Reaction of [SNS][AsF6] with Hg(CN)2 and PhHgCN: Preparation and crystal structures of [Hg()2][AsF6]2 and [PhS4N3Ph][AsF6]

Poh'hedron Vc4. 15, N o I I. pp. IN77 1886. [996

~

C o p y r i g h t ~ 1996 Elscvicr Sciencc l a d P r i n t e d in G r e a t Britain. All r i g h t s reserved I)277 3 3 8 7 ' 9 6 $15.110+0.00

Pergamon 0277-5387(95)00426-2

REACTION OF [SNSIIAsF6] WITH Hg(CN)2 AND PhHgCN: PREPARATION AND CRYSTAL STRUCTURES OF i

i

[Hg(CNSNS)2I[AsF6]2 A N D [PhS4N3Ph]IAsF6]

CHRISTINE M. AHERNE, ARTHUR J. BANISTER,* IAN LAVENDER, SIMON E. LAWRENCE and JEREMY M. RAWSON* Department of Chemistry, Durham University, South Road. Durham DH1 3LE, U.K.

and WILLIAM CLEGG Department of Chemistry, University of Newcastle upon Tyne, Newcastle upon Tyne NE1 7RU, U.K.

(Receired 12 July 1995 ; accepted 7 Auyust 1995) Abstract--Reaction of Hg(CN)2 with two equivalents of the salt [SNS][AsF,,] provided a i

i

high yield (92%) route to the first metallo-dithiadiazolylium salt, [Hg(CNSNS)2] [AsF¢,]2(I). Its structure and reactivity are compared with those of the analogous organic derivatives, r

I

[R.CNSNS] [AsF6] • I initiates the polymerization of tetrahydrofuran and undergoes metathesis reactions but reduction leads to decomposition (forming $4N4), whilst oxidation with I - - 1

the halogens provides a novel route to the salts [X.CNSNS][AsF6] (X = CI, Br and I). In contrast, reaction of PhHgCN with [SNS][AsF6] yielded the sulfur--nitrogen chain compound, [PhS4N3Ph][AsF6] (II) with a cation consisting of an alternating S/N chain strung between two phenyl groups.

The cycloaddition chemistry of [SNS][AsF6] with organic nitriles is now well-documented Land leads to the formation of the corresponding organo-substituted. 6~z heterocyclic 1,3,2,4-dithiadiazolylium salt (eq. (1)). Multiple cycloadditions have also been reported 2 4 and we have

R I Ill N

maintaining excellent yields. However. two aspects of this area of chemistry have not been fully addressed. First, the cycloaddition of [SNS][AsF6] with simple cyanides such as HCN, FCN, C1CN, etc., are not well documented, possibly because of the high toxicity and volatility of the cyanide,

S

~-'s

/ S`. N RmR\ II AsF6N.,- S+

AsF6-

shown that we can cyclo-add up to three units of [SNS][AsF6] under mild conditions whilst still

* Authors to whomcorrespondenceshould be addressed.

(1)

although cycloadditions of [SNS][AsF6] to ICN and HCN have been carried out recently, s Second, the cycloaddition chemistry of [SNS][AsF6] with metal cyanides has not been reported. We recently commenced a synthetic programme to investigate

1877

1878

C. M. AHERNE et al.

the reactivity of [SNS][AsF6] with metal cyanides and now report the full details of the cycloaddition chemistry of [SNS][AsF6] with Hg(CN)2 and i

I

PhHgCN, yielding [Hg(CNSNS)2][AsF6]2 (I) and [PhS4N3Ph][AsF6] (II), respectively. I constitutes the first example of a crystallographically characterized dithiadiazolylium ring covalently bound to a metal atom via carbon. We compare the chemistry of I with that of other 1,3,2,4-dithiadiazolylium salts and examine its redox behaviour through chemical and electrochemical experiments. A preliminary communication of this work has been published recently. 6 We show that oxidation of I with halogens (X2) leads to the previously unstudied halo-substituted dithiadiazolylium salts, i

pheric oxygen, but hydrolyses slowly over a period of hours. Although we have not carried out kinetic studies into this cycloaddition, reaction of Hg(CN)2 with one equivalent of [SNS] [AsF6] yielded only the 1:2 addition product, I. Such preferred multiple additions have been found to occur with other cycloaddition processes involving [SNS] [AsF6].2"4 I is insoluble in non-donor organic solvents (CH2C12, CHC13, CC14, C6H6, PhMe), sparingly soluble in liquid SO2 but dissolves readily in donor solvents such as MeCN, PhCN and THF. X-ray quality crystals of I were obtained by slow diffusion of CH2C12 into a saturated solution of I in acetonitrile, and a full crystal structure analysis confirmed the proposed structure.

