J. MATER. CHEM., 1991, 1(4), 691-697 69 I Synthesis and Characterisation of Crystal Structure of the One-dimensional Salt [(q-C,Me,)Ru(p,q-C,Me,)Ru(q-C,Me,)l +[TCNE]-Dermot O'Hare,*a Jillian Brookesa and David J. Watkinb a Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR, UK Chemical Crystallography Laboratory, 9 Parks Road, Oxford OX1 3PQ UK Charge-transfer salts [(q-Cp*)Ru(p,q-Cp*)Ru(q-Cp*)]+ [anion]-[Cp*=C,Me,; anion =tetracyanoethylene (TCNE, 2), 7,7,8,8-Tetracyano-pquinodimethane (TCNQ, 3), or C3[C(CN)J3(4)] prepared from [(q-Cp*)Ru(p,q-Cp*)Ru(q-Cp*)+ OTf-(1) (OTf-=trifluoromethanesulphonate) and M+[anion]- (M+ = Li+, NBuZ) salts are described. Single- crystal X-ray studies show that 2 crystallises in the trigonal system, in the non-centrosymmetric space group R3m with a=b= 14.432(3)A, c=14.432(3) A, a=B=90", y=120° with hexagonal indexing, V=2603.3 A3, pc= 1.41 g ~m-~, Z=3, R=0.0634 and Rw=0.0715.The unit cell in 2 comprises alternating cations and anions aligned parallel to the crystallographic c axis. The cation has a multidecker structure with parallel Cp* rings and Ru-Cp~,,,,,,,,, distances of 1.826(7), 1.89(8), 1.826(7), and 1.828(9)A. The diamagnetic [(q-Cp*)Ru(p,q-Cp*)Ru(q-Cp*)]+ cation and the S=1/2 [TCNEI-radical anion lie on the crystallographic three-fold symmetry axis and consequently are highly disordered. The disordered anions possess local D2,,symmetry with C-CN, CEN distances of 1.39(3)and 1.10(3)A, respectively. For 2 and 3 the magnetic susceptibility obeys the Curie-Weiss expression x= C/(T-0),with pefland O values of 1.73 pe and 0.07"for 2 and 1.45 pBand -3.7" for 3.Keywords: Charge-transfer salts; Metallocene; Crystal structure; Magnetism; Organometallic complex One-dimensional ( 1-D) charge-transfer complexes have been shown frequently to exhibit unusual optical and electrical properties. In particular, several organometallic charge- 9' transfer complexes containing alternating donor/acceptor lin- ear chains have been reported to exhibit co-operative magnetic properties3 For example, metarnagnetic behaviour (i.e. field-dependent switching from an antiferromagnetic ground state to a high moment state) has been observed for the 1-D phase +[Fe(Cp*),] [TCNQ] -.4 However, the tetracyanoethylenide and hexacyanobutadienide salts of Fe(Cp*), have been shown to exhibit ferromagnetic behaviour.' The former charge-trans- fer complex possesses a spontaneous magnetic moment at zero applied magnetic field.In the future, the design and synthesis of low-dimensional molecular organic, inorganic and organometallic solids with desirable electronic and/or magnetic properties will require an understanding of the factors that affect the formation of structural phases, coupled with elucidation of the structure- function relationships in these materials. Approaches to controlling solid-state architecture have been illustrated by the covalently linked metallophthalocyanine rings in polymeric-Si(Pc)O,-, (Pc=phthalocyanine), which upon doping exhibits metallic conductivity due to n-overlap of the Pc rings.6 Recently, Fagan et elegantly demon- ~1.~7~ strated the use of polycations based on [Ru( q-Cp*)( q-arene)] + complexes to control molecular architecture.Here, we report results of our investigations of the synthesis, structure and physical characterisation of charge-transfer salts derived from the multidecker 'cylinder-like' monocation +[( q-Cp*)Ru(p,q-Cp*)Ru( q-Cp*)] with the planar organic acceptors [TCNE] -, [TCNQl- and C3[C(CN)2];: Experimental General The reactions were carried out in an inert atmosphere of nitrogen by the use of vacuum line or inert atmosphere dry box. Solvents were rigorously dried under a continuous stream of nitrogen. THF and diethyl ether were refluxed over sodium/ potassium alloy, and DME was refluxed over potassium metal.Dichloromethane was dried by refluxing over P205, and nitromethane and acetonitrile by refluxing over CaH,. Solvents were distilled prior to use