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An Easily Prepared Air-Stable Compound with a Triple Metal-to-Metal (MoMo) Bond.

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C 0 M MU N I CAT10 N S
us quite clearly that we are dealing with a triple bond between the molybdenum atoms. The loss of one 6 electron in
the sulfato system increased the MoMo distance by 0.053 A;
An Easily Prepared, Air-Stable Compound with a
Triple Metal-to-Metal (MoMo) Bond[**]
By Avi Bin0 and F. Albert Cotton'"
Fig. 1. Structure of the [Mo2(HP0,),(H20),]'
Since double, triple, and quadruple metal-to-metal bonds
were first recognized, in 1963, 1966, and 1964, respectively,
hundreds of compounds containing such bonds have been
reported and scores of them have been structurally characterized by X-ray crystallography. Nonetheless it appears that
many chemists tend to think of compounds containing such
bonds, especially the triple and quadruple ones, as constituting chemical exotica. Nothing, of course, could be farther
from the truth, as many such compounds are actually among
the most easily prepared and stable ones formed by the elements in question. However, some such compounds, especially those with Mo=Mo and W=W bonds"], are indeed
highly reactive or thermally unstable and some contain relaor
tively uncommon ligands, such as R,N -, RO
Me,SiCH,-- .
This communication reports a striking example of how
easy it can be to prepare an air-stable, thermally stable compound containing an MGMO triple bond.
The compound Cs,[Mo2(HP04),(H20),] is prepared by
first dissolving K,Mo,CI,. 2 H,O['] in 2 M H,PO,. The resulting solution is then allowed to mix slowly, by diffusion
through a glass frit, with a solution of CsCI in 2~ H,PO,.
Over a period of a week a beautifully crystalline, purple solid
is precipitated. All these operations are conducted at ca.
25 " C in vessels open to the laboratory atmosphere. The compound appears to be stable indefinitely in ordinary laboratory air.
Figure 1 shows the result of routine X-ray crystallographyl31. The structure of the [Mo,(HPO~)~(H,O),]~-unit is
reminiscent of that found for [Mo,(SO~)~(H,O),]~and also
for Mo2(S04): -r41, but there are significant differences in detail. One of the most interesting differences is theo long
MoMo distance [2.223(2) A, as compared to 2.164(2) A and
2.111(1) A in the two sulfato species, respectively] which tells
[*] Prof. Dr. F. A. Cotton, Dr. A. Bino
Department of Chemistry
Texas A & M University
College Station, Texas 77843 (USA)
[**I
This work was supported by The Robert A. Welch Foundation (Grant No.
A-494).
462
0 Verlag Chemie, GmhH, 6940 Weinheim, 1979
ion in crystal.
if we assume that the phosphato system can be compared directly with the sulfato ones, a further increase of 0.053 A
upon loss of the second 6 electron would give a predicted triple bond distance of 2.164+0.053 =2.217 A in excellent
agreement with the observed value. The Mo=Mo distance
found here is also close to those found in a variety pf other
molecules such as Mo,Cl,(NMe,),
(2.201(2) A) and
Mo~(OC,H,),(O,COC~H~)~
(2.241(1) A ) [ ' I .
The hydrogen atoms of the HPO, groups were not found
directly, but their locations are clearly indicated by the P-0
bond lengths, 0- P .O angles, and the hydrogen bonding.
The eight P- -0bonds to coordinatedooxygen atoms (endo
oxygens) range from 1.51 to 1.56 A, with a mean of
1.54k0.015 A. The P-exo-0 distances clearly fall into two
sets. On each phosphato unit there is one such bond with a
length of 1.48&0.01 A and another with a length of
1.56k0.02 A. The former can be assigned to P-0 and the
latter to P--OH. Moreover, each 0 atom of the P - O H
groups is hydrogen bonded to an 0 atom of a P-=O group of
an adjacent molecule, with O . . . Odistances of 2.48 to 2.53 A,
and P-O...HO angles of 113 to 120".