I

[X-CNSNS][AsF6] [X = C1 and Br], and a less hazardous route to the iodo-derivative [X = I]. These indicate transformations that I may be suitable for some dithiadiazolylium ring-transfer reactions.

Structure

The structure 6 of I shows a dication in which two dithiadiazolylium rings are bound to a central

[AsF6-I2 +s-N

AsF6_ I O S~ N

S

S

N%S/Nxxs, N +

II

RESULTS AND DISCUSSION [SNS][AsF6] has been shown to react with a wide variety of organic nitriles through an asynchronous [4+2]~ cycloaddition process, 1 to form 1,3,2,4dithiadiazolylium salts in high yield (frequently quantitative according to N M R measurements). The chemistry of this reagent (particularly its reactivity towards nitriles and other unsaturated bonds) has been the subject of recent reviews. 1 Whilst examining the reactivity of this salt towards metal (and metalloid) cyanides, we have found two distinct reaction pathways which we now describe. Reaction

qf [SNS] [AsF6]

with

Hg(CN)2

When two equivalents of [SNS] [AsF6] are stirred with Hg(CN)2 in liquid SO2, a dense white precipitate is formed over a period 0f24 h under a pale solution. Micro-analytical data for this compound were consistent with the formation of the salt i

mercury atom. The two rings are related to each other through an inversion centre at mercury (Fig. 1). The geometry and bonding within I have been described previously6 in some detail. However, we feel that the relative arrangement of the dithiadiazolylium rings about Hg is worth further

~S(2)

SI1) N(1) ~" FI4) F(3) FC2)

i

[Hg(CNSNS)2][AsF6]2, I, IR data showed no vcN absorption (at ca 2200 cm -~) and the presence of AsF 6 vibrations. I appears to be stable to atmos-

Fig. 1. Structure of the cation and anion ofl, showing the atom numbering scheme and 40% probability ellipsoids.

Reaction of [SNS][ASF~,] with Hg(CN)2 and PhHgCN

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Frontier Molecular Orbitais of [Hg((:NsNs)2]2 +

LUMO+I [E =-10.05eV, syrmnetry 19ag]

LUMO [E= -10.06eV, symmetry 14au]

~HOMO

[E= -12.53eV, symmetry 13au]

Fig. 2. Frontier molecular orbitals of I from EHMO calculations.

comment. The molecule lies on an inversion centre and the rings are thus anti, with a non-crystallographic C2h symmetry. This is similar to r

that

observed

I

1

for I

)

r

I

[SNSNC.CNSNS][AsF6]2, 5 I

[SNSNC.C6H4.CNSNS] 2 and comparable to the essentially C3h symmetry found for the cation in i

i

[C(CNSNS)3][AsF6]2. 3 Previous work 3'4 has shown that electrostatic interactions which occur during the asynchronous cycloaddition may initially lead to such geometric preferences. However, M.O. calculations on these salts, 7 coupled with ~gF N M R I

I

measurements on [C6Fs.CNSNS][SbC16] (which show only three unique 19F N M R resonances at room temperature) 8 indicate that the barrier to rotation about the bond is low. Consequently we assume that the higher symmetry species (possessing a Cn axis) crystallize preferentially in the solid state. This process may be assisted through electrostatic and dipolar interactions. Molecular orbital calculations E H M O calculations were carried out on the dication in I using the crystal structure geometry and the CACAO package. 9 The energies and frontier molecular orbitals are depicted in Fig. 2. In contrast with most 1,3,2,4-dithiadiazolylium salts which have a H O M O of n-character, the

H O M O of I possesses r; character and contributes to the skeletal bonding. Of particular note is the H g - - C bonding contribution to this orbital. Oxidation of this material might therefore be expected to have an associated weakening of the H g - - C bond. Indeed, we shall see later that reaction of 1 with halogen leads to H g - - C bond cleavage. There is also a pair of essentially degenerate LUMOs which are of similar character to those observed for organic-l,3,2,4-dithiadiazolylium rings, which become populated when I is reduced. The antibonding nature of these orbitals coupled with the high energy of the a-bonding orbitals may play an important role in the decomposition of ! on reduction. The net charge distribution indicates that the dithiadiazolylium sulfur atoms bear the majority of the positive charge.

Reactit~ity We have found that the chemistry of I resembles that of organic 1,3,2,4-dithiadiazolylium salts in some ways. For example, anion metathesis reactions of I with two equivalents of [NBu4]X (X = C1,Br, I) led to the isolation of the cor[ - - 1

responding salts, [Hg(CNSNS)2]X2 as coloured solids which are insoluble in a variety of common organic solvents (toluene, acetonitrile, CH2C12,

C. M. AHERNE et al.

1880

I PA

-0.5

,\

-30

t

V

....

