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New binucleating amido ligands, synthesis and structures of copper(II) and manganese(III) complexes
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Po/yhedron Vol.9,No.23,pp.2867-2871, 1990 Printed
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COMMUNICATION NEW BINUCLEATING AMID0 LIGANDS, SYNTHESIS AND STRUCTURES OF COPPER@) AND MANGANESE(II1) COMPLEXES KAREN BERTONCELLO,
GARY D. FALLON and KEITH S. MURRAY*
Department of Chemistry, Monash University, Clayton, Victoria 3 168, Australia (Received 28 August 1990 ; accepted 27 September 1990) Abstract-New
binucleating ligands containing p-alkoxo backbones and amido-pyridyl or amido-phenol “end” groups have been synthesized. The syntheses and structures of mononuclear Cu” and binuclear (Cu”-Cu” and Mn”‘-Mn”‘) complexes are described. The crystal structure of a novel doubly-bridged Mn”‘-Mn”’ complex shows that each sixcoordinate manganese is bridged by endogenous p-alkoxo and exogenous CL-acetatogroups. Chemical or electrochemical oxidations will be required to obtain higher oxidation state metal10 species.
We are in the process of developing new binucleating ligand systems of the types shown, LH3 and L’H5, which differ from the well studied Schiffbase’ or tripodal amino-pyridy12 analogues in so far as the salicylideneimine or amino-pyridyl end groups of the latter are replaced by amido-pyridyl or amido-phenol groups. The endogenous p-alkoxo backbone remains common to all classes. These types of ligands are being used to prepare binuclear (or higher nuclearity) Cu-Cu, Ni-Ni, Fe-Fe and Mn-Mn complexes primarily to use as models for polymetallic bio-sites of these metal ions, for example in Type 3 copper-containing proteins,3 iron oxo-proteins4 or the manganese-water oxidation centre (W.O.C.) of Photosystem II.’ It was felt that incorporation of chelating amido fragments of the type shown, especially in deprotonated forms could potentially stabilize high oxidation state metal ion combinations such as Cul’-Cul”, Cu”‘-Cu”‘, Mn”‘-Mn”‘, Mn”‘-Mn”‘, etc., some of which have been postulated to be important in the biological systems mentioned above. Studies by other groupsG8 and our own’ on related mononuclear amido-chelate species have shown that these oxidation states can be obtained. It was also felt that the planar-deprotonated -CON--
groups might impose geometric features at the metal ions and the endogenous bridging moiety different to those observed in the Schiff-base and tripodal-pyridyl analogues.
L’H,
The ligands LH3 and L’H 5 were synthesized by reaction of 1,3-diaminopropan-2-01 with the corresponding ester of the 2-carboxypyridine or 2-carboxyphenol precursor, and were fully characterized by analytical and spectroscopic methods. Variations have been made, for instance, in the length * Author to whom correspondence should be addressed. and symmetry of the diamine backbone. Macro2867
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Table 1. Mononuclear and binuclear complexes of amido-pyridyl and amido-phenol (L’H,) ligands
Complex Ligand LH, Mn(LH,)Cl, Cu(LH,)(ClO& Cu(LH) - 2H,O Ni(LH).H,O Cu,L(OAc).2.5H,O Cu2L(CF,C02)*4H,0*MeOH
(LH,)
Colour
pe,R(BM) at 295 K (per M ion)
Colourless Pale blue Violet Orange Blue Blue
5.81 1.63 1.92 0 1.61” 1.61
Dark green Dark green
4.82 4.63
Ligand L’H,
[MG’(OAc)m41w - Hz0 Mn,L’(OAc)(MeOH),
“A value of 1.70 BM was obtained on a sample obtained by heating, in vucuo, the sample used for crystallography, viz. Cu,L(H,O) (OAc)*OSDMF. The DMF is easily lost at 295 K.
