Synthesis, Structure, and Reactivity of [Zr6Cl18H5]2- , the First Paramagnetic Species of Its Class

Article abstract of DOI:10.1021/ic960454q

Reaction of [Zr₆Cl₁₈H₅]^3- (1) with 1 equiv of TiCl₄ yields a new cluster anion, [Zr₆Cl₁₈H₅]^2- (2), which can be converted back into [Zr₆Cl₁₈H₅]^3- (1) upon addition of 1 equiv of Na/Hg. Cluster 2 is paramagnetic and unstable in the presence of donor molecules. It undergoes a disproportionation reaction to form 1, some Zr(IV) compounds, and H₂. It also reacts with TiCl₄ to form [Zr₂Cl₉]^- (4) and a tetranuclear mixed-metal species, [Zr₂Ti₂Cl₁₆]^2- (3). The oxidation reaction of 1 with TiCl₄ is unique. Oxidation of 1 with H⁺ in CH₂Cl₂ solution results in the formation of [ZrCl₆]^2- (5) and H₂, while in py solution the oxidation product is [ZrCl₅(py)]^- (6). There is no reaction between 1 and TiI₄, ZrCl₄, [TiCl₆]^2-, [ZrCl₆]^2-, or CrCl₃. Compounds [Ph₄P]₂[Zr₆Cl₁₈H₅] (2a), [Ph₄P]₂[Zr₂Ti₂Cl₁₆] (3a), [Ph₄P]₂[Zr₂Cl₉] (4a), [Ph₄P]₂[ZrCl₆]·4MeCN (5a·4MeCN), and [Ph₄P][ZrCl₅(py)]_(6a) were characterized by X-ray crystallography. Compound 2a crystallized in the trigonal space group R3? with cell dimensions (20 °C) of a = 28.546(3) A?, b = 28.546(3) A?, c = 27.679(2) A?, V = 19533(3) A?³, and Z = 12. Compound 3a crystallized in the triclinic space group P1? with cell dimensions (-60 °C) of a = 11.375(3) A?, b = 13.357(3) A?, c = 11.336(3) A?, a = 106.07(1)°, β= 114.77(1)°, γ = 88.50(1)°, V = 1494.8(7) A?³, and Z = 1. Compound 4a crystallized in the triclinic space group P1? with cell dimensions (-60 °C) of a = 12.380(5) A?, b= 12.883(5) A?, c= 11.000(4) A?, α = 110.39(7)°, β = 98.29(7)°, γ = 73.12(4)°, V= 1572(1) A?³, and Z = 2. Compound 5a-4MeCN crystallized in the monoclinic space group P2₁/c with cell dimensions (-60 °C) of a = 9.595(1) A?, b = 19.566(3) A?, c = 15.049(1) A?, β= 98.50(1)°, V = 2794.2(6) A?³3, and Z = 2. Compound 6a crystallized in the monoclinic space group P2₁/c with cell dimensions (20 °C) of a = 10.3390(7) A?, b = 16.491(2) A?, c = 17.654(2) A?, β= 91.542(6)°, V = 3026.4(5) A?³, and Z = 4.

Full text of DOI:10.1021/ic960454q

7364
Inorg. Chem. 1996, 35, 7364-7369
Synthesis, Structure, and Reactivity of [Zr6Cl18H5]2-, the First Paramagnetic Species of Its
Class
Linfeng Chen and F. Albert Cotton*
Department of Chemistry and Laboratory for Molecular Structure and Bonding, Texas A&M University,
College Station, Texas 77843
ReceiVed April 25, 1996X
Reaction of [Zr6Cl18H5]3- (1) with 1 equiv of TiCl4 yields a new cluster anion, [Zr6Cl18H5]2- (2), which can be
converted back into [Zr6Cl18H5]3- (1) upon addition of 1 equiv of Na/Hg. Cluster 2 is paramagnetic and unstable
in the presence of donor molecules. It undergoes a disproportionation reaction to form 1, some Zr(IV) compounds,
and H2. It also reacts with TiCl4 to form [Zr2Cl9]- (4) and a tetranuclear mixed-metal species, [Zr2Ti2Cl16]2- (3).
The oxidation reaction of 1 with TiCl4 is unique. Oxidation of 1 with H+ in CH2Cl2 solution results in the
formation of [ZrCl6]2- (5) and H2, while in py solution the oxidation product is [ZrCl5(py)]- (6). There is no
reaction between 1 and TiI4, ZrCl4, [TiCl6]2-, [ZrCl6]2-, or CrCl3. Compounds [Ph4P]2[Zr6Cl18H5] (2a), [Ph4P]2[Zr2-
Ti2Cl16] (3a), [Ph4P]2[Zr2Cl9] (4a), [Ph4P]2[ZrCl6]‚4MeCN (5a‚4MeCN), and [Ph4P][ZrCl5(py)] (6a) were
characterized by X-ray crystallography. Compound 2a crystallized in the trigonal space group R3h with cell
dimensions (20 °C) of a ) 28.546(3) Å, b ) 28.546(3) Å, c ) 27.679(2) Å, V ) 19533(3) Å3, and Z ) 12.
Compound 3a crystallized in the triclinic space group P1h with cell dimensions (-60 °C) of a ) 11.375(3) Å, b
) 13.357(3) Å, c ) 11.336(3) Å, R ) 106.07(1)°, â ) 114.77(1)°, γ ) 88.50(1)°, V ) 1494.8(7) Å3, and Z )
1. Compound 4a crystallized in the triclinic space group P1h with cell dimensions (-60 °C) of a ) 12.380(5) Å,
b ) 12.883(5) Å, c ) 11.000(4) Å, R ) 110.39(7)°, â ) 98.29(7)°, γ ) 73.12(4)°, V ) 1572(1) Å3, and Z ) 2.
Compound 5a‚4MeCN crystallized in the monoclinic space group P21/c with cell dimensions (-60 °C) of a )
9.595(1) Å, b ) 19.566(3) Å, c ) 15.049(1) Å, â ) 98.50(1)°, V ) 2794.2(6) Å3, and Z ) 2. Compound 6a
crystallized in the monoclinic space group P21/c with cell dimensions (20 °C) of a ) 10.3390(7) Å, b ) 16.491(2)
Å, c ) 17.654(2) Å, â ) 91.542(6)°, V ) 3026.4(5) Å3, and Z ) 4.
Introduction
clusters are potential reducing reagents. Reactions of the
hexazirconium clusters with TiCl4 and H+ have yielded several
new compounds, which are reported here.
