1972 503Crystal and Molecular Structure of Benzoylacetonato-[A"-ethylenebis-(salicylideneiminato)]cobalt (111)-1 -5 WaterBy N. A. Bailey, B. M. Higson, and E. D. McKenzie," Chemistry Department, The University, Sheffield S3 7HFThe structure of the title compound has been determined by three-dimensional X-ray structural analysis. Thecrystals are monoclinic with a = 11.51 (1). b = 19.57(1), c = 11.42(1) A, p = 110.3(1)", space-groupPZ,lc,andZ = 4. The structure was solved by conventional Patterson and Fourier techniques and was refined anisotropicallyby block-diagonal least-squares methods, using 2928 independent, photographically-collected reflections, to afinal R of 0.068. The cobalt(il1) molecule has a normal octahedral co-ordination, with a bidentate p-diketonateligand and a strained non-planar configuration of the quadridentate salicylaldiminate ligand.The water moleculesform a hydrogen-bonded chain of four waters linking phenolate oxygens of two different molecules across acrystallographic centre of symmetry. Bond lengths are normal with a mean cobalt-oxygen distance of 1.891 (4)and a mean cobalt-nitrogen distance of 1.889(5) 8. However, the molecule is distinctly strained as shown bysome quite significant distortions of bond angles of the ligands and the cobalt(ll1) co-ordination polyhedron.PODDAR and BISWAS have reported cobalt(rI1) com-pounds with the quadridentate ligand (I) (salen) andp-diketone ligands, which are of the type [ColIT(salen)(p-diketonate)]. They postulated a structure in whichthe diketonate anion was bidentate, and hence thequadridentate salen necessarily had a non-planar con-figuration such as (11).Since such compounds of non-planar salen wereS.N. Poddar and D. I<. Biswas, J . Inovg. Nucleav Chem.,1969, 31, 565.previously unrecognised, and must undoubtedly bestrained, and since an alternative structure (111) alsoappeared possible, we have studied these compounds inconsiderably more detail. Carbon-bonded metal-p-diketone compounds are now firmly characterised,2 andwe have proved3 that a structure such as (111), with aD. Gibson, Co-ordination Chem. Rev., 1969, 4, 225; J. Lewis,3 N. A. Bailey, B. M. Higson, and E. D. McKenzie, Inorg.R. I;. Long, and C. Oldham, J . Chem. Soc., 1965, 6740.Nuclear Chem.Letters, 1971, 7, 591J.C.S. Daltoncobalt-carbon bond, is formed when malononitrilereacts with the oxidised Co(salen) under the same condi-tions used to prepare the p-diketone compounds. How-ever we can find no evidence4 that structures such asW(I)ROC,, ,CORCHL(a(111) are significant in these p-diketone species, and haveshown that they do have the postulated structure (11).We here present the results of a three-dimensionalX-ray analysis of the structure of a crystalline compoundof benzoylacetone (bzacH) [Co(salen) (bzac)] ,1.5H20.Whilst this work was in progress, preliminary reportswere given of the structures of two other compoundswith the same basic molecular structure : [Co(salen)-(acac)] ,H,O and [Co2(3-0Me-salen),] (acac = acetyl-acetonate ; 3-OMe-salen = 3-methoxy-salen) .EXPERIMENTALGreen diamond-shaped prisms were obtained fromThe crystal used for data collection had dimen-Unit-cell data wereCrystal ~Uta.