Polyhedron Vol. 3, No. 5. pp. 535-544, 1984 Printed in Gnat Britain.

0277~5387/84 $3.00 + .cRl 0 1984 I4xgamon Fws.¶ Ltd.

THE FORMATION AND STRUCTURAL CHEMISTRY OF THE HEXA@-t-BUT’YLTHIOLATO) PENTACUPRATE(I) CAGE

ANION WITH TRIETHYLAMMONIUM AND TETRAETHYLAMMONIUM CATIONS

GRAHAM A. BOWMAKER, GEORGE R. CLARK* and JEFFREY K. SEADON

Department of Chemistry, University of Auckland, Auckland, New Zealand

and

IAN G. DANCE School of Chemistry, University of New South Wales, Kensington, NSW 2033,

Australia

(Received 28 June 1983; accepted 2 August 1983)

Abstract-Yellow (Et,N)[Cu,(SBu’),] crystallises from solutions prepared from Cu(II), Bu’SH, Et,N and Et,NBr in acetone/ethanol, while (Et,NH)[Cu,(SBu’),] crystallises from solutions of CuSBu’ and Bu’SH in Et,N. Crystal structure determinations reveal that both compounds contain the molecular cage [Cu,@-SBu’)d -, in which two copper atoms are three-coordinate (Cuti& three copper atoms are two-coordinate (Cu&, and all thiolate ligands are doubly-bridging. The polyhedral stereochemistry of the core is trigonal bipyramido-Cu,-trigonal antiprismo -Sd. The complete [Cu,@ -SBu’),] - cage in the Et,N + compound closely approaches O3 symmetry, but in the Et,NH+ compound one SBu’ ligand is inverted at the sulphur bridge, causing angular distortions in the cage.

Two structural features, the antiprismatic twist of the Sb polyhedron and the bending of Cu,, towards the cage centroid (S-Cu,,-S = 17 1 (l)“), provide evidence for weak Cu-Cu attractive interactions within the cage. Infrared data are discussed. Crystal data: (Et,N)[Cu,(SBu’)& C32H74C~SNS6, a = 45.500 (3), b = 11.805(l), c = 20.168(2) A, fi = 117.81 (l)“, C2/c, 2 = 8, R = 0.078 (2953 observed F); (Et,NH)[Cu,(SBu?,], C,,H,,Cu,NS,, a = 10.519(l), b = 21.457(l), c = 20.065(l), fl =95.11(l), P2,/c, 2 = 4, R = 0.072 (3093 observed F). (Et,N)[Ag,(SBu?,] is isostructural with (Et,N)[Cu,(SBu?,].

Although binary metal thiolates M(SR), have been Iong known, it is only in recent years that significant advances have been made in the syn- thetic and structural chemistry of homoleptic metal thiolate complexes.2 Newly discovered structures for copper(I) and silver(I) include the molecular cages [M,(SR)d2-*3p4 [M,(SR)d - ,s*6 [Ms(SR)7]2-, and [A&(SR),],,*- , p = 1,2,8 and the molecular cycle (AgSR)12.g,‘o A one-dimensionally non- molecular structure has been confirmed in only one compound, AgSC(CH3)2CH(CH3)2.10

*Author to whom correspondence. should be ad- dressed.

This paper deals with the [M,(SBu’)d- cage, M = Cu, Ag, providing previously unreported syn- thesis information, and giving full details and analysis of the cage structure and stereochemistry.

RESULTS

Synthesis. The yellow compounds (Et,N) [M,(SBu’)& M = Cu, Ag, crystallise from solutions prepared by dissolution of the metal(I) oxide in solutions containing BUSH, BUS-, and Et4N+.6 The copper compound can also be prepared by reaction of copper(I1) nitrate in ethanol with excess of an acetone solution of BUSH and equimolar tertiary amine, and crystallised by addition of Et,N + Br -. At room temperature the reduction of

535

536 G. A. BOWMAKER et al.

copper to copper(I) by excess thiolate occurs in less than one second, and there is no evidence that solutions containing Bu’S-Cu(I) complexes are not at equilibrium. Although it is expected that a range of anionic complexes [CU,(SBU’)~]X-Y(Y > x) may exist in solution, the only crystalline com- pounds isolated so far are those containing the [Cu,(SBu?,]- ion. Solutions from which (Et.,N)[Cu,(SBu’),J has been crystallised in yield > 50% have possessed a Bu’S -/Cu(I) molar ratio of ca. 2. Acetone solutions in which this ratio is much higher (> 10) are more intensely yellow, and probably contain higher proportions of species such as [Cu(SBu?J-, [Cu(SBu’),]‘-. When this ratio is < cu. 1.8 (depending on solvent) CuSBu’ crystallises. The presence of halide ion in solution has not interfered with the crystallisation of