A method to prepare new octahedral zirconium clusters,
different from the “stuffed” ones pioneered by Corbett and co-
workers,1,2 has been developed in our laboratory. Reduction
of ZrCl4 with HSn(n-Bu)3 followed by addition of Cl- or
phosphines has yielded a series of pentanuclear and hexanuclear
zirconium cluster compounds containing two or more cluster
hydrogen atoms.3-9 These hydrogen-containing hexazirconium
clusters ([Zr6Cl14H4(PR3)4],7 [Zr6Cl18H5]3-,6 [Zr6Cl18H4]4-,9 and
others) are different from the clusters formed in solid-state
reactions in that they have no alien atoms at the center but
instead have two to five hydrogen atoms in the clusters.
Experimental Section
All manipulations were conducted under an argon atmosphere by
using standard vacuum line and Schlenk technique. Glassware was
oven dried at 150 °C for 24 h prior to use. Solvents were predried
over molecular sieves and freshly distilled under nitrogen from
appropriate drying reagents. ZrCl4, TiCl4, TiI4, and CrCl3 were
purchased from Strem Chemicals and used as received. [Ph4P]Cl, PMe3,
PMe2Ph, Proton Sponge, and (i-Pr)2NLi were purchased from Aldrich.
[Ph4P]Cl was dried at 150 °C under vacuum for 24 h. [Ph4P]3[Zr6-
Cl18H5]‚3CH2Cl2 (1a‚3CH2Cl2),6 [Ph4P]4[Zr6Cl18H4]‚4MeCN,9 [Ph4P]2-
[ZrCl6]‚2CH2Cl2,10 and [MePPh3]2[TiCl6]11 were prepared by the
reported procedures. The ESR spectrum was recorded on a Bru¨ker
ESP 300 spectrometer at 100 K. The magnetic susceptibility was
measured on a magnetic susceptibility balance from Johnson Matthey
Chemicals Limited.
Even though so many hexazirconium clusters have been
prepared and structurally characterized, their reactivities have
scarcely been studied. With the Zr atoms in a low oxidation
state and hydrogen atoms on the cluster, our hexazirconium
Preparation of [Ph4P]2[Zr6Cl18H5] (2a). A 200 mg (0.081 mmol)
sample of [Ph4P]3[Zr6Cl18H5]‚3CH2Cl2 (1a‚3CH2Cl2) was dissolved in
50 mL of CH2Cl2. To this purple solution was added dropwise 0.81
mL of 0.1 M TiCl4/CH2Cl2 through a syringe. The solution turned
blue instantly, and a brown precipitate was formed. The brown
precipitate was separated from the solution by decantation. The blue
solution was then evaporated to ca. 10 mL. Tiny cubic dark blue
crystals of 2a appeared within 30 min. After 12 h, the solution was
decanted, and the crystalline yield of 2a was 91% (138 mg). This
reaction can be scaled up by a factor of 2-3. Attempts to grow crystals
of the brown solid from its MeCN and Me2CO solutions were
unsuccessful.
X Abstract published in AdVance ACS Abstracts, November 1, 1996.
(1) (a) Corbett, J. D.; Garcia, E.; Kwon, Y.-U.; Gulay, A. High Temp.
Sci. 1990, 27, 337. (b) Rogel, F.; Zhang, J.; Payne, M. W.; Corbet, J.
D. AdV. Chem. Ser. 1990, 226, 369. (c) Corbett, J. D.; Ziebarth, R. P.
Acc. Chem. Res. 1989, 22, 256.
(2) Hughbanks, T.; Rosenthal, G.; Corbett, J. D. J. Am. Chem. Soc. 1988,
110, 1511.
(3) Cotton, F. A.; Feng, X.; Shang, M.; Wojtczak, W. A. Angew. Chem.,
Int. Ed. Engl. 1992, 31, 1050.
(4) Cotton, F. A.; Wojtczak, W. A. Inorg. Chem. Acta 1994, 223, 93.
(5) Chen, L.; Cotton, F. A.; Wojtczak, W. A. Angew. Chem., Int. Ed.
Engl. 1995, 34, 1877.
(6) Chen, L.; Cotton, F. A.; Wojtczak, W. A. Inorg. Chem., in press.
(7) Chen, L.; Cotton, F. A.; Wojtczak, W. A. Inorg. Chem. 1996, 35, 88.
(8) Cotton, F. A.; Lu, J.; Shang, M.; Wojtczak, W. A. J. Am. Chem. Soc.
1994, 116, 4364.
(10) Hartmann, E.; Dehnicke, K.; Fenske, D.; Goesmann, H.; Baum, G. Z.
Naturforsch., B 1989, 44, 1155.
(9) Chen, L.; Cotton, F. A.; Wojtczak, W. A. Inorg. Chim. Acta, in press.
(11) Hey, E.; Muller, U. Z. Naturforsch., B 1981, 36, 135.
S0020-1669(96)00454-5 CCC: $12.00 © 1996 American Chemical Society

[Zr6Cl18H5]2-
Inorganic Chemistry, Vol. 35, No. 25, 1996 7365
The ESR spectrum of 2a in CH2Cl2 showed a broad signal with a g
value of 1.978. Magnetic susceptibility for 2a: ø ) 1.10 × 10-3 emu
(295 K) after diamagnetic correction; µeff ) 1.62 µB per cluster.
Crystals of 2a suitable for single-crystal diffraction study were
obtained by layering the blue solution with hexane. Cubic dark blue
crystals appeared on the wall of the Schlenk tube within 3 days.
Reactions of [Ph4P]3[Zr6Cl18H5] (1a) with [MePPh3]2[TiCl6], TiI4,
ZrCl4, [Ph4P]2[ZrCl6], and CrCl3. No reaction between 1a and up
to 10 equiv of [MePPh3]2[TiCl6], TiI4, ZrCl4, [Ph4P]2[ZrCl6], or CrCl3
was observed from studies in an NMR tube. There was no obvious
change in the intensities of the cluster hydrogen signal in 1a in 12 h.
Conversion of [Ph4P]2[Zr6Cl18H5] (2a) into [Ph4P]3[Zr6Cl18H5]
(1a). A 200 mg (0.102 mmol) sample of 2a was dissolved in 200 mL
of CH2Cl2 and the solution was placed in a dry ice-acetone bath. Then
2.2 mL of 0.5 M Na/Hg was introduced into the solution with stirring.
The color of the solution changed from blue to purple instantly. After
10 min, the dry ice-acetone bath was removed, and the solution was
warmed up to room temperature. The purple solution was separated
from the solid by decantation. The solution was reduced in vacuum
to ca. 30 mL and then layered with 50 mL of hexane. Crystalline
1a‚3CH2Cl2 was isolated (138 mg, 55%). When this reaction was
carried out in the presence of 1.0 equiv (0.102 mmol, 38 mg) of
[Ph4P]Cl, the isolated 1a‚3CH2Cl2 was 226 mg (90%).