(a)

-40

Fig. 3. Cyclic voltammogram of I in MeCN using [NBu4][BF4] supporting electrolyte and referenced to S.S.C.E. (a) at - 15°C, E~/2= +0.23 V, (b) at 0°C, Et = +0.43 V, E2 = +0.60 V.

liquid SOz, etc.).* During attempts to grow crystals of I, we also found that I acted as a cationic initiator for the polymerization of tetrahydrofuran; clear gels were formed over a period of ca 12 h in a manner similar to that observed for the salt f

i

[C6 H4 (CNSNS)2] [AsF6] 2. 'l

Cyclic voltammetry Cyclic voltammograms of I in M e C N were recorded in the region - 15 to 0°C using a variety of sweep rates. At low temperature ( - 15°C) and high sweep rates, reduction of I appeared almost completely reversible (Ipc/Ipa ,-~ 1) (Fig. 3a); the ratio Ir~/Ipa tends to unity with increasing scan rate and is characteristic of an EC mechanism.? The half-

*Exhaustive extraction of [Hg(CNSNS)2]CI2 with liquid SOz in a sealed extractor surprisingly yielded a few yellow crystals which were identified as [S4N3][HgC13] by X-ray crystallography, j° Since the IR spectra of [Hg(CNSNS)2]C12 and [S4N3][HgC13] are significantly different, we assume the latter compound is a minor decomposition product. ?An EC mechanism is a route in which electrochemically generated species react chemically, making the electrochemical process quasi-reversible. Such EC mechanisms can be identified by CV because the ratio I~/Iv, tends to unity at high scan rates. At elevated temperatures the kinetic rate increases and even at high scan rates the process may appear irreversible, as observed in this instance.

wave reduction potential of +0.23 V. As the temperature was raised, this redox process became irreversible (at 0°C, Ipc/Ipa = 12.5) and two new oxidation processes (El = + 0.43 V, E2 = + 0.60 V) became observable (Fig. 3b) indicating breakdown of the reduced product. The redox behaviour of I in the low temperature regime is analogous to that of other 1,3,2,4-dithiadiazolylium salts ~2 and is consistent with localization of the positive charge on the dithiadiazolylium sulfur atoms (the El/2(red) value for aryl-substituted-1,3,2,4-dithiadiazolylium salts is typically in the region + 0 . 2 to +0.3 V). ~2 As yet we have been unable to ascertain the nature of the break-down products leading to the new oxidation processes, E2 and E3, although they would not appear to be associated with simple S/N compounds such as SN +, SNS +, SzN 2 or 84N4 and may be associated with an Hg°/Hg~/Hg n process.

Redox Chemistry Chemical reduction of I (with silver powder under liquid SO2) at room temperature led to the formation of an insoluble white product (Hg(NCS)2 by IR) under a pale yellow solution. Filtration of the soluble fraction, followed by slow solvent removal yielded a few yellow crystals which were identified as $4N4 by I R and preliminary Xray analysis. Thus reduction of ! proceeds via reduction of the dithiadiazolylium ring and subsequent fragmentation of this ring to form thiocyanate ions and SN fragments which combine

Reaction of [SNS][ASF6] with Hg(CN)2 and PhHgCN to

form

S4N 4.

I

Our

attempts

to

observe

I

Hg(CNSNS)~" by low temperature in situ ESR experiments have proved unsuccessful. Molecular orbital calculations indicated that the H g - - C bond may be particularly susceptible to cleavage on oxidation, due to the high lying nature of the ~-bonding orbital. Chemical oxidation of I with the halogens X2(X---~C1, Br and I) in liquid SO, formed HgX2 and the halo-substituted dithiaI

I

diazoyllium salts, [X.CNSNS][AsF6], in good yield (75 92%). The salts were readily extracted from HgX> and were characterized by IR spectroscopy (comparable with the literature data s for X ~ I ) and I

I

elemental analysis. The salts [CI.CNSNS][AsF6] I

I

and [Br.CNSNS][AsF6] have not previously been reported although their isomeric counterparts, [X.CNSSI~I]X have been characterized.13 Although ICN is a well-characterized solid at room temperature, C1CN and BrCN are highly toxic gases. The ready availability and ease of handling of the halogens, coupled with the excellent recovered yields make this an alternative and more convenient route to such simple 1,3,2,4-dithiadiazolylium derivatives. We are continuing to examine the utility of this oxidative-addition reaction for the synthesis of other 1,3,2,4-dithiadiazolylium ring systems. Reaction ol'[SNS][AsF6] with PhHgCN

