Synthesis, properties and structures of eight-coordinate zirconium(IV) and hafnium(IV) halide complexes with phosphorus and arsenic ligands

Article abstract of DOI:10.1039/b409051a

Eight-coordinate [MX₄(L-L)₂] (M = Zr or Hf; X = Cl or Br; L-L =o-C₆H₄(PMe₂)₂ or o-C ₆H₄(AsMe₂)₂) were made by displacement of Me₂S from [MX₄(Me₂S) ₂] by three equivalents of L-L in CH₂Cl₂ solution, or from MX₄ and L-L in anhydrous thf solution. The [MI ₄(L-L)₂] were made directly from reaction of MI ₄ with the ligand in CH₂Cl₂ solution. The very moisture-sensitive complexes were characterised by IR, UV/Vis, and ¹H and ³¹P NMR spectroscopy and microanalysis. Crystal structures of [ZrCl₄{o-C₆H₄(AsMe₂) ₂}₂], [ZrBr₄{o-C₆H ₄(PMe₂)₂}₂], [ZrI ₄{o-C₆H₄(AsMe₂)₂} ₂] and [HfI₄{o-C₆H₄(AsMe ₂)₂}₂] all show distorted dodecahedral structures. Surprisingly, unlike the corresponding Ti(iv) systems, only the eight-coordinate complex was found in each system. In contrast, the ligand o-C₆H₄(PPh₂)₂ forms only six-coordinate complexes [MX₄{o-C₆H₄(PPh ₂)₂}] which were fully characterised spectroscopically and analytically. Surprisingly the tripodal triarsine, MeC(CH₂AsMe ₂)₃, also produces eight-coordinate [MX ₄{MeC(CH₂AsMe₂)₃}₂] in which the triarsines bind as bidentates in a distorted dodecahedral structure. There is no evidence for seven-coordination as found in some thioether systems.

Full text of DOI:10.1039/b409051a

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F U L L P A P E R
Synthesis, properties and structures of eight-coordinate
zirconium(IV) and hafnium(IV) halide complexes with phosphorus
and arsenic ligands
William Levason, Melissa L. Matthews, Bhavesh Patel, Gillian Reid and Michael Webster
School of Chemistry, University of Southampton, Southampton, UK SO17 1BJ
Received 14th June 2004, Accepted 30th July 2004
First published as an Advance Article on the web 1st September 2004
Eight-coordinate [MX4(L–L)2] (M = Zr or Hf; X = Cl or Br; L–L = o-C6H4(PMe2)2 or o-C6H4(AsMe2)2) were made by
displacement of Me2S from [MX4(Me2S)2] by three equivalents of L–L in CH2Cl2 solution, or from MX4 and L–L in
anhydrous thf solution. The [MI4(L–L)2] were made directly from reaction of MI4 with the ligand in CH2Cl2 solution.
The very moisture-sensitive complexes were characterised by IR, UV/Vis, and 1H and 31P NMR spectroscopy and
microanalysis. Crystal structures of [ZrCl4{o-C6H4(AsMe2)2}2], [ZrBr4{o-C6H4(PMe2)2}2], [ZrI4{o-C6H4(AsMe2)2}2]
and [HfI4{o-C6H4(AsMe2)2}2] all show distorted dodecahedral structures. Surprisingly, unlike the corresponding Ti(IV)
systems, only the eight-coordinate complex was found in each system. In contrast, the ligand o-C6H4(PPh2)2 forms only
six-coordinate complexes [MX4{o-C6H4(PPh2)2}] which were fully characterised spectroscopically and analytically.
Surprisingly the tripodal triarsine, MeC(CH2AsMe2)3, also produces eight-coordinate [MX4{MeC(CH2AsMe2)3}2] in which
the triarsines bind as bidentates in a distorted dodecahedral structure. There is no evidence for seven-coordination as found
in some thioether systems.
Here we report systematic studies of MX4 (M = Zr or Hf;
Introduction
X = Cl, Br or I) with the ligands o-C6H4(PMe2)2, o-C6H4(AsMe2)2,
Zirconium(IV) and hafnium(IV) are large, hard, oxophilic metal
o-C6H4(PPh2)2 and MeC(CH2AsMe2)3, with the aims of probing
centres whose coordination chemistry is dominated by neutral N
the existence of six-, seven- and eight-coordinate metals in these
or O donor and anionic ligands.1 There is also an extensive organo-
systems, obtaining detailed structural and spectroscopic data of the
metallic chemistry, much of it metallocene based, reflecting the
isolated complexes, and studying their interconversions.
importance of these metals in olefin oligomerisation, polymerisa-
tion and hydrozirconation.2,3 However their coordination chemistry
with neutral softer donor ligands is relatively poorly developed, and
studies have been hindered both by the extreme moisture sensitivity
of the complexes and their often poor solubility in non-donor sol-
vents. We recently reported the synthesis, properties and structural
characterisation of a variety of six-, seven- and eight-coordinate
complexes of ZrCl4 and HfCl4 with thio- and selenoether ligands,
examples including the six-coordinate ligand-bridged dimer [{ZrCl4
(MeS(CH2)3SMe)}2], the monomer [HfCl4(MeSeCH2CH2SMe)],
and the eight-coordinate [MCl4(MeSCH2CH2SMe)2] (M = Zr or
Hf), whilst rare examples of seven-coordination are the macrocyclic
[MCl4{[9]aneS3}].4,5 Eight-coordinate [MCl4{o-C6H4(AsMe2)2}2]
were reported many years ago,6,7 although with very limited
characterisation and the assignment of the structure is based on
a comparison of the X-ray powder patterns with that of [TiCl4{o-
C6H4(AsMe2)2}2]. There are a number of structurally characterised
examples with mono- and di-phosphines, most obtained during
attempts to prepare M–M bonded species in lower oxidation states
including, [HfCl4{Ph2P(CH2)nPPh2}] (n = 2, 3),8 [Zr2Cl8(PMe3)4]
and [ZrI4(PMe3)n] (n = 2, 3),9,10 although little spectroscopic data
are available. There is also an extensive organometallic chemistry
of zirconium and hafnium in lower oxidation states based upon an
M(Me2PCH2CH2PMe2)2 core.11 Dinuclear zirconium complexes
of diphosphinophosphide ligands, [P(CH2CH2PR2)2]− have been
described in which the phosphido groups bridge the zirconium
centres.12 We recently re-examined13,14 the complexes of TiX4
(X = Cl, Br or I) with diphosphine and diarsine ligands and found
that whilst most ligands gave only six-coordinate [TiX4(L–L)]
(X = Cl or Br), for o-C6H4(EMe2)2 (E = P or As) both six- and
eight-coordinate complexes could be obtained. The solution
behaviour and interconversions were probed by variable-tem-
Results and discussion
Synthesis
The synthesis of complexes of the oxophilic zirconium(IV) and
hafnium(IV) halides with phosphine and arsine ligands requires the
use of rigorously anhydrous conditions and careful choice of solvent.