-c26H26CON20,,,, &f = 513.5, Monoclinic,U = 2410.8 D, = 1.414 (by flotation), 2 = 4, D, =1.420.F(000) = 1068. Space-group, P2Jc (CihJ No. 14)from systematic absences: (hOZ}, for I = 272 + 1, and{OKO), for K = 2n + 1. Mo-K, radiation, h = 0-7107 A,p(Mo-K,) = 7.9 cm-1.Photographic X-ray data for the layers hk0-5, 0-5kZJand hk2h were collected by precession methods using zircon-ium-filtered Mo-K, radiation, and intensities were estimatedvisually. Corrections were applied for Lorentz and polaris-ation effects, and for the splitting of the - Ka,2doublet.No corrections were made for absorption. Datawere scaled together by means of common reflectioiis togive 2928 independent reflections.The Patterson function calculated from this data setgave the position of the heavy atom (cobalt), from which,after one cycle of least-squares refinement, an observed4 B. M. Higson and E. D. McKenzie, to be published.5 M. Calligaris, G. Nardin, and L. Randaccio, Chent. COMZMZ.,acet0ne.lsions of ca. 0.35 x 0.25 x 0.25 mm.obtained from precession photographs.= 11.51(1), b = 19*57(1), c = 11*42(1) A, p = 110.3(1)",1969, 1248.Fourier synthesis gave the positions of the remaining atomsexcept the water molecules and the hydrogen atoms. Fivecycles of block-diagonal least-squares refinement of posi-tional and isotropic thermal parameters reduced R to 0.169.A difference Fourier synthesis then revealed two oxygenatoms of separate water molecules with peak-heights of ca.TABLE 1Atomic positions ( x lo4) wTith estimated standarddeviations and the calculated hydrogen positions ( x 103)x/a241 1.0(8)1085(4)287 7 (4)1326(4)3710(4)2532(6)07 80 (1 4)1 993 (5)3511(5)0866(6)1527(6)247 3 (6)3 150 ( 5 )27 1 7 (6)3403(7)45 1 O( 7)4963(7)4281(6)0432(6)- 0 188 (6)- 0395(6)- 1333(7)- 1467(8)- 0666(8)0311(6)1087(6)47 79 (5)5474(7)6628(7)7106(7)6440(7)5286(6)4694(7)2668 (6)3023 (7)008128183306504584462- 049- 094- 029 - 197- 222- 079090509717802683526209350223373Ylb1372*2( 3)1099j2)0467 (2)Z 358(2)1653(2)0714(3)06 1 1 (5)2272 (2)14 1 7 (3)0406(3)0485(3)-0086(3)-- 0070(2)- 07043)- 1362(3)- 1936(3)- 1872(3)- 1228(3)-- 0651 (3)1805(3)1670(3)2118(4)2732(4)28 78 (3)2429(3)262 1 (3)132 8 (3)1229(3)0889(4)0651(5)07 7 0 (4)1 090 (3)1 280 (4)2503(3)187 l(4)090012015- 058- 141- 244- 233-118-01511919930933631114008004005913128427816419'7zlc0911*7(7)1465 (4)1827(4)2 3 64 (4)4 146 (6)5 162 ( 13)0285(5)- 0021 2 142( (6) 6)- 053 1 (4)- 0907(6)- 03 1 O( 6)0827 (6)14 13 (5)0971(6)15 16( 7)2484(7)2914(7)2394(6)1736(6)2341 (6)2289(7)161 7 ( 8 )1019(7)1 037 (6)0381(6)2 67 0 ( 6)42 87 (8)3414( 10)2 152(9)0484( 7)3947(7)1777(7)- 0521 (6)-1088(6)- 252- 280- 198- 07802 11172893672 76287279156049-010466527373144-014- 125002- 181- 1504.6 and 1.6 eA-3.The positions of these were consistentwith a hydrogen-bonded water chain linking oxygen atomsof the salen moieties of two molecules across the centre ofsymmetry (see Results and Discussion section). The rela-6 M. Calligaris, G. Nardin, and L. Raidaccio, Chem. Conzm,1970, 10791972tive peak-heights were consistent