摘要:
J . CHEM. SOC. DALTON TRANS. 1992 1869Ligand Design and Metal-ion Recognition. Comparisonof the Interaction of Cobalt(ii) and Nickel(1i) with 16- to19-Membered Mixed-donor Macrocycles tKenneth R. Adam,a Michael Antolovich,a Darren S. Baldwin,a Larry G. Brigden,aPaul A. Duckworth,B Leonard F. Lindoy,*e8 Alan Bashall! Mary McPartlin * s b andPeter A. Tasker*rCa Department of Chemistry and Biochemistry, James Cook University, Queensland 48 7 7, AustraliaDepartment of Applied Chemistry and Life Sciences, The Polytechnic of North London, LondonN78D6, UKResearch Centre, lCl Specialties, PO Box 42, Hexagon House, Blackfey, Manchester M.9 3DA, UK~~ ~~ ~ ~ ~ ~The interaction of cobalt(ii) and nickel(i1) with a range of 16- t o 19-membered ring macrocyclesincorporating nitrogen, oxygen and/or sulfur heteroatoms is reported.These ligands constitute anextensive array of related macrocyclic structures in which the positions of the donor atoms, theirspacing, and the macrocyclic ring size all vary in a systematic manner. Emphasis has been given tothe examination of structure-function relationships in the complexation behaviour. Physicalmeasurements confirm the 1 : 1 metal to macrocyclic ligand stoichiometry of the respective complexes.Stability constants for the metal complexes have been determined potentiometrically in 95% methanol(1 = 0.1 mol dm-3, NEt,CIO,). An X-ray crystallographic study of [NiL’8(H,0)][N0,], (L1* = 5,6,7,8,10,1 1,12,13,19,20-decahydrodibenzo[f,/] [1,8,11,4,15]oxadithiadiazacycloheptadecine) confirms that thenickel ion is six-co-ordinate with the complex cation exhibiting a distorted-octahedral geometrydefined by all five donor atoms of the ON,S, macrocycle and a water molecule; the macrocyclicbackbone incorporating the N-0-N donor fragment is arranged meridionally.Molecular mechanicsmodelling of selected nickel(ii) complexes has also been undertaken. As well as their considerableintrinsic interest, the results provide a potentially useful background upon which the design of newreagents for metal-ion discrimination may be based.The design and synthesis of organic substrates that prefer-entially interact with particular metal ions is of fundamentalimportance to many areas of chemistry. Metal complex stabilitywill be influenced by a range of factors, including (i) the numberand nature of the donor atoms and their spatial arrangement,(ii) the backbone structure of the ligand and its ability toaccommodate the preferred co-ordination geometries of therespective metal ions (including the degree of ‘preorganisation’present in the system),‘ (iii) the number and size of the chelaterings formed on complexation, and (iv), for transition-metalions, crystal-field effects of the type underlying the Irving-Williams stability order.2Relative to their open-chain analogues, macrocyclic ligandshave further stereochemical constraints associated with theircyclic nature which may influence their potental for metal-ionre~ognition.~ For macrocycles incorporating rigid or semi-rigid cavities, recognition (and hence discrimination) may beassociated with a close match or otherwise of the radius of themetal ion for the cavity.A further discrimination mechanisminvolves the use of a gradual change of properties (such asmacrocycle hole size or degree of ligand substitution) along aligand series to trigger a sudden change in the co-ordinationgeometry along the corresponding series of metal complexes. Aprocess of this type may form the basis for discriminatingbetween different metal ions and has been termed ‘dislocationdis~rimination.~ Several examples of structural dislocationshave now been do~umented.~-~In the present study a comparative investigation of the inter-t Supplementary data available: see Instructions for Authors, J.Chem.Soc., Dalton Trans., 1992, Issue 1, pp. xx-xxv.Non-Si units employed: dyn = lW5 N, D N“ 3.33 x C m.action of cobalt(u) and nickel(r1) with the extensive array of 16-to 19-membered macrocycles, L’-LZo, is reported. Incorporatedin the comparison are data for the interaction of these metalswith the O,N,-donor ligands L4 and L7-L9; log K data forthese systems have been reported previously (see be lo^).^Taken together, all the above macrocycles form a matrix ofstructural types in which a systematic variation in donor-atompattern and ring size occurs. One aim of the present study was toinvestigate structure-function relationships involving complexformation by this extensive ligand series. It has been ourexperience that comparison of the co-ordination behaviour ofa range of closely related ligand systems usually results in amore complete understanding of the often subtle factorsunderlying any observed discrimination. Such studies alsoprovide a useful background upon which further ligand designmay be based.The earlier study of the stabilities of the nickel(rr) complexesof 17-, 18- and 19-membered pentadentate macrocycles in-corporating O,N,-donor sets (namely, L4, L7-L9) stronglysuggested that a structural dislocation occurs along the serieson passing from the complex of the 18- to that of the 19-membered ring.Related dislocation behaviour may be inducedby substituting the ‘parent’ 17-membered ring L4 to yield itsdimethylated derivative L2 ’; the stability constants (log Kvalues) for the nickel(11) complexes of the last two ligands in95% methanol are 10.0 and 6.9, respectively. In both the aboveexamples the dislocations have been assigned to a change fromfacial to meridional co-ordination of the N,-donor backbone inthe respective octahedral co-ordination spheres.ExperimentalPhysical Measurements.