Synthesis and complexation studies of mesocyclic and macrocyclic polythioethers XIV. Crown thioether complexes of palladium(II) and platinum(II)

ELSEVIER

Inorganica Chimica Acta 246 (1996) 3 l-40

Synthesis and complexation studies of mesocyclic and macrocyclic polythioethers XIV Crown thioether complexes of palladium(I1) and platinum(I1)’ Gregory J. Grant a,*, Nathan J. Spanglera, William N. Setzerb, Donald G. VanDerveeTc, Larry F. Mehned ‘Department of Chemistry, The University of Tennessee at Chattanooga, Chattanooga, TN 37403-2598, USA bDepartment of Chemistry, The University of Alabama in Huntsville, Huntsville, AL 35899, USA ‘School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA dCovenant College, Lookout Mountain, GA 30750, USA

Abstract

This paper describes the synthesis and characterization of several crown thioether complexes of Pt(II) and Pd(II). We wish to report the syntheses and X-ray crystal structures of both the Pd(II) and Pt(I1) complexes with the macrocyclic thioether complex, 1,4,7,11,14,17- hexathiacycloeicosane (2OS6). Crystal data for [Pd(2OS6)](PF&: Ct4H2sFi2PZPdS6; monoclinic, space group P2,lc; u = 12.910(3) A, b = 9.810(20) A, c = 22.103(6) A; /I = 102.170(20)“, V= 2700.39 A3; Z= 4; R = 0.055; D = 1.931 g cmm3; 6346 reflections measured. Crystal data for [Pt(2OSS)](PF&CH,NOz: C15Hs1F12NOZP#tS6; monoclinic, space group Cc; a = 12.321(5) A, b = 14.608(7) A, c = 17.032(5) A; B = 98.15(3)“, V= 3034.55 A3; Z= 4; R = 0.036; D = 2.045 g cme3; 2777 reflections measured. Neither complex exhibits any significant electrochemistry or any visible absorption bands. Both complexes crystallize in the same linkage isomer where the metal ion is surrounded by a distorted square planar arrangement of four sulfur atoms. Two sulfur atoms that are adjacent to each other in the macrocyclic ring remain uncoordinated. r3C NMR spectroscopy reveals the presence of additional isomers in solution. We also wish to report the synthesis and X-ray crystal structure of the crown thioether complex, bis( 1,4,7-trithiacyclodecane)platinum(II) hexafluorophosphate, [Pt(lOS3)z](PF& The two lOS3 ligands are arranged around the platinum in pseudooctahedral fashion to yield the meso stereoisomer. Four of the six sulfur atoms from the lOS3 ligands form a square planar arrangement around the platinum (mean Pt-Sequatorialbond distance = 2.30 A). The remaining two sulfurs are coordinated axially at a much greater distance from the Pt (Pt-S,l,t= 3.21 A). Crystal data for [Pt(lOS3)2](PF&2CH3N02: Ct6H34PdS6P2Fr2NZ04; monoclinic, space group Q/c; a = 22.473(9) A, b = 12.071(4) A, c= 11.186(3) A; /I = 94.14(3)“, V= 3026.53 A3; Z= 4; R = 0.046; D = 1.991 g cmm3; 2836 reflections measured. Cyclic voltammetry measured in acetonitrile showed a single, reversible oxidation wave at +0.324 V versus F&F,+. Variable temperature t3C NMR spectroscopy shows no solvent-complex interactions, in contrast to the Pd(I1) analog. The palladium(I1) complex, [Pd(ttn)z](PF&, which contains the acyclic thioether 2,5,8-trithianonane (ttn) was also prepared. Keywords:

Crystal structure; Palladium complexes; Platinum complexes; Crown thioether complexes

1. Introduction * Corresponding author. ’ For Part XIII, see G.J. Grant,

B.M. McCosar,

W.N. Setzer, J.D.

Zubkowski, E.J. Valente and L.F. Mehne, Inorg. Chim. Acta, 244 (1996) 73. This work was initially presented in part at the 17th Intemational Symposium on Macrocylic Chemistry; Provo, UT; August 9-14, 1992; Paper Number 39; and the 203rd National Meeting of the American Chemical Society; San Francisco, CA; Division of Inorganic Chemistry; April 5, 1992; Paper Number 134.

0 1996 Elsevier Science S.A. All rights reserved 0020-1693/96/$15.00 PII SOOZO-1693(96)05047-S

The past several years has seen a period of intense activity in the research into the coordination chemistry of crown thioether ligands with several groups examining the complexation characteristics of ligands such as 1,4,7trithiacyclononane (9S3) and 1,4,7,10,13,16-hexathiacyclooctadecane (18S6) (see structures below) [ 141. An important focus of this work has been the platinum group

G.J. Grant et al. I Inorganica Chimica Acta 246 (1996) 3140

32

9s3 1,4,7-Trithiacyclononane

2OS6 1,4,7,11,14,17Hexathiacycloeicossne

1Os3 1,4,7-Trithiacyclodecsne

ttn 2,5,8-Trithianonane

18S6 1,4,7,10,13,16Hexathiacyclooctadefane

Fig. 1. Thioether ligands discussed in this paper.

metals. The coordination chemistry of the platinum group metals with these ligands has received a good deal of attention because of the ability of soft thioether ligands to bind very effectively to the soft metal ions and because of unusual stereochemical, spectroscopic, and electrochemical properties exhibited by the crown thioether complexes. These properties include the ability to stabilize uncommon oxidation states including Pd(III), Pt(III), Au(II), and Rh(I1) [5-lo], the ability to force metals ions into unusual geometries such as octahedral Rh(1) and Au(II1) [ 11,121, the formation of metal-carbon bonds [13-171, and the ability to activate carbon-hydrogen bonds in ring opening reactions [ 181. Due to its electronic requirements, palladium(I1) typically forms square planar complexes which are characterized by a yellow-orange color and limited electrochemical behavior. Several groups have now reported X-ray crystal structures of the bis(trithioether) complexes of Pd(I1) in which the crown trithioether (9S3 or lOS3) exhibits an unusual elongated pseudo-octahedral or [S4 + S2] coordination geometry. [5,19-211 In these reported structures, four sulfur atoms form a square planar arrangement around the Pd while the remaining two axial sulfur atoms interact from a greater distance. Despite this long Pd-S bond length the axial electronic interaction between the Pd and the sulfur results in an atypical green or blue color (Amax - 610 nm) and a reversible oxidation wave which has been assigned as a Pd(II)/Pd(III) oxidation. Interestingly, the linkage isomer that is obtained for the [Pd(lOS3>,]*+ complex recently reported by McAuley is different from the one reported by us [20,21]. Our structure is the linkage isomer in which the five-membered chelate ring lies between the equatorial sulfurs while the McAuley isomer has a six-membered chelate ring which

