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J. CHEM. SOC. DALTON TRANS. 1994 2483Bis(p-pyridazine)-bis[ (2-~yanoguanidine)copper( I)] Cation:A Molecule containing two Co-ordinatively UnsaturatedCopper([) CentrestMichael J. Begley, Peter Hubberstey," Claire E. Russell and Paul H. WaltonChemistry Department, Nottingham University, Nottingham NG7 2RD, UK2-Cyanoguanidine [ (NH,),CNCN (cnge)] stabilises co-ordinatively unsaturated copper(!) inbis(p-pyridazine)-bis[ (2-cyanoguanidine)copper(!)] tetrafluoroborate 1, which has been structurallycharacterised by single-crystal X-ray diffraction analysis [triclinic, space group P I , a = 754.8(2),b = 971.3(2), c = 937.2(2) pm, a = 118.94(2), p = 94.72(2), y = 107.44(2)"]. The cation in 1 containstwo trigonal-planar copper(!) atoms bridged by two pyridazine (pydz) molecules and terminallyco-ordinated by a cnge molecule.It acts as a receptor molecule binding a further pydz to form tris(p-pyridazine) -bis[ (2-~yanoguanidine)copper(!)] tetrafluoroborate 2. The structure of 2 was alsodetermined [monoclinic, space group C2/c, a = 2229.3(7), b = 850.0(3), c = 1568.5(3) pm,= 99.1 3(2)"]. It contains two distorted-tetrahedral copper(1) atoms bridged by three pydz molecules andterminally co-ordinated by a cnge molecule. Thermogravimetric analysis of 2 showed that heating removesthe third bridging pydz molecule to regenerate 1; this behaviour is ascribed to the unusually high stability ofthe co-ordinatively unsaturated copper(!) moiety in 1.A large number of copper(1) complexes have been structurallycharacterised. They are dominated by four-co-ordinate tetra-hedral copper(1) ions, with fewer examples of co-ordinativelyunsaturated (i.e. two- or three-co-ordinate) copper(1). '-'Recently, the isolation of co-ordinatively unsaturated copper(1)has become increasingly more significant owing to itspostulated importance in many catalyticsystems. We are thus engaged in the study of the successfulstabilisation and isolation of three-co-ordinate copper(1) with avariety of different ligands. From a study of the properties andreactions of the new copper(1) complexes we hope to gain aninsight into the mechanisms of action of many copper-containing catalysts and enzymes. Previously, we havepublished ' v 9 accounts of the structural characterisation ofthree-co-ordinate copper(1) moieties crystallised from aqueoussolution.The present paper reports the results from anextension to those studies, aimed at preparing and isolating adiscrete cation containing two unsaturated copper(1) centresseparated by ca. 350 pm, similar to the active centre in thedioxygen-carrying proteins, haemocyanins. ' '*'The factors which control the stabilisation of three-co-ordinate copper(1) have been shown to be based on steric orelectronic effects; 37431 ,-' early examples of complexes withapproximate local D,, symmetry used either very bulkyligands l 6 or ligands with n-acceptor capability (e.g. CN-) ' toprevent co-ordination by a fourth ligand. Recently, extended-Hiickel calculations ' have rationalised the ability of n-bondingligands including 2-cyanoguanidine (NH,),CNCN (cnge) aswell as CN- to stabilise unsaturated copper(1) to such an extentthat the copper(1) complex can be crystallised from an aqueoussolution without decomposition.'