The direct reaction of the polymeric MX4 (M = Zr or Hf, X = Cl or
Br) with o-C6H4(AsMe2)2 or o-C6H4(PMe2)2 in CH2Cl2 or toluene
was unsatisfactory even with long reaction times, the products being
mixtures of the desired complexes and unchanged MX4. However,
this approach was successful with the corresponding tetraiodides.
On stirring a suspension of MI4 with three molar equivalents of the
ligand (L–L) in CH2Cl2 the orange (Zr) or yellow (Hf) tetraiodide
slowly dissolved, and after some hours the paler [MI4(L–L)2] com-
plexes deposited, more complex being produced by concentrating
the solutions under vacuum. The [MX4(L–L)2] (X = Cl or Br) were
made by displacement of Me2S from [MX4(Me2S)2]15 by three
equivalents of L–L in CH2Cl2 solution, or directly from MX4 and
L–L in anhydrous thf solution. In the latter route which was most
convenient, the anhydrous MX4 was stirred with anhydrous thf at
ambient temperatures until it had completely dissolved, and then
three equivalents of L–L added. The reaction times are important,
ca. 24 h being optimum for M = Zr and ca. 36 h for M = Hf. Shorter
times appear to give incomplete conversion, whilst the products ob-
tained using much longer times (3–4 d) are contaminated with thf
cleavage products, especially in the case of the HfX4/o-C6H4(PMe2)2
systems. The displacement of the O-donor thf from the oxophilic
metal centres in thf solution by the softer Group 15 donor ligands
is notable and demonstrates the strong coordinating ability of these
o-phenylene bidentates. The poor solubility of the [MX4(L–L)2]
results in their precipitation from the reaction mixture, which may
also help to drive the reaction. Using 1:1 MX4 :L–L ratios led only
to mixtures containing [MX4(L–L)2] and starting materials. The
[MX4(L–L)] were not obtained in these reactions, which contrasts
with the reactions using MeSCH2CH2SMe or MeSeCH2CH2SeMe
1
perature H and 31P NMR spectroscopy. However, for TiI4 only
six-coordinate [TiI4{o-C6H4(EMe2)2}] form, an old report of a
yellow eight-coordinate species7 was shown to be erroneous, the
substance being a mixture of lower oxidation state complexes and
iodinated ligand.14
T h i s j o u r n a l i s
©
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
D a l t o n T r a n s . , 2 0 0 4 , 3 3 0 5 – 3 3 1 2
3 3 0 5

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(L′–L′), when either [MX4(L′–L′)] or [MX4(L′–L′)2] can be isolated
depending upon the conditions used.4,5
[MX4{o-C6H4(PPh2)2}]. The microanalyses are consistent with
1:1 stoichiometry and hence six-coordination, similar to that es-
tablished for the [HfCl4{Ph2P(CH2)nPPh2}] complexes.8 The IR
spectra of the six-coordinate complexes show for X = Cl or Br
(M–X) at significantly higher frequencies to those reported for the
eight-coordinate compounds, again consistent with results in other
systems.4,12 The poor solubility of the complexes made it difficult
to obtain 31P{1H} NMR data. However, from saturated CH2Cl2 so-
lutions under rigorously anhydrous conditions, there was a single
weak resonance in each complex, which shifted to high frequency
I < Br < Cl. The resonances in the iodo-complexes were slightly
to low frequency of that in o-C6H4(PPh2)2. The presence of added
o-C6H4(PPh2)2 did not produce any evidence for the formation of
eight-coordinate complexes. To probe this possibility further, 31P
NMR spectra were also recorded from the synthesis solutions, both
before isolation of the complexes, and from the residual filtrates
after removal of the bulk complex. For the chloride and bromides,
only the 1:1 complex and free o-C6H4(PPh2)2 were significant
components, however for the iodo-complex reactions, the spectra
showed several extra features. Some of these with (P) ca. 50 were
also present in solutions of o-C6H4(PPh2)2 + I2 and are attributable
to iodinated diphosphine, but there were also very broad features at
lower frequency which are probably due to lower oxidation state
(paramagnetic) compounds. These results are reminiscent of the
TiI4/o-C6H4(PMe2)2 system reported previously,.13 and with Cotton’s
The tripodal triarsine MeC(CH2AsMe2)3 reacted easily with the
suspended MI4 in CH2Cl2 to form [MI4(triarsine)2], but reaction of
the same ligand with MX4 (X = Cl or Br) in thf gave mixtures of
the triarsine complexes and the thf adducts. Probably the forma-
tion of six-membered chelate rings and the more flexible back-
bone accounts for the failure to completely displace thf in this
case. The [MCl4(triarsine)2] complexes were best obtained from
[MCl4(Me2S)2]15 and the triarsine in CH2Cl2 solution. Attempts to
synthesise [MCl4(triarsine)] complexes using a 1:1 molar ratio of
reactants were unsuccessful.
Finally the six-coordinate [MX4(o-C6H4(PPh2)2)] were prepared
by stirring 1.5 equivalents of o-C6H4(PPh2)2 with the anhydrous
metal tetrahalide in a moderately large volume of dry CH2Cl2 for
2–3 days. The iodo-complexes form relatively easily, but obtain-
ing complete reaction in the other cases requires rigorously dry
glassware, reagents and solvents or the reactions fail to proceed
or very impure products result. Using an excess of o-C6H4(PPh2)2
(>3 equivalents) does not produce 2:1 complexes.
Irrespective of the ligand, all isolated complexes were handled
in a dinitrogen filled dry box (<5 ppm water), since all hydrolyse
readily, although unlike the titanium analogues,13 this is not visually
evident through colour changes.
16
Properties
isolation of [(Ph3PI)2I3]I3 from reaction of ZrI4 with PPh3,
[MX4{o-C6H4(EMe2)2}2]. These complexes all have eight-
coordinate metal centres in a distorted dodecahedral geometry as
established by the crystal structures of [ZrCl4{o-C6H4(AsMe2)2}2],
[ZrBr4{o-C6H4(PMe2)2}2] and [MI4{o-C6H4(AsMe2)2}2] (M = Zr
or Hf) (see below). The chloro- and bromo-complexes are poorly
soluble in halocarbon solvents, and are partially or completely de-
composed by O or N donor solvents such as thf, MeNO2 or MeCN,
and very readily by moisture. The iodo-complexes are moderately
soluble in CH2Cl2. Diffuse reflectance UV/Vis spectra, recorded
from solid samples diluted with dry BaSO4, showed broad absorp-
tions in the near UV region (see Experimental section) which may
be assigned as (P,As) and (X) → Zr/Hf charge transfer (CT)
bands, consistent with the donor groups present and the white or
pale-cream colours†. The iodo-complexes have (I) → Zr/Hf CT
bands which lie in the region 24–30000 cm−1 and are responsible
for the yellow colours. As with the thioether or selenoether ana-
logues4 the band energies do not vary significantly with the metal
coordination number. The IR spectra of [ZrCl4{o-C6H4(EMe2)2}2]
show (Zr–Cl) at ca. 300 cm−1, and [ZrBr4{o-C6H4(EMe2)2}2]
(Zr–Br) at ca. 220 cm−1 with the corresponding values in the
hafnium analogues ca. 30 cm−1 to low frequency in each case.
