Controlled Formation of Tri- and Octanuclear Benzylthiolate Complexes of Zinc

Full text of DOI:10.1021/ic971402j

Inorg. Chem. 1998, 37, 2833-2836
2833
peptides.11 In the latter project we observed that the substituent
pattern of the (L-L) ligands exerts subtle control over the
isolability of (L-L)Zn(SR)2 species with aliphatic thiolates. For
instance these species could not be obtained for (L-L) )
o-phenanthroline, but were isolable for its 2,9-dimethyl deriva-
tive neocuproin. Similarly, of the R-BIMS ligands, the one with
R ) propyl stabilizes aliphatic (L-L)Zn(SR)2, but the one with
R ) methyl does not.11b This induced us to screen the R-BIMS
ligands and the thiolates to find out about the stability range of
mononuclear complexes and about alternative compositions.
This paper reports our observations for the benzylthiolate
system.
Controlled Formation of Tri- and Octanuclear
Benzylthiolate Complexes of Zinc
Rainer Burth, Michael Gelinsky, and
Heinrich Vahrenkamp*
Institut fu¨r Anorganische und Analytische Chemie der
Universita¨t Freiburg, Albertstrasse 21,
D-79104 Freiburg, Germany
ReceiVed NoVember 7, 1997
The tendency of transition metal thiolates, specifically those
of zinc, to form oligomeric and polymeric species is well-
established.1-3 In order for their nuclearity to be reduced, the
measures of using sterically demanding thiolates4 or of adding
appropriate counterions5 have been taken successfully in several
cases. The application of coligands containing heterocyclic
nitrogen donors has led to stable mononuclear complexes with
the highly preferred ZnN2S2 environment.6 The large majority
of zinc thiolate complexes described so far contain aromatic
thiolates. Aliphatic thiolates either are constituents of oligo-
nuclear species or are stabilized in ZnN2S2 complexes as parts
of chelating (N,S) ligands. Typically the coordination patterns
[Zn(SR)4]2- or [L2Zn(SR)2], which are the ones used by nature
for “structural zinc” in protein environments (L ) histidine,
i.e., a heterocyclic nitrogen donor; SR ) cysteinate, i.e., an
aliphatic thiolate),7 have not been obtained yet in the form of
simple coordination compounds with monodentate L and
aliphatic SR.
Experimental Section
The general experimental techniques were as described previously.12
All manipulations were done in an inert atmosphere and using solvents
which were degassed and saturated with nitrogen by several cycles of
evacuation and flooding with nitrogen. The ligand Me-BIMS was
prepared according to the published procedure.13 The spectroscopic
and analytical characterization of the new complexes is given in the
Supporting Information.
Preparations. [Zn3(Me-BIMS)(SBz)6] (1). A solution of benzyl
mercaptan (112 mg, 0.90 mmol) in methanol (150 mL) was treated
with sodium methoxide (3.8 mL (0.90 mmol) of a 0.24 M methanol
solution). Then Zn(NO3)2‚4H2O (134 mg, 0.45 mmol) in methanol
(50 mL) was added with vigorous stirring over a period of 1 h. Me-
BIMS (145 mg, 0.45 mmol), dissolved in 20 mL of boiling methanol,
was added, and the clear solution was stirred for 1 h. After the volume
was reduced to 25 mL in vacuo, the solution was allowed to stand.
Within 1 week a colorless precipitate had formed, which was filtered
off, washed with a few milliliters of ice-cold methanol, and dried in
vacuo. Recrystallization from hot acetonitrile (20 mL) yielded 85 mg
(45%) of 1 as colorless crystals, mp 134 °C dec, which were dried in
vacuo for several hours to remove all solvent of crystallization.