*'The complexes reported herein have cnge as a ligand,affording three-co-ordinate copper(1) centres. They also containpyridazine (pydz) to generate binuclear complexes withCu Cu separations close to that in deoxy- ( NN 360 pm) lo andoxy-haemocyanins ( M 340 pm). ' ' Although the use oftetradentate N-donor ligands based on pydz, typically 3,6-bis(2-and biologicalt Supplementary data available: see Instructions for Authors, J. Chem.SOC., Dalton Trans., 1994, Issue 1, pp. xxiii-xxviii.pyridyl)pyridazine, ' ' 3,6-bis(pyrazol-2-yl)pyridazine ' andpyridazine-3,6-dicarbaldehyde dioximate," to generatebinuclear complexes has been described in detail, the potentialof pydz and its alkyl and aryl derivatives as bridges has beenlittle considered.' Initially used mainly to bridge transition-metal carbonyl they are now being used in morediverse system^.^^-^' Structurally characterised pydz-bridgedcomplexes are rare; they are limited to rnolybden~m(v),~~iron-(0),22 -(I),,, ruthenium-(~),~~,~~ -(11),~' rhodium-(~~),~'and tin(^),,^ as well as copper-(I)35-37 and -(11)?*Although the majority of these are d i n ~ ~ l e a r , ~ ~ - ~ ~ * several are p ~ l y m e r i c . ~ ~ - ~ ~ In all the dinuclear complexes thepydz bridge is supported by either a metal-metal bond,2Z-25~40a second bridging unit (sulfide,32 o ~ i d e , ~ ~ .~ ' chloride,33meth~lene,~~ maleic anhydride,,, carbon monoxide 22 or metalcarbonyl fragment 24*25) or a binucleating macrocycle (L =5,5,16,16-tetramethyl-23,24-dioxa-3,7,14,18-tetraazatricyclo-C18.2.1.1 9~'2]tetracosa-2,7,9,1 1,13,18,20,22-octaene 35). All thecopper@ complexes contain four-co-ordinate copper; [ { Cu-(pydz)(CN)),] contains two interlocking copper(1) chainsbridged by either single pydz molecules or cyanide anions.36Tetra-(~r-3-methylpyridazine)-tri-~~-pyrazine-tetracopper(1)perchlorate comprises a chain of tetrameric copper(1) unitslinked by bridging pyrazine molecules; within each unit thefour copper atoms are bridged alternatively by two 3-methyl-pyridazine molecules and one pyrazine molecule.Thecomplex [Cu2L(pydz),][C1O4], comprises two copper(1)atoms located in the binucleating macrocycle and bridged bytwo pydz molecules.Results and DiscussionA novel, dimeric, unsaturated copper(1) cation has beenprepared by treating tetrakis(acetonitrile)copper(I) tetrafluoro-borate with equimolar amounts of pydz and cnge in aceto-nitrile (Scheme 1). The resulting air-sensitive yellow complexwas structurally characterised as the bis(ppyridazine)-bis[2-cyanoguanidine)copper(~)] tetrafluoroborate 1. This speciesreacts very readily with a further pydz molecule to forman orange complex which was structurally characterised asthe novel tris(~-pyridazine)-bis[(2-cyanoguanidine)copper(1)Tfluoroborate 2. The tris(pydz)-bridged complex is interestinginsofar as thermogravimetric analysis shows that heatingremoves one pydz molecule at ca.190 "C to regenerate the+ [Cu(MeCN)dBF4N-N N-CEN-8MeCN 1 2+2ca.190"C 11 ca.25OCScheme 1bis(pydz)-bridged species. This behaviour is reminiscent of thereversible binding of substrates to the unsaturated dicopper(1)site in deoxyhaemocyanins. It is rare that co-ordinativelysaturated copper@) will afford three-co-ordinate copper(1) byfacile ligand loss. This behaviour can be ascribed to the unusualhigh stability of the unsaturated copper(1) configuration in thepresence of cnge.Crystal and Molecular Structures of Complexes 1 and 2.