and were stored over molecular sieves in flame-dried ampoules under nitrogen. Equipment Infrared spectra were recorded on a Mattison Instruments Polaris Fourier Transform spectrometer as mulls in Nujol between KBr plates. UV-VIS spectra were recorded on a Perkin-Elmer Model 330 spectrophotometer. The samples were made up under nitrogen in CH2C12 or THF using an air-tight cell. Electron paramagnetic resonance spectra were obtained using the X-band of a Bruker ESP-300 spectrometer. The samples were made up under nitrogen and run in 4mm high-purity Spectosil quartz tubes fitted with a Young's Teflon stopcock.The solutions were made up in CH2C12 or THF. The magnetic susceptibility data were collected over the range 2-325 K by using a high-sensitivity computer-interfaced Faraday balance, which is described in detail elsewhere.8 The susceptibilities were corrected for the intrinsic diamagnetism of the sample container and the diamagnetism of the electronic cores of the constituent atoms (zdia=410 x lop6 emu mol-' for 2 and 448 xIO-~emu mol-' for 3). Elemental microanalyses were performed by the Analytical Services of the Inorganic Chemistry Laboratory. Synthesis of [Cp*RuCI2lx The compound [Cp*RuC121x was prepared by scaling-up the following literature procedure of Tilley et a1.' RuC1, *3H20 (20.00g) was dissolved in 400cm3 of CH30H and filtered into a flask containing 30 cm Cp*H; the mixture was refluxed for 3 h under N2.The volume was reduced to 350 cm3 under reduced pressure, the crystalline dark precipitate was isolated by filtration, washed with methanol and hexane, and dried under high vacuum, yield 21.1 g (91%). Typically 5-10% of Ru(Cp*), was also isolated as a side-product of the reaction from the hexane washings. Synthesis of [Cp*Ru(p,-Cl)], A 300cm3 round-bottomed flask was charged with log (66.0 mmol) of [Cp*RuC12], and 100 cm3 THF. Lithium triethylborohydride (33 cm3; 1 mol dm-3) in THF (33.0 mmol) was added with stirring. The reaction mixture turned a dark blue-green initially during the addition, and gas evolution was observed (CARE).After 45 min the crystalline orange precipitate which formed was isolated by filtration and rinsed twice with small amounts (ca.5 cm3) of THF. The orange precipitate was then dried in uacuo to yield 7.1 g of [Cp* Ru(~ 3-C1)]4 (79 YO). Synthesis of [Cp*Ru(MeCN),] OTf-+ A 300 cm3 round-bottomed flask was charged with [Cp*Ru(p3-C1)I4 (1 5 g, 13.8 mmol) and acetonitrile (100 cm3). The mixture was refluxed for 1 h and then allowed to cool to room temperature. To the stirred mixture was added 14.25 g (55.2 mmol) of silver trifluoromethanesulphonate (Ag+ OTf-) whereupon a white precipitate of AgCl formed. After 1 h of stirring, the solution was filtered, and the solvent was removed under reduced pressure. Diethyl ether (100 cm3) was added to the residue, and the orange-yellow crystalline solid was collected by filtration, washed twice with 20cm3 portions of diethyl ether and dried in uacuo to yield 26.7 g of [cp*R~(MecN)~]+ OTf- (95%).Synthesis of [(Cp*)Ru(p,q-Cp*)Ru( q-Cp*)] +OTf -(1) A small Schlenk tube (ca. 100cm3) was charged with [Ru( q-C,Me,)(MeCN),]OTf (1.42 g, 2.8 mmol), R~(q-c,Me,)~ (1.06 g, 2.85 mmol) and nitromethane (ca. 30 cm3), and the mixture was held at reflux for 11 h. The solvent was evaporated under reduced pressure and the dark-brown resi- due was washed with diethyl ether to remove any unreacted decamethylruthenocene. The residue was dissolved in acetone, and chromatographed on an alumina column made up with light petroleum (b.p.40-60 "C) and eluted with acetone. A yellow-orange band was collected and the solvent was removed in uacuo to give an orange powder. Recrystallisation from ethanol at -20 "C formed 0.53 g of orange-yellow +cry st als of [( q-C, Me ,)Ru(p,q-C ,Me,)Ru( q-C ,Me,)I OTf-(25%). The reaction was sensitive to the length of reflux and 11 h gave the optimum yield. Refluxing for 9 h gave a yield of 21% and 21 h gave a low yield of 