Mercury halide complexes of tertiary phosphines. Part XVI. Dimer-monomer trend in the 1:1 complexes of mercury(II) halides with bulky tris(2,6-dimethoxyphenyl)phosphine (DMPP)

Article abstract of DOI:10.1016/S0277-5387(00)00451-4

Reactions of HgX₂ (X = Cl, Br, I) with the very bulky tertiary phosphine, tris(2,6-dimethoxyphenyl)phosphine (DMPP), in either a 1:1 or a 1:2 ratio, result in only the isolation of the 1:1 adducts. The structures adopted in the solid state are markedly influenced by the steric requirement of the phosphine. In contrast to the 1:1 triphenylphosphine adducts reported earlier, which are dimeric, the DMPP mercury(II) chloride and bromide complexes are weakly linked dimers while the iodide is the first example of a mercury iodide-phosphine complex with a monomeric distorted trigonal-planar arrangement around mercury. All three complexes contain secondary interactions with the o-methoxy groups. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(00)00451-4

www.elsevier.nl/locate/poly
Polyhedron 19 (2000) 1719–1726
Mercury halide complexes of tertiary phosphines.
Part XVI. Dimer–monomer trend in the 1:1 complexes of
mercury(II) halides with bulky tris(2,6-dimethoxyphenyl)phosphine
(DMPP)
Norman A. Bell a,*, Simon J. Coles b, Michael B. Hursthouse b, Mark E. Light b,
K. Abdul Malik c, Rafizah Mansor a
a Di6ision of Chemistry, Sheffield Hallam Uni6ersity, Pond Street, Sheffield, S1 1WB, UK
b Department of Chemistry, Uni6ersity of Southampton, Highfield, Southampton, SO17 1BJ, UK
c Department of Chemistry, Uni6ersity of Wales Cardiff, PO Box 912, Cardiff, CF1 3TB, UK
Received 25 April 2000; accepted 23 May 2000
Abstract
Reactions of HgX2 (X=Cl, Br, I) with the very bulky tertiary phosphine, tris(2,6-dimethoxyphenyl)phosphine (DMPP), in
either a 1:1 or a 1:2 ratio, result in only the isolation of the 1:1 adducts. The structures adopted in the solid state are markedly
influenced by the steric requirement of the phosphine. In contrast to the 1:1 triphenylphosphine adducts reported earlier, which
are dimeric, the DMPP mercury(II) chloride and bromide complexes are weakly linked dimers while the iodide is the first example
of a mercury iodide–phosphine complex with a monomeric distorted trigonal-planar arrangement around mercury. All three
complexes contain secondary interactions with the o-methoxy groups. © 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Mercury(II) halides; Phosphine complexes; Crystal structures
exemplified by the series Pr3PHgX2 (X=Cl, Br, I) in
which the chloride and bromide are halogen-bridged
1. Introduction
dimers with increasing asymmetry in the HgX2Hg
bridge, whereas the b-iodide has a polymeric loosely
linked trigonal-planar arrangement [13] (the a-iodide is
unique in having both phosphines coordinated to the
same mercury atom in a dimeric arrangement [11]).
These variations stem from the increased donor capac-
ity from chloride to iodide towards mercury, resulting
in a weakening association from chloride to iodide.
Both tris(2,4,6-trimethoxyphenyl)phosphine (TMPP)
and tris(2,6-dimethoxyphenyl)phosphine (DMPP) are
sterically demanding ligands (cone angle 184° [14]) and
have very high basicities (pKa=11.02 and 9.33, respec-
tively [15]) and are therefore likely to result in the
formation of complexes with low coordination numbers
[14,16]. Transition-metal chemistry of TMPP has been
studied extensively by Dunbar and co-workers and the
phosphine has been shown to behave as a mono-, di-
and tri-dentate ligand [17]. Tertiary phosphines con-
Following Mann’s seminal work in 1940 [1], mer-
cury(II) halides are now known to form a wide range of
stoichiometries with tertiary phosphine ligands. By far
the most common are the 1:1 and 2:1 complexes,
(R3P)nHgX2 (n=1,2; X=Cl, Br, I). The 2:1 complexes
have a monomeric pseudo-tetrahedral structure with
the degree of distortion depending on the s-donor
ability and steric requirement of the phosphine [2–6].
