Group 6 transition metal carbonyl complexes with chalcogenbridged diarsenic(in) ligands

Article abstract of DOI:10.1039/b005269h

The neutral complexes [Cr(CO)4(Ph2AsOAsPh2)] 1, [Mo(CO)4(Ph2AsOAsPh2)2] 2, [Cr(CO)4(Ph2AsSAsPh2)] 3, [Mo(CO)4(Ph2AsSAsPh2)2] 4, [Cr(CO)5(Ph2AsOAsPh2)] 5 and [Cr(CO)5(Ph2AsSAsPh2)] 6 have been prepared. The crystal structures of compounds 1-5 were determin

Full text of DOI:10.1039/b005269h

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Group 6 transition metal carbonyl complexes with chalcogen-
bridged diarsenic(III) ligands
Linda H. Doerrer,a Jennifer C. Green,a Malcolm L. H. Green,*a Ionel Haiduc,c
Christian N. Jardine,a Sofia I. Pascu,a Luminita Silaghi-Dumitrescuc and David J. Watkinb
a Inorganic Chemistry Laboratory, South Parks Road, Oxford, UK OX1 3QR
b Chemical Crystallography Laboratory, South Parks Road, Oxford, UK OX1 3PR
c Department of Chemistry, Babes-Bolyai University Cluj-Napoca, Cluj-Napoca RO-3400,
Romania
Received 3rd July 2000, Accepted 7th August 2000
First published as an Advance Article on the web 18th September 2000
The neutral complexes [Cr(CO)4(Ph2AsOAsPh2)] 1, [Mo(CO)4(Ph2AsOAsPh2)2] 2, [Cr(CO)4(Ph2AsSAsPh2)] 3,
[Mo(CO)4(Ph2AsSAsPh2)2] 4, [Cr(CO)5(Ph2AsOAsPh2)] 5 and [Cr(CO)5(Ph2AsSAsPh2)] 6 have been prepared.
The crystal structures of compounds 1–5 were determined. The diarsenic ligand in 2, 4, and 5 is monodentate
and in 1 and 3 the ligand is bidentate. The crystal structure of the ligand Ph2AsOAsPh2 was redetermined and
the As–O–As angle found to be 115.98(17)Њ, significantly less than the value originally reported. Calculations,
using density functional theory, assist discussion of the steric and electronic factors influencing the choice of
binding mode.
Introduction
Results and discussion
Chelating phosphorus() ligands of the type R2PXPR2 where
R = alkyl or aryl and X = CH2, NH, O or S, are well established
in transition metal chemistry1,2 and the behaviour of this type
of ligand towards Group 6 metal carbonyls is well under-
stood.3–5 The related arsenic() ligands R2AsXAsR2 have also
been prepared and characterised,6–9 however only a few transi-
tion metal complexes have been described10–15 and only isolated
examples have crystallographically been characterised, for
X = O or S.12,14,16 Recently, a study on a number of bi- and tri-
metallic carbonyl complexes containing cobalt of Ph2AsOAs-
Ph2 and Me2AsOAsMe2, where these ligands are co-ordinated
in a bridging fashion, has been published.16 We have also
reported organoarsenic derivatives with two AsIII or AsV con-
nected by an oxygen or sulfur bridge.17–19 The various modes of
co-ordination that have been found for R2AsIII–X–AsIIIR2 lig-
ands (R = alkyl or aryl, X = CH2, NH, O or S) are shown below.
We now report the synthesis and structural investigations of
Group 6 metal carbonyl complexes with Ph2AsXAsPh2 ligands
(X = O or S) and density functional theory (DFT) calculations
on these systems with the model ligands H2AsXAsH2. DFT
calculations on the Ph2AsOAsPh2 and Ph2AsSAsPh2 systems
have also been performed. The large difference between the
DFT-calculated values of the molecular parameters and those
(i) Synthesis
Treatment of [Cr(CO)4(nbd)]21 with one equivalent of Ph2-
AsXAsPh2 led to the formation of the complexes [Cr(CO)4-
(Ph2AsXAsPh2)] (1, X = O and 3, X = S).13 Unexpectedly, the
reaction of [Mo(CO)4(nbd)]21 with either one or two equiv-
alents of Ph2AsXAsPh2 (X = O or S) gave only [Mo(CO)4-
(Ph2AsXAsPh2)2] (2, X = O and 4, X = S), with the arsenic
ligand co-ordinated in a monodentate fashion. The reaction
of Ph2AsXAsPh2 with [Cr(CO)6] in tetrahydrofuran (thf)
under photolytic conditions yielded compounds [Cr(CO)5(Ph2-
AsOAsPh2)] 5 and [Cr(CO)5(Ph2AsSAsPh2)] 6 (Scheme 1). The
progress of reactions was monitored via solution IR spec-
troscopy. Attempts to prepare the molybdenum complexes
analogous to 1 and 3 by heating solutions of the ligands in
benzene or toluene with [Mo(CO)5(thf)] were unsuccessful and
heating 2 and 4 in toluene led to decomposition.
The compounds 1–6 are thermally and air stable in the solid
state, but solutions exposed to air show slow decomposition.
The molybdenum complexes are more air-sensitive than the
chromium derivatives, as expected.22,23 The analytical and
spectroscopic data for 1–6 are summarised in Table 1.
(ii) Spectroscopy
20
reported in an earlier work on Ph2AsOAsPh2 generated the
need to redetermine the crystal structure of this ligand.
1
The H and 13C-{1H} NMR spectra of complexes 1–5 were
1
recorded and details are presented in Table 1. In the H NMR
spectra the ortho, meta and para resonances are not always dis-
tinguishable. However, the non-chelating co-ordination modes
in 2 and 4 generate multiple sets of phenyl resonances due to
non-equivalent phenyl groups which are expected on the basis
of the structure discussed above. Two sets of phenyl resonances
are also observed for 3, however this may be due to the increase
in strain in the ligand due to the S atom, when compared with 1.
In the case of compound 6 three different types of phenyl
groups ascribed to restricted rotation about the Cr–As bond
were observed in the 13C NMR spectrum, one for the two
phenyls connected to the unco-ordinated arsenic and one for
each phenyl group bound to the co-ordinated arsenic. The
DOI: 10.1039/b005269h
J. Chem. Soc., Dalton Trans., 2000, 3347–3355
This journal is © The Royal Society of Chemistry 2000
3347

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Fig. 1 ORTEP diagram of the molecular structure of [Cr(CO)4{(Ph2-
As)2O}] 1.
Fig. 2 ORTEP diagram of the molecular structure of [Mo(CO)4-
{(Ph2As)2O}2] 2.
Scheme 1 Reactions of substituted Group 6 metal carbonyls with the
Ph2AsXAsPh2 ligands, where X = O or S.
in all FABϩ spectra consistent with two phenyl groups π-co-
ordinated to the metal, [M(η6-C6H5)PhAsXAsPh(η6-C6H5)]ϩ.
This observation is supported by previously reported data.23,27
carbon atoms of the CO groups exhibit signals in the 13C NMR
around δ 200 with CO groups cis to the arsenic ligand more
deshielded than trans-CO groups.