-Proton and 3C NMR spectr1870 J.CHEM. SOC. DALTON TRANS. 1992X Y m n pL ' O N H 2 2 1L 2 0 S 2 2 1L 3 0 0 2 2 1L 5 0 s 2 2 2L 6 0 0 2 2 2L 4 0 N H 2 2 2L 7 0 N H 2 3 2L B O N H 3 3 2L 9 0 N H 2 4 2L" 0 NH 2 2 4L'OO s 3 3 2L ' * O s 2 2 4L ' ~ O o 2 2 4L 1 5 S s 2 2 1L " S s 2 2 2L i 8 S 0 2 2 2L 2 0 S s 2 2 3L14 S NH 2 2 1Li6 S NH 2 2 2L'' S NH 3 3 2were obtained at 25 "C on a Bruker AM300 spectrometer at 300and 75 MHz, respectively, infrared spectra as Nujol mulls on aPerkin-Elmer 197 spectrophotometer and positive-ion fastatom bombardment (FAB) mass spectra were determined bymeans of a JEOL-DX300 spectrometer (samples in 3-nitro-benzyl alcohol).Conductance measurements were obtainedusing a Philips conductivity bridge type PR 9501; all measure-ments were performed in methanol at ca. rnol dm-3 (and23 "C). The UV/VIS spectra were obtained on a BeckmanACTA IV spectrophotometer; solid-state spectra were deter-mined as Nujol mulls spread on filter-paper, solution spectra ofthe respective complexes at ca. rnol dm-3 in methanol.Magnetic moments were determined at 23 "C using a Faradaybalance calibrated against Hg[Co(NCS),].Macrocycle and Complex Synthesis.-The synthesis andcharacterisation of the macrocyclic ligands L'-LZo have beendescribed el~ewhere.~.~,'[Ni(NO3)L']CIO4~3H20.Nickel(1r) nitrate hexahydrate(0.1 g) in boiling ethanol (10 cm3) and solid lithium perchlorate(0.1 g) (CAUTION: perchlorates may be explosive) were addedto a stirred boiling solution of L' (0.10 g) in etha.nol (10 cm3).The volume was reduced to 5 cm' and the solution was filteredand then cooled. On standing, blue crystals separated fromthe solution; yield 0.07 g (Found: C, 40.5; H, 4.9; N, 10.7. Calc.for C1,H25C1N,Ni09-3H20: C, 40.3; H, 4.8; N, 9.9%).[Ni(N03)L' ']CIO,~C,H,OH~H,O. In a similar manner,Ni(N03)2-6H20 (0.08 g) and LiCIO, (0.09 g) in ethanol (15cm3) were added to L" (0.10 g in 10 cm3 ethanol) to yield darkblue crystals; yield 0.05 g (Found: C, 44.0; H, 6.2; N, 8.5.Calc. forC2,H3 ,CIN,NiO,~C2H,OH~H2O: C, 44.1; H, 6.0; N, 8.6%).[Ni(N03)L'4]C10,=3H20. In a similar manner, Ni(NO,),=6H20 (0.09 g) and LiClO, (0.09 g) in butanol (10 cm3) wereadded to LI4 (0.10 g in 10 cm3 butanol) to yield purple crystals;yield 0.03 g (Found: C, 35.6; H, 4.3; N, 8.4. Calc. forC,,H,,C1N,Ni0,S2~3H,0: C, 35.9; H, 4.9; N, 8.8%).[Ni(NO,)L' 6]C10,-C2H50H-0.5H20. In a similar manner,L16 (0.10 g) yielded dark blue crystals; yield 0.07 g (Found: C,40.8; H, 5.0; N, 9.0. Calc. for C20H,,CIN,Ni07S,~C,H50H~0.5-H,O: C, 40.8; H, 5.3; N, 8.6%).[NIL' 8(H20)][N03]2. Nickel(1r) nitrate hexahydrate (0.10g) in boiling ethanol (15 cm3) was slowly added to a stirredsolution of LI8 (0.10 g) in boiling ethanol (10 cm3).The bluesolution was filtered and butanol (10 cm3) was added to thefiltrate. The volume was reduced to 20 cm3 and the solutionwas then filtered and cooled. On standing dark blue crystalsformed; yield 0.05 g (Found: C, 41.6; H, 4.9; N, 9.7. Calc. forC ~ O H ~ ~ N , N ~ O ~ S ~ : c , 41.8; H, 4.9; N, 9.7%).Equilibrium Studies.-The reagents used for the equilibriumstudies were all analytical grade or better, Analytical grademethanol was fractionated and distilled over magnesium beforeuse. The potentiometric titration apparatus consisted of awater-jacketed titration vessel and a water-jacketed calomelreference electrode, connected by a salt bridge. A Philips glasselectrode (GA-110) was used for all pH measurements.Tetra-ethylammonium perchlorate (0.1 rnol dm-3) was used as thebackground electrolyte; the solvent was 95% methanol and thetemperature was maintained at 25During the course of each measurement, methanol-saturatednitrogen was bubbled through the solution in the measuringcell. Tetraethylammonium hydroxide solution was introducedinto the measuring cell using a Metrohm Dosimat 655automatic titrator. A Corning model 130 Research pH meterwas employed for the pH determinations. The microprocessor-controlled apparatus was calibrated daily by titration with asolution of standardised base. The data were processed using alocal version of MINIQUAD ' and selected data were alsoreprocessed using SUPERQUAD; ' the two programs gavevalues showing no significant differences.In a typical determination of protonation constants, ligand(1.3 x l e 3 rnol dm-3) in 25.00 cm3 of perchloric acid solution(4.0 x rnol dmT3, I = 0.1 rnol dm-3) was titrated withtetraethylammonium hydroxide solution (0.1 rnol dm-3).Eachquoted value is the mean of values (weighted according to thecorresponding 'R factors' as obtained from the respectiveMINIQUAD outputs) of at least three separate determinations(at different ligand concentrations). The stability constants forthe metal complexes were obtained by a similar procedureexcept that each titration was performed in the presence ofmetal ion. Typically, for a given system, titrations wereperformed using at least two different metal to ligand ratios.0.1 "C.Crystallography for [NiL'8(H20)][N03]2.