12%. After it had been refluxed for several days the product decomposed to give decamethylruthenocene (confirmed by NMR spectroscopy) and a brown-black tarry residue. (Found: C, 49.3; H, 6.2. Calc. for C, 49.2; H, 6.0%); A,,, (CH2C12) 232,284,368 and 408 nm; JH(solvent CD2C12, standard TMS, 300 MHz) 1.55 (s, q-C,Me,) and 2.16 (s, p,q-CSMe5).Preparation of [(q-C,Me,)Ru(p,q-C,Me,)Ru( q-C,Me,)] + [TCNEI-(2) A solution of [( q-CSMe,)Ru(p,q-CSMe,)Ru(q-C,Me,)]OTf (0.050 g, 0.066 mmol) in MeCN (ca. 1 cm3) was added drop- J. MATER. CHEM., 1991, VOL. 1 wise to a solution of Li+[TCNE]- (0.009 g, 0.67 mmol) in MeCN (ca. 3 cm3). After slow cooling to -20 "C overnight orange needle-shaped crystals were obtained in a quantitative yield. Orange crystals suitable for X-ray crystal-structure studies were obtained after 2 weeks from a three-compartment H-diffusion cell set-up using [( q-CSMe,)Ru(p,q-CSMe,)Ru(q-C,Me,)]OTf (0.030 g, 0.040 mmol) and Li+[TCNE]-(0.006 g, 0.044 mmol) in THF.(Found: N, 7.6; C, 59.0; H, 6.3. Calc. for Ru~C~~H~~N~: vmax (NujolN, 7.6; C, 59.0; H, 6.1YO); mull) 2181 (C=N), 2142 (C-N)cm-'; A,,, (CH2C12) 231, 282 and 418 nm; EPR, solid-state single isotropic resonance, g= 2.0068 with AHpp=5.0 G at 298 K, solution (THF) nine line multiplet, g= 2.0063, aN=1.61 G. Synthesis of [(q-C,Me,)Ru(p,q-C,Me,)Ru( q-C,Me,)] + CTCNQl-(3) To a concentrated solution of [( q-C,Me,)Ru(p,q-C,Me,)Ru( q-C,Me,)]OTf (0.030 g, 0.040 mmol) in DME (ca. 6 cm3) was added a solution of "But] [TCNQ] -(0.018 g,+ 0.040 mmol) in DME (ca. 4 cm3). A green precipitate formed immediately which was washed with diethyl ether (2 x 10 cm3) and dried in uacuo. Recrystallisation from THF-diethyl ether (1 : 1) at -20 "C gave large green needles.(Found: N, 6.9; C, 62.2; H, 6.4. Calc. for Ru~C~~H~~N~: N, 6.9; C, 62.1; H, 6.1 %); v,,, (Nujol mull) 2177 (C-N), 2152 (C-N) cm-'. A,,, (THF) 230, 284, 425, 686, 750 and 849 nm; EPR, solid-state single isotropic resonance, g =2.0066, solution (THF) 45 line mul- tiplet observed, g =2.0064, aN= 1.0 G, aH= l .4 G. Preparation of [(q-C,Me,)Ru(p,q-C,Me,)Ru( q-C,Me,)] + cc6(cN)61-(4) Addition of a concentrated solution of [( q-C5Me5)Ru(p,q-C,Me,)Ru( q-C,Me,)]OTf (0.030 g, 0.040 mmol) in DME (ca. 6 cm3) to a concentrated solution of "But] +C,(CN); (0.019 g, 0.040 mmol) in DME (ca. 2 cm3) immediately pro- duced a deep-blue precipitate. The precipitate was washed with diethyl ether and recrystallised from a mixture of CH2C12 and diethyl ether at -80 "C to form blue microcrystals.(Found: N, 9.9; C, 60.3; H, 5.4. Calc. for Ru2C42H45N6: N, 10.05; C, 60.34; H, 5.34%); v,,, (Nujol mull) 2207 (CEN), 2193 (C=N) cm-'; Amax (THF) 232,283,323,410,600,674 nm; EPR solid-state single isotropic resonance, g =2.0059, solution (THF) 13 line multiplet, g=2.0057, ~'~~=0.88G. Crystal-structure Determination Crystals of [( q-C,Me,)Ru(p,q-CSMe,)Ru( q-C,Me,)]+ [TCNEl-were sealed under nitrogen in Lindemann glass capillaries. All calculations were performed on a VAX 11/750 computer in the Chemical Crystallography Laboratory using the Oxford CRYSTALS system" and plotted using the CHEMX package.' Crystal Data. C3,H4,N4Ru2, M =735.92, trigonal, a =b = 14.432(3)A, c= 14.432(3)A, V=2603.3 Pi3 (by least-squares refinement on diffractometer angles of 25 accurately centred reflections), A =0.7 1069 A, space group R3m, 2=3, pc= 1.41 g cm- '.Orange, air-sensitive tablets. Crystal dimensions 0.88 mm x 0.64 mm x 0.32 mm, p(Mo-Kor)= 8.81 cm-', F(000)= 1131. Data Collection and Processing. CAD4 diffractometer, 0-28 mode, scan width = 1.OO +0.35 tan 8, scan speed 1 .O-6.6" min-',graphite-monochromated Mo-Kor radiation; a total of J. MATER. CHEM., 1991, VOL. 1 41 78 reflections were measured in the range (1 .OOo 68<2Y), including those absent due to the R centring in the index ranges -1 <h<17, -17<k<17, -1 <l<17 (more than the minimum requirement due to the initial space-group uncer- tainties).After merging in R3m this yields 585 unique reflec- tions (Sheldrick merging R =0.018 after absorption correction), giving 489 with I >341). This corresponds to a very complete set of data, with 120 out of the 120 possible reflections being measured in Sheldricks 'critical resolution' range of 1.1-1.2 A, with 100 at I>3o(I). Linear and approx. isotropic crystal decays, ca. 2%, corrected during processing; correction for Lorentz and polarisation effects.12 The authors were very surprised by the curious coincidences in the cell parameters. The hexagonal cell as reported with a =b -C-was subjected to intensive investigation. 