lies between the equatorial sulfurs. This change in linkage isomer seems to be due to packing forces associated when a particular solvent is used (nitromethane in the former, acetonitrile in the latter), and the solvent-complex interaction is confirmed via low temperature 13C NMR studies. The macrocyclic hexathioether 18S6 complexes with Pd(I1) to form two different salts with surprisingly different solid state structures [2,22], and counter-ion effects have also been observed in other crown thioether complexes [23]. The tetraphenylborate salt of [Pd(18S612+ is yellow-brown while the hexafluorophosphate salt is green. In addition to these color changes, differences in Pd-S bond lengths and conformations of ethylene linkages are observed for both structures. Our research interests with crown thioether ligands have focused on the effects that structural alterations, changes in crown thioether ring size, and the presence of ring functionalities such as keto or hydroxyl groups might have on the complexation properties of the ligands [24]. Unusual complex properties, such as those associated with Pd(II), are typical of smaller crown thioethers like 9S3 and lOS3. The unusual properties are a result of the preferred conformation displayed by the smaller crown ligands. Larger crown thioethers and acyclic thioethers (such as 2,5,8_trithianonane) often display very different complexation properties due to their greater conformational freedom [25-281. Therefore, we prepared novel thioether complexes with Pd(I1) to see if other thioethers might exhibit the unusual properties that have been observed for the 9S3 and lOS3 complexes of Pd(I1). We have also examined the complexation of crown thioethers with Pt(I1). Several homoleptic crown thioether complexes of Pt(I1) are known and have been structurally characterized [7,22,29-331. Surprisingly, the Pt(II) complex of 9S3 is not isostructural with the Pd(I1) complex. The Pt(I1) complex, [Pt(9S3),12+ exhibits a five-coordinate square pyramidal structure, not the S4 + S2 structure observed in the Pd(I1) complex. Even though this structure is exhibited in the solid state, the complex in solution exhibits an unusual d-d transition near 430 nm and a reversible, one-electron oxidation wave which has been assigned to the Pt(II)/Pt(III) couple [7,34]. Therefore, we also prepared two novel homoleptic crown thioether Pt(I1) complexes to further develop the coordination chemistry of thioether ligands with this particular transition metal ion. 2. Experimental 2.1. Materials The reagents 9S3, 18S6, K2PdC14, and K2PtC14 were purchased from Aldrich Chemical Company and used as received. The ligands lOS3, 2OS6, and ttn were prepared by the published methods [26,35]. All solvents were used as received.

G.J. Grant et al. I Inorganica

2.2. Measurements Cyclic voltammograms were recorded using a Princeton Applied Research Versastat Polarographic Analyzer. The supporting electrolyte was 0.1 M Bu4NBF4 in CHsCN or CH3N02. The ferrocene/ferrocenium couple was used as an internal reference. The standard threeelectrode configuration was as follows: Pt working electrode, Pt-wire auxiliary electrode, and Ag10.1 M AgNOs non-aqueous reference electrode. Proton and carbon13 NMR spectra were obtained on a Varian Gemini 300 MHz NMR spectrometer using either CD3N0, or CD&N for both the deuterium lock and reference. Magnetic susceptibility measurements on solid samples were obtained using a Johnson-Matthey magnetic susceptibility balance, and all of the Pt(I1) and Pd(I1) complexes reported here are diamagnetic. Ultraviolet-visible absorption spectra were obtained on a Varian DMS 200 Wvisible spectrophotometer. Fourier transform infrared spectra were obtained on a Beckman FT 1100 infrared spectrophotometer. Analyses were performed by Atlantic Microlab, Inc., Atlanta, GA. The three X-ray crystal structures were solved by Donald G. VanDerveer in the School of Chemistry at the Georgia Institute of Technology. 2.2.1, Preparation of [Pd(2OS6)](PF& A mixture of K,[PdCl,] (127 mg, 0.392 mmol) and 2OS6 (15 1 mg, 0.389 mmol) was refluxed in 29 ml of 2: 1 methanol/water (v:v) solution for 120 min. The resulting yellow solution was filtered and concentrated to 213 of its starting volume. Upon addition of NH4PF6 (135 mg, 0.828 mmol), yellow crystals of [Pd(20S6)](PF6)z formed. Cooling produced additional crystals which were isolated by filtration and washed with 3 x 15 ml portions of cold methanol followed by 3 x 15 ml washings of anhydrous ether. The sample was air dried. This gave a mass of 159 mg (52% yield) of 1,4,7,11,14,17hexathiacycloeicosanepalladium(I1) hexafluorophosphate. IR (KBr, cm-‘): 2961, 2921, 2854, 1644, 1633, 1427, 1415, 1111, 1090, 846 (s, PF,-), 561. The electronic absorption spectrum measured in acetonitrile showed a single A,,, at 275 nm (E = 20 900). Anal. Calc. for Ci4H2sS6P2Ft2Pd: C, 21.42; H, 3.59; S, 24.51. Found: C, 21.44; H, 3.60; S, 24.61%. The compound displayed no significant electrochemistry. ‘H NMR (CDsNO,): broad, poorly resolved resonances between 4.2 and 3.3 ppm. r3C{ ‘H] NMR (CDsN02): multiple resonances between 44.7 and 29.1 ppm. These are all confirmed to be methylene resonances by a DEPT experiment. 2.2.2. Preparation of [Pd(ttn)z](PF& A mixture of K2[PdCl,] (150 mg, 0.462 mmol) and the ligand ttn, 2,5,8_trithianonane, (173 mg, 0.946 mmol) were refluxed in 46 ml of 2: 1 methanol/water solution for 45 min. The resulting yellow solution was filtered and then concentrated to 2/3 of the starting volume. Upon

Chimicu Acts 246 (1996)

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addition of NH,PF6 (166 mg, 1.02 mmol), yellow crystals of [Pd(ttn)2](PF6)2 formed. Cooling in an ice bath produced additional crystals which were isolated by filtration. The yellow filtrate provided more [Pd(ttn)2](PF& crystals when the solvent was further concentrated by air evaporation. The crystals were washed three times with 15 ml of cold methanol followed by three anhydrous diethyl ether washings. The sample was air dried. This gave a mass of 298 mg (85% yield) of bis(2,5,8_trithianonane)palladium(I1) hexafluorophosphate. IR (KBr, cm-i): 2989, 2950, 2918, 2837, 1420, 1222, 1181, 1140, 981, 967, 834 (s, PFe-), 734, 685, 558. The electronic absorption spectrum measured in acetonitrile showed a single 1 max at 280 nm (E = 13 300). Anal. Calc. for C,2H28S6P2F12Pd: C, 18.94; H, 3.71; S, 25.28. Found: C, 18.71; H, 3.66; S, 25.15%. The complex displayed no significant electrochemistry. ‘H NMR (CD3N02): three resonances at 3.63 ppm (2 H), 3.34 ppm (2H), and 2.57 ppm (singlet, 3 H). t3C DEPT NMR (CDsNOZ): 39.40 ppm (-CH,), 37.12 ppm (-CH,), 19.48 ppm(-CH3). 2.2.3. Preparation of [Pt(20S6)](PFJ2 A mixture of K,[PtCl,] (158 mg, 0.380 mmol) and 2OS6 (151 mg, 0.388 mmol) was refluxed in 42 ml of 2:l methanol/water (v:v) solution for 6.5 h. The resulting yellow solution was filtered and then concentrated to 213 of the starting volume. Upon addition of NH4PF6 (135 mg, 0.826 mmol), white crystals of [Pt(20S6)](PF6)z formed. After the solution was chilled, the crystals were isolated by filtration and washed with 3 X 15 ml portions of cold methanol, followed by 3 x 15 ml portions of anhydrous ether. The sample was air dried. This gave a mass of 125 mg (38% yield) of hexathiacycloeicosaneplatinum(I1) hexafluorophosphate. IR (KBr, cm-‘): 3400 (s, broad), 2965, 2921, 1411, 1320, 1285, 1234, 1177, 1070, 1010, 884, 836 (s, PF,-), 574, 564. The electronic absorption spectrum measured in acetonitrile showed a single Amax at 291 nm (E = 3000). Anal. Calc. for C,4H28S6P2F,2Pt+2H20: C, 18.48; H, 3.55; S, 21.14. Found: C, 18.27; H, 3.29; S, 20.90%. ‘H NMR (CD,NO,): broad, poorly resolved resonances between 4.3 and 3.0 ppm. r3C( ‘H} NMR (CD,NO,): multiple resonances between 42.7 and 29.1 ppm. These are all confirmed to be methylene resonances by a DEPT experiment. The complex showed no significant electrochemistry. 2.2.4. Preparation of [Pt(lOS3)J(PF,& A mixture of K2[PtC14] (206 mg, 0.497 mmol) and lOS3 (195 mg, 1.OOmmol) was refluxed in 49 ml of 2:l methanol/water (v:v) solution for 19 h. The resulting yellow solution was filtered and concentrated to 213 of its starting volume. Upon addition of NH4PF6 (176 mg, 0.491 mmol), yellow crystals of the complex formed. After cooling to 0°C the crystals were isolated by filtration and washed with 3 X 15 ml portions of cold metha-