[BzEt3N]2[Zn8(S)(SBz)16] (2). Sodium methoxide (21.3 mL (4.25
mmol) of a 0.20 M methanol solution) and benzyl mercaptan (528 mg,
4.25 mmol) were combined in methanol (75 mL). Then Zn(NO3)2‚-
4H2O (421 mg, 1.42 mmol) in methanol (50 mL) was added with
vigorous stirring over a period of 2 h. Finally a solution of [BzEt3N]-
Cl (323 mg, 1.42 mmol) in methanol (20 mL) was added. The clear
solution was slowly reduced to 30 mL in vacuo in a warm water bath,
filtered through a fine-porosity frit, and left to stand under an inert
atmosphere. Over a period of 4 weeks the solution slowly turned yellow
and formed a partly crystalline precipitate. This was filtered off, washed
with a few milliliters of ice-cold methanol, and dried in vacuo for an
extended period, leaving behind 392 mg (76%) of solvent-free colorless
2, mp 136 °C dec.
We have contributed to this field by the stabilization of
monodentate thiolates (including aliphatic ones) with encapsu-
lating tripodal ligands,8 the construction of trigonal-bipyramidal
ZnN3S2 complexes,9 the use of chelating (N,S) ligands to obtain
thiolate-bridged oligonuclear species,10 and the application of
sterically demanding (N,N) chelate ligands to stabilize (L-L)-
Zn(SR)2 compounds with aliphatic thiolates including cysteinyl
(1) Krebs, B.; Henkel, G. Angew. Chem. 1991, 103, 785; Angew. Chem.,
Int. Ed. Engl. 1991, 30, 769.
(2) Dance, I. G. Polyhedron 1986, 5, 1037.
(3) Prince, R. H. In ComprehensiVe Coordination Chemistry; Wilkinson,
G., Gillard, R. D., McCleverty, J., Eds.; Pergamon Press: Oxford,
1987; pp 925-1045.
(4) (a) Koch, S. A.; Gruff, E. S. J. Am. Chem. Soc. 1989, 111, 8762. (b)
Power, P. P.; Shoner, S. C. Angew. Chem. 1990, 102, 1484; Angew.
Chem., Int. Ed. Engl. 1990, 29, 1403. (c) Bochmann, M.; Webb, K.
J.; Hursthouse, M. B.; Mazid, M. J. Chem. Soc., Dalton Trans. 1991,
2317.
(5) (a) Dance, I. G.; Choy, A.; Sendder, M. J. J. Am. Chem. Soc. 1984,
106, 6285. (b) Watson, A. D.; Rao, C. P.; Dorfman, J. R.; Holm, R.
H. Inorg. Chem. 1985, 24, 2820. (c) Hencher, J. L.; Khan, M. A.;
Said, F. F.; Tuck, D. G. Polyhedron 1985, 4, 1263.
(6) (a) Corwin, D. T.; Koch, S. A. Inorg. Chem. 1988, 27, 493. (b) Jordan,
K. J.; Wacholtz, W. F.; Crosby, G. A. Inorg. Chem. 1991, 30, 4588.
(c) Bochmann, M.; Bwembya, G. C.; Grinter, R.; Powell, A. K.; Webb,
K. J. Inorg. Chem. 1994, 33, 2290. See also further references cited
in these papers. The Cambridge Crystallographic Data File contains
63 entries for complexes with a ZnN2S2 coordination.
(7) Christianson, D. W. AdV. Protein Chem. 1991, 42, 281.
(8) (a) Alsfasser, R.; Powell, A. K.; Trofimenko, S.; Vahrenkamp, H.
Chem. Ber. 1993, 126, 685. (b) Burth, R.; Vahrenkamp, H. Z. Anorg.
Allg. Chem., in press.
(9) Brand, U.; Burth, R.; Vahrenkamp, H. Inorg. Chem. 1996, 35, 1083.
(10) (a) Brand, U.; Vahrenkamp, H. Inorg. Chem. 1995, 34, 3285. (b) Brand,
U.; Vahrenkamp, H. Z. Anorg. Allg. Chem. 1992, 622, 213. (c) Brand,
U.; Vahrenkamp, H. Chem. Ber. 1996, 129, 435.
(11) (a) Meissner, A.; Haehnel, W.; Vahrenkamp, H. Chem. Eur. J. 1997,
3, 175. (b) Burth, R.; Vahrenkamp, H. Inorg. Chim. Acta, in press.