(iii) X-Ray crystallographic studies
IR spectroscopy studies have been used previously17 for
structural characterisation of these ligands. As no coupling of
As–O–As stretching modes with other normal modes is
expected,17,18 a correlation between increasing As–O–As angles
and higher stretching frequencies for both symmetric (around
500 cmϪ1) and antisymmetric modes (around 700 cmϪ1) was
observed for the case of 1, 2 and 5. IR spectral assignments
in the 2200–1600 cmϪ1 region were made on the basis of the
literature data22,23 for Group 6 complexes with approximate
C2v symmetry containing methylene-, ethylene- or phenylene-
bridged diarsines() of the type [M(CO)4(Ph2AsXAsPh2)m],
m = 1 or 2. For compounds 1–4 four well spaced bands were
observed in the CO region of the spectra. In 5 and 6 the overall
symmetry is lower than C4v and the spectra are correspondingly
more complicated. Five absorption bands were observed
for CO stretching similar to the behaviour of [M(CO)5L]
The molecular structures of compounds 1–5 were determined
by X-ray crystallography and are shown in Figs. 1–5. Table 2
contains selected structural parameters. The redetermined
structure of free Ph2AsOAsPh2 (ORTEP28 diagram) is shown in
Fig. 6 and the relevant structural parameters are contained in
Table 2.
All five complexes display octahedral co-ordination at the
metal centre, with two cis arsenic-donor atoms in 1–4. The
bidentate chelating mode in 1 and 3 results in four-membered
inorganic chelate Cr–As–X–As rings. In 1 the oxygen atom is
essentially coplanar with the As–Cr–As best plane, whereas in 3
the Cr–S vector deviates from planarity with the As–Cr–As best
plane by 6Њ. In 1–5 each co-ordinated arsenic atom has dis-
torted tetrahedral geometry with angles around arsenic ranging
from 95 to 127Њ. Higher M–As–C angle values were found with
bidentate chelation in 1 and 3. The unco-ordinated arsenic
atoms in 2, 4 and 5 display a distorted pyramidal geometry with
angles from 95.0(1) to 97.6(1)Њ in 2, 92.6(1) to 101.68(11)Њ in 4,
and 92.38(7) to 98.27(9)Њ in 5. The Cr–As bond lengths in Table
2 compare closely with the literature values for [Cr(CO)5-
(Ph2AsNSO)],29 2.438(1) Å, and [Cr(CO)2{(η6-Ph)PhAsCH2-
AsPh2}],27 2.406(1) Å, as do the Mo–As bonds with the
monodentate co-ordinated Mo–As distance in [MoBr2(CO)2-
(Ph2AsCH2AsPh2)2],30 2.608(5) Å.
complexes with M = Cr, Mo or W and ligands such as
10
Me2AsSAsMe2
and Me2As(S)SAsMe2,11 Me2AsP(CF3)2,24
Ph3AsO,25 and Me2AsSMe.26
In the FABϩ mass spectra for complexes 1–6 the molecular
ion is observed as a peak of low intensity (with the correct
isotope pattern), except for 2 where the highest m/z value is
assigned to the [M Ϫ CO]ϩ ion. A peak corresponding to
[M(Ph2AsXAsPh2)]ϩ (M = Cr or Mo, X = O or S) is present
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J. Chem. Soc., Dalton Trans., 2000, 3347–3355

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Table 1 Analytical and spectroscopic data for compounds 1–6; 1H and 13C NMR data for the ligands
Compounda
NMR datab
1 [Cr(CO)4(Ph2AsOAsPh2)]
1H: 7.37 (m, C6H5)
orange
13C: 226.9 (s, cis-CO), 220.8 (s, trans-CO), 142.8 (s, ipso-C of C6H5),
131.4 (s, m-C of C6H5), 130.2 (s, p-C of C6H5), 129.4 (s, o-C of C6H5)
C 52.7 (52.7), H 3.45 (3.1), Cr 7.9 (8.15)
IRc (CsI): 2024m, 1923s, 1908vs, 1894s, 733m, 496m
Mass (FABϩ): m/z 639, [M ϩ H]ϩ; 526, [M Ϫ 4CO]ϩ; 229, [Ph2As]ϩ
(base peak); 227, [C12H8As]ϩ
2 [Mo(CO)4(Ph2AsOAsPh2)2]
white
1H: 7.39 (m, C6H5)
13C: 146.7 (s, ipso-C of C6H5), 144.8 (s, ipso-C of C6H5), 143.8 (s, ipso-C
of C6H5), 141.3 (s, ipso-C of C6H5), 131.8–128.6 (12 sets of resonances
corresponding to aromatic carbons)
C 53.95 (54.0), H 3.63 (3.5)
IR (CsI): 2022m, 1933s, 1910vs, 1898s, 754m, 739m, 579m, 534m
Mass (FABϩ): m/z 1128, [M Ϫ CO]ϩ; 1100, [M Ϫ 2CO]ϩ; 684,
[M Ϫ (Ph2As)2O]ϩ; 372, [M Ϫ 4CO Ϫ (Ph2As)2O]ϩ; 229, [Ph2As]ϩ
(base peak); 227, [C12H8As]ϩ
3 [Cr(CO)4(Ph2As)2S]
orange
C 51.3 (51.4), H 3.4 (3.1), As 23.4 (22.9), S 4.5 (4.9)
IR (CsI): 2015m, 1977s, 1929s, 1905vs
Mass (FABϩ): m/z 654, [M]ϩ; 542, [M Ϫ 4CO]ϩ (base peak); 229,
[Ph2As]ϩ; 227, [C12H8As]ϩ
4 [Mo(CO)4(Ph2AsSAsPh2)2]
light yellow
C 52.3 (52.55), H 3.6 (3.4), As 26.4 (25.2), S 5.2 (5.4)
IR (CsI): 2028m, 1924 (sh), 1916vs, 1883s
Mass (FABϩ): m/z 1188, [M]ϩ; 588, [M Ϫ 4CO Ϫ (Ph2As)2S]ϩ; 229,
[Ph2As]ϩ; 227, [C12H8As]ϩ; 107, [AsS] (base peak)
5 [Cr(CO)5(Ph2AsOAsPh2)]
orange
C 52.8 (52.3), H 3.2 (3.0)
IR (CsI): 2066w, 2017m, 1947 (sh), 1924s, 1907vs, 739m, 526w
Mass (FABϩ): m/z 666, [M]ϩ; 638, [M Ϫ CO]ϩ; 582, [M Ϫ 3CO]ϩ; 526,
[M Ϫ 5CO]ϩ (base peak); 229, [Ph2As]ϩ; 227, [C12H8As]ϩ
6 [Cr(CO)5(Ph2AsSAsPh2)]
orange
C 51.5 (51.05), H 3.3 (2.95)
1H: 7.64 (m, 4H, o-H of C6H5), 7.47 (m, 6H, m-H and p-H of C6H5),
7.52 (m, 4H, o-H of C6H5), 7.49 (m, 6H, m-H and p-H of C6H5)