Disproportionation of [Ph4P]2[Zr6Cl18H5] (2a). The blue color of
compound 2a in CH2Cl2 changed to purple with gas (presumably H2)
evolution upon addition of ligands, D: (D: ) MeCN, Me2CO, THF,
py, PMe3, and PMe2Ph) possessing a lone pair of electrons. By layering
of the purple solution with hexane, purple crystals of 1a‚3CH2Cl2, a
white precipitate, and a small amount (ca. 5%) of colorless crystals of
[Ph4P][Zr2Cl9] (4a) were isolated. Attempts to grow crystals from the
white precipitate by using different ligands, D:, and different solvents
failed. The isolated yields of compound 1a‚3CH2Cl2 from reaction of
compound 2a with 10 equiv of D: were 28% for MeCN, 25% for
Me2CO, 34% for THF, 20% for py, 29% for PMe3, and 30% for
PMe2Ph. It is believed that ligands D: participated in the reactions
because the yield of the product 1a‚3CH2Cl2 increased with the amount
of D: used (up to 10 equiv) and the blue color of 2 vanished only
after about 10 equiv of D: was added.
mL of CH2Cl2. To this solution was added 400 mL of 1.0 M of HCl/
Et2O. The purple color of the solution disappeared instantly, and an
amorphous white precipitate was formed with gas (H2) evolution. The
white precipitate was insoluble in THF, MeCN, Me2CO, CH2Cl2, and
py. The colorless solution was layered with 30 mL of hexane.
Colorless crystals of [Ph4P]2[ZrCl6]‚2CH2Cl210 (63 mg, 22%) were
obtained in 1 week. Use of less HCl resulted only in incomplete
reaction and a lower yield of [Ph4P]2[ZrCl6]‚2CH2Cl2, but no intermedi-
ate products. Reaction of 1a with 10 equiv of MeOH/CH2Cl2 was
similar. The yield of [Ph4P]2[ZrCl6]‚2CH2Cl2 was 18% (52 mg).
When 100 mg (0.041 mmol) of 1a‚3CH2Cl2 in 20 mL of MeCN
was treated with 400 mL of 1.0 M H2O/MeCN, the change of solution
color and bubbling were again observed. By layering of the resulting
colorless solution with 2 mL of hexane and then 30 mL of Et2O, 61
mg (22%) of colorless crystals of [Ph4P]2[ZrCl6]‚4MeCN (5a‚4MeCN)
was isolated in 10 days.
Reaction of 100 mg (0.041 mmol) of 1a‚3CH2Cl2 with 400 mL of
1.0 M H2O/py proceeded similarly to the above reactions. By layering
of the py solution with 30 mL of hexane, 70 mg (41%) of colorless
crystals of [Ph4P][ZrCl5(py)] (6a) were obtained in 1 week.
Reaction of [Ph4P]3[Zr6Cl18H5] (1a) with Proton Sponge. No
reaction between 1a and Proton Sponge (1,8-bis(dimethylamino)-
naphthalene) was observed from a 1H NMR study during a 12 h period
of time.
Reaction of [Ph4P]3[Zr6Cl18H5] (1a) with (i-Pr)2NLi. Compound
1a in CH2Cl2 decomposed gradually upon addition of 1 equiv of (i-
Pr)2NLi to form a brown solid. Attempts to identify the brown solid
by growing crystals were not successful because of its insolubility. No
1
formation of [Zr6Cl18H4]4- was observed during the reaction from H
NMR study.
Reaction of [Ph4P]4[Zr6Cl18H4] with H+. No formation of
[Zr6Cl18H5]3- was observed during the reaction of [Zr6Cl18H4]4- with
1 equiv of 1.0 M HCl/Et2O in CD2Cl2 from 1H NMR study. The
reaction between [Zr6Cl18H4]4- and 10 equiv of HCl/Et2O was similar
to that between
1
and H+ described above with H2 and
[Ph4P]2[ZrCl6]‚2CH2Cl2 (ca. 25% yield) as products.
X-ray Crystallography
CH2Cl2 is the only solvent that we have found so far for compound
2a that does not cause obvious decomposition during a short period of
time. Even in CH2Cl2 solution, however, compound 2a decomposed
slowly. Within 2 weeks the distinguishing blue color of 2a disappeared
and a white precipitate was observed on the wall of the Schlenk tube.
Layering the resulting purple solution with hexane allowed isolation
of 1a‚3CH2Cl2 (24%) and 4a (8%), as well as an amorphous white
solid.
Diffraction intensity measurements at low temperature were made
with crystals mounted on quartz fibers and placed in a cold stream of
nitrogen. Crystals that were used at room temperature were mounted
in thin-walled glass capillaries. Diffraction measurements were made
on an Enraf-Nonius CAD4 automated diffractometer with graphite-
monochromated Mo KR radiation for compound 2a, on a Rigaku
AFC5R automated diffractometer with graphite-monochromated Cu KR
radiation for compound 6a, and on an Enraf-Nonius FAST diffractom-
eter with an area-detector and graphite-monochromated Mo KR
radiation for compounds 3a, 4a, and 5a‚4MeCN. For the crystals on
the CAD4 and Rigaku diffractometers, unit cells were determined by
using search, center, index, and least-squares routines. The Laue classes
and lattice dimensions were verified by axial oscillation photography.
The intensity data were corrected for Lorentz and polarization effects
and for anisotropic decay. Empirical absorption corrections based on
ψ scans were also applied. For the crystals on the FR590 diffractom-
eter, preliminary data collection was carried out first to provide all
parameters and an orientation matrix. A total of 50 reflections were
used in indexing and 250 reflections in cell refinement. Axial images
were obtained to determine the Laue groups and cell dimensions. No
decay corrections or absorption correction were applied.12
CH2Cl2
[Ph4P]2[Zr6Cl18H5]
[Ph P] [Zr Cl H ]
+
4 3 6 18 5
2 weeks8
2a
1a
[Ph P][Zr Cl ]
+ white solid
4
2
9
4a
Reaction of [Ph4P]2[Zr6Cl18H5] (2a) with TiCl4. A 4.2 mL aliquot
of 0.1 M TiCl4/CH2Cl2 was added slowly through a syringe to 100 mg
(0.051 mmol) of 2a in 100 mL of CH2Cl2 with stirring. The blue color
of the solution changed to green with concomitant gas evolution
(presumably H2). After the volume of the solution was reduced to ca.
20 mL in vacuum, the solution was transferred to a Schlenk tube and
layered with 40 mL of hexane. Then 35 mg (15%) of green crystals
of [Ph4P]2[Zr2Ti2Cl16] (3a), 14 mg (11%) of colorless crystals of
[Ph4P][Zr2Cl9] (4a), and an amorphous brown solid formed in 1 week.
No crystals were obtained from the brown solid because of its
insolubility. No intermediate products were isolated when a smaller
amount of TiCl4 was used either.