41 78 reflections were measured when only ca. 600 reflections were in the final asymmetric region of reciprocal space; in addition, selected reflections were remeasured from all their potentially equival- ent positions. Structure Analysis and Refznement.Direct methods (Ru atoms) were followed by normal heavy-atom procedures. The crystal- lographic disorder of the structure resulted in an extremely low ratio of observations to refined parameters. To achieve an acceptable refinement of the structure, 145 non-crystallo- graphic chemical restraint^'^ were included in the least-squares refinement. These restraints took the form of equival- encing the internal bond lengths and angles of each of the Cp* ligands to their arithmetic mean. In addition, some slack chemical restraints were also applied to the [TCNE] -anion. Full-matrix least-squares refinement of 108 independent par- ameters with anisotropic thermal parameters for Ru( l), Ru(2) and the atoms comprising the [TCNEI- anion plus the 145 observations of restraint gave a final agreement R and R, of 0.0634 and 0,0715 and an observation to parameter ratio of 5.9 : I.We also note that, although the crystallographic mirror symmetry reduces the number of unique atoms defining the structure, the carbon atoms of the Cp* rings which lie on the mirror plane [C(l), C(4), C(7), C(lO), C(13), and C(16)] exhibit very large isotropic thermal parameters. However, refinement of the structure in the lower symmetry space group R3 gave a significantly less satisfactory refinement. Hydrogens were placed in calculated positions (C-H =0.95 A) and allowed to ride on their attached C atoms with one, overall refined Uiso[=0.2l(6) A2].Corrections for anomalous dispersion, and isotropic e~tinction'~ were made in the final cycles of refine- ment; a four-term Chebysev weighting scheme15 was applied with coefficients 3.23, 17.04, -1.27, and 4.25. Final residual electron density <0.91 e A-3. Atomic scattering factors and anomalous dispersion coefficients were taken from ref. 16. Results and Discussion The ability of Cp'M+ (Cp'=q-C5HS or q-C5Me,; M=Fe, Ru) moieties to form adducts with aromatic ligands has been known for some time.17 Recently, it has also been reported that these fragments may complex to the cyclopentadienyl ligands of simple metallocenes,18 and so we speculated that this may be a useful reaction to prepare 'cylinder-like' cations.Synthesis of [( q-Cp*)Ru(p,qCp*)Ru( q-Cp*)] [TCNE] (2) The multidecker 'cylinder-like' cation [( q-Cp*)Ru(p,q-Cp*)Ru( q-Cp*)] +OTf- (1) can be conveniently prepared in 25% yield by refluxing [Ru( q-Cp*)(MeCN)3]+OTf- (OTf- = trifluoromethanesulphonate) with an equimolar amount of Ru(Cp*), in CH3N02. Addition of a solution of 1 to an equimolar solution of Li+TCNE- in MeCN gave a green solution, which on slow cooling to -20 "Covernight gave orange needle crystals of [( q-Cp*)Ru(p,q-Cp*)Ru(q-Cp*)] [TCNE] (2). The orange crystals have been characterised by elemental microanalysis, infrared, UV-VIS, and EPR spectroscopy, magnetic susceptibility measurements, and a single-crystal X-ray structure determination.Crystal-structure determination Crystals suitable for X-ray structure determination were obtained by slow diffusion of solutions of 1and Li+[TCNE]- in THF for 2 weeks. Compound 2 crystallises in the trigonal non-centrosymmetric crystal system with space group R3m. The hexagonal