3139
J. Phys. Chem. 1991, 95, 3139-3148
Hexacyanobutadlene. Molecular and Electronic Structures of [C,(CN),]"
( n = 0, 2-)
Joel S. Miller,* Joseph C. Calabrese, and David A. Dixon* Central Research and Development Department,+ E. I . du Pont de Nemours & Co., Inc., Experimental Station E328, Wilmington, Delaware 19880-0328 (Received: October 4 , I990}
Hexacyanobutadieneand its dianions have been studied by X-ray diffraction. The electronic and vibrational spectra of [Cd(CN)6]" (n = 0,2-)have been determined and compared with the results obtained from ab initio molecular orbital theory. Calculations are reported for n = 0 and for three isomers of the dianion. The crystal and molecular structure of hexacyanobutadiene has been determined by single-crystal X-ray analysis at -100 OC. The pale yellow crystals belong to the orthorhombic PbcZl (no.29) space group [a = 10.138 (2)A,b = 10.256 (2)A,c = 19.862(2)A, V = 1025.4 A3, Z = 4,R = 0.086,R, = 0.080]. The central C - C and pair of C = C bonds are 1.487and 1.307 A, respectively, whereas the C - C N and C=N bonds average 1.448 and 1.124 A, respectively. The molecule is nonplanar with a 140.1' torsion angle about the central C-C bond. The rrans-[n-C,(CN),l2- and [i-C4(CN)6]2-dianions were crystallized as the [Fe(C5Me5)2]'+ salt (2:l). The former 2:l char e-transfer complex crystallizes in either the C ! / m (no. 12) space group [a = 10.010 (5) A,b = 14.677 (4)A,c = 14.825 (7) ,f l = 91.35 (3)', V = 2191.4 A31 or the monoclinic E i / c (no. 14) space group [ a = 10.056 (5) A,b = 14.679 (4) A, c = 14.826 (7)A, /3 = 91.54 (4),V = 2187.7A), Z = 2,R = 0.072,R, = 0.068at -100 "C]. The dianion in the former is disordered but is ordered in the latter. The DShcation is ordered and is essentially structurally equivalent to previously reported cations. The trans-[n-C,(CN),l2- structure possesses C2, local symmetry with the central C = C and pair of C - C bond distances of 1.342 and 1.401 A, respectively. The average C-CN and C s N bond distances are 1.459 and 1.128 A, respectively. The unit cell is comprised of an independent [Fe(C5Me5)2]'+ cation and a half-anion which form parallel D'+A2-D'+D'+A2-D'+... chains which have no unusual intra- or interchain contacts. The intrachain Felll-.Felll separations are 7.18 and 10.63A, and the interchain Felll...Felll distances less than IO A are 8.43,8.75,9.68,and 9.72 A. The latter 2:l char e-transfer complex belongs to the hexagonal R3 (no. 148) space group [a = 14.589 (6)A,c = 18.216 (16)A, V = 3357 Z = 3, R = 0.045,R, = 0.050at -40 'C]. The cation is poorly resolved, and the planar dianion sits on a 3-fold A2-D'+D'+A2-D'+... + chains which have no unusual intraaxis and is disordered. The unit cell is comprised of parallel ...D' or interchain contacts. The intrachain Felll--Felll separations are 7.17 and 11-04A, and the interchain Fe1I1-Fe1I1 distances less than IO A are 8.49 and 9.78 A.
di
...
i3,
Introduction With our discovery of molecular metamagneti~ml-~ in the 1:l T C N Q (TCNQ = 7,7,8,8-tetracyano-p-quinodimethane)salt of decamethylferrocene and the recent observation of bulk ferromagnetic behavior for the TCNE3+ salt (TCNE = tetracyanoethylene) and ferromagnetic coupling for the W C ~ ( C Nsalt3J )~ of decamethylferrocene, we are studying the structure-function relationship of metallocenium salts of strong acceptor anions with particular focus on understanding the microscopic basis for cooperative magnetic phenomena in molecular materials. As part of this effort, we are investigating the electronic structure of polycyano compounds and their anions and dianions and have already reported our work on [C(CN),]-,* [C,(CN),]" (n = 0, 1-, 2-)? and [C3(CN)S]-10as well as [TCNQ]" ( n = 0, 1-, 2-)" and perfluoro-TCNQ, [TCNQF,]" ( n = 0, I-, 2-).12 With our recent discovery of the means to stabilize dianionic acceptors13 which enables the structural and spectroscopic characterization of isolated dianions, we have prepared ([M(CsMe5)z]+)2[C4(CN),]> (M = Fe, Co) and studied its physical properties. We are particularly interested in this dianion as it allows comparison with other percyano anions, and it also provides a closed-shell model compound with which to compare other cyano radical anion complexes and their interactions with radical cations.