-Crystal data.C20H28N,Ni08S2, ki = 575.3, crystallised from ethanol aspurple crystals, crystal dimensions 0.21 x 0.21 x 0.17 mm,monoclinic space group Cc (C4s, no.9), a = 11.073(2), b =14.588(3), c = 15.561(3) A, p = 107.00(2)", U = 2403.8(8) A3,D, = 1.59 g ~ m - ~ , Z = 4, graphite-monochromated Mo-KaX-radiation (h = 0.710 69), p(Mo-Ka) = 9.66 cm-', F(OO0) =1200.Data were collected on a Philips PW1100 diffractometerin the range 8 3-25", with a scan width of 0.80", using thetechnique previously described.' No absorption correctionswere applied. The metal atom was located from a Pattersonsynthesis. l 4 The positions of the remaining non-hydrogenatoms and the N- and 0-bonded H atoms were found fromsubsequent Fourier and Fourier difference syntheses.ThJ . CHEM. SOC. DALTON TRANS. 1992 1871Table 1 Fractional atomic coordinates with estimated standarddeviation in parentheses for [NiL'8(H20)][N03]2\-o.Oo0 000.198 7(3)0.1 12 2(3)-0.009 5(8)-0.049 2(8)-0.171 4(7)0.306 9( 1 1)0.250 5( 10)0.339 5( 11)0.387 7( 12)0.351 6( 12)0.257 8( 11)0.207 9( 10)0.109 O( 10)-0.108 9(10)- 0.220 7( 1 1 )0.275 3( I 1)0.104 5( 10)0.129 3(12)0.120 l(12)0.089 7( 12)0.065 5( 11)0.071 3(11)0.042 O( 12)-0.175 8(10)-0.251 9( 10)-0.035 70-0.057 30-0.082 2(8)-0.162 80-0.072 300.957 8( 10)0.936 9(9)0.989 4(9)0.960 5( 11)0.138 9(10)0.063 3( 10)0.102 l(10)0.251 8(8)v0.1 12 04(9)0.039 3(2)0.244 3(2)0.160 3(6)0.072 2(6)0.1 78 7(5)0.1 13 3(8)0.055 7(8)-0.010 4(9)0.061 7(9)0.122 2(9)0.123 3(8)0.194 9(8)0.230 4(8)0.199 5(8)0.21 5 2(8)0.251 9(8)0.337 l(10)0.354 O( 10)0.285 3( 10)0.197 5(9)0.178 5(8)0.082 9(8)0.1 14 5(8)0.128 6(8)0.103 300.017 20-0.010 9(5)-0.048 80-0.047 100.818 l(8)0.879 9(6)0.838 O(7)0.737 9(6)0.459 l(8)0.427 6( 7)0.507 6(8)0.439 6(9)-0.003 8( 10)o.Oo0 000.057 9(2)-0.029 9(2)0.123 5(6)-0.134 6(6)- 0.044 5( 5 )0.021 5(8)0.178 O(7)0.223 2(9)0.3 16 O(9)0.363 2(9)0.3 18 2(8)0.225 7(8)0.185 2(8)0.105 l(8)0.030 4( 8)0.024 8(8)-0.146 5(7)- 0.173 4(9)- 0.264 6(9)-0.324 7( 10)-0.296 5 ( 8 )- 0.205 9(8)- 0.184 9(9)-0.181 3(8)-0.1 18 3(7)0.147 30-0.123 800.028 O(6)0.042 20-0.012 900.870 4(8)0.814 l(6)0.954 3(7)0.849 4(7)0.080 8(7)0.120 2(8)0.016 4(8)0.109 3(6)aromatic and aliphatic C-bonded H atoms were placed ingeometrically idealised positions (C-H 1.08 A), and con-strained to ride on the relevant C atom, with thermalparameters tied to single free variables which were refined [finalvalues 0.047 (aliphatic) and 0.073 81, (phenyl)]. The located N-and O-bonded H atoms were given fixed isotropic thermalparameters of 0.08 81' and their positions not refined.In thefinal cycles of full-matrix refinement, using 1421 unique datawith I > 30(I), the nickel, water and nitrate oxygen atomswere assigned anisotropic thermal parameters and refinementconverged at R = 0.051 and R' = 0.049 where R' = CI(F,( -IFcI~wt/XIF,Iw~ using a weighting scheme of w = 1/[02(F,,)].A final Fourier difference map showed no significant regions ofelectron density.Atomic coordinates are given in Table 1 with bond distancesand angles in Table 2.Additional material available from the Cambridge Crystal-lographic Data Centre comprises H-atom coordinates andthermal parameters.Molecular Mechanics Calculations.-As well as the abovestructural data for the nickel(1i) complex of the ON,S,-donorligand L", X-ray data were also available for the correspondingcomplexes of the 02N,-donor8 and N,S,-donor l 5 macro-cycles, L4 and L16. Each of these systems has been the subjectof molecular mechanics analysis in the present study.Theprovisional force-field parameter set for this series of complexeswas largely based on the parameters derived previously forhigh-spin nickel(r1) complexes of macrocyclic ligands incor-porating N4-, O,Nz- and S2N,-donor systems.I6 The force-field parametrisation employed is listed in Table 3. Theparametrisation for the nickel-nitrogen bonds was similar tothat used previously for high-spin nickel(r1) complexes oftetraazamacrocycles. The bending constants for angles aboutthe oxygen and nitrogen donor atoms were also the same asthose used for modelling the nickel(i1) complexes of the (related)0,N2-donor structures. However, slight modification of otherparameters associated with the metal ion from those usedpreviously was found to improve the 'fit' of each of the presentstructures.No attempt was made to refine the nickel to waterbond in each structure. Instead, the procedure employed was tofix the Cartesian coordinates of the nickel and water molecule inspace (based on the corresponding X-ray structure coordinates)while allowing the rest of the molecule to refine.X-Ray data provided the basis for setting up the 'startingcoordinates' for each of the three configurational isomersinvestigated while Drieding models were used to assist in theselection of likely conformations within individual structures.That is, for each isomer type different conformations of theco-ordinated ligand were investigated in an endeavour toensure that the lowest-energy structure was identified in eachcase.Results and DiscussionIsolation of Selected Metal Complexes.