Inorg. Chem. 1986, 25, 2799-2805 bridgehead atom to allow extensive delocalization. However, the present study shows that for the analogous complexes where the bridgehead atom is carbon (Le. X = COH in the title complex, and X = CHIo) the cyclic voltammetric behavior parallels that of C ~ ( b p y ) ~and ~ +not C0{(2-py)~Nj2~+. Furthermore, there is evidence from the coulometric studies reported above for the transient existance of the [C0{(2P Y ) ~ C O H ) ~ ]and + , the [ C 0 { ( 2 - p y ) ~ C H ) ~complex l+ can be synthesized by sodium amalgam reduction of the Co(I1) species and shows reasonable stability (several days) under inert conditions.lO” Since delocalization via da-pa bonding would not be anticipated in either of these ligands, the above observations argue against the necessity of extensive delocalization via the bridging atom to allow stabilization of the low-valent Co(1) species, unless there is a spatial electronic interaction between pyridine rings in these tripodal ligands.28 (28) In this case, the complex of tris(2-pyridy1)aminemay be the exception because of ligand distortion induced by the relative shortness of the bridgehead (N)-pyridine bonds. (29) The periodic group notation in parentheses is in accord with recent actions by IUPAC and ACS nomenclature committees. A and B notation is eliminated because of wide confusion. Groups IA and IIA become groups 1 and 2. The d-transition elements comprise groups 3 through 12, and the p-block elements comprise groups 13 through 18. (note that the former Roman number designation is preserved in the last digit of the new numbering: e&, I11 3 and 13).
-.
2799
Further studies of the Co(1) and Rh(1) complexes of a number of these tripodal ligands are in progresslob and will be reported subsequently. Acknowledgment. This research was performed partly a t Brookhaven National Laboratory (which is operated under Contract No. DE-AC02-76CH00016 with the Department of Energy and supported in part by its Office of Basic Energy Sciences) and partly a t James Cook University of North Queensland (where it was supported by the Australian Research Grants Scheme). D.J.S. thanks Baruch College for released time to do this research, and F.R.K. acknowledges the AustralianAmerican Educational Foundation for assistance through a Fulbright Award while on a Special Studies Program a t Brookhaven National Laboratory. The contribution of Tracy Wilson (an undergraduate student a t James Cook University) to aspects of the solvent dependence of linkage isomer formation is also acknowledged. Registry No. [CO((~-~~)~COH)((~-~~)~CO-}](C~O,),, 73580-28-6; [ C O ] ( ~ - ~ ~ ) ~ C O H } ~ ]102630-75( C ~ O ~ )1:~ , Li[Co{(2PY)~COH)~](S~O~)~.IOH~O, 102630-77-3. Supplementary Material Available: Tables of thermal parameters for the non-hydrogen atoms, positional parameters for the hydrogen atoms, interatomic distances and angles for the ligand, the anions, and the lithium coordination sphere, hydrogen bonding interactions, and leastsquares planes (9 pages). Ordering information is given on any current masthead page.
Contribution from the Departments of Chemistry, Rice University, Houston, Texas 7725 1, University of Houston, Houston, Texas 77004, and The State University of New York at Buffalo, Buffalo, New York 14214
Structural and Theoretical Discussion of [Bi4Fe4(CO),4*-: Application of MO and TEC Theories to a Zintl-Metal Carbonylate Kenton H. Whitmire,*+ Thomas A. Albright,** S u n g - K w o n K a n g , * M e l v y n Rowen Churchill,*$ and James C. F e t t i n g e r Q R e c e i v e d December 2, I985
The reaction of [Et,N] [BiFes(CO)lo] with CO in CH2C12cleanly produces [Et4N]2[Bi4Fe4(CO)13] and iron pentacarbonyl. The complex crystallizes in the centrosymmetric orthorhombic space group Pcab (No. 61), with a = 14.128 (3) A, b = 15.567 (4) A, c = 39.816 (18) A, V - 8756 ( 5 ) A’, and D(calcd) = 2.55 g cm-’ for Z = 8 and M, = 1683.96. Diffraction data (Mo Ka, 28 = 6-40’) were collected with a Syntex P21 automated diffractometer; the structure was solved and refined to RF = 7.8% for those 2926 reflections with lFol > 3.0a(lF0I). The [Bi4Fe4(C0)13]2dianion can be described as a hybrid Zintl ion-metal carbonyl, with three Fe(CO)3 units capping faces of a Bi, tetrahedron. An additional Fe(CO), fragment is apically bonded to that unique bismuth atom which is bonded to all three Fe(CO)3 units. The [Bi4Fe4(C0)13]2-dianion is involved in some significant intermolecular Bi-Bi contacts. Molecular orbital calculations have been carried out and are discussed along with qualitative electron-counting formalisms.
