摘要:
J. CHEM. SOC. DALTON TRANS. 1995 897Synthesis, Crystal Structure and Properties of NovelFerrocenyl Multisulfur Compounds tStephen 6. Wilkes,a Ian R. Butler/ Allan E. Underhill,a Michael B. Hursthouse,bDavid E. Hibbsb and K. M. Abdul Malikba Department of Chemistry, University of Wales, Bangor, Gwynedd LL57 2UW, UKCardiff CF1 3TB, UKSchool of Chemistry and Applied Chemistry, University of Wales, Cardiff, PO Box 912,Novel compounds and metal complexes containing both ferrocene and sulfur- based ligands havebeen prepared and their properties investigated. The reaction of [ N Et,],[Zn (C,S,),] with(c hloromethy1)ferrocene led to the compound 4.5- bis(ferrocenylmethylsu Ifanyl) - 1.3-dith iole-2 -thione. Similarly, the reaction of the salt Cs,[C,OS,], led to the ketone analogue, 4,5-bis(ferrocenylmethylsulfanyl) -1.3-dithiole-2-one. The latter has been used to prepare a monoanionictetraferrocenyl nickel dithiolene complex which shows an intense NIR absorption at 1250 nmrecorded in CH,CI,.Intermolecular coupling of the thione gave the noveltetra(ferrocenylmethylsuIfanyl)tetrathiafulvalene electrochemical investigations of which revealedcharacteristic ttf and ferrocenyl redox processes. The single-crystal structure of this compound hasalso been determined.The design and development of new materials with the potentialto operate at the molecular level has recently become aburgeoning topic within the physical sciences and chemistry inparticular. Examples of various devices and components areliquid crystals, molecular ferromagnets,2 non-linear optical(NLO) materials3 and molecular conductor^.^ Complex metalanions of sulfur-donor ligands and planar organic donormolecules derived from the ttf [tetrathiafulvalene, 2-( 1,3-dithiol-2-ylidene)-l,3-dithiole] unit have been extensivelystudied because of their capacity to form molecular metals andsuperconductors and more recently because of their potentialapplications as third-order NLOIn the past few years a number of studies have alsohighlighted the use of ferrocene-containing molecules withincertain areas of molecular electronics.The extensive substituentchemistry of ferrocenes combined with the high versatility ofthe Fe"-Fe"' redox couple of substituted ferrocenyl derivativeshas led to the recognition that ferrocene may be a usefulsynthon in device applications, for example in molecular~ e n s o r s , ~ - ' ~ NLO materials,' '-14 molecular switches l 5 andmolecular magnetic materials.l 6The possibility exists to combine together within a singlemolecular unit the chemistry of ferrocenes and that of sulfur-based ligands. As yet virtually unexplored, research in this areaoffers a new perspective with which to investigate the unusualsolid-state phenomena exhibited by molecular materials.Mueller-Westerhoff et al. ' have prepared a tetraferrocenylmetal dithiolene complex which shows an intense electronictransition in the 1.3 pm region of the near-IR. This highlightsthe potential use of ferrocenyl metal dithiolenes in the design ofNIR materials, e.g.dyes and lasers which utilise 1.3 and 1.5 pmradiation'* as well as in the construction of NLO materialsexhibiting enhanced second- and third-order properties.' '-I4 Afew compounds incorporating the organic donor unit of ttf witha second redox-active centre such as ferrocene have also beenreported. 19-21 The addition of ferrocene as an extra electron-t Supplementary data available: see Instructions for Authors, J. Chem.Soc., Dalton Trans., 1995, Issue 1, pp. xxv-xxx.donor site onto the ttf moiety might not only serve to enhanceits potential as an organic-based conductor but be ofconsiderable interest within the expanding areas of supra-molecular chemistry. 