(12) Fo¨rster, M.; Burth, R.; Powell, A. K.; Eiche, T.; Vahrenkamp, H. Chem.
Ber. 1993, 126, 2643.
(13) (a) Berends, H. P.; Stephan, D. W. Inorg. Chim. Acta 1984, 93, 173.
(b) Dagdigian, J. V.; Reed, C. A. Inorg. Chem. 1979, 18, 2623. (c)
Bouwman, E.; Driessen, W. L. Synth. Commun. 1988, 18, 1581.
S0020-1669(97)01402-X CCC: $15.00 © 1998 American Chemical Society
Published on Web 05/07/1998

2834 Inorganic Chemistry, Vol. 37, No. 11, 1998
Table 1. Crystallographic Details
Notes
1
2
formula
mol wt
space group
Z
C60H60N4S7Zn3‚2CH3CN C138H156N2S17Zn8‚5CH3OH
1339.76
P1h
3071.22
P1h
2
2
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
13.550(2)
15.313(2)
15.493(3)
90.25(2)
91.87(2)
95.68(2)
3197(1)
1.39
16.739(3)
16.762(3)
28.154(6)
106.82(3)
100.11(3)
91.14(3)
7423(3)
1.37
d
calc (g cm-3
)
µ(Mo KR) (mm-1) 1.39
R1 (obs reflns)a
0.074
wR2 (all reflns)b 0.265
1.56
0.050
0.137
a R1 ) ∑|Fo - Fc|/∑Fo. b wR2 ) [∑w(Fo - Fc2)2/∑w(Fo )2]1/2
.
2
2
Structure Determinations. Crystals of both compounds were taken
from the reaction products before drying in vacuo and sealed in glass
capillaries to avoid loss of solvent of crystallization. Diffraction data
were recorded with the image plate technique on a Stoe IPDS
diffractometer fitted with a molybdenum tube (KR, λ ) 0.7107 Å) and
a graphite monochromator. No absorption corrections were applied.
The structures were solved with direct methods and refined anisotro-
pically with the SHELX program suite.14 Hydrogen atoms were
included with fixed distances and isotropic temperature factors 1.2 times
those of their attached atoms. Parameters were refined against F2.
Drawings were produced with SCHAKAL.15 Table 1 lists the crystal-
lographic data.
Figure 1. Molecular structure of Zn3(Me-BIMS)(SBz)6 (1).
Table 2. Selected Atomic Distances in Complex 1 (Å)
Zn1‚‚‚Zn2
Zn1‚‚‚Zn3
Zn2‚‚‚Zn3
Zn1-N1
Zn1-N2
Zn1-S1
3.780(2)
3.958(2)
3.069(2)
2.026(9)
1.993(9)
2.324(3)
2.319(3)
Zn2-S1
Zn3-S2
Zn2-S4
Zn3-S3
Zn2-S5
Zn3-S5
Zn2-S6
Zn3-S6
2.359(3)
2.382(3)
2.273(4)
2.264(4)
2.388(4)
2.389(4)
2.397(4)
2.403(4)
Results and Discussion
Zn1-S2
We had observed previously11b that of the R-BIMS ligands
those with R ) propyl and R ) benzyl allow the formation of
the complexes (R-BIMS)Zn(SBz)2 with the standard tetrahedral
ZnN2S2 coordination pattern. Combining the reagents NaSBz,
Zn(ClO4)2, and Me-BIMS had originally produced an intractable,
probably polymeric, precipitate. Changing the conditions,
mainly by adding Zn(NO3)2 very slowly, has now allowed the
isolation of trinuclear 1 in a reasonable yield. 1 represents a
compromise between the polymerization tendency of Zn(SBz)2
and the confinement to mononuclearity brought about by the
donor quality and steric requirements of the chelate ligand. There
seems to be a delicate balance of these two forces, as complexes
like 1 were obtained neither with other R-BIMS ligands nor
with other thiolates.
thiolates under these conditions. The formation of sulfide has
also been observed by Dance in solutions containing thiolates
and alkylammonium ions and has tentatively been explained
by alkyl or aryl transfer,16 and the loss of sulfide from
benzylthiols due to the relative stability of benzyl cations is
known from organic chemistry.17 The sulfide ions seem to be
necessary as a nucleus around which an octameric unit of Zn-
(SBz)2 can assemble. The yield of compound 2 is quite good
and reproducible, indicating that its composition is highly
favored in the presence of sulfide. Addition of sulfide to the
fresh reaction mixture, however, produced precipitates whose
compositions were variable and not identical to those of 2.