-Thefractional coordinates of the atoms are given in Table 1, selectedinteratomic distances and angles in Table 2.The structure ofcomplex 1 consists of a centrosymmetric dicopper(1) cation withbridging pydz molecules and terminal cnge molecules andindependent BF, - anions. The cation is essentially planar (Fig.l), with the maximum deviation from the best-fit least-squaresplane being 17 pm (a pydz carbon atom, Table 3). The planarcations are stacked in a stepped fashion with the nitrile moietyof one cnge positioned directly above a copper atom in anadjacent cation. There is no significant interaction, other thanvan der Waals contacts, between adjacent cations. The BF,-anions lie between the cation stacks, and are held in place byweak hydrogen bonds to the cnge moiety via fluorine-aminohydrogen contacts (Table 4).These interactions, although longin comparison with the calculated NH, F- distance (290~ m ) , , ~ provide for a well ordered structure with no disorderingof the anions.The copper and its ligating atoms essentially lie in a planewith only a slight deviation of the copper atom (3.7 pm, Table 3)out of the plane towards the nitrile moiety of an adjacent planarcation. Best-fit least-squares planes were also calculated for thepydz (deviation from plane < 0.9 pm) and cnge (deviation fromplane G2.8 pm) molecules. The dihedral angles between thethree planes (Table 3) are all small (maximum 11.8" betweenpydz and cnge best-fit planes), the cnge molecule being almostTable 1 Fractional coordinates for all atoms in [Cu,(p-pyd~),(cnge)~][BF~]~ and [Cu2(p-pydz),(cnge)~][BF4],0.391 5(2)0.233( 1)0.21 l(1)0.287( 1)0.153( 1)0.33 5( 2)0.132(2)0.65 3(2)0.802(2)0.104( 2)0.167(2)0.596( 1)0.308(1)(b) CCu,(CI-PYdz),(cnge)zl CBF4IzCU( 1) 0.470 23(8) 0.164 5(2)C(1) 0.411 8(6) 0.17 1( 1)C(2) 0.343 7(7) 0.085(2)N(1) 0.435 l(5) 0.171( 1)N(2) 0.389 6(5) 0.178( 1)N(4) 0.322(1) 0.090(3)C(11) 0.579 7(9) 0.3 54(2)C( 12) 0.635( 1) 0.426( 2)C(13) 0.337 7(9) 0.41 8(2)C( 14) 0.367 7(7) 0.340( 2)N(1 1) 0.552 6(5) 0.277( 1)N( 12) 0.420 l(5) 0.273( 1)N(3) 0.319 7(6) -0.016(2)C(21) 0.47 1 5(7) - 0.187( 1)C(22) 0.485 6(7) -0.329(2)N(2 1) 0.486 6(4) -0.054( 1)B(1) 0.190(1) 0.192(2)F(1) 0.222 5(6) 0.187(2)0.482 3(2)0.454( 1)0.558(1)0.457( 1)0.428( 1)0.712(1)0.525(2)0.8 3 6( 2)0.990( 2)-0.001(2)0.140(1)0.702( 1)0.285( 1)0.332 8( 1)0.495 8(8)0.576 6(8)0.435 9(7)0.568 l(7)0.519 O ( 8 )0.650( 1)0.412(1)0.414( 1)0.158( 1)0.226( 1)0.343 6(6)0.228 8(8)0.320( 1)0.284( 1)0.284 3(6)0.078( 1)0.080 4(9)0.799(2)0.645( 1)0.743( 1)0.894( 1)0.926( 1)0.64( 1)0.84(2)0.94(2)0.8 l(2)0.40(2)0.45( 1)-0.27(2) -.0.02( 2)0.729(2)0.69 1 (1)0.7 14( 1)0.619 4(9)0.899( 1)0.40( 1)0.37(2)0.17(1)0.04( 2)0.59(1)0.84( 1).0.0 1 (2)0.1 O(2)0.173 5(5)0.136 9(6)0.226 6(6)0.180(3)0.198(3)0.14 l(4)0.238(6)0.336(8)0.284(4)0.34 1 (8)0.29(1)0.560( 6)0.658(7)0.29 5( 6)0.346( 5)0.450(7)0.474(9)0.346( 1 )0.104(1)0.144(1)0.178(9)0.036( 8)0.23( 1)0.20( 1)- 0.03(2)- 0.09( I)0.1 6(2)0.02(3)0.36(2)0.49(2)0.47(2)0.33(1)- 0.19(2)- 0.44(2)0.108(2)0.170( 1)0.090 O(9)0.227( 1)0.74(1)0.80(2)0.62(1)0.41(2)0.83(1)1.09( 1).0.11(2)0.13(2)'0.038 4(9)0.157 O(6)0.123 5(7)0.221 6(7)0.2 1 4(4)0.131(5)0.096(6)0.1 15(9)0.46( 1)0.526(7)0.70(1)0.66(2)0.468(9)0.47(1)0.160(9)0.281(7)0.37(1)0.31(1J. CHEM.SOC. DALTON TRANS. 1994 2485Table 2 Interatomic distances (pm) and bond angles (") in complexes 1 and 21332.5(3)188.5(9)197.2(9)197.6(8)115(1)133( 1)133(1)130( 1)134( 1)0.112309.8( 3)191(1)205( 1)204( 1 )206.3(9)114(1)131(1)132( 1)130( 1)132( 1)0.121174.7(9)172( 1)11 7.6(9)126( 1)115.8(9)119(1)119.1(4)1 20.1 (4)120.6(3)---119.6(6)1 2 1.8(7)Freecnge 421 17.4(3)130.7(4)134.3(3)134.4(3)133.5(3)02177( 1)174(2)118(1)125(1)118(1)117(1)11 3.4(5)114.6(5)1 17.4(4)103.0(4)104.1(4)102.6(4)15.2(9)126( 1)Difference fromfree cngeN( 1 1 )-N( 12')N(l1)-C(l1)C( 12)-C( 