34

G.J. Grant et al. I Inorganica Chimica Acta 246 (I 996) 31-40

no1 followed by 3 x 15 ml anhydrous ether. The sample was air dried. This gave 334 mg (77% yield) of bis (1,4,7trithiacyclodecane)platinum(II) hexafluorophosphate hydrate. FT-IR (KBr, cm-i): 3200 (s, b), 2995, 2944, 2925, 2848, 1444, 1410, 1290, 1272, 932, 837 (s, PF,-), 558. The electronic absorption spectrum measured in acetonitrile showed three L,, at 430 nm (E = 120), 287 nm (E = 11 000) and 250 nm (E = 15 000). Anal. Calc. for Ci4H2sS6P2Ft2Pt.H20: C, 18.86; H, 3.39; S, 21.57. Found: C, 18.61; H, 3.20; S, 21.37%. Cyclic voltammetry measured in acetonitrile showed a single, reversible oxidation wave at +0.324 V versus FJFc+. 2.3. X-Ray crystallography

The final atomic parameters for all three structures along with their standard deviations are given in Table 2. Selected bond distances and bond angles are given in Table 3. 2.3.1. X-Ray crystal structure of [Pd(2OS6) J(PF&. A yellow crystal of [Pd(2OS6)](PF& suitable for X-

ray diffraction was grown by ether diffusion into a nitromethane solution. The crystal, having approximate dimensions 0.44 X 0.34 X 0.31 mm, was mounted on a Syntex diffractometer equipped with a scintillation counter, MO&Z radiation (A= 0.71073 A), and a graphite monochromator. The unit cell dimensions and other key crystallographic data are given in Table 1 and in the supplementary material. The position of the palladium atom was located from a three-dimensional Patterson map, and the remaining atoms were located by subsequent structure factor calculations and difference electron density maps 1361.The refinement converged to an R value of 0.055 and an R, value of 0.064 with a maximum shift/e.s.d. of 0.007 in the final cycle. A final difference map had extremes of +0.900 e Ae3 and -0.610 e AW3.The residual electron density is located near the PF,- ion designated as Pl . 2.3.2. X-Ray crystal structure of [Pt(20S6)J(PF& CHjNOz

A colorless, needle of [Pt(20S6)](PF&CH3N02 suitable for X-ray diffraction was grown by ether diffusion into a nitromethane solution. The crystal, having ap-

Table 1 Crystallographic data and details of refinement for [Pd(2OS6)](PF& [Pt(lOS3)2](PF&2CH~NG2 (compound III)

Formula Fw (amu) Crystal size (mm) Crystal system Space group a, (A) b (A) c (A) v (A3) B (degrees) Dc,lc (g cmW3) Z / (cm-l) No. of reflections measured No, of unique reflections measured No. of independent reflections with 12 2.5a(l) F(OOO) scan type Scan speed Quadrant collected

%na,(“1

Ra

4Vb GGF Max. A/u (final cycle) T (W Number of variables Data/variable ratio

(compound I), [Pt(2OS6)](PF6)2’CH,NO2 (compound II), and meso-

I

II

III

W-MVW%

W-~FI~NO~W%

%H34Fd’bO@‘%

784.79 0.44 x 0.34 x 0.31 Monoclinic P2]/C 12.910(3) 9.6810(20) 22.103(6) 2700.39 102.170(20) 1.931 4 1.33 6346 6185 3971

934.44 0.05 x 0.17 x 0.61

12.321(5) 14.608(7) 17.032(5) 3034.55 98.15(3) 2.045 4 0.526 2771 2777 2418

995.50 0.37 X 0.31 x 0.27 Monoclinic c2/c 23.400(9) 12.043(4) 11.229(4) 3155.20 94.37(3) 2.096 4 0.507 2946 2788 2276

1568.00 0 13.05-27.50 i h, +k, *I 55.0 0.055 0.064 1.928 0.007 295 316 12.6

1836.00 w 10.00-19.62 zt h, +k, &I 50.0 0.036 0.035 1.668 0.006 297 356 6.9

1951.67 w 14.53-23.58 + h, +k, *l 50.0 0.042 0.045 2.696 0.012 295 197 11.6

aR = ZIIF,I - IF,,lEIF,I. bRw = [Zw(lF,,I - lFcl)21rwF,,2]“2. ‘GOF = [Zw(lF,,I - lFcD2 (no. of reflections -no. of parameters)tn.