13C: 226.7 (s, cis-CO), 221.3 (s, trans-CO), 141.9 (s, ipso-C of C6H5),
139.8 (s, ipso-C of C6H5), 132.8 (s, m-C of C6H5), 131.1 (s, m-C of
C6H5), 130.8 (s, p-C of C6H5), 129.9 (s, p-C of C6H5), 129.4 (s, o-C of
C6H5), 128.9 (s, o-C of C6H5)
1H: 7.67 (m, 8H, o-H of C6H5), 7.49 (m, 12H, m-H and p-H of C6H5),
7.53 (m, 8H, o-H of C6H5), 7.31 (m, 12H, m-H and p-H of C6H5)
13C: 141.9 (s, ipso-C of C6H5), 139.5 (s, ipso-C of C6H5), 132.9 (s, m-C
of C6H5), 131.3 (s, m-C of C6H5), 130.9 (s, p-C of C6H5), 129.7 (s, o-C of
C6H5), 129.4 (s, p-C of C6H5), 128.9 (s, o-C of C6H5)
1H: 7.44 (m, 20H, C6H5)
13C: 224.5 (s, cis-CO), 199.1 (s, trans-CO), 148.0 (s, ipso-C of C6H5),
143.0 (s, ipso-C of C6H5), 132.2 (s, m-C of C6H5), 132.1 (s, m-C of
C6H5), 130.5 (s, p-C of C6H5), 130.1 (s, p-C of C6H5), 130.0 (s, o-C of
C6H5), 130.0 (s, o-C of C6H5)
1H: 7.59 (m, 4H, o-H of C6H5), 7.35 (m, 6H, m-H and p-H of C6H5)
13C: 222.5 (s, cis-CO), 216.2 (s, trans-CO), 141.9 (s, ipso-C of C6H5),
140.2 (s, ipso-C of C6H5), 138.9 (s, ipso-C of C6H5), 133.1 (s, m-C of
C6H5), 132.9 (s, m-C of C6H5), 131.8 (s, m-C of C6H5), 130.9 (s, p-C
of C6H5), 129.6 (s, p-C of C6H5), 129.4 (s, p-C of C6H5), 129.3 (s, o-C of
C6H5), 129.0 (s, o-C of C6H5), 128.9 (s, o-C of C6H5)
IR (CsI): 2063m, 1990m, 1950s, 1923vs, 1919vs
Mass (FAB)ϩ: m/z 682, [M]ϩ; 654, [M Ϫ CO]ϩ; 542, [M Ϫ 4CO]ϩ
(base peak); 229, [Ph2As]ϩ; 227, [C12H8As]ϩ
6,17
Ph2AsOAsPh2
1H: 7.52 (m, 8H, o-H of C6H5), 7.34 (m, 12H, m-H and p-H of C6H5)
13C: 146.7 (s, ipso-C of C6H5), 131.1 (s, m-C of C6H5), 129.6 (s, p-C of
C6H5), 128.7 (s, o-C of C6H5)
17
Ph2AsSAsPh2
1H: 7.56 (m, 8H, o-H of C6H5), 7.35 (m, 12H, m-H and p-H of C6H5)
13C: 143.3 (s, ipso-C of C6H5), 134.1 (s, m-C of C6H5), 130.5 (s, p-C of
C6H5), 130.1 (s, o-C of C6H5)
a Analytical data given as found (calculated) in %. b NMR data (CD2Cl2, 298 K) given as chemical shift (multiplicity, relative intensity, assignment).
c IR spectra recorded in CsI in the region of the spectra between 4000 and 400 cmϪ1; only the most significant signals are reported (cmϪ1).
Fig. 4 ORTEP diagram of the molecular structure of [Mo(CO)4-
Fig. 3 ORTEP diagram of the molecular structure of [Cr(CO)4{(Ph2-
{(Ph2As)2S}2] 4. The asymmetric unit consists of half the molecule
As)2S}] 3. Only one molecule from the asymmetric unit is shown.
shown.
In complexes 1–5 the Cr–C bonds situated trans to arsenic
are shorter than those cis, as shown in Table 2, and the related
C–O bonds are somewhat longer in the trans carbonyl groups
than the cis ones. These data imply that the Ph2AsXAsPh2 lig-
ands are weaker π acceptors than CO. A similar feature was
reported for the phosphorus analogues [Cr(CO)4(Ph2POPPh2)]
and [Mo(CO)4(Ph2POPPh2)] in earlier studies.4 The Cr–Ctrans
bond lengths in compounds 1 and 3 are almost equivalent and
show that changing the chalcogen in the As–X–As bridge does
not significantly affect back donation.
J. Chem. Soc., Dalton Trans., 2000, 3347–3355
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The As–S–As angles found for the two molecules of the
asymmetric unit of complex 3 are 83.44(5) and 84.06(6)Њ,
31
smaller than in free Ph2AsSAsPh2
(97.21(13)Њ) and
bis(phenoxarsin-10-yl)sulfide32 (99.87(6)Њ). The As–S–As
angle found for the two ligand units monodentate in 4 are of
106.25(5) and 106.16(5)Њ, somewhat larger than in 3 or in free
Ph2AsSAsPh2.31
The ligand conformation changes noticeably upon co-
ordination, in either a mono- or bi-dentate mode. The As–X–
As angle increases from that observed in the “free” ligand in the
case of monodentate co-ordination and decreases when these
ligands are in a bidentate chelate. This contraction is expected
for bidentate chelates which form strained four-membered
rings, whereas monodentate co-ordination induces no steric
strain. Rather the change in angle reflects the new electron
distribution within the ligand.
Such changes in unstrained ligands have previously been
attributed to a pπ–dπ bonding between a chalcogen lone pair
and vacant arsenic 4d orbital.20 In many compounds of the type
O(MRn)2, where M belongs to the p block and n = 1–3, M–O–
M angles are larger than predicted by VSEPR theory and com-
pounds containing linear oxygen between two metal centres are
common.34 An alternative explanation was sought from the
Second-Order Jahn–Teller (SOJT) effect where a linear AX2
species containing one or two pairs of non-bonding electrons
localised in A will be unstable to bending, resulting in an
asymmetric bent conformation.35–37 The structure of free
Ph2AsOAsPh2 was represented so far by the resonance
structures below which show donation of electron density from
chalcogen to As with the corresponding increase in As–X bond
order and greater approach of the As–X–As unit to linearity.38
Fig. 5 ORTEP diagram of the molecular structure of [Cr(CO)5{(Ph2-
As)2O}] 5.