cyclic analogues of these open-chain amido ligands are also currently being explored. There is an early report of a related macrocyclic system based on the 4-methylphenol-2,6-dicarboxy backbone. ‘O Transition metal ions can readily be incorporated into these ligands and some results were noted which did not always accord with preconceived
* Crystal data on Cu(LH) *2Hz0 : Cl ,H, &uN,O,, fw = 397.9, monoclinic, a = 7.998(2), b = 22.696(6), c = 9.463(3) A, /3 = 109.94(2)“. Space group: P2,/a, Z= 4, D, = 1.64 g cme3, D, = 1.64(l) g cmp3, F(OOO)= 820, ~(Mo-K,) = 1.39 mm-‘, I(Mo-K,) = 0.71073 A, T = 2O(l)“C. Structure solved by Patterson and Fourier methods and refined by full-matrix leastsquares (positional and anisotropic thermal parameters for Cu, 0, N and isotropic thermal parameters for all other atoms). R =0.061, R, = 0.072 for 152 parameters and 1905 observed [F> 60(F)] data from 3716 measured. The limits of data collection were 3.5 < 20 < 55”. t Crystal data on Cu,L(H,O)(OAc) *0.5DMF : C, 8.5 fw = 538.0, triclinic, a = 8.662(l), HmCu,N,.,O,.,, b = 10.010(l), c = 12.833(2) A, tl = 83.27(l), /I = 73.61(l), y = 79.35(l)“. Space group: Pi, Z = 2, D, = 1.71 g cmm3, F(OOO)= 548, ~(Mo-K,) = 2.08 mm-‘, Structure I(Mo-K,) = 0.7107 A, T = - lOO(l)C. solved by Patterson and Fourier methods and refined by full-matrix least-squares (positional and anisotropic thermal parameters for Cu and isotropic thermal parameters for all other atoms). R = 0.045, R, = 0.052 for 147 parameters and 2716 observed [F > 60(F)] data from 3680 measured. The limits of data collection were 3.5 < 20 < 50”. DMF is disordered about the origin. C(8) is also disordered above and below the C(7), C(9), O(2) plane.
notions of the relative pK, values of the various donor groups on the ligand, and probably relate to a subtle interplay of acidity, stability, solubility, hydrogen bonding and nature of solvent. Thus, reaction of LH, with metal salts in methanol in the ratio 1: 2, in the absence of base, yielded crystalline 1 : 1 “adducts” such as Cu”(LHJ(ClO& and Mn” (LH3)C12 (Table 1). Similar adducts were obtained by Vagg and co-workers ’ ’ using related non-binucleating pyridyl-amide ligands and polymeric structures were postulated for such species in the solid state. Addition of a base such as NaOH, to a 1: 1 or 1 : 2 mixture of LH, and Cu(CF3C0J2, yielded the violet-coloured complex Cu(LH) - 2H20, in which the ligand acted as a tetradentate chelate and still retained the protonated, non-bonded alcohol moiety but had undergone deprotonation of the amido NH groups. A crystal structure determination* confirmed the planar CuN, coordination imposed by LH2- on copper [Fig. 1(a)] and showed hydrogen-bonded lattice interactions involving water molecules and amide-oxygen or alcoholoxygen atoms. The Cu-N(amido) and Cu-N (pyridyl) distances are normal. I2 The analogous square-planar Ni(LH) - Hz0 complex was likewise obtained and displayed IR, ‘H NMR and mass spectral data compatible with the copper(I1) structure. Binuclear p-carboxylate copper(H) complexes of LH3 were obtained using a 2 : 1 copper carboxylateto-ligand ratio with DMF or MeCN as preferred solvents. FAB mass spectral measurements clearly show the Cu,L(RCO,) parent ion. A low temperature crystal structure determinationt of Cu2L
