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910-1010 cm-', the value of 854 cm-' is the lowest u(V=O) frequency reported to date. Ginsberg" has tentatively suggested that low v(V=O) frequencies may be due to bridging vanadyl groups, although no structural data are available. We are currently investigating V0(2,2'-bipyridine)Clz and VO( 1,lO-phenanthro1ine)Clz, which also have low v(V=O) frequencies. l 2 Since the low v(V=O) frequency of 854 cm-l is within the range (650-920 cm-') expected for bridging M-0-M bonds,13 the presence of this band may prove to be an excellent diagnostic test for oxygen bridging in these systems. Acknowledgment. We wish to thank the National Research Council of Canada for financial support. Figure 1. A view of the VO(sa1pn) molecule illustrating the atomic numbering. The atoms V', 03', alid V" are from neighboring molecules and show the polymeric nature of the compound. The pertinent angles are 03-V-01, 104.0; 03-V-02, 103.3; 03-VN1, 94.0; 03-V-N2, 94.5; 03-V-03', 168.8; 01-V-02, 86.3; 01-V-N1, 88.4; NI-V-N2, 91.6; N2-V-02, 88.2; V-03-V', 158.2'. Allanglesare &0.6".
nitrogen trans to a vanadyl ~ x y g e n . ~The V-03 distance of 1.633 (9) A is one of the longest vanadyl oxygen distances reported to date, the range being from 1.571 (10) to 1.62 (1) Asg The longer V-0 distance in VO(sa1pn) is consistent with the lower stretching frequency vide infra and the bridging character of the vanadyl oxygen atom. The in-plane V-0 bond distances (those norqal to the vanadyl oxygen atom) are V-01 of 1.943 (9) A and 1.947 (9) A, average 1.945 (9) A, and are similar to those found in N,N'-ethylenebis( l-acetonylethylideniminato)oxova>adium(IV), VO(acen), where they average 1.950 ( 6 ) A,2 and are slightly shorter than the V-0 (water molecules cis to the vanadyl oxygen) bonds, average 2.040 ( 5 ) A, found in [OV(Hz0)4S04]H~0.8 Similarly the V-N bonds in VO(sa1pn) (cis to the vana(y1 group), V-N1 of 2.100 (13) and V-N2 of 2.124 (13) A, average 2.112 (13) A, are longer than in VO(acen),2 average 2.053 (6) A, but similar to the average of 2.08 (2) 8, found in deoxophylloerythroetioporphyrinoxovanadium(IV), VO(por). Therefore the V-ligand distances in VO(sa1pn) are similar t o those found in other vanadyl derivatives, and the unusual characteristics of VO(sa1pn) must be related to other properties of the molecule. The most striking difference between VO(sa1pn) and other vanadyl complexes involving chelating ligands is the more nearly planar nature of the molecule. The V atom is displaced by only 0.31 8, from the plane defined by the 0 1 , 0 2 , N l , and N2 atoms compared to 0.54-0.58 A in other complexes. lo The planar nature of the complex together with the interaction of the vanadyl oxygen atom with a second vanadium atom could account for the difference in color between VO(salpn) and other complexes. A comparison of the infrared spectra of VO(salpn), the free ligand, and the copper complex of the ligand shows that v(V=O) appears at 854 cm-l as a very intense absorption. Since the v(V=O) stretching mode of oxovanadium(1V) complexes generally is in the range (9) The earlier V-0 distances are summarized in ref 5. (10) The values for some individual complexes have been summarized in ref 2.
Journal of'the American Chemical Society
(11) A . P. Ginsberg, E. Koubek, and H. J. Williams, Inorg. Chem., 5 , 1656 (1966). (12) R. J. H. Clark,J. Chem. Soc., 1377(1963). (13) J. Selbin, Coord. Chem. Reu., 1,293 (1966).