'Towards these objectives, we recently reported the synthesisand properties of the first diferrocenyl metal dithiolenecomplex,22 which is similar to the Mueller-Westerhoff complexbut with two instead of four ferrocene units attached to themetal bis(dithio1ene) core.The work described in this paperconcerns the synthesis and evaluation of several new types ofmolecular materials which contain two redox-active centres,one based on ferrocenes and the other on metal bis(dithio1ene)and ttf-based organic donor molecules.ExperimentalSolvent and Reagent Pretreatment.-Where necessary sol-vents were purified by distillation prior to use. Dichloromethanewas distilled from P205, ethanol over magnesium and thenstored over 4 A molecular sieves under argon prior to use.Ferrocene carbaldehyde was obtained from Aldrich Chemi-cal.1 -Ferro~enylmethanol,~~ [NEt4]2[Zn(C,S5),]24 andCS,[C,OS,]~~ were prepared according to the literature pro-cedures.Instrumental Methods.-Melting points were determinedusing a Linkam hotstage (model TH600) with a heating rate of3 "C min-', in conjuction with an Olympus optical microscope(model BH2) fitted with polarising filters. Infrared spectra wererecorded as chloroform or dichloromethane solutions on aPerkin-Elmer 1600 series instrument, NMR spectra indeuteriochloroform on a Bruker AC-250 or SRC WH-400spectrometer (6 in ppm relative to tetramethylsilane as internalstandard), fast atom bombardment (FAB) mass spectra on aVG Analytical ZAB-E spectrometer using chemical ionisation(with ammonia as the reagent gas) and ultraviolet-visible andnear-infrared spectra on a Philips Analytical PU8800 and aBeckman DK-2A ratio-recording spectrophotometer respec-tively.All elemental analyses were carried out using a CarloErba 1 106 microanalyser898 J. CHEM. SOC. DALTON TRANS. 1995Electrochemical Measurements.-The electrochemical prop-erties of the new compounds were measured using cyclicvoltammetry (CV). All CV measurements were carried out atroom temperature in an electrochemical cell (volume 20 cm3)fitted with a gold working electrode, a platinum-spade counterelectrode, a saturated calomel reference electrode (SCE) and aninert-gas inlet. Dry degassed dichloromethane containing 0.1mol dm-, NBu,PF, as the background electrolyte was usedas the solvent. The scan rate applied was 100 mV-' ssl.Themeasurements were controlled by a microcomputer using aCondecon 3 10 cyclic voltammetry program. The apparatuswas an EG & G Princeton Applied Research Model 264Apolarographic analyser (stripping voltammeter connected toan EG & G Condecon 300 controller). The current vs. voltagecurves were recorded with a Philips X-Y recorder. The appara-tus was always calibrated using compounds of known redoxproperties (e.g. ferrocene or ttf).Syntheses. 4 , 5 - Bis(ferroceny1me th y lsulfan y l) - 1 ,3 -dith iole-2 -thione 4. Oxalyl chloride (0.88 cm3, 1.27 g, 10 mmol) was addedto a solution of 1-ferrocenylmethanol(2.16 g, 10 mmol) in drydichloromethane (200 cm3) and the mixture stirred undernitrogen at room temperature for 1.5 h.After removing thesolvent and unreacted oxalyl chloride under high vacuum, theproduct was redissolved in dry dichloromethane and added to asolution of [NEt,],[Zn(C,S,),] (1.37 g, 2.5 mmol) in drydichloromethane (100 cm3). The mixture was refluxed undernitrogen for 10 h. After allowing to cool to room temperature,the mixture was filtered through a silica gel plug, washedextensively with dichloromethane and the solvent removed ona rotary evaporator to reveal a viscous red oil. Purification ofthe crude product was best effected by column chromatographyon a silica gel support using light petroleum4ichloromethane(70: 30) as the eluent. After removing the solvents on a rotaryevaporator a fibrous red solid was obtained.Yield = 0.84 g(14%), m.p. 103-105 "C (Found: C, 50.60; H, 3.85. Calc forC2,H,,Fe2S,: C, 50.55; H, 3.70%). NMR (250 MHz): 'H, 63.70(~,2H),4.18(~,5H)and4.19(~,4H). 