-Nickel(rr) complexesof a selection of the present macrocycles have been isolated.Incontrast, attempts to obtain cobalt(I1) species using similarprocedures were not successful. Complexes of the ligands L',excess of nickel(I1) nitrate in ethanol to a boiling solution of theappropriate macrocycle in ethanol. In four instances it provednecessary to add excess of lithium perchlorate to the reactionmixture to aid crystallisation of the products. Microanalyticaldata indicated that these latter complexes contained one nitrateion per metal ion, with a perchlorate as the second anion.It should be noted that the attempted syntheses of the nickel(I1)complexes of many of the macrocyclic ligands containing otherthan an N,-donor aliphatic fragment resulted in the isolation ofcolourless crystalline products which were soluble in water.These products gave sharply defined (that is, not contact shiftbroadened) 'H NMR spectra in D20, their properties indicatedthat they are salts of the corresponding protonated ligands.Thestructure of one such product, the dihydronitrate salt of L", hasrecently been confirmed by X-ray analysis." The isolation ofthese salts is very likely a result of the strongly basic nature of therespective ligands and the low solubilities of the salts in alcoholrelative to the corresponding nickel complexes, coupled with therelatively moderate stabilities of the latter.Physical data for six nickel complexes are included in Table 4.The magnetic moments of these species all fall in the normalrange expected for complexes of high-spin nickel(r1).The infrared spectra of the complexes incorporating per-chlorate anions give no clear indication of perchlorate co-ordination; that is, while the broad strong absorptions at ca.1080 cm-' are generally not symmetrical, no splitting of thesebands was observed.The presence of peaks attributable to theligand partially masked the nitrate absorptions in each case andno attempt was made to assign these resonances. All the spectracontained bands between 3200 and 3300 cm-' arising from thepresence of (co-ordinated) amine groups. In all cases wherewater and/or ethanol were suggested to be present (on thebasis of their microanalytical data), the expected absorptions inthe range 340C3600 cm-' were observed.In two complexesalcohol of crystallisation was postulated to be present. Similarassociation of solvent has been shown to occur in particularnickel complexes of other O,N,-macrocyclic ligands of thepresent type,5 as well as in related N,S,-donor macrocycliccomplexes reported previously.20~ 1 1 , ~ 1 4 , ~ 1 6 and LI8 were prepared by the addition of a sligh1872 J. CHEM. SOC. DALTON TRANS. 1992Table 2 Bond lengths (A) and angles (") for [NiL*E(H,0)][N03]2Ni-O(7)Ni-S( 1 b)Ni-N( 1 b)O( 7)-H( 0 7 1)S( 1 a)-C( 1 a)S( 1 b)-C( 1 b)N( 1 a)-C(8a)N( la)-H(N la)N( 1 b)-C(9b)O( 1 c)-C( 1 Oa)C( 1 a)-C( 1 b)2.1 13(8)2.41 3(3)2.086(9)1.1261.821 ( 14)1.807( 1 1)1.470( 13)0.9881.510(13)1.456( 16)1.532( 17)S( 1 a)-Ni-O(7) 87.1(2)S( 1 b)-Ni-S( 1 a) 87.6( 1)N( 1 a)-Ni-S( 1 a) 95.3( 2)N( 1 b)-Ni-0(7) 88.2(4)N( 1 b)-Ni-S( 1 b) 91.6(3)O( 1 c)-Ni-O( 7) 93.4(3)O( 1 c)-Ni-S( 1 b) 91.9(2)O( 1 c)-Ni-N( 1 b) 8 1.4(3)H(072)-0(7)-Ni 102C( 1a)-S( la)-Ni 103.8(4)C(2a)-S( 1 a)-C( 1 a) 10 1.9( 5 )C(2b)-S( 1 b)-Ni 1 1 I .7(4)C(8a)-N( la)-Ni 116.4(8)C(9a)-N(la)-C(8a) 11 1.3(8)H(N la)-N( la)-C(8a) 110C(8b)-N(lb)-Ni 119.4(7)H(Nlb)-N(lb)-C(8b) 110C( 10a)-0( 1c)-Ni 110.6(6)C(9b)-N( 1 b)-C(8b) 11 2.9(9)Ni-S( 1 a)Ni-N( 1 a)Ni-O( 1 c)O( 7)-H(072)S( 1 a)-C(2a)S( 1 b)-C(2b)N( 1 a)-C(9a)N( 1 b)-C(8b)N( 1 b)-H(N 1 b)O(1c)-C(l0b)C(2a)-C(3a)S( 1 b)-Ni-0(7)N( 1 a)-Ni-O( 7)N( 1 a)-Ni-S( 1 b)N( 1 b)-Ni-S( 1 a)N( 1 b)-Ni-N( 1 a)O( 1 c)-Ni-S( 1 a)O( 1c)-Ni-N( la)H(071)-0(7)-NiH(072)-0(7)-H(071)C(2a)-S( 1a)-NiC( 1 b)-S( 1 b)-NiC(2b)-S( 1 b)-C( 1 b)C(9a)-N( 1a)-NiH(N la)-N( la)-NiH(N 1a)-N( la)-C(9a)C(9b)-N( 1 b)-NiH(N 1 b)-N( 1 b)-NiH(N 1 b)-N( 1 b)-C(9b)C( 10b)-0( 1c)-Ni2.370(3)2.078(9)2.063( 7)0.8581.804(11)1.795( 12)1.467( 14)1.457( 18)0.8291.431(12)1.41 l(16)174.5(2)87.5(3)94.3(3)101.4(3)162.5(3)1 77.2( 2)82.0(3)1 50971 08.3(4)102.8(4)103.7(6)107.1 (6)99111107.6( 7)941101 09 .O( 6)C(2a)-C(7a)C(4a)-C( 5a)C(6a)-C(7a)C(9a)-C( 1Oa)C(2 b)-C( 7b)C(4b)-C( 5b)C(6b)-C(7b)C(9b)-C(lOb)N( 1 ) - W )N(2)-0(4)N(2)-0(6)C( lob)-O( 1 c)-C( 1 Oa)C(3a)-C(Za)-S( l a )C(7a)-C(2a)-C(34C( 5a)-C(4a)-C(3a)C(7a)-C(6a)-C(5a)C(8a)-C( 7a)-C( 2a)C( 7a)-C(8a)-N( 1 a)C(9a)-C( 10a)-0( 1 c)C(3b)-C(2b)-S( 1 b)C( 7 b)-C( 2 b)-C( 3 b)C( 5 b)-C(4b)-C( 3 b)C(7b)-C(6b)-C(Sb)C(8b)-C( 7 b)-C(2b)C(7b)-C(8b)-N(lb)C(9b)-C( 10b)-0( lc)0(3)-N( 1 )-O( 1 )0(5)-N(2)-0(4)0(6)-N(2)-0( 5 )1.396( 17)1.336(21)1.383(16)1.498(15)1.392( 16)1.345(20)1.420( 1 8)1.482( 18)1.282( 16)1.260(18)I .23 1 (14)1 17.2(9)1 13.0(9)121(1)122(1)123(1)126(1)1 15.7(9)105( 1)114.4(9)122(1)120(1)122(1)127( 1)117(1)105.1 (9)122(1)121(1)120(1)C( 1 b)-C( 1 a)-S( 1 a)C(7a)-C(2a)-S( la)C(4a)-C( 3a)-C(2a)C(6a)-C(5a)-C(4a)C( 6a)-C( 7a)-C( 2a)C(8a)-C(7a)-C(6a)C( 10a)-C(9a)-N(la)C( 1 a)-C( 1 b)-S( 1 b)C(7b)-C(2b)-S( 