M. Mathew, A. J. Carty, Gus J. Palenik Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada Received January 28, 1970
Evidence for a Three-Coordinate Complex of Nickel(I1) Sir: We have obtained evidence for the formation of the very unusual three-coordinate NiC13- complex in liquid CsA1C14at 400-750'. Dilute solutions of Ni(I1) in liquid CsA1C14containing on the order of. 10-3 M added CsCl were found to have an unusual absorption spectrum. Upon increasing the CsCl concentration this spectrum was progressively replaced by that of NiCh2-. The equilibrium solubility of solid CsNiC13 in such melts was found to obey the relation [Ni(II), total] = a[CsCl] kl at 400-480°, where a and kl are constants at a given temperature. Quantitative spectrophotometric measurements showed unambiguously that the concentration dependence of this expression was due entirely to changes in the concentration of NiC14*- while the concentration of the new species stayed constant. Therefore, the new species has the stoichiometry of (NiC13)nn-,apart from solvation, and the dissolution of CsNiC1, may be represented by the two heterogeneous equilibria
+
+
nCsNiCls(s) = (NiCls),,"-(soln) nCs+(soln) CsNiCl,(s) C1-(soln) = NiC14a-(soln) Cs+(soln)
+
+
(1)
(2)
Because [Csi-] was essentially constant in these systems and because [Cl-] due to added CsCl was great enough to permit neglect of the equilibrium 2AlC1,- = AlzC1,C1-, it follows that (l/n)[(NiCl,),"] = kl and [NiC142-]/[Cl-] = a/(l - a) = kz, where [Cl-] = [CsCl] - [NiC142-]. Experimentally, log kl and log kz were found to be linear functions of 1/T. The homogeneous equilibrium between NiCL2-(soln) and (NiC13)nn-(~~ln) was studied spectrophotometrically over a wide C1- concentration range at 500-750' for nickel concentration below saturation with respect to solid phases. Absorbance values at 14 wavelengths accurately fitted the relationship k3 = [NiC13-][Cl-]/[NiC14z-], where k3 is a constant at a fixed temperature, Therefore, the homogeneous equilibrium is accurately represented by
+
92:lO 1 M a y 20, 1970
NiClaa-(soln) = NiCls-(soln)
+ Cl-(soln)
(3)
3199
apart from solvation of NiC13-, Le., n is unity. This I I I fitting was done by digital computer which simultaneously generated ka values and the spectra of the component species. The latter are shown in Figure 1. Band maxima for NiCla- are at 13,100 and 17,700 cm-I. The quantity log ka was a linear function of 1/Tover the range 500-750". From the temperature dependence of kl, kz, and ks it LL was found that AHl"z 25.8 kcal, ASl"E 23.5 cal/deg, AH2" = 13.1 kcal, AS," 14.6 cal/deg, AH," = (13.3 f 0.2) kcal, and AS," = (9.8 f 0.1) cal/deg. Since eq 1,2, and 3 are interdependent, AH,' - AHz" AHl" and AS," - AS2" AS," should equal zero, a: which they do to within experimental uncertainty. 4 5 0 The spectrum of NiC1,- differs markedly from the a spectra for approximately octahedral 1--3 and approximately tetrahedral chloronickel(I1) entities in crys0 tals, molten salts, and other solutions. In this respect WAVENUMBER (cm-'l the absence of a spin-allowed band between 5000 and 13,000 cm-' is noteworthy. This result rules against Figure 1. Spectra of NiCIIZ- and NiCls- in molten CsAlCl, the monosolvated species NiC13AlC142-, which, in containing small amounts of added CsCl at 600". Calculated from spectra of mixtures using exprimental k3 value. analogy to NiC13ZnC143-, would be expected to consist of (NiC14) and (A1C14)tetrahedra that share a ~ o r n e r . ~ @ye and Gruenh have given preliminary evidence for precisely this entity in liquid KA1Cl4. field due to solvent ions above and below the molecular The unusual spectrum of NiCla- is satisfactorily plane in a way that is analogous to the perturbation of rationalized in terms of Dlh point group geometry. nitrate ions by surrounding ions in a molten