Polyhedron 20 (2001) 949–956

Zinc tri-tert-butoxysilanethiolates. Syntheses, properties and crystaland molecular structures of [Zn{�-SSi(OBut)3}(acac)]2 and

[{(ButO)3SiS}(H2O)2Zn{�-SSi(OBut)3}Zn(acac){SSi(OBut)3}]�

Barbara Becker *, Anna Dołega, Antoni Konitz, Wiesław WojnowskiDepartment of Chemistry, Technical Uni�ersity of Gdansk, G. Narutowicz Str. 11/12, 80-952 Gdansk, Poland

Received 10 October 2000; accepted 17 January 2001

Abstract

Heteroleptic, neutral tri-tert-butoxysilanethiolates of zinc, incorporating acetylacetonate (1) or acetylacetonate and water (2) asadditional ligands, have been prepared by a reaction of zinc acetylacetonate with tri-tert-butoxysilanethiol in acetonitrile andcharacterized by IR, NMR and MS techniques. Crystal and molecular structures have been determined by single crystal X-raystructural analysis. Both are bimetallic with a distorted tetrahedral ligand arrangement at the zinc and ZnO2S2 core. Complexes1 and 2 are the first structurally characterized thiolates where the metal is also bonded to acetylacetonate and 2 is the first neutralaqua-ligated zinc thiolate. © 2001 Elsevier Science Ltd. All rights reserved.

Keywords: Zinc complexes; S ligands; Silanethiolates; O ligands; Synthesis; Crystal structures

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1. Introduction

Zinc complexes have been the subject of numerousinvestigations. This stems at least in part from theirusefulness as models for zinc-containing sites in metal-loproteins. Zinc is an essential element for both animalsand plants [2]. It is present in a very large number ofenzymes, where it can have either a catalytic or astructural role [3].

For many years we have been interested in the chem-istry of compounds containing silicon–sulfur bonds. Apart of this interest is devoted to the synthesis and thestructural chemistry of metal trialkoxysilanethiolates[1]. Trialkoxysilanethiols — derivatives of hitherto un-known monothioorthosilicic acid — may be obtainedby the alcoholysis of silicon disulfide [4]. Like othersilanethiols they are susceptible to hydrolysis with evo-lution of H2S and so far it has hindered their wider usein the preparation of metal complexes. The only excep-

tion is tri-tert-butoxysilanethiol — under normal con-ditions it is resistant toward water [5].

We successfully prepared and characterized struc-turally several metal complexes, which, presumably dueto the steric congestion imposed by the bulky Si(OBut)3

substituent on sulfur, invariably showed to be molecu-lar. We also tried to prepare the homoleptic zinc tri-tert-butoxysilanethiolate. Despite numerous efforts theonly product obtained contained undefined amounts ofwater, clearly bonded to zinc [6]. Its very good solubil-ity in nonpolar solvents (e.g. hexane) suggested that weshould deal with a mixture of very similar aqua zincthiolates of low nuclearity rather than polymericspecies.

Zn(II) is an ion of borderline hardness and displays ahigh affinity for nitrogen and oxygen donor atoms aswell as for sulfur. It is therefore found to be bound tohistidine, glutamate or aspartate and cysteine moieties.When zinc has a catalytic role it is exposed to a solventand generally one water molecule completes the coordi-nation sphere [3]. Structural zinc sites are usually coor-dinated to four cysteines, although some othercoordination environments were also found (e.g. Zn-(his)2(cys)2 in ‘zinc finger’ domains of gene regulatoryproteins [7]). In the one of most widely studied zinc

� Contributions to the chemistry of silicon–sulfur compounds. 73[1].

* Corresponding author. Tel.: +48-58-3472592; fax: +48-58-3472694.

E-mail address: beckerb@altis.chem.pg.gda.pl (B. Becker).

0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.PII: S 0277 -5387 (01 )00748 -3

B. Becker et al. / Polyhedron 20 (2001) 949–956950

enzymes, alcohol dehydrogenase, two zinc sites, onestructural and one catalytically active, have differentcoordination environments — Zn(cys)4 and Zn-(his)(cys)2(L), respectively, where L stands for alcoholor aldehyde and water in resting enzyme [3].