In contrast the 1:1 complexes exhibit a remarkable
variety of structures in the solid state, ranging from
weakly linked polymeric units with strong s-donors
such as Me3P and Et3P, to discrete dimeric structures
for weak donors such as Ph3P [6–13]. The nature of the
halide also has an effect on the adopted structure,
* Corresponding author. Tel.: +44-114-2253002; fax: +44-114-
2253066.
E-mail address: n.a.bell@shu.ac.uk (N.A. Bell).
0277-5387/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(00)00451-4

1720
N.A. Bell et al. / Polyhedron 19 (2000) 1719–1726
taining 2,6-dimethoxyphenyl groups, including DMPP,
have also been the subject of study, forming transition-
metal complexes with a variety of modes of coordina-
tion of the ligand [18]. However, interest in these types
of extremely bulky ligands with non-transition metals
has been very limited. Bowmaker and co-workers [19]
have formed only complexes of unusual stoichiometry
(e.g. of empirical formula TMPPHg2X4 and
(TMPP)2Hg3X6) with TMPP and suspensions of HgX2
in acetonitrile and our studies with this ligand and the
Group 12 metal halides will be reported elsewhere.
Herein we report the formation and structures of a
series of 1:1 complexes of HgX2 (X=Cl, Br, I) with
DMPP.
(30 cm3) of mercury(II) bromide (0.360 g, 1.0 mmol).
The immediate white precipitate was filtered off under
suction and dried in vacuo, yielding a white powder;
m.p. 265–268°C (Found: C, 35.15; H, 3.35.
C24H27O6PHgBr2 requires C, 35.89; H, 3.36%) 31P-{1H}
NMR (MeCN solution) l −27.88(s).
2.1.3. Tris(2,6-dimethoxyphenylphosphine)-
diiodomercury(II) (3)
A warm ethanolic solution (25 cm3) of DMPP (0.442
g, 1.0 mmol) was added to a similar solution (30 cm3)
of mercury(II) iodide. A slight cream precipitate was
formed, which increased as the solution was steadily
evaporated down to 30 cm3. Filtration under suction
yielded very pale cream crystals which were dried in
vacuo; m.p. 194–197°C (Found: C, 32.15; H, 3.03.
C24H27O6PHgI2 requires C, 32.13; H, 3.01%) 31P-{1H}
NMR (MeCN solution) l −26.31(s).
2. Experimental
DMPP was prepared using the Aldrich as supplied
reagents, 1,3-dimethoxybenzene, butyllithium and
triphenylphosphite, by the previously described method
[14]. Melting points were obtained using an electrother-
mal melting point apparatus and are uncorrected. 31P-
{1H} NMR spectra were recorded as solutions in
acetone and acetonitrile using a Bruker AC250 spec-
trometer with 85% H3PO4 as external reference. Far IR
spectra were recorded with background subtraction us-
ing a Magna-IR750 Nicolet spectrometer from 600–50
cm−1, to a resolution of 2 cm−1 on samples dispersed
in a paraffin wax disk. Raman spectra were obtained
from a Renishaw Ramascope 1000 Raman Microscope
using a 780 nm near IR laser. All spectra were recorded
using a 200 exposure ‘extended’ scan between 3400 and
2.2. X-ray crystallography
Crystals suitable for X-ray analysis were grown by
slow evaporation of ethanolic solutions of the com-
plexes, mounted on glass fibres and intensity data was
collected. A summary of crystal data, data collection
strategy and model refinement parameters are given in
Table 1.
The structures were solved via direct methods and
then subjected to full-matrix least-squares refinement
on Fo2 using the SHELXL-97 [20] suite of programs. For
all structures non-hydrogen atoms were made an-
isotropic, with hydrogens in calculated positions
,
(CꢀH=0.96 A, with Uiso tied to Ueq of the parent
300 cm−1 and a 0.5 s static scan down to 50 cm−1
.
atoms). Absorption corrections were applied using the
RefDelf approach of DIFABS [21] for DMPPHgCl2 and
the semi-empirical comparison of multiple and symme-
try equivalent reflections employed in SORTAV [22] for
DMPPHgBr2 and DMPPHgI2. Large residual electron
density is observed as satellite peaks around mercury in
all three structures. These are commonly attributed to
the inability to correctly account for the large absorp-
tion effects of heavy metal centres.