In contrast to the reaction of [SNS][AsF,] with Hg(CN)2 [slowly forming colourless l], reaction of [SNS][AsF6] with PhHgCN gave an immediate deep red coloration, which on stirring at room temperature turned purple and (over 24 h) eventually royal blue. The solution was filtered off to leave a pale residue (Hg[AsF6] 2 and Hg(NCS)2 by IR) and an intense blue filtrate. The soluble fraction was recrystallized from CH2C12 by slow solvent removal to yield lustrous b l u e , old crystals which were characterized by X-ray analysis as [PhS4N3Ph] [AsF,,], II. Instead of the anticipated cycloaddition reaction, it would appear that phenylation of [SNS] ~ occurs coupled with sulfur-abstraction to form a PhSN fragment. We assume this is likely to occur through a metallo-complex. Reaction of two PhSN fragments with [SNS][AsF6] then provides II. The overall reaction can then be written : 2PhHgCN + 3[SNS][AsF6] --+ Hg[AsF(,]2 + Hg[NCS]2 + [PhS4N3Ph] [AsF6] Structure

The structure of 11 was determined by single crystal X-ray diffraction. Bond lengths and angles are

1881

given in Table I. The cation of I! is completely planar and possesses non-crystallographic C> symmetry with an approximate plane of symmetry perpendicular to the cation plane through N(2) (Fig. 4). II possesses a similar structure to the previously described ~4 $4N3 chain compound [Me.C6H4.S4N3.C6H4.Me]CI, except that there is some deviation from planarity in the latter compound the S/N chain forms a mean plane with deviations between + 0.06 and - 0 . 0 7 / ~ , whilst the two aryl groups are twisted (14.4 and 4.1 ) with respect to this plane. The lower symmetry of this tolyl system appears to arise through a series of strong and uneven anion-cation interactions, particularly between S(2) and S(3) and the chloride anion (3.056(3) and 3.237(3) t~, respectively). In comparison there are negligible interactions between the ~'hard' AsF6 anion and the cation in I1, the closest S . . . F contact being 3.119 /~,. The solid state packing of the cations in this structure provides planes of wave-like chains along the zaxis, with the AsF6 anions located in the interstices which run parallel to the y-axis as illustrated in Fig. 5. Although the inter-plane distance at 3.37/~ should facilitate intermolecular contacts, the staggered nature of the packing minimizes cation-cation interactions. Instead, the capacity for secondary S . . . N bonding is satisfied internally. Within the $4N3 chain there are a pair of strong intramolecular S . . - N interactions; S ( I ) . . . N ( 2 ) and S(4)-.. N(2) (at 2.772(3) and 2.767(3) /~), respectively. These secondary interactions between atoms can be considered as having both covalent and electrostatic contributions, in agreement with molecular orbital calculations.

Molecular orbital calculations

E H M O calculations were carried out on the cation in II using the crystal structure geometry and the CACAO package. 9 The energies, frontier molecular orbitals and charge distributions are depicted in Fig. 6. The calculations show there is a strong electrostatic attraction between S(l) and N(2) and S(4) and N(2) which contributes to the "horseshoe" shape of the cation and we suggest these constitute a substantial factor in determining the structural motif [Mayerle et al. ~4 previously suggested the horse-shoe configuration in tolylS4N3 tolyl + was preferred to that observed in (SN)~] 5 and more recently RSNSNR, ~6 because this achieved the maximum packing efficiency within the crystal structure]. These electrostatic attractions are also enhanced by 7r-bonding interactions between S(1), N(2) and S(4) in the HOMO. In

1882

C. M. AHERNE et al. Table 1. Bond lengths (]k) and angles (°) for II C(1)--C(6) C(2)--C(3) C(4)--C(5) C(6)--S(I) N(1)--S(2) N(2)--S(3) N(3)--S(4) C(7)--C(8) C(8)--C(9) C(10)--C(ll) As--F(2) As--F(4)

1.383(5) 1.377(6) 1.376(6) 1.756(4) 1.562(3) 1.595(3) 1.618(3) 1.383(5) 1.389(5) 1.367(7) 1.693(3) 1.700(2)

C(1)---C(2) C(3)--C(4) C(5)--C(6) S(I)--N(1) S(2)--N(2) S(3)--N(3) S(4)--C(7) C(7)--C(12) C(9)--C(10) C(11)--C(12) As--F(1) As--F(3)

C(6)--C(1)--C(2) C(2)--C (3)--C(4) C(4)--C(5)--C(6) C(1)--C(6)--S(1) N(1)--S(1)--C(6) N(1)--S(2)--N(2) N(3)--S(3)--N(2) N(3)--S(4)--C(7) C(8)--C(7)--S(4) C(7)--C(8)--C(9) C(11)--C(10)--C(9)

118.8(4) 120.1(4) 118.9(4) 124.5(3) 102.1(2) 104.8(2) 104.6(2) 101.4(2) 124.0(3) 118.4(4) 121.1(4)