13')C( 14)-N( 12)N( 2 1 )-N( 2 1 ')N(2 1 )-C(2 1)C(1 1)-C(12)C( 1 3)-C(14)C(2 1 )-C(22)C(22)-C(22')Cu(l)-N(12)-N(ll)Cu( 1 )-N( 12)-C( 14)Cu( 1 )-N(2 1 )-N(2 1 ')Cu( 1 )-N(21 )-C(2 1)N(l2')-N(ll)-C(ll)C( 1 l)-C( 12)-C( 13')C( 12')-C( 13)-C( 14)C( 1 3)-C( 14)-N( 12)C( 14)-N( 12)-N( 1 1 ')N(2 l')-N(2 1 )-C(21)N(2 1 )-C(2 1 )-C(22)N(1 lW(11)-C(12)C(2 l)-C(22)-C(22')1Significant137(1)132( 1)138(2)135( 1)137( 1)132(1)1119.4(6)122.0(7)--118.3(9)123(1)118(1)117(1)125(1)118.6(8)Free2 cnge 42Significant None137( 1)131(2)137(2)137(2)135(2)130( 1)131(2)133( 1)138(2)133(3)2114.5(9)127(1)11 5.6(2)122.9(8)119(1)123( 1)118(2)1 17(2)125( 1)119(1)12 1.4(7)119(1)119.5(7)Symmetry operations for X': - x , 1 - y , 1 - z (for 1) and 1 - x , y , - z (for 2)."H(121)d 'H(131)Fig.1cation [ Cu ( p- p y dz) (cnge) 2] +Molecular structure of the bis(pyridazine)-bridged dicopper(1)coplanar with the plane described by the copper co-ordinationsphere (dihedral angle 3.8", Table 3).The cation in complex 1 contains two symmetry-related co-ordinatively unsaturated copper(1) atoms, bridged in a typicalp-1,2 fashion by two pydz molecules and separated by 332.5 pm.The ligand cnge, co-ordinating via its nitrile nitrogen, completesthe copper's co-ordination sphere, which can be described asslightly distorted trigonal planar.At the copper centre,deviations from the ideal 120" angle are small, with an averageof 119.6(4)" between the cnge nitrogen atom and pydz nitrogenatoms and 120.6(4)" between the two pydz nitrogen atoms(Table 2). Distances between the pydz nitrogen atoms and thecopper atom (197.2 and 197.6 pm, Table 2) are typical for aCu N interaction. That between the cnge nitrogen atom andthe copper atom, although somewhat shorter (188.5 pm, Table2), is typical of cnge terminally co-ordinated to copper(r).*Munakata et al.44 have published an empirical correlationbetween the angles and distances around three-co-ordinatecopper(1) for a variety of complexes. Riehl et aZ.45 have studiedthe distortion from ideal trigonal geometry to Y- and T-shapedstructures by means of extended-Huckel and ab initio calcul-Fig. 2 Molecular structure of the tris(pyridazine)-bridged dicopper(1)cation [C~,(p-py~)~(cnge)~]~+. The numbering scheme for thehydrogen atoms IS similar to that in Fig. 1ations. The empirical correlation predicts that a copper(1) centrewith angles of 120" will have equal copper-to-ligating atomdistances. Clearly, in this cation this is not the case, with therather short copper-to-cnge nitrogen distance differing from theother two Cu N distances by ca. 9 pm.This again highlightsthe unusual co-ordination properties of cnge when interactingwith copper@.The crystal structure of complex 2 (Fig. 2) shows a dicopper(1)cation with bridging pydz molecules and terminal cngemolecules and BF4- anions. The cation lies on a diad axis,which passes through the plane described by one bridging pydzmolecule. As in the structure of 1, the cations lie in a stack, butwith the BF4- anions between the cations. Weak hydrogenbonds (Table 4) between the cnge amino hydrogen atoms an2486 J. CHEM. SOC. DALTON TRANS. 