Elemental analyses were carried out by the Sheffield
University Centre for Chemical Instrumental Analytical
Services.
2.1. Preparations
2.1.1. Tris(2,6-dimethoxyphenylphosphine)-
dichloromercury(II) (1)
To a solution of mercury(II) chloride (0.270 g, 1.0
mmol), dissolved in warm ethanol (30 cm3), was added
DMPP (0.442 g, 1.0 mmol) also dissolved in warm
ethanol (25 cm3) with stirring. The white precipitate
which formed immediately was filtered off under suc-
tion and dried in vacuo, yielding a white powder; m.p.
273–275°C (Found: C, 40.21; H, 3.80. C24H27O6PHgCl2
requires C, 40.37; H, 3.81%) 31P-{1H} NMR (MeCN
solution) l −31.19 (s).
3. Results and discussion
Reaction of mercury(II) halides in ethanol solution
with DMPP, also dissolved in ethanol, in a 1:1 mole
ratio resulted in the formation of solid deposits of
complexes having 1:1 stoichiometry. The addition of a
solution of 1 mol of the mercury(II) halides to 2 mol of
the phosphine also resulted in the formation of the 1:1
complexes: clearly the bulk of the phosphine precludes
the formation of the 2:1 complexes, which are readily
formed with triphenylphosphine [1] (pKa=2.73 [23])
and several other tertiary phosphines [2–6].
2.1.2. Tris(2,6-dimethoxyphenylphosphine)-
dibromomercury(II) (2)
DMPP (0.442 g, 1.0 mmol), dissolved in warm etha-
nol (25 cm3), was added to a warm ethanolic solution

N.A. Bell et al. / Polyhedron 19 (2000) 1719–1726
1721
,
shorter of the two bridging distances (2.6272(6) A) (c.f.
Colourless crystals of all three complexes, suitable for
X-ray analysis, were grown by slow evaporation from
ethanolic solutions. In the only other complete series of
1:1 tertiary phosphine–mercury(II) halides structurally
characterised, the tripropylphosphine series [13], the
structures vary from a slightly asymmetrically bridged
dimer for the chloride, through a much more asymmet-
ric bromide, to a weakly linked polymeric arrangement
for the iodide reflecting the stronger donor ability I−\
Br−\Cl− to mercury. In marked contrast the struc-
tures of the DMPP complexes are overwhelmingly
dominated by the steric bulk of the phosphine ligand
with the HgꢀP bond length increasing along the series
chloride to iodide (Table 2), all being longer than in the
corresponding Pr3P [13] and Ph3P [7,12] complexes due
to the buttressing effect of the ortho methoxy groups.
The chloride (Fig. 1) is a very weakly linked centrosym-
metric dimer with a much greater degree of asymmetry
,
the longer bridging HgꢀBr distance of 2.9195(6) A) and
with similar angles to the chloride, indicating that this
is an even weaker linked dimeric structure.
The trend is complete with the iodide which shows a
completely monomeric structure (Fig. 3), with both
HgꢀI distances agreeing to within ca. 0.04 A, the PHgI2
unit being planar and there being no intermolecular
,
,
Hg···I distances less than 4 A. This represents the first
structurally characterised tertiary phosphine–mer-
cury(II) iodide complex which has a monomeric essen-
tially trigonal-planar arrangement, with angles around
mercury varying from 107.95(3) to 132.86(4)°. How-
ever, the two PHgI angles are quite different (119.12(4)
and 132.86(4)°), which is due to some particularly
strong interactions between the central mercury atom
and oxygens [O(2), O(4) and O(6)] of the methoxy
,
groups (3.089, 3.268 and 2.672 A, respectively). These
,
in the bridging region (HgꢀClbr; 2.475(3), 2.902(4) A cf.
contacts are within the sum of the van der Waals radii
for the interacting atoms and may be considered to be
bonding, resulting in six-coordinate mercury. The ge-
ometry about Hg(1), when considering the interactions
with methoxy group oxygens, is very distorted from
idealised octahedral geometry (see Table 2).