C(7)--C(12)--C(11) F(2)--As--F(4) F(4a)--As--F(4) F(1)--As--F(3) F(4)--As--F(3)

118.8(4) 90,72(10) 88,9(2) 89,72(9) 91.38(13)

1.388(5) 1.381(6) 1.399(5) 1.618(3) 1.598(3) 1.560(3) 1.762(4) 1.387(6) 1.375(6) 1,388(6) 1.693(3) 1.711 (2)

C(3)--C(2)--C(1) C(5)--C(4)--C(3) C(1)--C(6)--C(5) C(5)--C(6)--S(1) S(2)--N(1)--S(1) S(3)--N(2)--S(2) S(3)--N(3)--S(4) C(8)--C(7)--C(12) C(12)--C(7)--S(4) C(10)--C(9)--C(8) C(10)--C(I 1)--C(12) F(2)--As--F(1) F(1)--As--F(4) F(2)--As--F(3) F(4a)--As--F(3) F(3)--As--F(3a)

120.6(4) 120.6(4) 121.0(4) 114.4(3) 119.6(2) 129.3(2) 119.7(2) 121.5(4) 114.5(3) 120.1 (4) 120.0(4) 179.13(13) 89.89(9) 89.66(9) 179.53(12) 88.3(2)

Symmetry transformations used to generate equivalent atoms : a: x, - y + 1/2, z.

C("C) ~

F(2)

~

,.~C(ll) ~ 1 0 )

c(7)L

~S(1) F(4) i(3)~F(1)

SN}.,~"w"~,~C[9 j''

N(1)~N(3) S(2)

S(3)

Fig. 4. Structure of the cation and anion of II, showing the atom numbering scheme and 40% probability ellipsoids.

principle the n-bonding interaction between S(1) and S(4) should lead to a weak S.-. S interaction across the ring in a similar manner to that observed in $3N202.17 However, the secondary distance [ds...s = 3.766(1) &] is somewhat greater than the sum of the van der Waals radii 18 [3.2 &] and any contributions to the molecular geometry from this

interaction are likely to be small. The electrostatic and bonding interactions between S(1) and N(2) and equally between S(4) and N(2) may explain the ready loss of an SN unit during aerial decomposition TM of [ArS4N3Ar]C1 (forming [ArS3N2Ar]), i.e. through loss of the N(1)--S(2) fragment and formation of a formal S(1)--N(2) bond.

Reaction of [SNS][ASF6] with Hg(CN)2 and PhHgCN

b Fig. 5. Packing diagram of II, as projected along the crystallographic h axis.

Charge distribution

~

S

+0.49 O R R -0.67N~ ~ /N -0.67 +1.13S S4-1.13

along the thiazyi chain in [Ph.S4N3.Ph] +

LUMO (E = -10.388eV)

HOMO (E= -11.582eV)

Fig. 6. Frontier molecular orbitals and charge distribution in the cation of II.

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C. M. AHERNE et al. CONCLUSIONS

Reaction of [SNS][AsF6] with Hg(CN)2 yields the corresponding metal-substituted 1,3,2,4-dithiadiazolylium salt in good yield. This salt appears structurally similar to the organo-substituted derivatives, but its reaction chemistry is more complex; reduction of I leads to decomposition but I undergoes oxidative addition with halogens to form halo-substituted-l,3,2,4-dithiadiazolylium salts. The tendency for I to disproportionate on reduction, coupled with the decomposition of r

i

Hg(CNSNS)2C12 to give [S4N3][HgC13] indicates some lattice stabilization of I. In contrast, the reaction of [SNS][AsF6] with PhHgCN is complex, finally leading to the formation of [PhS4N3Ph][AsF6], II. Initial reactions with some other aryl-metalloid-cyanides, e.9. Ph3SnCN, also appear to form II. EXPERIMENTAL

General procedures All reactions and manipulations were carried out under an atmosphere of dry nitrogen, using standard double-manifold techniques and a glove-box (Vacuum Atmospheres Corporation HE43-2 fitted with an HE 493 Dri-Train). Solvents were distilled, dried and degassed prior to use. Infra-red spectra were recorded as Nujol mulls between KBr or Csl plates using a Perkin-Elmer 577 grating spectrophotometer. C, H and N analyses were carried out using a Carlo-Erba elemental analyser, Hg and As analyses were determined by atomic absorption spectrophotometry, F analysis was carried out by fusion with potassium metal and titration of HF after passing through an ion exchange column, and S analysis by oxygen combustion and titration with BaCIO4.

