Clusters

163 Pages·1985·8.88 MB·English

by  F Albert Cotton, et al

STRUCTURE
AND BONDING
62
F.A. Cotton R.A. Walton
Metal-Metal Multiple Bonds ni Dinuclear Clusters
.G Schmid
Developments ni Transition Metal Cluster Chemistry
.G Gliemann .H Yersin
Spectroscopic Properties of the Quasi lanoisnemiD-enO
Tetracyanoplatinate(ll) Compounds
Clusters
62
erutcurtS
dna Bonding
Editors:
M. J. Clarke, Chestnut Hill
J. B. Goodenough, Oxford (cid:12)9 J. A. Ibers, Evanston
C. K. Jr Gen~ve (cid:12)9 D. M. P. Mingos, Oxford
J. B. Neilands, Berkeley (cid:12)9 G. A. Palmer, Houston
D. Reinen, Marburg (cid:12)9 P. J. Sadler, London
R. Weiss, Strasbourg (cid:12)9 R. J. P. Williams, Oxford
Clusters
With Contributions by
F.A. Cotton G. Gliemann G. Schmid
R.A. Walton H. Yersin
With 94 Figures and 18 Tables
galreV-regnirpS
Berlin Heidelberg New York Tokyo
Editorial Board
Professor Michael d. Clarke, Boston College, Department of Chemistry, Chestnut
Hill, Massachusetts 02167, U.S.A.
Professor John B. Goodenough, Inorganic Chemistry Laboratory, University of
Oxford, South Parks Road, Oxford OX1 3QR, Great Britain
Professor James A. Ibers, Department of Chemistry, Northwestern University, Evan-
ston, Illinois 60201, U.S.A.
Professor Christian K. Jcrgensen, D6pt. de Chimie Min6rale de l'Universit6, 03 quai
Ernest Ansermet, CH-1211 Gen~ve 4
Professor David Michael P. Mingos, University of Oxford, Inorganic Chemistry
Laboratory, South Parks Road, Oxford OX1 3QR, Great Britain
Professor Joe B. Neilands, Biochemistry Department, University of California, Ber-
keley, California 94720, U.S.A.
Professor Graham A. Palmer, Rice University, Department of Biochemistry, Wiess
School of Natural Sciences, P. O. Box 1892, Houston, Texas 77251, U.S.A.
Professor Dirk Reinen, Fachbereich Chemic der Philipps-Universitiit Marburg,
Hans-Meerwein-StraBe, D-3550 Marburg
Professor Peter J. Sadler, Birkbeck College, Department of Chemistry, University of
London, London WC1E 7HX, Great Britain
Professor Raymond Weiss, Institut Le Bel, Laboratoire de Cristallochimie et de
Chimie Structurale, 4, rue Blaise Pascal, F-67070 Strasbourg Cedex
Professor Robert Joseph P. Williams, Wadham College, Inorganic Chemistry
Laboratory, Oxford OX1 3QR, Great Britain
ISBN 3-540-15731-X Springer-Verlag Berlin Heidelberg New York Tokyo
ISBN 0-387-15731-X Springer Verlag New York Heidelberg Berlin Tokyo
Library of Congress Catalog Card Number 08211-76
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Table of Contents
Metal-Metal Multiple Bonds in Dinuclear Clusters
F. A. Cotton, R. A. Walton ................
Developments in Transition Metal Cluster Chemistry.