1994Table 3Cation in 1Equation of best plane: 3.3427~ + 6.6423~ - 6.67762 = -0.01 8 (plane 1)Atom Cu(1) N(1) C(l) N(2) C(2) N(3) N(4) N(11) N(12) C(11) C(12) C(13) C(14)Deviationfromplane/pm -13.7 -6.8 -0.8 3.8 3.1 -6.6 14.7 12.2 -7.4 17.4 8.8 -10.5 -16.2Copper co-ordination sphere in 1Equation of best plane: -3.298~ - 6.728~ + 6.5952 = 0.050 (plane 2)Atom Cu(1) N(l) N(11) N(12)Deviation from plane/pm 3.7 - 1.3 - 1.2 - 1.2Dihedral angles/ O between planes in 1Plane cnge pydzCopper co-ordination sphere 3.8 8.4cnge - 11.8Dihedral angles/” between planes in 2cnge 89.0 13.6 - 102.3 135.5- - - 115.4 122.3* Symmetry related by the operations: 1 - x, y , i - z.Best-fit least-squares planes for complexes 1 and 2Plane cnge * PYW 1) PYdZ( 1) * PYdZ(2)PYW 1)Table 4 Possible hydrogen-bond contacts in complexes 1 and 2Interaction X‘ SymmetryX-H .. . X’(4 C ~ ~ z ~ C I - P Y ~ ~ ~ z ~ ~ ~ ~ ~ ~ z l ~ ~ ~ , I ,N(3)-H(31)-*.F(l) IN(3)-H(31) - F(2) I1N(3)-H(32) * * F(3) I11N(3)-H(32) F(3) IVN(4)-H(41) - * - F(4) VN(4)-H(42) F(4) VI(b) CCUz(P-PY ,(cnge)zlCBF,1zN(3)-H(31) * * F(2) VIIN(3)-H(31) - - F(7) VIIN(3)-H(32) * * F( 1) VIIIN(3)-H(32) * * * F(l) VIIN(3)-H(32) * * F(8) VIIIN(4)-H(41) * * * F(2) IXN(4)-H(41) * * F(5) IXN(4)-H(42) * * F(4) VIIIN(4)-H(42) * F(6)N(4)-H(42) * * * F(8)properties *VIIIVIIIr(X - X’)/pm310(1)322( 1)309( 1)306( 1 )301(1)300( 1)302(2)302(2)290(2)299(2)300(2)307(1)291(7)323(2)292(7)31 l(14)r(X - H)/pm100100100100100100103103103103103I02102102102102r(H - X’)/pm24425621 125021 121021 1230192247209236204224202227123124158117148148146125160110145126142166147138* I 1 - x, 1 - y , 1 - z; IIx,y, 1 + z; I112 - x, 1 - y , 1 + z; IVx,y, 1 - z; v 2 - x, 1 - y , 1 - z; VIx, - 1 + y , z ; v11: - x, -+ + y , + - z;VIII x, -y, + + z; I X i - x, + - y , 1 - z.anion fluorine atoms again afford a fairly well ordered structurewith only slight rotational disorder of the anions.The Cu...Cu separation in complex 2 is maintained bythree bridging pydz molecules which co-ordinate in an expectedp-1,2 fashion.Triply bridged dicopper(1) complexes areextremely rare.46 The reduced Cu Cu interatomic distance(309.8 pm, Table 2) compared to that in 1 (332.5 pm) is part ofthe trend towards decreasing interatomic distance withincreasing number of bridging ligands, the separation in thepolymeric mono(pydz)-bridged species [(Cu(pydz)(CN)},]being 368 pm.36 The ligand cnge, co-ordinating via its nitrilenitrogen, completes the distorted-tetrahedral co-ordinationgeometry around the copper in 2.The angles subtended at thecopper between the cnge nitrogen atom and the nitrogen atomsof the pydz rings range from 1 13.4 to 117.4’, all slightly largerthan the ideal angle for tetrahedral co-ordination. This isprobably due to the strain imposed on the co-ordinationgeometry by the tris(pydz) bridge which gives bond anglesbetween the bridging pydz molecules at the copper ranging from102.6 to 104.1” (Table 2); the limited range in these angles isreflected in the dihedral angles between the pydz planes(deviation from best-fit least-squares planes \< 1.1 pm) whichrange from 11 5.4 to 122.3’ (Table 3).There is also a difference inthe interatomic distance between the copper and cnge nitrogen(191 pm, Table 2) and the copper and pydz nitrogens (average205 pm).The cnge molecules in complex 2 are essentially planar(deviation from best-fit least squares plane < 1.3 pm). Thedihedral angle between the cnge planes for any given cation is89.0’ (Table 3). Therefore, the planes described by the cngemolecules are almost perpendicular and not coplanar as in 1.Multivariate comparison 47*48 of the bond lengths in the cngemolecules in complexes 1 and 2 and free cnge (Table 2) gives asemiquantitative assessment of the overall perturbation to theligand caused by co-ordination to the copper centre.Thecomparison indicates that the cnge molecules in the two cationsare ‘significantly’ perturbed (Table 2). In the case of theunsaturated complex the structural changes are probably partlydue to the inductive effect of three-co-ordinate copper(1). Theymay also be related to fact that, as proposed from extended-Huckel molecular orbital calc~lations,~ the interaction of cngewith three-co-ordinate copper(1) involves both n-donor cnge(x)-copper (4p,) and x-acceptor cnge (.n*)-copper (3d,,,y,)interactions. In the absence of strong steric effects thesJ. CHEM. SOC. DALTON TRANS. 