cell as reported has a curious coincidence of the three cell parameters (see Experimental); we can see no way to make use of this extra symmetry they may imply in addition to the evident symmetry. The molecular structure is shown in Fig. 1, and selected bond distances and angles are given in Tables 1 and 2.7 The positional parameters are given in Table 3. The elemental analysis, infrared, and EPR spec- troscopy, and magnetic susceptibility measurements are in agreement with the X-ray analysis. The asymmetric unit consists of one cation and one anion, in which the metal atoms of the [(q-Cp*)Ru(p,q-Cp*)Ru(q-Cp*)]+ cation lie on the special positions (0, 0, z) and (0, 0, z').Consequently, both the crystallographic three-fold rotation axis and mirror plane pass through the ruthenium atoms, the ring centroids of the cyclopentadienyl rings, and the plane containing the [TCNE-J- anion. Thus, the three q-C,Me, rings and the [TCNE] -ion exhibit three-fold disorder. The least-squares plane containing the [TCNE] -anion was very poorly resolved; however, we were able to model the observed electron density by using a model consisting of three overlap- ping TCNE moieties as shown in Fig.2. Centrosymmetric t Supplementary data available from the Cambridge Crystallo- graphic Data Centre: see Information for Authors, J. Mater. Chem., 1991, Issue 1. Fig. 1 Molecular structure of 2, showing the atomic labelling scheme. Atoms suffixed by B were generated by the crystallographic symmetry operator (-x+y, y, 2). Atoms suffixed by C were generated by the crystallographic symmetry operator (x, y -x, 2). Atoms suffixed by D were generated by the crystallographic symmetry operator (-Y, X-Y, 4 J. MATER. CHEM., 1991, VOL. I Table 1 Selected intramolecular distances for 2 (R3 and R3m) and space groups containing two-fold axes ~~ (R32) were rejected because they introduced unnecessaryatoms distance/8i atoms distance/A disorder in the TCNE group.The large Uequivof atoms C(7), Ru( 1)-C( 1) 2.2 17(6) C(2)-C(5) 1.56(2) C(1), and C(13), which lie in the mirror plane already reflect Ru(1)-C(2) 2.223(4) C(3)-C(36) 1.450(6) the extensive disorder. Ru( 1)-C(3) 2.233(5) C(3)-C(6) 1.59( 1) In view of the extensive disorder in the structure determi- Ru( 1)- C(7) 2.19q4) C(7)-C(8) 1.432(4) nation and the relatively small number of unique observations Ru( 1)- C( 8) 2.19 l(3) C( 7)- C( 10) 1.58(3) a number of non-crystallographic restraints13 were imposed Ru(1)- C( 9) 2.193(3) C(8)-C(9) 1.433(6) on the internal geometry of the Cp* and TCNE moieties in Ru(2)-C( 1) 2.198(6) C(9)-C(9C) 1.427(7) order to achieve a satisfactory refinement. Consequentially it Ru(2)-C(2) 2.202(4) C(8)-C(11) 1.58(2) Ru(2)-C( 3) 2.208(5) C(9)-C( 12) 1.59(2) would not be appropriate to discuss in detail any of these Ru(2)- C( 13) 2.206(4) C( 13)- C( 14) 1.353(4) dimensions; however, we can conclude that the observed mean Ru(2)-C( 14) 2.208( 3) C( 13)- C(16) 1.57(3) distances and angles are in close agreement with other crystal- Ru(2)- C( 1 5) 2.2 1 O( 3) C( 14)- C( 1 5) 1.353(6) lographically determined structures containing either q-Cp* N( 1)-C(2 1) 1.IO(3) C( 15)-C( 1 5B) 1.349(7) ligands" or [TCNE] -anions.20N(2)-C(20) 1.1 3(4) C( 14)-C( 17) 1.58(2) The X-ray structure confirms the triple-decker structure for N(2)-C(2 1) 1.28(2) C( 15)- C( 18) 1.60(2) C( I)-C(2) 1.45 l(4) C(19)- C(20) 1.37(3) the cation.Other crystallographically characterised multi- C(1)-C(4) 1.56( 3) C(20)- C(2 1) 1.39(3) decker sandwich complexes containing q-C5H, or q-C,Me, C(2)-C(3) 1.453(5) rings include [( q-Cp)Ni(p,q-Cp)Ni( q-Cp)] 'BF, 21 and [( q-Cp*)Ru(p,q-Cp*)Ru( q-Cp)] PF6+.18The Ru-C distances+ E.s.d.s are given in parentheses.in 2 range from 2.192(3) to 2.221(4)A and agree well with those found for [( q-Cp*)Ru(p,q-Cp*)Ru( q-Cp)] +PF, (2.11-Table 2 Selected intramolecular angles for 2 atoms angle (") atoms angle (") C(4)-C( 1) -C(2) 125.999(7) C( 1 7)- C( 14)-C(13) 125.999(6) c(3)-c(2) -C( 