The Way to Large Clusters
G. Schmid ......................... 51
Spectroscopic Properties of the Quasi One-Dimensional
Tetracyanoplatinate(II) Compounds
G. Gliemann, H. Yersin .................. 87
Author Index Volumes 1-62 ................. 155
Metal-Metal Multiple Bonds in Dinuclear
Clusters
F. A. Cotton I and R. A. Walton 2
I Department of Chemistry, Texas A & M University, College Station, Texas 77843, USA
2 Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA
Just over 02 years have elapsed since the first recognition of the existence of compounds that contain
metal-metal multiple bonds. The present article surveys many of the important developments that
have occurred in this field since the publication in 2891 of the text "Multiple Bonds Between Metal
Atoms" by the present authors. Detailed updates are provided of the chemistry surrounding ditung-
sten, ditechnetium, and dirhenium complexes that possess quadruple bonds 264n2o( electronic con-
figuration) and electron-rich triple bonds 6264~za( 2. electronic configuration). The rapidly develop-
ing chemistry of multiply bonded diruthenium and diosmium complexes that possess the 2M 4+ , zM S+ ,
2~lv/dna + cores, especially those containing ligand bridges, is also surveyed. Additional topics that
have been covered are the following: the reactivity of dimolybdenum(III) and ditungsten(III) hexa-
alkoxides; the chemistry of singly bonded diplatinum(III) complexes; experimental and theoretical
aspects of the bonding in (Cr~Cr) §4 complexes; the diatomics Mo2, Cr2, 2V and Ru2; and the
photoelectron spectroscopy, optical activity, and M-M bond length/bond order and charge correla-
tions that characterize compounds that contain metal-metal multiple bonds.
Introduction ....................................... 2
Detailed Update of Ditechnetium and Dirhenium Chemistry ............... 2
Detailed Update of Ditungsten(II) Chemistry ...................... 21
Detailed Update of Diruthenium and Diosmium Chemistry ............... 91
Survey of Highlights in Other Areas 26
1.5 The 2M Molecules .................................. 62
5.2 Compounds With Chromium(II)-Chromium(II) Quadruple Bonds ......... 82
5.3 Platinum(III)-Platinum(III) Bonds ......................... 33
5.4 Chemistry of Dimolybdenum and Ditungsten Hexalkoxides ............ 63
5.5 Photoelectron Spectroscopy ............................ O4
5.6 M-M Bond Lengths ,sv Bond Order and Charge .................. 42
5.7 Optical Activity ................................... 34
6 References ........................................ 54
Structure and Bonding 62
@ Springcr-Vcrlag Berlin Heidelberg 1985
2 F.A. Cotton and R. A. Walton
1 Introduction
Our book Multiple Bonds Between Metal Atoms was published in March of )12891 , but
systematic coverage of the literature ceased during mid 1981. Since that time the field has
continued to expand rapidly. Over the approximately three-year period in question,
approximately 350 new research papers have appeared, bringing the total number of
publications in the field to well over 1000.
The purpose of this review is to summarize important developments that have oc-
curred since we finished writing our book, which we shall henceforth refer to, for brevity,
as MBBMA. In view of the enormous amount of new literature - about half again as
many papers as we covered in the book itself - it is obvious that this can only be done
selectively. Accordingly, we have chosen a few areas where comprehensive reviewing
seemed appropriate and treated them in detail, while in a final section we present an
overview of novel discoveries from other parts of the field.
It may be noted that over the past several years reviews covering larger or smaller
parts of the subject of multiple bonds between metal atoms have appeared. See, for
examples, Refs. 2-8.
2 Detailed Update of Ditechnetium and Dirhenium Chemistry
nruitenhcetiD Compounds. While the development of ditechnetium chemistry has pro-
ceeded relatively slowly over the last few years there have, nonetheless, been some
noteworthy advances. Until 1980, all attempts to isolate and characterize the oetachloro-
ditechnetate(III) anion had failed, an important reason being the surprising stability of
the odd electron Tc2Cls 3- anion, a derivative of the ~cT + core .)1 However, in 1980,
Preetz and Peters )9 were successful in preparing (BuaN)2Tc2CIs, together with
(Bu4N)3Tc2CIs, by a procedure that involved the mossy zinc reduction of (NH4)zTcCI6 in
aqueous HC1 followed by cation exchange using Bu4NCI. The green complex
81C2cT2)N4uB( can be converted to the bromide derivative (Bu4N)zT%Br 8 by dissolving it
in aqueous acetone/HBr .)9 The successful completion of an X-ray crystal structure deter-
mination on (Bu4N)2Tc2CI8 provided incontrovertible proof as to the structure of the
8IC2cT 2- anion l~ This salt is isostructural with (BuaN)2Re2Cls and, like the latter,
possesses a quadruply bonded dimetal unit with an eclipsed rotational conformation.