The exact structures of the zinc sites in many metal-loproteins are still unknown and the preparation ofcomplexes with simple ligands able to mimic the imme-diate coordination environment of zinc sites is of im-portance. The strong bridging property of thiolatesulfur makes simple neutral thiolates not readily acces-sible, and those where water enters the metal coordina-tion sphere are scarce. To our knowledge, even forwidely studied zinc, although they are frequently postu-lated, the structural data are still lacking. Taking theabove into account we decided to reinvestigate thetri-tert-butoxysilanethiol–zinc system. This paper de-scribes the results obtained.

2. Results and discussion

2.1. Synthesis

Metal thiolates are most commonly prepared accord-ing to Eq. (1):

MXn+nRS−�M(SR)n+nX− (1)

where RS− comes from an alkali metal or tertiaryamine thiolate, frequently generated in situ. Less com-mon are methods where thiol reacts with a suitablemetal source. The preparation of zinc thiolate com-plexes from reactive zinc silylamides may serve as anexample [8].

In our previous attempt we also tried to prepare ahomoleptic zinc silanethiolate by a direct reaction be-tween metallic zinc and tri-tert-butoxysilanethiol, butthe reaction product always captured an unrepro-ducible amount of water [6]. Now, we turned ourattention to zinc acetylacetonate. We expected thatacetylacetone, being a weaker acid (pK about 9) thansilanethiol (pK about 8 [9]) should be displaced fromzinc. Such an exchange was demonstrated by the prepa-ration of [Au(SSiPh3)(Ph3P)] from triphenylphosphine-gold(I) acetylacetonate and Ph3SiSH [10], but to thebest of our knowledge, for zinc, exhibiting a muchgreater affinity for oxygen-containing ligands than gold,it was never investigated.

Zinc acetylacetonate we prepared from ZnO andacetylacetone following the simple procedure given byHassanein and Hewaidy [11], albeit with a differentfinal result. Although the authors described the ob-tained complex as zinc acetylacetonate, its meltingpoint (138°C) was identical to that reported by Grad-don and Weedon [12] for the water-containing com-pound [Zn(acac)2(H2O)] [13]. Our product melted at126°C. The same melting point was reported previouslyfor anhydrous zinc acetylacetonate by Rudolph andHenry [14] and confirmed by Bennnett et al. who finallydetermined the well-known trimeric structure of the[Zn(acac)2]3 complex [15]. We would like to point outthat we did not try to keep the conditions anhydrous— the solvents and acetylacetone were only distilledand the reaction was performed without any protectionof a neutral gas atmosphere.

We found that zinc acetylacetonate dissolves well inwarm dry acetonitrile and therefore used this solvent asthe reaction medium. The reaction was performed byfirst dissolving the zinc substrate, followed by additionof the silanethiol (molar ratio of Zn to the silanethiolwas 1:1) to the Zn(acac)2 solution. A colorless crys-talline complex 1 was formed with a sharp m.p. at 195°.The elemental analysis and spectral data pointed to theZn(acac){SSi(OBut)3} formula.

Taking into account the chelating nature of theacetylacetonate ligand and the steric hindrance causedby the bulky silanethiolate ligand, we could not excludethe monomeric molecule with triply bonded zinc. Whatwas more, in some metal tri-tert-butoxysilanethiolates,including those of Cd [16] and Hg [17], the oxygenatom from the Si�O�But fragment was able to interactwith the metal center, and the same interaction in 1would lead to the completion of the coordinationsphere around the zinc to tetrahedral. We determinedthe molecular structure of 1 (Fig. 1) and found that inthe solid state it forms dimeric molecules. Preparationof 1 proved that silanethiolate is able to replace (at leastin part) the acetylacetonate ligand bonded to zinc.

On one occasion, when distilled but not dried aceto-nitrile was used, we observed that zinc acetylacetonate

Fig. 1. Molecular structure of [Zn{�-SSi(OBut)3}(acac)]2 (1) withatom labeling scheme (hydrogen atoms omitted, thermal ellipsoids30%).