Introduction The interest in metal cluster chemistry has dramatically increased during the last decade. The structures, the nature of the bonding, and the reactivity of metal cluster compounds are generally well established by synthetic, spectroscopic, and theoretical studies.’-, There are a number of transition-metal c o m ~ l e x e s that contain A, or A, groups, where A is phosphorus or arsenic, bonded to the transition-metal atoms. Most of the complexes show v3-A3-ML3, q3-A,-M2L6 and v1,v2-A4-ML3geometrie~.~Among the group 15 elements, unfortunately, bismuth-transition-metal cluster chemistry is not well-known. A few cationic or anionic polybismuth clusters have been known for some time,’ and a few organic derivatives containing Bi-Bi bonds have also been reported re~ently.~ A preliminary account of the structure of a [Bi4Fe,(C0)13]2cluster compound has appeared7 and has encouraged us to undertake M O studies to understand the bonding in it. This cluster
Rice University. *University of Houston. *The State University of New York at Buffalo. 0020-1669/86/1325-2799$01 S O / O
compound is an electron-rich Zintl-metal carbonylate that is based on a p-block cluster framework. The complete structural details D. M. P. Polyhedron 1984,3, 1321. (b) (1) (a) McParSn, M.; Ming;, Teo, B. K. Inorg. Chem. 1984,23, 1251. (c) Teo, B. K.;Longoni, G.; Chung, F. R. K. Inorg. Chem. 1984.23, 1257. (d) Johnson, B. F. G. Transition Metal Clusters; Wiley-Interscience: Chichester, England, 1980. (e) Nicholls, J. N. Polyhedron 1984, 3, 1307. (2) Burdett, J. K. Molecular Shapes: Wiley-Interscience: New York, 1980. (3) Albright, T. A.; Burdett, J. K.; Whangbo, M.-H. Orbital Interactions in Chemistry; Wiley: New York, 1985. (4) (a) Dapporto, P.; Sacconi, L.; Stoppioni, P.; Zanobini, F. Inorg. Chem. 1981, 20, 3834. (b) Bianchini, C.; Mealli, C.; Meli, A.; Sacconi, L. Inorg. Chim. Acta 1979, 37, L543. (c) Dapporto, P.; Middollini, S.; Sacconi, L. Angew. Chem., Int. Ed. Engl. 1979, 18, 469. (d) DiVaira, M.; Sacconi, L. Angew. Chem., Int. Ed. Engl. 1982, 21, 330. (e) Lindsell, W. E.; McCullough, K. J.; Welch, A. J. J. Am. Chem. SOC. 1983, 105, 4487. (f) DiVaira, M.; Midollini, S.; Sacconi, L. J. Am. Chem. Sac. 1979, 101, 1757. (g) Bernal, I.; Brunner, H.; Meier, W.; Pfisterer, H.; Wachter, J.; Ziegler, M. L. Angew. Chem., Inl. Ed. Engl. 1984, 23, 4381. (h) DiVaira, M.; Mani, F.; Moneti, S.;Peruzzini, M.; Sacconi, L.; Stoppioni, P. Inorg. Chem. 1985, 24, 2230. (5) (a) Corbett, J. D. Prog. Inorg. Chem. 1976, 21, 129. (b) Adolphson, D. G.; Corbett, J. D.; Merryman, D. J. J. A m . Chem. Sac. 1976, 98, 7234. (c) Cisar, A.; Corbett, J. D. Inorg. Chem. 1977, 16,2482. (d) Critchlow, S.C.; Corbett, J. D. Inorg. Chem. 1982, 21, 3286. 0 1986 American Chemical Society
2800 Inorganic Chemistry, Vol. 25, No. 16, 1986
Whitmire e t al. Table I. Experimental Data for the X-ray Diffraction Study of W4NI +2[Bi4Fe4(Co)1312-
043
(A) Crystal Parameters at 24 'C (297 K) cryst syst: orthorhombic V = 8756.4 (48) AS space group: Pcab [No. 611 2 = 8 u = 14.1276 (30) A formula: C2,H40N2013Bi4Fe4 b 15.5670 (37) A M, = 1683.96 c = 39.816 (18) A D(calcd) = 2.55 g ctK3