The water molecules are quite loosely bound to Mo at distances of 2.46(1) A and 2.53(1) A and each of them also
forms one strong (2.70 A or 2.78 A) and one weak (ca. 2.90
A) hydrogen bond to phosphate oxygen atoms of adjacent
molecules.
Since the [ M O , ( H P O ~ ) ~ ( H ~ Ounit
) ~ ] is
~ -not subject to any
crystallographic symmetry element and the existence of only
a triple bond imposes no barrier to internal rotation, it is pertinent to examine the rotational conformation. The four torsional angles (dihedral angles between OMoMo' and
MoMo'O planes) that should be equal to zero for the ideal
eclipsed structure have values of O S " , 1.6", 2.1", and 2.1";
the structure is thus essentially eclipsed, presumably because
this conformation is favored by the ligands.
This substance belongs to the still rare but growing class of
compounds containing simple triple M=M bonds'51 in an
environment of four-fold ligation of each metal atom. These
include La,Re,0,,[61 as well as several molecules that result
0570-0X3.~/79/0606-0462$02.50/0
Aiigew. Chem. Int. Ed. Engl. 18 ( 1 9 7 9 ) No. 6
from addition of donors to M02L6[7d1
or W2L6[7b1
molecules.
Cs2[Mo,(HP0,),(H,0),] is unique, however, in the simplicity
and ease with which it can be prepared and in its chemical
stability. It is also the first definite example of phosphato
bridging of a bonded pair of metal atoms. In view of the possibility of adjusting the overall charge by changing the degree of protonation of the exo oxygen atoms, phosphatobridged species may prove to be numerous and diverse.
r
123
Received: January 29. 1979 (2 213 IE]
German version: Angew. Chem. 91. 496 (1979)
CAS Registry numbers:
Cs,[Mo,(HPO,),( H,O),], 70281-26-4: K,Mo2CI8.2H,O, 22239-46-9
[ I ] M. H Chisholm, F. A. Cotron, Act. Chem. Res. 1 1 , 356 (1978).
121 J. V Arencic. F. A. Cotton, Inorg. Chem. X . 7 (1969); 9, 351 (1970).
131 Crystal data: space group P2,/c; a= 8.75!(3)
b = 11.217(3) c = 17.938(4)
K /3=90.92(2)". V=1761(1) A'. Z = 4 ; 1515 independent reflections with
I > 3 c r ( l ) ; R , =0.051. R2=0.079. [Enraf-Nonius Structure Determination
package at the Molecular Structure Corporation, College Station, Texas.]
[4] I; A. Cotton. B. A. Frenz, E. Pedersen, T. R. Webb, Inorg. Chem. 14, 391
(1975).
[ 5 ] It mu\t he kept in mind that there are two principal types of MM triple
bonds: I ) those with no 6 bond (rr2m4) and 2) those in which there is cancellation ofthe 6 bond by electrons occupying the 6* orbital ( ~ * . i r ~ 8 ' 6 *We
~ ) . refer l o the former as simple triple bonds and only they are considered in our
present discussion.
[ h ] K. Wulter.rson, Acta Crystallogr. B 32. 1485 (1976).
[7] a) M. H . Chisholm. F. A. Cotton, M. W. Exfine, W W. Reicherr, J . Am.
Chem. Soc. 100.153, 1727 (1978). b) M. H. Chisholm, ?I A. Cotton, P. E. Fanwick, unpublished work on W,(OCHMe,),py,.
A,
A.
Transition Metal Complexes with the Tetrathiosquarate Dianion as Bridging Bischelate Ligand
By Franz Gotzfried, Wolfgang Beck, Anton Lerf; and
Angelika Sebald['I
Organometallic compounds having chain structures are of
interest as potential one-dimensional electrical conductod'l.
Tetrathiosquarate dianion C4S: - appears to be especially
suitable for the production of such catena complexes on account of its high symmetry (D4,,) and readily polarizable S
atoms.