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a
Fig. 1. (a) ORTEP drawing of Cu(LH)*2H,O. The solvated Hz0 molecules are not shown. Selected bond lengths (A) : Cu( l)--N( 1) = 2.064(5) ; Cu( 1)-N(2) = 1.956(S) ; Cu( 1)-N(3) = 1.949(5) ; Cu(l)-N(4) = 2.026(6); Cu(l)-O(l) = 2.533; C(6)-O(1) = 1.257(8); C(6)-N(2) = 1.291(g); C( 10)-O(3) = 1.259(g) ; C( 10)-N(3) = 1.309(g). Hydrogen-bonded contacts : 0( 1). . .0(5) = 2.78 ; O(2). . .0(5) = 2.69; O(3). . .0(4) = 2.80; O(3). . .0(4’) = 2.82; O(4). (5) = 2.72 [where O(4) and O(5) are water oxygens]. (b) ORTEP drawing of Cu,L(H,O)(OAc)O.SDMF. The solvated DMF molecules not shown. C(8) is disordered, only the site above the C(7), C(9), O(2) plane is shown. Selected bond lengths (A) : Cu( 1)--N(3) = 1.913(4) ; Cu(l)--N(4) = 2.003(4) ; Cu(l)-O(2) = 1.907(4) ; Cu( 1)-O(4) = 1.963(3) ; Cu( 1)-O(6) = 2.344(4) ; Cu(2)-N( 1) = 1.992(4) ; Cu(2)-N(2) = 1.899(5) ; Cu(2)-O(2) = 1.874(3) ; Cu(2)-O(5) = 1.923(4) ; C(6)-0( 1) = 1.250(6) ; C(6)-N(2) = 1.317(6); C(lO)-O(3) = 1.258(6); C(lO)-N(3) = 1.312(6). Cu(1). . Cu(2) = 3.416. Selected bond angle (“) : Cu(l)-0(2)-Cu(2) = 129.2(2).
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Communication C(311( ) ) Cl321
Fig. 2. ORTEP drawing of [MnzL’(OAc)py,]py *H20. The solvated py and H,O molecules are not shown. Selected bond lengths (A) and angles (“) : Mn( l)-0( 1) = 1.938(5) ; Mn( 1)-O(6) = 1.995(5) ; Mn(l)-O(2) = 1.848(5); Mn(l)-N(1) = 1.919(6); Mn(l)-N(3) = 2.362(6); Mn(l)-N(4) = 2.389(7); Mn(2)-0( 1) = 1.942(4) ; Mn(2)-O(7) = 1.977(5) ; Mn(2)-O(5) = 1.851(5); Mn(2)-N(2) = 1.927(6); Mn(2)-N(5) = 2.410(6) ; Mn.. .Mn = Mn(2)-N(6) = 2.389(7). 3.552(2); Mn(l)-O(l)--Mn(2) = 132.5(2).
(H,O)(OAc) *OSDMF confirmed that the binucleating ligand had been fully deprotonated and that the two CuN202 planar moieties were coplanar and were bridged, as desired, by the endogenous p-alkoxo-oxygen atom and the exogenous q ’ : q ’ : p,-bridging acetate group. One of the copper atoms has an axially-bonded water molecule [Fig. l(b)]. A Cu-Cu distance of 3.416 A and Cu-O(R)-Cu angle of 129.2(2)’ were generally in accord with the observed magnetic moment of 1.70 BM (at 295 K), which in turn is indicative of weak antiferromagnetic coupling. Interestingly, * Crystal data on [Mn,L’(OAc)py,]py - H,O : C,, H,,Mn,N,O*, fw = 907.7, triclinic, a = 9.218(3), b = 13.637(4), c = 17.291(5) A, u = 99.50(2), p = 91&I(2), y = 100.14(3)“. Space group: PT, Z= 2, D,= 1.43 g cm- 3, F(OOO) = 940, ~(Mo-K,) = 0.63 mm-‘, ~(MoK,) = 0.71073 & T = 2O(l)“C. Structure solved by Patterson and Fourier methods and refined by full-matrix least-squares [positional and anisotropic thermal parameters for Mn, 0, N and C(7) through C(11) and isotropic thermal parameters for all other atoms]. R = 0.062, R, = 0.079 for 355 parameters and 3456 observed [F> 60(F)] data from 5489 measured. The limits of data collection were 4.0 < 28 < 45”. The stereochemistry around C(9) is trigonal but should be tetrahedral and is, therefore, disordered. An attempt to refine C(9) as occupying two sites, above and below the C(8), C( lo), 0( 1) plane, was unsuccessful.