(B) Measurement of Intensity Data diffractometer: Syntex P21 = 0.710730 A) radiation: Mo K& monochromator: pyrolytic graphite (28, = 12.160' for the 002 reflcn), equatorial mode, assumed 50% perfect/50% ideally mosaic for polarization cor reflcns measd: +h,+k,+l for 28 = 6.0-40.0'; 4726 reflcns collcd, yielding 4072 unique data scan type: w-scan over a symmetrical range of 0.9' with an ofset of 0.5O for bkgd measurements scan speed: l.O'/min std reflcns: 3 mutually orthogonal reflcns re-collcd after every 97 reflcns; no decay or significant fluctuations obsd abs cor: ~ ( M Ka) o = 165.9 cm-I; an empirical abs cor made based upon interpolation (both in 28 and 4) between $-scans of a set of close-to-axial reflcns
(x
912
0
012
Figure 1. Labeling of atoms in the [Bi4Fe4(C0),3]2-dianion. Note the approximate C,, symmetry of the system.
and results from these theoretical considerations are presented here.
Results and Discussion Synthesis and Structure of [Et4N]2[Bi4Fe4(CO)13] (I). This molecule is obtained via the reaction of carbon monoxide with the cluster [Et4N][(p3-Bi)Fe3(CO),(p3-CO)](11) in CHzClz and can be easily obtained under moderate pressures (500 psi).' The cluster is obtained from the autoclave reaction in roughly 35% yield based on bismuth. It has been isolated as a minor product from the synthesis of [BiFe3(CO),o]- (probably because carbon monoxide is present as a byproduct of that reaction) and can be obtained along with Fe(C0)4PPh3 and Fe(CO)3(PPh3)2 when [BiFe3(CO)lo]-is treated with PPh3 in CH2C12.The molecular structure of I is shown in Figure 1. The crystal consists of a 2:l ratio of disordered Et4N+ ions' (centered on N ( l ) and N(2)) and ordered [Bi4Fe4(CO)13]2-dianions. The labeling of atoms within a [Bi4Fe4(C0)13]2ion is shown in Figure 1. A stereoscopic view of the cluster is provided in Figure 2. Interatomic distances and angles are listed in Tables I11 and IV. The four bismuth atoms define a tetrahedron in which three triangular faces are capped by p,-Fe(CO), fragments, while the fourth triangular face is bare. Bi-Bi distances around the bare face [Bi(2)-Bi(3) = 3.162 (2), Bi(3)-Bi(4) = 3.168 (2), Bi(4)-Bi(2) = 3.140 (2) A] are systematically reduced by about 0.3 A relative to the other three Bi-Bi distances within the Bi4 core of the anion [viz., Bi(1)-Bi(2) = 3.473 (2), Bi(l)-Bi(3) = 3.473 (2), Bi(1)-Bi(4) = 3.453 (2) A]. The p3-Fe(C0), fragments are linked to the Bi4 tetrahedron such that the Bi( 1)-Fe linkages are slightly shorter than the other two Bi-Fe distances in each case (viz., Bi(1)-Fe(1) = 2.708 ( 5 ) A vs. Bi(2)-Fe(l) = 2.753 (6) and Bi(3)-Fe( 1) = 2.736 (6) A; Bi(1)-Fe(2) = 2.699 (6) 8, vs. Bi(2)-Fe(2) = 2.733 ( 5 ) and Bi(4)-Fe(2) = 2.729 (6) A; Bi(1)-Fe(3) = 2.701 (6) A vs. Bi(3)-Fe(3) = 2.714 (6) and Bi(4)-Fe(3) = 2.729 (6) A). The fourth iron atom is the central atom of an Fe(CO), unit that is linked only to the apical Bi(l), (6) (a) Breung, H. J.; Muller, D. Angew. Chem. 1982, 94,448. (b) Ashe, A. J.; Ludwig, E. G. Organometallics 1982, I , 1408. (c) Calderazzo, F.; Morvillo, A.; Pelizzi, G.; Poli, R. J . Chem. SOC.,Chem. Commun. 1983, 507. (7) Whitmire, K. H.; Churchill, M. R.; Fettinger, J. C. J. Am. Chem. SOC. 1985, 107, 1056. (8) Whitmire, K. H.; Lagrone, C. B.; Churchill, M. R.; Fettinger, J. C.; Biondi, L. V. Inorg. Chem. 1984, 23, 4227. (9) Churchill, M. R.; Change, S . W.-Y. Inorg. Chem. 1974, 13, 2413.
