666 Organometallics 1995, 14, 666-675

Nickel(IV) Bis( (3)-1,2=dicarbollide) as an Acceptor Molecule in the Synthesis of Electrically Conducting

Charge Transfer Complexes Peter A. Chetcuti," Walther Hofherr, Andre LiBgard, Grety Rihs, and

Gunther Rist" Material Science and Physics Department] Ciba-Geigy Ltd., CH-4002 Basel, Switzerland

Hugo Keller and Damian Zech Physics Institute, University of Zurich, CH-8001 Zurich, Switzerland

Received February 22, 1994@

The reaction of {cZoso-(3)-1,2-C~BgH~~}2Niw (1) with tetrathiotetracene (TTT) and tetra- selenotetracene (TSeT) leads to novel electrically conducting charge transfer complexes. The ESR and magnetic susceptibility of the complexes ~TTT~l'+[{cZoso-(3)-1,2-C2B9H11}~Ni1111*- (2) and [TSeT]*+[{cZoso-(3)-1,2-C~B~H~~}~Ni1111'~ (3) were studied. The susceptibilities of both complexes exhibit approximately Curie- Weiss behavior. Complex 2 shows a slight deviation from the Curie-Weiss law in the temperature region where the crystals show a significant electrical conductivity. An electron transfer mechanism exists between the T" radical cations and the [(cZos0-(3)-1,2-CzBgHll)zNi~~~~- anions, which is slowed with decreasing temperature. The single-crystal room-temperature electrical conductivities of 2 and 3 are 23.3 and 17.3 S-cm-l, respectively. Single-crystal X-ray structures of 2 and 3 are reported and consist of segregated stacks of conducting TTT or TSeT cations and nickel dicarbollide anions. Crystal data for 2: C ~ O H ~ ~ B ~ ~ N ~ S S -k CsH3Cl3, triclinic, pi, a = 6.834(1) A, b = 12.368(1) A, c = 16.077(2) A, a = 86.75(1)", ,f3 = 101.54(1)", y = 102.54(1)", V = 1299.5(5) Hi3, 2 = 1, D(ca1cd) = 1,546 g - ~ m - ~ , T = 295 K, A = 0.7107 A, crystal size 0.50 x 0.32 x 0.05 mm, and p = 8.76 cm-l. Of the 4252 reflections measured, in the range 6" < 28 > 48", 2937 were considered observed (I > 341)). The final R factor was R = 0.038, R, = 0.043. Crystal data for 3: CzzHsoB18NiSe*, triclinic, P i , a = 7.010 (1) A, b = 14.567 (1) A, c = 15.589 (3) A, a = 94.60 (l)', ,4 = 89.92 (2)", y = 99.03 (2)", V = 1567.0(8) Pi3, 2 = 1, D(ca1cd) = 1.830 gcmP3, T = 295 K, A = 1.5418 A, crystal size 0.50 x 0.11 x 0.01 mm, and p = 64.85 cm-l. Of the 5812 reflections measured, in the range 6" < 28 > 134", 4689 were considered observed ( I > 341)). The final R factor was R = 0.071, R, = 0.074.

Introduction

The design and synthesis of novel charge transfer complexes and the investigation of their electricall and magnetic2 properties is currently an area of considerable research interest. Although there are a number of ~~~~~ ~

@ Abstract published in Advance ACS Abstracts, December 1, 1994. ( l ) (a ) Marks, T. J . Angew. Chem., Int. Ed. Engl. 1990, 29, 857-

859. (b) Williams, J. M.; Beno, M. A,; Wang, H. H.; Leung, P. C. W.; Emge, T. J.; Geiser, U.; Carlson, K. D. Acc. Chem. Res. 1986,18,261- 267. (c) Saito, G.; Ferraris, J. P. Bull. Chem. SOC. Jpn. 1980,53,2141- 2145. (d) Torrance, J. B. Acc. Chem. Res. 1979,12,79-86. (e) Garito, A. F.; Heeger, A. J. Acc. Chem. Res. 1974, 7, 232-240. (2) (a) Miller, J. S.; Epstein, A. J.; Reiff, W. M. Chem. Rev. 1988,

88, 201-220. (b) Miller, J. S. Adv. Mater. 1992, 4 , 298-300. (3) (a) Yee, G. T.; Manriquez, J. M.; Dixon, D. A.; McLean, R. S.;

Groski, D. M.; Flippen, R. B.; Narayan, K. S.; Epstein, A. J.; Miller, J. S. Adu. Mater. 1991, 3, 309-311. (b) Broderick, W. E.; Hoffman, B. M. J . Am. Chem. SOC. 1991,113,6334-6335. (c) Ward, M. D.; Fagan, P. J.; Calabrese, J. C.; Johnson, D. C. J . Am. Chem. SOC. 1989, 111, 1719-1732. (d) Ward, M. D.; Calabrese, J. C. Organometallics 1989, 8, 593-602. (e) Miller, J. S.; Calabrese, J. C.; Rommelmann, H.; Chittipeddi, S. R.; Zhang, J . H.; Reiff, W. M.; Epstein, A. J. J . Am. Chem. SOC. 1987, 109, 769-781. (0 Lequan, R. M.; Lequan, M.; Jaouen, G.; Ouahab, L.; Batail, P.; Padiou, J.; Sutherland, R. G. J . Chem. SOC., Chem. Commun. 1986, 116-118. (g) Shibaeva, R. P.; Atovmyan, L. 0.; Orfanova, M. N. Chem. Commun. 1969, 1494. (h) Goldberg, S. Z.; Spivack, B.; Stanley, G.; Eisenberg, R.; Braitsch, D. M.; Miller, J. S.; Abkowitz, M. J . A m . Chem. SOC. 1977, 99, 110-117. (i) Green, M. L. H.; Bin, J.; O'Hare, D.; Bunting, H. E.; Thompson, M. E.; Marder, S. R.; Chatakondu, K. Pure Appl. Chem. 1989, 61, 817- 822.