Experimental Section I [ C ~ ( C , M e , ) ~ ] + l ~ - t r a n s - [ n - was C ~ (prepared C ~ ~ ] ~ from Co(C5Me5)zand C4(CNI6in an inert atmosphere glovebox. Hexacyanobutadiene was prepared via a modification? of Webster's route.14 Decamethylcobaltocene, prepared from decamethyl(95 mg, 0.289 mmol; cobaltocenium hexafluoroph~sphate~~ Strem), was dissolved in 30 mL of hot acetonitrile (distilled under argon from P2O5 and subsequently CaH,). This solution was added to 29 mg (0.144mmol) of C4(CN)6dissolved in 2 mL of MeCN. After the volume was reduced by half via distillation of the solvent, the solution was cooled to room temperature overnight; 81 mg of the product (65%) was collected by vacuum filtration. 'Contribution No. 5551.
Anal. (Galbraith Labs, Knoxville, T N ) Calcd for C&IaCo2N6: C, 69.59;H, 7.00;N, 9.74. Found: C, 69.57,69.54;H, 6.94;N, 9.90. Infrared spectra (Nujol):)"(Y 2124 (s), 2152 (s), and 2200 (w) cm-'. The unit cell lattice parameters were determined a t room temperature to be a = 14.973 (10) A, b = 14.784 (4) A, c = 10.010 (3) A, /3 = 91.84 (4)O, and V = 2215 A3 and belonging to either the C2,Cm, or C2lm space group. Thus, this complex is isomorphous to the Fell1 analogue (vide infra). [M(C,Me,),]'-trans-[n-C4(CN)61'+ ( M = Fe, Co) salts were prepared as previously reported.? I[Fe(C,Me,),]'+J2-tranr-[n-C4(CN)J2was prepared from decamethylferrocene (1 50 mg, 0.46 mmol) and hexacyanobutadiene (1) Candela, G. A.;Swartzendruber,L. J.; Miller, J. S.;Rice, M. J. J. Am. Chem. Soc. 1979, 101,2755. (2) Miller, J. S.;Epstein, A. J.; Reiff, W. M. Isr. J . Chem. 1987, 27,363. (3) (a) Miller, J. S.; Epstein, A. J.; Reiff, W. M. Chem. Reo. 1988, 88, 201. (b) Miller, J. S.;Epstcin, A. J.; Reiff, W. M. Isr. J. Chem. 1987, 27, 363. Miller, J. S.;Epstein, A. J. NATO Ado. Stud. Ser. B 1988, 168, 159. Miller, J. S.; Epstein, A. J.; Reiff, W. M. Acc. Chem. Res. 1988, 21, 114. Miller, J. S.;Epstein, A. J.; Reiff, W. M. Science 1988, 240, 40. Miller, J. S.;Epstein, A. J. New Aspects oforganic Chemistry;Yoshida, Z., Shiba, T., Ohsiro, Y., Eds.; VCH Publishers: New York, 1989; p 237. (4) Miller, J. S.;Calabrese, J. C.; Epstein. A. J.; Bigelow, R. W.; Zhang, J. H.; Reiff, W. M. J . Chem. Soc., Chem. Commun. 1986, 1026. (5) Miller, J.. S.;Calabrese, J. C.; Rommelman, H.; Chittapeddi, S.; Zhang, J. H.; Reiff, W. H.; Eptein, A. J. J . Am. Chem. Soc. 1987, 109,769. (6) Chttapeddi, S.;Cromack, K. R.; Miller, J. S.; Epstein, A. J. fhys. Rev. Lett. 1987, 58. 2695. (7) Miller, J. S.; Zhang, J. H.; Reiff, W. M. J . Am. Chem. Soc. 1987,109, 4584. (8) Dixon, D. A.; Calabresc, J. C.; Miller, J. S.J . Am. Chem. Soc. 1986, 108,2582. (9) Dixon, D. A.; Miller, J . S. J . Am. Chem. Soc. 1987, 109, 3656. (IO) Dixon, D. A.; Farnham, W. B.; Middleton, W. B.; Roe, D. C.; Davidson, F.; Smart, B. E.; Miller, J. S.J . fhys. Chem. 1988, 92, 2137. (11) Miller, J. S.;Zhang, J. H.; Reiff, W. M.; Dixon, D. A.; Preston, L. D.; Rers, A. H., Jr.; Gebert, E.; Extine. M.; Troup, J.; Epstein, A. J.; Ward, M. D. J . fhys. Chem. 1987,91, 4344. (12) Dixon, D. A.; Calabrese,J. C.; Miller, J. S. J. Phys. Chem. 1989, 93, 2284. (13) Miller, J . S.; Dixon. D. A. Science 1987, 235, 871. (14) Webster, 0. J . Am. Chem. Soc. 1964.86, 2898. (15) Robbins, J. L.; Edelstein, M.; Spenser, B.; Smart, J. C. J. Am. Chem. Soc. 1982, 104, 1882.
