Electronic and Vibronic Spectra of Transition Metal Complexes II

265 Pages·1997·12.956 MB·English

by  H. Yersin

Electronic dna
Vibronic Spectra
of Transition
Metal Complexes II
Volume Editor: H. Yersin
With contributions by
.T Azumi, H. .B Gray, .W Humbs,
H. Miki, .V M. Miskowski, H. H. Patterson,
.T Sch6nherr, . Strasser, H. Yersin
Springer
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Volume Editor
Prof. Hartmut Yersin
Institut ftir Physikalische
und Theoretische Chemie
Universit~it Regensburg
Universit/itsstr. 13
D-93053 Regensburg, Germany
Editorial Board
Prof. Dr. Armin de Meijere Prof. K. N. Houk
Institut fiir Organische Chemie Department of Chemistry and Biochemistry
der Georg-August-Universit/it University of California
Tammannstrat~e 2 504 Higard eunevA
77073-D G6ttingen, Germany soL ,selegnA AC ,9851-42009 ASU
E-mail: [email protected] E-mail: [email protected]
Prof. Jean-Marie Lehn Prof. Steven .V Ley
Institut de Chimie University Chemical Laboratory
Universitd de Strasbourg dleifsneL Road
1 rue Blaise Pascal, .B .P Z 8R/692 2BC WE1 Cambridge, Great Britain
80076-F Strasbourg Cedex, France E-mail: svll ku.ca.mac.suc@00O
E-mail: [email protected]
Prof. Dr. Joachim Thiem Prof. Barry M. Trost
Institut ftir Organische Chemie Department of Chemistry
ti~tisrevinU Hamburg Stanford University
Martin-Luther-King-Platz 6 Stanford, AC ,0805-50349 ASU
64102-D Hamburg, Germany E-mail: [email protected]
E-mail: [email protected]
Prof. Dr. Fritz V6gtle Prof. Hisashi Yamamoto
Institut ftir Organische Chemie School of Engineering
und Biochemie der ti/tisrevinU Nagoya University
Gerhard-Domagk-Strafle 1 10-464 Chikusa, ,ayogaN Japan
12135-D Bonn, Germany E-mail: pj.ca.u-ayogan.cc.ccun@a88954j
:liam-E eimehcnS@eltgeov l.chemie.uni-bonn.de
ecaferP
The properties of transition metal compounds have fascinated physicists and
chemists for a long time. These compounds have an enormous potential for
future applications of solar energy conversion, information storage systems,
chemical or biochemical sensors, lowdimensional semiconductors, supramole-
cular systems, chemical synthesis, etc. Most of these applications are related to
the characteristics of the low-lying electronic and vibronic states. In the present
volume as well as in its companion volume 1 leading researchers - physicists and
chemists - present theoretical as well as experimental approaches towards a
deeper understanding of these compounds. Both volumes build a bridge between
physicists and chemists by showing how controlled chemical variations can be
applied to tune physical properties in a defined way and vice versa, "yb demon-
strating how detailed spectroscopical and quantum mechanical investigations
allow the chemical characterization of ground and excited states.
In particular in this volume, an introduction into properties of spin sublevels
of metal centered (MC), ligand centered (LC) and metal-to-ligand-charge-trans-
fer (MLCT) states is given by .T Azumi and H. Miki. Further, a modern ligand field
theory based on the Angular Overlap Model is presented by .T Sch6nherr. In the
contribution by .V M. Miskowski and H. .B Gray it is shown how to characterize
bi-nuclear Os(III) complexes from polarized single-crystal electronic spectra
and magnetic susceptibility measurements. In experimental case studies H.H.
Patterson discusses selected d-electron systems in a variety of environments such
as neat and mixed crystals as well as on surfaces. On the basis of highly
frequency-resolved and time-resolved spectra, H. Yersin, .W Humbs, and .J Stras-
ser investigate and characterize a series of metal bipyridine compounds. Con-
sequences of adjustable metal d-orbital involvement, which leads to variable
spin-orbit coupling, zero-field splittings, and spin-lattice relaxation processes in
the time domain, are treated. Further, several specific effects such as magnetic-
field induced tunability of Herzberg-Teller to Franck-Condon activity,
chromophore-matrix interactions, and spectroscopic fingerprints of localiza-
tion/delocalization processes in the excited states are also studied.