[BzEt3N]2[Zn8(S)(SBz)16]
Zn3(Me-BIMS)(SBz)6
2
1
The compositions and constitutions of 1 and 2 became clear
only after the structure determinations. Figure 1 and Table 2
give the result for 1. The three zinc ions form an isosceles
triangle, and their coordination is tetrahedral to a good ap-
proximation. The zinc-sulfur distances fall into three catego-
ries, those to terminal thiolate being the shortest and those from
Zn2 and Zn3 to the bridging thiolates being the longest. The
Cambridge Crystallographie Data File contains no entry on a
L2M3(ER)6 complex like 1 for any metal or any chalcogen yet.
So far the structures of two other trinuclear zinc-thiolate
During the preparation of 1, NaSBz and Zn(NO3)2 are
combined first, producing a clear solution, presumed to contain
solvated monomeric Zn(SBz)2 and anionic thiolatozincates of
varying nuclearity. We made various attempts to isolate one
of these compounds in a crystalline form. During these attempts
we observed that in a period of weeks and in the presence of
alkylammonium cations a chemical change occurs which shows
up in a color change of the solution to yellow. In the presence
of benzyltriethylammonium chloride, compound 2 precipitated
from the solution. 2 contains sulfide, which was not present in
the initial reaction solution and which cannot have formed from
benzylthiolate by oxidation, as air was carefully excluded and
nitrate has never been observed by us to oxidize thiols or
18
complexes have been described. Zn3(CH2SiMe3)3(SC6H2iPr3)3
and Zn3(o-phen)2(toluene-3,4-dithiolate)319 have little similarity
(16) Dance, I. G. Aust. J. Chem. 1985, 38, 1391.
(17) Wallace, T. J.; Pobiner, H.; Schriesheim, A. J. Org. Chem. 1964, 29,
(14) Sheldrick, G. M. SHELXS-86 and SHELXL-93, Universita¨t Go¨ttingen,
1986 and 1993.
(15) Keller, E. SCHAKAL for Windows, Universita¨t Freiburg, 1997.
888.
(18) Olmstead, M. M.; Power, P. P.; Shoner, S. C. J. Am. Chem. Soc. 1991,
113, 3375.

Notes
Inorganic Chemistry, Vol. 37, No. 11, 1998 2835
Table 3. Zinc-Sulfur Distances in Complex 2 (Å)
(a) Central Sulfide
Zn1-S
Zn2-S
2.305(2)
2.429(2)
Zn3-S
Zn7-S
2.557(2)
2.186(2)
(b) Inner Zn4 Unit
Zn1-S(Zn5)
Zn1-S(Zn6)
Zn1-S(Zn8)
Zn2-S(Zn4)
Zn2-S(Zn5)
Zn2-S(Zn6)
2.182(2)
2.534(2)
2.430(2)
2.338(2)
2.171(2)
2.528(2)
Zn3-S(Zn4)
Zn3-S(Zn5)
Zn3-S(Zn8)
Zn7-S(Zn4)
Zn7-S(Zn6)
Zn7-S(Zn8)
2.320(2)
2.148(2)
2.413(2)
2.310(2)
2.528(2)
2.434(2)
(c) Peripheral Zn (Bridging)
Zn4-S(Zn2)
Zn4-S(Zn3)
Zn4-S(Zn7)
Zn5-S(Zn1)
Zn5-S(Zn2)
Zn5-S(Zn3)
2.358(2)
2.413(2)
2.344(2)
2.385(2)
2.427(2)
2.491(2)
Zn6-S(Zn1)
Zn6-S(Zn2)
Zn6-S(Zn7)
Zn8-S(Zn1)
Zn8-S(Zn3)
Zn8-S(Zn7)
2.304(2)
2.379(2)
2.302(2)
2.333(2)
2.400(2)
2.245(2)
(d) Outer Terminal Thiolates
Zn4-S
Zn5-S
2.215(2)
2.174(2)
Zn6-S
Zn8-S
2.476(2)
2.363(2)
Figure 2. Structure of the anion of [BzEt3N]2[Zn8(S)(SBz16)] (2)
(central SZn4 tetrahedron outlined by dashed lines, sulfur atoms shaded,
phenyl rings omitted).