13C,637.55(CH2),68.47, 68.72, 82.53 (ferrocenyl), 137.75 (W), and 211.74(GS). IR (CH,Cl,): 1064.2 cm-' (C=S). FAB mass spectrum:m/z 594 ( M + ) . UV/VIS (CH,Cl,): h,,,(ln E ) 234 (10.17) and378 nm (9.47).4,5-Bis(ferrocenylmethylsuEfanyl)- 1,3-dithioI-2-one 5. Thesame procedure was employed as for the preparation ofcompound 4 but using Cs,[C30S4] instead of[NEt,],[Zn(C,S,),]. As for 4, purification was best effected bycolumn chromatography on a silica gel support using lightpetroleum-dichloromethane (70 : 30) as the eluent. Afterremoving the solvents on a rotary evaporator a red-brownpowder was obtained.Yield = 1.51 g (20%), m.p. 95-98 OC(Found: C, 50.45; H, 3.80. Calc for C,,H,,Fe,OS,: C, 51.90;H, 3.80%). NMR (250 MHz): 'H, 6 3.70 (s, 2 H), 4.18 (s, 5H) and 4.19 (s, 4 H); 13C, 6 37.36 (CH,), 68.39, 68.74, 82.84(ferrocenyl), 128.76 (W) and 189.93 (M). IR (CH,Cl,):1667.7 cm-' (W). FAB mass spectrum: m/z 578 ( M + ) .UV/VIS (CH,Cl,): h,,,(ln E ) 231 (10.17) and 373 nm(9.39).Tetra(ferrocenylmethy1sulfanyl)tetrathiafulvalene 6 . Com-pound 4 (0.50 g) was suspended in freshly distilledtriethyl phosphite (1 5 cm3) under nitrogen. The stirred reactionmixture was heated at between 110 and 120 "C for 45 min, thencooled to room temperature whereupon methanol was addedto precipitate a red solid. After decanting off the triethylphosphite, the red solid was redissolved in chloroform and theexcess of phosphite removed under high vacuum.The productwas filtered through a silica gel plug using dichloromethane, thesolvent was concentrated and the product recrystallised fromdichloromethane-hexane at - 20 OC. After filtering thesolution, an orange powder was obtained. Yield = 0.15 g(16%), m.p. 75-77 "C (Found: C , 53.20; H, 4.30. Calc. forC5,H4,Fe4S8: C, 53.40; H, 3.90%). NMR (400 MHz): 'H,6 3.73 (s, 2 H), 4.14 (t, 2 H), 4.15 (s, 5 H) and 4.19 (t, 2 H); 13C,6 36.83 (CH,), 68.21, 68.70, 68.74, 83.39 (ferrocenyl), 110.20(W) and 129.15 (C=C). IR (CHCI,): 822,1000,1105 and 1413cm-'. FAB mass spectrum: m/z 1124 (M' - H). UV/VIS(CH,Cl,): hmax(ln E ) 230 (1 1.28), 332 (7.44) and 404 nm (6.48).Tetrapheny Iphosphonium bis[ 1,2-bis(ferrocenylmethylsuIfa-ny1)ethene -1,2-dithiolato] nickelate 8.To a slurry of compound5 (0.30 g, 0.52 mmol) in ethanol was added dropwise sodiummetal (0.024 g, 1.04 mmol) in ethanol under an inertatmosphere. The mixture was stirred at room temperaturesealed under nitrogen for 15 h until a deep brown colourationwas obtained. The solution was quickly filtered into anethanolic solution of the counter cation, tetraphenylphospho-nium bromide (0.22 g, 0.52 mmol) and then NiC1,*6H2O (0.062g, 0.26 mmol) in ethanol was added dropwise. The resultinggreen solid was filtered off, washed with ethanol and dried invacuo. Yield = 0.32 g (46%) (Found: C, 55.20; H, 5.50. Calc.for C72H,,Fe4NiPS,: C, 56.05; H, 5.25%).FAB massspectrum: m/z 988 ( M + ) , 775,650,483 and 461. NIR (CH,Cl,):h,,, 1250 nm.Crystal Structure Determination of Compound 6.-Crystaldata. C,OH,,F~,S~*O.