0276-7333195123 14-0666$09.00/0

examples of organometallic metallacene and arene donor complexes that form charge transfer complexes with organic acceptor~,~ there are only a few examples of inorganic and organometallic anions that constitute the acceptor moiety of charge transfer complexe~.~ With exception of the bis(dithio1ine) metal complexe~,~ there i s no class of inorganic or organometallic acceptors that can be used for the synthesis of new charge transfer complexes. For this reason, the known ability of the dicarbollide dianion [C2BgH11l2- to stabilize metals in

(4) (a) PBnicaud, A.; Batail, P.; Davidson, P.; Levelut, A. M.; Coulon, C.; Perrin, C. Chem. Mater. 1990,2,117-123. (b) Pgnicaud, A.; Batail, P.; Coulon, C.; Canadell, E.; Perrin, C. Chem. Mater. 1990, 2, 123- 132. ( c ) Morse, D. B. Chem. Mater. 1990,2, 33-38. (d) Morse, D. B.; Rauchfuss, T. B.; Wilson, S. R. J . Am. Chem. SOC. 1988, 110, 2646- 2648. (5) (a) Gama, V.; Henriques, R. T.; Bonfait, G.; Almeida, M.;

Meetsma, A.; van Smaalen, S.; de Boer, J. L. J . Am. Chem. SOC. 1992, 114, 1986-1989. (b) Heuer, W. B.; Mountford, P.; Green, M. L. H.; Bott, S. G.; O'Hare, D.; Miller, J. S. Chem. Mater. 1990,2, 764-772. (c ) Miller, J . S.; Calabrese, J. C.; Epstein, A. J. Znorg. Chem. 1989,28, 4230-4238. (d) Broderick, W. E.; Thompson, J . A,; Godfrey, M. R.; Sabat, M.; Hoffman, B. M. J . Am. Chem. SOC. 1989,111,7656-7657. (e) Interrante, L. V.; Bray, J . W.; Hart, H. R., Jr.; Kasper, J. S.; Piacente, P. A.; Watkins, G. D. J . Am. Chem. SOC. 1977, 99, 3523- 3524. (0 Interrante, L. V.; Browall, K. W.; Hart, H. R., Jr.; Jacobs, I. S.; Watkins, G. D.; Wee, S. H. J . A m . Chem. SOC. 1975,97, 889-890. (g) Kasper, J . S.; Interrante, L. V.; Secaur, C. A. J . Am. Chem. SOC. 1975, 97, 890-891. (h) Browall, K. W.; Interrante, L. V. J . Coord. Chem. 1973,3,27-38.

0 1995 American Chemical Society

Nickel(N) Bis((3)-1,2-Dicarbollide) Organometallics, Vol. 14, No. 2, 1995 667

Figure 1. (a, top) Molecular packing of [TTT~~’+[(~ZO~O-(~)-~,~-C~B~H~~}~N~~~~~’- (2) viewed down the a-axis. Hydrogen atoms have been omitted for clarity. (b, bottom) Molecular packing of [TTT~~’+[(C~OSO-(~)-~,~-C~B~H~~)~N~~~~~’- (2) viewed down the b-axis. Hydrogen atoms have been omitted for clarity.

high oxidation states’ suggested that metallacarboranes containing the dicarbollide ligand of formula M(C2- B9H11)2’- (n = 0, 1, 2)s may provide a new class of compounds capable of acting as electron acceptors in the synthesis of charge transfer complexes. The polariz- ability of these moleculesg would be expected to enhance

(6) (a) Hawthorne, M. F.; Young, D. C.; Wegner, P. A. J . Am. C h m . Soc. 1967,87,1818. (b) Warren, L. F.; Hawthorne, M. F. J . Am. Chem.

(7) (a) Zakharkin, L. I.; Kobak, V . V . Zzv. Akad. Nauk SSSR, Ser. Khim. 1985, 6, 1449-1451. (b) Brown, D. A.; Fanning, M. 0.; Fitzpatrick, N. J. Znorg. Chem. 1980, 19, 1823-1824. (c) Brown, D. A.; Fanning, M. 0.; Fitzpatrick, N. J. Znorg. Chem. 1978, 17, 1620- 1623. (d) Harris, C. B. Znorg. Chem. 1988, 7 , 1517-1521.

(8) Hawthorne, M. F.; Young, D. C.; Andrews, T. D.; Howe, D. V.; Pilling, R. L.; Pitts, A. D.; Reintjes, M.; Warren, L. F., Jr.; Wegner, P. A. J . Am. Chem. SOC. 1968, 90, 879-896.

SOC. 1967, 89, 470-471.

intermolecular interactions between donor and acceptor moieties and the symmetric structures of the bisdicar- bollide metal complexes would facilitate the molecular packing. The use of metallacarborane acceptors allows for a systematic variation of the spin system on the acceptor moiety of the charge transfer complex and should give rise to interesting magnetic properties with the appropriate donors. Another important feature of metallacarborane acceptor anions is their hydrolytic and oxygen stabilities,8 which facilitates synthetic proce- dures and results in stable charge transfer salts.

We report the synthesis and properties of electrically conducting charge transfer complexes using the nickel

~~

(9)Adler, R. G.; Hawthome, M. F. J. Am. Chem. Soc. 1970, 92, 6174-6182.

668 Organometallics, Vol. 14, No. 2, 1995

Table 1. Atomic Coordinates and Equivalent Isotropic Disdacement Parameters for 2"

Chetcuti et al.

~~

atom X Y Z B (AZ) NI 1 CL2 CL3 s4 s5 S6 s 7 c 1 c 2 C19 c20 c 2 1 c22 C23 C24 C25 C26 C27 C28 C29 C30 C3 1 C32 c33 c34 c35 C36 c37 C38 c39 B4 B5 B6 B7 B8 B9 B 10 B11 B12

1.000 0.7572(5) 0.9447(3) 0.3631(2) 0.6500(2) 0.89 1 O(2) 0.9774(2) 0.8917(7) 0.9605(8) 0.57 16(6) 0.5475(6) 0.5885(7) 0.5636(8) 0.4983(8) 0.4569(7) 0.4810(6) 0.4429(6) 0.4675(6) 0.9847(6) 1.0215(6) 0.9150(6) 0.8810(7) 0.8184(9) 0.7833(8) 0.8141(7) 0.8819(6) 0.9193(6) 0.6171(9) 0.6979(8) 0.5821(9) 1.0731(8) 1.0293(9) 0.9569(9) 1.2 108(8) 1.2834(9) 1.279( 1) 1.2076(9) 1.1599(9) 1.3641(9)

O.OO0 0.3445(3) 0.5912(2) 0.2295( 1) 0.6978( 1) 0.4426( 1) 0.6139(1) 0.0370(4)