When the above reaction of 2a and TiCl4 was conducted in the
presence of 480 mg (0.408 mmol) of [Ph4P]2[ZrCl6]‚2CH2Cl2, 223 mg
(96%) of 3a was isolated. Because crystals of both 4a and
[Ph4P]2[ZrCl6]‚2CH2Cl2 are colorless, they were not distinguishable
from each other, and therefore it was impossible to determine the yield
of 4a in this reaction.
Each structure was solved by a combination of direct methods using
the SHELXS-86 program13a and least-square refinement using SHELXL-
93.13b Crystallographic data and results are listed in Table 1.
Compound 2a crystallized in the rhombohedral crystal system. It
was transformed into the R-centered trigonal cell. The Laue class 3h
(12) For more details of using area-detectors, see: Scheidt, W. R.;
Turowska-Tyrk, I. Inorg. Chem. 1994, 33, 1314.
(13) (a) Sheldrick, G. M. SHELXS-86 Program for Crystal Structure
Determination; University of Cambridge: Cambridge, England, 1986.
(b) Sheldrick, G. M. SHELXL-93: Fortran-77 program for the
refinement of crystal structures from diffraction data; University of
Go¨ttingen: Go¨ttingen, Germany, 1993.
Reactions of [Ph4P]3[Zr6Cl18H5] (1a) with HCl, H2O, and MeOH.
Compound 1a‚3CH2Cl2 (100 mg, 0.041 mmol) was dissolved in 20

7366 Inorganic Chemistry, Vol. 35, No. 25, 1996
Chen and Cotton
Table 1. Crystal Data for Compounds 2a, 3a, 4a, 5a‚4MeCN, and 6a
2a
3a
4a
5a‚4MeCN
6a
formula
fw
cryst syst
space group
a, Å
b, Å
c, Å
R, (deg)
â, (deg)
γ, (deg)
V, Å3
C48H46Cl18P2Zr6
1870.21
trigonal
R3h
28.546(3)
28.546(3)
27.679(2)
90
90
120
19533(3)
12
1.906
C48H40Cl16P2Ti2Zr2
1524.18
triclinic
P1h
11.375(3)
13.357(3)
11.336(3)
106.07(1)
114.77(1)
88.50(1)
1494.8(7)
1
1.693
13.99
FR590
Mo KR
(λ ) 0.709 30 Å)
-60
45
3718
C24H20Cl9PZr2
840.86
triclinic
P1h
12.380(5)
12.883(5)
11.000(4)
110.39(7)
98.29(7)
73.12(4)
1572(1)
2
C56H52Cl6N4P2Zr
1146.88
monoclinic
P21/c
9.595(1)
19.566(3)
15.049(1)
90
98.50(1)
90
2794.2(6)
2
C29H25Cl5NPZr
686.94
monoclinic
P21/c
10.3390(7)
16.491(2)
17.654(2)
90
91.542(6)
90
3026.4(5)
4
1.508
76.89
Rigaku
Cu KR
(λ ) 1.541 84 Å)
20
Z
d
calc, g/cm3
1.777
14.94
1.363
5.81
µ, cm-1
17.44
CAD-4
data collcn instrument
FR590
Mo KR
(λ ) 0.709 30 Å)
-60
45
3879
325
0.050, 0.112
1.065
FR590
Mo KR
(λ ) 0.709 30 Å)
-60
50
4818
315
0.082, 0.145
1.110
radiation (monochromated) Mo KR
(λ ) 0.709 30 Å)
temp, °C
2θmax, deg
20
40
120
4495
334
0.067, 0.155
1.028
no. of observns (I > 2σ(I))
no. of variables
4028
472
0.050, 0.094
1.032
-0.01
0.6((1)
empirical
316
0.053, 0.120
1.007
residuals: R1,a wR2b
quality-of-fit indicatorc
max shift in final cycle
largest peak, e/Å3
abs cor
0
0
0
0
0.7(1)
none
0.5(1)
none
0.73(9)
none
1.3(2)
empirical
2
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo| (based on reflections with Fo2 > 2σFo ). b wR2 ) [∑[w(Fo2 - Fc2)2]/∑[w(Fo )2]]1/2; w ) 1/[σ2(Fo ) + (0.095P)2]; P
) [Max(Fo , 0) + 2Fc2]/3 (also with Fo > 2σFo ). c Quality-of-fit (on F2) ) [∑[w(Fo - Fc2)2]/(Nobservns - Nparams)]1/2
.
2
2
2
2
Scheme 1
was identified from the lack of the m symmetry, and the space group
R3h (No. 148) was assumed and confirmed by successful solution and
refinement of the structure. There are two independent [Zr6Cl18H5]2-
cluster anions in the unit cell, one located at an inversion center and
the other on the 3h axis. All the non-hydrogen atoms were refined with
anisotropic thermal parameters. Electron densities, which might be
contributed from the cluster hydrogen atoms, were observed on or very
close to the centers of the eight triangular faces of the Zr6 octahedron.
The positions of the hydrogen atoms in the [Ph4P]+ cations were
calculated by assuming idealized geometry, C-H ) 0.94 Å. Their
positions were refined with fixed thermal parameters set at 1.2Beq of
the corresponding carbon atoms.
Compound 3a crystallized in the triclinic crystal system. The space
group P1h (No. 2) was assumed and confirmed by successful solution
anisotropic thermal parameters. The hydrogen atoms were treated as
in compound 2a.
and refinement of the structure. There are one [Zr2Ti2Cl16]2- anion
and two [PPh4]+ cations in the unit cell, and the [Zr2Ti2Cl16]2- unit
resides on an inversion center. All the non-hydrogen atoms were
refined with anisotropic thermal parameters. The positions of the
hydrogen atoms on the [PPh4]+ cations were calculated by assuming
idealized geometry, C-H ) 0.93 Å. They were refined with fixed
thermal parameters set at 1.2 Beq of the cooresponding carbon atoms.
Results and Discussion
The hydrogen-containing hexazirconium cluster [Zr6Cl18H5]3-
(1) is chemically reactive in general and could be a reducing
species. The work reported here was undertaken to explore its
reactivity with particular attention to its redox behaviors. For
example, will a one-electron oxidation take place without
significant structural change? Is it possible to remove one of
the hydrogen atoms without rupturing the Zr6 octahedron? And
under what conditions will the cluster be broken?
Compound 4a also crystallized in the triclinic crystal system. Again,
the space group P1h (No. 2) was assumed and confirmed by successful
solution and refinement of the structure. There are two [Zr2Cl9]- anions
and two [Ph4P]+ cations unit in the unit cell. All the non-hydrogen
atoms were refined with anisotropic thermal parameters. The hydrogen
atoms on the phenyl rings were treated as in the previous compound.
Compound 5a‚4MeCN crystallized in the monoclinic crystal system.
The space group P21/c (No. 14) was identified uniquely from the
systematic absence in the data. There are two [ZrCl6]2- anions, four
[Ph4P]+ cations, and eight MeCN solvent molecules in the unit cell.