This depiction is not supported by the newly determined
structure of Ph2AsOAsPh2. The As–O separations of 1.809(3)
and 1.814(3) Å are comparable with the corresponding bond
39
lengths found in (C6F5)2AsOAs(C6F5)2 (of 1.792(3) Å), and
Fig. 6 ORTEP diagram of the molecular structure of Ph2AsOAsPh2.
with the As–O single bond separation found in Ph2As(O)OH40
(of 1.724(3) Å). These values are larger than the ones determined
for the As–O separation in an earlier work20 (i.e. mean As–O
of 1.67 Å). This suggests an arsenic–oxygen bond order no
greater than one. Also, the As–O–As angle of 115.98(17)Њ
determined by us for the structure of this ligand is comparable
with the one determined in (C6F5)2AsOAs(C6F5)2 of 116.3(2)Њ
and much smaller than the previously determined value,
i.e. 137(1)Њ.20
The newly determined molecular parameters of Ph2-
AsOAsPh2 are consistent with the ones predicted by calcu-
lations at the DFT level and do not favour the possible
explanation offered by pπ–dπ or SOJT theory for an unusually
large As–O–As.
The two As–O bond lengths are not equal in the mono-
dentate complexes 2 and 5, a minimal difference is observed in
the bidentate ligand in 1 where the As–O bond lengths are close
to those found in [Co3(CO)7(µ-CCl){µ-Ph2AsOAsPh2}]16
(of 1.921(7) and 1.886(6) Å), [Co3(CO)7(µ-CMe){µ-Ph2-
AsOAsPh2}]16 (of 1.808(3) and 1.802(3) Å) and [Co2(CO)4-
(µ-PhCCH){µ-Ph2AsOAsPh2}]16 (of 1.806(3) and 1.791(3) Å).
The As–S bond lengths in the chelate complex 3 and the co-
ordinated As–S distances in 4 are similar to the corresponding
bond lengths in [(Me3PtBr)2({µ-(Me2AsSAsMe2)}]14 (2.223(7)
and 2.232(7) Å). The non-co-ordinated As–S distances in 4
31
more closely match those in free Ph2AsSAsPh2 (of 2.257(3)
and 2.43(3) Å), and in bis(phenoxarsin-10-yl)sulfide32 (of
2.266(3) and 2.282(3) Å).
The variety of As–O–As angles observed in all the studied
examples suggests a very flexible nature of this linkage, and
domination of packing forces in angle determination.
The As–O–As angle (115.98(17)Њ in the redetermined struc-
ture of the “free” ligand) increases upon monodentate co-
ordination to the metal centre in complex 2 (122.2(1)Њ and
121.73(9)Њ) or 5 (122.44(7)Њ). These values are similar to that
reported for the free bis(phenoxarsin-10-yl)oxide (of 122.3(1)Њ33)
and larger than the ones determined in [Co3(CO)7(µ-CMe)-
{µ-Ph2AsOAsPh2}]16 (of 114.4(1)Њ), [Co2(CO)4(µ-PhCCH)-
{µ-Ph2AsOAsPh2}]16 (of 118.4(2)Њ), and [Co3(CO)7(µ-CCl)-
{µ-Ph2AsOAsPh2}]16 (of 108.8(4)Њ), with bidentate-bridging
co-ordination of Ph2AsOAsPh2 ligand to two Co. The form-
ation of a four-membered ring in 1 leads to an As–O–As angle
of only 99.79(8)Њ.
(iv) DFT calculations
Density functional calculations were carried out in order to
investigate possible electronic reasons for the relative stability
of monodentate versus bidentate co-ordination. Phenyl groups
were substituted by hydrogen atoms to reduce computational
time. Geometry optimisations were initially carried out for
H2AsXAsH2 (X = O or S), [M(CO)4(H2AsXAsH2)] (M = Cr or
Mo; X = O or S) and [M(CO)4(H2AsXAsH2)2] (M = Cr or Mo;
X = O or S).
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a
Table 2 Selected molecular parameters (distances in Å, angles in Њ) of compounds 1–5 and Ph2AsOAsPh2
1 [Cr(CO)4(Ph2AsOAsPh2)] Molecule 2 (continued )
As1–Cr1
As1–O1
As2–Cr1
As2–O1
As1–C10
As1–C20
As2–C30
As2–C40
2.4441(4)
1.8211(15)
2.4262(4)
1.8081(15)
1.934(2)
1.927(2)
1.936(2)
Cr1–C1
Cr1–C2
Cr1–C3
Cr1–C4
O2–C1
O3–C2
O4–C3
O5–C4
1.903(2)
1.900(2)
1.857(2)
1.863(2)
1.137(3)
1.144(3)
1.157(3)
1.149(3)
Cr2–As3–C51
S2–As3–C51
Cr2–As3–C61
S2–As3–C61
Cr2–As4–S2
As3–Cr2–As4
As3–Cr2–C5
As4–Cr2–C5
As3–Cr2–C6
As4–Cr2–C6
122.79(19)
As4–Cr2–C7
As3–Cr2–C8
As4–Cr2–C8
C5–Cr2–C8
C6–Cr2–C8
C7–Cr2–C8
Cr2–C5–O5
Cr2–C6–O6
Cr2–C7–O7
Cr2–C8–O8
86.60(19)
97.3(2)
170.5(3)
94.0(3)
88.1(3)
87.3(3)
178.3(6)
174.3(7)
176.4(7)
177.9(8)
103.27(19)
123.9(2)
102.5(2)
99.12(5)
75.67(3)
168.7(2)
93.2(2)
1.928(2)
92.6(2)
98.5(2)
As1–O1–As2
Cr1–As1–O1
Cr1–As2–O1
As1–Cr1–As2
As1–Cr1–C1
As2–Cr1–C1
As1–Cr1–C2
As2–Cr1–C2
99.79(8)
94.88(5)
95.83(5)
69.495(12)
90.94(7)
91.25(7)
91.38(7)
91.56(7)