(EtNPG=WJ The compound (Et,NH)[Cu,(SBu’),J was ob-

tained during experiments aimed at preparing crys- tals of CuSBu’ suitable for X-ray diffraction stud- ies. It was found that CuSBu’ could be dissolved in Et,N containing a small amount of BUSH. While it is clear that the solubility is probably due to complexation of CuSBu’ by BUS- produced by deprotonation of the thiol, elemental analysis of the product which crystallised from such solutions was not consistent with its formulation as an E&NH + salt of an anionic [CU,(SBU~,]“-~ complex, and seemed to suggest that it was an adduct of Et,N with CuSBu’. The IR spectrum showed only a very weak band at 2380 cm- * in the region expected for v(NH) of Et3NH + . The ‘H NMR spectrum of the compound dissolved in [D,] pyri- dine showed no signal which could be assigned to an NH proton, but the integrals of the signals assigned to the t-butyl and ethyl protons (see Experimental) yielded a value of 2.0 & 0.1 for the number of t-butyl groups per ethyl group. This is consistent with the formula (Et,NH)[Cu,(SBu’)J found for this compound from the crystal structure analysis (see below).

Crystal and molecular structures. The molecular cage anion [Cu,(SBu’)J (see Figs. 1 and 2) occurs in crystals with Et.,N+ and with Et,NH+, and the molecular cage anion [Ag,(SBu’)J- occurs in (Et,N)[Ag,(SBu’),] which is isostructural with the copper analogue. There is no structural evidence for cation-anion association, nor for the inter- anion M-S secondary bonding which is known in some related silver-thiolate compounds.8*9 The lat- tice packing of (Et,NH)[Cu,(SBu?,] is shown in Fig. 3.

In both [Cu,(SBu’)J - compounds the Cu& core of the cage may be described as a trigonal bi- pyramid of metal atoms, each axial-equatorial

Fig. 1. The [Cu&-SBu’)J- molecular cage (excluding hydrogen atoms) in (Et.,N)[Cu,(SBu’) a]: carbon atoms

are presented as arbitrary spheres.

V

-\o Cl611

Fig. 2. The [Cu,@-SBu’),$ molecular cage (excluding methyl groups) in (Et,NH)[Cu,(SBu%J

edge of which is bridged by a thiolate sulphur atom (see Fig. 3). The equatorial-equatorial edges of the trigonal bipyramid are not bridged by sulphur atoms, and so the equatorial metal atoms are only two-coordinate, whereas the axial metal atoms are trigonally coordinated. Therefore the axial and equatorial copper atoms will1 be denoted as Ch, and Cu,, respectively. The sulphur atoms of the six doubly-bridging thiolate ligands are located at the vertices of a trigonal antiprism. Accordingly, the cage structure is best described in terms of the interpenetrating metal and sulphur polyhedra,’ as trigonal bipyramido -Cu,-trigonal an tiprismo -S+ It should be noted that the S6 polyhedron does not approximate an octahedron.

Chemistry of the hexah-r-butylthiolato)pentacuprate(I) cage anion

Fig. 3. The trigonal-bipyramido-M,-trigonal-antiprbto- S, core of [Cu,(SBu’)J- .

Although the essential cage structure and atom connectivity in the anion is the same in both the Et,N+ and EtsNH+ compounds of [Cu,(SBu’),]-, some differences occur in the t-butyl substituents, the pseudosymmetry of the cage, and in geometric details. The cage in the Et,,N+ compound has the higher pseudosymmetry, which is approximately that of point group D,, and therefore presentation of the stereochemistry and geometrical details of both compounds will be made with reference to the D, idealisation. One atom labelling scheme is used for both compounds, as defined in Figs. 1 and 2, and consistent atom labelling is adopted for the carbon atoms of all Bu’ groups with respect to rotamerism about the S-C bonds, as defined in Fig. 4. Selected intramolecular distances and an- gles are presented in Table 1.

The Et,N+ crystal is slightly distorted, to the extent that 12% of the anionic cage sites are occupied by a similar cage which is approximately the enantiomer of the predominant cage. The positions of the copper and sulphur atoms in the alternative cage have been refined (see Expexi- mental section) and the core dimensions are in-

Fig. 4. Definition of the SBu’ atom lahelling scheme in terms of the projection along the S-C bond.

0

I w 0 t

rji

s2

s4 ss

cu3

w

\?

cu5 cu2

s3 Cu4

?P

%tY \o

Sl

1

0 S6

b

Fig. 5. Pseudo-threefold views of the [Cu,(SBu’),]- mo- lecular cages: (a) in the E&NH+ compound (excluding methyl groups); (b) the predominant cage of the Et,N+ compound; (c) the less abundant cage of the Et4N+ compound (Cu,S, only). The cages in (b) and (c) popu- late virtually the same locations with the same pseudo-

threefold axis.

eluded in Table 1. Figure 5 compares pseudo-three- fold views of the three cages in the two crystals.