alkali Computer calculations of the energy levels for this metal nitrate. geometry utilized the tensor operator equations deFinal values of Bo2and Bo4 for NiC13- were 13,300 scribed by Wybourne6 with Bo2 and Bo4 as potential and - 3900 cm- l, respectively. These compare7 with parameters. Values of the two electronic repulsion - 12,600 and -4200 cm-I, respectively, for gaseous parameters and the spin-orbit coupling constant were NiC12 and, hence, have a reasonable magnitude. the same as those used by DeKock and Gruen7 for Acknowledgment. The work described here was gaseous NiC12. (The latter three parameters have sponsored by the U. S. Atomic Energy Commission about the same values for all chloronickel(I1) entities.) under contract with the Union Carbide Corporation. Best fits between calculated and observed transition Jorulf Brynestad, G . Pedro Smith = -813 and 513. In energies were achieved with Bo2/Bo4 Metals and Ceramics Division, Oak Ridge National Laboratory the electrostatic point-charge model the former corOak Ridge, Tennessee 37830 responds to a weak axial perturbation and the latter to Received January 29, 1970 a strong axial perturbation, Le., NiC13(AlC14)23-. The latter entity cannot be reconciled with the large, positive value as AS3" unless the reaction is accompanied by a Photodimerization of Norbornadiene Using large structural change in the solvent. But the availChromium Hexacarbonyl able evidence indicates that liquid alkali metal tetrachloroaluminates containing an excess of alkali metal Sir: chloride do not have elaborate or rigid interionic During the course of our investigations into the structure^.^,*-^^ For this reason we discard the fivemechanistic details of metal carbonyl assisted photocoordinate entity NiC13(AlC14)23-as very improbable dimerization of norbornadiene, we have extended the and conclude that NiC1,- is not complexed to solvent number of useful metal carbonyls and identified one of ions. It is, of course, weakly perturbed by the coulomb the intermediates in the reaction. Norbornadiene was first dimerized photochemically (1) R. W. Asmussen and 0. Bostrup, Acia Chem. Scand., 11, 745 ( 1957). by Pettit2 using Fe(C0)5, and the reaction was further (2) J. Brynestad, H.L. Yakel, and G. P. Smith, J . Chem. Phys., 45, characterized by Lemal. a Other workers have shown 4652 (1966). that norbornadiene can be dimerized thermally using (3) C . R.Boston, J. Brynestad, and G. P. Smith, ibid., 47,3193 (1967). (4) C. A.Angel1 and D. M. Gruen, J. Phys. Chem., 70,1601 (1966). Ni(C0)4, ((C6H6)3P)2Co2(CO)aY6Fe(N0)2( CO)zy6 Co(5) H. A. @ye and D. M. Gruen, Inorg. Chem., 4, 1173 (1965); see (C0)&Oy6 and Fez(C0)9.7 Schrauzer has added other last paragraph on p 1176. olefins to norbornadiene thermally and suggested (6) B. G. Wybourne, "Spectroscopic Properties of Rare Earths," lL
+
+
Interscience, New York, N.Y.,1965,pp 26,38,164,and 165. (7) C. W. DeKock and D. M. Gruen, J. Chem. Phys., 46, 1096
(1967). (8) B. Trbmillon and G . Letisse, J . Electroanal. Chem. Interfacial Elecfrochem.,17,371 (1968). (9) J . R. Morrey and R. H . Moore, J. Phys. Chem., 67,748 (1963). (10) G. L. Carlson, Spectrochim. Acra, 19,1291 (1963). (11) G. Begun, G. Torsi, and G. Mamantov, private communication on the Raman spectroscopy of tetrachloroaluminate melts. 112) D. E. H.Jones and J. L. Wood, Spectrochim. Acta. Parr A, 23, 2697 (1967).
(1) Bicyclo[2.2.l]hepta-2,5-diene. (2) R. Pettit,J. Amer. Chem. Soc., 81.1266 (1959).
(3) D.M. Lemal and K. S. Shim, TetruhedronLeir., 368 (1961). (4) C.W. Bud, R. C. Cookson, and J. Hudec, Chem. Ind. (London), 20 (1960). (5) D. R. Arnold, D. J. Trecker, and E. B. Whipple, J. Amer. Chem. Soc., 87,2596 (1965). (6) P. W.Jolly, F. G. A. Stone, and K. MacKenzie, J . Chem. Soc., 6416 (1965). (7) Reference 3,footnote 4.
Communications to the Editor