~C~H,,, M = 1 181.84, monoclinic, spacegroup P2,/a, a = 9.483(3), b = 27.8536(9), c = 10.5534(9)&p = 105.42(2)O (by least-squares refinement of the settingangles for 250 reflections having 8 = 2.34-25.09"), U =2687.2(9) A3, 2 = 2, D, = 1.461 g cm-,, T = 298 K, ~ ( M o -Ka) = 14.04 cm-l, F(OO0) = 1218, crystal size =0.10 x 0.03 x 0.02 mm.Data were collected on a FAST TV Area detectordiffractometer following previously described methods.,,From the ranges scanned, 10 572 data were recorded(2.34 < 8 < 25.09'; - 8 < h < 10, -31 < k < 31, -11 <I < 12) and merged to give 4074 unique (Rint = 0.075).The structure was solved via direct methods 27 and refined byFo2 by full-matrix least squares28 using all unique data correctedfor Lorentz and polarisation factors and also for absorption2'(minimum and maximum absorption correction factors 0.887and 1.097). All non-hydrogen atoms were anisotropic.Withinthe unit cell, each molecule of compound 6 was accompanied bya half-occupied solvent molecule of what appeared to be acentrosymmetric octane chain. The four unique carbon atomsof this molecule were also treated anisotropically but it wasnecessary to restrain their displacement coefficients by using theinstruction ISOR 0.01 0.02 in the refinement procedure.28 Thehydrogens of the solvent were ignored and those on the complexmolecule were included in idealised positions with Uis0 freeto refine.The weighting scheme was w = 1/[02(FJ2 +(0.0777P)2], where P = [max(Fo)' + 2(FJ2]/3; this gavesatisfactory agreement analyses. Final R, (on F) and wRZ (onFo2) values were 0.1053 and 0.1343 for all 4074 data and 338parameters. The corresponding R values were 0.0537 and0.1248 for 2001 data with I > 2o(I). Sources of scatteringfactors were as in ref. 28. The fractional atomic coordinates arelisted in Table 1, selected bond lengths and angles in Table 2.The numbering of the atoms is shown in Fig. 2.Additional material available from the Cambridge Crystallo-graphic Data Centre comprises H-atom coordinates, thermalparameters and remaining bond lengths and angles.Results and DiscussionSyntheses.-The synthesis of compound 4 and its ketoneanalogue 5 is shown in Scheme 1.Lithium aluminium hydridereduction of ferrocenecarbaldehyde 1 in diethyl ether gave 1-ferrocenylmethanol2. (Chloromethy1)ferrocene 3 was preparedby the reaction of oxalyl chloride with 2 in dry dichloromethane.After removal of unreacted oxalyl chloride in uacuo, compounds4 and 5 were prepared by refluxing 3 with [NEt4],[Zn(C3S5),]and Cs,[C,OS,] respectively in dry dichloromethane overnight.Conventional coupling of compound 4 in neat triethyJ. CHEM. SOC. DALTON TRANS. 1995 899Table 1 Atomic coordinates ( x lo4) for compound 6* Atom in the half-occupied octane solvent molecule.X2 436.0(9)8 73 1.2(9)6 350(2)8 028(2)5 086(2)6 723(2)3 905(8)4 61 l(7)4 109(6)3 113(7)2 988(8)1 205(14)2 037( 13)1 682(15)599( 13)33 1 ( 1 0)4 507(6)6 174(6)6 897(5)6 747(6)5 364(5)7 506(5)6 902(6)7 929(6)9 202(7j8 951(6)10 169(11)10 431(11)9 167(14)8 090( 12)8 723( 11)4 859(41)3 663(47)2 389(34)1051(53)Y1 670.1(3)635.7(3)1517(1)592( 1)779( 1)1289(3)1572(2)1432(2)1065(2)980(3)2 089(4)2 362(4)2 264(5)1913(5)1813(4)1653(2)921(2)55 l(2)362(2)154(2)222(2)220(2)37(3)40(2)- 17( 1)- 72(2)1 146(3)1 031(3)1 131(3)1 302(3)1 315(3)2 285(11) -2 238( 1 1)2 402(9)2 513(13)Z4 313.7(10)7 922.0(8)2 359(2)4 203(2)298(2)1858(2)5 690(9)4 959(8)3 629(7)3 562(9)4 861(9)5 236( 16)4 655(20)3 336( 19)3 062(15)4 286( 18)2 496(7)1 874(5)2 600(6)5 064(5)444(5)6 426(6)7 520(6)8 6 18(7)8 230(6)6 895(6)7 678(12)9 006( 12)9 403( 10)8 310(13)7 242(10)-1 538(31)- 938(27)-561(23)- 829(35)phosphite yielded the tetra(ferrocenylmethylsulfany1)tetra-thiafulvalene donor 6 as shown in Scheme 2.The metal complex formation reaction of compound 5 isdepicted in Scheme 3.Treatment of the ketone 5 with sodiumethoxide under nitrogen required more than 15 h of vigorousstirring