As1–Cr1–C3
As2–Cr1–C3
As1–Cr1–C4
As2–Cr1–C4
Cr1–C1–O2
Cr1–C2–O3
Cr1–C3–O4
Cr1–C4–O5
165.58(7)
96.38(7)
100.70(7)
170.08(7)
176.7(2)
176.2(2)
177.3(2)
177.4(3)
4 [Mo(CO)4(Ph2AsSAsPh2)2]
Mo1–As1
Mo1–As3
Mo1–C1
Mo1–C2
Mo1–C3
Mo1–C4
As1–S1
As1–C11
As1–C21
As2–S1
2.6037(7)
2.6030(5)
2.045(5)
1.980(5)
1.992(7)
2.042(5)
2.2258(11)
1.940(5)
1.955(4)
2.2703(12)
1.972(4)
As2–C41
As3–S2
As3–C51
As3–C61
As4–S2
As4–C71
As4–C81
O1–C1
1.957(5)
2.2267(12)
1.941(5)
1.946(5)
2.272(1)
1.965(5)
1.977(5)
1.136(6)
1.146(6)
1.14(1)
2 [Mo(CO)4(Ph2AsOAsPh2)2]
As1–Mo1
As1–O1
As2–O1
As3–Mo1
As3–O2
As4–O2
Mo1–C1
Mo1–C2
Mo1–C3
Mo1–C4
O3–C1
2.6080(3)
1.7952(17)
1.8098(18)
2.6048(3)
1.7886(17)
1.8155(17)
2.042(3)
1.996(3)
1.984(3)
2.047(3)
1.147(3)
O4–C2
O5–C3
O6–C4
1.143(3)
1.149(3)
1.142(3)
1.934(2)
1.945(2)
1.966(2)
1.951(3)
1.941(2)
1.957(2)
1.955(2)
1.947(3)
O2–C2
O3–C3
O4–C4
As1–C10
As1–C20
As2–C30
As2–C40
As3–C50
As3–C60
As4–C70
As4–C80
As2–C31
1.144(6)
As1–Mo1–As3
As1–Mo1–C1
As3–Mo1–C1
As1–Mo1–C2
As3–Mo1–C2
C1–Mo1–C2
As1–Mo1–C3
As3–Mo1–C3
C1–Mo1–C3
C2–Mo1–C3
As1–Mo1–C4
As3–Mo1–C4
C1–Mo1–C4
C2–Mo1–C4
C3–Mo1–C4
Mo1–As1–S1
Mo1–As1–C11
S1–As1–C11
Mo1–As1–C21
S1–As1–C21
93.059(18)
91.16(16)
88.92(13)
89.1(3)
177.2(2)
89.3(2)
176.76(19)
89.3(2)
91.1(2)
C11–As1–C21
S1–As2–C31
S1–As2–C41
C31–As2–C41
Mo1–As3–S2
Mo1–As3–C51
S2–As3–C51
Mo1–As3–C61
S2–As3–C61
C51–As3–C61
S2–As4–C71
S2–As4–C81
C71–As4–C81
As1–S1–As2
As3–S2–As4
Mo1–C1–O1
Mo1–C2–O2
Mo1–C3–O3
Mo1–C4–O4
102.7(2)
92.76(15)
101.69(16)
97.26(19)
108.06(3)
117.32(16)
101.55(16)
118.29(13)
107.47(16)
102.6(2)
102.04(13)
92.20(12)
97.5(2)
106.25(5)
106.16(5)
177.1(5)
As1–O1–As2
As3–O2–As4
Mo1–As1–O1
Mo1–As3–O2
As1–Mo1–As3
As1–Mo1–C1
As3–Mo1–C1
As1–Mo1–C2
As3–Mo1–C2
122.2(1)
121.73(9)
120.82(6)
120.68(5)
93.182(9)
95.45(7)
85.58(8)
87.51(8)
174.69(8)
As1–Mo1–C3
As3–Mo1–C3
As1–Mo1–C4
As3–Mo1–C4
Mo1–C1–O3
Mo1–C2–O4
Mo1–C3–O5
Mo1–C4–O6
176.07(8)
88.39(8)
90.61(7)
98.69(7)
175.0(2)
179.0(2)
178.5(3)
172.3(2)
88.6(3)
88.99(15)
91.58(12)
179.47(17)
90.14(19)
88.7(2)
108.06(4)
118.37(15)
107.41(14)
117.04(17)
101.70(13)
175.9(7)
177.6(7)
178.4(5)
3 [Cr(CO)4(Ph2AsSAsPh2)]
Molecule 1
As1–Cr1
As1–S1
As2–Cr1
As2–S1
As1–C11
As1–C21
As2–C31
As2–C41
2.4629(9)
2.2647(15)
2.439(1)
2.2440(14)
1.946(5)
1.945(5)
1.934(5)
1.947(5)
Cr1–C1
Cr1–C2
Cr1–C3
Cr1–C4
O1–C1
O2–C2
O3–C3
O4–C4
1.862(6)
1.893(6)
1.894(7)
1.855(5)
1.133(7)
1.138(7)
1.146(7)
1.143(7)
5 [Cr(CO)5(Ph2AsOAsPh2)]
As1–Cr1
As1–O6
As2–O6
As1–C11
As1–C21
As2–C31
As2–C41
Cr1–C1
Cr1–C2
2.4309(3)
1.7787(13)
1.8380(13)
1.9409(19)
1.9421(19)
1.955(2)
1.949(2)
1.869(2)
1.899(2)
Cr1–C3
Cr1–C4
Cr1–C5
O1–C1
O2–C2
O3–C3
O4–C4
O5–C5
1.907(2)
1.903(2)
1.912(2)
1.147(2)
1.145(2)
1.141(2)
1.142(3)
1.139(3)
As1–S1–As2
Cr1–As1–S1
Cr1–As2–S1
As1–Cr1–As2
As1–Cr1–C1
As2–Cr1–C1
As1–Cr1–C2
As2–Cr1–C2
83.44(5)
98.98(4)
100.28(4)
75.49(3)
98.53(19)
173.23(19)
93.04(17)
88.01(18)
As1–Cr1–C3
As2–Cr1–C3
As1–Cr1–C4
As2–Cr1–C4
Cr1–C1–O1
Cr1–C2–O2
Cr1–C3–O3
Cr1–C4–O4
90.19(17)
93.68(18)
169.0(2)
93.6(2)
178.3(6)
176.5(5)
176.9(5)
178.8(6)
As1–O6–As2
Cr1–As1–O6
As1–Cr1–C1
As1–Cr1–C2
As1–Cr1–C3
As1–Cr1–C4
122.44(7)
107.92(4)
178.44(6)
90.18(5)
92.03(6)
92.47(6)
As1–Cr1–C5
Cr1–C1–O1
Cr1–C2–O2
Cr1–C3–O3
Cr1–C4–O4
Cr1–C5–O5
85.13(6)
178.51(17)
177.07(16)
176.58(16)
177.27(17)
179.28(18)
Molecule 2
As3–Cr2
As3–S2
As3–C51
As3–C61
As4–Cr2
As4–S2
2.4648(12)
2.2495(17)
1.938(6)
1.945(7)
2.448(1)
2.2512(19)
1.943(6)
1.941(6)
Cr2–C5
Cr2–C6
Cr2–C7
Cr2–C8
O5–C5
O6–C6
O7–C7
O8–C8
1.847(7)
1.902(7)
1.868(6)
1.841(7)
1.139(8)
1.145(8)
1.144(8)
1.157(8)
Ph2AsOAsPh2
As1–O2
O2–As3
As1–C16
1.809(3)
1.814(3)
1.969(4)
As1–C22
As3–C4
As3–C10
1.966(5)
1.966(4)
1.958(5)
As4–C71
As4–C81
As1–O2–As3
O2–As1–C16
O2–As1–C22
C16–As1–C22
115.98(17)
99.83(16)
94.06(17)
97.13(18)
O2–As3–C4
O2–As3–C10
C4–As3–C10
96.02(16)
96.84(16)
98.27(17)
As3–S2–As4
Cr2–As3–S2
84.06(6)
98.66(5)
C5–Cr2–C6
As3–Cr2–C7
86.9(3)
92.0(2)
a Numbers in parentheses are estimated standard deviations of the last significant figure. Atoms are labelled as indicated in Figs. 1–6.
J. Chem. Soc., Dalton Trans., 2000, 3347–3355
3351

View Article Online
The results for H2AsXAsH2 (X = O or S) are given in Table 3.