B. Becker et al. / Polyhedron 20 (2001) 949–956 951

Fig. 2. Molecular structure of [{(ButO)3SiS}(H2O)2Zn{�-SSi(OBut)3}Zn(acac){SSi(OBut)3}] (2) with atom labeling scheme (hy-drogen atoms omitted, thermal ellipsoids 20%).

We also increased the molar ratio silanethiol:Zn to1.5:1. The reaction gave the colorless complex 2 with alow and quite broad melting point. Elemental analysis,IR and NMR spectra showed the presence of threecomponents — water, acetylacetonate and tri-tert-bu-toxysilanethiolate. The structure of 2 determined byX-ray analysis revealed a bimetallic silanethiolate com-plex (Fig. 2) with two molecules of water bonded to oneZn and the acetylacetonate ligand still left on thesecond zinc atom. When we tried to displace all theacetylacetonate ligands and increased the molar ratiosilanethiol:Zn to 2:1, again 2 was obtained.

1 and 2 are stable and can be stored without specialprecautions. They are readily soluble in benzene, CHCl3and acetone, and less soluble in acetonitrile and hep-tane. Attempts to recrystallize them from hot acetoni-trile gave unidentified gelatinous products.

To the best of our knowledge, 1 and 2 are the firstmetal thiolate complexes also containing the acetylacet-onate ligand. Moreover, 2 is the first example of struc-turally characterized neutral zinc thiolate with waterbonded to Zn. Only two thiolates are known wherewater enters the zinc coordination sphere — derivativesof benzothiazole-2-thiol [18] and bis(1,3-diamino-propane) - N,N � - bis(4 - methyl - 2,6 - dimethylenephenyl-thiol) [19]. Both are ionic. The only neutral, water-lig-ated thiolate-like complexes are restricted to derivativesof monothiobenzoic acid [20], 1- and 2-thiooxamates[21,22], 6-amino-2-thiouracil [23] and thiosemicarba-zones [24,25]. Recently, the structure of the mono-thioacetic acid derivative [Ph4P][ZnSC{O}Me)3(H2O)]has been reported [26].

2.2. Molecular structures

2.2.1. [Zn{�-SSi(OBut)3}(acac)]2 (1)Complex 1 forms colorless prisms of triclinic crystals.

Fig. 1 gives a view of the molecule; the selected bondlengths and angles are listed in Table 1.

Two zinc atoms are linked by the bridging sulfuratoms from two tri-tert-butoxysilanethiolate ligandsand the coordination at each Zn is completed by thechelating acetylacetonate (ZnO2S2 core). The moleculehas a symmetry center located in the middle of thecentral Zn2S2 ring and may be regarded as a result ofdimerization of the two monomeric Zn(acac)(SR) units.

The symmetry-related, six-membered acetylaceto-nate–Zn rings are essentially planar — the greatestdeviation from the best least-square plane does notexceed 0.0240 A� . They are not perpendicular to theZn2S2 ring, but most probably due to the bulkiness ofthe silanethiolate ligand, bisect the Zn2S2 plane at anangle of 74.6°. This, as well as an involvement of all theZn-bonded atoms into the ring structures, causes asevere distortion of the tetrahedral ligand arrangement

Table 1Selected bond lengths (A� ) and angles (°) for 1 a

Bond lengthsSi1�O12.3578(12)Zn1�S1 1.596(3)

2.3532(12)Zn1�S1� Si1�O2 1.606(3)Zn1�O4 1.954(3) Si1�O3 1.612(3)Zn1�O5 1.944(3) 1.263(5)O4�C14

1.267(5)O5�C16S1�Si1 2.1185(15)

Valence anglesO1�Si1�S1 112.45(13)95.15(12)O5�Zn1�O4

103.54(9) O2�Si1�S1O4�Zn1�S1 104.10(11)122.25(9) O3�Si1�S1O4�Zn1�S1� 111.30(11)

123.9(3)C14�O4�Zn1O5�Zn1�S1� 109.16(9)128.88(8) O4�C14�C15O5�Zn1�S1 124.8(4)100.10(4)S1��Zn1�S1 C16�O5�Zn1 123.2(3)