with the presence of one of the cobalt atom increased R marginally to 0.068, butfull and one half water, as suggested by the chemical reduced the shifts in the positional parameters.analyses and the measured density.Accordingly, they The atomic positions with estimated standard deviationswere inserted as such into the set of atomic positions, and are listed in Table 1, together with the calculated positionsbll837(1)948(7)962 (7)815(6)871(6)1953 ( 13)2541 (31)989(8)985(8)1035(11)SSS(l0)908( 10)761(8)781(8)1003 (10)1223[12)12 15 (12)1067(11)987 (1 0)872(9)945(10)1257(13)1329 ( 14)1400 (1 4)1003 (1 0)1041 (10)836(9)944(12)978( 12)1069( 12)862(10)1238( 13)1086t11)1264( 13)111 1( 12)TABLE 2Anisotropic thermal parameters * ( x lo5)b22 b,3 b23142(0) 741 (1) 18(1)185(2) 802(6) W5)180(1) 876(6) 23(5)142(1) 822 (6) -80(5)197(1) 839(6) 144(6)432 (3) 1464( 10) 372(10)314(5) 2203(28) 556(20)171(2) 822 (8) 107(6)263(2) 774(7) 124(7)271(3) 87 1 (1 0) 14(9)192(2) 908( 10) - 99(8)167(2) 849 (8) - 7(7)156(2) 832(9) 42(7)162(2) 1153(11) 38W199(2) 1084( 11) 181[8)181(2) 875(9) - 9(8)266(3) 978( 10) - 109(9)302(3) 1249( 13) -201 (11)303(3) 152 1 [ 15) O(12)244 (3) 1157( 12) 10(9)173(2) 906(10) 6(8)157(2) 854[9) 92(7)179(2) 972(9) 98P)217(2) 975(9) - 14(8)141(2) 121 8( 11) -28(9)208(3) 1132( 11) lOl(8)162(2) 762(8) -58(7)222( 3) 1187( 12) 125(9)352(4) 1605( 16) 263(13)485(5) 20 1 9 (20) 701( 17)381(4) 1953( 19) 269(30)231(2) 122 1 ( 12) 164(21)245(3) 908(10) 340(21)343(3) 890(10) 275(23)293(3) 1297 (1 3) 854(25)bl,390(2)132( 13)307(12)436(12)248(12)456(22)2705(58)420(15)667( 15)197(21)521(19)357 ( 19)703(17)729(17)751(21)1007(23)1123(23)751(22)272( 19)3 17( 17)742 (2 1)1 072 (2 6)10 18 (28)829(25)349(19)2 96 [ 1 9)533(18)23(23)61 l(31)986 ( 30)853(21)962(25)605(21)881 (23)- 80(27)b l ,-23(1)56(5)-39(5)49 (6)-72(5)- 394( 11)- 112(6)571(21)98(8)--48(9)-91(8)3.2 (8)--44(7)31(7)-76(8)- 59(8)147(9)153(8)19(8)- 45( 7)-23(9)128( 11)361(11)330(10)97P)- 203 (8)-230(9)- 158( 11)230( 13)208( 12)139( 11)96( 1 I)-66(8)-30(9)* The expression for the temperature factor is: exp[- (h2b,, + k2b2, + Z2b3, + kZb,, + hZb13 + hkb,,)].their unexceptionable behaviour on further refinement wastaken as proof of the assignment, No attempt has beenmade to refine population parameters of the half oxygen.Further refinement with isotropic thermal parametersnow reduced R to 0.12, and with anisotropic thermal para-meters to 0.080.A difference Fourier revealed most of the hydrocarbonhydrogen atoms at the expected positions.The meanpeak-height was 0.35 eA-3 and no other density >0.3 eA-3was observed, except for residual peaks of 0.6 eA-3 a t dis-tances of ca. 1 A from the cobalt atom. The density aroundthe water chain was ill-defined, with no peak >0-25 eA-3,so that unambiguous assignment of the hydrogen atoms ofthe water molecules was not possible. Except for these,the hydrogen-atom positions were calculated assumingC-H 1-08 A. For the methyl group, two of the hydrogenatoms were generated from the position of the carbon andthat of the highest peak (0.35 eA-3) corresponding to areasonable hydrogen position.These (with isotropicthermal vibrations of 7-3 A2) were included, but not varied,of the hydrogen atoms ; and the anisotropic thermal para-meters are listed in Table 2. The molecular geometry of thein the further refinement.reduced R to 0.069.ing scheme of the form: w = 1/(1 + [(IFol - b)/u]2), cobalt(m) species and the atom numbering system are givenwhere n = 2000 and b = 1800, caused further con- in Figure 1, and the hydrogen-bonded water chain invergence to 0.067. Hydrogen atoms are given the same numbers asFIGURE 1 The molecular geometry of Co(salen)(bzac) withFurther cycles of block-diagonal least-squares refinementIntroduction of a non-unit weight-the atom and chelate-ring labelling systemAllowance for the anomalous scattering Figure 2.506 J.C.S.Daltonthe carbon atoms to which they are bonded, with superiorfigures denoting the different hydrogens attached to thesame atom.Atomic scattering factors and the anomalous dispersioncorrections are taken from ref. 7 . Observed and calculatedstructure factors are listed in Supplementary PublicationNo. SUP 20282 (27 pp., 1 microfiche) *, together with aTable of the dimensions and orientations of the thermalellipsoids of vibration of the atoms.I 2*823(a3 AFIGURE 2 The hydrogen-bonded water chain with bondEstimated standard deviations lengths (A) and angles (").are given in parenthesesRESULTS AND DISCUSSIONDetails of the various bond lengths and angles aregiven in Table 3.There are no intermolecular contactsshorter than the sum of the van der Waals' radii.The molecule [Co(salen) (bzac)] has the same basicstructure (Figure 1) as that of [Co(~alen)(acac)].~ Thecobalt has the normal octahedral co-ordination foroxidation state +3, the P-diketonate anion is oxygen-bonded bidentate, and the salen has the cis-P configura-tion of a facultative quadridentate ligand.Bond lengths are generally normal, but a variety ofangular distortions are observed. The salen ligandadopts a significantly strained configuration about themetal, and there are also significant distortions of theco-ordination polyhedron of the latter.The Cobalt (111) Co-ordination Polyhedron.-The Co-0and Co-N bond lengths are all very similar at ca.1-89 A.The four Co-0 bond lengths appear to be identical[mean 14391(4)] ; but the Co-N distances of 1.898(5) and1.881 (5), although not experimentally different, mayreflect the different bonding situations of the two nitrogenatoms.The bond angles at cobalt deviate significantly fromgo", ranging between 83.3(2) and 95.3(2)". Such devi-* For details of Supplementary Publications see Notice toAuthors No. 7 in J. Chem. SOC. (A), 1970, Issue No. 20.' International Tables for X-ray Crystallography,' vol. 111,Kynoch Press, Birmingham, 1962.A. M. Sargeson and G. H. Searle, Nature, 1963, 200, 366;Inorg. Chem., 1965, 4, 45.TABLE 3Bond lengths (A) and angles (") with estimateddeviations in parentheses(a) The c(i) Bond lengthsco-O( 1)co-0 (2)O( 1)-co-O(2)(20-0 (3)(ii) Bond angles0 (l)-C0-0 (3)O( l)-C0-0(4)0 (l)-CO-N (1)O( l)-Co-N(2)0(2)-C0-0 (3)0(2)<0-0(4)0 (2)-Co-N( 1)(i) Bond lengths0(1)-C(2)0(2)-C(4) c (1 )-C (2)C(2)-C(3)C(3)-C(4)C(41-475)O( l)-C(2)-C( 1)C( 1)-C(2)-C(3)0(1)-C(2)-c(3)c (2)-c (3)-c (4)C( 3)-C( 4)-c (5)(ii) Bond anglesC( 3)-C( 4)-0 (2)0 (2)-C (4)-C (5)[i) Bond lengths0(3)-C(11)0 (4)-C ( 1 8)N( l)-C(17)N ( 1 )-C (25)N (2) -C( 24)N (2)-C( 26)C( ll)-C(12)C( 12)-C( 13)C( 13)-C( 14)C(14)-C( 15)C(15)-C( 16)C( 11)-C(16)(ii) Bond anglesCO-0 (3)-C ( 1 1)Co-O(4)-C( 18)Co-N(l)-C( 17)CO-N ( 1 )-C (25)C( 17)-N ( 1)-C (25)CO-N (2)-C (24)Co-N(2)-C(26)C (24)-N (2) -C( 26)0 (3)-C( 1 1)-C( 12)O( 3)-C( ll)-C( 16)C( 12)-C ( 1 1) -C (1 6)C( 1 1)-C( 12)-C( 13)C(12)-C(13)-C(14)c(13)-c( 14)-c(15)C( 14)-C( 15)-C( 16)C( 1 1)-C( 16)-C ( 15)C( 15)-C( 16)-C( 17)C(l l)-C(16)-C( 17):o-ordination sphere of the metal1*893(4) c0-0(4)1*896(4) Co-N( 1)1.887(4) Co-N(2)94.3 (2) 0 (2)-Co-N (2)89.4 (2) 0 (3)-C0-0 (4)178-8(2) 0(3)-Co-N(1)85*0( 2) 0 (3)-Co-N( 2)91 *9( 2) 0(4)-Co-N( 1)88.1(2) 0(4)-C0-N(2)86-2(2) N (l)-Co-N( 2)17 6.5 (2)(b) The diketone ligand1*271(8) C(5)-C(z)1.270(7) C(6)-C( i)1*515(9) C(7)-C(8)1 ~392 (9) C( 8)-C (9)1.375(9) C(9)-C(lO)1-495(8) C(5)-C( 10)114*4(5) C(4)-C(5)-C(6)119-9(6) C(4)-C(5)-C( 10)125*7(6)C(6)-C(5)-C(lO)124.3 (6) C( 5)-C( 6)-C( 7)C (6)-C (7)-C(8)12 1 *4 (5) C (7)-C (8)-C (9)125*0(6) C(8)-C(9)-C(lO)113*6(5) C(5)-C(lO)-C(9)(c) The salen ligand1.327(7)1.3 1 9 ( 7)1*284( 8)1.467(9)1*306(9)1 *4 88 (9)1 * 38 3 (9)1-375(11)1.405 ( 12)1 *355( 12)1*439(9)1-439(9)12 6.3 (4)1 1 8.3 (4)124*7(4)113-8(4)120*8(5)125.1 (5)1 1 1.2 (4)119*9(6)119-0(6)12 1 -7 (5)119.3(6)12 1.5( 7)120-2 (7)1 1 9.4 ( 8)122.4(7)1 1 7- 1 (6)118*4(6)1 24.6 (6)C( 16)-C( 17)C( 18)-C( 19)C( 19)-C(20)C(2O)-C(2 1)C( 2 1)-C(22)C(22)-C(23)C ( 1 8)-C (2 3)C(23)-C(24)C(25)-C(26N( 1)-C( 17)-C( 16)N ( 1) -C (25)-C (2 6)N (2)-C(26)-C( 25)N (2)-C( 24)-C (2 3)0(4)-C(18)-C(19)0 (4)-C [ 1 8)-C (23)C(19)-C( 18)-C(23)C(18)-C( 19)-C(20)C( 19)-C(20)-C(21) c (20)-c (2 1)-c (22) c (2 l)-C(22)-C (2 3)C(22)-C(23)-C (24)C( 18)<(23)-C(22)C ( 1 8)-C( 23)-C (24)standard1 *88 8 (4)1*898(5)1*881(5)93 * 3 (2)89*5(2)95-3(2)178-0(2)94*7(2)98.2(2)83.3(2)1*409(9)1 388 (9)1 - 3 72 ( 1 0)1.387(10)1 * 385 (9)1.396 (9)122.3 (5)119*5(5)1 1 8.2 (6)120.2 (6)120*8(6)119*8(7)120.1(6)120.9(6)1.401 (9)1.412(9)1 *415( 11)1 * 3 7 6 ( 1 3)1*397(13)1*396(12)1 *4 1 8 ( 9)1.440(10)1*517(10126.2(6)107.2(6)101.7( 6)1.2 1-4( 7)1 18.8 (6)123.1 (6)1 18.1 (6)1 19.3 (7)122 * 3 (8)1 1 8.5 (9)120-9(8)120.9 (7)11 9.3(7)119.1(61972 507ations are larger than normal for the compounds of suchligands, and they have their origin in the various ligandsteric constraints (see later).The Salen Ligand.-The strain here is convenientlynoted under three headings.It is apparent largely asangular distortions, and none of the bond-length dif-ferences are experimentally significant.(a) Angular strain in the ' en ' chelate ring is apparentin : (i) the smaller-than-tetrahedral angles at the methyl-ene carbon atom, especially the angle N(2)-C(26)-C(25),which is only 101.7"; (ii) the conformation of the chelatering [C(25) is almost exactly in the Co, N(l), N(2) plane];and (iii) the acute angle subtended by N(1) and N(2)a t the cobalt, which at 83.3" is much less than the morenormal 87".9(b) The co-ordination polyhedra of the azomethinenitrogens [especially N(2)] are non-planar. N(2) is0.17 A out of the plane of Co, C(24), and C(26), and N(1)0.08 A out of the plane of Co, C(17), and C(25).