at room temperature in order to open the ketone ringand generate the disodium salt 7. This intermediate afforded thecorresponding complex 8 on treatment with tetraphenylphos-phonium bromide, followed by addition of exactly half anequivalent of NiC1,*6H2O.Metal complexes of dithioleneligands are known to form anionic and neutral complexes withformal charges of - 2, - 1 and 0.30 In the present study only themonoanionic complex 8 was isolated. With Ni2 + the dianioniccomplex would be expected to form initially, at least, butalthough the reactions were carried out under an inertatmosphere up to the complex-formation stage, the dianionicspecies oxidised spontaneously during work-up. This is notsurprising in view of the fact that dithiolene complexes aresusceptible to oxidation by oxygen.The FAB mass spectrum of complex 8 is shown in Fig. 1 .Dithiolene complexes are known to have low volatility,decomposing near the melting point' and therefore thefragmentation patterns are generally very complex for anythingother than simple dithiolenes.Although the molecular ion peakfor complex 8 of m/z 1158 does not appear in the FAB massspectrum, the correct fragmentation pattern clearly appears,showing molecular ion peaks for three (m/z 988) and two (m/z775) ferrocenyl ligands which are connected to the metaldithiolene core.The structures of all these new air-stable compounds werecharacterised by elemental analysis, NMR and IR spectroscopyand FAB mass spectrometry (see Experimental section).Table 2 Selected bond lengths (A) and angles (")1.98 1 (9)2.01 l(6)2.025(7)2.01 5( 10)2.036(7)2.023(6)2.032(8)2.029(7)2.034( 8)2.048( 6)1.732(6)1.749(6)1.753(6)1.753(6)1.480(8)1.478(7)101.7(3)1 25.7( 7)115.6(4)11644)125.8(5)1 16.9(4)123.4(6)113.6(3)127.5(5)95.9(3)C( 13j-S(2)-C( 14)C(13)-S(4)-C(15)C(2)-C(3t-C( 1 1)C( 13 j-c( 12)-S( 1)S( 1 K( 12)-S(3)C( 12)-C( 13)-S(4)C( 16)-C( 14)-S(2)C( 15')-C( 15)-S(3)C( 17)-C( 16)-C( 14)2.004( 9)2.028(8)2.022(5)2.038(7)2.068( 10)2.023( 8)2.034(6)2.028(8)2.043(8)2.048( 7)1.83 l(6)1.816(5)1.760(6)1.759(5)1.357( 8)1.323(10)98.1(3)126.7(6)124.5(4)1 18.9(4)1 1744)1 1 1.2(4)122.9(6)126.4(5)9533)Geometry of the C5H, rings C-C 1.353(12>-1.427(9), average 1.396C-C-C 1O4.6( 12)-109.9(12), average 108.0.Symmetry transformationused to generate equivalent atoms: I --x + 1, -y, --z .2 1i e34Scheme 1(iv C%CC,OS4I( i ) LiAIH,; (ii) oxalyl chloride; (iii) ~Et,],[Zn(C,S,),]900 J.CHEM. SOC. DALTON TRANS. 1995t e4Scheme 25 768Scheme 3 (i) NaOEt; (ii) (a) [PPhJBr, (b) NiCI2.6H,OCrystal Structure of Compound 6 . 4 r a n g e single crystals ofcompound 6 suitable for X-ray diffraction investigations wereobtained by the technique of dichloromethane-hexane(1 : 2) layering at room temperature. The structure which iscentrosymmetric is shown in Fig. 2. This also illustrates therelative orientations of the ferrocene units with respect to thecentral ttf moiety. The relevant bond lengths and angles aresummarised in Table 2. On comparing the structure to that ofthe extended ttf analogue bis(ethy1enedithio)tetrathiafulvalene(bettf) 31 the presence of the peripheral ferrocene unitslengthens C(12)-C(13) from an average of 1.331 A in bettf tobetlf1.357 8, in 6.The central C==C bond in 6 is shorter by 0.012 8,than that observed in bettf. In each of the ferrocene unitsthe two cyclopentadienyl rings are eclipsed and coplanar. Thecentral ttf unit is planar within 0.063 8, and each ferroceneligand is twisted out of the plane of the ttf core due to thepresence of the CH, linking units. The random orientation ofthe ferrocene units means that there are no intermolecularS S contacts less than twice the van der Waals radius forsulfur of 3.70 A. Although good intermolecular orbital overlapof the sulfur atoms in the solid state is a usual prerequisite forelectrical conduction, the lack of short S S contacts does notnecessarily preclude the possibility that charge-transfer salts of6 will show high room-temperature conductivities. 