The values in the chloro-complexes correlate well with those
reported for eight-coordinate thio- and selenoether complexes.4
Solution studies were hampered by the poor solubility, however
the 1H NMR spectra of complexes of o-C6H4(AsMe2)2 show
single methyl resonances which shift to high frequency with
halide Cl < Br < I; the same trend is apparent in the complexes
of o-C6H4(PMe2)2, although the resonances appear either as broad
signals approximating to doublets or multiplets with weaker outer-
lines indicating second-order features. The 31P{1H} NMR spectra
also show systematic high frequency shifts with halide Cl > Br > I,
but with very similar values for both metal centres. In the presence
of added diphosphine in CH2Cl2 solution at 295 K, the resonances
of the complexes are unchanged showing exchange is slow on the
NMR time scale. The NMR spectra of the [MX4{o-C6H4(EMe2)2}2]
in CH2Cl2 also show no evidence for significant dissociation into
[MX4{o-C6H4(EMe2)2}] and o-C6H4(EMe2)2, which contrasts
with the behaviour of the corresponding [TiX4{o-C6H4(EMe2)2}2]
(X = Cl or Br)12 where all but the diphosphine chloro-complex are
extensively dissociated.‡
[MX4{MeC(CH2AsMe2)3}2] (X = Cl or I). The triarsine com-
plexes were initially obtained from reactions of [MCl4(Me2S)2]
with MeC(CH2AsMe2)3, which it was hoped might afford examples
of seven-coordination. We note that MeC(CH2AsMe2)3 gives
only six-coordinate 1:1 complexes [TiX4{MeC(CH2AsMe2)3}]12
in which the triarsine is bound as a bidentate ligand. However,
the crystal structure described below, showed that crystals ob-
tained from the [ZrCl4(Me2S)2]/MeC(CH2AsMe2)3 reaction were
[ZrCl4{MeC(CH2AsMe2)3}2] with the triarsine coordinated as a
bidentate on an eight-coordinate zirconium centre. The (Zr–Cl)
modes at 304, 296 cm−1 are also consistent with eight-coordination.
The complex is poorly soluble in chlorocarbons, but at 300 K the 1H
NMR spectrum shows only three singlets all to high frequency of the
resonances in the MeC(CH2AsMe2)3, consistent either with symmet-
rical coordination of the ligand or with fast exchange. The complex
precipitates on cooling the solution and no low-temperature NMR
studies were possible. The Hf analogue is very similar, but essentially
insoluble in chlorocarbons preventing any NMR studies, although
its IR spectrum also suggests eight-coordination. An exploratory
study of the MBr4/MeC(CH2AsMe2)3 systems also found insoluble
products, and these were not pursued, but fortunately the MI4/
MeC(CH2AsMe2)3 reactions yielded [MI4{MeC(CH2AsMe2)3}2]
complexes which were reasonably soluble in CH2Cl2, permit-
ting H and 13C{1H} VT NMR studies. The H NMR spectrum of
[ZrI4{MeC(CH2AsMe2)3}2] at 300 K contains three singlets assign-
able to MeC, CH2 and MeAs groups similar to the chloride case.
However, on cooling to 273 K these resonances broaden and then
by 223 K the spectrum is that shown in Fig. 1, which is unchanged
on further cooling, the changes reversing on warming the solution.
The spectrum is readily assigned as due to 2-coordinated triarsine
(see Fig. 1 caption) and hence at ambient temperatures the complex
is exchanging the free and coordinated AsMe2 groups. The 13C{1H}
NMR spectrum is ill-defined at 300 K, but on cooling the resonances
sharpen and split and at 220 K the spectrum in Fig. 2 is obtained,
again readily assigned to bidentate triarsine. The VT NMR spectra
of [HfI4{MeC(CH2AsMe2)3}2] are very similar. Notably there is no
evidence in either set of NMR spectra for [MI4{MeC(CH2AsMe2)3}]
complexes (either six- or seven-coordinate).
1
1
‡ The complexes are very readily hydrolysed which can result in the appear-
ance of uncoordinated diphosphine or diarsine resonances in some samples,
but these contain no features attributable to 1:1 complexes which would be
formed by dissociation.
† The report of pink coloured Hf complexes6 is in error, and presumably
arose from impurities in the Hf halide.
3 3 0 6
D a l t o n T r a n s . , 2 0 0 4 , 3 3 0 5 – 3 3 1 2

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Fig. 3 The structure of [ZrCl4{o-C6H4(AsMe2)2}2] showing the atom
labelling scheme. Atomic displacement ellipsoids are drawn at the 50%
probability level and H atoms are omitted for clarity. Symmetry operation:
a = −x, −y, z.
Fig. 1 The 1H NMR spectrum of [ZrI4{MeC(CH2AsMe2)3}2] in CD2Cl2 at
223 K showing the 2-coordinated triarsine.  0.95 (s) (AsMe-free), 1.29 (s)
(CMe), 1.62 (s), 1.64 (s) (AsMe-coord), 1.80 (s) (CH2-free), 2.16 (d), 2.26
(d) (CH2-coord).
Fig. 4 The structure of [ZrBr4{o-C6H4(PMe2)2}2] showing the atom label-
ling scheme. Refinement in space group I42m. Atomic displacement el-
lipsoids are drawn at the 50% probability level and H atoms are omitted for
clarity. Symmetry operation: a = −x, −y, z.
Fig. 5 The structure of [ZrI4{o-C6H4(AsMe2)2}2] showing the atom label-
ling scheme. Atomic displacement ellipsoids are drawn at the 50% prob-
ability level and H atoms are omitted for clarity. Note that the structure of
[HfI4{o-C6H4(AsMe2)2}2] is the same.