In the case of H2AsOAsH2 there was a large discrepancy
between the calculated As–O–As angle of 112Њ and that pub-
lished for Ph2AsOAsPh2 of 137 1Њ.20 The calculation was
repeated with a variety of functionals and basis sets but the
angle at O was always predicted to be between 111 and 120Њ.
In case the phenyl groups made a substantial difference to
this angle a geometry optimisation was carried out for Ph2-
AsOAsPh2. The results are given in Table 3. The introduction
of the phenyl groups was found to make very little difference
to either the As–O distance or the As–O–As bond angle. The
crystal structure of Ph2AsOAsPh2 was therefore redetermined
and the experimental results were in accord with the calcu-
lations. As determination of the structure of Ph2AsSAsPh2 had
failed to proceed to a full refinement31 the structure of Ph2-
AsSAsPh2 was also calculated in order to seek confirmation of
the values obtained by partial refinement of the X-ray data for
the “free” ligand. These values are also given in Table 3.
The results of the geometry optimisations on the complexes
are given in Table 4 together with experimental values for com-
parative purposes. Reasonable agreement in the case of the
bidentate chromium compounds with both O and S confirms
that the model works well for these complexes in spite of the
absence of phenyl groups. In these compounds the angle at X
(O or S) is doubtless constrained by the four membered ring. In
the case of the bidentate molybdenum complexes where com-
parison with the crystal structures is also possible the biggest
deviation between model and experiment is also found in the
As–X–As angle, the crystal structures showing a larger angle
than the optimised models. In the case of the model mono-
dentate compounds the angles at both O and S lie very close to
those calculated for the “free” ligands. This strongly suggests
to us that the factors controlling the change in this angle on
co-ordination commented on above are steric not electronic.
Table 5 gives the energy of formation of the bis-monodentate
complexes from the bidentate complex and the “free” ligand for
M = Cr or Mo and X = O or S. These energies would of course
model best the internal energy change in a gas phase reaction.
In all cases the bis-monodentate complexes are found to be
more stable. The absolute value of the energy difference is such
that entropy effects could favour co-ordination in the chelate
mode as is found for Cr. The most striking result is the similar-
ity of the energies for Cr and Mo both with O and S as the
bridging ligand. This result suggests that there is no electronic
reason for the chelate binding with Cr and the monodentate co-
ordination with Mo. The explanation must be sought elsewhere.
Table 6 shows the charges calculated for the chelated com-
pounds using both Mulliken and Voronoi charge partitioning.
Though the values of the charges differ between the two
methods the trends on chemical substitution are the same. Mo
is more positively charged than Cr, and the charge carried is
insensitive to whether the ligand contains O or S. O is more
negatively charged than S and the charge carried by O or S is
insensitive to the nature of the metal. The charge carried by the
intervening As atoms depends both on M and X. It is most
positive for Cr and O and least positive for Mo and S. The As
atoms appear to play the role of a charge buffer in the complex.
Changing X has about twice the effect of changing M. The C
atoms of the CO groups also show a buffering effect. They are
less positively (or more negatively) charged for the molybdenum
than the chromium complexes consistent with greater back
donation to CO in the former cases. The charge of C is
independent of the nature of X.
Conclusion
A series of Group 6 carbonyl complexes with Ph2AsXAsPh2
(X = O or S) ligands in mono- and bi-dentate co-ordination
modes have been synthesized. In general, the complexes are
Table 3 Selected calculated and experimental distances and angles for
R2AsXAsR2
Table 5 Estimated energy difference between monodentate and biden-
tate binding. [M(CO)4(H2AsXAsH2)] ϩ H2AsXAsH2 → [M(CO)4-
(H2AsXAsH2)2]
X–As/Å
As–X–As/Њ
M
X
∆E/kJ molϪ1
X = O, R = H calc.
X = O, R = Ph calc.
exp.
X = S, R = H calc.
X = S, R = Ph calc.
exp.
1.82
1.83
112
111
115.98(17)
95
97
1.809(3), 1.814(3)
2.26
2.31
Cr
Cr
Mo
Mo
O
S
O
S
Ϫ45
Ϫ25
Ϫ45
Ϫ24
2.257(3), 2.243(3)
97.21(13)
Table 4 Selected distances (Å) and angles (Њ) calculated for [M(CO)4{(R2As)2X}n]; (R = H). Where available the X-ray values for R = Ph are
included in parentheses
n = 1
M–As
As–X
As–M–As
As–X–As
M = Cr, X = O
M = Cr, X = S
M = Mo, X = O
M = Mo, X = S
2.36 (2.43)
2.38 (2.44)
2.53
1.83 (1.82)
2.26 (2.26)
1.83
71 (69)
77 (75)
67
97 (100)
82 (83)
99
2.54
2.27
74
85
n = 2
M–As(1)
M–As(2)
As(1)–X(1)
As(2)–X(2)
As(3)–X(1)
As(4)–X(2)
As–X(1)–As
As–X(2)–As
M = Cr, X = O
M = Cr, X = S
M = Mo, X = O
M = Mo, X = S
2.33
2.35
2.50 (2.61)
2.52 (2.60)
2.34
2.36
2.52 (2.61)
2.53 (2.60)
1.80
2.27
1.80 (1.80)
2.26 (2.26)
1.80
2.24
1.79 (1.79)
2.24 (2.23)
1.83
2.27
1.83 (1.81)
2.27 (2.27)
1.82
2.26
1.83 (1.82)
2.26 (2.27)
91
93
113
95
113
97
113 (122)
96 (106)
90 (93) 113 (122)
92 (93) 96 (106)
3352
J. Chem. Soc., Dalton Trans., 2000, 3347–3355

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Table 6 Mulliken and Voronoi charges calculated for [M(CO)4(H2AsXAsH2)], where M = Cr or Mo and X = O or S
M, X
Method
M
As
X
C1
O1
C2
O2
Cr, O
Cr, S
Mulliken
Voronoi
Mulliken
Voronoi
Mulliken
Voronoi
Mulliken
Voronoi
Ϫ0.62
0.79
Ϫ0.62
0.79
Ϫ0.04
1.51
Ϫ0.05
1.52
0.93
1.78
0.75
1.54
0.84
1.69
0.65
1.44
Ϫ0.72
Ϫ0.68
Ϫ0.37
Ϫ0.06
Ϫ0.71
Ϫ0.68
Ϫ0.35
Ϫ0.05
0.38
Ϫ0.12
0.39
Ϫ0.12
0.28
Ϫ0.25
0.27
Ϫ0.25
Ϫ0.37
Ϫ0.14
Ϫ0.37
Ϫ0.14
Ϫ0.36
Ϫ0.13
Ϫ0.35
Ϫ0.13
0.39
Ϫ0.09
0.39
Ϫ0.09
0.29
Ϫ0.23
0.29
Ϫ0.23
Ϫ0.37
Ϫ0.14
Ϫ0.38
Ϫ0.14
Ϫ0.37
Ϫ0.13
Ϫ0.37
Ϫ0.13
Mo, O
Mo, S
quite similar to their phosphorus analogues with regard to their
physical properties and spectroscopic characterisation. In con-
trast to the phosphorus systems, we were unable to synthesize
molybdenum tetracarbonyl bidentate chelate complexes. DFT
calculations suggested that such compounds may be thermo-
dynamically stable, though no synthetic route has been found.