The dimeric Cl and Br complexes also exhibit weak
secondary interaction with the ortho methoxy groups at
around the sum of the van der Waal’s radii [24], as seen
,
HgꢀClterm, 2.514(4) A) than in the corresponding Ph3P
,
[7] (2.623(8), 2.658(8) A) or Pr3P [13] complexes
(2.638(4), 2.780(4) A) and with the angles PꢀHgꢀClterm
,
(113.11(12)°) and PꢀHgꢀClbr (105.78(11)°) to the longer
bridging bond being much smaller than the angle be-
tween phosphorus and the shorter bridging chloride
(138.95(14)°). The bromide (Fig. 2) shows an even
,
closer similarity in the HgꢀBrterm (2.6129(6) A) and the
Table 1
Crystal data, data collection strategy and model refinement parameters
DMPPHgCl2
DMPPHgBr2
DMPPHgI2
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C24H27O6PHgCl2
713.92
293(2)
C24H27O6HgBr2
802.84
150(2)
C24H27O6PHgI2
896.82
150(2)
monoclinic
P21/n
12.607(3)
14.050(3)
16.354(3)
90.0
107.96(3)
90.0
2755.6(10)
4
2.162
7.920
triclinic
triclinic
(
(
P1
P1
,
a (A)
10.056(2)
10.849(2)
14.211(2)
78.783(14)
69.49(2)
10.1414(2)
11.0219(2)
14.4192(2)
78.6299(9)
69.7350(7)
64.6536(7)
1364.16(4)
2
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
64.680(10)
1310.8(4)
2
1.809
6.173
3
,
Volume (A )
Z
Dcalc (Mg m−3
)
1.955
8.644
768
Absorption coefficient (mm−1
F(000)
)
696
1680
Crystal size (mm)
Diffractometer
qmax (°)
0.22×0.16×0.12
Nonius FAST
24.95
0.25×0.2×0.1
Nonius KappaCCD
25.03
0.2×0.2×0.01
Nonius KappaCCD
30.48
Reflections collected
Independent reflections
Rint
5211
3589
0.1147
26 242
4811
0.0689
35 933
7750
0.0642
Absorption correction/transmission factors
DIFABS [21]
0.794/1.024
R1=0.0569
wR2=0.1516
1.872/−1.799
S
ORTAV [22]
SORTAV [22]
0.970/0.623
R1=0.0503
wR2=0.1301
3.581/−2.750
0.578/0.306
R1=0.0349
wR2=0.0861
1.259 and −1.801
Final R indices
−3
,
z max/min (e A
)

1722
N.A. Bell et al. / Polyhedron 19 (2000) 1719–1726
3.1. Solution 31P NMR spectra
Table 2
,
Selected bond lengths (A) and angles (°)
The spectra of all three complexes were recorded as
solutions in acetone and acetonitrile solutions, though
the solubility was low in both solvents. The spectra all
contained a single line due to species which contain the
non-magnetic isotope of mercury. The expected satel-
lites due to 1J(199Hg31P) coupling (199Hg 16.84% natural
abundance, nuclear spin I=1/2) were not observed in
acetone solution due to the weak intensity of the spec-
tra because of the very low solubility of the complexes.
The chemical shifts in acetonitrile were slightly larger
(Table 3) and also the slightly greater solubility allowed
observation of mercury–phosphorus coupling. The
DMPPHgCl2
DMPPHgBr2
DMPPHgI2
HgꢀP
HgꢀXterm
2.436(3)
2.514(4)
2.4490(12)
2.6129(6)
2.4656(16)
2.7428(11)
2.7016(7)
HgꢀXbr
2.475(3)
2.902(4)
3.106(6)
3.126(4)
2.805(6)
113.11(12)
132.86(4)
105.78(11)
138.95(14)
2.6272(6)
2.9195(6)
3.157(6)
3.140(5)
2.825(6)
Hg···O
3.0895(45)
3.1678(46)
2.6718(39)
119.12(4)
PꢀHgꢀXterm
PꢀHgꢀXbr
112.41(3)
107.79(3)
136.09(3)
107.95(3)
109.13(2)
96.145(18)
83.855(18)
58.22(8)
1
XterꢀHgꢀXter
XterꢀHgꢀXbr
l(31P) and J(199Hg31P) coupling constants are listed in
109.23(14)
102.0(2)
80.71(11)
58.74(9)
58.16(10)
67.82(9)
153.00(11)
91.53(10)
84.58(8)
Table 3, together with the results reported by Bow-
maker et al. for 1:1 mixtures of HgX2 and TMPP in