The [ZrCl6]2- units are located at the inversion centers. All the non-
hydrogen atoms were refined with anisotropic thermal parameters. The
positions of the hydrogen atoms were calculated by assuming idealized
geometries with C-H ) 0.93 Å for phenyl groups and C-H ) 0.98
Å for methyl groups. They were refined with fixed thermal parameters
of 1.2Beq and 1.5Beq for the corresponding carbon atoms, respectively.
The attempt to reduce TiCl4 with 1 equiv of 1 resulted in the
formation of a new and unexpected cluster species, [Zr6Cl18H5]2-
(2), in 91% yield (Scheme 1). The yellow TiCl4 was reduced
to form a brown solid. Because of the difficulties in separating
it from the [Zr6Cl18H5]2- compound, we have not yet been able
to characterize the brown solid. The reaction is a one electron
oxidation process and is reversible. By adding 1.1 equiv of
Na/Hg to [Ph4P]2[Zr6Cl18H5] (2a) in the presence of 1.0 equiv
of [Ph4P]Cl, a 90% yield of [Ph4P]3[Zr6Cl18H5] (1a) was
isolated. [Ph4P]Cl was needed in this reaction because the
product 1a has one more [Ph4P]+ cation than the starting
material 2a. Without addition of [Ph4P]Cl, the yield of 1a was
only 55% based on Zr (but 82% based on [Ph4P]+). The
Compound 6a also crystallized in the monoclinic crystal system.
The space group P21/c (No. 14) was identified in the same way as
described above. There are four [ZrCl5(py)]- anions and four [Ph4P]+
cations in the unit cell. All the non-hydrogen atoms were refined with

[Zr6Cl18H5]2-
Inorganic Chemistry, Vol. 35, No. 25, 1996 7367
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 2aa
Zr(1)-Zr(3)′
Zr(1)-Zr(2)′
Zr(1)-Zr(2)
Zr(2)-Zr(3)′
Zr(2)-Zr(3)
Zr(3)-Zr(1)′
Zr(11)-Zr(11)′′′
Zr(11)-Zr(11)′
Zr(11)-Zr(11)′′
Zr(2)-Cl(6)
Zr(1)-Cl(8)
Zr(3)-Cl(9)
Zr(1)-Cl(7)
Zr(1)-Cl(4)
Zr(1)-Cl(3)
3.451(2)
3.464(2)
3.465(2)
3.453(2)
3.454(2)
3.451(2)
3.442(3)
3.442(3)
3.489(3)
2.436(4)
2.430(4)
2.414(5)
2.545(4)
2.546(4)
2.557(4)
Zr(1)-Cl(1)
Zr(2)-Cl(2)
Zr(2)-Cl(1)′
Zr(2)-Cl(3)
Zr(2)-Cl(5)
Zr(3)-Cl(4)
Zr(3)-Cl(2)′
Zr(3)-Cl(7)′
Zr(3)-Cl(5)
Zr(11)-Cl(13)
Zr(11)-Cl(11)
Zr(11)-Cl(12)
Zr(11)-Cl(12)′
Zr(11)-Cl(11)′′
2.568(4)
2.551(4)
2.565(4)
2.569(4)
2.571(4)
2.534(5)
2.552(4)
2.560(4)
2.561(4)
2.427(5)
2.549(4)
2.551(5)
2.556(5)
2.567(4)
Zr(3)′-Zr(1)-Zr(2)′
Zr(3)′-Zr(1)-Zr(2)
Zr(3)′-Zr(2)-Zr(1)′
Zr(3)-Zr(2)-Zr(1)′
Zr(3)′-Zr(2)-Zr(1)
Zr(3)-Zr(2)-Zr(1)
Zr(1)′-Zr(3)-Zr(2)′
Zr(1)′-Zr(3)-Zr(2)
59.93(4) Zr(1)′-Zr(2)-Zr(1)
59.90(4) Zr(2)′-Zr(3)-Zr(2)
90.16(5)
90.20(5)
60.12(5) Zr(11)′-Zr(11)-Zr(11)′′ 90
59.86(4) Zr(2)′-Cl(1)-Zr(1)
59.86(4) Zr(2)-Cl(2)-Zr(3)′
60.11(4) Zr(1)-Cl(3)-Zr(2)
60.24(4) Zr(3)-Cl(4)-Zr(1)
60.22(4) Zr(3)-Cl(5)-Zr(2)
84.9(1)
Figure 1. X-ray structure of one of the two independent [Zr6Cl18H5]2-
ions in [Ph4P]2[Zr6Cl18H5] (2a) showing 30% probability thermal
ellipsoids of Zr and Cl atoms.
85.2(1)
85.0(1)
86.0(1)
84.6(1)
85.1(1)
reactions were carried out in CH2Cl2, even though CH2Cl2 reacts
with Na/Hg, because it is the only solvent we have found so
far for compound 2a in which it is moderately soluble and stable.
Fortunately, at low temperature (-78 °C) the reaction between
cluster 2 and Na/Hg is much faster than the reaction between
CH2Cl2 and Na/Hg, and the yield of compound 1a from
compound 2a was almost quantitative (90%). Since the
interconversions between 1 and 2 are one-electron processes,1
and 2 must contain the same number of hydrogen atoms, namely,
5. Cluster 2 has only 13 cluster-based electrons (CBE) with
one unpaired electron in one of the bonding orbitals.14 Its
paramagnetism has been confirmed by an ESR spectrum and a
magnetic susceptibility measurement. The ESR spectrum of
compound 2a showed a g value of 1.978, indicating the
existence of an unpaired electron. The appearance of this signal
indicates that the odd electron occupies a nondegenerate MO.
From magnetic susceptibility measurement, the magnetic mo-
ment for each cluster is 1.62 µB, close to the value (1.73 µB) of
spin-only magnetic moment for one unpaired electron.
Zr(11)′′′-Zr(11)-Zr(11)′ 60.91(6) Zr(1)-Cl(7)-Zr(3)′
Zr(11)′′′-Zr(11)-Zr(11)′′ 59.54(3) Zr(11)-Cl(11)-Zr(11)′ 86.0(1)
Zr(2)′-Zr(1)-Zr(2)
Zr(3)′-Zr(2)-Zr(3)
89.84(5) Zr(11)-Cl(12)-Zr(11)′′′ 84.7(1)
89.80(5)
a Numbers in parentheses are estimated standard deviations in the
least significant digits.
Figure 2. X-ray structure of [Zr2Ti2Cl16]2- in [Ph4P]2[Zr2Ti2Cl16] (3a)
showing 30% probability thermal ellipsoids.
