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Center, University of Wisconsin (Madison), was made available through partial support of the National Science Foundation and the Wisconsin Alumni Research Foundation administered through the University Research Committee.
information concerning the structural interrelationships and bonding of the complexes. The [Ni3(C0)3(pKO)3]22-dianion was prepared by reduction of nickel tetracarbonyl. The reduction reaction is extremely dependent on the reducing agent used and upon the experimental conditions with infrared Supplementary Material Available. A listing of atomic cosolution spectra providing evidence for at least six ordinates will appear following these pages in the microfilm edition different anionic species, of which one of intense red of this volume of the journal. Photocopies of the supplementary material from this paper only or microfiche (105 X 148 mm, 24X color predominates on account of its relative ease of reduction, negatives) containing all of the supplementary material formation and stability to hydrolysis. For example, for the papers in this issue may be obtained from the Journals this anion can be prepared through the reduction of Department, American Chemical Society, 1155 16th St., N.W., Ni(C0)4 either with sodium metal in T H F (60°,20 hr) Washington, D. C. 20036. Remit check or money order for $3.00 for photocopy or $2.00 for microfiche, referring to code 5 hr). or with potassium hydroxide in methanol (So, number JACS-74-2614. Evaporation of solvent followed by redissolution in water and saturation with solid potassium bromidc Joseph C. Calabrese, Lawrence F. Dah]* yields the potassium salt in a crystalline dark red form Department of Chemistry, Utiioersity of Wisconsin Madison, Wisconsin 53706 (ca. 25-60 % yield). The corresponding tetramethylammonium salt, obtained from metathesis of the poPaolo Chini, Giuliano Longoni, Second0 Martinengo tassium salt in water and recrystallized from acetoneIstituto di Chimica Generale ed Inorganica, Universith degli Studi isopropyl alcohol, is diamagnetic6 and moderately Milan 20133, Italy stable in air. An infrared spectrum of the sodium salt Received December 12. 1973 in T H F solution reveals carbonyl absorption bands at 1975 (s), 1810 (m), 1790 (m), and 1743 (w) cm-’; the reasonable agreement of these values with those preSynthesis and Structure of a Hexanuclear Nickel viously reported’ for the sodium salt of the presumed Carbonyl Dianion, [Ni3(C0)3(pz-CO)3]2z-,and [Ni4(CO)9]2- anion (uiz., 1985 (s), 1818 (ms), and 1799 Comparison with the [Pt3(C0)3(~z-C0)3]22Dianion. (ms) cm-I in T H F solution) offers convincing evidence An Unprecedented Case of a Metal Cluster System that the two anions may in fact be identical. Since our Possessing Different Metal Architectures for Congener elemental analyses instead suggested an empirical Transition Metals formula ,of [ N ~ ~ ( C O ) G ]its ~ ~actual -, composition as a [Ni3(C0)3(p2-C0)3]22dianion was ascertained from an Sir : X-ray diffraction analysis of the tetramethylammonium We wish to report the isolation and structural charac~alt.