MeCN solution for comparison [19]. The signals are
clearly halogen-dependent with chemical shifts and cou-
pling constants increasing from iodide to chloride, in
accordance with observations elsewhere [26]. These re-
sults, together with the non-electrolytic behaviour of
the complexes in MeCN solution, clearly show the
presence of only one phosphorus-containing species in
solution. This is in marked contrast to Bowmaker’s
work [19] on the very similar TMPP–HgX2 system in
which NMR studies (Table 3) of equimolar mixtures in
MeCN solution showed the presence of halogen-depen-
dent parameters assigned to [TMPPHgX]+ and a non-
XbrꢀHgꢀXbr
PꢀHg···O
59.36(11)
57.02(10)
69.85(10)
57.59(8)
66.94(10)
158.15(8)
87.87(11)
84.20(8)
168.48(9)
89.98(9)
XbrꢀHg···O
XterꢀHg···O
170.04(9)
91.38(11)
79.48(11)
129.49(9)
76.45(9)
103.90(10)
86.84(10)
71.08(13)
96.33(10)
80.05(7)
halogen-dependent parameter due to [(TMPP)2Hg]2+
,
in Table 2. A comparison of the phosphine moiety,
with the previously determined structure [25] shows
some distortions, due to the interaction of the methoxy
groups with the mercury centre.
both associated with [Hg2X6]2− anions. For the chlo-
ride these two species were present in approximately
equal amounts, decreasing to ꢀ13% of the latter for
the iodide.
Fig. 1. The molecular structure of DMPPHgCl2 with ellipsoids at 30% probability.

N.A. Bell et al. / Polyhedron 19 (2000) 1719–1726
1723
Fig. 2. The molecular structure of DMPPHgBr2 with ellipsoids at 30% probability.
Fig. 3. The molecular structure of DMPPHgI2 with ellipsoids at 30% probability.
3.2. Vibrational spectra
gives rise to differences in vibration spectra. For exam-
ple terminal and bridging HgꢀCl stretching frequencies
[26] in symmetrical (or near symmetrical) halogen
The assignment of vibrational spectral features of a
range of R3PHgX2 complexes has previously been cor-
related with their full crystal and molecular structures
[26]. The structural variety found for these complexes
bridged dimers are usually separated by ꢀ120 cm−1
.
The absorptions below 600 cm−1 found in the IR and
Raman spectra of DMPPHgX2 are listed in Table 4 and

1724
N.A. Bell et al. / Polyhedron 19 (2000) 1719–1726
Table 3
31P NMR parameters for DMPPHgX2 in MeCN solution with data in acetone solution in parentheses a
DMPPHgX2
[TMPPHgX]+
l
[(TMPP)2Hg][Hg2X6]
X
Cl
Br
I
l
1J(199Hg31P) (Hz)
1J(199Hg31P) (Hz)
l
1J(199Hg31P) (Hz)
−31.19
(−30.17)
−27.87
(−26.61)
−26.31
9022
8030
7066
−30.21
−26.62
−24.59
9190
8405
6839
−30.70
−30.84
−30.76
5217
5219
5275
(−25.29)
a Data for [TMPPHgX]+ and [(TMPP)2Hg]2+ shown for comparison [19].
the Raman spectra are shown in Fig. 4. There are
several bands common to all three spectra which must
be due to skeletal vibrations of the phosphine ligand,
but the halogen-dependent bands can readily be iden-
tified. In the spectra of the chloride the closeness of the
two wHgꢀCl vibrations at 250(vs) and its shoulder at
230 cm−1 (Raman) may be ascribed to the weak nature
of chloride bridging in the complex.
sharper, very strong absorption bands at 148 and 118
cm−1, which may be ascribed to the wHgꢀI symmetric
and asymmetric stretching vibrations, respectively. Ter-
minal HgꢀI vibrations have been assigned [27] at ꢀ
150/135 cm−1 in [Hg2I6]2− and 160/154 cm−1 in
[HgI3]−.