The close approach to D3 symmetry by the [Cu,(SBu’),]- cage in the Et,N+ compound is

538 G. A. BOWMAKER et al.

Table 1. Selected intramolecular dimensions of (cation) [Cu,(SBu?,J, cation = Et4N+, E&NH+, with estimated standard deviations in parentheses

Dimension Cation

EtlN+ qiH+

ala-s1

Cu2-S4

Cu3-S2

cu3-s5

cu4-s3

Cu4-S6

cudi9-s (Xl

2.196(U) 12.186U9]la

2.136(U) [2.127(18)]

2.164(9] [2.166(181]

2.162(e) 12.157(19]1

2.163(q) [2.166(20]1

2.163(9] [2.165(17)]

2.158(4)

2.153(4)

2.15214)

2.178(4)

2.166(4]

2.16014)

all-Sl

CUl-s2

CIA-S3

cu5-s4

cu5-s5

Cu5-S6

Sl-Cl1

sz-c21

s3-c31

s4-c41

s5-c51

S6-C61

Sl-C&!-s4

sz-cu3-s5

S3-Cu4-~6

Sl-Cul-s2

sz-Cul-s3

s3-ml-s1

s4-cu5-s5

S5-Cu5-S6

S6-Cu5-S4

Cul-Sl-aI2

Cul-S2-Cu3

Cul-s3-cu4

Cu5-.94-Cu2

cu5-s5-Cu3

Cu5-S6-Cu4

cuz-Sl-Cl1

Cu3-SZ-C21

cu4-s3-c31

Cu2-S4-C41

cu3-s5-c51

Cu4-S6-C61

cutrig-S rx, 2.271(7] [2.286(17)]

2.287(6) [2.299(19]]

2.277(61 [2.283(17)]

2.281(6] [2.289(17)]

2.270(6] [2.272(16]]

2.283(6] [2.291(16)]

s-c (X, 1.80(21

1.91(l)

1.90(l)

1.88(2]

1.92(l)

1.89(l)

S-Cud_-S Ldeg]

170.9(4J 1167(3Jl

169.2(4] 11175113)l

170.3(4] 1171(3]1

S-Cutrig-S (deg]

124.3(2] [124(2] 1

114.6(3] [118(Z) 1

120.9(2] I117(2]1

115.5(2] 1116(2]1

124.5(Z) I120(2]1

119.7(3] [123(2] 1

Cu-S-Cu (deg]

74.8(2] [74.6(7)

75.9(2] [75.4(8]

74.7(Z) t74.6(7)

75.7(Z) [75.6(7]

76.4(2] 176.517)

75.1(2] [74.9(7)

Cudi -S-C (deg]

106.2(5] 108.3(5]

106.1(5] 111.0(4]

106.8(41 106.7(3)

108.7(6] 105.6(4]

106.9(5] 107.9(4)

103.9(51 107.0(4)

2.303(4]

2.265(4]

2.272(4)

2.371(4]

2.251(4]

2.239(5]

1.85

1.85

1.85

1.85

1.85

1.85

170.7(2]

170.8(2]

173.4(2]

118.5(l)

120.9(2]

120.6(2]

95.1(l)

147.5(2]

117.2(2]

73.3(l)

79.3(l)

75.7(l)

77.1(l)

80.9(l)

75.4(l)

Chemistry of the hexa@-t-butylthiolato)pentacuprate(I) cage anion

Table 2 (Coned)

539

Dimension Cation

Et4N+ Et3NH+

CIA+_,_-S-C (deg)

ml-Sl-Cl1

ml-sz-c21

Cul-s3-c31

cu5-s4-c41

cu5-s5-c51

Cu5-S&C61

Cu2--013

cu3--Cu4

Cu4--Cu2

all--Cu2

cxl--Cu3

CIA--Cu4

Cu5--Cu2

Cu5--Cu3

cu5--Cu4

Sl--52

S2--53

s3--Sl

s4--s5

s5--S6

S&-S4

Sl--54

SZ--S5

S3--96

Sl--56

S2--54

s3--55

110.8(61

111.3(4)

113.915)

114.3(6)

111.1(5)

113.3(5)

cudig --Cudi cR,

3.271(12) 13.27(9)1

3.258(12) 13.22(9)1

3.168(13) [3.17(9)1

cu trig --cudi (RI

2.715(4) [2.72(2)1

2.735(4) [2.74(2)1

2.691(3) I2.69(2)1

2.717f4) I2.72(2)1

2.749(4) I2.75(2)1

2.718(3) [2.72(2)1

(RI s--s

4.029(61 [4.07(4)1

3.848(6) [3.93(4)

3.94917) [3.88(4)

3.848(7) [3.89(4)

4.028(6) [3.91(41

3.944(6) [4.04(4)

4.317(6) [4.31(3)

4.311(6) [4.32(2)

4.309(6) [4.31(2)