Compound 2a was also characterized by a single-crystal X-ray
diffraction study. The molecular structure of the entire cluster
anion, [Zr6Cl18H5]2- is shown in Figure 1. Selected bond
distances and angles are listed in Table 2. The structure of
cluster 2 in compound 2a is similar to that of 1.6 Six Zr atoms
are arranged in an octahedron with six terminal and 12 edge-
bridging Cl atoms. The average Zr-Zr distance is 3.459(2) Å,
longer than that in [Zr6Cl18H5]3-, 3.407(1) Å.6 Similar changes
have been observed in other hexanuclear metal cluster systems,
Cluster hydrogen atoms were converted to H2, which escaped
from the solution during the reaction. Two new compounds,
[Ph4P]2[Zr2Ti2Cl16] (3a) and [Ph4P][Zr2Cl9] (4a), were isolated
in 15% and 11% yields, respectively (Scheme 1). Addition of
less TiCl4 resulted in lower yields of 3a and 4a. Disintegration
of the cluster in 2a into smaller units requires additional Cl
ligands. When the reaction of 2a with TiCl4 was carried out in
the presence of [ZrCl6]2-, the yield of 3a increased to 96%.
However, the mechanisms of the conversions of cluster 2 into
[Zr2Ti2Cl16]2- (3) and [Zr2Cl9]- (4) are not understood.
The structure of [Zr2Ti2Cl16]2- is shown in Figure 2, and
selected bond lengths and angles are listed in Table 3. The
four metals are arranged in a nonlinear, centrosymmetric chain.
The angle Zr(1)-Ti(1)-Ti(1)′ is 137.34(6)°. Clearly, two of
the metal atoms are in oxidation state 4+, and the other two
are in oxidation state 3+. Considering that Ti(IV) is much the
easier to reduce, we propose to assign the Ti atoms as 3+. The
distance between the two Ti atoms is 3.467(3) Å, longer than
that between the Ti atom and the Zr atom, 3.429(2) Å. There
is probably no metal-metal bond between the Ti atoms since
the distance is longer than that in [Ti2(µ-Cl)3Cl6]3- (3.191 Å)
which is without a Ti-Ti bond.17 No compound containing a
similar Cl4TiIII(µ-Cl)2TiIIICl4 unit has been reported. The angle
Ti(1)-Cl(6)-Ti(1)′ is 90.87°, close to the value 90° of the ideal
such [Nb6Cl18]2-, [Nb6Cl18]3-, and [Nb6Cl18]4- 15
as well as
,
[Ta6Cl14(PEt3)4]+ and [Ta6Cl14(PEt3)4].16 In contrast, the aver-
age bond lengths of Zr-Clt (2.427(4) Å) and Zr-Clb (2.557(4)
Å) in cluster 2 are slightly shorter than those in cluster 1, Zr-
Clt ) 2.484(4) Å and Zr-Clb ) 2.568(4) Å.6
Surprisingly, the simple one-electron redox process between
1 and 2 could not be observed with cyclic voltammetry. A white
film was formed and stuck firmly on the electrode surface. This
might be the cause of failure to observe the expected reversible
CV diagram.
Compound 2a reacts further with TiCl4. The distinguishing
blue color vanished only after 8 equiv of TiCl4 was added.
(14) For MO diagrams of M6 clusters, see: Lin, Z.; Williams, I. D.
Polyhedron 1996, 15, 3277.
(15) Koknat, F. W.; McCarley, R. E. Inorg. Chem. 1974, 13, 295.
(16) Imoto, H.; Hayakawa, S.; Morita, N.; Saito, T. Inorg. Chem. 1990,
29, 2007.

7368 Inorganic Chemistry, Vol. 35, No. 25, 1996
Chen and Cotton
Table 3. Selected Bond Lengths (Å) and Angles (deg) for 3aa
Zr(1)‚‚‚Ti(1)
Ti(1)‚‚‚Ti(1)′
Zr(1)-Cl(8)
Zr(1)-Cl(5)
Zr(1)-Cl(7)
Zr(1)-Cl(3)
Zr(1)-Cl(1)
3.429(2)
3.467(3)
2.341(2)
2.351(2)
2.364(2)
2.590(2)
2.590(2)
Zr(1)-Cl(2)
Ti(1)-Cl(4)
Ti(1)-Cl(6)′
Ti(1)-Cl(6)
Ti(1)-Cl(1)
Ti(1)-Cl(2)
Ti(1)-Cl(3)
2.601(2)
2.241(2)
2.431(2)
2.435(2)
2.479(2)
2.480(2)
2.511(2)
Zr(1)-Ti(1)-Ti(1)′ 137.34(6) Cl(4)-Ti(1)-Cl(6)
97.10(9)
89.13(8)
92.20(9)
94.35(8)
169.66(9)
95.08(9)
Ti(1)-Cl(1)-Zr(1)
Ti(1)-Cl(2)-Zr(1)
Ti(1)-Cl(3)-Zr(1)
Ti(1)′-Cl(6)-Ti(1)
Cl(8)-Zr(1)-Cl(5)
Cl(8)-Zr(1)-Cl(7)
Cl(5)-Zr(1)-Cl(7)
Cl(8)-Zr(1)-Cl(3)
85.11(7) Cl(6)′-Ti(1)-Cl(6)
84.85(7) Cl(4)-Ti(1)-Cl(1)
84.48(6) Cl(6)′-Ti(1)-Cl(1)
90.87(8) Cl(6)-Ti(1)-Cl(1)
97.13(9) Cl(4)-Ti(1)-Cl(2)
97.87(9) Cl(6)′-Ti(1)-Cl(2) 168.49(9)
Figure 3. X-ray structure of [Zr2Cl9]- in [Ph4P][Zr2Cl19 ](4a) showing
30% probability thermal ellipsoids.