Okawa and co-workers13 have recently observed weak ferromagnetic coupling in a p-acetate-bridged Cu’*--Cu*’ complex of another binucleating amido ligand system which contains a p-pyrazolato endogenous bridging group. Unfortunately, no structural data were obtainable which could be compared with those for Cu,L(H,O)(OAc) 0.5DMF. Crystalline CL-pyrazolate-bridged complexes such as [Cu2L(3,5-Me2-pyz)] were obtained using Cu(ClO& in the presence of NaOH and ligand. Na+ and Clod- ions were incorporated into the lattice of some of these derivatives. This is a feature sometimes observed in metal-amid0 chelate compound&’ and is related to the ability of amide oxygen atoms to bind to Na+ as well as to the chelated metal. One of the most interesting groups of binuclear complexes is that formed from manganese(II1) and the ligand L’H,. These complexes are of general formula Mn,L’(OAc)(B)4, where B = pyridine, ypicoline and methanol, and are formed by reacting [Mn,0(OAC),py,](C10,)‘4 or Mn(OAc),, in air, with L’HS using the neat pyridine base or methanol as solvent. Such conditions are basic enough to cause removal of five protons from L’HS. The molecular structure* of the pyridine derivative, shown in Fig. 2, consists of two octahedrally-coordinated manganese(II1) ions bridged by both
Communication the p-alkoxo-oxygen atom of (L’)‘-, with a Mn-0-Mn angle of 132.5(2)“, and by a q’ : q’ : p,-bridging acetate group. The Mn-Mn distance is 3.552(2) A. A doubly-bridged Mn’nz structure of this, or any other type, is quite rare in the general context of models for the polynuclear manganese site in the W.O.C. or in manganese catalase enzymes.5 The whole of the binucleating (L’)5ligand moiety is remarkably planar, presumably through a combination of favourable geometry around the manganese atoms and incorporation of deprotonated amide fragments along the backbone. It is interesting to note that the Mn-0 and Mn-N distances provided by (L’)5- are similar to those recently deduced from EXAFS for the W.O.C. of Photosystem II, whereas the Mn-N(pyridine) and Mn*. .Mn distances are longer than those obtained from fits of the first and second shell EXAFS peaks. ” The room temperature magnetic moment, per manganese, of [Mn&‘(OAc)py,]py * Hz0 is 4.82 BM, which is close to the uncoupled S = 2 value. Similar weak coupling has been observed recently in other doubly- and triply-bridged Mn”‘-Mn”’ systems.’ An irreversible oxidation wave, observed in the cyclic voltammogram of DMF solutions of this complex at + l.lV (reference to SCE), is assigned to Mnin -+ Mn’“. Thus, in contrast to other recently reported mononuclear amidomanganese chelates,7,8 a stronger oxidant than air is required to obtain Mn’” or Mn” species. Studies of reactivity, electrochemistry and variable temperature susceptibility are in progress on the various compounds described here. Supplementary data. Tables of atomic coordinates, thermal parameters, bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre.
2.
3.
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9. 10. 11. 12.
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REFERENCES 1. (a) D. E. Fenton, in Advances in Inorganic Bioinorganic Mechanisms (Edited by A. G. Sykes), Vol. 2, p. 187. Academic Press, New York (1983) ; (b) F. L.