4.537(6) [5.91(4)

4.602(7) [5.97(3)

4.604(6) [5.83(3)

‘1

Torsional angles (deg) Cudi -Sn-Cnl-Cn4

Cu2-Sl-Cll-Cl4 -13.9(1.7)

Cu3-SZ-C21-C24 -12.2l1.2)

cu4-s3-c31-c34 -25.4t1.2)

CuZ-S4-C41-C44 -26.6(1.6)

cu3-s5-CSl-c54 -10.0(1.2)

Ch4-S6-C61-C64 -36.2t1.4)

111.2(5)

112.4(4)

109.4(4)

115.8(4)

119.7(4)

115.4(5)

3.202(3)

3.554(3)

3.255(31

2.667(3)

2.82013)

2.724(3)

2.825(3)

2.874(3)

2.691(3)

3.926(6)

3.947(6)

3.973(6)

3.413(6)

4.312(6)

3.937(6)

4.296(6)

4.316(6)

4.318(6)

4.520(6)

4.545(6)

5.044(6)

9.3

-18.5

-21.1

-29.6

-75.2

-5.4

Twist angles (deg) S(n)-Cutri --Cutri -S(n+3)

.91-Cu1--Cu5-s4 54.9(2) [-50.0(1.5)1 54.7

SZ-Cul--Cu5-S5 45.9(2) I-58.3(1.5)1 31.2

S3-Cul--Cu5-S6 56.0(2) L-58.8(1.5)1 57.8

a Dimensions in square brackets are for the alternative cage in the Et4N+ crystal.

540 G. A. BOWMAKER et al.

substantiated by the small sample standard devi- ations of each of the following sets of six dimen- sions: CL&-S, 0.02 A; cl&-s, 0.007 w; cudigcutrig, 0.02 A; S-S(via Cu,), 0.08 A; Cu-S-Cu, 0.7”; S-Cuti~-S, 4.2”. The largest devi- ations from threefold equivalence occur in the angles S-G,,-S which range 115-124”. This close approach to D, symmetry extends also to the locations and conformations of the Bu’ groups in the Et.,N+ compound, as shown by the following sample standard deviations for sets of six compara- ble dimensions: Cu,,Sn-Cnl, 1.6”; Cutii,-Sn-Cnl, 1.6”; Cu,,-Sn-Cnl-Cn4 torsional angles, 10.3”; Cuti,-Cn4, 0.06 A.

In the Et,NH+ compound the high pseudo- symmetry of the cage does not occur because one of the Bu’ groups, that on S5, has been inverted through the Cudi,--S5-Cuti~ plane as shown in Fig. 5. This conformational change at S5 leads to increased steric repulsion with the Bu’ group on S6, which is relieved by a 27” rotation of the Cu5-S5 bond about the CbBC&, axis within the Cu5 coordination plane. Concomitant with this is a lengthening of the Ct.&S4 bond, an effect which is electronic rather than steric, and which has been observed in related silver thiolate complexes.2,9 In distorted three coordination

the distance d increases as the opposite angle 8 increases, in regular transition from trigonal to linear coordination.

The effects of the distortions due to the irregular ligand 5 in the E&NH + compound are also appar- ent (see Table 1) in the secondary dimensions S-S (long S5-S6, short S4-S5) and, to a lesser extent, Cu-Cu (long Cu3-Cu4). No specific cause for the reversal of ligand 5 can be identified from a study of the crystal packing nor are any intermolecular contacts abnormally short. It is assumed that subtle and relatively low-energy crystal packing forces are responsible. It may be noted that in- version at sulphur atoms allows a total of ten stereoisomers for the [M,(SR),] cage.2

Two small but regular features appear in the copper atom positions of both structures. The CG, atoms are displaced slightly outward from their S, coordination planes, by 0.06, 0.09 8, (Cul, Cu5) for the Et4N+ compound and 0.02, 0.04A (Cul, Cu5) for the Et,NH + compound. Also, all CU,i, atoms are displaced from their S-S lines

towards the centroid of the cage, by distances of 0.17 8, (CUE), 0.218, (CUE), 0.18 A (Cu4) in the Et,N + compound, and 0.18 8, (CUE), 0.17 A (CUE), 0.13 A (Cu4) in the Et,NH + compound. The mean S-J&,-S angle is 170.9”.

The orientations of the Bu’ groups on the minor alternative cage in the disordered EtdN+ crystal could not be determined, but there is virtual D3 symmetry in the dimensions of the Cu&& core, indicating a similarly symmetrical (Bu’), set. There is one significant difference between the major and minor component Ct.@, cages in the E&N+ crys- tal, in the angle of antiprismatic twist of the Ss polyhedron. In the minor component the mean S(n)-Cul-Cu5-S(n + 3) torsional angle is 55.7”, and the mean distance between S atoms not con- nected by Cudis or Cu, is 5.90& in contrast to values of 52.3” and 4.58 1 respectively in the major component.