1 b)C(4b)-C( 3b)-C(2b)C( 6b)-C( 5b)-C(4b)C( 6b)-C( 7b)-C( 2b)C( 8 b)-C(7b)-C(6b)C( lOb)-C(Ob)-N( 1 b)0(2)-N( 1 )-O( 1)O(3l-W 1 )-ow0(6)-N(2)-0(4)1.388( 18)1.385( 17)1.5 12( 15)1.364( 19)1.414(20)1.404(20)1.489( 17)1.231( 15)1.21 8( 15)1.197( 1 6)113(1)126.1(8)118(1)119(1)117(1)117(1)110.2(9)114.7(8)123.3(9)120( 1)120(1)116(1)117(1)11 1.5(9)120(1)118(1)119(1)C(5b)@5 C(6b)Fig.1 The X-ray structure of the cation [NiL'E(H,0)]2+Conductance values in methanol for the nickel(r1) complexes{with the exception of [NiL18(H20)][N03]2) indicate orapproximate to 1 : 1 electrolytes (80-1 15 S cm2 mol-') in thissolvent ' (Table 4) and hence at least one anion is present in theco-ordination sphere.There is much evidence in the literaturethat nitrate co-ordination will be favoured over perchlorate co-ordination in such complexes. Consequently, a nitrate ion ispostulated to occupy one co-ordination position in eachcomplex in solution and it seems likely that such anarrangement persists in the solid state. The nickel complex ofL" is a 2: 1 electrolyte in methanol, hence non-co-ordination ofthe anions occurs in solution (and also in the solid state asshown by the X-ray structure).In accordance with the predicted structures, the positive-ionFAB source mass spectra of the mixed-anion complexes allshow strong peaks corresponding to [Ni(N03)L"] +, althoughweaker peaks attributable to [Ni(C104)L"] + are also presentfor most complexes, presumably reflecting ion rearrangement inthe vapour phase.The solution and solid-state electronic spectra of the com-plexes are typical of octahedral or pseudo-octahedral nickel(I1)species.' In the majority of cases the spectra contained threemajor bands which may be assigned to the following transitionsin Oh symmetry: 3A2,- 3T1, (P), 3 A 2 , - - + 3T1, (F) and3A2,--+ 3T2,.However, it is noted that in many cases thebands are somewhat broad and unsymmetrical, indicating thatthe real symmetry is, not unexpectedly, somewhat lower thanoctahedral. In particular, the solution spectra of [Ni(N03)L16]-C1O4-C2H,OH~O.5H20, and [NiL' 8(H20)][N03]2 both showa clear splitting of the 3A2, --+ 3T2g transition, indicating thatsignificant distortion from octahedral symmetry is present inthese complexes. In the solution and solid-state spectra of thecomplex of the sulfur-containing ligand L16 the 3A2s --+ 3T1,(P) transition is obscured by the edge of an intense charge-transfer band.It is not possible to assign specific modes of macrocycleco-ordination in the respective complexes from the spectro-photometric data.However, with the possible exception of thecomplexes of L' and L18, the strong similarities between thespectra of individual complexes in the solid and in solutionsuggest that similar geometries occur in both states.X-Ray Crystal Structure.-The structure of [NIL' 8(H20)]-[NO3I2 is shown in Fig.1. The nickel atom is six-co-ordinatewith the complex cation exhibiting a distorted-octahedralgeometry comprising all five donor atoms of the ON2S2-donormacrocycle, and a water molecule trans to S(1b). The maindistortions from regular octahedral geometry appear to resultfrom the steric requirements of the macrocyclic ligand. Theangles around the nickel in the five-membered chelate rings are,as usual, less than the ideal value of 90" [81.4(3), 82.0(3) and87.6( l)"] whereas those in the six-membered rings are greateJ. CHEM. SOC. DALTON TRANS. 1992 1873Table 3L'. L"and L18Force-field parameters for high-spin nickel(i1) complexes ofNon-bonded parametersAtomNir * / A &/kJ mol-'2.30 0.71 IBond stretching parameters and bond momentsBond type ro/A molecule-'Ni-N 2.05 1.80Ni-O(aromatic ether) 2.14 0.60Ni-O(a1iphatic ether)' 2.1 1 0.80Ni-S 2.49 0.65O(aromatic et hert Lp '.0.60 6.10S-LP 0.60 5.30k,/mdyn A-'O(aliphatic ether)-Lp' 0.60 4.60C(SP3W(SP3) 1.46 4.00Bond bending parametersBond anglek,/mdyn A rad-2 e,/" molecule-'Ni-N-C 109.5Ni-N-H 109.5Ni-0-C 109.5Ni-0-Lp 109.5Ni-O(a1iphatic etherkc 109.5Ni-O(a1iphatic ethertlp 105.16Ni-S-C 100.0Ni-S-Lp 1 15.0N-Ni-N 90.0N-Ni-0 90.0N-Ni-S 90.00-Ni-0 90.00-Ni-S 90.0S-Ni-S 90.0C-s-c 100.0C-s-Lp 115.0Stretch-bond constantsBond angleC-N-NiH-N-NiC-O-NiC-S-Nik,,/mdyn rad-'molecule-'0.120.090.120.250.500.500.350.100.400.350.500.500.250.500.500.500.500.500.500.50Torsional constantsTorsion V,/kJ mol-' YJkJ mol-'C-C-N-Ni - 0.84 3.05H-C-N-Ni 0.00 0.00C-C-0-Ni 1.67 2.18H-C-O-Ni 0.00 0.00C-C-S-Ni - 2.59 1.26H-C-S-Ni 0.00 0.00PlD0.0 14O.OO00.2900.8000.6000.6000.8000.027complex with H(N1b) 0(1) 2.22, H(072) O(2) 1.93 andH(07 1) .O(6) 1.6 1 A.Stability Constants.-The protonation constants for L'-L3,L5, L6 and L'O-LZ0 were obtained by potentiometric titrationin 95% methanol, containing 2 or 3 equivalents of perchloricacid (I = 0.1 mol dm-j, NEt4C104), with tetraethylammoniumhydroxide at 25 "C. The corresponding constants for themacrocycles L4 and L7-L9, have been determined previouslyand are also listed in Table 5 for comparison.6Stability constants for the 1 : 1 (L: M) complexes of cobalt(r1)and nickel(r1) of the macrocyclic ligands were also determinedpotentiometrically in 95% methanol.A summary of therespective values is given in Table 5. From the data listed it isapparent that the systematic changes in the macrocyclic ligandstructures (variation of the donor-atom set, the macrocyclic ringsize and/or the chelate ring sizes) are clearly reflected in thestabilities of the resultant metal complexes and the followinggeneral observations may be made.