~,~ terization of the [Ni3(C0)3(p2-C0)3]22dianion which This dianion of crystallographic C3,-3 site symmetry represents the first unambiguous example of a hexahas an idealized D3,-j2/m geometry (Figure 1) which nuclear metal carbonyl cluster system with 12 ligands. may be envisioned as a trigonal-antiprismatic array of Of prime importance to the field of metal carbonyl metal atoms formed from the dimerization of two chemistry is that this research combined with the subplanar Ni3(C0)3(pz-C0)3moieties through direct Ni-Ni sequent preparation and structural analysis2 of the hexaplatinum carbonyl analog, [Pt3(C0)3(p~-C0)3]22-, interactions involving the two additional anionic electrons. has established for the first time that direct metal-metal The symmetry-related oNi-Ni bonds within both Ni3interactions involving a first-row transition metal can be (CO)s triangles are 2.38 A in length, while the other sjx sufficiently different from those involving a congener equivalent Ni-Ni bonds between them are 2.77 A. third-row transition metal such as to give rise to two This elongated distortion of the octahedron of nickel different metal frameworks which are conformers of atoms along the crystallographic threefold axis thereby each other.3s4 results in two smaller transoid, equilateral triangular Prior to this work, the syntheses of various nickel metal faces, whose edges are symmetrically bridged by carbonyl anions formulated as [Ni2(Co)#-, [Ni3carbonyls, and six isosceles triangular faces with two (CO)8]2--, [Ni4(C0)9]2-, and [Ni5(C0)9]2- have been longer edges. The two independent Ni-CO(bridging) reported5 in the literature. Since the stoichiometries of bond lengths are both 1.90 A which is 0.25 A longer these unusual polymeric species cannot be unequivocally than theoone independent Ni-CO(termina1) bond length characterized by the usual chemical and physical of 1.75 A ; th? bridging and terminal C-0 distances are methods, a reinvestigation of the nickel carbonyl anions 1.17 and 1.13 A, respectively. has been initiated involving X-ray diffraction studies to The transformation from a trigonal-antiprismatic (or ascertain their formulas as well as to obtain definitive octahedral-like) metal arrangement in [Ni3(C0)3(p2(1) Presented in part at the 165th National Meeting of the American CO)3]r2- dianion to a trigonal-prismatic one in the cor-
Chemical Society, Dallas, Texas, April 1973. (2) J. C. Calabrese, P. Chini, L. F. Dahl, G. Longoni, and S. Martinengo, J. Amer. Chem. Soc., 96,2614 (1974). (3) Previously determined structural dissimilarities between polynuclear metal carbonyl complexes (of the same general formula) for first-row transition metals compared to those for third-row transition met& have involved different arrangements of carbonyl ligands, e.g., F e d C O ) d j t ~ - C 0 OS. ) ~ OS~(CO)IZ and Coi(CO)e(pz-CO)s cs. Ir4(CO),?. (4) P. Chini, Inorg. Chim.Acta Rec., 2, 31 (1968). ( 5 ) Cf.F. Calderazzo, R. Ercoli, and G. Natta in “Organic Synthesis Via Metal Carbonyls,” I. Wender and P. Pino, Ed., Interscience, New York, N. Y.,1968, pp 68-70, and references cited therein.
Journal of the American Chemical Society
96:8 1 April 17, 1974
(6) We are indebted to Mr. James Kleppinger at the University of Wisconsin (Madison) for making the magnetic susceptibility measurements aia the Faraday method. (7) W. Hieber and J. Ellermann, Z . Nafurforsch.B, 18, 595 (1963). trigonal, P 3 ; a = b = 11.003 (8) [N(CH~)~~Z[N~~(CO)~(~Z-CO)~]~: ( I ) , c = 7.045 (1) A; Y = 738.7 As; ,pcalod = 1.88 g cm-3 for z = 1. Anisotropic least-squares refinement gave R I ( F ) = 3.9% and RdF) = 4 . 0 Z for 614 independent diffractometry data ( I > 2 4 1 ) ) . (9) For computation of distances and bond angles, see paragraph at end of paper regarding supplementary material.