A series of compounds is investigated in detail, for example Rh(phen)3 ,+3 cis-
Rh(CN)z(phen)2 ,+ Pt(bpy)2 ,+2 Ru(bpy)3 +2 , Ru(i-biq)2 (bpy) +z , Os(bpy)3 +z ,
1 ehT first ,emulov scipoT ni Current Chemistry 171 Electronic and Vibronic Spectra of Tran-
sitions Metal Complexes I de( .H ,)nisreY appeared ni .4991
VIII ecaferP
Cr(bpy)3 ,÷3 Cr(urea)6 ,÷3 Cr(acac)3, Cr(III) and Cr(IV) doped oxide lattices,
6FnM ,-a 6rBeR ,-2 61CsO ,-2 bi-nuclear Os(III) complexes, Mo(II) chloride
clusters, and two-dimensional layers of Au(CN)2- complexes.
I hope that the contributions in the present volume will not only stimulate
the interaction between the different fields of basic research in chemistry and
physics but will also open pathways for new applications.
Regensburg, May 1997 Hartmut Yersin
Contents
Spectroscopy of the Spin Sublevels of Transition Metal Complexes
.T Azumi, H. Miki ...............................
Magnetic and Spectroscopic Properties of 0s2(02CR)4C12 .
Evidence for a 3(6*rr*) Ground State
.V M. Miskowski, H. .B Gray .......................... 14
Luminescence and Absorption Studies of Transition Metal Ions
in Host Crystals, Pure Crystals and Surface Environments
H. H. Patterson ................................ 59
Angular Overlap Model Applied to Transition Metal Complexes
and dtC-Ions in Oxide Host Lattices
.T Sch6nherr .................................. 87
Characterization of Excited Electronic and Vibronic States
of Platinum Metal Compounds with Chelate Ligands
by Highly Frequency-Resolved and Time-Resolved Spectra
H. Yersin, .W Humbs, . Strasser ....................... 351
Author Index Volumes 151-191 ....................... 152
Contents of Volume 171
cinortcelE dna Vibronic artcepS
of Transition Metal sexelpmoC I
Volume Editor: H. Yersin
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
Vibrational Progressions in Electronic Spectra
of Complex Compounds Indicating Strong Vibronic Coupling
H.-H. Schmidtke
Sharp-Line Electronic Spectra and Metal-Ligand Geometry
.P .E Hoggard
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 Gfidel
Spectroscopic Manifestations of Potential Surface Coupling
Along Normal Coordinates in Transition Metal Complexes
.D Wexler, .J .I Zink, .C Reber
ypocsortcepS of the Spin slevelbuS of noitisnarT
Metal sexelpmoC
Tohru Azumi* and Hisayuki Miki
Department of Chemistry, Faculty of Science, Tohoku University, Sendai, Japan
* e-mail: azumi @ orgphys, chem. tohoku, ac.jp
The theoretical and experimental aspects of the spin sublevels of transition metal complexes
are briefly reviewed. First, the complexes with organic ligands are discussed. For metal-local-
ized dd states and metal-to-ligand charge transfer drr* states, the splitting among spin sub-
levels is mainly governed by the spin-orbit coupling, and the magnitude of the splitting is of
the order of 10-100 cm .x- For ligand-localized triplet *-nrr states, the splitting is mainly
governed by the spin-spin coupling, and the magnitude of the splitting is mainly governed by
the spin-spin coupling and the magnitude of the splitting is of the order of .O 1 cm .~- Theoret-
ical evaluation of the radiative rate constants for the individual spin sublevels is discussed,
and is compared with experimental data. Finally, the spin sublevels of metal clusters are
discussed.
Introduction ............................... 2
2 Experimental Methods to Obtain Energies and Other Spectroscopic
Properties of the Spin Sublevels .................... 2
2.1 Direct Spectroscopic Observation ................... 2
2.2 Microwave Resonance in Zero Magnetic Field ............ 3
2.3 ESR Spectroscopy ............................ 4
2.4 Temperature Dependence of Lifetime and Intensity
of Luminescence ............. " ............... 4
3 Theory and Experimental Results ................... 5
3.1 Spin Sublevels of dd States ....................... 5
3.1.1 Spin Sublevels of a System of a Single d Electron
in a Cubic Field ............................. 6
3.1.2 Spin Sublevels of a System of Six d Electrons ............. 14
3.2 Spin Sublevels of the Ligand-Localized 3rrw* State .......... 20
3.2.1 Spin-Spin Interaction .......................... 21
3.2.2 Spin-Orbit Coupling .......................... 23
3.2.3 Experimental Results on Some Ligand-Localized 3rrrr* States
and Their Interpretation ........................ 25
3.3 Spin Sublevels of a Metal-to-Ligand Charge-Transfer
Triplet State ............................... 31
scipoT ni Current ,yrtsimehC .loV 191
(cid:14)9 galreVregnirpS Berlin Heidelberg 7991
2 .T imuzA and .H ikiM
4.3 Spin Sublevels of the Hexanuclear Molybdenum (II)
Chloride Cluster ............................. 43
References ................................ 93
1
Introduction
When an eigenstate of the electronic Hamiltonian of a molecular system is split
into several states by a perturbation involving spin, the set of split levels are cal-
led spin sublevels. In this paper we focus attention on spin sublevels in the zero
external magnetic field. Thus, the splitting of a level by the Zeeman effect is not
considered.