-0.0827(4) 0.5626(4) 0.4686(4) 0.4761(4) 0.3824(5) 0.2777(5) 0.2666(4) 0.3605(4) 0.3526(4) 0.4466(3) 0.5066(4) 0.6124(4) 0.2929(4) 0.1833(4) 0.0941(4) 0.1071(4) 0.2094(4) 0.3057(4) 0.4132(4) 0.4277(5) 0.5400(5) 0.6110(5) 0.1338(4) 0.1249(5)

-0.0167(5) -0.0638(5)

0.0773(5) 0.1510(5) 0.0539(5)

-0.0796(5) 0.0244(6)

1 .ooo 1.0882(2) 1.0896(1) 0.47751(8) 0.64212(8) 1.29567(7) 1.30848(7) 1.11 16(3) 1.1164(3) 0.6060(3) 0.6600(3) 0.7495(3) 0.7988(3) 0.7627(3) 0.6767(3) 0.6222(3) 0.5338(3) 0.4815(3) 1.4553(3) 1.4191(3) 1.5301(3) 1.5650(3) 1.5133(4) 1.425 l(4) 1.3881(3) 1.4392(3) 1.4040(3) 1.0425(3) 1.0382(3) 0.9962(4) 1.0837(3) 1.188 l(4) 1.2101(3) 1.0965(3) 1.0755(3) 1.1664(4) 1.2467(4) 1.2014(4) 1.1786(4)

2.48(2) 5.61(8) 8.07(6) 3.47(3) 3.40(3) 3.17(3) 3.14(3) 3.0(1) 3.7(1) 2.58(9) 2.70(9) 3.5(1) 4.4(1) 4.3(1) 3.6(1) 2.8(1) 2.59(9) 2.26(9) 2.38(9) 2.51(9) 2.67(9) 3.7(1) 4.6(1) 4.4(1) 3.5(1) 2.71(9) 2.47(9) 4.9( 1) 4.7( 1) 5.0(1) 2.8(1) 3.6(1) 3.4(1) 3.3(1) 3.4(1) 4.0(1) 3.4(1) 3.5(1) 3.9(1)

Anisotropically refined atoms are given in the form of the isotropic equivalent displacement parameter defined as (4/3)[a2B(l,l) + bZB(2,2) + cZB(3,3) + ab(cos y)B(1,2) + ac(cos B)B(1,3) + bc(cos a)B(2,3)].

complex {closo-(3)-1,2-C2B9H11)2NiTV ( 1)8Jo as an accep- tor moleculell with tetrathiotetracene (TTT) and tetra- selenotetracene (TSeT) as donor molecules. The X-ray crystal structure of the complex [TTT2~+[{closo-(3)-1,2- C2BgH11)2Ni1I11.- (2) and [TSeTl'+[{cZoso-(3)-1,2-C~B~- H11}2Ni1I1I*- (3) are reported together with a study of their ESR and magnetic properties.12

Results and Discussion

Complex 1 has two reversible one-electron reductions at f0.25 and -0.59 v8 (us SCE) forming the monoanion and dianion, respectively; both the neutral complex and its monoanion are moisture and oxygen stable. The

(10) (a) Warren, L. F., Jr.; Hawthorne, M. F. J. Am. Chem. SOC. 1970, 92, 1157-1173. (b) St. Clair, D.; Zalkin, A.; Templeton, D. H. J. Am. Chem. SOC. 1970,92, 1173-1179.

(11) Complex 1 has been shown to form adducts involving partial charge transfer with Lewis bases and electron-rich aromatic systems (see ref loa). While this paper was in preparation, we learned that another group was active in the area and will be publishing a paper on charge transfer complexes resulting from reaction between metal- locene donors and metallacarborane acceptors. See: Forward, J . M.; Mingos, D. M. P.; Powell, A. V. J . Organomet. Chem., in press. See also: Klikorka, J.; Pavlk, I.; Vecemikovl, E.; Fojtkovl, M. Proc. Conf. Coord. Chem. 1971,3 (51, 171-178.

(12) Tetramethyltetrathiofulvalene and tetrathiofulvalene charge transfer complexes of metallacarboranes have also been isolated. Mingos, D. M. P.; et al. Manuscript in preparation. Personal com- munication.

Figure 2. (a, top) Numbering scheme for [{closo-(3)-1,2- CZBSH~I}~N~I~T- anions of complex 2. (b, bottom) Number- ing scheme for [TTT23'+ cations of complex 2.

strong reduction potential of 1 and its high stability and solubility properties make it a very versatile acceptor molecule for a wide range of donor molecules.ll Reac- tion of 1 with equivalent amounts of TTT or TSeT dissolved in 1,2,4-trichlorobenzene (TCB) at 150 "C yielded on cooling black needle-shaped crystals of the complexes ~TTT~~'+[{~ZOS~-~~~-~,~-C~B~H~~}~N~~~~I'~~TCB (2) and [TSeTl'+[{closo-(3)-1,2-C~B~Hll}~Ni~~~~~ (31, re- spectively. When a 2:l ratio of donor to 1 was used, the same product was obtained when TTT was the donor; however, in the case of TSeT, a mixture of 3 and TSeT was obtained. X-ray Crystal Structure of [ ~ l ~ ~ + [ { c l o s o - ( 3 ) - 1 , 2 -