cc

&I. Grant

et al. I Inorganica Chimica Acta 246 (1996) 31-40

proximate dimensions 0.05 X 0.17 X 0.361 mm, was mounted on a Syntex diffractometer equipped with a scintillation counter, MoKa radiation (J. =,0.7 1073 A), and a graphite monochromator. The unit cell dimensions and other key crystallographic data are given in Table 1 and in the supplementary material. The position of the platinum atom was located from a three-dimensional Patterson map, and the remaining atoms were located by subsequent structure factor calculations and difference electron density maps [36]. The refinement converged to an R value of 0.036 and an R, value of 0.034 with a maximum shiftie.s.d. of 0.006 in the final cycle. A final difference map had extremes of +l.OlO e Ae3 and -0.710 e AW3. The residual electron density is located approximately 1 A from the Pt ion. 2.3.3. X-Ray crystal structure of [Pt(lOS3),](PF& 2 CH3N02 An orange prism of Pt( 10S3)2](PF6)2*2CH3N02 suitable for X-ray diffraction was grown by ether diffusion into a nitromethane solution. The crystal, having approximate dimensions 0.37 x 0.31 x 0.27 mm, was mounted on a Syntex diffractometer equipped with a scintillation counter, MoKa radiation (A = 0.7 1073 A), and a graphite monochromator. The unit cell dimensions and other key crystallographic data are given in Table 1 and in the supplementary material. The position of the palladium atom was located from a three-dimensional Patterson map, and the remaining atoms were located by subsequent structure factor calculations and difference electron density maps [36]. The refinement converged to an R value of 0.042 and an R, value of 0.045 with a maximum shiftie.s.d. of 0.012 in the final cycle. A final difference map had extremes of +1.240 e A-3 and 1.030 e Ae3. The residual electron density is located approximately 1 A from the Pt ion. 3. Results

and discussion

3.1. Syntheses The syntheses of the four homoleptic complexes were straightforward and based upon the method used by Schrader [5]. Four stable complexes of Pd(I1) and Pt(I1) were characterized by elemental analyses, cyclic voltammetry, UV-visible and FT-IR spectra, and both proton and carbon NMR spectra. Three of the complexes were additionally characterized by single crystal X-ray diffraction. The complex [Pd(ttn)zl(PFs)z tended to oil, and the difficulty in obtaining crystals suitable for X-ray diffraction is a characteristic that has been noted in other complexes of this ligand [27]. 3.2. Structural

studies

Three structural

perspectives

of the complex cations of

35

Table 2 Selected atomic positional parameters for non-hydrogen atoms and thermal parameters with e.s.d.s in parentheses x

Y

Z

ho

Compound I: [Pd(2OS6)](PF& Pd Sl c2 c3 s4 CS C6 c7 S8 c9 Cl0 Sll Cl2 Cl3 s14 Cl5 Cl6 Cl7 S18 Cl9 c20

0.27077(4) 0.41096;16) 0.4416(11) 0.3629(10) 0.28032(17) 0.1528(8) 0.0665(8) 0.0302(6) 0.12469(15) 0.0661(6) 0.1520(7) 0.26452(16) 0.2183(7) 0.2324(6) 0.36696( 17) 0.4149(8) 0.5327(8) 0.5995(7) 0.58390(23) 0.5841(15) 0.5293(9)

0.20884(6) 0.3586(j) 0.4063(16) 0.4096( 14) 0.25625(22) 0.3267(9) 0.2187(12) 0.1858(11) 0.0743 l(23) 0.0662(11) 0.0216( 11) 0.14009(24) 0.2836( 11) 0.2569( 10) 0.23029(23) 0.4055(9) 0.4079( 11) 0.3383( 1 I) 0.4202(3) 0.2876(24) 0.2576(13)

0.152201(21) 0.18460( ;O) 0.1112(6) 0.0622(5) 0.05216(8) 0.0147(3) 0.0072(4) 0.0665(4) 0.11676(9) 0.1847(4) 0.2389(4) 0.25213(8) 0.2901(3) 0.3595(3) 0.39983(9) 0.4056(4) 0.4315(4) 0.3922(5) 0.31709(12) 0.2649(7) 0.2184(8)

3.466(23) 5.31(9) I 1.6(9) 9.2(7) 4.68(9) 5.8(4) 7.4(5) 6.3(5) 4.75(9) 6.3(5) 6.1(4) 4.85(9) 6.1(4) 5.5(4) 4.99( 10) 6.4(5) 7.1(5) 6.8(5) 7.41(14) 18.9(14) I1.8(9)

Compound II: [Pt(2OS6)](PF&CH3NO2 Pt Sl c2 c3 s4 c5 C6 c7 S8 c9 Cl0 Sll Cl2 Cl3 s14 Cl5 Cl6 Cl7 S18 Cl9 c20

0.00000 -O&%284(24) -0.1905(11) -0.2086( 11) -0.1690(3) -0.1447(12) -0.0959(13) 0.0220( 13) 0.0355(3) 0.1824(12) 0.2163(12) 0.1702(3) 0.2607( 12) 0.2311(10) 0.2346(3) 0.1756(11) 0.1572(12) 0.0786(13) -0.0576(3) -0.0986(12) -0.0467( 11)

0.19201(3) 0.18214(23) 0.1553(12) 0.0856( 12) 0.1319(3) 0.0310(11) 0.0522(10) 0.0814(10) 0.1976(3) 0.2131(11) 0.2815(10) 0.25564(24) 0.1610(10) 0.1125(10) 0.1908(3) 0.1167(9) 0.1686(10) 0.2477( 11) 0.2137(3) 0.3027( 11) 0.2985(10)

0.12749(18) 0.1095(10) 0.0464(9) -0.04440(23) -0.1003(9) -0.1759(9) -0.1640(9) -0.12846(21) -0.1162(9) -0.0543(9) 0.03969(21) 0.0682(9) 0.1406(9) 0.22416(23) 0.2917(9) 0.3661(9) 0.3539(9) 0.31552(23) 0.2426(9) 0.1644(8)

2.551(25) 2.81(14) 5.2(8) 5.0(8) 3.91(17) 4.9(7) 4.9(8) 4.9(8) 3.73(16) 4.6(7) 4.4(7) 3.26(15) 4.2(7) 4.0(7) 4.25(17) 3.8(6) 4.3(7) 4.7(7) 4.52(19) 4.9(8) 4.0(6)

0 -0.23154(21) 0.3403(8) 0.2983(8) 0.2104(8) 0.06068(19) -0.0296(8) 0.0331(8) 0.06709(19) -0.0306(8) -0.1662(9)

1.972( 19) 2.95( 10) 2.9(4) 2.6(4) 2.6(4) 2.26(9) 2.9(4) 2.9(4) 2.30(8) 3.1(4) 3.0(4)

O.OOOOO

Comp ound III: [Pt(10S3)2](PF&CCH3N02 Pt Sl c2 c3 c4 s5 C6 c7 S8 c9 Cl0

l/4 0.26749( 10) 0.2173(4) 0.2210(4) 0.1717(4) 0.19362(9) 0.1268(4) 0.3910(3) 0.33168(9) 0.3396(4) 0.3378(4)

l/4 0.09809(19) 0.2951(8) 0.1749(7) 0.1381(7) 0.10775(17) 0.1342(8) 0.2441(8) 0.15558(18) 0.0361(7) 0.0584(7)

36

G.J. Grant et al. I Inorganica Chimica Acta 246 (1996) 31-40

Table 3

Table 3 (continued)

Selected bond lengths (A) and bond angles (“) (e.s.d.s are given in parentheses)

[Pt(lOS3)2](PFg)2’2CH3N02 Pt-S5

lPd(2us6)1(PQj)2 W-S 1

2.3118(22)

Pd-S4 Pd-S8 Pd-S I 1 Sl-C2 Sl-C20 C2-C3 c3-s4 C9-ClO Sll-Cl2 Cl2-Cl3 Cl5-Cl6

2.2869(19) 2.2899(20) 2.3246(19) 1.810(12) 1.835(12) 1.319(20) 1.814(12) 1.513(13) 1.789(9) 1.529(11) 1.508(14)