0022-3654/91/2095-3139$02.50/0 0 1991 American Chemical Society
3140 The Journal of Physical Chemistry, Vol. 95, No. 8,1991
compound formula formula mass space group a, A b, A
CION6
204. I5 Pra2, (no. 29) 10.138 (2) 10.256 (2) 19.862 (2)
c, A
P, deg v, A' Z p(cak), g cm-3 crystal dimensions, mm temp, OC radiation absorpn coeff, em-' scan mode 24", deg total data measd unique data with (F0),> 3u(F0), final no. of variables weighting scheme refinement method
R,,O Rib largest residue, e diffractometer
Miller et al.
A"
R3 (no. 148) 14.589 (6)
1025.4 4 1.322 0.21 X 0.17 X 0.20 -100 Mo Ka 0.85
P 2 , l c (no. 14) 10.056 (5) 14.679 (5) 14.826 (7) 91.54 (4) 2187.7 2 1.300 0.40 X 0.17 X 0.40 -100 Mo Ka 7.02
w
w
w-e
50.0
48.0 3764 1973 262 unit weights Patterson analysis 0.072 0.068 0.90d CAD4
50.0 3255 939 146 4 F:/ uzF: Patterson analysis 0.045 0.050 0.26 CAD4
1112 483 64 unit weights direct methods 0.086 0.080 0.39< Syntex R 3
18.213 (16)
3357 3 1.27 0.44 X 0.46 X 0.64 -40 Mo K a 6.9
' R = E[lFol - ~ F c ~ ] / ~ ~b RF ,o=~ [Ew[lFol . - lFc1]2/~3wlFo12]1/2. CMidwaybetween C(1) and C(2). dNear Fe(1).
refined anisotropically, and all hydrogen atoms were fixed. One (50 mg, 0.23 mmol) (2:l) as discussed above. Anal. Calcd for of the CsMe5 rings shows large thermal ellipsoids and may be CSoH,#e2N6: C, 70.09; H, 7.06; N, 9.81. Found: C, 69.86; H, partially disordered. Several additional peaks suggest slight 7.19; N, 9.82. Infrared spectra (Nujol): u(*N) 2123 (s), 2151 population of a second orientation of the C4 dianion with additional (s), and 2200 (m) cm-I. peaks near atom C(28). ([Fe(C,Me,),]"~2[i-C4(CN)6]2was prepared from decaA dark violet conical crystal of [Fe(C5Me5)2]2[i-C4(CN)6] was methylferrocenium fl~oroborate~ (I44 mg, 0.348 mmol) and [nused for the structure determination. Data were collected in the Bt~,N]~[i-c,(cN),]'~(120 mg, 0.174 mmol) dissolved in 4 mL usual manner, and the experimental parameters are listed in Table of MeCN. After the volume was reduced to 2 mL and refrigI. From the systematic absences (hkl: -h + k I = 3n 1, eration at -25 OC overnight, the crystalline product separated (60 3n 2) the space group was determined to be R5 (no. 148). As mg, 40%) and was collected by vacuum filtration. Infrared spectra a check on crystal and electronic stability, three representative (Nujol): u(C=N) 2158 (m) and 2174 (s) cm-'. reflections were measured every 30 min. The slope of the X-ray Data Collection and Data Reduction. A pale yellow least-squares line through a plot of intensity versus time data was octahedral crystal of C4(CN), was recrystallized from 1,2-di388 (75) counts/h, which corresponds to a total gain in intensity chloroethane. Data were collected in the usual manner, and the of 18.8%. An anisotropic decay correction was applied with experimental parameters are listed in Table I. There was a 1% correction factors to I ranging from 0.749 to 1.I 65 with an average variation of the intensities of the standard reflections during the value of 0.939. Intensities of equivalent reflections were averaged, data collection. The structure was solved by direct methods and 1166 reflections were rejected from the averaging process (MULTAN) with refinement by full-matrix least squares on F."