1) 108.000(9) C( 17)-C( 14)-C( 15) 125.999(7) C(5)-C(2)-C(1) 126.00( 1) C( 1 8)-C( 15)-C( 14) 125.998(6) C(5)-C(2)-C(3) 126.00( 1) C( 1 9)-C(20) -N( 2) 179.6(5) C( 6)- C( 3)- C(2) 126.00( 1) C( 2 1)-C( 20) -N(2) 60.00( 4) C(10)-C( 7)- C(8) 125.998(8) C(21)-C(20)-C( 19) 120.00(4) C( 9) -C(8)-C(7) 108.00(1) C( 2 1)-C( 20) -C( 20E) 120.00(7) C(l l)-C(8)-C(7) 126.0q2) N(2)-C(21)-N( 1) 130.0(22) C(1I)-C(8)-C(9) 126.0q2) C(20)-C(2 1)- N( 1) 1794 10) C( 12) -C(9)- C( 8) 126.Oq2) C(20)-C( 2 1)-N(2) 49.6(20) C( 16)- C( 1 3)- C( 14) 125.998(5) C(21)-N(2)-C(20) 70.4(20) C( 1 5)-C( 14)- C( 1 3) 108.002(7) ~ ~~ E.s.d.s are given in parentheses.Table 3 Fractional atomic coordinates, isotropic thermal parameters or equivalent isotropic parametef, and crystallographic site occupancies for 2 atom X Y Z U(equiv.)/U(iso) crystallographic site occupancy 0.0000 0.0000 0.068 l(2) 0.0459 0.1667 0.0000 0.0000 0.3229(2) 0.0504 0.1667 -0.044(2) 0.2 lO(3) 0.6924(4) 0.1456 0.3334 0.1OO(2) 0.200(4) 0.6925(5) 0.4143 0.3334 -0.0978(6) -0.0489(3) 0.1963(4) 0.2( 1) 0.1667 -0.0295(6) 0.0666( 3) 0.1964(3) 0.037(7) 0.3334 0.08 lO(6) 0.0908(3) 0.1966(3) 0.024(4) 0.3334 -0.223(2) -0.1 11( 1) 0.1957(6) 0.1 q3) 0.1667 -0.068 l(7) 0.150( 1) 0.1964(4) 0.08(1) 0.3334 0.184( 1) 0.207( 1) 0.1972(4) 0.032(6) 0.3334 -0.0846(8) -0.0423(4) -0.0648(4) 0.5(3) 0.1667 -0.0176(7) 0.0715(4) -0.0598(3) 0.03(2) 0.3337 0.091 l(7) 0.095 l(4) -0.0519(4) 0.016(5) 0.3337 -0.21 l(2) -0.105(1) -0.0731(6) 0.20(6) 0.I667 -0.0565(8) 0.156( 1) -0.0625(4) 0.09(2) 0.3334 0.194(1) 0.21 l(1) -0.0456(4) 0.044(7) 0.3334 0.045 l(4) 0.0901(8) 0.4544(4) 0.17(6) 0.1667 -0.0626(4) 0.0265( 7) 0.4538(3) 0.033(7) 0.3337 -0.085 l(4) -0.0764(7) 0.4528(3) 0.08(2) 0.3337 0.108( 1) 0.2 1 6( 2) 0.4544(6) 0.09(2) 0.1667 -0.147( 1) 0.0656(8) 0.4539(4) 0.08(2) 0.3337 -0.202(1) -0.180( 1) 0.453 l(4) 0.047(7) 0.3337 0.0000 0.0000 0.6956( 6) 0.1789 0.1667 0.055( 1) 0.1 lO(3) 0.6942(4) 0.23 16 0.5000 -0.00 l(2) 0.166( 3) 0.6929(4) 0.1340 0.3337 U(equiv.)= 1/3[U(ll)+ U(22)+ U(33)].J. MATER. CHEM., 1991, VOL. 1 .. NA N Fig. 2 (a) Observed molecular structure of the TCNE anion, showing the full crystallogaphic disorder. Atoms suffixed by B were generated by one of the crystallographic mirror symmetry operators. Atoms suffixed by C, D, E, or F were generated by one of the crystallographic three-fold symmetry operators. (Note some atoms possess more than one label since they can be generated by several symmetry operators.) (b)The observed electron density can be modelled by three overlap- ping TCNE groups 2.26 A).The pentamethylcyclopentadienylrings (A, B, C) are almost parallel with angles between the normals to the least- squares planes A/B, A/C, and B/C equal to 4.73, 4.61 and 0.4", respectively. The Ru-Ru separation is 3.677(1) A. The distances of Ru(1) and Ru(2) to the ring centroids of the terminal q-C5Me5 rings are 1.826(7) and 1.89(8) A, respect-ively, which are within experimental error equal to the dis- tances of the Ru(1) and Ru(2) to the bridging q-C5Me5 ring of 1.826(7) and 1.828(9) A, respectively. This compares to a mean value of 1.917 A quoted by Orpen et al. for the Ru- Cpgentroid)distance for all crystallographically characterised ruthenium complexes containing Cp* ligands.However, we were particularly interested in determining the three-dimensional arrangement of the cations and anions in the solid state. Selected packing diagrams are shown in Figs. 3, and 4. The solid-state structure consists of 1-D stacks of alternating [( q-Cp*)Ru(p,q-Cp*)Ru( q-Cp*)] cations (D') + and [TCNEI- anions (A-) i.e. ... A-*D'*A-*D+*A-.... The 1-D stacks are orientated parallel to the principle three- fold symmetry axis of the trigonal crystal system. Adjacent stacks are out of registry and have an interchain separation of 8.33(2)A (Fig. 3). 