99.15(8) Cl(6)-Ti(1)-Cl(2)
96.00(8) Cl(1)-Ti(1)-Cl(2)
91.26(7)
83.39(7)
171.76(9)
88.15(8)
89.89(8)
80.51(7)
80.35(7)
123.24(8)
Cl(5)-Zr(1)-Cl(3) 163.31(7) Cl(4)-Ti(1)-Cl(3)
Table 4. Selected Bond Lengths (Å) and Angles (deg) for 4aa
Cl(7)-Zr(1)-Cl(3)
Cl(8)-Zr(1)-Cl(1) 167.41(8) Cl(6)-Ti(1)-Cl(3)
89.19(8) Cl(6)′-Ti(1)-Cl(3)
Zr(1)‚‚‚Zr(2)
Zr(1)-Cl(4)
Zr(1)-Cl(7)
Zr(1)-Cl(8)
Zr(2)-Cl(5)
Zr(2)-Cl(9)
Zr(2)-Cl(2)
3.562(3)
2.322(3)
2.325(3)
2.347(2)
2.336(3)
2.339(2)
2.350(2)
Zr(1)-Cl(1)
Zr(1)-Cl(3)
Zr(1)-Cl(6)
Zr(2)-Cl(6)
Zr(2)-Cl(1)
Zr(2)-Cl(3)
2.562(2)
2.580(3)
2.580(2)
2.573(3)
2.578(2)
2.585(2)
Cl(5)-Zr(1)-Cl(1)
Cl(7)-Zr(1)-Cl(1)
Cl(3)-Zr(1)-Cl(1)
Cl(8)-Zr(1)-Cl(2)
Cl(5)-Zr(1)-Cl(2)
88.15(7) Cl(1)-Ti(1)-Cl(3)
92.53(8) Cl(2)-Ti(1)-Cl(3)
77.00(6) Cl(4)-Ti(1)-Zr(1)
89.35(8) Cl(6)′-Ti(1)-Zr(1) 121.80(7)
93.20(7) Cl(6)-Ti(1)-Zr(1)
121.40(7)
48.81(5)
49.07(5)
48.74(5)
99.41(8)
44.60(5)
44.53(5)
Cl(7)-Zr(1)-Cl(2) 164.76(8) Cl(1)-Ti(1)-Zr(1)
Cl(3)-Zr(1)-Cl(2)
Cl(1)-Zr(1)-Cl(2)
76.67(6) Cl(2)-Ti(1)-Zr(1)
78.91(6) Cl(3)-Ti(1)-Zr(1)
Zr(1)-Cl(1)-Zr(2)
Zr(1)-Cl(3)-Zr(2)
87.7(1)
87.20(8)
Zr(2)-Cl(6)-Zr(1)
87.45(9)
Cl(8)-Zr(1)-Ti(1) 121.74(7) Cl(4)-Ti(1)-Ti(1)′
Cl(5)-Zr(1)-Ti(1) 116.87(6) Cl(6)′-Ti(1)-Ti(1)′
Cl(7)-Zr(1)-Ti(1) 119.37(7) Cl(6)-Ti(1)-Ti(1)′
a Numbers in parentheses are estimated standard deviations in the
least significant digits.
Cl(3)-Zr(1)-Ti(1)
Cl(1)-Zr(1)-Ti(1)
Cl(2)-Zr(1)-Ti(1)
Cl(4)-Ti(1)-Cl(6)′
46.78(5) Cl(1)-Ti(1)-Ti(1)′ 138.08(8)
46.08(5) Cl(2)-Ti(1)-Ti(1)′ 134.64(8)
Scheme 2
46.08(5) Cl(3)-Ti(1)-Ti(1)′
96.28(9)
88.62(7)
a Numbers in parentheses are estimated standard deviations in the
least significant digits.
edge-sharing bioctahedron, consistent with there being no
attraction between the two Ti atoms. Ti-Clt is shorter than
Zr-Clt as expected, 2.241(2) Vs 2.352(2) Å. The bond length
between a Ti atom and the Cl atom bridging two Ti atoms is
slightly shorter than that between a Ti atom and the Cl atom
bridging a Ti atom and a Zr atom, Ti(1)-Cl(6) ) 2.433(2) Vs
Ti(1)-Clb ) 2.490(2) Å. However, both of them are signifi-
cantly shorter than Zr(1)-Clb, 2.594(2) Å. The average of the
Ti-Clb-Zr angles is 84.81(7)°, significantly larger than the
value of 70.53° in the ideal face-sharing bioctahedron, indicating
repulsion between the Zr and Ti atoms.
Although many phosphonium salts of [Zr2Cl9]- (4a) are
known,18 the structure of [Zr2Cl9]- has never been published.
Compound [Ph4P][Zr2Cl9] (4a) was characterized by X-ray
crystallography. The structure of 4a is shown in Figure 3. The
selected bond lengths and angles are listed in Table 4. The
distance between the two Zr atoms is long, 3.562(3) Å. Zr-
Clt ) 2.336(3) Å, Zr-Clb ) 2.576(3) Å, and the angle Zr-
Clb-Zr ) 87.4(1)°, all of which are consistent with a repulsive
force between the ZrIV atoms.
The reaction of 1 with TiCl4 is unique. No reaction was
found between 1 and [TiCl6]2-, nor does cluster 1 react with
[ZrCl6]2-, TiI4, ZrCl4, or CrCl3. The reactivity of TiCl4 may
be associated with the tendency of TiIII to become 6-coordinated.
It was expected that H+ (from HCl, MeOH, or H2O) might serve
as a one-electron oxidant. In fact, reaction of 1 with H+ led to
the rupture of the Zr6 cluster to form [ZrCl6]2- in ca. 20% yield.
Gas evolution (H2) was observed during the reactions (Scheme
2). When the reaction was conducted in MeCN, a new
crystalline form of [Ph4P]2[ZrCl6] (5a), 5a‚4MeCN was ob-
tained. When the reaction was carried out in py, a new Zr(IV)
compound ([Ph4P][ZrCl5(py)] (6a)) was isolated.
The structure of [ZrCl6]2- in [Ph4P]2[ZrCl6]‚4MeCN is shown
in Figure 4. Selected bond lengths and angles are given in Table
5. The average Zr-Cl distance is 2.469(1) Å, close to those in
other [ZrCl6]2- compounds (2.463(8) Å in [NEt4]2[ZrCl6],19a
2.468(2) Å in [(Et2N)3PCH3]2[ZrCl6],19b and 2.463(1) Å in
[Ph4P]2[ZrCl6]‚2CH2Cl210). It is slightly longer than Zr-Clt in
2 (2.427(4) Å) and shorter than that in 1 (2.484(4) Å).6
The structure of the octahedral [ZrCl5(py)]- (6) is shown in
Figure 5. The average bond lengths and angles are given in
Table 6. The py plane bisects angles Cl(5)-Zr(1)-Cl(1) and
Cl(2)-Zr(1)-Cl(3). It is interesting to note that the Cl atoms
In the presence of ligands such as MeCN, Me2CO, THF, py,
and PR3, cluster 2 disproportionates into 1 (in 20-34% yields),
4a (ca. 5%) and a white solid, presumably a Zr(IV) compound
since white is the typical color in amorphous form (Scheme 1).
Cluster 2 is unstable even in CH2Cl2. Within 2 weeks,
compound 2a decomposed completely into 1a (24%), and 4a
(8%), as well as an amorphous solid.
(17) Briat, B.; Kahn, O.; Morgenstern-Badarau, I.; Rivoal, J. C. Inorg.
Chem. 1981, 20, 4200.
(18) (a) Bullock, J. I.; Parret, F. W.; Taylor, N. S. Can. J. Chem. 1974, 52,
2880. (b) Latah, S. Indian Chem. Soc. 1983, 60, 911.
(19) (a) Ruhlandt-Senge, V. K.; Bacher, A.-D.; Mu¨ller, U. Acta Crystallogr.
1990, C46, 1925. (b) Schmidbauer, H.; Pichl, R.; Mu¨ller, G. Z.
Naturforsch., B 1984, 41, 395.