(andrelated earlier s t ~ d i e s ) , ~ * ~ ~ the nickel@) complex in each caseis more stable than the corresponding cobalt(i1) complex.Secondly, the observed log K values for the complexes of L'-LZ1 show the expected dependence on the nature of the donorFirst, in accordance with the Irving-Williams orderatom Y.Thus, when Y = NH, the stabilities of the corre-sponding complexes are invariably higher than for complexesinvolving ligands where Y is a thioether sulfur or an etheroxygen. This is clearly seen on comparing the stabilities of thenickel(r1) complexes of the 17-membered rings L4-L6 (YN,O,-donor set) or L16-L18 (YN,S,-donor set): each series spans astability range of 106-107 as Y varies from NH, through S, to 0.In this context it is noted that thermodynamic studies on nickelcomplexes of linear polyamines of the type H2NCH2CH2-ZCH,CH,NH, (for which 2 = NH, 0 or S) indicate that theenhanced stability of the triamine complex derives primarilyfrom an enhanced enthalpic contribution to binding by the NHgroup, relative to the complexes in which S or 0 donors areThus, co-ordination of the ether oxygen orthioether donors, with the concomitant displacement of waterligand(s), appears to be an endothermic process in theformation of these complexes.25Thirdly, the stabilities of the respective metal complexes tendnot to depend greatly on whether X = 0 or S.This is inaccordance with the well documented weak donor capacity ofether and thioether groups towards most divalent, first-rowtransition-metal Affinities are expected to be even lessin the present systems which contain aryl moieties adjacent tothe X donor groups. However, it is noted that these donors arestill sufficiently different to influence the configuration adoptedby the macrocycle on co-ordination around five positions ofFourthly, the dependence of metal complex stability on thesize of the chelate rings formed by individual macrocyclicligands is also apparent.As expected (if it is assumed that alldonors co-ordinate), the complexes of L1-L3, L14 and LI5VJkJ mol-'3.3s octahedral nickel(11) (see later).2.181.952.221.052.26The same values were used by Drew et a/." Based on Allinger'svalues.'s Lp = Lone pair.[9 143) and 95.3(2)"]. The two longest bonds to the metal atomare from the sulfur donors with Ni-S(1b) at 2.413(3) beingsignificantly longer than Ni-S(1a) at 2.370(3) A. The etheroxygen O( Ic) lies closer to the nickel ion than the oxygen of thewater molecule [Ni-O(1c) 2.063(7) versus Ni-0(7) 2.1 13(8) A],which is in accordance with the operation of a chelate effectinvolving the co-ordinated N(CH2),0(CH2),N fragment ofthe molecule.The nitrogen and sulfur donor groups areeffectively chiral in the crystal with prochiral RSSS (or SRRR)configurations for N( 1 a), S( la), S( 1 b) and N( 1 b), respectively.The nitrate anions are strongly hydrogen-bonded to theincorporating four-membered chelate rings tend to be lessstable than the complexes of ligands (incorporating the samedonor set) in which the corresponding chelate rings are five-membered (L4-L6, L16, L17). In turn, complexes of the latterligands tend to be more stable than complexes of ligands inwhich the corresponding chelate rings are six- or seven-membered (L"-L13, LZo).It needs to be kept in mind that theoverall macrocyclic ring size will also usually vary concomitantlywith chelate ring size; this may in turn influence complexstability by restricting the number of possible conformationsand/or configurations of the ligand about the central metal. Thedislocation behaviour as reported previously for the nickel(@complexes [and, to a less obvious degree, the cobalt(n)complexes] of the O,N,-donor ligand series (L4, L7 and L8)appears to be associated with the 'sudden' release of ligandstrain along the series of c~mplexes.~ While this might b1874 J. CHEM. SOC. DALTON TRANS. 1992Table 4 Physical data for the nickel(i1) complexes of selected macrocyclic ligandsIR (cm-')' Electronic spectra, h/nmComplex A '/s cmZ mol-' p v(OH) V(NH) Anion Solid Solutiond m/ze[Ni(N03)L']CI04~3H20 95 3.05 3460 3250,3220 1030 360 (sh)5558955509855308608059005901070[Ni(NO,)L1 ']CIO,-C,H ,0H-H20 117 3.16 3450 3270,3260 1065 360 (sh)[Ni(N03)L'4]C104-3H20 I17 3.07 3600,3520 3340,3290 1090 345 (sh)[Ni(N03)L'6]C104~C2H50H-0.5H20f 134 3.13 3545 3380,3245 1070 555[NiL'8(HZO)lCN0,1 205 3.10 3360 3260 355 (sh)365(25) 447600 (13)965 (10)365(27) 489585 (1 5)965 (12)350(22) 479540 (6)870 (6)535(8) 493860 (5)1015 (5)340(sh) 494615 (29)870 (29)1055 (10)In methanol (23 %C).