COMMUNICATIONS  a ) M . I.Arriortua. R. CortPs. L. Lemma. T. RoJo. X. Solans. M. Font-Bardia. /my:. C ' h i n i . A<,trr 1990, 174. 263: h) R. Cortes, J. I. Ruiz de Larramendi. L. Lezama. 'T.R o p . K. Urtiaga. M . I. Arriortua. J Chrm. SOC.Dulron Trans. 1992. 3 7 3 [ 3 ] a ) J. Ribas. M. Monfort, C. Diaa. C. Bastos. X. Solans. Inorg. Chern. 1993. 32. 3557. b) A . Escuer. R. Vicente, M. S. El Fallah, J. Ribas, X. Solans. M. FontBardia. J. C'/IIW. Sor. Dalrori Truns. 1993, 2975; c) A. Escuer, R. Vicente. J. Ribas. M. S. El Fallah. X. Solans. Iriorg. C / ~ e m1993. . 32, 1033: d) A. Escuer. R Vicente. .I Ribas. M. S. El Fallah. X. Solans, M. Font-Bardia, ihid. 1993.32. 3727. ?) l / J i l / 1994. 33, 1842.  a ) R . Viccnte. A. Escuer. J. Ribas. M . S. El Fallah, X. Solans. M. Font-Bardia. Iriorg. C ' / ~ ~ w i 1993. . 32. 1920; b) J. Ribas, M. Monfort. C. Diaz. C. Bastos. X. Solan\. I n o r x . C 7 / 1 c n i . 1994, 33, 484. c) J. Ribas. M. Monfort, R. Costa. X. Sol.in\. / h i d . 1993. 32. 695.  'I) M Monfort. J. Ribas. X. Solans. J. Chrm. SOC.C ' / t r m . Comiiwn. 1993. 350: b) J. Ribas. M. Monfort. X . Solans, M. Drillon, Iriors. Clirm. 1994. 33. 742. [6) R Cortks. M. K Urtiaga. L. Lemma. J. 1. Ruizde Larramendi, M . I. Arriortud. T. Rojo. J C ' / r ~ w r .So(,. Dultori Truns. 1993, 3685, and references therein.  R. CortCs. J. L . Pizarro. L. Lemma. M. I. Arriortua. T. RoJo, I n o q . Chcm. 1994. 33. 2697. The Mn-N-Mn-angle IS 104.6 and J,k is t 3 . 5 K . [X] a ) B R Stults. R. S. Marianelli. V. W. Day. Inorg. Choii. 1975, 14. 722: b) A K Gi-cgaon. N. T. Moxon. rhrd 1982. 21, 586.  A Benciiii, C . A. Ghilardt. S. Midollini. A. Orlandini. Iriorg. CAm. 1989. 28, 195x [lo] X-r:i> \tructure analyses: Enraf-Nonius CAD4 diffractometer. Mo,, irradiation. 0.71069 A. graphite monochromator. 298 K. Lorenti: polarization but no ;ibxxption corrections. Data collection. solution and refinement d;ird Patterson methods Nith SHELXS computer program, SHELXS93 computer program. The positions of the twelve methyl H atoms were determined by difference synthesis. while the position of the remaining four Mere computed a n d refined h i t h a n overall isotropic temperature factor .id I-ding model. C,,H,,N,,Ni, ( M = 517.92). monoclinic. apace group C?,III. I I = l6.360(3). h=11.3944(12). ~ = 3 3 . 4 8 5 ( 3 ) A . [$=113.34(1). r'=2?WY(h).&'. 2 = 4 . J I ~ ~ , ~ <1.489gcm-". , = p = 1 6 . 6 1 c1n-l. c i q s t a l size 0.1 x 0.2 x 0.1 mni". F(000)= 1088.0. 1843 unique reflections and 1793 assumed a s observed wzith / > I n ( / ) . 189 parameter% b!(<,) = 0.031. R,(S.) = 0 07/16. and S = 0.982 Further details of the crystal structure inbestig;itioii iirc available on request from the Director of the Cambridge Crystallographic Data (entre. 1 1 Union Road. GB-Cambridge CB2 1EZ ( U K ) . on quoting the 1~111journal citation. [ I I ] a ) J. .I Rorrns-Almenar. Dissertation. Universitat de Valencia. 1992 (Address: Departament de Quimica Inorglinica Universitat de Valencia Doctor Moliner. 5 0 , E-46100 Burjassot (Valencia. Spain); J. J. Borris-Almenar. E Coronado. J. Curel). R. Georges. Iriorg. C/t~w..in press: b) G . de Munno. M. Julve. F, Llciict. J. Fau\. M . Verdaguer, A . Caneschi. A n g ~ i v C . / i c m 1993. 10.7. 1122: .Aiiyr>ii. C ' / i i v i i . I n r , G I . €rig/. 1993. 32. 1046.  C. J. O'Conno?, Prug. liiorg. C/ri~ni.1982, 2Y. 239. [I31 J. C'oinai-nmond. P. Plumere. J.-M. Lehn, Y Agnus. R. Louis, R. Weiss. 0 . K'ihn. I.Morgciistern-Badarau. J A m C/icm?.Soc. 1982, 1/14, 6330. (141 M . F Charlot. 0 . K:ihn. M . Chail!ct. C. Larrieu. J. A m . C/?mn..%c. 1986, /OX. 2574. i. Ci. A. Rusholme. C/riwr. Currimrm. 1971. 