3.514Ai kG-A Fig. 3 Packing diagram for 2 viewed perpendicular to the c axis Fig. 4 Packing diagram for 2 viewed along the c axis The 3-D arrangement of the cations and anions is similar to the stacking motif observed for the molecular ferromagnet [Fe( q-Cp*),][TCNE] *MeCN22 which has a 1-D structure with alternating [Fe( q-Cp*),] radical cations and [TCNE] -+ radical anion in a ...D'A-D'A-D'A-... motif. The unit cell of [Fe( q-Cpf)2][TCNE] MeCN contains two pairs of chains; an out-of-registry pair separated by 8.23 A, and a pair of in-registry chains separated by 8.73 A. Infrared Spectroscopy Infrared spectroscopy has proven a useful tool to elucidate the degree of charge transfer for complexes containing polycy- ano electron acceptors.20 The v(C-N) stretching frequencies for a series of charge-transfer salts containing [TCNE]"- anions are given in Table 4.The infrared spectrum of 2 as a Nujol mull exhibits, inter ah, peaks at 2181 and 2142 cm-' assignable to v(C=N) stretches, which strongly indicates that solid 2 contains the [TCNE] -radical monoanion. U V-VIS Spectroscopy The UV-VIS spectrum of a solution of 2 in CH2C1, exhibits the absorbances characteristic of 1 at 282 and 231 nm. In addition, the spectrum contains an absorbance at 418nm with additional fine structure. This absorbance can be assigned to an internal (n)2(n*)' +( n)'( n*)' transition in the [TCNE] -radical anion.,' The spacing of the fine structure (ca. 520 cm-') is consistent with a vibrational transition. The vibration spectrum of the [TCNEI- anion contains an aB transition at 532 cm-' which can be assigned to this mode.EPR Spectroscopy The EPR spectrum of a single crystal of 2 exhibits a single isotropic resonance with a g-value equal to 2.0068. The line Table 4 Infrared vibrational transitions observed for v(C=N) in [TCNE]"- salts compound v(C =N)/cm- ref. TCNE TCNE- 2221, 2259 2144,2183 23 20 TCNE2- 2069,2104 20 (TCNE); - 2159, 2170, 2189 24 CRU2(CP*)31 CTCNEI(2) 2142,2181 this work width at half height (AH,,)=5.0 G at 298 K. The isotropic nature of the signal together with a g-value close to the 'free electron' value is consistent with a signal derived from the [TCNE] -radical anion. The temperature dependence of the integrated signal intensity obeys the Curie law IccC/T expected for magnetically isolated radicals.Solutions of 2 in THF exhibit nine lines EPR spectrum with g-value of 2.0063. The hyperfine splitting (aN)= 1.61 G arises from coupling of the unpaired electron with the four equivalent I4N [I(I4N)= 13 nuclei. Magnetic Susceptibility Measurements Faraday balance magnetic susceptibility measurements in the temperature range 2-300 K indicate that 2 obeys the Curie- Weiss law, 2-'=C/(T-0), with 8 =0.07 "C and an effective moment of 1.71 pB (Fig. 5). The magnitude of the observed paramagnetism indicates that the [TCNE] -S = 1/2 radical anion is the sole contributor to the observed moment. We can therefore conclude that the diamagnetic cations are acting as magnetic insulators preventing co-operative magnetic inter- actions between the unpaired spins on neighbouring anions.Synthesis of [(q-Cp*)Ru(p,q-Cp*)Ru( q-Cp*)] [TCNQ] (3) Addition of a solution of 1 in dimethoxyethane (DME) to an equimolar solution of [NBuz] +[TCNQ] -in DME instantly gave a green precipitate. The green precipitate was recrystal- lised from THF as green needle-shaped crystals of [(q-Cp*)Ru(p,q-Cp*)Ru( q-Cp*)] [TCNQ] -(3).It was not poss- +-ible to grow crystals suitable for an X-ray structure determi- nation, although a wide range of common solvents and crystal growing techniques were used. The green needles have been characterised by elemental microanalysis, infrared, UV-VIS, and EPR spectroscopy, and magnetic susceptibility measurements. Infrared Spectroscopy The v(C=N) stretch frequencies for a series of charge-transfer salts containing [TCNQ]"- anions are given in Table 5.The infrared spectrum of 3 as a Nujol mull exhibits, inter alia, peaks at 2178 and 2152 cm-' assignable to v(C=N) stretches, which strongly indicates that the solid 3 contains the [TCNQ] -radical monoanion. 