125.8(4)O5�C16�C15Zn1��S1�Zn1 79.90(4)102.49(6)Si1�S1�Zn1 C16�C15�C14 127.1(4)

Si1�S1�Zn1� 99.68(5)

Torsion anglesS1��Zn1�S1�Si1 97.78(5) O4�Zn1�S1�Si1 −135.32(10)

−27.10(11)O5�Zn1�S1�Si1−124.88(11)O5�Zn1�S1�Zn1�126.90(9)O4�Zn1�S1�Zn1�

a Symmetry transformation used to generate equivalent atoms:−x+1, −y+1, −z+1.

did not dissolve completely but formed a colloidalsuspension with a silky luster. The observed differencecould be attributed to water undoubtedly present in thesolvent. Since our main objective was to prepare thewater-ligated zinc silanethiolate complex, we decided toperform the reaction without any humidity precautions.

B. Becker et al. / Polyhedron 20 (2001) 949–956952

at zinc. The values of the respective angles vary from95.15° (O4�Zn1�O5) to 128.88° (O5�Zn1�S1).

2.2.2. [{(ButO)3SiS}(H2O)2Zn{�-SSi(OBut)3}-Zn(acac){SSi(OBut)3}] (2)

Complex 2 forms colorless plates of monoclinic crys-

tals. Fig. 2 gives a view of the molecule; the selectedbond lengths and angles are listed in Table 2.

Like 1, the molecule of 2 is bimetallic. Althoughevery Zn atom is bonded to two sulfur and two oxygenatoms, and the immediate environments of both metalcenters are the same (ZnO2S2), the coordination spheresare not. Only one tri-tert-butoxysilanethiolate ligandforms a bridge between two metal centers; two othersilanethiolate ligands are bonded terminally, each toone Zn. Two water molecules at Zn1 and the chelatingacetylacetonate ligand at Zn2 complete the molecule.

Four short intramolecular atomic distances,O1···O12, 2.808(4) A� , O11···O12, 2.689(4) A� , O5···O13,2.914(4) A� and O7···O13, 2.863(4) A� , are clearly indica-tive of the presence of four O�H···O hydrogen bondsbetween the water molecules and all the remainingligands (Fig. 3).

They are also evidenced by small differences of thegeometry at the oxygen atoms acting as hydrogen bondacceptors (O1, O5, O7 and O11) compared with theoxygen atoms that are not involved in such interac-tions. Thus, in (ButO)3SiS ligands the appropriate Si�Obonds are slightly longer and the Si�O�C angles,slightly smaller. The spatial arrangement of the hydro-gen bonds may also contribute to the difference be-tween the O13�Zn1�S1 and the O12�Zn1�S1 bondangles. In the Zn(acac) fragment the Zn2�O11 bond islonger than the Zn2�O10 bond, and the Zn2�O11�C40angle is smaller than the Zn2�O10�C38 angle. Theplanarity of the Zn(acac) chelate ring is retained — themean deviation from the best least-squares plane is only0.0243 A� .

Although the presence of water molecules has somestructural implications, the appropriate Zn�O bondlengths (2.045 and 2.050 A� ) are rather unexceptional.The similar Zn�O(water) bond lengths were found inother tetrahedral complexes — the anionic aqua-com-plex formed by benzothiazole-2-thiol (2.036 A� —ZnNOS2 core) [18], neutral diaqua-bis(monotioben-zoato-S)zinc(II) (2.031 A� — ZnO2S2 core) [20] and theaqua-tris(monotioacetato-S)zinc(II) anion (2.084 A� —ZnOS3 core) [26].

Two Zn and two S atoms are almost coplanar (Fig.3) — the S1�Zn1�S2�Zn2 dihedral angle approaches180°. For both the Zn atoms in 2 the tetrahedralarrangement of the ligands is far from ideal as evi-denced by narrow O�Zn�O angles accompanied bywide S�Zn�S angles.