496. The authors reported iietic dinuclear Mn'complex with one CO and three EO azido ligands. rqstal structure determination was not good. .I aldehydes has limited the types of well-characterized metal -aldehyde complexes to some organometallic species of the inert heavy transition metals[*]and to classical chelate complexes like those of salicylic aldehyde.[31The number of known adducts of metal halides with simple aldehydes14] o r aldehyde solvates of metal saltsis surprisingly small, and to our knowledge only one such complex['] has been structurally characterized.['] We became interested in this type of compound through our work on the bioinorganic chemistry of zinc, specifically by attempts to model the active site of the zinc enzyme alcohol dehydrogenase. The immediate coordination sphere of the metal in this enzyme is S,NZn-~ubstrate,['~and the closest approach to its static nature was achieved by Bochmann et al., who isolated complexes [Zn(SeR), . R'CHO], (R = C,H,rBu,, R' = aromatic group) and determined the structure for R ' = p-C,H,OMe.['ol In addition to working on this problem by preparing cysteine-zinc-(0 donor) complexes we carried out ii general screening of the donor/acceptor relations between simple zinc salts and monofunctional aldehydes. Here we report our findings for the zinc chloride system. For aliphatic aldehydes. condensations and polymerizations seem to be preferred over coordination in the presence of ZnCI, . But by dissolving anhydrous zinc chloride in a 100-fold excess of benzaldehyde and crystallizing by diffusion of petroleum ether into the solution, the compound [ZnCI, . benzaldehyde] ( 1 ) is obtained as colorless crystals." ' 1 Similarly, from p-methoxybenzaldehyde (anisaldehyde) the colorless 1 :2 complex [ZnCI, . 2 anisaldehyde] (2) is formed. Reacting the potentially chelating aldehyde pyridine-2-carbaldehyde (L) in stoichiometric amounts with zinc chloride and one half equivalent of water in ether, a product with yet another stoichiometry, [L,Zn,CI, H,O] (3). is precpitated as colorless crystals. ~ On the Nature of Zinc Chloride-Aldehyde Interactions"" Bod0 Muller, Michael Ruf, and Heinrich V a h r e n k a m p " Among the large number of organic reactions that involve aldehydes as starting compounds or products, many are catalyzed by simple metal salts, ZnCI, being the most prominent co-reagent for carbonyl conversions."] This should imply that the Coordination chemistry of aldehydes or the reactivity of aldehydes in the hgdnd sphere of complexes are attractive objects of study. However, the inherently low donor strength of [*] Prof. Dr. H. Vahrenkamp. Dipl.-Chem. B. Muller. DipLChem. M. Ruf Institiit f u r Anoiginische und Analytische Chemte der Universitit Albertstrasse 21. D-79104 Freiburg ( F R G ) Telekir. Int. cudc + (761)203-6001 [**I Thi\ \\oi-k w a s supported by the Deutsche Forschungsgemeinschaft. I In 1, 2, and 3 the aldehyde v(C0) bands in the I R spectrum at 1682, 1677. and 1663 cm-', respectively, are shifted by 2050 cm-' to lower wavenumbers, indicating coordination of the aldehydes through their oxygen 'I Similarly the ' H N M R signals in acetone of the aldehyde protons for I (6 = 10.02), 2 (6 = 9.91), and 3 (6 = 10.27) respond to the complexation by low-field shifts of Ad = 0.1 -0.2. The crystals of 1 were not suitable for a structure detemination. The solubility of I , however, indicates the presence of a molecular species which, in accordance with Bochmann's selenolate complex,"01 may be formulated as a chloride-bridged dimer. The structure of 2 was obtained crystallographically." Figure 1 shows one molecule of 2, which to our knowledge is the first structurally characterized transition metal halide complex of a simple aldehyde. Complex 