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responding platinum analog, [ P ~ ~ ( C O ) ~ ( ~ Z - C O )rep~]Z*-, resents the first known instance that metal-metal interactions involving first-row transition metals can be sufficiently different from those involving third-row transition metals such as to produce two different metal architectures which are conformers of each other. This conformational change, by which in the trigonal prismatic cluster system each metal atom in one planar M3(C0)3(p2-C0)3fragment is only bonded to one corIN i3(C0I3(pyco)Al responding metal atom in the other identical fragment in Figure 1. Architecture of the [Ni3(CO)8(ccl-CO_))3]22dianion which contradistinction to each metal atom in the trigonalpossesses crystallographic site _symmetry C8,-3; its geometry exantiprismatic cluster system being coordinated to two perimentally conforms to D ~ 3 2 / msymmetry with the six nickel metal atoms in the opposite fragment, presumably reatoms at the vertices of a trigonal antiprism. flects from a viewpoint of total energy minimization the inherently greater strength of a given kind of Pt-Pt bond turally ordained members include Ru6(C0)18H2, lZa L'S. a corresponding Ni-Ni bond such that a trigonal M6(CO)16 (M = C O , ' ~Rh,ljC ~ Ir15d), [M6(CO)~5]2prismatic conformation (with only three intertriangular ~ ~ ~ 1rlsd), [M6(C0)14I4dianions (M = C O , Rh, Pt-Pt bonds of a given type) is stabilized in the solid tetraanions (M = Co,l59 RhlSh), and the [Ni2CoIstate for the [Pt3(C0)3(p2-C0)3]22-dianion. lo The ( C O > I ~ ]dianion15' ~as well as the carbidocarbonyl [Feemarked difference between the much longer intertri(co)16c]2dianion, 15j Ru6(C0)&, l j k and RuG(CO)I Iangular Pt-Pt distances of 3.04 A in the prismatic plati(arene)C. l 5 l . The corresponding isoelectronic [Pt6num cluster cs. the corresponding Ni-Ni distances of (CO)I~]*-dianion is the second member of the hexa2.77 A in the antiprismatic nickel cluster is in accord nuclear metal carbonyl complexes possessing a trigonalwith the premise that repulsive forces between the two prismatic metal arrangement, the other member being halves of the dianion sufficiently increase at the smaller the carbidocarbonyl hexarhodate dianion, l 6 [RhsNi-Ni distance to give the staggered conformation. ( c 0 ) 6 ( ~ 2 ~ c 0 ) ~ c ] *which, - - , with the carbide atom at the Since the metal-metal interactions within each M3center of the prism and symmetrically bridging carbonyl (C0)3(p2-CO)3fragment in both the nickel and platigroups spanning the polyhedral metal edges, further num clusters are presumed to correspond to normal differs from the [Pt3(C0)3(pZ-C0)3]22dianion in that its electron-pair bonds, 1,12 the similarity of the ratio for electronic configuration involving metal-metal interthese (Ni-Ni) to (Pt-yt) boad lengths within the M3actions conforms to a so-called electron-precise metal (CO)6triangles of 2;38A/2.?6A = 0.89 to the correspondpolyhedron. An outline of a qualitative molecular ing ratio of 2.77 Ai3.04 A = 0.91 for the metal-metal orbital representation utilized for an octahedral-like distances between the two M3(C0)6 triangles suggests metal carbonyl cluster system with 86 valence electrons that the conformational change from an antiprismatic has been given elsewhere. l Z e metal array to a prismatic one has no appreciable effect The above work suggests that some of the other nonon the intertriangular metal-metal distances. characterized nickel carbonyl anions may likewise conAs an initiate to the homologous series of hexanuclear tain Ni3(C0)3(p2-C0)3fragments. As an operational metal carbonyl complexes which possess an octahedral test of this hypothesis, crystalline salts of other nickel (or trigonal-arztiprismatic) metal arrangement and an electronically equivalent configuration of 86 valence (1 3) This stereochemistry offers additional support for the proposed electrons available for metal-metal and metal-ligand arrangement of hydrogen atoms (which were not located from the X-ray bonding, the [Ni6(C0)12]2-dianion represents the first diffraction study) in the Cus(P(CsHs)8)sHs molecule. l 4 The six copper atoms, to each of which is bonded a terminal triphenylphosphine ligand, such member with only 12 ligands. l 3 < I 4 Previous struclsdlf
(10) CY. F. A. Cotton, Accozrnrs Chem. Res., 2, 240 (1969). An illustration of the much more robust character of Pt-Pt bonding in coordination compounds is given by plntinum bis(ethylene-1,2-dithiolene) being a (metal-metal)-bonded dimer with a short Pt-Pt distance of 2.77 A in contrast to the corresponding planar Ni(SGH2)2 moleculc being monomeric with no exceptionally close intermolecular contacts: I