Anionic thio ligands often act as bridging ligandsl3I, and d8
metal ions such as Ni" are known to form polymeric complexes with, e. g., ethylene tetrathi~late~~l.
Whereas squaric acid['"] and its dianion C40$-[5bldo not
occur as 0,O-chelate ligands in transition metal complexes~5'1,the dithiosquaric dianion C40,S: can form S,Schelate complexes[5d1.We have now found that the dianion
of tetrathiosquaric acid forms numerous compounds having
bischelate structure with transition metals.
Thus the highly air-sensitive compounds (1) are formed by
reaction of hexacarbonyl-6A metals with the potassium salt
-
['I
Prof. Dr. W. Beck, Dipl.-Chem. F. Gotzfried, A. Sebald
Institut f u r Anorganische Chemie der Universitat
Meiserstrasse 1. D-8000 Miinchen 2 (Germany)
Dr. A. Lerf
lnstitut fur Tieftemperaturforschung
Hochschulgelande, D-8046 Garching (Germany)
[**I This work was supported by the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie.
A n y m Cliein. l i i r . Ed. Engl. 18 (1979) No. 6
(3), orange
0 Verlay
(4a), M
= Rh, r e d - b r o w n
(46), M = I r , b r o w n
C4S4KZ.HZO[21
in diglyme at 120 " C and subsequent precipitation with Ph,AsCl; the neutral complexes (2)-(5) are obtained from the corresponding halometal derivatives by stirring for several hours with the thioligand at 20 "C in tetrahydrofuran (THF).
The IR, NMR, and mass spectra are in agreement with the
expected structures:
(la): v(CO)=1985m, 1 8 8 7 s 1861 vs. 1820scm-':(lb): u(CO)=1998m, 1894
s. 1863 s, 1822 s cm-'; (Ic): u(C0)=1992 m, 1886 s. 1861 s, 1828 m cm
(in
THF); "C-NMR (in D,-DMSO, int. TMS): K O . C,S,= 171.27 (s). 176.85 (s),
179.21 (s), (2): v(CO)= 2093 m, 2023 s. 2002 s, 1956 s cm (solid in Nujol); (3):
'H-NMR (in CDCI,, int. TMS): 6CH, =2.17 (d, J,, = 10 Hr): (3): 'H-NMR (in
CDCI,. int TMS): K H ? = 1.17 (s): MS (70 eV): m / e = 630 ( M ' ). correct isotope
'
~
'
pattern
The characteristic intense C C S stretching vibration is
always observed at higher wave numbers (max. 1305 cm I )
in the complexes (1)-(5) than for the free ligand
(uC
s = 1235 cm-I); the broad band is often split into several intense sharp bands.
Complex (5) can be irreversibly reduced in two steps (at
-0.75 and -1.52) by voltammetry[61. The reduction of
squaric acid derivatives is particularly interesting, because it
must ultimately lead to substituted cyclobutadienes! In contrast to C40:-[71, the C,S:- dianion can be smoothly reduced polarographically[Xl in two one-electron steps (halfwave potentials: - 1.53 V and - 1.79 V) in aqueous solution
to the tetraanion C4Si-.
Reaction of aqueous solutions of NiC1, or Na,PdCI, with
K2C4S4affords diamagnetic products
Ni2s(C,S,)2,K2~xH20(x -c 8) (6). dark-red
Pd,,(C,S,),Cl,K,~xH,O (7), brownish black
The composition of these lustrous compounds is in agreement with a chain structure, the chain terminals being saturated with tetrathiosquarato ligands in (6) and by chloro ligands in (7). K,PtC14 or (PhCN),PtCl, react with K2C4S4to
give blackish green complexes (8) containing Pt and C4S4 in
the ratio of 1 :1 and also varying amounts of K, 0, C1, and H,
depending upon the reaction conditions.
Chemie, GmbH, 6940 Weinheim, 1979
0s 70-0x33/ 79/0606- 046.1 $ 02.s0/0
463
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