The distinct change in Cu-S bond length with coordination numbeti*3 is again apparent, the mean values Cudig - b-SBu’) = 2.163, o,,,,, = 0.004 8,

(12 values) and Cu,, - @-SBu’) = 2.273, t7 mean = 0.005 8, (11 values, excluding Ct.&S4 in the E&NH + crystal) compares well with the previously reported values’ Cudig - (p-SPh) = 2.160 A, Cutrig - @ -SPh) = 2.270 z&.

In the pyramidal geometry at the sulphur atoms the Cu-S-C angles fall into two distinct classes, CU,i,-S-C, mean 106.3, o,,,,,, 0.5” (12 values), being less than Cu,,-S-C, mean 113.2, a,,, 0.8” (12 values).

100 200 300 400

Wavenumber /cm-’

Fig. 6. Far-infrared spectra (at cu. 125 K) of (a) @tNMMSBu’),l; (b) P,NW[Cu,SW,l.

Chemistry of the hexah-t-butylthiolato)pentacuprate(I) cage anion

A In both the EtsNH+ and Et.,N+ cations there exist planar CzNCz units, with maximum devi- ations from the three best atomic planes of 0.05, 0.03 and 0.03 A. Mean values of C-N and C-C bond lengths in the cations are 1.55, G_,, 0.01 A and 1.55, e,,,_ 0.02 A, respectively.

IR spectra. The far IR spectra of (Et,N) [Cu,(SBu’),] and (Et,NH)[Cu,(SBu’)J (Figure 6) show some evidence of the structural differences found for the anions in these compounds. As discussed previously,‘j the bands in the range 300400 cm-’ are due to the coordinated thiolate ligand and these occur at similar frequencies in both spectra. The band at about 270 cm - ’ is assigned to the antisymmetric stretching mode of the diagonal S-Cu-S units in the anion,6 and this has virtually the same frequency and intensity in both spectra. The region 150-250 cm-’ pre- sumably includes bands due to the trigonal Cu-S bonds, and here there are marked differences be- tween the two spectra. No specific assignments are possible, but the greater complexity of the spec- trum of (Et,NH)[Cu,(SBu?,] in this region is prob- ably a consequence of the more distorted structure of the anion in this compound.

DISCUSSION

The [Cu,(SBu?,]- molecular cage is easily crys- tallised, and easily decomposed by visible- and X-radiation. It is presumed that the decomposition is initiated by S-C homolysis, generating copper sulphides. At room temperature atomic thermal motions in the crystals, particularly at the cation and the Bu’ groups, are relatively large.

A

4,‘-------_____ --em

----__ \ \ -_ I

\ I \ \ I

\ I \ \ I \ ,I \ I/ \ I yr \

I’ \ I

\

\ \ ’ \ I’ \ / \

\ 4’ \ ’ \ I

\ \ t’

The cage structure, a trigonal bipyramid of metal atoms within a trigonal antiprism of doubly- bridging thiolate ligands, is unprecedented. A structural relationship can be drawn with the [MS(SPh),]‘- (M = Cu, Ag) molecular cage 1 as shown in Fig. 7. If the thiolate group opposite the two-coordinate metal in 1 is removed, and both of the two-coordinate metals so generated drop into linearity, the trigonal bipyramido -M,-trigonal prismo-S6 StIUCtUrC, 2, reSUk3 and may be twisted to the antiprismo form 3.

The predominance of two- over three-coordinate metal in [h&,(Sh~‘)~]- further accents the general tendency to low metal coordination numbers with thiolate ligands.’ As the electrophilicity of cop- per(1) and silver(I) can be satisfied with two double-bridging alkylthiolate ligands, it could be postulated that a complex [M(SR)J2- with non- bridging alkylthiolate ligands would be electron excessive at the metal and unstable with respect to dissociation to [M(SR),] - .

Fig. 7. M,S, polyhedra in thiolate cages M,(SR),, 1, trigonal-prismo-M,(SR),, 2, and trigonal-antiprismo-

M,(SR),, 3.

the bridging thiolate ligands, but the question arises as to the possibility of some direct metal-metal bonding. Several structural properties hear on this question.

(a) The CudigCutig and Cs,-Cudi, distances, averaging 2.74 and 3.28 8, respectively, are sub-

The [M&!%u’&- cage is clearly held together by stantially greater than the Cu-Cu distance (2.55 A)

542 G. A. BOWMAKER et al.

in copper metal. It can be argued’ that the Cu-Cu bonding of order one would not be longer than this.

(b) The Cu,, atoms are systematically displaced from linear coordination towards the centroid of the cage, decreasing Cu-Cu distances slightly.

(c) The Cutrig atoms are systematically displaced away from the centroid of the cage, increasing the CU,,,-CU~, distances slightly.