2 is a quite normal tetrahedral zinc complex with all bond lengths and angles at zinc within the COMMUNICATIONS Cyanide- lsocy anide Isomerism in CN-Bridged Organometallic Complexes** N i a n y o n g Zhu and Heinrich Vahrenkainp* Fig. 1. Molecular structure of 2. Selected bond length, [pni] and angles [ I: Zn-CI 219.8(1). Zn-O 202.0(4): 0 - Z n - 0 100.2(2). C1-Zn-Cl 130.0(1). CI-Zn-0 105.0(1) and 106.5(1). Zn-0-C 127.3(4). standard range, except for a slight increase of the CI-Zn-CI angle. Thus, there are no bonding features supporting the argument that such complexes should be difficult to obtain. This in turn means that unusual steric hindrance or the presence of special chalcogenolate hgands"*] are not prerequisites for their isolability. However. care must be taken in handling the compounds, since they are extremely hygroscopic. The structure (also obtained crystallographically) of 3, which initially resulted from accidental access of water, underlines this. The comparison of 1.2, and 3 points to the subtleties governing the coordination behavior of the three aldehydes. In solid 1 the aldehyde donor seems to be unable to compete with a Zn-CI unit for a coordination position on zinc despite the large excess of the aldehyde in solution. In 2 the p-methoxy substituent on the phenyl ring has sufficiently increased the donor capacity of the aldehyde to enable this. Complex 3 shows yet another way of balancing the donor abilities of the aldehyde and chloro ligands: one zinc ion binds both chelating aldehydes. the second one is only coordinated by chloro ligands. These findings underline the ambiguity about the inode of coordination of the aldehydes. which is due to their low donor capacity. This in turn means that mechanistic implications about metal salt mediated organic reactions of aldehydes[" 1 3 ] may have an equally high degree of ambiguity. Received: May 9, 1994 [Z 6911 IE] Geriixin version: Ati~zcii.Chrtii. 1994. 106. 2164 [ I ] a) C h n t ~ " h r r , . s i l r Organic C h e n i u r r j , V d . I (Eds.: D. Barton. W D. Ollis. J. F. Stoddart). Pergamon, Oxford. 1979; b) R. Brettle in ref [ l a ] , pp. 943- 1016; c)T. Laird in ref. [ l a ] . pp. 1105 -1160 121 Y. H. Huanp. J. A. Cladysr. J Climi. €dirt. 1988. 6i. 298 303.  Papers [hat conlain srructural data: D. Hall. A. J. McKinnon. T. N . Waters. J. C h i . Snc. 1965.425 -430; M. R. Truter. R . C. Watling, J C'hrm. So<..4 1967. 1955-1963, R. J. Hill. C. E. F. Rickard. J. Inorg. Nircl. Chcni. 1977. 3Y. 1593 1596; J. B. Hodgson. C C. Percy. S p ~ r r o c h i n iActa . Purr A 1978.34.777 780.  F. Filippini. B. P. Suw. Hrlr. Chrnr. A ~ r u1971. 54. 1175 1178. and references therri n  P. L. Verheijdt. P. H. van der Voort. W. L. Groeneveld. W. L. Driessen. R d . TYIIK C'iiini. P l i ~ - B a . !1972. 91. 1201 - 1204. and references therein.  S. E. Denmark. B. R. Henke. E. Weber. J. A i n Clinii. So(. 1987. I O Y . 2512 2514. 17) Further structural studie3 involve ii Bi-, adduct of' anisaldehyde [ X a ] and a MeAI(OR), adduct of rBuCHO [8 b] [XI a ) T. M. Reetr, M . Hullmann, W. Massa. S. Berger. P. Radeinacher. P. Heyrnanns. J A m . C/iem. Soc. 1986. IOH. 2405-2408; b) M. €3. Power. S. G. Bott. U. L. Clark. J. L. Atwood, A. R. Barron. Orxunonierullics 1990.9,3086-3097. \ I. Bertini. C. Luchi[Y] H. Eklund, A. Jones. C . Schneider in Zinc,€ n ; y n i ~ ~(Eda.: nat. W. Maret. M. Zepperauer). BirkhBuser, Basel. 1986. p p 377-392. [lo] M. Bochmann, K. J. Webb, M. B. Hursthouae, M. Mazid. J C I i ~ n iSO<. . Cheni. Coi?iniitii. 1991, 1735- 1737. [ l l ] Previously described as a yellow powder: F. Filippini. B. P. Susz. H e h . Chnn. 4crn 1971. 54. 