Fig. 2 The 13C{1H} NMR spectrum of [ZrI4{MeC(CH2AsMe2)3}2] in
CH2Cl2 at 220 K showing the 2-coordinated triarsine.  11.2 (AsMe-free),
17.6, 18.9 (AsMe-coord), 31.8 (CH2-free), 38.6 (C), 41.4 (CH2-coord), 50.2
(Me); the resonance marked ¥ is an impurity.
in [ZrBr4{o-C6H4(PMe2)2}2] Zr–Br = 2.649(1), Zr–P = 2.800(3) Å
may be compared with the corresponding values in [TiBr4{o-
C6H4(PMe2)2}2] Ti–Br = 2.578(1), Ti–P = 2.672(2) Å. Notably, the
increase in M–Br betweenTi and Zr is ca. 0.07 Å whilst that in M–Pis
0.13 Å suggesting rather weaker interaction of the hard oxophilic Zr
with the soft phosphine compared to the halide. The result of the long
Zr–P distance is an acute (70°) P–Zr–P chelate angle. In [ZrCl4{o-
C6H4(AsMe2)2}2] the As–Zr–As angle within the chelate ring is also
ca. 70°, whilst Zr–Cl = 2.515(1), Zr–As = 2.846(1) Å. The data on
[TiCl4{o-C6H4(AsMe2)2}2]17 are old and not of high precision, but
the reported values of Ti–As = 2.71(2) Å and Ti–Cl = 2.46(2) Å
show similar trends between Ti and Zr analogues.
The two iodo-complexes are very similar with slightly smaller
corresponding bond lengths in the hafnium complex, reflect-
ing the slightly smaller covalent radius of hafnium.10 Again, the
As–M–As angles within the chelate rings are ca. 70°, although in
[ZrI4{o-C6H4(AsMe2)2}2] the Zr–As distances are ca. 0.05 Å longer
than in the chloro-analogue. This may be due to either the greater
steric requirement of the larger iodide co-ligands, or to the weaker
Lewis acidity of the ZrI4. We also note that the Zr–I bond lengths
in this complex (2.8835(6)–2.9332(6) Å), compared to those in the
Crystal structures
X-Ray quality crystals were difficult to obtain from these sys-
tems, and except for the iodo-complexes, which were grown
from solutions of pre-isolated samples, could only be obtained
from the mother-liquors from the bulk syntheses. The structures
of [ZrCl4{o-C6H4(AsMe2)2}2], [ZrBr4{o-C6H4(PMe2)2}2] and
[MI4{o-C6H4(AsMe2)2}2] (M = Zr or Hf) all reveal eight-coordinate
metal centres with a dodecahedral geometry (Figs. 3–5, Tables
1–4), similar to those reported previously for the Ti(IV) chloro- and
bromo-complexes of these two ligands,13 although these are the first
Zr and Hf examples to be structurally authenticated. As before, the
halogens occupy the “B” sites of the flattened tetrahedron.17 The
chloro- and bromo-complexes have 2m (D ) crystallographic
4
2d
symmetry whereas the iodides have no crystallographic symmetry
but the geometry is in good accord with the D2d model. There are few
directly analogous structures of phosphine or arsine complexes of
these two metals from which to draw comparisons. The bond lengths
D a l t o n T r a n s . , 2 0 0 4 , 3 3 0 5 – 3 3 1 2
3 3 0 7

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Table 1 Selected bond lengths (Å) and angles (°) for [ZrCl4{o-C6H4(AsMe2)2}2]
Zr1–Cl1
As1–C1
2.5145(11)
1.939(3)
Zr1–As1
As1–C2
2.8460(6)
1.953(5)
As1–Zr1–As1a
As1–Zr1–As1b
Zr1–As1–C
70.45(2)
131.86(1)
117.0(1), 116.2(2)
Cl1–Zr1–Cl1a
Cl1–Zr1–Cl1b
C–As1–C
146.29(5)
94.82(2)
101.0(2), 101.4(2)
Symmetry operations: a = −x, −y, z. b = −x, y, −z.
Table 2 Selected bond lengths (Å) and angles (°) for [ZrBr4{o-
increasing the steric bulk of the diphosphine, as in o-C6H4(PPh2)2,
leads to six-coordination only.
C6H4(PMe2)2}2]c
The coordination chemistry of zirconium and hafnium tet-
raiodides has been very little studied, and the much improved
solubilities of their complexes in non-coordinating solvents was
unexpected. Usefully, this permitted much better quality solution
spectroscopic data being obtained. We suggest that MI4 should be
considered as the reagent of choice in other studies where good
solubility is required.
Zr1–Br1
P1–C1
2.6488(13)
1.825(10)
Zr1–P1
P1–C2
2.800(3)
1.822(10)
P1–Zr1–P1a
70.25(12)
Br1–Zr1–Br1a
146.00(6)
94.90(2)
101.7(4), 103.0(9)
P1–Zr1–P1b 131.99(8)
Br1–Zr1–Br1b
Zr1–P1–C
115.3(4), 116.4(4) C–P1–C
Symmetry operations: a = −x, −y, z. b = −x, y, −z. c Refinement in space
group I42m.
Experimental
Physical measurements were made as described previously.4,13 All
preparations were carried out under a dry dinitrogen atmosphere
using standard Schlenk and dry-box techniques. Zirconium and
hafnium halides were obtained from Aldrich. The ligands were
made by literature methods: o-C6H4(AsMe2)2,18 o-C6H4(PMe2)2,19
MeC(CH2AsMe2)3,18 and o-C6H4(PPh2)2.20 Toluene, tetrahydro-
furan (thf) and n-hexane were dried by distillation from sodium/
benzophenone ketyl, dichloromethane from CaH2.
seven-coordinate [ZrI4{PMe3)3}] (2.829(2)–2.904(2) Å),10 and the
six-coordinate [ZrI4(PMe2Ph)2] (2.7787(6), 2.7902(7) Å),9 show the
expected (small) increase with increasing coordination number. The
Hf–I bonds in [HfI4{o-C6H4(AsMe2)2}2] (2.8722(5)–2.9096(5) Å)
are significantly shorter than those in the eight-coordinate Hf(II) car-
bonyl [HfI2(CO)2(Me2PCH2CH2PMe2)2] (2.986(1), 3.028(1) Å).11
Eight-coordination
also
occurs
for
the
complex
[ZrCl4{MeC(CH2AsMe2)3}2] which involves two bidentate tri-
arsine ligands, (Fig. 6, Table 5), with the remaining free AsMe2
groups directed away from and not interacting with the zirconium
centre. The complex has crystallographic two-fold symmetry, with
the Zr on the two-fold axis. It is also possible to compare the key
structural features of [ZrCl4{o-C6H4(AsMe2)2}2] and [ZrCl4{MeC-
(CH2AsMe2)3}2], which show that whilst the Zr–Cl are little differ-
ent, the Zr–As distance in the triarsine complex is ca. 0.05 Å longer
and the As–Zr–As angle some 4° wider, both attributable to the
larger six-membered chelate ring present.