Sl-PdS4 S I-Pd-S8 Sl-W-S11 S4-Pd-S8 S4-Pd-Sll SS-Pd-Sll Pd-S l-C2 Pd-S l-C20 c2-Sl-C20 Sl-C2-C3 C7-S8-C9 S8-C9-C10 Pd-Sl l-Cl2 Cl2-C13-S14 Sl4-Cl5-Cl6 C16-C17-S18 Sl8-C19-C20

88.59(8) 175.72(8) 93.84(8) 89.53(7) 174.84(8) 88.34(8) 100.8(4) 108.8(4) 100.4(8) 117.8(9) 100.8(4) 107.6(6) 107.8(3) 114.9(5) 110.2(7) 111.5(7) 134.0(12)

[Pt(20S6)](PF&CH,N02 2.31 l(3) Pt-s 1 2.288(3) Pt-s4 2.293(4) Pt-S8 2.306(3) Pt-Sll 1.843(14) Sl-C2 1.815(15) Sl-C20 I .473(24) C2-C3 1.817(16) c3-s4 1.803(17) M-C5 1.529(23) C5-C6 1.812(14) CIO-Sll 1.51 l(22) Cl2-Cl3 s 1-pt-s4 Sl-Pt-S8 Sl-R-S11 S4-Pt-S8 s4-Pt-s 11 S8-Pt-S 11 Pt-s l-C2 Sl-C2-C3 Pt-s4-C5 c3-w-C5 C5-C6-C7 Pt-S8-C7 C7-S8-C9 c9-C10-Sll Pt-Sl l-Cl2 Sl l-Cl2-Cl3 c13-s14-Cl5

88.17(13) 177.33(12) 93.96(12) 89.21(14) 177.60(13) 88.66(13) 102.0(5) 108.2(11) 106.1(5) 103.3(8) 115.7(12) 105.4(5) 101.5(7) 113.6(10) 105.8(5) 111.6(10) 98.9(7)

Cl7-S18 S18-Cl9 Cl9-C20 s--C5 C5-C6 C6-C7 C7-S8 S8-C9 CIO-Sll c13-s14 s14-C15 ClWl7 Pd-S8-C9 C2-C3-S4 Pd-S4-c3 Pd-SW5 c3-w-C5 S&C5-C6 c5-C6-C7 C6C7-S8 Pd-S8<7 c9-C10-Sll Pd-Sl l-Cl0 CIO-Sl l-cl2 SllGCl2-Cl3 c13-Sl4-Cl5 Cl5<16-Cl7 Cl7-Sl8-Cl9 Sl-C2M19

s14C15 Cl5-Cl6 Cl6-Cl7 Cl7-S18 Sl8-Cl9 C19-C20 c&-C7 C7-S8 S8-C9 c9-Cl0 Sl l-Cl2 c13-s14 Cl6-C17-S18 C2-C3-S4 Cl7-Sl8Cl9 Cl5-Cl6-Cl7 Sl8-C19-C20 Pt-s 1-C20 c2-s l-C20 Pt-m-C3 S1~2O-C19 S&C5-C6 C6<7-S8 Pt-S8-c9 S8-C9-C10 Pt-Sl l-Cl0 ClO-Sll-Cl2 Cl2-C13-S14 Sl4-Cl5-Cl6

1.813(10) 1.727(17) 1.155(20) 1.812(9) 1.512(15) 1.515(14) 1.820(9) 1.821(9) 1.826(9) 1.796(9) 1.800(9) 1.506(16) 101.4(3) 114.3(9) 101.3(4) 106.7(3) 101.6(5) 111.6(6) 113.9(7) 111.3(6) 105.6(3) 111.9(6) 102.3(3) 103.3(4) 111.0(6) 100.5(5) 115.4(8) 105.7(9) 122.0(11)

1.806(15) 1.520(21) 1.504(22) 1.784(16) 1.819(16) 1.558(20) 1.500(22) 1.802(14) 1.806(14) 1.469(21) 1.799(15) 1.822(15) 113.0(11) 109.4( 11) 101.9(8) 115.9(12) 116.6(10) 106.7(S) 100.6(7) 101.7(5) 111.5(10) 113.2(10) 110.8(11) 102.6(5) 110.3(10) 102.2(5) 97.9(7) 111.2(10) 110.7(10)

Pt-S8 Sl-C2 Sl-ClO c2-s 1 C2-C.3 C6-C7

2.2971(21) 2.3010(22) 1.828(9) 1.813(9) 1.828(9) 1.527(13) 1.525(14)

s5-Pt-s5 S5-Pt-S8 S5-Pt-S8 S8-Pt-S8 cz-Sl-ClO Sl-C2-C3

179.9 90.91(8) 89.09(8) 180.0 103.8(4) 116.2(6)

c3-u-s5 Pt-S5-C4 Pt-S5-C6

113.7(6) 109.3(3) 101.1(3)

C7-S8 S8-C9 C9-ClO c3-C4 c4s5 S5-C6

Pt-S8-C7 Pt-S8-C9

1.814(9) 1.827(9) 1.543(14) 1.526(13) 1.831(9) 1.825(9)

C7-SS-C9 S8-C9-C10 Sl-ClO-c9 C2-C3-C4

105.7(3) 108.2(3) 102.8(4) 117.3(6) 113.7(6) 114.6(7)

C&S5-c6 S5-C6-C7

100.8(4) 113.8(6)

[Pd(20S612+, [Pt(2OS6)]*+, and [Pt( 10S3)2]2+ are shown in Figs. 2-4. A summary of key bond lengths in all three structures is presented in Table 4 along with comparison data of other known hexakis(thioether) complexes of Pt(I1) and Pd(I1). The two 2OS6 structures are similar with the same linkage isomer being obtained in both cases. In contrast to the other known structures of hexakis(thioether) complexes, these two structures are indeed exclusively fourcoordinate. Surprisingly, a less symmetrical linkage isomer is obtained in both cases with the metal off to one side of the ligand and bonded to four adjacent sulfur atoms. The Pd(I1) or Pt(I1) ion is surrounded by a distorted square planar array of four sulfur atoms. Two ethylene bridges are truns around the metal center with a trimethylene bridge in the remaining position. The sixmembered chelate ring formed by this trimethylene bridge adopts a chair conformation in both structures. Two adjacent sulfur atoms, bridged by the second trimethylene unit, remain uncoordinated and offer the possibility of chelating a second metal center and thereby forming heterometallic binuclear complexes. Investigations of these possibilities are now underway in our laboratories. The linkage isomer obtained in the two 2OS6 complexes is in contrast to all three reported 18S6 structures where that ligand forms a double boat or S-shape structure around the metal center [2,22]. As mentioned previously, counterion effects have been demonstrated in complexes of [Pd(18S612+. We have also isolated the BF,- and ClO,- salts of [Pd(18S612+, both of which are green and presumably isostructural to the reported green hexafluorophosphate salt. The tetrafluoroborate salt readily redissolved in acetonitrile to reform a brown colored solution. However, we do not observe similar counter-ion effects with [Pd(20S612+ with tetrafluoroborate or per-

31

G.J. Grant et al. I Inorganica Chimica Acta 246 (1996) 3140

Fig. 2. Structural

perspective

of [Pd(20S6)]2+.