For atoms, spin sublevels have been well studied. One of the typical examples is
the splitting of sodium D line, the emission from the p3 state to the s2 state. In the
p3 state, the orbital part is three-fold degenerate and the spin part si doubly degen-
erate, and thus the total degeneracy is six. This six-fold degeneracy is partially lif-
ted by spin-orbit interaction. The state is split into two sublevels one correspon-
ding to j = 3/2 and the other corresponding to j = 1/2. This type of the splitting of
atomic levels is well discussed in standard textbooks 1 of atomic spectroscopy
and of quantum chemistry, and thus there is nothing to discuss here any further.
The spin sublevels for organic molecules in their triplet excited states have
been well studied by RSE and ODMR (gptical detection of magnetic resonance)
spectroscopy.
However, for metal complexes, research on spin sublevels is rather scarce. In this
paper we try to review the spectroscopy of the spin sublevels for metal complexes.
2
Experimental Methods to Obtain Energies and Other Spectroscopic
Properties of the Spin Sublevels
We briefly summarize various experimental methods to determine the sublevel
properties.
1.2
tceriD cipocsortcepS noitavresbO
In atomic spectroscopy, to experimentally observe the spin-sublevel structures
is quite easy. However, for large organic molecules and for metal complexes, to
detect the splitting directly in the luminescence is difficult because of a number
of reasons.
In order for the sublevel luminescence to be observed, the population of the
individual sublevels should be sufficiently large. Thus, the energy separation
among sublevels should be of the order of kT or less. However, even if the tem-
perature is of the order of kT, the inhomogeneous broadening still may prevent
the resolution of the spectrum, and thus the bands from different sublevels are
ypocsortcepS of the nipS slevelbuS of noitisnarT Metal sexelpmoC
hard to detect separately. An ingenious way to avoid this inhomogeneous broad-
ening is the site-selection spectroscopy using narrow band laser excitation. In
this method only a few sites are selected by narrow band excitation. The method
is schematically illustrated in Fig. .1 In the case of a triplet state, three sites are
excited. If the relaxation among the sublevels is suppressed, we would observe
only one emission line. If, on the other hand, the relaxation among the sublevels
exists, each excited site emits three lines, and thus we should observe total of
3 x 3 = 9 lines, among which three lines are at the same energy. Thus, we have
7 lines. The sublevel properties such as energies and relative radiative rate con-
stants can be obtained by analyzing the observed spectrum. Various modifica-
tions of this spectroscopy have been made, and they are discussed in a number
of review articles 2 -6.
2.2
Microwave Resonance in Zero Magnetic Field
If the separation among the sublevels is in the range of microwave frequency,
sublevel properties can be obtained by observing the effect of microwave reso-
nance on the emission from this state. The zero-field splitting is of the order of
microwave frequency for most of 3rrn* states. Thus, the sublevel properties can
be obtained by analyzing the effect of microwave resonance on the phosphores-
cence intensity. The method is called phosphorescence-microwave double reso-
nance (PMDR) or optical detection of magnetic resonance (ODMR).
The information that can be obtained from this method is as follows: a) zero-
field splitting, b) decay rate constants for individual sublevels, c) relative radia-
_,!
demussA Triplet ledoM
ygrene,
etis a etis b etis c
D -
f /
noitaticxE
yb deworran laser
.giF .1 Schematic illustration of the direct observation of the sublevel phosphorescence in a
zero external magnetic field. In this example, the relative radiative rate constants of the sub-
levels are set 1:10: .5 Three different sites are excited by a narrow laser band, and total of nine
bands (of which there appear at the same location) are observed in the manner illustrated in
the figure