For the bromide a similar picture emerges with peaks
which are clearly associated with wHgꢀBr vibrations
occurring at 161(vs) cm−1 and a strong shoulder at 142
cm−1, again illustrating the weak association of the
dimer as confirmed by the crystallographic data. The
monomeric nature of the iodide results in two much
4. Conclusions
The bulky nature of DMPP precludes the formation
of the well known 2:1 tertiary phosphine–mercury(II)
halide complexes and only 1:1 complexes have been
isolated. This is in marked contrast to the structurally
similar TMPP system where only ionic complexes of
somewhat unusual stoichiometry (L2Hg2X8 and
L2Hg3X6) have been isolated [19]. X-ray structures of
DMPPHgX2 (X=Cl, Br, I) display a trend from
weakly linked dimers for the chloride and bromide,
while the iodide is unique in being the first example of
a monomeric tertiary phosphine–mercury(II) iodide
complex, having a distorted trigonal-planar arrange-
ment around mercury. 31P NMR and conductance stud-
ies show the presence of only one non-ionic species in
solution and vibrational spectral data are consistent
with the structural results.
Table 4
a
IR and Raman spectral data for DMPPHgX2 (cm−1
)
X
Cl
Br
I
Raman
IR
Raman
IR
Raman
529w
IR
524m
531w
525m
528w
525m
519vw
509mw
431mw
372m
520vw
509mw
448vs 428mw
370mw
509w
423mw
372mw
447vs
451m
338vw
250vs*
230msh*
265s* 251w
245s*
217w
249w
5. Supplementary material
206w
Full details of atomic coordinates, bond lengths and
angles and thermal parameters have been deposited as
supplementary material; CCDC reference numbers,
CCDC 133199–133201. Supplementary data are avail-
able on request from The Director, CCDC, 12 Union
Road, Cambridge, CB2 1EZ, UK (fax: +44-1223-
336033; e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
161vs*
161m*
147m*
148vs*
146m
124m
142msh*
154m
119m
106ms
91ms
118vs*
111s
92m
109vs
94s
a *Mercury–halogen vibrations.

N.A. Bell et al. / Polyhedron 19 (2000) 1719–1726
1725
References
[1] R.C. Evans, F.G. Mann, H.S. Peiser, D. Purdie, J. Chem. Soc.
(1940) 1209.
[2] N.A. Bell, T.D. Dee, M. Goldstein, P.J. McKenna, I.W. Nowell,
Inorg. Chim. Acta 71 (1983) 135.
[3] N.A. Bell, T.D. Dee, M. Goldstein, T. Jones, I.W. Nowell, P.L.
Goggin, R.J. Goodfellow, K. Kessler, D.M. McEwan, J. Chem.
Res. (S) 2 (1981) (M) 0201.
[4] D.W. Allen, N.A. Bell, S.T. Fong, L.A. March, I.W. Nowell,
Inorg. Chim. Acta 99 (1985) 157.
[5] N.A. Bell, L.A. March, I.W. Nowell, Inorg. Chim. Acta 156
(1989) 195.
[6] N.A. Bell, M. Goldstein, L.A. March, I.W. Nowell, J. Chem.
Soc., Dalton Trans. (1984) 1621.
[7] N.A. Bell, M. Goldstein, T. Jones, I.W. Nowell, Inorg. Chim.
Acta 43 (1980) 87.
[8] N.A. Bell, M. Goldstein, T. Jones, I.W. Nowell, Inorg. Chim.
Acta 48 (1981) 185.
[9] N.A. Bell, M. Goldstein, T. Jones, L.A. March, I.W. Nowell,
Inorg. Chim. Acta 61 (1982) 83.
[10] N.A. Bell, T.D. Dee, M. Goldstein, I.W. Nowell, Inorg. Chim.
Acta 70 (1983) 215.
[11] N.A. Bell, N.A. Chudley, L.A. March, I.W. Nowell, Inorg.
Chim. Acta 141 (1988) 155.
[12] N.A. Bell, L.A. March, I.W. Nowell, Inorg. Chim. Acta 156
(1989) 201.
[13] N.A. Bell, L.A. March, I.W. Nowell, Inorg. Chim. Acta 162
(1989) 57.
[14] M.S. Wada, S. Higashizaki, A. Tsubo, J. Chem. Res. (S) 38
(1985) (M) 0467.
[15] Y. Yamashoji, T. Matsushita, M. Tanaka, T. Shono, M. Wada,
Polyhedron 8 (1989) 1053.
[16] M.S. Wada, S. Higashizaki, J. Chem. Soc., Chem. Commun.