(d) The S, polyhedron is antiprismatic (3), with an antiprismatic twist angle of CCI. 50”. Lesser twists, or even prismatic S, (2) appear to be feasible geometries. One consequence of the antiprismatic twist is substantially reduced Cu-Cu distances (assuming unchanged Cu-S distances). For in- stance, in structure 2 the Cu,,-Cu distance would be 3.14& rather than the 2.742 observed for structure 3.

These structural properties may be the con- sequence of electronic factors other than copper-copper bonding. The antiprismatic twist and the inwards displacement of the Cbg atoms both reduce the Cu-S-Cu angles from 90” to an average value of 75”. Angles M-S-M at doubly- bridging thiolate are known over a wide range,2 but values of 76-80” predominate where the metal is copper or silver. It is not yet clear whether these acute values are a consequence of the cage struc- ture, or whether details of the cage structure are determined by a preference for M-S-M angles at 75”. Therefore, the available structural data do not permit unequivocal conclusions about the bonding in the Cu,S, core of [Cu,(SBu’)J-, although it appears that some Cu&&, attractive forces be present.

There exist patterns in two aspects of the SBu’ group conformations which appear not to be caused by steric effects, and for which bonding explanations could be sought. First, the S-C bonds are closer to S-Cudi~ than to S-CQ~, and second the Cud,,-Sn-Cnl-Cn4 torsional angle is consis- tently smaller than the CGg-Sn-Cnl-Cn4 tor- sional angle. Neither of these effects appears to be due to methyl-methyl group repulsions on the surface of the cage, and in fact the second effect results in unusually short CnbCu,, contacts which average 3.21 A” (asampk 0.06 A) in the EtaN+ compound.

All interligand CH&H, distances on the sur- face of the cage are greater than 4A, and the Cn3-Cqti, distances over the trigonal faces are all greater than 3.5 A. The positions of the Bu’ groups on the surface of the cage are determined also by the magnitude of the antiprismatic twist.

It can be concluded from the two structures reported here that the [Cu,(SBu?,]- is angularly

non-rigid. An irregular position of one Bu’ group in the Et,NH+ compound causes large angular distortions. This is consistent with the general notion that cage structures are floppy when con- nectivities are 10w,~ and supports the contention that any secondary interactions such as Cu-Cu bonding on Cn4-Cu,,, Cn3-C%, repulsions are not pronounced.

A relevant comparison structure is [CuOBu),,” which contains a planar square of copper atoms, situated at the midpoints of a coplanar square of oxygen atoms. All four Bu’ groups are directed to the same side of the Cu,O, plane. There is a simple relationship between the [CuXBu), structure (X = 0) and the prismatic [Cu,(XBu’),] - structure (X = S), 2, namely addition/elimination of a [BuX-Cu-XBul moiety across opposite copper atoms.

The structure of [CuOBu’], is also pertinent to the question of direct Cu-Cu bonding in these XBu’ bridged compounds. The facts that the Cu-Cu distances in [CuOBul, (range 2.65-2.77 A) are slightly less than the Cu-Cu distance in

[Cu,WW,l - , and the lack of evidence of significant contraction of the Cu, square, indicate that any direct Cu-Cu bonding is at best weak.

A species [Cu,Ph,J has recently been character- ized, and has been shown to have a structure similar to that of [Cu,(SBu?,] -. The size of the Cu, cage is smaller by about 10% in the former com- plex. In this species, too, the presence of a weak Cudig~utrig bonding interaction has been sug- gested.12

EXPERIMENTAL

All preparative solutions containing t- butylthiol and its metal complexes were maintained under an atmosphere of dinitrogen. All reagents and sol- vents were laboratory grade, and were used as received. Infrared spectra were obtained on a Perkin-Elmer 397 spectrometer. Spectra were run on Nujol mulls between KBr plates, and were calibrated by using the spectrum of polystyrene. Far IR spectra were obtained on a Grubb-Parsons Cube Mk II interferometer fitted with a 6.25 pm Mylar-film beam splitter. Far IR spectra were run on petroleum jelly mulls between polythene plates at cu. 125 K and were calibrated by using the spectrum of water vapour. ‘H NMR spectra were run at cu. 308 K on a Varian T60 spectrometer.

Tetraethylammonium hexa -t -butylthioIatopenta - cuprate( (EtN)[Cu5Wu%l

A solution of Cu(NG,)23H@ (4.8 g, 20 mmol) in absolute ethanol (55 cm’) was added slowly to a solution of t-butylthiol (5.4g, 60mmol) and tri-

Chemistry of the hexah-t-hutylthiolato)pentacuprate(I) cage anion 543

ethylamine (6.0 g, 60 mmol) in acetone (90 cm3) at room temperature. To the resulting bright yellow solution was added a solution of tetra- ethylammonium bromide (7.5 g, 36 mmol) in eth- anol (75 cm3). This solution, sealed and protected from light, was allowed to stand at ca. 0°C for several days, while large multifaceted crystals grew. The product was filtered, washed with 2-propanol, and vacuum dried in the dark.