While there is disorder associated with the orientation of the sIC2cT z- ions, the struc-
ture is of high precision; the Tc-Tc distance is 2.147(4)/~, this being the weighted
average of Tc-Tc distances of 2.151(1) A and 2.133(3) A for the major and minor orienta-
tions ~1 One result that remains somewhat controversial is the electrochemical redox
characteristics of the Tc2Cls2-/Tc2Cls 3- couple. It had previously been demonstrated )11
that in a mixed hydrochloric acid-ethanol solvent 1( : 9 by volume) the Tc2CIs 3- ion (as
its yttrium salt) is reversibly oxidized to 81C2cT 2- at + 0.14 V vs. SCE. On the other
hand, solutions of (Bu4N)2T%CIs in 1.0-21C2HC M Bu4NC104 are characterized by 2/1E =
- 0.13 V vs. SCE at a rotating platinum electrode ~1 so that the electrochemical poten-
tial for this process is solvent dependent; it is possible that solvolysis of the Te2CIs 3- ion
occurs in HC1-EtOH solutions (vide infra).
lateM-lateM Multiple Bonds in Dinuclear sretsulC
The Tc-Tc bond distance of 2.147/~ in IC2cT2)N4uB( s has itself posed an interesting
dilemma, namely, why is this distance longer than the Tc-Tc distances reported for the
81C2cT 3- ion in its ammonium and potassium salts (2.13(1) and 2.117(2)~, respec-
.)31,21)ylevit This result is the opposite of that which might be expected based upon a
simple bond length-bond order correlation. To provide further supporting experimental
evidence, the crystal structure of the yttrium salt YTc2CIs.9 H20 has been deter-
mined .)41 Once again, the Tc-Tc distance (2.105(1)~) was found to be shorter than in
the sIC2cT 2- ion. The explanation for this phenomenon is provided in Sect. 5.6.
While quadruply bonded carboxylate-bridged dirhenium(IIt) complexes of the type
Re2(OzCR)aX2 are easily prepared and have been thoroughly characterized, comparable
ditechnetium(III) carboxylate compounds are still very rare .)1 The pivalate derivative
2IC4)3eMCCEO(2cT was prepared in low yield and structurally characterized a few years
back .)51 More recently, the diamagnetic acetate complex xIC4)3HCC2O(~cT was prepared
as cherry red crystals from the reaction between KTcOa and hydrochloric and acetic acids
in a hydrogen atmosphere .)61 The product yield was not reported. A comparison between
the IR spectra and X-ray diffraction powder patterns of Tc2(O2CCH3)4CI2 and
Rez(OzCCH3)4CI 2 has led to the suggestion that these complexes are isostructural.
The autoclave reaction (120 ~ 30 arm) between sIC2cT3K (cid:12)9 2 H20 and glacial acetic
acid in an atmosphere of argon or hydrogen has been used to prepare the crystalline ~cT §
derivatives Tc2(O2CCH3)4C1 (green) and 21C4)3HCC2O(2cTK (pale brown), admixed
with K2TcCI6 and a material purported, but not proven, to be a Tc(II) complex .)7t
Unfortunately, the product yields were not reported, and the crystals in the mixture were
apparently separated by hand or by use of a solvent. Various other autoclave reductions
have been carried out using mixtures containing MTcO4, M2TcX6, sIC2cT3M (cid:12)9 3 H20 , or
51COcT2M (M = NH4 or K; X = CI, Br, or I) and concentrated HX in an 2I-I atmosphere,
and these have been described as affording the brown or black crystalline Tc(II) com-
pounds 6X2cT2M (cid:12)9 2 H20 (X = CI or Br) and (TcX2 (cid:12)9 0.5 1-I20) (X = Br or I) .)81 The
correct formulation of these materials remains to be proven. Whereas the chloride salts
61CacT2M" (cid:12)9 2 H20" react with hot hydrochloric acid to give sIC2eT 3-, the bromides give
solutions containing TcBr6 2- when they are dissolved in hydrobromic acid in the pres-
ence of air is). The reaction between "M2Tc2Br6 (cid:12)9 2 H20" and glacial acetic acid in an
argon atmosphere (50 arm) at 230-250 ~ gives green crystalline Tc2(O2CCH3)4Br (yield
not specified) .)si
The complexes Tc~(O2CCHa)4X (X = CI or Br) and zIC4)3HCC2O(~cTK are clearly
authentic derivatives of the ~cT + core. They are paramagnetic and ESR-active, and
possess magnetic moments in accord with the presence of a l*5~264r~2o ground
state electronic configuration 17'w). X-ray crystal structure determinations on
21C4)3HCC2O(2cTK and Tca(O2CCH3hCI have been completed ~2 .)12 The former salt
contains the dinuclear Tc2(O2CCH3)4CI2- anion with Tc-Tc and Tc-CI distances of