chlorate counterions since all three salts of this complex are yellow. The Pd-S bond lengths in [Pd(20S612+ group into two pairs. The sulfurs of the trimethylene chelate ring are closer to the Pd(I1) center (average 2.289(20) A) than are the other two sulfur atoms (average 2.319(21) A). Similarly, the internal angle of the six-membered chelate ring is a little larger, 89.53(7)“, compared to the internal angles of the two five-membered chelate rings, 88.46(S)” reflecting the greater flexibility of the larger chelate ring. The remaining internal angle, Sl l-Pd-Sl, is 93.84(g)“. This larger value is due to the fact that these two coordinated sulfurs atoms are not linked by a methylene bridge and thus have greater conformational freedom. Two of the carbon-carbon bonds in the macrocyclic ring are surprisingly short. The bond distance for C2-C3 is 1.319(20) A and C19-C20 is 1.155(20) A. The short bond distance for the former carbon-carbon bond probably reflect structural distortions imposed upon the macrocycle by its coordination to the Pd center since this bond is within one of the five-membered chelate rings. The latter carbon-carbon bond is unrealistically short and arises from a disorder in the two carbons. An identical disorder has been observed in the crystal structures of the ligands 18S6 and 2OS6 [37,28]. The Pd atom lies only 0.04 A above the plane defined by the square planar array of the

Fig. 4. Structural

Table 4 Comparison of mean metal-sulfur crown trithioether and hexathioether Complex

Pd(II) complexes [Pd(9S3),12+ [Pd(10S3)2]2+ [Pd(10S3)2]2+ [Pd( 18S6)]2+ [Pd( 18S6)12+ [Pd(20S6)12+

[Pt(lOS3)21*+ [Pt(18S6)12+ [Pt(20S6)12+ [Pt( 12s4)]2+ [Pt(14s4)]2+ perspective

of [Pt(20S6)12+.

of [Pt( lOS3)2]*+.

four coordinated sulfur atoms. Three of the four lone pairs point up while the lone pair of Sl is oriented down. The structure of [Pt(20S612+ is quite similar to the Pd analog. Again, the Pt-S bond lengths group into two pairs. The sulfurs of the trimethylene chelate ring are closer to the Pt(I1) center (average 2.290(4) A) than are the other two sulfur atoms (average 2.308(3) A). The internal angle of the six-membered chelate ring is a little larger, 89.21(14)“, compared to the internal angles of the two five-membered chelate rings, 88.41(14) A, reflecting the greater flexibility of the larger chelate. The remaining internal angle, S 1 l-Pt-Sl, is 93.96( 12)“, almost identical to the angle in the Pd structure. In contrast to [Pd(20S612+, the carbon-carbon bond lengths are all about the same, with a variation of less than 0.1 8, from

Pt(II) complexes [Pt(9S3)#+ [Pt(lOS3)#+

Fig. 3. Structural

perspective

Overall solid state structure

bond lengths complexes

of Pd(Il) and Pt(l1)

M-Sequatorial (A)

M-SaxiaI

2.32 2.21 2.33 2.31 2.33 2.30

2.95 3.11 3.03 3.27 3.01 None

2.29 2.30

2.89 3.21

171 This work

S4

2.30 2.30 2.30

3.23 3.38 None

1291 1221 This work

2.29 2.29

None None

13t.321

::

s4+s2 s4+s2 s4+s2 s4+s2 s4+s2

S4

S4+% s4 + s2

s4+s2 s4+s2

Ref.

(8)

[51

1201 1211

WI 1231 This work

1331

G. J. Grant et al. I Inorganica Chimica Acta 246 (I 996) 31-40

38

highest to lowest. The structure also resembles that obtained for [Pt( 14S4)]*+ which shows similar deviations in the internal angles for PtS, coordination sphere [33]. The Pt ion lies about 0.03 A below the plane of the four sulfur atoms. The lone pairs of the sulfur atoms point in the same direction as they do in the Pd structure, with the lone pair on S 1 pointing down. The structure of [Pt(10S3)2]2+ is similar to the one reported by Schroder except that two nitromethane solvent molecules are incorporated in the lattice in our structure 1301. The structure is remarkably similar to our structure of [Pd(10S3)2]2+ with identical space group and cognate unit cell constants [20]. The complex involves a tetragonally distorted pseudo-octahedral environment of sulfur atoms [S, + S,] about the platinum. The two lOS3 ligands are centrosymmetrically oriented around the Pt center in trans fashion to yield the meso stereoisomer. The linkage isomer of [Pt(lOS3),]*+ is identical to the one that we previously obtained for [Pd(10S3)2]2+ when the crystals were also grown from nitromethane [20]. In this linkage isomer, an ethylene bridge is located between the two equatorial sulfur atoms and the trimethylene bridge is between one equatorial and one axial sulfur. The ligand adopts a conformation [2233] in which all three sulfur atoms are necessarily syn endodentate, and the six-membered chelate ring is nearly in a chair form [24]. Four sulfur atoms (two from each of the two lOS3 ligands) form a square planar arrangement around the platinum with an average Pt-S bond distance of 2.2991(21) 8, (2.2971-2.3010(21) A). This distance is considerably shorter than the sum of the covalent radii which is 2.35 A [38]. In our structure the axial sulfur atoms, one from each lOS3 ligand, interact with the Pt from a distance of 3.231(9) A. Thus, both the equatorial and axial metal-sulfur interactions are longer in the Pt structure than in the analogous Pd structure. The internal angles of the PtS, coordination sphere average 90” (90.91(8)“, 89.09(8)“) in contrast to the Pd structure where they are 88.8”. The angle between the axial sulfur

atoms and the plane formed by the platinum and the four equatorial sulfur atoms is 86”, larger than observed for [Pt( 18S6]*+and [Pt(9S3),]*+ [7,22]. 3.3. Spectroscopic studies Summaries of the spectroscopic and electrochemical data are found in Table 5 for the complexes reported here and also for some comparison complexes. Except for the 9S3 and lOS3 complexes of both Pd and Pt, no visible absorption bands are observed in solution. Therefore, the color of these complexes is dominated by the location of charge transfer bands. For the Pd complexes the bluegreen color is seen when the axial sulfur atoms are at least within 3.11 8, of the Pd center [20]. Otherwise, a yellow color is observed. In the case of the Pt complexes, a transition near 430 nm is seen for both [Pt(9S3),]*+ and [Pt(lOS3),]*+, resulting in the observed orange color for these complexes. Note that these are also the two complexes that have the strongest axial sulfur-platinum interactions. When these strong axial interactions are not present, the color of the complex is again dominated by the position of charge transfer bands, and the complex may range from yellow to colorless. The absorption bands observed in the visible region for all 9S3 and lOS3 complexes are confirmed to be d-d transitions by the relatively small value for their extinction coefficients (near 100 M-i cm-i). The proton NMR spectra of the complexes are of limited value with the exception of the [Pd(ttn)2]2+ complex which clearly shows only a single methyl resonance. This is in marked contrast to other previously reported bis(ttn) complexes which show two methyl resonances [12,39]. Furthermore, a i3C DEPT NMR experiment verifies only a single methyl group to be present. There are three possible stereoisomers for a bis(ttn) complex; an unsymmetrical facial isomer, a symmetrical facial isomer, and a meridional isomer. The simplicity of our spectra are consistent with the latter two, both of which contain centro-

Table 5 Spectroscopic

and electrochemical

Complex

Pd(I1) complexes [Pd(9S3),]*+ [Pd(10S3),]2+ [Pd(lSSS)]*+ [Pd(2OS6)]*+ [Pd(ttn)212+

data for Pd(I1) and Pt(II) trithioether

and hexathioether

complexes

Solution color

Visible absorbance Amax (nm)

E” (V) versus Fe/F,+ oxidation

Blue-green Blue-green Yellow-brown Yellow Yellow

615 603 None None None

+0.605 +0.606 None None None

Orange

432 430 None None

+0.39 +0.324 None None

Ref.