(1984) 482.
[17] (a) K.R. Dunbar, S.C. Haefner, L.E. Pence, J. Am. Chem. Soc.
111 (1989) 5504. (b) K.R. Dunbar, S.C. Haefner, D.J. Burzynski,
Organometallics 9 (1990) 1347. (c) S.-J. Chen, K.R. Dunbar,
Inorg. Chem. 29 (1990) 588. (d) K.R. Dunbar, S.C. Haefner, A.
Quillevere, Polyhedron 9 (1990) 1695. (e) K.R. Dunbar, S.C.
Haefner, P.M. Swepston, J. Chem. Soc., Chem. Commun. (1991)
460. (f) S.-J. Chen, K.R. Dunbar, Inorg. Chem. 29 (1990) 2018.
(g) K.R. Dunbar, A. Quillevere, S.C. Haefner, Acta Crystallogr.,
Sect. C 47 (1991) 2319. (h) K.R. Dunbar, L.E. Pence, Acta
Crystallogr., Sect. C 47 (1991) 23. (i) S.C. Haefner, K.R. Dun-
bar, C. Bender, J. Am. Chem. Soc. 113 (1991) 9540. (j) S.C.
Haefner, K.R. Dunbar, Organometallics 11 (1992) 1431. (k) J.I.
Dulebophn, S.C. Haefner, K.R. Dunbar, K.A. Berglund, Chem.
Mater. 4 (1992) 506. (l) K.R. Dunbar, Comments Inorg. Chem.
6 (1992) 313. (m) K.R. Dunbar, A. Quillevere, Polyhedron 12
(1993) 807. (n) K.R. Dunbar, J.H. Matonic, V.P. Saharan,
Inorg. Chem. 33 (1994) 25. (o) K.R. Dunbar, S.C. Haefner, C.E.
Uzelmeier, A. Howard, Inorg. Chim. Acta 240 (1995) 527. (p)
L.-J. Baker, R.C. Bott, G.A. Bowmaker, P.C. Healey, B.W.
Skelton, P.A. Schwerdtfeger, A.H. White. J. Chem. Soc., Dalton
Trans. (1995) 1341, and references therein. (q) K.R. Dunbar,
J.-S. Sun, J. Chem. Soc., Chem. Commun. (1994) 2387. (r) J.-S.
Sun, C.E. Uzelmeier, D.L.Ward, K.R. Dunbar, Polyhedron 11/
12 (1998) 2049. (s) K.R. Dunbar, J.-S. Sun, A. Quillevere, Inorg.
Chem. 33 (1994) 3598.
[18] Y. Yamamoto, K. Sugawara, T. Aiko, J.-F. Ma, J. Chem. Soc.,
Dalton Trans. (1999) 4003.
[19] L.-J. Baker, G.A. Bowmaker, B.W. Skelton, A. H. White. J.
Chem. Soc., Dalton Trans. (1993) 3235.
[20] G.M. Sheldrick, SHELXL-97. Program for the refinement of
crystal structures, University of Go¨ttingen, 1997.
Fig. 4. Raman spectra (600–50 cm−1) of 1 (a), 2 (b) and 3 (c).

1726
N.A. Bell et al. / Polyhedron 19 (2000) 1719–1726
[21] N.P.C. Walker, D. Stuart, Acta Crystallogr., Sect. A 39 (1983)
158; adapted for FAST geometry by A. Karaulov, University of
Wales, Cardiff, 1991.
[22] (a) R.H. Blessing, Acta Crystallogr., Sect A 51 (1995) 33. (b)
R.H. Blessing, J. Appl. Cryst. 30 (1997) 421.
[25] P. Livant, Y.J. Sun, T.R. Webb, Acta Crystallogr., Sect. C 47
(1991) 1003.
[26] N.A. Bell, M. Goldstein, T. Jones, I.W. Nowell, Inorg. Chim.
Acta 75 (1983) 21.
[27] P.L. Goggin, P. King, D.M. McEwan, G.E. Taylor, P.
Woodward, M. Sandstro¨m, J. Chem. Soc., Dalton Trans. (1972)
647.
[23] T. Allman, R.G. Goel, Can. J. Chem. 60 (1982) 716.
[24] A. Bondi, J. Phys. Chem. 68 (1964) 441.
.