5 1200 E 1000 600 400 200 0 0 50 100 J. MATER. CHEM., 1991, VOL. I Table 5 Infrared vibrational transitions observed for v(C-N) in [TCNQ3" -salts compound v( C=N)/cm -ref. TCNQ 2222, 2226 25 TCNQ-2153, 2179 26 TCNQ2-2105, 2150 26 CCPWzl CTCNQI(3) 2178, 2152 this work EPR Spectroscopy The EPR spectrum of a crystal of 3 exhibits a single isotropic resonance with a g-value equal to 2.0066 and AH,, =20 G at 298 K.The isotropic nature of the signal together with a g-value close to the 'free electron' value is consistent with a signal derived from the [TCNQ] -radical anion. Solutions of 3 in THF exhibit a 45 line EPR spectrum with a g-value of 2.0064. The hyperfine splitting (a") =1.O G and aH = 1.4 G arises from coupling of the unpaired electron with the four equivalent I4N nuclei and four equivalent 'H nuclei. A full simulation of the spectrum has been performed previo~sly.~~ Magnetic Susceptibility Measurements Faraday balance magnetic susceptibility measurements in the temperature range 2-300 K indicate that 3 obeys the Curie- Weiss law, x-'=C/(T-0),with 8= -3.7 "C and an effective moment of 1.46 pB (Fig. 5). The observed paramagnetism indicates that the [TCNQl- S= 1/2 radical anion is the sole contributor to the observed moment.The observed effective magnetic moment is significantly less than expected for one unpaired electron using the spin-only formalism. The origin of this disagreement is unknown in view of the lack of structural characterisation. Synthesis of [( q-Cp*)Ru(p,q-Cp*)Ru( q-Cp*)] [C3{ C(CN),),] (4) Addition of a solution of 1 in DME to an equimolar solution of [NBu~]+[C,{C,(CN),),]- 28 also in DME gave an in-stantaneous blue precipitate. The blue precipitate was recrystallised from a mixture of CHzC12 and diethyl ether giving blue microcrystals of [( q-Cp*)Ru(p,q-Cp*)Ru(q-Cp*)][C,{C(CN),),] (4). It was not possible to grow crystals 150 200 250 300 TIK Fig. 5 Plot of inverse molar susceptibility (x-') us.T for 2 (A) and for 3 (B) J. MATER. CHEM., 1991, VOL. 1 suitable for X-ray structure determination despite using a wide range of common solvents and crystal-growth techniques. The blue needles were characterised by elemental microanal- ysis, infrared, UV-VIS and EPR spectroscopy. Infrared Spectroscopy The infrared spectrum of 4 as a Nujol mull exhibits, inter ah, peaks at 2207 and 2194 cm-' assignable to v(C=N) stretches, which agree closely with the v(C=N) stretches +observed for [NBu;] [C,(C,(CN),},] -at 22 10 and 2196 ~m-'.~' EPR Spectroscopy The EPR spectrum of a crystal of 4 exhibits a single isotropic resonance with a g-value equal to 2.0059 and AH,,=20 G at 298 K.The calculated g-value is in close agreement with the value previously reported for the [C,(C,(CN),>,] -radical anion.28 Solutions of 4 in THF exhibit a 13 lines EPR spectrum with g-value of 2.0057. The hyperfine splitting (a") = 0.88 G arises from coupling of the unpaired electron with the six equivalent 14N nuclei. Conclusions Charge-transfer salts containing the 'cylinder-like' cation [( q-Cp*)Ru(p,q-Cp*)Ru( q-Cp*)] have been prepared containing + the planar organic radicals TCNE, TCNQ, and C,{C,(CN),},. The X-ray structure determination of the [TCNE] -salt indicates that using cations of this type we can achieve 1-D stacking in an analogous fashion to the molecular ferromagnet [Fe(Cp*),] + [TCNE] -.Unfortunately, these materials do not exhibit co-operative magnetic interactions. However, further research is in progress to synthesise paramagnetic multidecker cations. We would like to thank SERC and The Nuffield Foundation for financial support. We also thank S. McLean, CR&D, E.I. duPont, U.S.A. for conducting the Faraday magnetic suscepti- bility experiments. References Synthesis and Properties of Low Dimensional Materials, Ann. N.Y. Acad. Sci., ed. J. S. Miller and A. J. Epstein, 1978, 313, and refeences therein. Extended Linear Chain Compounds, ed. J. S. Miller, Plenum Press, 1982, vol. 2. 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