(c) The angular strain in the salicylaldimine ring B(Figure 1) is quite clearly shown by comparison withring A, for which the bond lengths and angles are veryclose to those observed in most relatively unstrainedsalicylaldimine chelate compounds.1° The light atomsof ring A are closely co-planar (Table 4) with the cobalt0.21 A out of this plane, whereas those of ring B alldeviate markedly from the least-squares plane, and thecobalt is 0.86 A out of this plane (Table 4).C(17), but not C(24), is in the same plane (Table 4) asthe phenyl ring to which it is attached.Further there is a marked difference between the anglesubtended at the cobalt by N(l) and O(3) (95.3", whichcorresponds to the normal situationlo) and the acuteangle subtended by N(2) and O(4) (89.2").Together these distortions must add up to a quitesignificant steric strain for the salen ligand in its adoptedconfiguration, and it would obviously prefer an essenti-ally planar configuration.It is also apparent that thechances of salen adopting a cis-a-configuration * (apossibility noted by Calligaris et aL5) must be negligible.The Benxoylacetonato-1igand.-Bond distances andangles in the P-diketonate ligand are all normal withinexperimental error, but the ligand adopts an unstableconfiguration which may also contribute to angle strainat the cobalt atom.The phenyl substituent is nearly co-planar with thesix-membered C,O,Co chelate ring (angle between planes13.7").This moiety is closely equivalent to the bicyclicaromatic systems such as biphenyl, for which co-planarityof the rings is a strained situation,ll and in the presentcase strain is indicated by the relatively short calculatedH * * - H interaction [H(3) * H(6) 1.96 A]. Furtherrotation of the phenyl group out of the chelate-ringplane, which would relieve this strain, is inhibited byintermolecular contacts.This configuration of the ligand may also contribute todistortion of the cobalt co-ordination polyhedron. ThusB. Bosnich, R. D. Gillard, E. D. McKenzie, and G. A. Webb,J. Chem. SOL. ( A ) , 1966, 1331.O(2) is 0.03 A out of the Co, 0(3), N(l) plane, in thedirection of O(1).Yet with the large angle subtendedby O(2) and O(1) at the cobalt [94.3(2)"], O(2) would beTABLE 4Equations of the least-squares planes given in the formIX + mY + nZ = d (where X, Y, and Z are co-ordinates in Thedeviations of various atoms from these planes are givenin square brackets. Angles between some of the planesare listed at the end of the Tablereferred to the axes a, b*, and d).1 m n dPlane (1) : Co, 0(3), N ( l ) 0.4789 0.3670 0.7975 2.9199Plane (2) : Co, 0(4), N(2) -0.1855 0.9659 -0-2276 1.8971Plane (3) : Co, 0(1), O(2) 0-8539 -0.0214 -0.5201 1.4953Plane (4) : C(ll)-(16) 0.3420 0.4605 0.8191 3.0834Plane (5) : C(18)-(23) 0.4743 0.8797 0.0351 4.5005[0(2) -0.026, N(2) 0.0471[0(1) 0.017, O(3) 0.0501[0(4) -0.036, N(l) 0.1131[0(3) 0.018, N(l) -0.040, C(17) -0.0111[0(4) 