C2BsHll)2Nim]*-*TCB (2). Slow cooling of the reaction

Nickel(N) Bis((3)-1,2-Dicarbollide) Organometallics, Vol. 14, No. 2, 1995 669

solution between T" and 1 yielded crystals suitable for an X-ray diffraction study. The crystal structure of 2 is best described as a centrosymmetric structure with disorder both at the nickel dicarbollide anion and at the solvent trichlorobenzene. It consists of separate stacks of formally l"'.5+ cations and [{closo-(3)-1,2-CzBgH11}~- Ni1I11*- anions shown in Figure la,b. Each planar TTT cation is rotated by 72" relative to its adjacent neighbor and tilted at an angle of 3" to the stack direction with an interplanar spacing of 3.40 8. This spacing is shorter than that observed for the T" complexes of tetracy- anoquinodimethane, "T(TCNQ)2, and bis(ethy1ene-1,2- ditholenelnickel, TTT~.zN~(CZH~SZ), which have inter- planar spacings at 3.52 l3 and 3.63 85e, respectively. These complexes, however, have different overlap modes since the TTT cations are not rotated relative to one another in the stacks as in the case of 2. Positional and thermal parameters for 2 are listed in Table 1, and the numbering scheme for the cations and the nickel dicarbollide anions are given in Figure 2. The bisdi- carbollide nickel anions stack with a nickel-nickel separation along the stacking axis of 6.834 8 and are arranged such that the molecular axis passing through the nickel and the apical boron atoms of each cage lies at an angle of 83" to the TTT stacking axis. There are three short interstack S-B interactions of 3.494,3.588, and 3.641 8 between a sulfur atom on alternating TTT cations and a triangle of boron atoms (Figure 1) of the dicarbollide ligand. As evidenced from electron spin resonance (ESR) and magnetic susceptibility studies discussed below, electron transfer between the TTT stacks and the Ni(II1) complex correlates with the electrical conductivity of the complex. It is possible that the short S-B interactions are important in the electron transfer process despite the fact that the delocalizations of the unpaired electron from the nickel center to the boron atoms of the dicarbollide cage not directly coor- dinated to the metal are small.14 The S(4)-S(5) and S(6)-S(7) bond lengths are 2.070(2) and 2.082(2) 8, respectively, shorter than the S-S bond length in neutral TTT15 and similar to other complexes in which the TTT has a formal charge of + O S 6 as (TTTz)+I3- (2.078(2) 8) or a charge of +1 as TTT(tetracyan0quin- odimethane), 2.083 8.13J7

Single X-ray Crystal Structure of [TSeTl*+[{closo- (3)-1,2-C2BsHll}zNim]*- (3). Fine black needles of 3 suitable for a single-crystal X-ray diffraction study were obtained by slow cooling of the reaction mixture between TSeT and 1. The structure of 3 is shown in Figure 3, and positional and thermal parameters are listed in (13) Shibaeva, R. P.; Rozenberg, L. P. Sou. Phys. Crystullogr. 1976,

20,581-583. (14) Wiersema, R. J.; Hawthorne, M. F. J. Am. Chem. SOC. 1974,

96, 761-770. (15) Dideberg, 0.; Toussaint, J. Acta Crystullogr. 1974, B30,2481-

2485. (16) (a) Smith, D. L.; Luss, H. R. Acta Crystullogr. Sect. B 1977,33,

1744. (b) Inabe, T.; Mitsuhahsi, T.; Maruyama, Y. Chem. Lett. 1988, 429-432. (17) (a) Shibaeva, R. P.; Kaminskii, V. F. Sou. Phys. Crystullogr.

1981,26, 188-190. (b) Shibaeva, R. P.; Kaminskii, V. F.; Eremenko, 0. N.; Yagubskii, E. B.; Khidekel, M. L. Sou. Phys. Crystullogr. 1980, 25, 31-33. (18) (a) Hilti, B.; Mayer, C. W.; Rihs, G. Solid State Commun. 1982,

41, 787-791. (b) Zolotukhin, S. P.; Kaminskii, V. F.; Kotov, A. I.; Khidekel, M. L.; Shibaeva, R. P.; Yagubskii, I?.. B. Izv. &ad. Nuuk SSSR, Ser. Khim. 1978, 8, 1816-1821. (c) Hilti, B.; Mayer, C. W.; Rihs, G. Helv. Chim. Acta 1978, 61, 1462-1469. (d) Schlueter, J. A.; Orihashi, Y.; Kanatzidis, M. G.; Liang, W.; Marks, T. J.; DeGroot, D. C.; Marcy, H. 0.; McCarthy, W. J.; Kannewurf, C. R.; Inabe, T. Chem. Muter. 1991, 3 , 1013-1015.

i. Figure 3. (a, top) Molecular packing of [TSeT]'+[{cZoso- (3)-1,2-CzBgHll}zNi1"l'- (3) viewed down the a-axis. Hy- drogen atoms have been omitted for clarity. (b, bottom) Molecular packing of [TSeT~+[{closo-(3)-1,2-CzB~H11}~- N i l V (3) viewed down the b-axis. Hydrogen atoms have been ommited for clarity.

Table 2. The numbering scheme for 3 is shown in Figure 4. Complex 3 is a 1:l charge transfer complex consisting of stacks of formally TSeT+ cations and nickel dicarbollide anions lying with their molecular axes (passing through the nickel and apical borons) inclined at an angle of 62" to the stacking axis. The stacking arrangement of 3 is very similar to that of complex 2. Each TSeT+ cation is rotated relative to its adjacent neighbor in the stack by 72", which is the same degree of rotation observed between adjacent TTT cations in the structure of complex 2. The interplanar separation of 3.49 8 is a particularly short spacing when compared to other structurally characterized TSeT complexes in which the TSeT cations are not rotated relative to one another in the stacks.18 The Se-Se bond distances for the TSeT cations (2.315(2) and 2.328(2) 8) are shorter

670 Organometallics, Vol. 14, No. 2, 1995 Chetcuti et al.

Table 2. Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 3"

atom X Y Z B (A2) SEI SE2 SE3 SE4 NI 1 c 1 c 2 c 3 c 4 c 5 C6 c 7 C8 c 9 c10 c11 c12 C13 C 14 C15 C16 C17 C18 C19 c20 c21 c22 B4 B5 B6 B7 B8 B9 B 10 B11 B12 B13 B 14 B15 B 16 B 17 B18 B 19 B20 B2 1

-0.0349(2) 0.0061(2) 0.438 l(2) 0.4393(2) 0.2078(3) 0.438(2) 0.485(2) 0.273(2) 0.124(2)

-0.026( 1) -O.O03( 1)

0.015( 1) 0.039( 1) 0.056(2) 0.079(2) 0.088(2) 0.069(2)

-0.045(2) 0.472( 1) 0.488(1) 0.475( 1) 0.488( 1) 0.476(2) 0.494(2) 0.526(2) 0.538(2) 0.482( 1) 0.215(2) 0.434(2) 0.604(2) 0.294(2) 0.127(2) 0.236(2) 0.475(3) 0.5 17(3) 0.283(3)

-0.066(2) -0.092(2)

0.133(3) 0.205(2)

-0.026(2) -0.184(2) -0.061(2)

0.182(2) -0.01 7(2)

-0.1078(1) 0.0524( 1)

-0.2403( 1) -0.208 1 (1)

0.3534(2) 0.465( 1) 0.397( 1) 0.2572(9) 0.321(1)