2.126/~ and 2.589 A, respectively ~2 The complex 1C4)3HCC2O(2cT has a structure
closely akin to that of To2(hphCl (hp is the anion of 2-hydroxypyridine) ,)22 in which
chains of Tc2(O2CCH3)4 + units are linked by bridging chloride ligands .)12 In all in-
stances, the To-To distances of the acetate and hp derivatives of the T~ + core are shorter
than the To-To distance in the quadruply bonded pivalate 21C4)3eMCC2O(2cT (2.192/~);
this trend mirrors that found for the Tc2Cls 3- and sIC2cT 2- ions (vide supra). In
passing, we should mention that a proposal has recently surfaced which attributes the
decrease in Te-Tc bond length on going from ~cT + complexes to those of T~ + to an
4 F.A. Cotton dna R. A. Walton
increase in Tc-Tc bond order from 4 to .)325.4 This interpretation is not supported by any
meaningful theoretical calculations ,)1 and neither is there any experimental evidence
which favors such an interpretation over the more commonly accepted one ~1 .41 It must
be emphasized that any simplistic interpretation which assumes that an esaercni in bond
length will necessarily correlate with a esaerced in bond order in multiply bonded dimetal
systems is fraught with danger.
Spectrophotometric studies have been used to investigate the stability of solutions of
the sIC~eT 3- anion in hydrochloric acid '42 .)52 At HC1 concentrations below 3 M, hydro-
lysis to give n)02H(n_81C2cT n-3 is said to occur, while for HCI > 3 M, disproportio-
nation to generate TcCIr 2- (i.e. Tc(IV)) and Tc(II) species (identity unknown) is a
dominant process. The presence of dissolved 2O leads to oxidative cleavage of 81C2cT 3-
to give TcCI6 2- and 4IC)HO(OcT .-2
Dirhenium Compounds. In the case of dirhenium chemistry, the most striking advances
have been encountered in the case of the so-called electron-rich Re--Re triple bonds
~2i~4n20( .2 electronic configuration) where a variety of new reactivity patterns have been
established. Studies on such species constitute one of the most rapidly developing areas
of multiple bond chemistry.
)a( Rhenium-Rhenium Quadruple Bonds ~t4~20( .)noitarugifnoC The quadruply bonded
octahalodirhenate(III) anions and the halide-carboxylate complexes Re2(O2CR)4X2 and
Re2(O2CR)2X4 continue to be the main focus of interest in the chemistry of the Re +6
core. Of special note has been the discovery of a new one-pot, high yield synthesis of
,8IC2eR2)N4uB( the key starting material in multiple bond dirhenium(III) chemistry. The
reaction of Bu4NReO4 with refluxing benzoyl chloride at - 210 ~ has provided a means
whereby (Bu4N)2Re2Cls can be prepared easily, quickly, and in high (90%) yield .)62 In
view of the high cost of rhenium (as perrhenate) and the rather low overall yield in which
(Bu4N)2Re2Cls is produced by other methods ,)1 this constitutes a very important develop-
ment in dirhenium(III) chemistry. An alternative starting material for the synthesis of
8IC2eR2)N4uB( is ,)622)3hPP(3ICOeR a complex which is itself prepared from MIReO4 in
high yield. It is believed that this reaction proceeds via the intermediacy of
Re2(O2CPh)2CI4; thus the role of PhCOC1 is to reduce and chlorinate the metal centers
and then couple them via the agency of benzoate bridges .)62
Further refnements have been made in the assignment of the electronic absorption
spectrum of the Re2Cls 2- ion, especially with regard to the identification of the weak,
forbidden bands that lie between the 8 ~ b* transition (~ 14,200 cm -1) and the intense
near-UV absorptions .)72 These assignments have been aided by an MO calculation using
the relativistic SCF-Xa-SW method ,)72 while details of another theoretical study have
been reported by Hay )82 that involve multiconfignration valence bond calculations in
conjunction with relativistic effective core potentials. Of further importance insofar as
the electronic structures and spectroscopic properties of the Re2Xs 2- ions (X = F, ,1C
Br, or I) are concerned, have been the results of a very thorough resonance Raman
spectral study .)92 It was found that with excitation within the contours of the i~ ~ *i~ and
X(n) ~ *i~ electronic transitions, progressions in lV (i.e. v(Re-Re)) and 2v (i.e.