Redetermination of the crystal structure of Ph2AsOAsPh2
established that there was no unusual change in bond angle
at the ligand O atom on monodentate co-ordination, thus no
special bonding interactions are indicated.
CH2Cl2 and pentane. Cooling to Ϫ20 ЊC gave orange block-
shaped crystals of complex 3 with mp 112 ЊC (300 mg, 60%
yield).
[Mo(CO)4(Ph2AsSAsPh2)2] 4. A solution of [Mo(CO)4(nbd)]
(100 mg, 0.33 mmol) in 50 mL pentane was treated with Ph2As-
SAsPh2 (164 mg, 0.33 mmol) dissolved in 50 mL pentane. A
light yellow precipitate occurred after stirring for 1 h at room
temperature. After removal of solvent the resultant solid was
dried in vacuo and washed with pentane. Recrystallisation from
a 1:4 mixture of CH2Cl2 and pentane at Ϫ20 ЊC gave pale
yellow crystals of complex 4, mp 115 ЊC (89.5 mg, yield 45%).
Experimental
Fourier-transform 1H NMR spectra were recorded on a Bruker
[Cr(CO)5(Ph2AsOAsPh2)] 5. A suspension of [Cr(CO)6] (100
mg, 0.45 mmol) in THF (50 mL) was irradiated with a broad
band UV lamp for 5 h at room temperature under N2.
Ph2AsOAsPh2 (215.5 mg, 0.45 mmol) was added and the
mixture stirred for 24 h at room temperature. Volatiles were
removed in vacuo and traces of [Cr(CO)6] were removed by
sublimation. The residual solid was washed with pentane.
Recrystallisation from a 1:4 mixture of CH2Cl2 and pentane at
Ϫ20 ЊC gave bright yellow crystals of complex 5, mp 80 ЊC (151
mg, yield 49%).
AM 300 spectrometer at 300 MHz and 13C-{H} NMR spectra
1
on a Varian Unity plus 500 spectrometer at 125 MHz. H and
13C shifts are reported with respect to δ 0.0 for SiMe4. Infrared
spectra were recorded in CsI between 4000 and 400 cmϪ1 on a
Perkin-Elmer FT-IR spectrometer. Microanalyses were per-
formed by the microanalytical laboratory of the Inorganic
Chemistry Laboratory, University of Oxford and FABϩ mass
spectra by the EPSRC National Mass Spectrometry Service
Centre, University of Wales, Swansea, UK. All reactions
were carried out under N2 using standard Schlenk techniques.
Solvents were dried over suitable reagents and freshly distilled
under N2 before use.
[Cr(CO)5(Ph2AsSAsPh2)] 6. A suspension of [Cr(CO)6] (160
mg, 0.72 mmol) in THF (50 mL) was irradiated with a broad
band UV lamp for 5 h at room temperature under N2.
Ph2AsSAsPh2 (356.4 mg, 0.72 mmol) was added and the
mixture stirred for 24 h at room temperature. After filtration
the solution was stored at Ϫ20 ЊC overnight and orange crystals
of complex 6 mp 122 ЊC, precipitated in an almost quantitative
yield.
The compounds [Mo(CO)4(nbd)],21 [Cr(CO)4(nbd)],21 Ph2-
7,8
AsOAsPh2,6 and Ph2AsSAsPh2 were prepared as previously
described. Preparation of [Cr(CO)4(Ph2AsOAsPh2)] and
[Cr(CO)4(Ph2AsSAsPh2)] has previously been reported13 and
here we present a modified synthetic route for isolating these
compounds.
Preparations
Crystal structure determination
[Cr(CO)4(Ph2AsOAsPh2)] 1. A portion of [Cr(CO)4(nbd)]
(500 mg, 1.95 mmol) in 100 mL of benzene was treated with
Ph2AsOAsPh2 (920 mg, 1.95 mmol). After stirring for 12 h the
volatiles were removed in vacuo. The orange solid (920 mg,
crude yield 74%) was washed with pentane and crystals with
mp 125 ЊC appeared from a 1:4 mixture of diethyl ether and
pentane after storing at Ϫ20 ЊC.
Crystals of compound 1 were grown from a mixture of Et2O
and pentane (1:4) at Ϫ20 ЊC, those of 2, 3, 4 and 5 from (1:4)
CH2Cl2 and pentane at 0 ЊC and isolated by filtration. Crystals
of ligand Ph2AsOAsPh2 were grown from slow diffusion of
pentane into a concentated solution of ligand in benzene at
room temperature, under N2. Attempts to crystallise this ligand
under air lead to the isolation of two different forms of arsinic
acid Ph2As(O)OH40 and [Ph2As(O)OH]2,41 with known crystal
structures. In all cases, a specimen crystal was selected under an
inert atmosphere, covered with paratone-N oil, and mounted
on the end of a glass fibre. Crystal data are summarised in
Table 7.
[Mo(CO)4(Ph2AsOAsPh2)2] 2. The compound [Mo(CO)4-
(nbd)] (250 mg, 0.84 mmol) and Ph2AsOAsPh2 (400 mg, 0.84
mmol) were stirred together in 50 mL pentane for 3 h at room
temperature. The white precipitate formed was filtered off,
washed with pentane and recrystallised from a 1:4 mixture of
CH2Cl2 and pentane to give white crystals of 2 with mp 114 ЊC
(150 mg, yield 43%) after storing at Ϫ20 ЊC. Repeating this
experiment with a 1:2 ratio of reagents resulted in the same
product [Mo(CO)4(Ph2AsOAsPh2)2] (771 mg, yield 80%).
Data collection and processing. Data were collected on
an Enraf-Nonius DIP2000 image plate diffractometer with
graphite monochromated Mo-Kα radiation (λ = 0.71069 Å).
The images were processed with the DENZO and SCALE-
PACK programs.42 Corrections for Lorentz and polarisation
effects were performed.