The observed Zn�S bond lengths in both the com-plexes vary according to the bonding mode of thesilanethiolate ligand — the respective mean values are2.347 A� for the bridging (Sb) and 2.240 A� for theterminal sulfur (St). Although related complexes areunknown, similar Zn�S bond lengths were frequentlyencountered in many other zinc thiolates (compare, e.g.

Table 2Selected bond lengths (A� ) and angles (°) for 2

Bond lengthsZn1�O13 2.045(3) Si1�O3 1.612(3)

2.050(3)Zn1�O12 Si1�O1 1.649(4)Si2�O42.2284(16) 1.535(4)Zn1�S1

2.3237(15)Zn1�S2 Si2�O6 1.546(4)1.960(4)Zn2�O10 Si2�O5 1.595(4)2.010(4)Zn2�O11 Si3�O9 1.607(4)2.2531(16)Zn2�S3 Si3�O8 1.622(4)2.3548(15)Zn2�S2 Si3�O7 1.629(4)

O10�C382.0808(19)S1�Si1 1.264(7)2.1195(17)S2�Si2 O11�C40 1.281(7)2.077(2) 1.391(10)S3�Si3 C38�C39

C39�C40 1.366(10)1.607(3)Si1�O2

Valence anglesSi3�S3�Zn2 106.30(7)95.40(14)O13�Zn1�O12

O13�Zn1�S1 106.99(14)O2�Si1�S1114.26(10)O3�Si1�S1 112.40(15)106.90(11)O12�Zn1�S1O1�Si1�S1 113.12(14)102.14(10)O13�Zn1�S2

101.91(11)O12�Zn1�S2 O4�Si2�S2 112.29(18)S1�Zn1�S2 130.26(6) O6�Si2�S2 109.7(2)

106.49(14)O5�Si2�S2O10�Zn2�O11 93.05(17)110.28(13)O10�Zn2�S3 O9�Si3�S3 116.11(19)

O11�Zn2�S3 121.70(13) O8�Si3�S3 111.05(15)O10�Zn2�S2 110.24(14) O7�Si3�S3 107.14(14)

97.04(11)O11�Zn2�S2 C38�O10�Zn2 125.5(5)S3�Zn2�S2 120.76(5) C40�O11�Zn2 123.0(4)

95.81(6)Si1�S1�Zn1 O10�C38�C39 124.4(6)102.32(6)Si2�S2�Zn1 C40�C39�C38 128.2(6)

Si2�S2�Zn2 106.56(6) O11�C40�C39 125.5(6)Zn1�S2�Zn2 97.58(6)

Torsion angles−161.09(14)O13�Zn1�S2�Zn −46.98(11) O10�Zn2�S2�Zn

2 1O12�Zn1�S2�Zn 51.29(11) O11�Zn2�S2�Zn −65.20(13)

2 1175.89(6)S1�Zn1�S2�Zn2 S3�Zn2�S2�Zn1 68.41(7)

Fig. 3. Hydrogen bonds in 2. For clarity only the central C atoms ofthe But groups and the H atoms of the H2O molecules are shown.

B. Becker et al. / Polyhedron 20 (2001) 949–956 953

Scheme 1.

shorter than the Zn�O(water) bonds found in the samemolecule.

2.3. Spectral measurements

Vibrational spectra were recorded for solutions of 1and 2 in carbon tetrachloride (400–4000 cm−1). Theyare similar, although the presence of coordinated waterin 2 is clearly documented by a broad band at 3000–3500 cm−1, characteristic for the O�H stretching fre-quencies. Both complexes also show a pair ofwell-resolved bands of equal intensity at 1523 and 1592cm−1, originating from the acetylacetonate ligand. Inaccordance with the molecular structures, these bandsin the spectrum of 1 are the strongest ones, beingapproximately two times more intense than those in thespectrum of 2. Below 1500 cm−1 the spectra of boththe compounds are dominated by a set of bands origi-nating from the (ButO)3SiS ligand, which are present inthe spectra of all the tri-tert-butoxysilanethiolates so farobtained. A detailed examination, however, revealedsome subtle differences in the regions usually attributedto the Si�O�C (near 1000 cm−1) and the Si�S (near 600cm−1) vibrations.