Found: C, 39.65; H, 7.77; N, 1.23. CU,S,NC,,H,~ requires C, 39.09; H, 7.59; N, 1.42.

This compound is easily soluble in acetone and in acetonitrile, appreciably soluble in ethanol and less so in methanol or 2-propanol. On exposure to light, solutions of this compound become green, while the solid becomes orange then brown.

Tetraethylammonium hexa-t-butylthiolatopenta- argentate(Z), (Et,N)[Ag,(SBu’),]

The preparation of this compound has been described previously.6 Powder diffraction patterns (CuK, radiation) reveal that it is isostructural with the copper analogue.

Triethylammonium hexa-t-butylthiolatopenta- cuprate (I) (Et,NH)[Cu,(SBu’),]

t-butylthiol (2 cm3) was added to triethylamine (200 cm3), and the mixture degassed. CuSBu’ (0.5 g) was added, and the mixture was heated to 67°C to produce a yellow solution which was filtered while hot. Fine yellow needles were ob- tained by preparing the yellow solution as above and seeding it with crystals of (Et,NH) [Cu,(SBu’),]. No satisfactory elemental analysis could be obtained for this compound.

Found: C, 46.7; H, 9.0; Cu, 31.5. C~H,Cu,NS, requires C, 37.7; H, 7.4; Cu, 33.3%. ‘H NMR ([D,] pyridine solution) G/p.p.m. from t.m.s. (multi- plicity, integral, assignment): 1 .O (triplet (J = 7 Hz), 13.5, ethyl CH,), IR (nujol mull): 2720 m, 2680 sh, 2380 vw, 1360 s, 1300 vw, 1216 w, 1074vw, 105Ovw, 1023 w, 1017 sh, 841 w, 819 w, 782 vw, 577 m [v(CS)], 435 w. The ‘H NMR and the X-ray crystal structure determination show conclusively that this compound is (Et,NH)[Cu,(SBu’),]. Other crystals chosen at ran- dom gave identical diffraction patterns.

X-Ray crystallography. The following general information applies to the two crystals. Data were collected at 293 f 1 K; scattering factors for un- charged atoms, corrected for dispersion, were from International Tables;13 residuals quoted are

=TFt Iy4-Ifw~lg~ Rw = [,Xw(lf’o I-IFc I)‘/ * ‘/* Full matrix least-squares weights were

w = [a(F)]-? (&NH)[cu,(sh?,]. C,,H,Cu,NS,, M =

954.96, yellow needles. The direction of elongation is always along (10 0), but the cross sectional shape varies depending on the relative devel- opment of the [0 k Z] faces. Monoclinic, space

group 14), b = 21.457;:;” c %:065(l) 8,

a = 10.519(l),

iJ=4511A3;’ D, = 1.39 g cm-’ /I = 95.1 l(1)” (flotation ii

n -hexane/ 1,3-dibromopropane), z =4, D, = 1.41 g cm - 3; F(0 0 0) = 1992. Nickel-filtered Cu-K, radiation, A = 1.5418 A; ,u = 51.86cm-‘; Crystal faces: (a) (100, 100, 010, 001, 011, 021, 034 02% (b) (100, TOO, 010, 014, 027, OZl,OT4,021). Crystal dimensions: (a) 0.34 x 0.14 x 0.20 mm; (b) 0.34 x 0.25 x 0.30 mm. Mosaic spreads 0.11”. In- tensity data (Nonius CAD-4) to 0_ 57” (sine/l 0.54) were collected by a symmetric 28-o scan of 70 steps of 0.01” in theta. The background was counted for 15 s at each end of the scan range. After every 200 measurements, three standard reflections were remeasured to monitor crystal alignment and stability. It was found that the crystals suffered radiation damage on prolonged exposure to X-rays, and it was necessary to employ two crystals to complete the data collection. The first crystal was used to collect data in the theta range O-45” (the intensities of its standard reflections had then declined by approx. 17%). The second crystal underwent a similar degree of de- composition during the collection of the high-theta data. The combined data set comprised 3093 unique reflections with Z > 2.58 a(Z) [where o(Z) = {T + t2B + (pZ)*}“*T = integrated peak count, B = average background count, t = ratio of scan to background times, p was assigned a value of 0.041. The data were corrected for intensity decay and for absorption.

The positions for the copper and sulphur atoms were determined using direct methods (MUL- TAN), with carbon and nitrogen atoms being located from subsequent “difference” electron den- sity syntheses.

After refinement (SHELX) with copper and sulphur atoms anisotropic and all other non- hydrogen atoms isotropic, R = 0.073, the tem- perature factors of the methyl-carbon atoms at- tached to C(11) were high, indicating a considerable degree of disorder in that t-butyl group. Accordingly, these atoms were placed in positions such that the geometry of the group equated with the average geometry of the other five t-butyl groups. Thereafter, all t-butyl groups were refined as groups with bond length and angle constraints. The final values of R and Rw were 0.072 and 0.082 respectively.