-0.0953(9) -O.O062(9)

0.0734(9) 0.1647(9) 0.244( 1) 0.333( 1) 0.344( 1) 0.267( 1)

-0.176(1) -0.1 129(9) -0.0490(9) -0.0788(9) -0.0152(9) -0.046( 1)

0.017( 1) 0.1 15(1) 0.147(1)

-0.084( 1) 0.499( 1) 0.577( 1) 0.5 10( 1) 0.379( 1) 0.448( 1) 0.566( 1) 0.573( 1) 0.458( 1) 0.491(2) 0.321(1) 0.254( 1) 0.215(1) 0.207( 1) 0.243( 1) 0.203( 1) 0.136( 1) 0.141( 1) 0.13 1( 1)

0.69139(9) 0.721 63(9) 0.4511(1) 0.5998( 1) 1.1211(1) 1.108( 1) 1.185( 1) 1.0217(9) 0.9895(9) 0.5737(8) 0.5455(8) 0.6047(8) 0.5770(8) 0.636( 1) 0.607( 1) 0.5 17( 1) 0.458( 1) 0.5 134(9) 0.4332( 8) 0.5055(9) 0.5885(8) 0.6625(9) 0.7468(9) 0.8 18( 1) 0.807( 1) 0.7258(9) 0.3478(8) 1.125( 1) 1.154( 1) 1.190( 1) 1.253( 1) 1.220( 1) 1.226( 1) 1.266( 1) 1.283(1) 1.306( 1) 1.058( 1) 0.956( 1) 0.931(1) 1.1 14( 1) 1.140( 1) 1.05 1 ( 1) 0.972( 1) 1.011(1) 1.083 1)

3.25(3) 3.20(3) 3.30(3) 3.36( 3) 2.67(4) 3.5(3) 3.6(3) 2.9(3) 3.1(3) 2.4(2) 2.3(2) 2.5(2) 2.5(2) 3.7(3) 4.4(4) 4.3(3) 3 3 3 ) 2.9(3) 2.5(2) 2.6(2) 2.5(2) 2.7(2) 3.4(3) 4.2(3) 4.0(3) 3.6(3) 2.6(2) 3.1(3) 3.6(4) 3.9(4) 3.7(3) 3.1(3) 3.8(4) 4 3 4 ) 4.4(4) 4 3 4 ) 3.2(3) 3.9(4) 3.6(3) 2.8(3) 3.3(3) 3.8(4) 3.7(3) 3.2(3) 3.4(3)

oAnisotropically refined atoms are given in the form of the isotropic equivalent displacement parameter defined as (4/3)[a2B( 1,l) + b2B(2,2) + c2B(3,3) + ab(cos y)B(1,2) + @cos B)B(1,3) -t- bc(cos a)B(2,3)].