with Bi(1)-Fe(4) = 2.752 (6) A. Atoms Fe(l), Fe(2), and Fe(3) are each in a distorted-octahedral coordination environment, whereas Fe(4) has a trigonal-bipyramidal geometry. The [Bi,Fe,(CO),,]" cluster as a whole has approximate C3, symmetry. Other distances and angles within the [Bi4Fe4(C0)13]2-anion are in agreement with known values but are of limited precision because of the dominance of the heavy atoms (Le., four bismuth atoms with Z = 83 and four iron atoms with Z = 26) in the X-ray structural analysis. Thus Fe-CO distances are 1.61 (8)-1.80 (6) A (average, 1.72 f 0.06 A), C - O distances are 1.1 1 (6)-1.31 (6) A (average, 1.19 f 0.06 A) and Fe-C-0 angles are 169 (4)-179 (4)O (average, 174 f 3'). The two Bi-Bi distances observed for I (ca. 3.16 and 3.46 A) are comparable with the two closest Bi-Bi contacts in the pure crystalline element (3.07 and 3.53 A).lo Compound I may be compared to the Bi42-anion, which has been crystallographically c h a r a c t e r i ~ e d . In ~ ~ this molecule, a square-planar array of Bi atoms is observed with two unique Bi-Bi distances of 2.936 (2) and 2.941 (2) A. These distances are noticeably shorter than for I, and this may arise via ?r interactions in the square-planar molecule since it is an aromatic 6-T-electron system. Unfortunately, the Bi-Bi distances cannot be directly compared to these in tetrahedral Sn2Bi2- since in the latter molecule the Sn and Bi atoms are equally disordered over all sites.5d The Bi-Bi distance in the cationic cluster Bi8(A1Cl4), of 3.100 A (average) compares favorably to the basal Bi-Bi distance in I and suggests that they represent a Bi-Bi single bond." As shown in Figure 3, there are weak Bi ...Bi interactions between the dianions. Close intercluster contacts observed in I (ca. 3.980 A) are also comparable to those observed for B':i at 3.900 (6)-4.109 (6) A1'and CallBi1,.l2 The longer Bi-Bi distances in I indicates appreciably weakened bonding as will be discussed in the next section. Theoretical Considerations. In [ Bi4Fe4(CO)13]2- the one Fe(CO),unit that is connected to only one Bi atom can be considered a two-electron acceptor. W e assume that two electrons on the Bi atom, a lone pair of electrons directed toward the outside of the tetrahedral cage, are used to form a dative bond to the Fe(CO), group and the skeletal bonding in the cluster compound will not be affected by this interaction. Therefore, the model for our studies does not include the Fe(CO), unit. Three F e ( C 0 ) 3 moieties are coordinated in an p 3 fashion to three faces of the Bi4 tetrahedron. The nine Bi-Fe bonding distances are almost the (IO) Curka, P.; Barrett, C. S. Acta Crystallogr. 1962, 15, 865. (1 1) Krebs, B.;Hucke, M.; Brendel, C. J. Angew. Chem., Int. Ed. Engl. 1982,
21, 445. (12) Deller, K.; Eisenmann, B. 2. Naturforsch, B: Anorg. Chem., Org. Chem. 1976, 31, 29.
Inorganic Chemistry, Vol. 25, No. 16, 1986 2801
Figure 2. Stereoscopic view of the [Bi4Fe4(C0),J2-dianion.
I
c
1. -x
'[J-
1. -Y 1.-2
A
Figure 3. Interactions between the central and surrounding [Bi4Fe4-
(C0),,l2- dianions. Note that all interactions involve the "bare" faces (Bi(2)-Bi(3)-Bi(4)) of the anions. Interionic distances