(~t,N)[CU,(~BZd)6]. C,,H,&U,NS,, M = 983.04; equi-dimensional multifaceted triangular or hexag-

544 G. A. BOWMAKER et al.

onal prisms, which are decomposed by X-rays (Ct.&) at room temperature. Monoclinic, C2/c

(No. 15), a = 45.500(3), b = 11.805(l), c = 20.168(2) A, /? = 117.81(l)“; U = 9582A3; Z=8, D,= l.37gcm-3, D,,,= 1.37(2)g ~rn-~; Cu(K,), 1 = 1.5418 A, ,U = 37.3 cm-‘. The crystal was bounded by 14 faces in the zones (lOO){lOl}{lO2}{2ll}{3ll}, with maximum and minimum crystal dimensions 0.42 and 0.25 mm. Intensity data (Siemens AED) to 0_ = 50” by e/201 scan; intensity loss due to radiation damage of up to SO%, for which appropriate corrections were made. Data reduction, including absorption corrections, was performed as for the Et3NHf compound, yielding 3965 independent reflections of which 2953 have Z > 2.58 o(Z). The crystal decay limited the quality of these data.

Structure solution by Patterson and Fourier methods proceeded normally. During the least- squares refinement two scale factors were included to account for some of the effect of crystal decay. Hydrogen atoms were not included. At con- vergence of refinement (temperature factors aniso- tropic for Cu, S, isotropic for C, N) based on 2629 observed reflections wih sin 9/lz > 0.2, R = 0.096, Rw = 0.087. However, a difference map at this stage revealed slight disorder of the [Cu,(SBu?,] - cage, appearing as weak additional peaks (3 e A-‘) for sulphur atoms related to the predominant atoms by reflection through the (CudiJ3 plane. Further refinement (BAELS) therefore included an alternative Cu,S, cage, slack constrained to the predominant cage with occupancies refined to sum to unity. The alternative cage was unconstrained in location, but slack constrained to the main cage by means of Cu-S and Cu-Cu distances, and fully constrained to the Cu, S thermal parameters of the major cage. In addition the C-C distances of each Bu’ group were slack constrained, as were the C-C and C-N distances of the cation, and TLX thermal motion was refined for the Bu’ groups.

This refinement proceeded well, to R, Rw = 0.078, 0.088 for all 2953 observed data, and R, Rw = 0.072, 0.068 for data with sin 0/n > 0.2. The occupancy for the alternative cage refined to 0.117(2). A final difference map gave some evi-

dence (cu. 1 e A-‘) of the a-carbon atoms of the alternative cage, in positions which maintained the mirror relationship with the predominant cage. Some evidence of Bu’ hydrogen atoms for the main cage also appeared, but as it was clear that no new information could be extracted from the diffraction data no further refinement was undertaken.

The estimated standard deviations in atomic parameters and derived quantities are influenced by the atomic (Cu) overlap in the disordered model, and by the constraints used during matrix inversion.

Atomic coordinates and thermal parameters for the two structures have been deposited with the Editor as supplementary material; copies are avail- able on request. Atomic coordinates have also been deposited with the Cambridge Crystallographic Data Centre.

Acknowledgements-We thank the ARGC for financial support, D. C. Craig for assistance with diffraction data collection, and Dr. A. D. Rae for the constrained least-squares refinement.

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REFERENCES

E. E. Reid, Organic Chemtitry of Bivalent Sulfur, Vol. I, Chap. 2. Chemistry Publishing Co., New York (1958). I. G. Dance, Coord. Chem. Rev., to be published. 1. G. Dance and J. C. Calabrese, Znorg. Chim. Acta 1976, 19, L41. G. A. Bowmaker, G. R. Clark, J. K. Seadon and I. G. Dance, Polyhedron, in press. I. G. Dance, J. C. S. Chem. Comm. 1976, 68. G. A. Bowmaker and L.-C. Tan, Aust. J. Chem. 1971, 32, 1443. I. G. Dance, Aust. J Chem. 1978, 31, 2195. I. G. Dance, Znorg. Chem. 1981, 20, 1487. I. G. Dance, Znorg. Chim. Acta 1977, 25, L17. S. Hong, A. Olin and R. Hesse, Acta Chem. &and. 1975, A29, 583. T. Greiser and E. Weiss, Chem. Ber. 1976, 109, 3142. P. G. Edwards, R. W. Gellert, M. W. Marks and R. Bau, J. Am. Chem. Sot. 1982, 104, 2072. International Tables for X-Ray Crystallography, Vol. IV, Tables 2.2A and 2.3.1. Kynoch Press, Birmingham (1974).