The peculiarities of the IR spectra of zinc tri-tert-bu-toxysilanethiolates containing ammonia–[Zn{SSi(OBut)3}2(NH3)]2, or varying and undefinableamounts of water as additional ligands, were mentionedby us previously [6]. Unfortunately, the molecularstructures of the respective complexes could not bedetermined and the conclusions drawn were limited.The knowledge of the molecular structures of 1 and 2enables a more detailed discussion, especially if onerecalls the spectrum of the aforementioned water lig-ated zinc tri-tert-butoxysilanethiolate. Since the ho-moleptic tri-tert-butoxysilanethiolate is still unknownthe spectra recorded for homoleptic tri-tert-butoxysi-lanethiolates of heavier zinc group members,[Cd{SSi(OBut)3}2]2 [16] and [Hg{SSi(OBut)3}2] [17], areadded for the reference; their molecular structures aresketched below (Scheme 1; only the oxygen atoms ofthe ButO groups are shown). The respective cutoffs ofthe IR spectra are given in Fig. 4.

At 940–1000 cm−1 the spectra reveal a broad bandwith varying intensity centered at approximately 980cm−1 for the Zn complexes, and for the Cd and Hgderivatives, shifted to higher frequencies. Although thisband is also noticeable in the spectrum of 1 dissolved inCCl4 (1a) it is absent in the spectrum recorded for solid(1b). It is also absent in the spectra of such complexesas, e.g. [MSSi(OBut)3]4, where M=Cu, Ag, Au [29–31]but present in the case of [Tl{SSi(OBut)3]2 [32], to quoteonly a few other examples. All the complexes, where thediscussed property was observed, have a common struc-tural feature — an oxygen atom from some of theSi�O�But fragments interacts with a metal or, as in 2, isan acceptor of a hydrogen bond. It seems reasonable

Fig. 4. Cut-offs from the infrared spectra of 1, 2 and related com-plexes where R=Si(OBut)3 (all in CCl4 solution except 1b, measuredin KBr pellet).

2.363 and 2.379 A� for Zn�Sb in di-�-(N-methylpiperi-dinium-4-thiolate)-bis[dichlorozinc(II)] [27] or 2.2475and 2.2970 A� for Zn�St in bis(tri-tert-butoxysilanethio-late)(bipyridine)zinc(II) [6]). The mode of sulfur bond-ing is also reflected in the S�Si bond lengths — thatfound in 1 is similar to the S2�Si2 bond (Sb) length, butlonger than the S1�Si1 and S3�Si3 bond (St) lengths in2. We observed the same features previously for othersilanethiolates — dimeric bis(tri-tert-butoxysilanethio-late)cadmium(II) [16], with the terminal and bridgingthiolate ligands within the same molecule, may be givenas example.

There are many five- and six-coordinated zinc com-plexes containing chelate ligands based on the pentane-2,4-dione backbone. The short Zn�O bonds found in 1match closely that found in the one rare tetrahedralexample — bis(dipivaloylmethanido)zinc(II) — wherethe Zn�O bond length equals 1.941 A� [28]. In principle,the same holds for the respective Zn2�O(acac) bonds in2. Although the Zn2�O11 bond is slightly longer (oxy-gen also serves as the hydrogen bond acceptor), it is

B. Becker et al. / Polyhedron 20 (2001) 949–956954

that the IR spectra reflect some alteration in the Si�O�Cbonding characteristics. In a complex described by us as[Zn{SSi(OBut)3}2(H2O)x ]y [6], where the band in ques-tion is rather a result of superposition of at least threebands, we most probably deal with a mixture of verysimilar compounds. In all of them H2O bonded to zincmay form hydrogen bonds similar to these in 2 — thespectrum reveals an intense broad band at 3000–3500cm−1.

