantization treatment. .P Hoggard applies the angular
overlap model to interpret spectra of Cr +3 complexes. H.-H.
Schmidtke discusses the vibronic Herzberg-Teller and Franck-
Condon coupling schemes and their importance to the vibrational
satellite structures of different types of electronic transitions in
various metal complexes. D. Wexler, J. I. Zink, and Ch. Reber
examineef fects of vibrational coordinate coupling on optical spectra.
In a mainly experimentally based description G. Blasse presents a
summary of vibronic properties found for ions doped into various
solid matrices, And M. G. Colombo, A. Hauser and H. U. GiJdel
investigate, in a spectroscopically based contribution, the interplay
of CL3 and 3MLCT states with respect to optical properties of Rh +~
and Ir~+complexes. I would like ttoh ank the authors for their efforts.
• In this field, the late Professor Dr. Giinter Gliemann was deeply
involved. He became known to the scientific community through a
large number of important publications and his and H. L. Schl/ifer's
excellent textbook "Basic Principles of Ligand Field Theory", which
has appeared in German, English, and even in Chinese. As my "Dok-
torvater" GiJnter Gliemann initiated my interest in transition metal
complexes. Subsequently, we enjoyed very fruitful scientific
cooperation, which led to numerous common publications, in
particular, about chromium(III) complexes and
tetracyanoplatinates(II). Professor G/inter Giiemann died too early,
at the end of 1990 at the age of 58. This volume is dedicated to him.
Regensburg, June 1994 Hartmut Yersin
Table of Contents
Vibrational Structure in the Luminescence Spectra
of Ions in Solids
G. Blasse .........................................
The Doublet States in Chromium (III) Complexes.
A Shell-Theoretic View
A. Ceulemans ..................................... 27
Vibrational Progressions in Electronic Spectra
of Complex Compounds Indicating Strong
Vibronic Coupling
H.-H. Schmidtke ................................... 69
Sharp-Line Electronic Spectra and Metai-Ligand
Geometry
.P E. Hoggard ..................................... 311
Competition Between Ligand Centered and Charge
Transfer Lowest Excited States in bis Cyclometalated
Rh +3 and Ir ÷3 Complexes
M. G. Colombo, A. Hauser, H. U. Gtidel ................. 143
Spectroscopic Manifestations of Potential Surface
Coupling Along Normal Coordinates in Transition
Metal Complexes
D. Wexler, J. I. Zink, C. Reber ........................ 173
Author Index Volumes 151 - 171 ...................... 205
Vibrational Structure in the Luminescence Spectra
of Ions in Solids
G. Blasse
Debye Research Institute, Utrecht University, P. O. Box 80.000, 3508 TA Utrecht, The Netherlands
Table of Contents
1 Introduction ................................. 2
2 Theoretical Models ............................. 3
3 Luminescence of Ions with s z Configuration .............. 5
3.1 General ................................. 5
3.2 Overview of Results .......................... 6
3.3 Interpretation of Results ....................... 9
4 Luminescence of Rare Earth Ions .................... 14
5 Luminescence of Transition metal Ions ................. 17
6 Concluding Remarks.
........................... 23
7 References .................................. 24
The luminescence spectra of metal ions in solids show often vibrational structure at low temperature.
This structure yields direct information on the interaction between the metal ion and the lattice. This
interaction is often strongly dependent on the nature of the surroundings of the emitting ion. This
paper reviews this important aspect using illustrative examples out of the recent literature. The types
of ions to be discussed are the following: ions with dl°s 2 configuration, rare earth ions and transition
metal ions.
Topics in Curr~n! Chemistry, Vol. ! 17
© Springer-Verlag Berlin Heidelberg 1994
T
I Introduction
The optical spectra of ions in solids have been studied intensively, in absorption
as well as in emission. A good and recent survey of the theory illustrated by
many examples has been given by Henderson and Imbusch [1].
These spectra exist, characteristically, of bands which may be very broad or
very narrow, and which may show vibrational structure. Examples of very
broad bands without any structure at all, not even at very low temperatures, are
found in the spectra of the F centre (an electron trapped at a halide vacancy in
the alkali halides), and the tungstate (WO 2-) group in CaWO4. The spectral
width may approach a value of 1 eV, and the Stokes shift of the emission band
may be 2 eV.
The intraconfigurational transitions of the rare earth ions (4)" )n are examples
of ions which, even in solids, show sharp lines in their spectra. The width is of the
order of wavenumbers and is at 4.2 K usually determined by inhomogeneous
broadening. These lines are true zero-phonon lines. The vibronic transitions
belonging to these lines are weak and often overlooked.
In between these two extremes there are ions which show spectra with bands,
the width of which ranges between a few hundred and a few thousand wave-
numbers. At low temperature these bands show often vibrational structure.
These spectra are of a considerable interest, since they reveal in a direct way
information on the interaction between the ion and the host lattice.
If this interaction is very weak, the zero-phonon line dominates in the
spectrum (like in the rare earth ions). If the interaction is very strong, the spectra
contain only broad bands from which not much information can be obtained.
These situations are known as the weak- and strong-coupling case, respectively.
Vibrational structure of any importance is usually only observed for the
intermediate-coupling case. This is, for example, encountered for transition
metal ions and uranate complexes.
It is not so simple that certain ions show no structure in their spectra,
whereas other do. The nature of the host lattice plays also an important role.
This is illustrated in an impressive way by the Bi 3 + (6s )1 ion. Depending on the host
lattice its spectra may show narrow bands with vibrational structure or very
broad and structureless bands, and the Stokes shift of the emission may vary
from 1000 to 20000cm -~ [2].
By dealing with metal ions with different configurations this paper will
illustrate the dependence of the spectral band shape on the nature of the metal
ion. This, however, is a well-known and reasonably well understood pheno-
menon, By dealing with a given ion in different host lattices we will illustrate
how the spectral band width depends on the nature of the host lattice. This
dependence is of a larger complexity.
The structure of this review is as follows. In Chap. 2 we will survey shortly
and nonmathematically the theories in use to explain spectral band width and
structure. In subsequent chapters we will deal with a couple of different metal