*'* because their intensities differed significantly from the average. The solution was difficult and required six ambiguities. Because The agreement factors for the averaging of the 1681 observed and of the low data/parameter ratio only an isotropic solution could accepted reflections were 3.9% based on intensity and 3.3% based be employed. on Fo. A black irregular plate crystal of [Fe(CSMe5)2]2-trans-[n-C4(CN),] suitable for data collection was grown from an acetonitrile The structure was solved by using the Patterson heavy-atom method which revealed the position of the Fe atom. The dianion solution. Data were collected in the usual manner at both -100 was placed on a special position at the origin of site symmetry and -155 "C, and no difference in structure was observed; the 3. Thus, there is a 50% disorder of the dianion about this position. data taken at -100 OC are reported herein. Initially several crystals The central carbon atom of the cyanide (C23) groups coincide belonging to the C2/m space group with unit cell constants [a in the two models. The cation is located on a 3-fold axis. This = 10.010 (5) A, b = 14.677 (4) A, c = 14.825 (7) A, 6 = 91.35 special positioning generates three positions for each of the C5 ( 3 ) O , V = 2191.4 AS]identical with those of the monoclinic P2,/c unit cell given in Table 1 were examined; however, the refinement rings which are seen as four unique peaks generating 12 atom sites. Each pair of peaks (C1 and C2; C3 and C4) generates a sixlead to disordered dianions. The phases were obtained by Patmembered ring, using the 3-fold axis. Since both C1 and C2 have terson analysis. The solution required the cations to lie in a general the same intensity, a 50% disorder must also exist such that there position with a tran~-[n-C,(CN),]~-near the center of symmetry. are three corresponding C5 rings generated by also beginning at Hydrogen atoms were idealized from positions obtained by difeach of the C2 positions. If this were not so, then the C1/C2 ference Fourier maps. The coordinates were refined via full-matrix intensity ratio would be 2.0. Since it is 1.0, there must be a 50% anisotropic least squares on F. All non-hydrogen atoms were disorder and thus six equivalent cyclopentadiene positions. This analysis generates the multiplicities of 0.5 for each of the crys(16) Middleton, W. J.; Little, E. L.; Coffman, D. D.; Englehardt, V. A. tallographic C1, C2, C6, and C7 atom positions and 0.33 for the J . Am. Chem. Soc. 1958.80.2795. C3, C4, CS, and C9 atom positions. Hydrogen atoms were not (17) Main, P.; Lessinger, L.; Woolfson, M. M.; Germain, G.; Declarq, J. P. MULTAN, York, England, and Louvain-la-Neuve, Belgium, 1978. included in the calculations. The structure was refined by full( I 8) (a) Cromer, D. T.; Waber, J. T. International Tables /or X-Ray matrix least squares where the function minimized was Zw(lF,I Crystallography; Vol. IV: The Kynoch Press: Birmingham, England, 1974; and the weight w is defined as 4F2/a2(F2). Scattering Table 2.28. (b) Cromer, D. T.; Waber, J. T. International Tables for X-Ray factors were taken from standard tables, and anomalous dispersion Crystallography; Vol. IV; The Kynoch Press: Birmingham, England, 1974; effects were included.Is Table 2.3.1.
+
+
+
Structures of Hexacyanobutadiene n-C4(CN 16 NI'
The Journal of Physical Chemistry, Vol. 95, No. 8, 1991 3141 TABLE 11: Bond Distnnces nnd Bond Angles for [i-C4(CN)$- in I[Fe(C,Ms)d'+ldi-G(CN),lb a
a
N23-C23 N24-C23 C22-C22 C21-C22
U-
1.438(171 C22-C21-C22 C22-C21-C22 C21-C22-C23 C21C22-C23 C23-C22-C23
Bond Distances, 1.244 (6) C22-C23 1.269 (6) C22C23 1.412 (8) Cll-Cl4 1.411 (4) Bond Angles! deg 119.9 (3) N23