1994 2487electronic effects are expected to ensure that the cnge molecule iscoplanar with the copper co-ordination plane.Notably, theorientation of the cnge molecule in 1 is coplanar with the copperco-ordination plane such that a cnge x-molecular orbital couldoverlap with the unoccupied copper 4p orbital in the putativeinteraction.Infrared Spectra of Complexes 1 and 2.-The IR spectra ofpressed KBr pellets of 1 and 2 were obtained; for 1 the spectrumwas found to change slowly with time and had to be recordedimmediately after sample preparation. The IR spectrum of free~ n g e , ~ contains a diagnostic doublet at ca. 2200 cm-'. Uponco-ordination to a metal this changes in shape and moves tohigher w a v e n ~ m b e r . ~ * ~ . ~ ~ - ~ ~For complex 1, vasym[N( 1)-C( 1)-N(2)] was shifted to2228/2185 from 2209/2165 cm-' for free cnge. This large shift(+ 19/20 cm-') corresponds to a significant perturbation to theforce constants in cnge when co-ordinated to copper in 1.For2, vasym[N( 1)-C( 1)-N(2)] occurred at 2210/2165 cm-', which,within experimental error, is the same position as for free cnge.Furthermore, the fingerprint region of the spectrum for 2 didnot exhibit any significant shifts for the cnge bands. Overall, theperturbation to the cnge structure is far greater in 1 than in 2.This evidence further supports the possibility of a cnge-copperx-donor/x-acceptor interaction in 1.Thermogravimetric Analysis of Complexes I and 2.-Thestability of complex 1 with respect to 2 was investigated byexamining the thermal decomposition of the latter. Thethermogravimetric analysis showed the loss of 1 equivalent ofpydz per dimer at ca.190°C. At temperatures greater than200 "C further weight loss was observed until completedecomposition. A similar analysis of 1 showed no weight lossuntil 200 "C, whereupon weight loss was observed untilcomplete decomposition. The weight-loss pattern at greaterthan 200 "C for 1 matched that for 2 at similar temperatures.The loss of one pydz molecule from 2 at 190 "C to generate 1describes these data adequately. Since 2can be prepared from 1 itis proposed that the addition of one pydz molecule to 1 isreversible.ConclusionThe structures and properties of two novel copper(1)-pydz-cngecomplexes have been presented. To our knowledge, theirconstituent cations, Cu',(p-pydz),(cnge), and Cu',(p-~ydz)~-(cnge),, are the first examples of discrete dinuclear cationsbridged solely by pydz molecules to be characterised by single-crystal X-ray diffraction techniques. Although similar cationscontaining pydz-bridged transition-metal fragments have beenstudied by IR method^,,^.