vsm(Re--Cl)), respectively, dominate the RR spectrum of each ion .)92
An interesting facet of the photochemistry of sIC2eR 2- involves the electron-transfer
chemistry of the luminescent excited state 8IC2eR 2-*, which is an *i~8 singlet ~a
lateM-lateM Multiple Bonds in Dinuclear sretsulC
D Re2CI82-" A
57.1 Ve
-58IC2eR ..-0.85 V _ -28IC2aR ..I.24V r O2eR 8"
Fig. 2.1. Modified Latimer diagram for the
glCaeR/-nlslCEeR "- system (E~ .sv SCE).
By permission from Ref. 13 -A A
Various electron acceptors (e.g. TCNE) quench the 81C2eR 2-* luminescence in non-
aqueous solvents to produce Re2CIs- and the reduced acceptor. The luminescence is
also quenched by secondary and tertiary aromatic amines (e.g. N,N,N',N'-tetramethyl-
p-phenylenediamine) in acetonitrile solution ~3 Thus the 66* singlet provides a facile
route to the powerful oxidant Re2CI8-, a species that has its own interesting chemistry.
For example, it reacts with C1- to generate the well known mixed-valence species
;)1-291CaeR
this can in turn be oxidized to Re2C19- by a suitable acceptor .)13 This
transformation corresponds to a net two-electron photochemical oxidation of Re2Cls 2-
to Re2C19- .)13 The potentials for the Re2Cls n- and gIC2eR n- systems that have been
measured or estimated from the results of various spectroscopic and electrochemical
experiments can be shown most appropriately in a modified Latimer diagram (Fig. 2-
1) )13 .
Several X-ray crystal structures have been determined for salts that contain the
slC2eR 2- and ge2Brs 2- anions, all of which were published pre-19821'8) The only
recent structure determination that has been carried out is that of the salt
(DMA)2H2Re2Brs (DMA = dimethylacetamide) ,)2a but details of the structure are not
yet available. Of the octahalodirhenate(III) anions, the crystal structures of the fluoride
and iodide salts (Bu4N)2Re2Xs remain to be determined. However, there can be no doubt
that both anions possess the typical Re2Xs 2- structure, with an eclipsed rotational
conformation and a very short Re-Re bond. In this regard, the isolation of the novel
compound Re4Is(CO)6 is of special relevance .)33 It is prepared by the 2I oxidation of
Re212(CO)6(THF)2 in heptane, and has a structure that can be viewed formally as involv-
ing interaction between two Re(CO)a + fragments and R~Is2-; this association occurs
via bent Re-I-Re bridges that involve six of the iodine atoms of Re2Is 2-. As a conse-
quence of this interaction, which gives rise to (CO)3ReI3 units, the rotational conforma-
tion within the 812eR unit is staggered rather than eclipsed and, as a result, the Re-Re
bond length is longer (2.279(1)A) )33 than that found in eclipsed Re2Xs 2- species
(X = 1C or Br) where the distance is typically 2.22-2.25 A .)1 In accord with the usual
bonding scheme for Re2L8 species ,)1 as the conformation changes from eclipsed to stag-
gered, the 6 bonding diminishes (i.e. the yxd-yxd overlap) and the metal-metal bond order
decreases from four to three.