Cyclic voltammetrv Cyclic voltammograms were recorded using a methodology previously described.~2 All potentials are corrected and referenced to the S.S.C.E. Solutions of the electroactive species (ca 10-3M) were prepared in MeCN and 0.1 M [NBu4][BF4] supporting electrolyte. Temperature gradients were achieved using a Haake C bath fitted with an F2 control unit.

Molecular orbital calculations Molecular orbital calculations were carried out at the EHMO level on an Opus 486-DX2 66MHz

PC using the program CACAO (PC Version 4.0, 1994), 9 and inlaid parameters. Calculations were carried out on orthogonal coordinate geometries derived directly from the crystal structures using inhouse software (J. M. Rawson, 1994). No geometry optimization was applied.

Starting materials The salt [SNS][AsF6] was prepared according to the literature method 19with our own modification.3 [NBu4][BF4] (Fluka, electrochemical grade), Hg(CN)2, PhHgC1 and AgCN (Aldrich) were used without further purification. Synthesis ofPhHgCN. PhHgC1 (3.5 g, 11 mmol) and AgCN (1.5 g, 11 mmol) were stirred for 3 days at room temperature in MeCN (15 cm 3) to provide a grey-purple suspension. The AgC1 was filtered off at a water-pump using a Zitex filter. Evaporation of the filtrate in vacuo provided a white solid, PhHgCN (2.85 g, 84%). IR Vm,x(cm J): 1460mbr, 1335w, 1310w, l160w, 1083w, 1060w, 1028m, 999m, 909m, 860w, 805w, 770w, 730vs, 690vs, 610w, 455s, 395vs. Found : C, 27.6 ; H, 1.6 ; N, 4.6. Calc. : C, 27.7 ; H, 1.7 ; N, 4.6%. i

i

Synthesis q[" [Hg(CNSNS)2][AsF6]2, I. The salt [SNS][AsF6] (2.02 g, 7.6 mmol) and Hg(CN)2 (0.96 g, 3.8 mmol) were stirred in liquid SO2 for 24 h to leave a white solid under a pale yellow solution. Solvent removal and a single wash with CH2C12 afforded a white powder (2.87 g, 96%) which analysed as I. IR v.....(cm-I): 1335m, 1019w, 984m, 874m, 766s, 703vsbr, 583s, 560s, 449s, 398vs. Found: C, 3.1 ; N, 7.1 ; As, 18.6; S, 16.1; F, 28.8. Calc.:C, 3.1;N, 7.1;As, 19.0;S, 16.3;F. 29.0%. Crystals suitable for single crystal X-ray structure determination were obtained by slow addition of CH2C12 to a saturated solution of I in MeCN. r

Synthesis of [Hg(CNSNS)2]CI2. I (200 rag, 0.25 retool) and [NBu4]C1 (141 rag, 0.51 retool) were placed in one limb of a two-limbed reaction vessel with a magnetic follower and MeCN (7 cm 3) syringed in. After stirring (18 h) an orange solid was visible under a pale orange solution. Filtration and solvent removal gave an orange yellow solid (156 mg, 64%). IR v.... (cm - l ) 1308m, 1186m, 1082w, 1034w, 1007w, 965w br, 931w, 892w, 799m, 580w, 548w, 463w. Found : C, 5.3 ; N, 12.0. Calc. : C, 5.0 ; N, 11.7%. r 1 Synthesis of [Hg(CNSNS)2]Br2. l (200 rag, 0.25 retool) and [NBu4]Br (164 rag, 0.51 mmol) were placed in one limb of a two-limbed reaction vessel with a magnetic follower and MeCN (7 cm 3) syringed in. After stirring (18 h) a dark orange solid was visible under a pale orange solution. Filtration

Reaction of [SNS][ASF6] with Hg(CN)2 and PhHgCN and solvent removal gave an orange solid (169 rag, 58%). IR Vm~x(Cm-I) 1315m, 1182m, 1157w, 1078w, 1032w, 999w, 962w br, 930w, 887w, 798m, 579w, 546w, 462w. Found : C, 4.5 ; N, 10.0. Calc. : C, 4.2 ; N, 9.8%. I 1 Synthesis o f [Hg(CNSNS)2]I> I (200 rag, 0.25 mmol) and [NEt4]I (128 rag, 0.5 mmol) were placed in one limb of a two-limbed reaction vessel with a magnetic follower and M e C N (6 cm 3) syringed in. The mixture of white solids immediately turned brown under a colourless solution. Over a period of 4 h, the solution turned cherry-red and then orange and left only a small residue of brown solid. The mixture was cooled to 0~C, precipitating a white solid, which was filtered off. The solvent was removed in vacuo to give a burgundy solid ( 157 rag, 46%). IR Vm~×(cm ~) 1310m, 1185m, 1143w, 1078w, 1032w, 1015sh, 1004w, 962w br, 930w br, 890w, 796m, 582w, 550w, 466w. Found: C, 3.8: N, 8.8. Calc. : (', 3.6 ; N, 8.5%. i