* At 23 'C. '' Nujol mull. " In methanol; 4dm3 mol-' cm-' given in parentheses. Positive-ion FAB mass spectral peak for[ML(N03)] +.The related species [NiL'6(Hz0)][C104]2 has recently been investigated by X-ray diffraction (ref. 15).Table 5dm-, (NEt4CI04) at 25 "C]Ligand protonation constants and stability constants for the complexes of cobalt(ii) and nickel(I1) with L'-LZo [95% MeOH, I = 0.1 molFree ligand log KMLa (M2+ + L e ML2+)LigandL'L2L3L4L5L6L7L8L9L'OL"L12LI3L14L15LI6LI7L'*LI9LZOlog K,"9.388.3 18.959.698.648.6710.05 '10.33'10.24 '9.389.568.9 19.138.967.829.137.798.1310.287.9 1log Kz"8.277.127.9 18.45 '7.397.688.228.367.84'8.368.327.688.0 16.866.527.056.466.877.376.70log K,"2.32.0'3.73'5.59'4.42'2.41.92.15.3 1M = CO"6.Ih< 3.57.7= 3.3< 3.57.3 "5.1"> 5.0" = 3.47.3z 3.4 = 3.55.5< 3.5h< 3.5< 3.5 = 3.4< 3.5Ni"8.3= 3.0< 3.510.05.5< 3.59.gd = 6.25.1 "< 3.59.7h3.58.4h9.5< 3.5 = 3.45.7a Unless otherwise indicated, the error is estimated to be fO.l for each log K value. Precipitation prevented usable data being obtained. Value fronref. 6. Value from ref. 5 (95% MeOH, I = 0.1 mol drn-,, NMe4CI).considered to be primarily a function of macrocyclic ring size,the situation is unlikely to be quite this simple and contributionsfrom a number of sources are also undoubtedly important.Fifthly, the 'dislocation' study just mentioned gave log Kvalues for the nickel(r1) complexes of L4 and L8 in 95%methanol (with I = 0.1 mol dm-3 and NEt4CI as backgroundelectrolyte) which indicated that the complex of L4 was afactor of about lo4 more stable than the correspondingcomplex of L8.' As expected, the values obtained in thepresent study (for which I = 0.1 mol dm-, NEt4C104) (Table5) confirm that this effect is essentially independent of thebackground electrolyte.Sixthly, a related pattern to that just described is presentwhen the ether oxygen donors of L4 and L8 are replaced bythioether donors to yield L16 and L19; the nickel(I1) complex ofL16 is again a factor of about lo4 more stable than the complexFinally, in the present study, a dislocation was not observedof L ' ~ .between the complexes of the 17- and 19-membered ringstructures L4 and L" (in contrast with that which occursbetween the complexes of L4 and L').In this case, however, the19-membered ring of L' is achieved by increasing the numberof methylene carbons between the oxygen donors rather thanbetween the amine donors as in the case of L8; the logKdifference between the nickel complexes of L4 and L' is onlyabout 0.3. This result supports the previous postulate that theco-ordination geometries adopted by the O,N,-donor ligandseries are largely associated with steric factors involving thechelate rings formed by the respective N, backbones.Molecular Mechanics Srudy.-The force-field parameters fora wide range of low- and high-spin nickel(I1) complexes oftetraaza macrocycles together with parameters for high-spincomplexes of 0,N2- and S2N2-donor macrocycles, based on asomewhat restricted number of X-ray structures, have beenderived recently, 1 6 + 2 8 7 2 9 These prior results have now been useJ .CHEM. SOC. DALTON TRANS. 1992 1875Table 6 Bond distances (A) and angles ( L ' ) involving nickel(n) in the X-ray structures and the structures calculated using molecular mechanics"Distance X-Ray Calculated Angle[NiL4(H 20)][C104] 2 hNi-O( 1 a) 2.23 2.20 O( 1 a)-Ni-O( 1 b)Ni-O( 1 b) 2.13 2.15 O( 1 a)-Ni-N( 1 a)Ni-N( 1 a) 2.05 2.07 O( 1 b)-Ni-N( 1 b)Ni-N( 1 b) 2.06 2.08 N( la)-Ni-N( 1 b)Ni-N( 1 c) 2.07 2.08 N( 1 a)-Ni-N( 1 c)N( 1 b)-Ni-N( lc)N( 1c)-Ni-O( la)N( 1 c)-Ni-O( I b)[NiL "( H,O)][ClO,] z cNi-N( 1) 2.07 2.06Ni-N( 2) 2.08 2.07Ni-N(3) 2.09 2.09NILS( 1 ) 2.40 2.42Ni-S(2) 2.43 2.4 1N( 1)-Ni-N(2)N( 1 )-Ni-N( 3)N( 1 )-Ni-S( 1 )N(2)-Ni-N(3)N(2)-Ni-S(2)N(3)-Ni-S( 1)N(3)-Ni-S(2)S( 1 )-Ni-S(Z)X-Ray Calculated78 8189 9289 90105 9785 8685 8693 94101 9884100918210293938486100938597939585[NIL' 8(HzO)][N0,]zdNi-O( 1 c) 2.06 2.06Ni-N( 1 a) 2.08 2.07Ni-N( 1 b) 2.09 2.06Ni-S( 1 a) 2.37 2.39Ni-S( 1 b) 2.41 2.40O( 1 c)-Ni-N( 1 a) 82 83O( 1c)-Ni-N( 1 b) 81 82O( 1 c)-Ni-S( 1 b) 92 92N( 1 a)-Ni-S( I a) 95 95N( 1 a)-Ni-S( 1 b) 94 97N( 1 b)-Ni-S( 1 a) 10 1 100N( 1 b)-Ni-S( 1 b) 92 92S( 1 a )-Ni-S( 1 b) 88 85' Atom labels correspond to those used originally for the X-ray structure determination. Crystallographic R factor = 0.073 (ref.8).'. Crystallographic R factor = 0.085 (ref. 15). Crystallographic R factor = 0.051 (this work).Fig. 2mechanics: ((I) facial I, ( b ) facial I1 and ( c ) meridonalThe three configurational isomers investigated by molecularas a basis for the development of a provisional force-fieldparametrisation for use in calculations involving nickel(r1)complexes of the present macrocycles. Further refinement of theforce field for these pentadentate systems was limited by theavailability of only three X-ray structures. As well as thestructural data for the nickel(rr) complex of the ON,S,-donorligand L l 8 discussed above, previously determined data for thecorresponding complexes of the O,N,- and S,N,-donor ligands,were also available.It is noted that particularparameters from those developed previously proved satisfactoryfor use in modelling the present species without modification.Inspection of molecular models (Drieding) indicated thatthree major isomers appeared likely for the 17-membered ringcomplexes of L4, L'" and L18. These are illustrated in Fig. 2and, interestingly, each arrangement corresponds to that in oneof the X-ray structures mentioned above. The starting co-ordinates for the respective molecular mechanics calculationswere either the X-ray coordinates themselves or were generatedby modification of the appropriate set of X-ray coordinates.The nickel to donor atom bond distances as well as the anglesabout nickel for the calculated structures and the correspondingX-ray structures are presented in Table 6.The co-ordinationsphere is modelled reasonably well in each complex.L" and L16 8 . 