^^ in all previously structurallycharacterised species the pydz bridge is supported by either ametal-metal bond,22-25,40 a second bridging moiety 22-25*32-34or a binucleating macrocycle.The bis(pydz)-bridged cation,which is the first structurally characterised planar three-co-ordinate copper(1) complex containing pydz, will bind a furtherpydz molecule to generate the tris(pydz)-bridged cation whichcontains two four-co-ordinate copper(1) centres; the latter is arare example of a triply bridged dicopper(1) complex.46Remarkably, on heating, the latter complex loses a single pydzmolecule, presumably to regenerate the former complex.Thereversible addition of a pydz molecule to the unsaturatedcopper(1) centres is probably due to the unusual stability of thelatter when ligated by cnge. The stability is thought to arise fromproposed interactions between cnge and the copper(1) centre,the existence of which is supported by the orientation of thecnge molecule with respect to the copper centre in the structureof the unsaturated complex and also by the IR spectra of thetwo complexes. These interactions could be important inunderstanding the properties of three-co-ordinate copper(1)moieties in other systems, such as the copper atoms at thedioxygen binding site of the dioxygen-carrying proteinhaemocyanin.Experiment a1All reactions were carried out under an argon or nitrogenatmosphere unless otherwise noted.Infrared spectra, massspectra and elemental analyses were consistent with theproposed structures. Infrared spectra were obtained on aPerkin-Elmer PE983G spectrometer as KBr pressed pellets.Thermogravimetric analyses were carried out with a StantonRedcroft TG-750 balance controlled by a TG-750/770 lineartemperature programmer. Microanalyses were carried out byMr. T. J. Spencer at the microanalysis facility at the Universityof Nottingham Chemistry Department.Prior to use, acetonitrile and tetrahydrofuran were distilledfrom CaH, and sodium-benzophenone, respectively.Thecomplex [Cu(MeCN),]BF, was prepared using a literatureprocedure 5 3 involving the addition of wO][BFJ to coppermetal suspended in dry acetonitrile. The compounds cnge andpydz were obtained from Aldrich Chemical Company Ltd.Whereas cnge was purified by recrystallisation from water anddried at room temperature in vucuo prior to use, pydz was usedwithout further purification.Bis(~-pyridazine)-bi[(2-~yanoguanidine)copper(1)] Tetra-Buoroborate 1 .-Freshly prepared [Cu(MeCN),]BF, (3.14 g,10 mmol) was added with stirring to a solution of pydz (0.80 g,10 mmol) and powdered cnge (0.84 g, 10 mmol) in acetonitrile.The solution was stirred for 3 h. Removal of the solvent in vacuoat room temperature afforded a viscous, orange oil.Subsequentwashing of the oil with CH,Cl, afforded a yellow solid under ayellow solution. The air-sensitive solid was isolated by cannulafiltration and washed with cold CH,Cl, to give complex 1 (2.04g, 65% yield) [Found (Calc. for C,H,BCuF,N,): C , 22.70(22.90); H, 2.50 (2.55); N, 26.85 (26.75%)]. Complex 1 could berecrystallised by diffusion of hexanes into an acetone solution ofthe product.Tris(p-pyridazine)-bis[(2-cyanoguunidine)copper(1)] Tetra-Puoroborate 2.--Method (a). Freshly prepared [Cu(MeCN),]-BF, (3.14 g, 10 mmol) was added with stirring to a solution ofpydz (0.40 g, 5 mmol) in dry deoxygenated tetrahydrofurancontaining powdered cnge (0.84 g, 10 mmol). The mixture wasstirred for 100 h. The product was obtained as an insolubleorange powder.It was isolated by cannula filtration and washedwith cold CH,Cl,. Drying in vacuo afforded complex 2 as anorange-brown powder (2.66 g, 75% yield) [Found (Calc. forC8HIoBCuF4N,): C, 27.45 (27.10); H, 2.95 (2.85); N, 26.60(27.65731,Method (b). Complex 1 (3.14 g, 5 mmol) was added to pydz(0.40 g, 5 mmol) in acetone. Crystals of 2 were obtained bydiffusion of hexanes into the acetone solution of the product.X-Ray Crystallographic Analyses.