with 1, however. But fragments of 1 can be compared with
known zinc complexes. Thus the (Me-BIMS)Zn(SBz)2 part of
1 represents quite a normal ZnN2S2 complex, immediately
comparable with the mononuclear (R-BIMS)Zn(SR)2 com-
plexes,11b and the Zn2(SBz)6 part of 1 corresponds to the
2-
Zn2(SR)6 units with R ) Et5b or R ) Ph20 and with R )
cysteinate in the GAL4 transcription factor.21
The octanuclear anion of compound 2 (see Figure 2) displays
a central SZn4 unit which is capped on all four faces by ZnS4
units. All zinc ions are surrounded by four sulfur atoms in an
approximately tetrahedral arrangement. The 32 zinc-sulfur
distances range from 2.15 to 2.56 Å with no systematic
distributions, as evidenced by Table 3. The literature contains
structure determinations of three complexes with a M8(E)X16
arrangement, namely, [NMe4][Zn8(Cl)(SPh)16]16 and [NEt4]2-
[Cd8(S)(SePh)16] by Dance22 and two structures of salts of
[Cd8(S)(SPh)12Cl4]2- by Tang.23 Unlike 2, all three show very
little variation in their M-E and M-X bond lengths. Other
Figure 3. The Zn8S17 core of 2 (viewing direction as in Figure 2,
sulfur atoms shaded, cuboctahedral arrangement of the 12 bridging
thiolate sulfur atoms indicated by dashed lines).
core is ZnS-like, but the face capping of the SZn4 unit by the
four external ZnS4 units generates an arrangement of Zn and S
which is unlike those around a SZn4 center in cubic or hexagonal
ZnS. However, limiting the discussion to the twelve µ2 sulfur
atoms reveals a spatial arrangement which does conform to that
in zinc sulfide. Figure 3 shows that they span a cuboctahedron
around the central sulfur atom, which is the pattern of cubic
close packing. Thus the location of the zinc and sulfur atoms
in the inner Zn4S13 shell of 2 is that of zinc blende. Thereby 2
differs from its M8(E)X16 analogues16,22,23 which display an
icosahedral arrangement of the 12 µ2 sulfur or selenium atoms.
The question of why the spontaneous aggregation of the
species Xn-, ER-, and M2+ leads to just the [XM8(ER)16]n-
composition in 2 and its analogues has not been asked yet. We
found an answer to this kind of question for the compound [Zn7-
(2-pyridylmethanolate)12]Cl2 in the stacking of the aromatic rings
creating a symmetrically and completely covered surface of the
globular complex cation.28 This explanation does not work for
2. Space-filling plots (of which one example is given in the
24
reported M8Ex(ER)y complexes such as Gd8S6(SPh)12(THF)8
25
and Sm8Se6(SePh)12(THF)8 contain a cubelike arrangement
of the eight metal ions.
Polynuclear metal thiolates are often displayed as sections
of the corresponding metal sulfide (e.g., zinc blende),1,2 as
evidenced in an aesthetically very pleasing way by
[Zn10S4(SPh)16]4- 26 and Cd32S14(SPh)36.27 This cannot be done
for compound 2 and its M8(E)X16 analogues.16,22,23 Their SZn4
(19) Halvorson, K.; Wacholtz, W. F.; Crosby, G. A. Inorg. Chim. Acta
1995, 228, 81.