[ZrCl4{o-C6H4(AsMe2)2}2]
Method 1. The diarsine (0.24 g, 0.84 mmol) in dry CH2Cl2
(10 cm3) was added to a solution of [ZrCl4(Me2S)2] (0.10 g,
0.28 mmol) in CH2Cl2 (50 cm3), and the reaction stirred for 1 h.
The mixture was concentrated in vacuo to ca. 20 cm3, and the white
solid isolated by filtration, washed with dry n-hexane (5 cm3) and
dried in vacuo. Yield 0.17 g (77%). Required for [C20H32As4Cl4Zr]:
C, 29.8; H, 4.0. Found: C, 30.1; H, 4.0%. IR (Nujol mull)/cm−1
(Zr–Cl): 300, 295. UV/Vis (Diffuse reflectance in BaSO4)/cm−1:
1
32200, 35700 (sh), 38500. H NMR (300 K, CD2Cl2):  1.62 (s,
[3H]), 7.6, 7.7 (m, [H]).
Method 2. ZrCl4 (0.07 g, 0.3 mmol) was dissolved in the mini-
mum amount of dry thf (ca. 10 cm3) and a solution of the diarsine
(0.25 g, 0.86 mmol) in thf (10 cm3) added and the reaction mixture
stirred for 24 h. The solution was concentrated in vacuo to ca. 5 cm3,
and the white solid filtered off, rinsed with thf and dried in vacuo.
Yield 0.15 g (62%).
[ZrBr4{o-C6H4(AsMe2)2}2]
Fig. 6 The structure of [ZrCl4{MeC(CH2AsMe2)3}2] showing the atom
labelling scheme. Atomic displacement ellipsoids are drawn at the 50%
probability level and H atoms are omitted for clarity.
The diarsine (0.26 g, 0.91 mmol) in dry CH2Cl2 (10 cm3) was added
to a solution of ZrBr4 (0.15 g, 0.37 mmol) in dry thf (50 cm3),
and the reaction stirred for 24 h. The mixture was concentrated
in vacuo to ca. 10 cm3, and the white solid isolated by filtration,
washed with dry n-hexane (5 cm3) and dried in vacuo. Yield 0.26 g
(41%). Required for [C20H32As4Br4Zr]: C, 24.4; H, 3.3. Found:
C, 24.3; H, 3.1%. IR (Nujol mull)/cm−1 (Zr–Br): 225, 222.
UV/Vis (Diffuse reflectance in BaSO4)/cm−1: 29000 (sh), 32500.
1H NMR (300 K, CD2Cl2):  1.74 (s, [3H]), 7.6, 7.7 (m, [H]).
Conclusions
The detailed studies of the Zr(Hf)X4/o-C6H4(EMe2)2 (X = Cl or Br,
E = P or As) systems show that only eight-coordinate [MX4(L–L)2]
form. This is in marked contrast to the corresponding titanium sys-
tems where both 1:1 and 2:1 L–L:Ti species can be isolated under
appropriate conditions. For these two larger metal ions, the MI4 also
form 2:1 complexes only, whereas with titanium(IV) iodide the six-
coordinate [TiI4(L–L)] are obtained, probably due to steric factors
at the smaller titanium centre. The preference for eight-coordination
is also demonstrated by the triarsine ligand, where there is no
evidence for 1:1 complexes with either six- or seven-coordinate
metal centres. These results suggest a significant electronic driv-
ing force for eight-coordination in these compounds, since with
low ligand:metal ratios the reactions still proceed to form the
eight-coordinate complexes (leaving unreacted MX4), but no six-
coordinate species. However, weakening the donor power and
[ZrI4{o-C6H4(AsMe2)2}2]
ZrI4 (0.15 g, 0.25 mmol) was suspended in dry CH2Cl2 (20 cm3) and
a solution of the diarsine (0.21 g, 0.75 mmol) in dry CH2Cl2 (5 cm3)
added. The reaction was stirred for 24 h, the solution reduced in
vacuo to ca. 5 cm3, and the yellow precipitate filtered off and dried
in vacuo. Yield 0.21 g (71%). Required for [C20H32As4I4Zr]·CH2Cl2:
C, 20.0; H, 2.7. Found: C, 19.4; H, 2.6%. UV/Vis (Diffuse reflec-
tance in BaSO4)/cm−1: 24000 (sh), 27000, 33000. 1H NMR (300 K,
CD2Cl2):  2.1 (s, [3H]), 7.65, 7.85 (m, [H]).
3 3 0 8
D a l t o n T r a n s . , 2 0 0 4 , 3 3 0 5 – 3 3 1 2

View Article Online
Table 3 Selected bond lengths (Å) and angles (°) for [ZrI4{o-C6H4(AsMe2)2}2]
Zr1–I1
Zr1–I2
Zr1–I3
Zr1–I4
As–C
2.8982(6)
2.9086(6)
2.8835(6)
2.9332(6)
Zr1–As1
Zr1–As2
Zr1–As3
Zr1–As4
2.9073(7)
2.8844(7)
2.8842(7)
2.8977(7)
1.939(6)–1.957(5)
As1–Zr1–As2
As3–Zr1–As4
As1–Zr1–As3
As1–Zr1–As4
As2–Zr1–As3
As2–Zr1–As4
Zr1–As–C(Ph)
C–As–C
70.25(2)
69.94(2)
130.35(2)
132.64(2)
130.17(2)
135.02(2)
114.4(2)–115.3(2)
98.2(3)–102.1(2)
I1–Zr1–I2
I3–Zr1–I4
I1–Zr1–I3
I1–Zr1–I4
I2–Zr1–I3
I2–Zr1–I4
Zr1–As–C(H3)
145.47(2)
145.50(2)
93.78(2)
94.24(2)
96.68(2)
95.46(2)
118.6(2)–120.1(2)
Table 4 Selected bond lengths (Å) and angles (°) for [HfI4{o-C6H4(AsMe2)2}2]
Hf1–I1
Hf1–I2
Hf1–I3
Hf1–I4
As–C
2.8843(5)
2.9096(5)
2.8796(6)
2.8722(5)
Hf1–As1
Hf1–As2
Hf1–As3
Hf1–As4
2.8781(8)
2.8966(7)
2.8665(7)
2.8847(7)
1.919(8)–1.969(7)
As1–Hf1–As2
As3–Hf1–As4
As1–Hf1–As3
As1–Hf1–As4
As2–Hf1–As3
As2–Hf1–As4
Hf1–As–C(Ph)
C–As–C
70.20(2)
70.18(2)
130.18(2)
134.69(2)
130.55(2)
132.57(2)
114.4(2)–115.6(2)
97.4(3)–102.1(3)
I1–Hf–I3
I2–Hf–I4
I1–Hf–I2
I1–Hf–I4
I2–Hf–I3
I3–Hf–I4
Hf1–As–C(H3)
145.65(2)
145.10(2)
94.36(2)
93.53(2)
95.71(2)
96.67(2)
118.6(3)–120.1(2)
Table 5 Selected bond lengths (Å) and angles (°) for [ZrCl4{MeC(CH2AsMe2)3}2]
Zr1–Cl1
Zr1–Cl2
As–C
2.5314(14)
2.4943(14)
1.929(6)–1.974(6)
Zr1–As1
Zr1–As2
2.8976(7)
2.9064(7)
As1–Zr1–As2
As1–Zr1–As1a
As1–Zr1–As2a
As2–Zr1–As2a
Zr1–As–C(H2)
74.64(2)
122.65(3)
130.53(2)
132.70(4)
Cl1–Zr1–Cl2a
Cl1–Zr1–Cl2
Cl1–Zr1–Cl1a
Cl2–Zr1–Cl2a
Zr1–As–C(H3)
143.12(5)
93.87(5)
99.41(7)
95.77(8)
111.6(2)–116.1(2)
127.8(2), 126.0(2)
Symmetry operation: a = y, x, 1 − z.