Some interesting features may also be noticed on ex-amining the spectra in the 500–670 cm−1 region. Allcompounds with (t-BuO)3SiS- group show here twobands of medium intensity. They are sharp and symmet-ric for the complexes where only the terminal or only thebridging sulfur is present — [Hg{SSi(OBut)3}2] [17] withits terminal thiolate ligand may serve as an example. Thesame we observed for [MSSi(OBut)3]4 (M=Cu, Ag, Au)[29–31] or [TlSSi(OBut)3]2 [32], where all the thiolate lig-ands are bridging. For the complexes where both typesof sulfur are present — as in [Cd{SSi(OBut)3}2]2 [16],each of these bands is composed of at least two superim-posed bands and is shaped unsymmetrically. The spec-trum of 2 belongs to this category. The most interestingare small differences between the spectra recorded for 1in solution (1a) and in KBr pellet (1b). The spectrum 1b,remarkably simpler (weak band at approximately 590cm−1, also noticed by us for zinc acetylacetonate), is notonly in accordance with our observations presentedabove but also the determined molecular structure of 1,with both silanethiolate ligands strictly identical andbridging. We think therefore that the spectrum 1a maywell demonstrate the partial dissociation of the complexin solution.

We gathered much experimental IR data for thesilanethiolate complexes of known molecular structures;here only a small part has been presented. We think itgives us a chance to anticipate the structural features (atleast to some extent) for those complexes for which X-ray data are still lacking. It should also be possible to seehow these features are changing on going from the solidstate to solution.

The 1H and 13C NMR spectra in the solutions of com-plexes 1 and 2 were consistent with the proposed formu-las and similar to each other (see Section 3).

The structures of 1 and 2 are not preserved in the va-por phase; the mass spectra show no molecular ions. Themost characteristic fragments are those of (ButO)3-SiS2Zn2

+, with m/z 442 (1, 54%; 2, 60%) and{(ButO)3SiS}2Zn+ with m/z 622 (1, 28%; 2, 100%). Themain decomposition pathway is realized by the stepwiseelimination of butene.

3. Experimental

Tri-tert-butoxysilanethiol, (ButO)3SiSH, was obtained

by alcoholysis of SiS2 [4]. Zinc acetylacetonate was pre-pared according to Ref. [11]. Acetylacetone was distilledbefore use. Solvents were distilled before use and driedby standard procedures if needed. IR spectra wererecorded on a Mattson Genesis II Gold FTIR spectrom-eter (CCl4 or KBr pellet), 1H and 13C NMR spectra on aGemini 200 (200 MHz) spectrometer (TMS int.), andmass spectra on Finnigan Mat 8200 apparatus (E.I., 70eV, direct inlet). Elemental analyses were performed onElemental Analyzer EA 1108 (Carlo Erba Instruments).

3.1. [Zn{�-SSi(OBut)3}(acac)]2 (1)

Zinc acetylacetonate (1 mmol, 0.27 g) was warmed in5 ml of acetonitrile (dried over molecular sieves 3A andfreshly distilled before use). To the obtained clear solu-tion tri-tert-butoxysilanethiol (1 mmol, 0.3 ml) wasadded. The mixture was gently stirred for 10 min andfinally simply poured onto a 5 cm petri dish. After ap-proximately 2 h of evaporation of the solvent, small crys-tals were collected and washed with a small portion ofacetonitrile. The remaining solution was discarded. Theobtained product melted sharply at 195°C. Yield 0.145 g,33%.

1H NMR (CDCl3): � 1.36 (s, 54H, But), 1.98 (s, 12H,Me), 5.34 (s, 2H, CH). Anal. Found: C, 46.61; H, 7.84; S,7.17. Calc. for C34H68O10S2Si2Zn2, (M=887.98): C,45.99; H, 7.72; S, 7.22%.

3.2. [{(ButO)3SiS}(H2O)2-Zn{(-SSi(OBut)3}Zn(acac){SSi(OBut)3] (2)

Zinc acetylacetonate (1 mmol, 0.27 g) was warmed in5 ml of acetonitrile (distilled before use but not dried). Awhite, milk-like suspension was formed as a result ofwarming. Tri-tert-butoxysilanethiol (1.5 mmol, 0.45 ml)was added to the suspension and the flask was gentlyshaken until the clear solution was obtained. This waspoured onto a 5 cm petri dish and after approximately 1h small but well-formed crystals were collected, washedwith cold acetonitrile and dried. Yield 0.2 g (36%). Theproduct had no sharp melting point; signs of decomposi-tion were observed starting from 58°C, and finally thesubstance melted at 82–86°C.