0.014, N(2) -0.148, C(24) 0.1931Plane (6) : C(5)-(10) 0.7510 0.0465 -0.6587 1.2440[C(4) 0.0581Plane (7) : 0(3), N(I), 0.3520 0.4666 0.8114 3.1003C(11), C(16), C(17)[CO -0.206, O(3) 0.010, N(1) -0.010, C(11) -0.011, C(16)O*OOO, C(17), 0*011]Plane (8) : 0(4), N(2), 0.4235 0.9056 0.0218 4.3299C(18), C(23), C(24)[CO -0.855, O(4) 0.065, N(2) -0.111, C(18) -0.033, C(23)-0.078, C(24) 0.1661Plane (9) : 0(1), 0(2), 0.8766 0.1134 -0.4676 1,7727C(2)-(4)[CO 0.191, O(1) 0.016, O(2) -0.010, C ( l ) -0.055, C(2) -0.024C(3) 0.012, C(4) 0.006, C(5) 0*050]Plane (10) : Co, C(24), 0.1358 0.8621 0.4882 3.1194C(26)"(2) -0.171]Plane (11): Co, C(17), 0.4060 0.4083 0-8176 2.8744C(25)"(1) 0.0761Plane (12): Co, N(I), 0.4569 0-3687 0.8095 2.8832N (2)[0(2) -0.029, O(3) 0.047, C(25) -0.031, C(26) -0.6891Angles between planes (")(4)-(7) 0.8 ${$; 3:::(3)-(9) 8.4expected to be out of this plane in the other direction.But in such a case, H(10) would be too close to C(18)and C(23) of the salicylaldimine chelate ring.Themarked difference in the angles 0(3)-Co-0(2) andN(2)-Co-0(2) may have a similar origin.We have no evidence for the apparently less strainedlo M. Gerloch, E. D. McKenzie, and A. D. C. Towl, J . Chent.SOC. (A), 1969, 2850, and references therein; M. Calligaris, D.Minichelli, G. Nardin, and L. Randaccio, J. Chem. SOG. ( A ) , 1971,2702, and references therein.11 G.Casalone, C. Mariani, A. Mugnoli, and M. Simonetta,A d a Cryst., 1969, B25, 1741J.C.S. Daltonisomer in which the positions of the methyl and phenylsubstit uent s are interchanged.The Hydrogen-bonded Water Chain.-The full watermolecule is hydrogen bonded to the phenolic oxygenatom O(3) at an O(3) - - - O(5) distance of 2.82 A, andthe half-water molecule is so placed that it forms, with0(5), a chain qf four water molecules across a crystallo-graphic centre of symmetry. Thus the waters linksymrnetry-related [Co(bzac) (salen)] molecules (Figure 2).All oxygen-oxygen contacts are within the range ex-pected for hydrogen bonding and all angles subtendedat the oxygen atoms are fairly close to tetrahedral(Figure 2).One explanation of the occurrence of O(6) with onlyhalf population could be that O(6) only occurs on oneside of the inversion centre at any one time, the occur-rence being random (i.e., some molecules could have achain of two water molecules attached to 0(3), and someonly one molecule). However, since only one site hasbeen observed for 0(6), and this is such (Figure 2) thatthe formation of the full water chain is facilitated, apreferred explanation is that approximately half thepairs of [Co(bzac)(salen)] molecules are linked by a fullchain of four water molecules, and the remainder haveonly the O(5) water molecules directly attached to them.In this latter case, the population of O(6) would not beconstrained to 0.5, although peak-heights suggested thisvalue.As can be seen from Figure 2, hydrogen atoms cannotbe associated with the water molecules in an ordered wayso as to conform to the space-group symmetry. Thus thefailure of the difference Fourier to show such atoms ispartially explained.[1/1624 Received, September 7th, 1971