32NIR Studies on Complex &-Metal dithiolenes display anintense electronic transition in the near-IR region, the originof which was discussed by Mueller-Westerhoff and co-workers.' 7 7 1 He considered the square-planar nickel groupdithiolenes to possess low-lying empty 7c molecular orbitalscomprising various metal and ligand characters. The intenseNIR absorption arises from a transition between the highestoccupied (HOMO) and lowest unoccupied molecular orbital(LUMO) states.The 'ground-state' metal dithiolene is considered to be theneutral pi(edt),] complex with a HOMO - LUMO energygap AE as shown in Fig.3(a). Shifting the HOMO - LUMOrelative energies such that AE decreases is the key toobtaining complexes with absorption at lower energy. Thepresence of electron-withdrawing R groups on the metalbis(dithio1ene) unit leads to stabilisation of the HOMO andLUMO by approximately equal amounts (AE z AEA) [Fig.3(b)] which does not appreciably shift the electronic transition.Electron-donating R groups destabilise the HOMO morethan the LUMO (AE > A&) [Fig. 3(c)], resulting in abathochromic shift of the absorption maximum.There are several important factors which need to beconsidered in any attempt to shift the absorption maximum ofdithiolenes to lower energy: '' (1) the presence of an extended x:system in the molecule; (2) the presence of electron-donatingsubstituents on the molecule; (3) coplanarity of the ligand x:system and the metal dithiolene core.By altering the nature ofthe R groups and the central metal it is possible to synthesisecomplexes which absorb at specific wavelengths, i.e. 'fine-tuning' the absorption maximum. This has many applications,especially in the area of non-linear optics and telecommunic-ations.Compared with the absorption of certain nickel dithiolenecompound^,'^*^^ for example [Ni(edt),] absorbs at 720 nmin h e ~ a n e , ~ ~ the absorption maximum for complex 8, indichloromethane, is at a considerably lower energy and occurJ. CHEM. SOC. DALTON TRANS. 1995 90 123 120142I184O I100 300 500 700 900 1100m /z368 I 1 578 650 tFig. 1 Fast atom bombardment mass spectrum of complex 8; R = ferrocenyl[Ni(ed)d when R = HFig.2 Crystal structure of compound 6at 1250 nm (In E = 9.62) (Fig. 4). This absorption band inmonoanionic dithiolenes is associated with a transition fromthe highest-energy filled IT orbital of the molecular complex,NHOMO (2b, "), to the highest-energy half-filled molecularorbital, HOMO (3b2g).33334 It is of lower energy than might be(b )Fig. 3 Frontier orbitals in metallic dithiolene complexesexpected because there exists no possibility for the ferrocenesto adopt a coplanar configuration with the dithiolene core,suggesting very little interaction between the two moieties. Itwould, however, seem that the electron-donating properties ofthe ferrocene.substituents are able to transmit effectivelythrough the non-conjugated CH, spacer-links resulting in thislarge shift in the NIR region as compared with simple dithiolenesystems. We are presently working on incorporating aconjugated link between the ferrocenes and dithiolene core,thus possibly shifting the NIR absorption maximum towardsthe 1500 nm region, thereby enhancing its potentially usefuloptical properties.Electrochemical Studies.