835-845. (121 Crystal data for 2: space group P2,2,2, u = 896.4(1). h = 1991.8(6), I' = 417 6( 1) pm, 1689 reflections. 105 parameters. R = 0.053. The inoleculc of 2 is bisected by ii twofold symmetriy axis. Further details of the crystal structure inve5tigation may be obtained from the Fachinformationszentrum Karl?. ruhe. D-76344 Eggenstein-Leopoldshafen (FRG). on quoting the depository number CSD-380052. [I 31 ('~~nrpri,li(,/i.si,.e O,-goiik S1.nrhrsr.s. I,ii/. 3 (Eds.: B. M. Trost. I. Fleming), Pergainon. Oxford. 1991 Bridged dinuclear complexes are a prime object of studies for mixed valence and electron transfer."] Among these complexes those with cyanide bridges have often been mentioned because of their obvious relation with Prussian Blue.[21The actual number of studies of their redox and mixed-valence behavior. however, is still rather small.13] We have started a systematic preparative, structural, and electrochemical investigation of cyanide-bridged complexes, in search of "organometallic Prussian Blue".[41 Such complexes are amazingly easy to prepare, since almost any organoinetallic complex with cyanide ligands (neutral o r anionic) can be used as a ligand itself for another organometallic unit. thereby establishing the CN links. Furthermore the oligonuclear species obtained this way seem to be highly inert towards M-CN-M' + M -NC-M' isomerizations, which are a common fate of classical complexes with C N links. leading to the thermodynamically preferred isomers.[', 5 1 This behavior has allowed us to prepare and characterize for the first time stable pairs of organometallic species with cyanideiisocyanide isomerism, that is species which exist in the M(p-CN)M' as well as in the M(pNC)M' forms.[61 Here we report on two such pairs which relate to complexes that we have described before. The first pair, 1 a and 1 b, can be [CP(CO),F~(~J-CN)M~(CO),CPI [ C P ( C O ) ~ F ~ ( ~ ~ - N C ) M I ~ ( C O ) ~ C ~ I la Ib derived from the pseudosymmetrical anion [Cp(CO),Mn(V-CN)M~(CO)~C ~ ]Replacing one neutral Cp(CO),Mn .I4] fragment on the left- or right-hand side of this complex by an isoelectronic cationic Cp(CO),Fe fragment results in the pair of isomers 1. Chemically this is achieved by either reacting [Cp(CO),FeCN] in T H F with [(thf)Mn(CO),Cp] to give 1 a or [Cp(CO),Fe(thf)]BF, in CH,Cl, with Na[Cp(CO),Mn-CN] to give 1 b. Recrystallization from CH,CI,/petroleum ether provides 1 a and 1 b in 25 and 4 5 % yield, respectively. Complexes 1 a (orange-red) and 1b (red) can be distinguished by their colors, as evidenced by their absorptions in the visible range showing a broad featureless band extending from the U V for 1 a and one exhibiting a weak maximum at 495 nm for 1 b. The differences in their vco bands and 'H N M R spectra are very small.[91 However, the CN stretching frequency for l b (2100 c m - ' ) is 50 cm-' lower than that for 1 a, which means that for this pair of isomers the different electronic situations are not accommodated by the M-CO units but by the bridging CN ligand. The redox behavior of 1 a and 1 bI9' reflects the orientation of the bridging CN by a difference of 0.24 V in the E,:,(ox) values. The second pair of isomers completes a series of compounds starting with 2 a and [2a]i.['01 While 2 a was obtained from Na[Cr(CO),CN] and [BrFe(dppe)Cp] (dppe = 1,2-bis(diphenylphosphano)ethane),['O1 2 b was prepared from [(CO),Cr(thf)] - [*I Prof. Dr. H Vahrenkamp. N . Zhu Institut fur Anorganische und Analytische Chemie der Unikcrsitlt Albertstrasse 21. D-79104 Freiburg (FRG) Telefax: Int code + (761)203-6001 [**I This work was supported by the Ciraduiertenkolleg "Systeme mit ungepaarten Elektronen" 'ind by the Landes-Sciiwerpunktprogwmm ..Elektroaktive Systeme fur die Sensorik".