1H NMR (CDCl3): � 1.42 (s, 81H, But), 1.97 (s, 6H,Me), 4.54 (s, broad, 4H, H2O), 5.35 (s, 1H, CH). 13CNMR (CDCl3, �): But 31.43 (Me), 74.40 (C); acac 27.94(Me), 100.10 (CH), 192.39 (CO). Anal. Found: C, 45.00;H, 8.45; S, 9.01. Calc. for C41H92O13S3Si3Zn2, (M=1104.40): C, 44.59; H, 8.40; S, 8.71%.

3.3. Structure determinations

Crystals grown directly from the reaction solutionswere of a quality suitable for X-ray measurements.

B. Becker et al. / Polyhedron 20 (2001) 949–956 955

Diffraction data were recorded on a KUMA KM4diffractometer with graphite-monochromated Mo K�radiation. No absorption corrections were applied. Thestructures were solved with direct methods and refinedwith the SHELX-97 program package [33,34] with thefull-matrix least-squares refinement based on F2. Allnon-hydrogen atoms were refined anisotropically. Hy-drogen atoms, except for those of the water moleculesin 2, were refined in geometrically idealized positionswith isotropic temperature factors 1.2 times the equiva-lent isotropic temperature factors Ueq of their attachedatoms. Water molecules in 2, for which approximatehydrogen positions were found from difference maps,were refined as rigid molecules with O�H distance 0.82A� and H···H distance 1.3 A� . Crystal data, a description

of the diffraction experiment and details of the struc-ture refinement are presented in Table 3.

4. Supplementary material

Crystallographic data for the structural analysis havebeen deposited with the Cambridge CrystallographicData Center, CCDC Nos. 149970 and 149971 for 1 and2, respectively. Copies of this information may be ob-tained free of charge from The Director, CCDC, 12Union Road, Cambridge CB2 1EZ, UK (fax: +44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:http://www.ccdc.cam.ac.uk).

Acknowledgements

Financial support from the Polish State Committeeof Scientific Research (project No 3 T09A 136 16) isgratefully acknowledged.

References

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Table 3Crystal data and structure refinement parameters for 1 and 2a

21

C34H68O10S2Si2Zn2 C41H92O13S3Si3Zn2Empirical formula887.92Formula weight 1104.34293(2)Temperature (K) 293(2)0.71073 0.71073Wavelength (A� , Mo

K�)Crystal system triclinic monoclinicSpace group P21/cP1�Unit cell dimensions

9.578(2)a (A� ) 24.869(5)10.293(2)b (A� ) 13.415(3)

c (A� ) 13.290(3) 19.018(4)104.37(3)� (°) 90

� (°) 105.45(3) 103.35(3)� (°) 98.47(3) 90

V (A� 3) 1191.0(4) 6173(2)41Z

1.238 1.188Dcalc (Mg m−3)0.9851.189Absorption coefficient

(mm−1)F(000) 2368472

0.4×0.3×0.3Crystal size (mm) 0.4×0.3×0.3� Range for data 1.68–27.001.67–30.06

collection (°)Index ranges 0�h�31,−10�h�13,

−14�k�+14, −16�k�0,−24�l�210�l�1712381/12273Reflections 6440/5105

collected/unique(Rint) (0.1241) (0.0310)

72.8Completeness to � (%) 91.112273/0/559Data/restraints/paramete 5105/0/226

rsGoodness-of-fit on F2 0.9691.026

R1=0.0571,Final R indices R1=0.0547,wR2=0.1248 wR2=0.1337[I�2�(I)]R1=0.1054,R indices (all data) R1=0.2080,wR2=0.1485 wR2=0.1798

Largest difference peak 0.723 and −0.6830.724 and −0.736and hole (e A� −3)

a R indices defined as: wR2={�[w(Fo2−Fc

2)2]/�[w(Fo2)2]}1/2,

R1=���Fo�−�Fc��/��Fo�.

B. Becker et al. / Polyhedron 20 (2001) 949–956956

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.