-The electrochemistry of com-pounds 4 and 5 and of the corresponding organic donor 6 wereinvestigated using cyclic voltammetry. The results together withthe corresponding half-wave potentials for ferrocene, ttf andbettf (recorded under the same conditions) are given in Table 3.The ferrocene groups in compounds 4 and 5 have a half-wave potential of + 564 and + 560 mV respectively comparedwith +471 mV for ferrocene.This shift in potential comparedto ferrocene is due to the electron-withdrawing effect of theneighbouring multisulfur ring system in 4 and 5 with n:electrons of the cyclopentadienyl rings able to delocalise intovacant d orbitals of the sulfur atoms.In the related organic donor 6 the electron-donating effect ofthe central ttf moiety upon each ferrocene ligand is negligible.This is evident from 'H NMR studies which show that theferrocenyl signals for compounds 4 and 6 are of similar fieldstrength (see Experimental section). Therefore, in the CV of 6(Fig. 5) the first oxidation peak can be attributed to the process[Fe(q5-C5H5)2] --+ [Fe(q5-C5H,),]+ by comparison tothe half-wave potential for 4.Oxidation of the four ferrocenegroups appears to occur at the same potential, suggesting thatthe CH, spacer units prevent electronic interactions betweenthe ferrocene groups. Based upon the difference between the E+value for the process ttf+ ttf2+ in bettf (+929 mV) and 6(+ 1059 mV), the redox process ttf F+ ttf+ in 6 is expected t902IJ. CHEM. SOC. DALTON TRANS. 1995__c*OI 10c1800 1000 1200 1400 1600UnrnFig. 4 The NIR spectrum of complex 8occur at a similar potential to that of the oxidation of ferrocenegroups. This explains the broadening of the ferrocene-ferrocenium oxidation peak between 600 and 650 mV. Boththe first and second oxidations of the ttf moiety in 6 occur at ahigher potential than for ttf and bettf.This is because theoxidation of ferrocene to ferrocenium in 6 increases the positivecharge on the ferrocene ligands which in turn reduces electrondensity within the central ttf moiety, thus making it moredifficult to oxidise. This high oxidation potential of thecentral ttf moiety in 6 indicates that charge-transfer com-plexation with acceptors such as tetracyanoquinodimethane(tcnq) and partially oxidised salts with inorganic anions maynot occur.ConclusionNew types of molecular materials containing ttf and metaldithiolene units attached to ferrocene ligands have beenprepared and their properties investigated. The chemistry offerrocenes and sulfur-based ligands combined together withinone molecular unit offers a new perspective in the design anddevelopment of materials exhibiting novel electrical conduction,optical and magnetic properties.The design of such materialsshould lead to: (1) the development of third-order NLOmaterials with enhanced responses, due to extensive delocalis-ation, in the 1.3 and 1.5 pm regions; (2) compounds containingseveral magnetic centres with varying degrees of interactiondepending on the nature of the linkage between the ferroceneand dithiolene units; this will result in unusual magneticand electronic properties; (3) applications in molecular sensors;(4) the development of new layered structures containinginteracting magnetic centres capable of forming inclusioncompounds with a variety of molecules.AcknowledgementsWe thank the SERC for funding, the SERC Mass SpectrometryService at Swansea and the SERC WH-400 NMR SpectroscopyService at Warwick University.We acknowledge the assistanceof Dr. Maher Kalaji in the use of electrochemical equipmentand Dr. Callum A. 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ISSN:1477-9226
DOI:10.1039/DT9950000897
出版商:RSC
年代:1995
数据来源: RSC