[Zr6Cl18H5]2-
Inorganic Chemistry, Vol. 35, No. 25, 1996 7369
Table 6. Selected Bond Lengths (Å) and Angles (deg) for 6aa
Zr(1)-N(1)
Zr(1)-Cl(4)
Zr(1)-Cl(1)
2.405(8)
2.398(2)
2.422(2)
Zr(1)-Cl(5)
Zr(1)-Cl(2)
Zr(1)-Cl(3)
2.424(3)
2.454(2)
2.457(3)
Cl(4)-Zr(1)-N(1)
177.1(2)
Cl(1)-Zr(1)-Cl(2) 171.2(1)
Cl(1)-Zr(1)-Cl(3) 91.7(1)
N(1)-Zr(1)-Cl(1)
N(1)-Zr(1)-Cl(5)
N(1)-Zr(1)-Cl(2)
83.5(2)
86.1(2)
87.7(2)
Cl(5)-Zr(1)-Cl(3) 169.5(1)
Cl(4)-Zr(1)-Cl(1)
Cl(4)-Zr(1)-Cl(5)
Cl(1)-Zr(1)-Cl(5)
Cl(4)-Zr(1)-Cl(2)
Cl(4)-Zr(1)-Cl(3)
94.3(1)
95.9(1)
90.7(1)
Cl(5)-Zr(1)-Cl(2) 88.4(1)
N(1)-Zr(1)-Cl(3)
84.0(2)
94.43(9) Cl(2)-Zr(1)-Cl(3) 87.69(9)
94.13(9)
a Numbers in parentheses are estimated standard deviations in the
least significant digits.
Figure 4. X-ray structure of [ZrCl6]2- in [Ph4P]2[ZrCl6] (5a‚4MeCN)
showing 30% probability thermal ellipsoids.
Conclusions
The hexazirconium clusters with main-group interstitial
elements, obtained from solid-state reactions, generally contain
the optimal, closed-shell complement of 14 cluster-based
electrons (CBE).1c,20 It is believed that the central atom and
the electrons it could contribute to the bonding of the Zr6 cluster
are essential to the stabilization of the cluster.2 It seems that
the 14-electron rule also applies to the hydrogen-containing
hexazirconium clusters: [Zr6Cl18H5]3-,6 [Zr6Cl18H4]4-,9 [Zr6-
Cl14H4(PR3)4],7 [Zr6Cl12H2(PMe2Ph)6],21 [Zr6Cl12H3(PEt3)6]+,21
and [Zr6Cl13H3(PEt3)5].21 It is difficult to oxidize [Zr6Cl18H5]3-
(1) to [Zr6Cl18H5]2- (2), and the only reagent yet found to do
Table 5. Selected Bond Lengths (Å) and Angles (deg) for
5a‚4MeCNa
Zr(1)-Cl(1)
Zr(1)-Cl(2)
2.473(1)
2.458(1)
Zr(1)-Cl(3)
2.477(1)
Cl(2)′-Zr(1)-Cl(1) 89.77(5) Cl(2)-Zr(1)-Cl(3)
90.44(4)
89.43(5)
Cl(2)-Zr(1)-Cl(1)
90.23(5) Cl(1)-Zr(1)-Cl(3)
Cl(2)-Zr(1)-Cl(3)′ 89.56(4) Cl(1)′-Zr(1)-Cl(3) 90.57(5)
Cl(1)-Zr(1)-Cl(3)′ 90.58(5)
a Numbers in parentheses are estimated standard deviations in the
least significant digits.
this is TiCl4. No reaction was found between 1 and [TiCl6]2-
,
TiI4, ZrCl4, [ZrCl6]2-, or CrCl3. Reaction of 1 with H+ led to
decomposition of the Zr6 cluster to form [ZrCl6]2- and H2. The
cluster 2 is similar in structure to 1 with the five hydrogen atoms
distributed over all eight triangular faces of the Zr6 octahedron.
However, the 13-electron cluster 2 is not stable in solution,
where it disproportionates into the more stable 14-electron
cluster 1, [Zr2Cl9]-, and H2. Cluster 2 can be reduced and
converted back into 1 almost quantitatively by reaction with 1
equiv of Na/Hg. However, the one-electron oxidation by TiCl4
for 1 is not suitable for 2. Reaction of 2 with TiCl4 results in
rupture of the Zr6 cluster and formation of a new mixed-metal
tetranuclear compound, [Zr2Ti2Cl16]2- (3), [Zr2Cl9]-, and H2.
Although electron change has now been achieved in hydrogen-
containing Zr6 clusters by interconverting 1 and 2, hydrogen
atom change in these clusters has not as yet been achieved. Thus,
while treatment of 1 with H+ did not lead to [Zr6Cl18H4]2-
+
,
Figure 5. X-ray structure of [ZrCl5(py)]- in [Ph4P][ZrCl5(py)] (6a)
showing 30% probability thermal ellipsoids.
H2, it is interesting that protonation, leading to [Zr6Cl18H6]2-
did not occur either. This may be compared with the fact that
even though the difference between [Zr6Cl18H5]3- and
[Zr6Cl18H4]4- is one H+, and both of these exist, attempts to
introduce one H+ into [Zr6Cl18H4]4- to form [Zr6Cl18H5]3- or
remove one H+ from [Zr6Cl18H5]3- with Proton Sponge or (i-
Pr)2NLi to form [Zr6Cl18H4]4- have not succeeded.
at the equatorial positions (Cl(1), Cl(2), Cl(3), and Cl(5)) are
all bent toward the py ligand. The average angle Cl(4)-Zr(1)-
Clequatorial is obviously larger than N(1)-Zr(1)-Clequatorial
,
94.7(1)° Vs 85.3(2)°. The driving force might be the existence
of the hydrogen bonding between H(1) and H(5) on the py
ligand and the equatorial Cl atoms, Cl‚‚‚H ) 3.21 Å.
In a previous paper,9 we reported the synthesis and structure
of [Zr6Cl18H4]4-. There are four hydrogen atoms in [Zr6Cl18H4]4-.
The difference between [Zr6Cl18H4]4- and 1 is only one H+.
But the addition of one H+ to [Zr6Cl18H4]4- to form 1 is not
feasible. The addition resulted in decomposition of the Zr6
cluster to form [ZrCl6]2-. Attempts to remove one H+ from
cluster 1 to form [Zr6Cl18H4]4- with Proton Sponge and
(i-Pr)2NLi also failed.
Acknowledgment. We thank the Robert A. Welch Founda-
tion for support under Grant A-494.
Supporting Information Available: An X-ray crystallographic file
in CIF format is available on the internet. Access and ordering
information is given on any current masthead page.
IC960454Q
(20) Rogel, F.; Corbett, J. D. J. Am. Chem. Soc. 1990, 112, 8198.
(21) Chen, L.; Cotton, F. A. Inorg. Chim. Acta, in press.