-Suitable crystals of eachcomplex were selected and mounted in Lindemann tubes underdry nitrogen. Preliminary oscillation and Weissenberg photo-graphs indicated that the unit cell of 1 was triclinic and that of 2was monoclinic, space group C2/c (no. 15). After transfer to aHilger and Watts Y290 four-circle diffractometer and prior todata collection, the cell constants were accurately determinedby least-squares refinement of 24 reflections well positionedthroughout reciprocal space.Throughout the data collection,intensity-control reflections were monitored periodically; nosignificant decrease in intensity was observed. Lorentz andpolarisation corrections were applied to the data. Crystal data,together with details of the diffraction experiments are listed inTable 5.The structures of complexes 1 and 2 were solved byidentifying, in the respective Patterson maps, the copper-copper2x,2y,2z vector (for 1) and the copper-copper Harker peaks (for2). Subsequent refinement with the copper atoms in positionrevealed the rest of the complexes in Fourier differencesyntheses, including hydrogen atoms and the BF, - anions, TheBF,- anion in 2 was found to be disordered about twoorientations.The relative occupancy (82% : 18%) of the disorde2488 J. CHEM. soc. DALTON TRANS. 1994Table 5 Data collection parameters for complexes [Cu,(p-pydz),-(cnge)2lCBF412 1 and [Cu2(CI-PYdz),(cnge)2lCBF412 2 *1 2Formula cl 2H16B2Cu2F8N12 C16H20B2Cu2F8N14M 629.04 709.13Crystal system Triclinic MonoclinicSpace group P i (no. 2) C2/c (no. 15)a/Pm 754.8(2) 2229.3(7)blpm 97 1.3(2) 8 50.3( 3)clpm 93 7.2( 2) 1568.5(3)a/" 118.94(2) 9094.72(2) 99.13(2)107.44(2) 90P/"Y I"Z 1 4PL,alc/cm-l 20.2 15.4DJg 1.89 1.6D,/g cm-3 1.84 1.7F(OO0) 312 1416Crystal dimensions/Reflections collected 1399 1997Unique reflections 1399 1997Reflections with 1023 1030Number of 195 246R = [ZlAF@(AF,,(] 0.065 0.062R' = [Zw(AF')2/ 0.070 0.061* Details in common: Mo-Ka radiation (h 71.07 pm); 28,,, 44'; -28scan.U/pm3 553(1) 2934(3)(bromoform-hexane)0.15 x 0.1 x 0.1 0.45 x 0.2 x 0.1mmF 2 > 2o(Fo2)parametersWAFJ21was included as a parameter in the least-squares refinement ofthe model.Full least-squares calculations, using the CRYSTALSsuite of programs,54 were carried out to refine the positions andanisotropic thermal parameters of all the atoms except the 18%occupancy fluorine atoms in 2 and the hydrogens, which wererefined isotropically. For 1 the final cycle of refinement, withunit weighting scheme, gave residuals of R = 0.065 and R' =0.070 for 1023 data with Fo2 > 2a(F02) and data to parameterratio of 5.25: 1 .For 2 the final cycle of refinement, with unitweighting scheme, gave R = 0.062 and R' = 0.061 for 1030data with F02 > 30(F02) and data to parameter ratio of 4.19 : 1.Additional material available from the Cambridge Crystallo-graphic Data Centre comprises thermal parameters andremaining bond lengths and angles.AcknowledgementsWe thank the SERC for financial support (to P. H. W.).References1 F. H. Jardine, Adv. Znorg. Chem. Radiochem., 1975,17, 116.2 B. P. Murphy, Coord. Chem. Rev., 1993,124,63.3 S . Jagner and G. Helgesson, Adv. Inorg. Chem., 1991,37, 1.4 G. A. Bowmaker, A. Camus, B. W. Skelton and A. H. White, J. Chem.5 T.N. Sorrel1 and D. L. Jameson, J. Am. Chem. SOC., 1983,105,601 3.6 E. Spodine and J. Mansur, Coord. Chem. Rev., 1992,119,171.7 K. D. Karlin and Y. Gultneh, Prog. Inorg. 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ISSN:1477-9226    

DOI:10.1039/DT9940002483

出版商:RSC    

年代:1994

数据来源: RSC