[Cr(CO)4(Ph2AsSAsPh2)] 3. A mixture of [Cr(CO)4(nbd)]
(200 mg, 0.78 mmol) and Ph2AsSAsPh2 (383 mg, 0.78 mmol) in
100 mL benzene was stirred for 12 h. The volatiles
were removed in vacuo and the residual solid was purified by
washing with pentane and recrystallised from a mixture of
Structure solution and refinement. All solution, refinement,
and graphical calculations were performed using the CRYS-
TALS43 and CAMERON44 software packages. The crystal
J. Chem. Soc., Dalton Trans., 2000, 3347–3355
3353

View Article Online
Table 7 Crystallographic data for compounds 1–5 and Ph2AsOAsPh2
[Cr(CO)4(Ph2-
AsOAsPh2)] 1
[Mo(CO)4(Ph2-
AsOAsPh2)2] 2
[Cr(CO)4(Ph2-
AsSAsPh2)] 3
[Mo(CO)4(Ph2-
AsSAsPh2)2] 4
[Cr(CO)5(Ph2-
AsOAsPh2)] 5
Ph2AsOAsPh2
Formula
M
C28H20As2CrO5
638.30
C52H40As4MoO6
1156.52
C28H20As2CrO4S
1308.73
C26H20As2Mo0.5O2S6
C29H20As2CrO6
666.31
C24H20As2O
474.27
Crystal system
Space group
Triclinic
P1
Triclinic
P1
Triclinic
P1
Monoclinic
C2/c
Monoclinic
P21/c
Monoclinic
P21/n
¯
¯
¯
a/Å
b/Å
c/Å
α/Њ
9.939(2)
11.591(5)
13.010(5)
106.770(2)
95.13(2)
112.79(2)
1288.2
150
10.831(4)
13.264(4)
17.913(6)
86.080(2)
87.157(2)
65.773(2)
2340.6
125
10.790(6)
13.288(7)
19.381(6)
79.572(3)
85.858(3)
82.035(3)
2766.1
298
10.456(2)
26.817(5)
17.543(4)
10.6640(3)
9.160(3)
26.2380(5)
11.4240(9)
29.9061(3)
5.8810(4)
β/Њ
96.14(3)
92.816(2)
92.863(3)
γ/Њ
V/Å3
4890.7
150
2687.3
125
2006.7
150
T/K
Z
2
7268
4872
0.034
2
2
8
4
4
Total no. data
No. unique data
13000
9009
0.043
3.12
13010
10569
0.053
2.88
12945
4703
0.038
3.07
18543
5582
0.036
2.89
10812
4079
0.0007
3.34
Rint
µ(Mo-Kα)/mmϪ1
3.01
R
wR
0.0282
0.0327
0.0265
0.0307
0.0444
0.0489
0.0379
0.0373
0.0272
0.0325
0.0563
0.0394
structures were solved by direct methods using the SIR 9245
program and refined by full-matrix least squares procedure on
F. All non-hydrogen atoms were refined with anisotropic dis-
placement parameters. All carbon-bound hydrogen atoms were
generated and allowed to ride on their corresponding carbon
atoms with fixed thermal parameters. An empirical absorption
correction46 was applied.
CCDC reference number 186/2138.
See http://www.rsc.org/suppdata/dt/b0/b005269h/ for crystal-
lographic files in .cif format.
10 H. Vahrenkamp, Chem. Ber., 1972, 105, 3574.
11 E. W. Ainscough, A. M. Brodie and G. Leng-Ward, J. Chem. Soc.,
Dalton Trans., 1974, 2437.
12 H. Beurich and H. Vahrenkamp, Chem. Ber., 1981, 114, 2542.
13 L. Weber and D. Wewers, Organometallics, 1985, 4, 841.
14 E. W. Abel, M. A. Beckett, P. A. Bates and M. B. Hursthouse,
J. Organomet. Chem., 1987, 325, 261.
15 E. W. Abel and M. A. Beckett, Polyhedron, 1987, 6, 1255.
16 N. Choi, C. Conole, J. D. King, M. J. Mays, M. McPartlin
and C. L. Stone, J. Chem. Soc., Dalton Trans., 2000, 395.
17 L. Silaghi-Dumitrescu, M. N. Gibbons, I. Silaghi-Dumitrescu,
J. Zukermann-Schpector, I. Haiduc and D. B. Sowerby,
J. Organomet. Chem., 1996, 517, 101.
18 L. Silaghi-Dumitrescu, S. Pascu, I. Silaghi-Dumitrescu, I. Haiduc,
M. N. Gibbons and D. B. Sowerby, J. Organomet. Chem., 1997, 549,
187.
19 L. Silaghi-Dumitrescu, S. I. Pascu, I. Silaghi-Dumitrescu and
I. Haiduc, Rev. Roum. Chim., 1997, 42, 747.
20 W. R. Cullen and J. Trotter, Can. J. Chem., 1963, 41, 2983.
21 M. A. Bennett, L. Pratt and G. Wilkinson, J. Chem. Soc., 1961,
2037.
22 R. Colton and C. J. Rix, Aust. J. Chem., 1970, 23, 441.
23 R. Colton and C. J. Rix, Aust. J. Chem., 1971, 24, 2461.
24 J. Grobe and D. Le Van, J. Flourine Chem., 1984, 24, 25.
25 E. W. Ainscough, A. M. Brodie and A. R. Furness, J. Chem. Soc.,
Dalton Trans., 1973, 2360.
26 H. C. Boehm, R. Gleiter, J. Grobe and D. Le Van, J. Organomet.
Chem., 1983, 247, 203.
27 G. B. Robertson and P. O. Whimp, Inorg. Chem., 1974, 13,
1047.
Computational details
All calculations were carried out using the Amsterdam
density functional (ADF) program system.47 The electronic
configurations of the molecular systems were described by an
uncontracted triple-ζ basis set of Slater-type orbitals (STOs).
Hydrogen, carbon, oxygen, sulfur and arsenic were given an
extra polarisation function. The cores of the atoms were frozen,
C and O up to 1s, S up to 2p, As up to 3p, Cr up to 2p and Mo
up to 3d. First-order relativistic corrections were made to the
cores of all atoms using the Pauli formalism. Energies were
calculated using Vosko, Wilk and Nusair’s local exchange
correlation potential48 with non-local-exchange corrections by
Becke49 and non-local correlation corrections by Perdew.50,51
The non-local correction terms were not utilised in calculating
gradients during geometry optimisations.
28 C. K. Johnson, ORTEP II, Report ORNL-5138, Oak Ridge
National Laboratory, Oak Ridge, TN, 1976.
29 T. Chivers, K. S. Dhathathreyan, C. Lensink and J. F. Richardson,
Inorg. Chem., 1988, 27, 1570.
Acknowledgements
30 M. G. B. Drew, J. Chem. Soc., Dalton Trans., 1972, 627.
31 S. I. Pascu and L. H. Doerrer, unpublished results. Partially refined
crystal structure of C24H20As2S, M = 490.33, monoclinic, space
group P21/c, a = 5.9470(3), b = 17.0500(12), c = 20.5860(16) Å,
β = 90.741(5)Њ, V = 2087.2 Å3, Z = 4, T = 125 K, µ(Mo-Kα) 3.30
mmϪ1, R = 0.1633, wR = 0.1412. Selected molecular parameters:
As1–S1–As2 97.21(13)Њ; As1–S1 2.257(3), As2–S1 2.243(3), As1–C1
1.950, As1–C11 2.001(12), As2–C21 1.946(12) and As2–C31
1.940(15) Å.
32 W. K. Grindstaff, A. W. Cordes, C. K. Fair, R. W. Perry and L. B.
Handy, Inorg. Chem., 1972, 11, 1852.
33 E. A. Meyers, C. A. Applegate and R. A. Zingaro, Phosphorus,
Sulfur Relat. Elem., 1987, 29, 317.
We thank the University of Oxford for a Georgescu Scholar-
ship (to S. I. P.), St. John’s College Oxford for a Junior Research
Fellowship (L. H. D.) and the EPSRC for support of this work.
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