26800, 33200. 1H NMR (300 K, CD2Cl2):  2.29 (d, [3H], J = 7 Hz)
7.66, 7.86 (m, [3H]). 31P{1H} NMR (300 K, CH2Cl2):  −14.5.
[ZrCl4{o-C6H4(PMe2)2}2]
ZrCl4 (0.06 g, 0.26 mmol) was dissolved in the minimum amount
of dry thf (10 cm3) and a solution of o-C6H4(PMe2)2 (0.15 g,
0.75 mmol) in thf (10 cm3) added and the reaction mixture stirred
for 24 h. The resulting solution was concentrated in vacuo to ca.
5 cm3, and the white solid filtered off, rinsed with thf and dried in
vacuo. Yield 0.062 g (38%). Required for [C20H32Cl4P4Zr]: C, 38.2;
H, 5.1. Found: C, 37.8; H, 4.9%. IR (Nujol mull)/cm−1 (Zr–Cl):
303, 285. UV/Vis (Diffuse reflectance in BaSO4)/cm−1: 32800,
37000. 1H NMR (300 K, CD2Cl2):  1.74 (d, [3H], J = 6 Hz), 7.6,
7.8 (m, [H]). 31P{1H} NMR (300 K, CH2Cl2):  +2.2.
[HfCl4{o-C6H4(AsMe2)2}2]
HfCl4 (0.16 g, 0.5 mmol) was dissolved in dry thf (30 cm3) and a
solution of the diarsine (0.44 g, 1.5 mmol) in thf (10 cm3) added
and the reaction mixture stirred for 36 h. The solution was con-
centrated in vacuo to ca. 5 cm3, and the white solid filtered off,
rinsed with thf and dried in vacuo. Yield 0.35 g (40%). Required
for [C20H32As4Cl4Hf]: C, 26.9; H, 3.6. Found: C, 26.5; H, 3.6%.
IR (Nujol mull)/cm−1 (Hf–Cl): 272 vbr. UV/Vis (Diffuse reflec-
tance in BaSO4)/cm−1: 32300 (sh), 36300, 40000. 1H NMR (300 K,
CD2Cl2):  1.60 (s, [3H]), 7.55, 7.66 (m, [H]).
[ZrBr4{o-C6H4(PMe2)2}2]
This was made similarly to the above from ZrBr4 (0.15 g,
0.37 mmol) and o-C6H4(PMe2)2 (0.18 g, 0.90 mmol). Yield 0.17 g
(56%). Required for [C20H32Br4P4Zr]: C, 29.8; H, 4.0. Found: C,
30.4; H, 4.5%. IR (Nujol mull)/cm−1 (Zr–Br): 221, 218. UV/Vis
(Diffuse reflectance in BaSO4)/cm−1: 29000 (sh), 33000. 1H NMR
(300 K, CD2Cl2):  1.89 (d, [3H], J = 6 Hz), 7.62, 7.66 (m, [H]).
31P{1H} NMR (300 K, CH2Cl2):  −3.1.
[HfBr4{o-C6H4(AsMe2)2}2]
This was made similarly from HfBr4 (0.25 g, 0.5 mmol) and the
diarsine (0.42 g, 1.5 mmol) in thf. White solid. Yield 0.19 g (40%).
Required for [C20H32As4Br4Hf]: C, 22.4; H, 3.1. Found: C, 22.4; H,
3.1%. IR (Nujol mull)/cm−1 (Hf–Br): 200, 190. UV/Vis (Diffuse
reflectance in BaSO4)/cm−1: 29070 (sh), 32250, 36000 (vbr). H
1
NMR (300 K, CD2Cl2):  1.77 (s, [3H]), 7.61, 7.73 (m, [H]).
[HfI4{o-C6H4(AsMe2)2}2]
[ZrI4{o-C6H4(PMe2)2}2]
This was made similarly to [ZrI4{o-C6H4(AsMe2)2}2] from ZrI4
(0.15 g, 0.25 mmol) and the diphosphine (0.15 g, 0.75 mmol) in
CH2Cl2.After 24 h the yellow solution was concentrated to ca. 5 cm3
and the pale yellow solid filtered off and dried in vacuo. Yield 0.17 g
(68%). Required for [C20H32I4P4Zr]: C, 24.1; H, 3.2. Found: C, 23.7;
H, 3.1%. UV/Vis (Diffuse reflectance in BaSO4)/cm−1: 25000 (sh),
This was made from HfI4 (0.23 g, 0.33 mmol) and the ligand (0.29 g,
1.0 mmol) in CH2Cl2 (50 cm3) in a similar manner to the zirconium
analogue above, except that the reaction mixture was stirred for
36 h before work up. Cream solid. Yield 0.30 g (72%). Required for
[C20H32As4HfI4]: C, 19.1; H, 2.6. Found: C, 18.8; H, 2.6%. UV/Vis
D a l t o n T r a n s . , 2 0 0 4 , 3 3 0 5 – 3 3 1 2
3 3 0 9

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(Diffuse reflectance in BaSO4)/cm−1: 25000 (sh), 29400, 32250. 1H
NMR (300 K, CD2Cl2):  2.08 (s, [3H]), 7.65, 7.81 (m, [H]).
After 24 h the solution was concentrated to ca. 10 cm3, and the
white solid separated by filtration, rinsed with hexane and dried in
vacuo. Yield 0.40 g (73%). IR (Nujol mull)/cm−1 (Hf–Cl): 284, 275
(sh). UV/Vis (Diffuse reflectance in BaSO4)/cm−1: 33900, 41300.