1 5 ,The total strain energies for the three geometric isomers ofeach of the three complexes are listed in Table 7 and overall datadescribing the respective 'fits' of individual isomers to the X-raystructures are given as footnotes to this table (torsional anglesinvolving bond angles above 170" were not included in theanalysis since they are usually associated with an unrealisticallyhigh error).,*As already discussed, in our previous study it was proposedthat the difference in the stability of the nickel(r1) complexes ofthe 17-membered macrocyclic ligand L4 and its 19-memberedanalogue L8 arises from a 'structural dislocation'.' For thecomplex of L4 the X-ray study shows that the three aminedonors are arranged facially (and this arrangement waspostulated to be maintained in solution) while it was proposedthat, for the complex of L8, the amine donors are arrangedmeridionally.The present molecular mechanics study of the 17-membered ring complex (of L4) indicates that the facial isomerobserved in the X-ray investigation appears indeed to bepreferred over the second facial or the meridional isomer (Table7) even though the calculated energy difference between the twofacial forms is small. Similarly, the calculations predict that thecorresponding complex of L' will have its meridional isomeras the lowest-energy form and this isomer is also the one foundto occur in the solid state.For the complex of L16 thecalculations predict that the lowest-energy isomer will also bethe meridional form. However, the X-ray structure shows thatthe complex is in fact facial I1 in the solid state. Nevertheless,the apparent strain-energy difference between the meridionaland facial I1 forms is not great (at approximately 6.5 kJ mol-')and this difference may not be significant given the approximatenature of the present calculations.Previously we have demonstrated that energy differencesbetween isomeric metal complexes can be quite dependent onrelatively minor changes in the force field employed.'6*28Further, with respect to the above result, it is important to kee1876 J.CHEM. SOC. DALTON TRANS. 1992Table 7 Relative strain energies of facial and meridional isomers of thenickel(i1) complexes of L4, L16 and LI8Structure Geometric isomer[NiL4( H20)]2 + Facial IFacial I1MeridionalFacial IFacial I1MeridionalFacial I1Meridional[ Ni L '( H 20)] +[NIL' '(H20)l2 + Facial IRelative" strainenergy (kJ mol-')0.0 b,c3.612.817.56.5 b*d0.018.311.20.0 b.e* Relative to the lowest-energy isomer. Geometry observed in X-raystructure. An earlier study (ref. 8) based on the modified MMl forcefield also gave the same relative order for the facial I and meridionalisomers while this order was reversed for the corresponding isomersincorporating the dimethylated derivative, L2', a result which wasconfirmed on use of the present (updated) force field.Total bonddistance root mean square (r.m.s.) differences = 0.019 A, total bondangle r.m.s. differences = 2.7", total torsional angle r.m.s. differences =4.7". Total bond distance r.m.s. differences = 0.033 A, total bond angler.m.s. differences = 2.4", total torsional angle r.m.s. differences = 5.5".'Total bond distance r.m.s. differences = 0.025 A, total bond angler.m.s. differences = 1.7", total torsional angle r.m.s. differences = 5.9".in mind two general limitations of the molecular mechanicsmethod for determining the strain energies of metal complexesof the present type. First, there is an absence of properthermodynamic calibration for those parts of the structuresassociated with the metal ion and the calculated energydifferences between corresponding isomers will be, at best,only semiquantitative. Secondly, the calculated steric energiesrefer to gas-phase structures and intermolecular interactions,such as those arising from crystal packing, are not taken intoaccount.In summary, it is clear that molecular mechanics calculationson metal-containing systems of the present type are useful forpredicting likely complex structures (and hence for liganddesign) provided appropriate caution is exercised wheninterpreting small differences in the calculated strain energiesbetween particular isomers.AcknowledgementsWe thank the Australian Institute of Nuclear Science andEngineering, the Australian Research Council, the SERC andICI plc for assistance.References1 D.J. Cram, Angew. Chem., Int. Ed. Engl., 1988,27, 1009.2 H. Irving and R. J. P. Williams, J. Chem. 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SOC., Dalton Trans., 1991,2493.1985,1195.J. Chem. SOC., Dalton Trans., 1982, 757.determination, University of Cambridge, 1976.Received 12th February 1992; Paper 2/00760
ISSN:1477-9226
DOI:10.1039/DT9920001869
出版商:RSC
年代:1992
数据来源: RSC