(20) Abrahams, I. L.; Garner, C. D. J. Chem. Soc., Dalton Trans. 1987,
1577.
(21) Marmorstein, R.; Carey, M.; Ptashne, M.; Harrison, S. C. Nature 1992,
356, 408.
(22) Lee, G. S. H.; Fisher, K. J.; Craig, D. C.; Scudder, M. L.; Dance, I.
G. J. Am. Chem. Soc. 1990, 112, 6435.
(23) Tang, K. L.; Jin, X. L.; Jia, S. J.; Tang Y. Q. Jiegou Huaxue (J. Struct.
Chem. China) 1995, 14, 399.
(24) Melman, J. H.; Emge, T. J.; Brennan, J. G. J. Chem. Soc., Chem.
Commun. 1997, 2269.
(26) Dance, I. G.; Choy, A.; Scudder, M. L. J. Am. Chem. Soc. 1984, 106,
6825.
(27) Herron, N.; Calabrese, J. C.; Farneth, W. E.; Wang, Y. Science 1993,
259, 1426.
(25) Freedman, D.; Emge, T. J.; Brennan, J. G. J. Am. Chem. Soc. 1997,
119, 11112.
(28) Tesmer, M.; Mu¨ller, B.; Vahrenkamp, H. J. Chem. Soc., Chem.
Commun. 1997, 721.

2836 Inorganic Chemistry, Vol. 37, No. 11, 1998
Notes
Supporting Information) show that the complex anion is not of
globular shape nor are its zinc and sulfur constituents hidden
under a well-stacked coverage of aromatic rings. Thus it seems
to us that, once the central XM4 core is assembled and there is
no excess of Xn-, the ER- and M2+ ions in solution can only
be attached to this core in the observed way, the reason for this
being the preferred tetrahedral coordination of M2+. It remains
open whether thermodynamic stability or low solubility allows
the observed composition to be isolated rather than any other
Mx(ER)y composition.
(S)y(SR)z complexes were of the arylthiolate type. Obviously
the aggregation tendency of benzylthiolate, halfway between
those of the aliphatic and aromatic thiolates, is, besides the
nature of the coligands, the second decisive factor for the
observed assemblies.
The M3L2(SR)6 composition and structure of 1 seems to be
without precedent in coordination chemistry, and we are not
aware of any other reported [M8(S)(SR)16]2- complex. The
anion [Zn8(S)(SBz)16]2- also represents a new structural type
for oligonuclear metal thiolates. Its cuboctahedral array of the
bridging thiolate sulfur atoms around the central sufide consti-
tutes a S13 unit corresponding to the first coordination shell in
a cubic close-packed lattice. Altogether compounds 1 and 2
are two more examples of the growing group of complexes
between small molecular entities and extended lattice species.
Conclusions
The preferred composition and spontaneous formation of 1
and 2 are proven by the fact that both result reproducibly and
in good yields from solutions whose compositions are different
from those of the products. Obviously the aggregation of the
zinc-benzylthiolate entities is controlled by the coligands which
act as nucleation starters. When the coligand is a spatially
demanding (N,N) chelator, the products are monomolecular Zn-
(SR)2 complexes.11 Coligand Me-BIMS is a unique borderline
case, allowing the combination of one ligated and two unligated
Zn(SR)2 units in the neutral complex 1. Slow delivery of sulfide
allows the growth of the octanuclear anions around the central
SZn4 core. Compounds like 1 and 2 could only be obtained by
us with benzylthiolate. In contrast, all previously reported Znx-
Acknowledgment. This work was supported by the Deutsche
Forschungsgemeinschaft. We thank Prof. D. Fenske and co-
workers for obtaining the X-ray data set for 2.
Supporting Information Available: Spectroscopic and analytical
characterization of and fully labeled ORTEP plots for 1 and 2 and one
space-filling plot for 2 (4 pages). Two crystallographic files, in CIF
format, are available on the Internet only. Ordering and access
information is given on any current masthead page.
IC971402J