[51

1201 1221 This work This work

Pt(I1) complexes [Pt(9S3),]*+ [pt(10S3)2]2+ [Pt(lss6)]*+ [Pt(20S6)]*+

Orange Yellow Colorless .-

171 This work [221 This work

G.J. Grant et al. I Inorganica Chimica Acta 246 (1996) 31-40

symmetrically coordinated ttn ligands. However, the symmetrical facial isomer is the more likely since it allows the C-S bonds to adopt more favorable gauche conformations, and a meridional stereoisomer has not been observed with this ligand [25,28]. Carbon NMR spectroscopy was undertaken on both 2OS6 complexes to see if there was evidence for additional isomers in solution. The linkage isomer obtained in both X-ray structures would show an eight line NMR spectrum. The i3C NMR spectra for the two complexes are complicated with over 20 different resonances observed in each case. Therefore, there are at least one and probably more isomers present in solution, and our crystal structures presumably represent the precipitation of a less soluble one. Additionally, the presence of two additional isomers for [Pt(20S6)12+ is further demonstrated by a 195Pt NMR spectrum which shows three distinct Pt resonances. McAuley had noted strong solvent-complex interactions for [Pd(10S3)2]2+ [21]. Hence, we undertook a variable temperature t3C NMR study for [Pt(10S3)2]2+ in both CD3N02 and CD,CN, monitoring the line broadening of the methyl resonances for the two solvents. In contrast to the Pd analog, no line broadening was observed, even at temperatures near the freezing point of each solvent. Therefore, the solvent-complex interaction observed for [Pd(10S3)2]2+ is not present with Pt(10S3),12+. Although the packing in [Pt(10S3),12+ is similar to [Pd(10S3)2]2+, the nitromethane molecules are further from the metal center. A shortening of the distances between the metal ion and the axial sulfurs seems to enhance the solvent effect. 3.4. Electrochemical

studies

The three complexes which lacked visible absorption bands also did not exhibit any electrochemical activity. These complexes are [Pd(20S6)]2+, [Pt(20S6)12+, and [Pd(ttn)2]2+. Under the conditions of our cyclic voltammetry study, the complex [Pt( 10S3)2]2+ exhibited a chemical reversible oxidation wave at +0.324 V versus ferrocene/ferroceniurn. In this respect, the complex resembles the electrochemical behavior of the [Pt(9S3)2]2+ which also exhibits a reversible one-electron oxidation wave at +0.39 V versus ferrocenium/ferrocene (71. The reversibility of the oxidation wave for [Pt(10S3)2]2+ is proven by two methods. First, the peak-to-peak separation is 62 mV while the peak-to-peak separation for the internal ferrocene standard under identical scan conditions is 63 mV (scan rate 25 mV s-l). Secondly, the i,$i,, ratio for the couple in [Pt( 10S3)2]2+ is 1.02. We would like to note that scan rate, solvent, and the nature of the working electrode do affect the reversibility of this peak. Schroder had obtained a quasi-reversible process for the process with a peak-topeak separation of about 400 mV [29]. Going to faster scan rates, we do observe an increase in the peak separa-

39

tion. Also, we would like to note that we did obtain a quasi-reversible wave in nitromethane at a working glassy carbon electrode. The reversible oxidation wave is assigned as a Pt(II)/Pt(III) one-electron oxidation. The one-electron nature of this process is demonstrated in several ways. First, as noted previously, the value of the peak-to-peak separation is 62 mV, close to the expected value of 59 mV for a reversible, one-electron process. Secondly, the values of the anodic peak currents, i,,, for the internal ferrocene and for the [Pt(10S3)2]2+ complex are in the ratio of their concentrations [40]. This relationship would hold only for reversible systems with an equal number of transferred electrons. If the oxidation had been a twoelectron process, the platinum complex would show a current increase of 23’2 or 2.8 times greater in value than F,+IF,. Thirdly, the measured peak areas of the two couples are in the ratio of their concentrations. Again, this observation is consistent with a one-electron transfer. Lastly, when oxidized with concentrated HC104, we do observe an ESR signal consistent with the formation of [Pt(10S3)2]3+. The formation of the trivalent Pt had also been observed via ESR previously for the complex by Schroder et al. [30]. 4. Conclusions Our results extend the coordination chemistry of trithioether and hexathioether ligands with divalent Pd and Pt. There is a correlation with the metal-axial sulfur distance and the unusual electrochemical and spectroscopic properties exhibited by the Pd and Pt complexes. When shorter axial sulfur-metal distances are present, dd transitions are observed in the visible absorption spectra and reversible oxidation waves are seen in the cyclic voltammograms. The structure of the thioether ligands plays a key role in determining their coordination behavior, and the shorter axial sulfur distances tend to be observed in the smaller crown thioethers. 5. Supplementary

material

Supplementary tables are available which list the following: variable temperature t3C NMR studies (2 pages), CyCliC voltammogram of [Pt( 10S3)2]2+ (1 page), structural data for [Pd(20S6)](PF6)2 including ORTEP perspective (1 page), complete atom positional parameters (3 pages), a listing of complete bond lengths and bond angles, (6 pages), anisotropic thermal parameters (3 pages), and observed and calculated structure factors (41 pages); structural data for [Pt(20S6)](PF6)2CH3N02 including ORTFP perspective (1 page), complete atom positional parameters (3 pages), a listing of complete bond lengths and bond angles (4 pages), anisotropic thermal parameters (3 pages), and observed and calculated structure factors (20 pages); structural data for [Pt( 10S3)2](PF6)2*