i

Synthesis ~[" [CI.CNSNS][AsF6]. 1 (160 rag, 0.2 retool) was placed in one limb of a two-limbed reaction vessel with a magnetic follower and SOe (8 cm ~) was condensed on. C12 (excess) was condensed on and the vessel allowed to warm to room temperature. Initially, a bright magenta-coloured solution was present over a white solid. After stirring (30 h) a pale yellow solid was visible under a colourless solution. This was filtered, washed twice with back-condensed SO~ and the solvent removed in t'actto. The filtrate was washed twice with hexane (solvent removal in l~acuo after each wash) to give a white crystalline solid (139 rag, 85%). IR vm:,~(cm ~) 1303w, 1290sh, 1157m, 1036msbr, 953w sh, 935m, 883m, 837w, 798m, 721vs br, 651sh, 579ms, 441ms. Found : C, 3.4; N, 8.3. Calc. : C, 3.7 ; N, 8.5%. i i Synthesis ~[' [Br.CNSNS][AsF6]. I (150 rag, 0.19 retool) was placed in one limb of a two-limbed reaction vessel with a magnetic follower and SO2 (8 cm') was condensed on. Br2 (excess) was condensed on and the vessel allowed to warm to room temperature. After stirring (2 days) a pale yellow solid was visible under a colourless solution. This was filtered, washed twice with back-condensed SO~ and the solvent removed in vacuo. The filtrate was washed twice with hexane (solvent removal in t,acuo alter each wash) to give a yellow solid (113 nag, 81%). I.R. v......(cm ~) 1352m, 1291sh, l170w br, 1050sh. 1036w, 997m, 923w, 912m, 882sh, 860m, 802w. 791m, 779w, 695vs br, 654sh, 585m, 566sh, 440m, 370s. Found: C, 3.1 ; N, 7.2; Br, 21.0. Calc. : C, 3.2; N, 7.5; Br, 21.4%. i

i

Synthesis o[ [I.CNSNS][AsF6]. I (197 rag, 0.25 mmol) and 1~_ (126 mg, 0.5 mmol) were placed in

1885

the front limb of a two-limbed reaction vessel and SO2 (8 cm 3) was condensed on. After stirring (4 days) a vermilion solid was visible under a pale pink solution. This was filtered, washed twice with backcondensed SOz and the solvent removed in t'acuo. The filtrate was washed twice with hexane (solvent removal in ~acuo after each wash) to give a mimosayellow solid (165 rag, 78%). IR vm~,~(cm ~) 1332m, 1152m vbr, 1075w, 1030w, 977m, 893w, 877w, 846w, 83lw, 784w, 768w, 720vs, 695vs br, 660sh, 584m, 563w, 450m, 434w. Found: C, 3.2" N, 6.4. Calc. • C, 3.1 • N. 6.7%. Synthesis o / [PhS4N3Ph][AsF6], II. PhHgCN (0.303 g, 0.1 retool) and [SNS] [AsF~,] (0.270 g, 0.101 mmol) were placed in one limb of a two-limbed reaction vessel and liquid SO2 condensed on. There was an immediate red coloration which became increasingly purple and finally deep blue alter a period of 24 h. The solvent was then removed and the crude product transferred to a sealed extractor 2° and extracted with CH2CL to leave a pale blue residue and a deep blue filtrate of !! (65% after evaporation), ii was recrystallized from CH2C12 by slow solvent removal using a slight temperaturegradient, to form many lustrous blue-gold diamond shaped crystals, which were identified by X-ray analysis.

Crystal data Jor II

[C12H~0N3S4]AsF6, M = 5 1 3 . 4 , orthorhombic, space group P b ~ , a = 17.3546(11), b = 6.7359(7), c = 15.7608(9) A. V = 1842.4(2) /~, Z = 4 , D~= 1.851 g cm ~, 2 ( M o - K ~ ) = 0 . 7 1 0 7 3 ,~, p=2.36mm ',F(000) = 1016, T - - 2 4 0 K .

Data collection and processing

A crystal of size 0.16 x0.24 x 0.56 mm, sealed in a capillary tube, was examined on a Stoe-Siemens diffractometer equipped with a Cryostream cooler. 2~ Cell parameters were refined from 20 values ( 2 0 - 2 5 ) of 32 reflections measured at _+~ to minimize systematic errors. Data collection employed an eJ/O scan mode with on-line profile fitting, 22 20 ..... = 5 0 , index ranges h --20 to +20, k - 8 to 8, l 18 to 18. No significant variation in intensity was observed for three standard reflections. Semiempirical absorption corrections were applied2~; transmission factors were in the range 0.342 0.386. Merging of the 7487 measured reflections yielded 1768 unique data (Rm~ = 0.0506).