1H NMR (300 K, CD2Cl2): insoluble.
[HfCl4{o-C6H4(PMe2)2}2]
HfCl4 (0.16 g, 0.50 mmol) was dissolved in the minimum amount
of dry thf (ca. 15 cm3) and a solution of o-C6H4(PMe2)2 (0.30 g,
1.5 mmol) in thf (10 cm3) added and the reaction mixture stirred for
36 h. The resulting solution was concentrated in vacuo to ca. 5 cm3,
and the white solid filtered off, rinsed with thf and dried in vacuo.
Yield 0.062 g (42%). Required for [C20H32Cl4HfP4]: C, 33.5; H, 4.5.
Found: C, 32.6; H, 4.7%. IR (Nujol mull)/cm−1 (Hf–Cl): 267 (vbr).
UV/Vis (Diffuse reflectance in BaSO4)/cm−1: 33900 (sh), 36400,
40000. 1H NMR (300 K, CD2Cl2):  1.79 (br s, [3H]), 7.62, 7.87 (m,
[H]). 31P{1H} NMR (300 K, CH2Cl2):  +1.0.
[HfI4{MeC(CH2AsMe2)3}2]
This was made similarly to the zirconium complex from HfI4 (0.23 g,
0.33 mmol) and the triarsine (0.32 g, 0.83 mmol). Pale yellow solid.
Yield 75%. Required for [C22H54As6HfI4]: C, 18.2; H, 3.7. Found: C,
17.7; H, 4.5%. UV/Vis (Diffuse reflectance in BaSO4)/cm−1: 25500
(br sh), 30300, 35000. 1H NMR (300 K, CD2Cl2):  1.02 (s), 1.07
(sh), 1.17 (br), 1.80 (br); (223 K) 0.94 (s) [6H] (AsMe-free), 1.22 (s)
[3H] (CMe), 1.60 (s), 1.61 (s) [6H, 6H] (AsMe-coord), 1.80 (s) [2H]
(CH2-free), 2.14 (d), 2.20 (d) [2H, 2H] (CH2-coord). 13C{1H} NMR
(220 K, CD2Cl2):  11.1 (AsMe-free), 17.0, 18.2 (AsMe-coord),
31.9 (CH2-free), 38.6 (C), 41.4 (CH2-coord), 50.2 (Me).
[HfBr4{o-C6H4(PMe2)2}2]
This was made similarly from HfBr4 (0.25 g, 0.5 mmol) and the
ligand (0.30 g, 1.5 mmol) in thf. Cream solid. Yield 0.23 g (51%).
Required for [C20H32Br4HfP4]: C, 26.9; H, 3.6. Found: C, 26.4; H,
4.1%. IR (Nujol mull)/cm−1 (Hf–Br): 192, 183. UV/Vis (Diffuse
[ZrCl4{o-C6H4(PPh2)2}]
ZrCl4 (0.20 g, 0.86 mmol) was suspended in dry CH2Cl2 (60 cm3)
and powdered o-C6H4(PPh2)2 (0.57 g, 1.3 mmol) added. The mix-
ture was stirred for 48 h during which time the zirconium halide
dissolved to give a clear solution, which slowly re-precipitated a
white powder. The latter was filtered off and dried in vacuo. Yield
0.40 g (59%). Required for [C30H24Cl4P2Zr]·CH2Cl2: C, 48.7; H,
3.5. Found: C, 49.5; H, 3.8%. IR (Nujol mull)/cm−1 (Zr–Cl): 350
(br). UV/Vis (Diffuse reflectance in BaSO4)/cm−1: 31250, 36000.
31P{1H} NMR (300 K, CH2Cl2):  +13.5.
1
reflectance in BaSO4)/cm−1: 34500 (br), 42500. H NMR (300 K,
CD2Cl2):  1.99 (br s [3H]), 7.62, 7.83 (m, [H]). 31P{1H} NMR
(300 K, CH2Cl2):  −3.8.
[HfI4{o-C6H4(PMe2)2}2]
This was made from HfI4 (0.23 g, 0.33 mmol) and the ligand (0.20 g,
1.0 mmol) in CH2Cl2 (50 cm3) in a similar manner to the zirconium
analogue above, except that the reaction mixture was stirred for
36 h, before work up. Cream solid. Yield 0.30 g (83%). Required for
[C20H32HfI4P4]: C, 22.2; H, 3.0. Found: C, 22.4; H, 3.2%. UV/Vis
(Diffuse reflectance in BaSO4)/cm−1: 24400 (sh), 28800, 33780. 1H
NMR (300 K, CD2Cl2):  2.33 (d, [3H] J = 8 Hz), 7.71, 7.90 (m,
[H]). 31P{1H} NMR (300 K, CH2Cl2):  −15.2.
[ZrBr4{o-C6H4(PPh2)2}]
This was made similarly in 72% yield. Required for
[C30H24Br4P2Zr]·CH2Cl2: C, 39.5; H, 2.8. Found: C, 39.1; H,
2.8%. IR (Nujol mull)/cm−1 (Zr–Br): 261 (br). UV/Vis (Diffuse
reflectance in BaSO4)/cm−1: 29850, 33000. 31P{1H} NMR (300 K,
CH2Cl2):  +11.5.
[ZrCl4{MeC(CH2AsMe2)3}2]
The triarsine (0.28 g, 0.70 mmol) in dry CH2Cl2 (10 cm3) was added
to a solution of [ZrCl4(Me2S)2] (0.10 g, 0.28 mmol) in CH2Cl2
(50 cm3), and the reaction stirred for 1 h. The mixture was slowly
concentrated in vacuo over ca. 3 h to 10 cm3, and the white solid
isolated by filtration, washed with dry n-hexane (5 cm3) and dried in
vacuo. Yield 0.19 g (70%). Required for [C22H54As6Cl4Zr]: C, 26.4;
H, 5.5. Found: C, 26.0; H, 5.0%. IR (Nujol mull)/cm−1 (Zr–Cl):
304, 296. UV/Vis (Diffuse reflectance in BaSO4)/cm−1: 31100,
[ZrI4{o-C6H4(PPh2)2}]
This was made similarly, the ZrI4 dissolved very slowly in the
CH2Cl2 in the presence of the diphosphine, but the resulting com-
plex was more soluble and the solution was concentrated to ca.
20 cm3 before removal of the yellow complex by filtration. Yield
60%. Required for [C30H24I4P2Zr]: C, 34.4; H, 2.3. Found: C, 34.5;
H, 2.1%. UV/Vis (Diffuse reflectance in BaSO4)/cm−1: 24000,
30300 (sh), 32000. 31P{1H} NMR (300 K, CH2Cl2):  −15.7.