than those observed for neutral TSeT derivativeslg as bis(dise1eno)naphthalene (2.364 A) and are about the as same observed for TSeT cations having a +0.5 charge20 as (TSeT#(SCN)- (2.320(7) A) or having a charge of +121 as (TSeT)+(CuBr& (2.317(3) A). There are three short Se-B interactions at distances of 3.478- (6), 3.551(6), and 3.590(6) A (Figure 3) between a tri- angle of boron atoms of a dicarbollide cage and alternat- ing TSeT+ cations on the stack. The structure repre- sents one of the few examples of a charge transfer complex of TSeT having a 1:l stoichiometry.

~~~ ~

(19) (a) Endres, H.; Keller, H. J.; Schweitzer, J. Q. D.; Veigel, J. Acta Crystallogr. Sect. B 1982,38,2855-2860. (b) Stark, J. C.; Reed, R.; Acampora, L. A.; Sandaman, D. J.; Jansen, S.; Jones, M. T.; Foxman, B. M. Orgunometallics 1984,3, 732-735. (20) (a) Shibaeva, R. P.; Kaminskii, V. F. Sou. Phys. Crystullogr.

1978,23,669-672. (b) Shibaeva, R. P.; Kaminskii, V. F.; Kotov, A. 1.; Yagubskii, E. B.; Khidekel, M. L. Sou. Phys. Crystallogr. 1979,24,154- 157. (21) (a) Shibaeva, R. P.; Kaminskii, V. F.; Yagubskii, E. B.; Kushch,

L. A. Sou. Phys. Crystullogr. 1983, 28, 48-50. (b) Shibaeva, R. P.; Kaminskii, V. F. Sou. Phys. Crystullogr. 1983, 28, 173-176. (c) Shibaeva, R. P.; Kaminskii, V. F. Sou. Phys. Crystallogr. 1984,29,361- 363.

C

C

c 19

B 10

11

10

B 19

Figure 4. (a, top) Numbering scheme for [{cZoso-(3)-1,2- C2B9H11)fiiIn].- anions of complex 3. (b, bottom) Number- ing scheme for [TSeT3.+ cations of complex 3.

Electronic Studies. Single-crystal conductivity mea- surements of complexes 2 and 3 both show significant room-temperature electrical conductivities along the chain axes which decrease with temperature as is typical for semiconductors (Figure 5). Discontinuities in the curves are probably due to microcracks caused by thermal stress in the sample. Single crystals of 2 had an average room-temperature conductivity of 23.3 Scm-l (compact powder o = 0.21 Scm-l). Complex 3 shows a higher compact powder conductivity of 2.02 S-cm-l, two separate samples of single crystals had room-temperature conductivities of 17.3 and 7.7 S.cm-l, respectively. The relatively high conductivity of 3 is unusual for a simple salt having a formal TSeT+ stack of cations and must be a consequence of electron transfer between the nickel dicarbollide anions and the

Nickel(N) Bis((3)-1,2-Dicarbollide) Organometallics, Vol. 14, No. 2, 1995 671

I \ 100 T[KI 2W

220 K

194 K pl300KI

10' ,

g = 2.0217

3.5 K /------

I 100 mT

I 0

Figure 6. Line shape variation with temperature of the ESR spectrum of complex 2.

1 1 100 200 300

TiKI

Figure 5. (a, top) Electrical conductivity of complex 2 as a function of temperature. (b, bottom) Electrical conductiv- ity of complex 3 as a function of temperature.

TSeT cations, thereby creating a partially oxidized conducting stack. The high room-temperature conduc- tivity of these complexes demonstrates that the struc- ture of the nickel dicarbollide acceptor does not prevent the formation of electrically conducting stacks of donor cations in spite of the large size and nonplanar geometry of the anion.

ESR and Magnetic Studies. Complex 2. Transfer of a single electron from the TTT stacks to the nickel dicarbollide acceptor should in theory lead to two species with an unpaired spin. The two systems are the electron hole on the TTT stack (one hole for each TTT cation pair) and the spin of the unpaired electron on

the [{closo-(3)-l,2-C~B~H~~)~Ni1111'- ion. The electron holes on the TTT stacks may be paired or unpaired. The nickel(II1) ion is a d7 spin system, and in a strong ligand field six electrons are paired resulting in a net spin of S = 1/2.22 The ESR powder spectrum at room tempera- ture of complex 2 consists of a single broad resonance at g = 2.0233 (Figure 6). On cooling the polycrystalline sample to 3.5 K, the resonance at room temperature resolves itself to a powder spectrum typical of a g-tensor slightly distorted from axial symmetry with components of either rhombic or lower symmetry. The g-parameters along the three main axes (Figure 6) assume values g3

= 2.0895, g2 = 2.0217, andgl= 1.9697 with an isotropic value ofgiso = 2.0270. These values are typical for a nickel(II1) ionz3 and are also in good agreement with the low symmetry of the nickel dicarbollide anion

(22) Schlaler, H. L.; Gliemann, G. Einfihrung in die Ligaandfeld- theorie; Akademische Verlagsgesellschaft: Frankfurt am Main, 1967; p 137.

672 Organometallics, Vol. 14, No. 2, 1995 Chetcuti et al.

mT 10 T

I tl 8 -

6 -

0

0 50 100 150 200 250 300 T (IO

Figure 7. ESR line width of complex 2 as a function of temperature (single crystal, arbitrary orientation of the magnetic field in the crystal bc plane).

resulting from distinguishable boron and carbon atoms on the dicarbollide cages. In frozen solution the g-tensor of [{closo-(3)-1,2-C2B~H11)2Ni"I3'- is axial (911 = 2.06 and gl = 2.01).14 For symmetry reasons the uniqueg-value at 2.06 of this axial system has to be the one cor- responding to the axis passing through the nickel- apical borons of the nickel dicarbollide anion. For planar nickel(II1) complexes,23 gll .e gl holds, with the unpaired electron residing mainly in the dzz orbital. The relationship gll > gl is indicative of an unpaired electron in a dxy or dxz-yz orbital (gll = gz) and a compressed arrangement of the ligand atoms.23d

The observed variation of the ESR spectrum of 2 with temperature can be explained by an electron transfer occurring at room temperature between the 'I".5+ and the nickel dicarbollide anions leading to a single broad signal. As the temperature is decreased the electron transfer is slowed down and the spectrum increasingly reflects that of a low-spin nickel(II1) complex.23 The electron transfer process between the nickel dicarbollide anions and the !MY stacks is also reflected in the temperature dependence of the ESR line width of a single crystal of 2, which decreases drastically with the slowing down of the electron transfer process (Figure 7). The magnetic susceptibility (x) of 2 was measured and corrections were made for the background signal originating from the quartz sample holder. A plot of XT (where T is the absolute temperature) against T is shown in Figure 8a. In the temperature region where the complex shows a significant electrical conductivity, XT shows a slight deviation from the Curie-Weiss law. The temperature dependence of l/x is shown in Figure 8b. Neglecting spin exchange, an estimate of the number of unpaired electron spins can be obtained from Figure 8 by use of the Curie-Weiss law.= The magnetic susceptibility x is given by

x = C/(T - 0)

where

(23) (a) Bemtgen, J. M.; Gimpert, H. R.; von Zelewsky, A. Znorg. Chem. 1983,22,3576-3580. (b) Wieghardt, K.; Walz, W.; Nuber, B.; Weiss, J.; Ozarowski, A.; Stratemeier, H.; b inen, D. Znorg. Chem. 1986,25, 1650-1654. (c) de Castro, B.; Freire, C. Znorg. Chem. 1990,

Johnson, M. K. Znorg. Chem. 1993,32, 375-376. (24) Carlin, R. L. Mugnetochemistry; Springler-Verlag: Berlin,

Heidelberg, 1986; pp 10-12.

29, 5113-5119. (d) Huang, V.-H.; Park, J.-B.; Adme, M. W. W.;

1

0.8

3 0.6

0.4

\ ? $

!T * 0.2

0

6.0 -1 O2

1 4.0.102