40

G.J. Grant et al. I Inorganica Chimicu Acta 246 (1996) 31-40

2 CH3N02 including ORTEP perspective (1 page), complete atom positional parameters (2 pages), a listing of complete bond lengths and bond angles (3 pages), anisotropic thermal parameters (2 pages), and observed and calculated structure factors (20 pages). Acknowledgements This research was generously supported by grants from the Petroleum Research Fund, administered by the American Chemical Society, the National Science Foundation, Research at Undergraduate Institutions Program, and the Grote Chemistry Fund (UTC). One of us (G.J.G.) would like to thank both Professor John Gladys2 of the Department of Chemistry at the University of Utah for hosting a sabbatical leave during which a portion of this work was completed and the National Science Foundation, Research Opportunity Award Program for partially funding that sabbatical. N.J.S. would like to acknowledge his support by the Petroleum Research Fund, administered by the American Chemical Society, as an Undergraduate Research Scholar. We also thank Sabrina Lee, Rebecca Kirk, Chad Hadden, Mary Jo Gray, and Kristi Loveday for their contributions to the experimental portion of this work. References [II M. Schrijder, Pure Appl. Chem., 60 (1988) 517. 121 A.J. Blake and M. Schrader, in A.G. Sykes (ed.) Advances in Inorganic Chemistry, Vol. 35, Academic Press, New York, 1990, p. 2. [31 S.R. Cooper and S.C. Rawle, Structure Bonding, 72 (1990) 1. 141 S.R. Cooper,Acc. Chem. Res., 21 (1988) 141. [51 A.J. Blake, A.J. Holder, T.I. Hyde, Y.V Roberts, A.J. Lavery and M. Schrijder, J. Organomet. Chem., 323 (1987) 261. 161 A.J. Blake, A.J. Holder, T.I. Hyde and M. Schriider, J. Chem. Sot., Chem. Cummun., (1987) 987. [71 A.J. Blake, R.O. Gould, A.J. Holder, T.I. Hyde, A.J. Lavery, M.O. Odulate and M. Schriider, J. Chem. Sot., Chem. Commun., (1987) 118. WI S.C. Rawle, R. Yagbasan, K. Prout, S.R. Cooper, J. Am. Chem. Sot., 109(1987) 6186. [91 A.J. Blake, R.O. Gould, A.J. Holder, T.I. Hyde and M. Schriider, J. Chem. Sot., Dalton Trans., (1988) 1861. DOI A.J. Blake, J.A. Greig, A.J. Holder, T.I. Hyde, A. Taylor and M. Schriider, Angew. Chem., Int. Ed. Engl., 29 (1990) 197. [ill A.J. Blake, R.O. Gould, J.A. Greig, A.J. Holder, T.I. Hyde and M. Schrlider, J. Chem. Sot., Chem. Commun., (1989) 876. u21 S.R. Cooper, S.C. Rawle, R. Yagbasan and D.J. Watkin, J. Am. Chem. Sot., II3 (1991) 1600. r131 G.S. Hanan, J.E. Kickham and S.J. Loeb, J. Chem. Sot., Chem. Commun., (1991) 894. [I41 G. Giesbrecht. G.S. Hanan, J.E. Kickham and S.J. Loeb, Inorg. Chem., 31 (1992) 3286. D51 G.S. Hanan, J.E. Kickham and S.J. Loeb, Organomerallics, II (1992) 3063. [I61 A.J. Blake, M.A. Halcrow and M. Schriider, J. Chem. Sot., Chem. Commun., (1991) 253.

r171 M.A. Bennett, A.J. Canter, J.K. Felixberger, L.M. Rendins, C. Sutherland and A.C. Willis, Inorg. Chem., 32 (1993) 1951. [I81 A.J. Blake, A.J. Holder, T.I. Hyde, H.-J. Kuppers, M. Schrijder, S. Stozel and K. Wieghardt, .I. Chem. Sec., Chem. Commun., (1989) 1600. u91 K. Wieghardt, H.-J. Kuppers, E. Raabe, C. Kruger, Angew. Chem., Inr. Ed. EngZ., 25 (1986) 1101. r-w G.J. Grant, K.A. Sanders, W.N. Setzer and D.G. VanDerveer, Inorg. Chem., 30 (1991) 4053. WI S. Chandrasekhar and A. McAuley, Inorg. Chem., 30 (1992) 2663. WI A.J. Blake, R.O. Gould, A.J. Lavery and M. Schrader, Angew. Chem., Int. Ed. Engl., 25 (1986) 274. 1231 A.J. Blake, D. Collison, R.O. Gould, G. Reid and M. Schrijder, J. Chem. Sot ., Dalton Trans., (1993) 521. ~241 W.N. Setzer, E.L. Cacioppo, Q. Guo, G.J. Grant, D.D. Kim, J.L. Hubbard and D.G. VanDerveer, Inorg. Chem., 29 (1990) 2672. v51 R.S. Glass, G.S. Wilson, W.N. Setzer, J. Am. Chem. Sot., 102 (1980) 5068. P61 W.N. Setzer, S. Afshar, N.L. Bums, L.A. Ferrante, A.M. Hester, E.J. Meehan, G.J. Grant, S.M. Isaac, C.P. Laudeman, CM. Lewis and D.G. VanDerveer, Heteroatom Chem., I (1990) 375. P71 S.R. Cooper, S.C. Rawle, J.R. Hartman, E.J. Hintsa and G.A. Admans, Inorg. Chem., 27 (1988) 1209. LW R.E. Wolf, J.R. Hartman, J.M.E. Storey, B.M. Foxman and S.R. Cooper, J. Am. Chem. Sot., 109 (1987) 4328. v91 This work was initially presented at the 17th International Symposium on Macrocyclic Chemistry; Provo, Utah, August 9-14, 1992, Paper Number 39. Following our presentation, the work described in [30] appeared. [301 A.J. Blake, R.D. Crofts and M. Schrijder, J. Chem. Sot., Dalton Truns., ( 1993) 2259. 1311 A.J. Blake, A.J. Holder, G. Reid and M. Schriider, J. Chem. Sot., Dalton Trans., (1994) 627. ~321 M.A. Watzky, D. Waknine, M.J. Heeg, J.F. Endicott and L.A. Ochrymowyzc, fnorg. Chem., 32 (1993) 4882. r331 D. Waknine, M.J. Heeg, J.F. Endicott and L.A. Ochrymowyzc, Inorg. Chem., 30 (1991) 3691. [341 We would also like to note that the solution structure of [Pt(9S3)2]*+ does appear to be very different from the reported crystal structure. In solution [Pt(9S3)2]*+ gives only a single 13C NMR resonance whereas the crystal structure [7] shows the two 9S3 ligands not to be centrosymmetric around the Pt center. [351 G.J. Grant. J.P. Carpenter, W.N. Setzer and D.V. VanDerveer, Inorg. Chem., 28 (1989) 4128. [361 The programs used for the solution and refinement of this structure were those in NRCVAX from the National Resource Council, Ottawa, Canada. [371 W.N. Setzer, G.J. Grant and E.J. Meehan, unpublished. [381 S.G. Murray and F.R. Hartley, Chem. Rev., 81(1981) 365. r391 S.C. Rawle, T.J. Sewell and S.R. Cooper, Inorg. Chem., 26 (1987) 3769. 1401 A.J. Bard and L.R. Faulkner, Electrochemicul Methods: Fundumentuls und Applications, Wiley, New York, 1980, p. 218. The relationship between peak current ip and n. the number of electrons transferred for a reduction, is given by the equation: ip = (2.69 X 105)n3”AD, ~%J’~M where A is the electrode surface area, DO the diffusion coefficient for the oxidized form of the electroactive species, v the scan rate, and M the molarity of the sample. The two couples were run under identical conditions. The diffusion coefficients of ferrocene and the platinum complex are assumed to be approximately equal.