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C. M. A H E R N E et al.

Structure determination 23

Solution was by direct methods. Full-matrix least squares refinement was carried out on F 2 for all data, with weighting w ~ = a 2 ( F Z ) + ( O . O 3 6 P ) 2 +0.8887P, where P = (2F~+Fo2)/3. Anisotropic displacement parameters were refined for all nonh y d r o g e n atoms, and H a t o m s were included with a riding model. The isotropic extinction parameter x refined to 0.0017(3), where Fc is divided by (1 +O.O01xF~A3/sin20) TM. At convergence, R' = [Zw(Fo2 -F2)Z/]~N(Fo)2] '/2 = 0.0812 for all data, conventional R = 0.0270 on F values o f 1444 reflections with F~, > 2a(F2), goodness o f fit = 1.091 on F 2 for all data and 152 parameters. All features in a final difference synthesis were within 4-0.43 e 3.

Acknowledgements--We thank the analytical section at Durham University for microanalyses, S.E.R.C. for three studentships (C. M. Aherne, I. Lavender and S. E. Lawrence) and post-doctoral funding (I. Lavender and J. M. Rawson) and S.E.R.C. and the Royal Society for equipment grants (W. Clegg).

REFERENCES 1. S. Parsons and J. Passmore, Acc. Chem. Res. 1994, 27, 101. See also, J. M. Rawson, A. J. Banister and I. Lavender, Adv. Het. Chem. 1995, 62, 137. 2. A. J. Banister, J. M. Rawson, W. Clegg and S. L. Birkby, J. Chem. Soc., Dalton Trans. 1991, 1099. 3. A. J. Banister, I. Lavender, J. M. Rawson and W. Clegg, J. Chem. Soc., Dalton Trans. 1992, 859. 4. (a) S. Parsons, J. Passmore, M. J. Schriver and P. S. White, J. Chem. Soc., Chem. Commun. 1991, 369; (b) S. Parsons, J. Passmore and P. S. White, J. Chem. Soc., Dalton Trans. 1993, 1499.

5. S. Parsons, J. Passmore, M. J. Schriver and X. Sun, Inorg. Chem. 1991, 30, 3342. 6. A. J. Banister, I. Lavender, S. E. Lawrence, J. M. Rawson and W. Clegg, J. Chem. Soc., Chem. Commun. 1994, 29. 7. J. M. Rawson, unpublished results. 8. B. Ayres, A. J. Banister, P. D. Coates, M. I. Hansford, J. M. Rawson, C. E. F. Rickard, M. B. Hursthouse, K. M. A. Malik and M. Motevalli, J. Chem. Soc., Dalton Trans. 1992, 3097. 9. C. Mealli and D. M. Proserpio, J. Chem. Ed. 1990, 67, 399. (PC Version 4.0, 1994.) 10. S. E. Lawrence, Ph.D. thesis, University of Durham, U.K. (1995). 11. A. J. Banister and A. W. Luke, J. Polym. Sci., Part A, Polym. Chem. 1992, 30, 2653. 12. C. M. Aherne, A. J. Banister, I. B. Gorrell, M. I. Hansford, Z. V. Hauptman, A. W. Luke and J. M. Rawson, J. Chem. Soc., Dalton Trans. 1993, 967. 13. H. U. H6fs, R. Mews, W. Clegg, M. Noltemeyer, M. Schmidt and G. M. Sheldrick, Chem. Ber. 1983, 116, 416. 14. J. J. Mayerle, J. Kuyper and G. B. Street, Inor9. Chem. 1978, 17, 2610. 15. M. M. Labes, P. Love and L. F. Nichols, Chem. Revs. 1979, 9, 1. 16. K. Bestari, R. T. Oakley and A. W. Cordes, Can. J. Chem. 1991, 69, 94. 17. R. Gleiter and G. Bartetzko, Z. NaturJbrsh. 1981, 36B, 492. 18. S. C. Nyburg and C. H. Faerman, Acta Cryst., Sect. B 1985, 41,274. 19. A. J. Banister, R. G. Hey, G. K. McLean and J. Passmore, Inorg. Chem. 1982, 21, 1679. 20. R. W. H. Small, A. J. Banister and Z. V. Hauptman, J. Chem. Soc., Dalton Trans. 1984, 1377. 21. J. Cosier and A. M. Glazer, J. Appl. Crystallogr. 1986, 19, 105. 22. W. Clegg, Acta Cryst., Sect. A 1981, A37, 22. 23. G. M. Sheldrick, SHELXTL manual, Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, U.S.A., 1990; SHELXL-93, program for crystal structure refinement, University of GOttingen (1993).