h 1

W

r - 2.0.102

0

Figure 8.

0. . .*

0 100 200 300 T 6)

(a, top) Plot of XT versus temperature for complex 2 at 50 mT. (b, bottom) Plot of inverse susceptibil- ity versus temperature for complex 2 at 50 mT.

C = NP2g2S<S + 1)3k = O.l25g?S(S + 1) (K-emdmol)

where p is the Bohr magneton, K the Boltzmann constant, S the electron spin, 0 the Curie-Weiss constant, and N the number of spins per mole. At room temperature, electron transfer between the spins on the TTT stacks and the nickel(II1) ions precludes the application of the Curie-Weiss law. At low tempera- tures, however, in the temperature region below 100 K where only the spins localized on the nickel(II1) ion are observed in the ESR spectrum, the susceptibility ex- hibits Curie behavior with a small @ value so that one obtains

where ,l.dNieff is the effective magnetic moment in units of Bohr magnetons B. The experimental value for p ~ i ~ ~ is in agreement with S = l/2 and g = 2 characteristic of nickel(II1) complexes. To evaluate the susceptibility at room temperature, a model including electron transfer and spin exchange is needed.

The angular dependence of the g-values for a single crystal was measured at five different temperatures (Figure 9). The a-axis of the crystal was used as the rotation axis and the magnetic field was oriented perpendicular to this crystal axis in the bc plane. The temperature dependence of the g-value for a given angle reflects the temperature-dependent electron transfer process as observed in the ESR powder spectra of 2 (Figure 6). The maximum and minimum g-values at 5 K from Figure 9 very closely match two of the g-tensor main values observed in the powder spectrum at 3.5 K (Figure 6) (93 = 2.0895 and gl = 1.9697). This implies

Nickel(N) Bis((3) - 1,2- Dicarbollide) Organometallics, Vol. 14, No. 2, 1995 673

g-Value I I

2.0800

2.0600

2.0400

2.0200

2.0000

1.9800

0 50 100 150 200 250 300 350 Rotation Angle

I ++ 5 K --Ef 130 K * 293 K 323 K -3- 363 K 1 Figure 9. Variation of the g-values of complex 2 with temperature for a single crystal rotated around the a-axis.

Table 3. Details of Crystallographic Data Collection for 2 and 3 2 3

formula ~ ( C I ~ H ~ S ~ ) N ~ ( B ~ C Z H I 1)C6H3C13 C I ~ H ~ S ~ ~ N ~ ( B ~ C Z H I 1) Mw 1209.96 863.61 crystal system triclinic ttclinic

P1 P1 6.834( 1) 7.010(1) 12.368( 1) 14.567( 1) b (A)

c (A) 16.077(2) 15.589(3) a C) 86.75( 1) 94.60( 1) B (") 101.54( 1) 89.92(2) Y ("1 102.54(1) 99.03(2) v (A3) 1299.3(5) 1567.0( 8) 2 1 2 Dcalc ( g ~ m - ~ ) 1.546 1.830 crystal size (mm) 0.50 x 0118 x 0.01 diffractometer Philips PW1100 Enraf-Nonius

CAD4 radiation (gra hite monochromated) Mo K a Cu K a wavelength (1) 0.7107 1.5118 scan mode e120 8/28 P (cm-9 8.76 64.85 F(000) 614 832 scan range (20) 6-48 6-134 transmission factors 1.00/0.7 1 no. of unique reflctns 4252 5812 no. of observed reflctns (1>3u(I)) 2937 4689 refinement method full matrix full matrix no. of params 429 406 R 0.038 0.071 R W 0.043 0.074 madmin density in final difference map (eA-3) 0.6221-0.558 1.232/-09833

:pE

0.50 x 0.32 x 0.05

that the corresponding g-tensor axes must nearly lie in the bc crystal plane. In frozen solution as mentioned earlier, the g-tensor of the nickel complex is axial14 the main axis with the largest g-value = 2.06) being oriented parallel to the nickel-apical boron molecular axis. It follows that the g3 value of 2.0895 corresponds to gll, indicating that the nickel-apical boron axis lies in the bc plane. This is in agreement with the X-ray analysis, which locates this axis approximately in the bc crystal plane. The orientation of thegl= 1.9697 axis in the molecular frame may then approximately be deduced from the X-ray analysis. If one makes the assumption that the g-tensor reflects the symmetry and

strength of the crystal field exerted by the dicarbollide ligand, the orientation of the g-axes should be related to the local symmetry of the nickel dicarbollide complex. The crystal structure of 2 is described as a centrosym- metric structure with disorder at the nickel dicarbollide anion. ESR experiments do not reveal any disorder among the nickel complexes; the disorder must therefore arise within each nickel complex. As illustrated in Figure 10 (lower part), a model of the disorder is possible such that each nickel complex has a local twofold symmetry axis approximately perpendicular to the crystal a-axis. With this assumption, the g3 and gl axes would be approximately oriented along the symmetry

674 Organometallics, Vol. 14, No. 2, 1995 Chetcuti et al.

Figure 10. Orientation of gl-axis with respect to the dicarbollide ligand: (upper) assumes a center of symmetry at the nickel site; (lower) assumes a local twofold axis at the nickel site.

axis of the complex. In the case of a local center of inversion, no relation would be present between the symmetry elements of the ligand arrangement and the gl and g3 axes (Figure 10, upper part).

The observed temperature dependence of the g-value for the single-crystal ESR measurements (Figure 6) of 2 distinguishes it from the bis(ethylene-1,2-ditholene)- nickel complex of tetrathiotetracene, TM'1,2(NiS4C4H4).se The single-crystal ESR spectrum of T'M!I.z(N~S~C~H~) shows a single line in the temperature range 1.7-300 K attributed to the spin on the anion. The g-value was temperature independent, indicating that no interaction existed between the unpaired spins of the TTT cations with the nickel dithiolene anions.

Complex 3. The ESR spectra of a powder of 3 exhibited a temperature dependence similar to that observed for complex 2 (Figure 61, once again suggesting an electron transfer between electron holes on the conduction stacks and the nickel dicarbollide anions. At very low temperatures, the powder pattern was again typical for an S = l/2 nickel(II1) complex. The three canonical values of the low symmetry g-tensor were g3 = 2.0688, gz = 2.0332, and gl = 1.9707. While the values go and gl were very similar to those measured for complex 2, the value for g3 deviated substantially from the corresponding value for complex 2 (91 = 2.0895) but was close to the parameter measured in frozen solution.22 The magnetic susceptibility of 3 was mea- sured and corrected for the background signal of the quartz sample holder. A plot of xT and llx against T is shown in Figure 11. At low temperature ('10 K) a least-squares fit of the experimental susceptibility leads to a value of 0 = -1.42 K, and below 100 K, pNieff = 1.65. The experimental susceptibility again agrees well with a spin S N ~ = l/Z at most nickel sites. Over the whole temperature range the susceptibilities for com- plexes 2 an 3 follow approximately the Curie-Weiss law. Apparently the main contribution to the suscep- tibilities stems from the unpaired spins on the nickel ions and not from the electron spins on the conducting stacks. One of the TSeT molecules in each unit cell

0.33 3

E Y

0.17 1 v

t X i

0 0 100 200 300

T (K)

1 . 0 ~ 1 0 ~

h 8.0,102

3 6.0.102

4.0.1d

i Eo 25 c

L

t 0 . . 1

0

0 0 100 200 300

Figure 11. (a, top) Plot of XT versus temperature for complex 3 at 50 mT. (b, bottom) Plot of inverse susceptibil- ity versus temperature for complex 3 at 50 mT.