1
39200. H NMR (300 K, CD2Cl2):  1.04 (s), 1.31 (s), 1.79 (s);
(248 K) insoluble.
[HfCl4{o-C6H4(PPh2)2}]
[ZrI4{MeC(CH2AsMe2)3}2]
This was made similarly to the zirconium chloride complex but with
stirring for 72 h. Yield 70%. Required for [C30H24Cl4HfP2]: C, 47.0;
H, 3.2. Found: C, 46.8; H, 3.5%. IR (Nujol mull)/cm−1 (Hf–Cl):
325, 302. UV/Vis (Diffuse reflectance in BaSO4)/cm−1: 30300,
35000. 31P{1H} NMR (300 K, CH2Cl2):  +18.0.
Zirconium tetraiodide (0.20 g, 0.33 mmol) was suspended in dry
CH2Cl2 (25 cm3), and the triarsine (0.32 g, 0.83 mmol) added. On
stirring the orange tetraiodide slowly dissolved forming a deep
yellow solution, which slowly deposited some yellow solid. After
24 h the solution was concentrated in vacuo to ca. 5 cm3 and the
yellow powder filtered off, rinsed with dry n-hexane, and dried
in vacuo. Yield 0.20 g (45%). Required for [C22H54As6I4Zr]: C,
19.3; H, 4.0. Found: C, 19.6; H, 4.3%. UV/Vis (Diffuse reflec-
[HfBr4{o-C6H4(PPh2)2}]
This was made as above in 45% yield. Required for [C30H24Br4HfP2]:
C, 38.2; H, 2.6. Found: C, 38.2; H, 2.7%. IR (Nujol mull)/cm−1 (Hf–
Br): 219 (br), 206 (sh). UV/Vis (Diffuse reflectance in BaSO4)/cm−1:
30000 (sh), 33000. 31P{1H} NMR (300 K, CH2Cl2):  +13.5.
1
tance in BaSO4)/cm−1: 25000 (br sh), 27000, 32500. H NMR
(300 K, CD2Cl2):  1.30 (s), 1.35 (s), 2.01 (s); (223 K) 0.95 (s)
[6H] (AsMe-free), 1.29 (s) [3H] (CMe), 1.62 (s), 1.64 (s) [6H, 6H]
(AsMe-coord), 1.80 (s) [2H] (CH2-free), 2.16 (d), 2.26 (d) [2H, 2H]
(CH2-coord). 13C{1H} NMR (220 K, CD2Cl2):  11.2 (AsMe-free),
17.6, 18.9 (AsMe-coord), 31.8 (CH2-free), 38.6 (C), 41.4 (CH2-
coord), 50.2 (Me).
[HfI4{o-C6H4(PPh2)2}]
This was made similarly in 65% yield. Required for [C30H24HfI4P2]:
C, 31.8; H, 2.2. Found: C, 31.4; H, 2.4%. UV/Vis (Diffuse reflec-
tance in BaSO4)/cm−1: 24100 (sh), 30300, 33000. 31P{1H} NMR
(300 K, CH2Cl2):  −17.0.
[HfCl4{MeC(CH2AsMe2)3}2]
This was made by reacting HfCl4 (0.16 g, 0.50 mmol), Me2S
(0.12 g, 1.9 mmol) in CH2Cl2 (50 cm3). After 24 h the solution
was filtered and the filtrate taken to dryness in vacuo. Dry CH2Cl2
(30 cm3) was added followed by the triarsine (0.45 g, 1.2 mmol).
X-Ray crystallography
Brief details of the crystal data and refinement are given in Table 6.
DatacollectionswerecarriedoutusingaBruker-NoniusKappaCCD
3 3 1 0
D a l t o n T r a n s . , 2 0 0 4 , 3 3 0 5 – 3 3 1 2

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diffractometer with graphite-monochromated Mo-K radiation
( = 0.71073 Å) and with the crystals held at 120 K in a gas stream.
Crystals of [ZrCl4{o-C6H4(AsMe2)2}2], [ZrBr4{o-C6H4(PMe2)2}2]
and [ZrCl4{MeC(CH2AsMe2)3}2], were obtained with difficulty
by allowing the filtrate from the preparations to evaporate slowly
in the glove box. Crystals of [MI4{o-C6H4(AsMe2)2}2] (M = Zr
or Hf) were obtained by allowing dichloromethane solutions of
the pre-formed complexes to evaporate slowly in the glove box.
Structure solution and refinement were routine21–24 (except as de-
scribed below) with H atoms introduced in calculated positions.
[ZrCl4{o-C6H4(AsMe2)2}2] was initially solved in the space group
I4 (no. 82) by comparison with previous related structures,13 but
it became clear that the space group I42m (no. 121) in the higher
symmetry Laue group 4/mmm gave an equally satisfactory structure
solution and this was adopted.§ The Flack parameter25 established
the absolute structure. The tetragonal [ZrCl4{MeC(CH2AsMe2)3}2]
belongs to one of a pair of enantiomorphous space groups and cor-
rect choice for the crystal selected (P43212) was also established
from the Flack parameter. [ZrBr4{o-C6H4(PMe2)2}2] presented
a difficulty in that the crystal system, unit cell and lattice type
produced by the diffractometer software and the intensity data col-
lected yielded a satisfactory structure. However, this orthorhombic
A lattice can be transformed more easily to a smaller tetragonal I
lattice. Following the transformation the rejected reflections were
on average much lower in intensity and among these there were no
very intense reflections. The tetragonal structure in the I 2m space
4
group found for related compounds has a marginally better fit to the
data and has lower residual peaks in the difference electron-density
map. Both sets of crystallographic data are included in Table 6
and Table 2 presents the bond lengths and angles in the tetragonal
model. Attempts to grow other crystals of this complex have not
been successful so the question of whether the structure really is
orthorhombic with a sub-cell which is very close to tetragonal is
unresolved (although in chemical terms the two answers are identi-
cal). The two tetraiodides have a cell metrically close to tetragonal
but the absences do not correspond to a tetragonal space group and
a satisfactory solution in an orthorhombic space group emerged.
Racemic twinning was observed and the DELU command22 was
used in the Hf compound to control non-positive definite anisotro-
pic thermal parameters which probably arose from an inadequate
absorption correction.
CCDC reference numbers 241865–241869.
See http://www.rsc.org/suppdata/dt/b4/b409051a/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
We thank the EPSRC for support, (B. P. and M. L. M.), Mr M. D.
Brown for assistance with X-ray data collection, and Rhodia for a
generous gift of chemicals.
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D a l t o n T r a n s . , 2 0 0 4 , 3 3 0 5 – 3 3 1 2
3 3 1 1

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