exhibits very short Se-B distances to two adjacent Ni- (111) complexes, the other TSeT cation was more iso- lated. The short Se-B distances are much shorter than the sum of the van der Waals radii. Two of the interactions involve boron atoms directly bonded to the nickel center, and these interactions might be respon- sible for the observed spin and electron transfer interac- tions.

In order to account for the susceptibility observed at high temperatures, a model needs to be invoked that includes electron transfer and coupling between electron spins. Single-crystal ESR measurements would be necessary in order adequately investigate the coupling mechanism; however, adequate crystals of 3 could not be grown.

Conclusion The first electrically conducting charge transfer com-

plexes have been synthesized using the metallacarbo- Fane complex {cZoso-(3)-l,2-CzBsHll)zNiTV as an accep- tor molecule with the donors TIT and TSeT. The X-ray crystals structures of 2 and 3 demonstrate that the nickel dicarbollide anion does not hinder the formation of electrically conducting stacks of donor cations and allows for interstack interactions which in the case of complexes 2 and 3 are essential in maintaining electrical conductivity. The further use of metallacarborane complexes as electron acceptors in combination with donor molecules should lead to a new family of charge transfer complexes with interesting electrical and mag- netic properties.

T (K)

Experimental Section The preparation of complex 3 was carried out under an

argon athmosphere using oxygen-degassed solvents; all other

Nickel(N) Bis((3)-1,2-Dicarbollide) Organometallics, Vol. 14, No. 2, 1995 675

the centrosymmetric space group Pi with disorder both in the nickel anion and in the solvent molecule trichlorobenzene. The two crystallographically independent TTT molecules lie on inversion centers. After refinements had converged to the R-factor of 0.044, a Fourier map was calculated. All hydrogen atoms could be located, and after including their positional parameters in the final refinements, the R-factor was lowered to 0.039. The nickel dicarbollide anion of structure 3 exhibits C1 symmetry. Refinements of all cage atoms taken as boron gave in both pentagons coordinated to the nickel atom one short bond length. The corresponding atoms were taken to be carbon atoms. Further refinements resulted in physically reasonable anisotropic thermal vibration factors for all atoms. The hydrogen atoms could not be located.

Synthesis of [~~l.+[{closo-(3)-1~-C~~~}~i~l.-rl'CB (2). To a solution of 100 mg (0.284 mmol) of TTT in 100 mL of 1,2,4-trichlorobenzene at 120 "C was added a solution of {cZoso-(3)-1,2-CzB~HIl)zNi" (1),0.047 g (0.142 mmol) in 30 mL of 1,2,4-trichlorobenzene, at the same temperature. After being stirred for a few minutes, the solution was filtered and allowed to cool slowly to room temperature over 48 h. Black needles formed at about 40 "C which were filtered rinsed with hexane and dried under vacuum to yield 0.114 g (0.105 mmol) (74%) of 2. Anal. Calcd for C ~ O H ~ E B ~ E N ~ S E . ~ . ~ ~ C ~ H ~ C ~ ~ : C, 46.31; H, 3.52; B, 17.86; Ni, 5.39; S, 23.55. Found: C, 46.52; H, 3.65; B, 16.8; Ni, 5.5, S, 23.68.

Synthesis of [TSeTl'+[{cZoso-(3)-l,2-C~~~}~iml*~ (3). To a solution 0.100 g (0.185 mmol of TSeT in 130 mL of 1,2,4- trichlorobenzene at 150 "C was added a solution of {cZoso-(3)- 1,2-CzBsHll}zNiTV (l), 0.060 g (0.185 mmol) in 30 mL of 1,2,4- trichlorobenzene, at the same temperature. The solution was stirred for a few minutes and then filtered hot and allowed to cool slowly over 48 h. Black needles formed at about 60 "C which were filtered, washed with hexane, and dried to yield 0.141 g (88%) of complex 3. Anal. Calcd for CzzHjoBlsNiSec: C, 30.60; H, 3.50; B, 22.53; Ni, 6.80; Se, 35.67. Found: C, 31.12; H, 3.40; B, 21.3; Ni, 6.8; Se, 36.6.

reactions were carried out without any precautions to exclude oxygen or moisture. Solvents were reagent grade and used without any further purification. TTT5 and TSeTZ6 were prepared according to literature procedures as was the accep- tor molecule nickel bisdicarbollide.E

Magnetic Measurements. The magnetic susceptibility x of complexes 2 and 3 was measured in the temperature range of 2-300 K in an external magnetic field of 50 mT by means of Quantum Design superconducting quantum interference device (SQUID) magnetometer. The polycrystalline samples were mounted in a sample holder tube made of quartz glass in order to keep the magnetic background as low as possible.

Electrical Conductivity Measurements. dc conductivity measurements were carried out using the four-probe method. The crystals were mounted on gold wires of 10 pm thickness and placed in contact with Degussa platinum paste. The homemade sample holders were then placed in a Cryogenera- tor with two-stage cold head (Leybold), and the electrical conductivity was measured along the chain axis at tempera- ture intervals of 2 K.

ESR Measurements. ESR experiments were performed on a Varian E9 ESR spectrometer equipped with an Oxford Instruments continuous-flow cryostat ESR 910 and a tem- perature controller ITC4.

Crystal Structure Analyses of Complexes 2 and 3. Crystal data for complexes 2 and 3 are given in Table 3. A suitable crystal of each complex was glued on top of glass fibers for data collection. No significant intensity variation was observed for three standard reflections during data collection. The measured intensities were corrected for Lorentz and polarization effects. For complex 3, absorption corrections were applied, based on azimuthal scans of seven reflections with a diffractometer angle K near 90". The two structures were solved by direct methods. There were some problems encountered in distinguishing between boron and carbon atoms in the dicarbollide cages. The structure of 2 was first solved in space group P i with the nickel complex having Ci symmetry. Refinements with anisotropic temperature factors and all cage atoms taken as boron revealed two similar short (1.64 A) bond lengths of adjacent bonds in the pentagon coordinated to the nickel atom, indicating a disorder. As ESR results indicated that the disorder must arise within each nickel complex, the structure was therefore transformed into the noncentrosymmetric space group P1. With this space group, however, the structure could not be properly refined. The best R-factor obtained was 0.076 having bond lengths between 1.52 and 1.92 A with estimated standard deviations of 0.05 A. It seems that structure 3 is best described having

(25) Marschalk, C. Bull. SOC. Chim. Fr. 1948,15, 418-428. (26) Marschalk, C. Bull. SOC. Chim. Fr. 1952, 46, 1462-1469.

Acknowledgment. We acknowledge Professor D. M. P. Mingos of the Imperial College of Science, London, for disclosing his results prior to publication. The technical assistance of T. Lochmann, J. Pfeiffer, and H. R. Walter are also gratefully acknowledged.

Supplementary Material Available: Listings of bond distances and bond angles for 2 and 3, listings of general displacement parameters for 2 and 3, and listings of atomic coordinates for 2 (15 pages). Ordering information is given on any current masthead page.

OM940 13 17