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Urbach, in Metal Ions in Biological Systems (Edited by H. Sigel), Vol. 13, Ch. 3. Marcel Dekker, New York (1982) ; (c) K. S. Murray, in Biological and Inorganic Copper Chemistry (Edited by K. D. Karlin and J. Zubieta), Vol. 2, p. 161. Adenine Press, New York (1986). (a) K. D. Karlin and Y. Gultneh, Prog. Inorg. Chem. 1987, 35, 219; (b) T. N. Sorrell, Tetrahedron 1989, 45, 3. E. I. Solomon, in Metal Clusters in Proteins (Edited by L. Que Jr), ACS Symposium Series No. 372, p. 116 (1988). (a) S. J. Lippard, Angew. Chem. Znt. Edn 1988, 27, 344; (b) L. Que Jr and R. S. Scarrow, in Metal Clusters in Proteins (Edited by L. Que Jr), ACS Symposium Series No. 372, p. 152 (1988). (a) G. Christou, Accts Chem. Res. 1989,22, 328 ; (b) K. Wieghardt, Angew. Chem. Znt. Edn 1989, 28, 1153 ; (c) G. Brudvig and R. H. Crabtree, Prog. Znorg. Chem. 1989,37,99 ; (d) V. L. Pecoraro, Photothem. Photobiol. 1988,49, 249. T. J. Collins and S. W. Gordon-Wyllie, J. Am. Chem. Sot. 1989, 111, 4511, and refs therein. M. Koikawa, H. Okawa and S. Kida, J. Chem. Sot., Dalton Trans. 1988, 641. S. K. Chandra, S. B. Choudhury, D. Ray and A. Chakravorty, J. Chem. Sot., Chem. Commun. 1990, 474. K. Bertoncello, G. D. Fallon and K. S. Murray, Inorg. Chim. Acta 1990, 174, 57. H. Okawa, M. Honda and S. Kida, Chem. Lett. 1972, 1027. D. J. Barnes, R. L. Chapman, F. S. Stephens and R. S. Vagg, Znorg. Chim. Actu 1981, 51, 155. (a) R. L. Chapman, F. S. Stephens and R. S. Vagg, Inorg. Chim. Acta 1980, 43, 29; (b) M. Antolovich, D. J. Phillips and A. D. Rae, Znorg. Chim. Acta 1989, 156, 189. T. Kamiusuki, H. Okawa, E. Kitaura, M. Koikawa, N. Matsumoto, S. Kida and H. Oshio, J. Chem. SOL, Dalton Trans. 1989, 2077. J. B. Vincent, H. R. Chang, K. Folting, J. C. Huffmann, G. Christou and D. N. Hendrickson, J. Am. Chem. Sot. 1987,109,5703. J. E. Penner-Hahn, R. M. Fronko, V. L. Pecoraro, C. F. Yocum, S. D. Betts and N. R. Bowlby, J. Am. Chem. Sot. 1990,112,2549.
Po/yhedron Vol.9,No.23,pp.2867-2871, 1990 Printed
in Great
Pergamon
Britain
Press plc
COMMUNICATION NEW BINUCLEATING AMID0 LIGANDS, SYNTHESIS AND STRUCTURES OF COPPER@) AND MANGANESE(II1) COMPLEXES KAREN BERTONCELLO,
GARY D. FALLON and KEITH S. MURRAY*
Department of Chemistry, Monash University, Clayton, Victoria 3 168, Australia (Received 28 August 1990 ; accepted 27 September 1990) Abstract-New
binucleating ligands containing p-alkoxo backbones and amido-pyridyl or amido-phenol “end” groups have been synthesized. The syntheses and structures of mononuclear Cu” and binuclear (Cu”-Cu” and Mn”‘-Mn”‘) complexes are described. The crystal structure of a novel doubly-bridged Mn”‘-Mn”’ complex shows that each sixcoordinate manganese is bridged by endogenous p-alkoxo and exogenous CL-acetatogroups. Chemical or electrochemical oxidations will be required to obtain higher oxidation state metal10 species.
We are in the process of developing new binucleating ligand systems of the types shown, LH3 and L’H5, which differ from the well studied Schiffbase’ or tripodal amino-pyridy12 analogues in so far as the salicylideneimine or amino-pyridyl end groups of the latter are replaced by amido-pyridyl or amido-phenol groups. The endogenous p-alkoxo backbone remains common to all classes. These types of ligands are being used to prepare binuclear (or higher nuclearity) Cu-Cu, Ni-Ni, Fe-Fe and Mn-Mn complexes primarily to use as models for polymetallic bio-sites of these metal ions, for example in Type 3 copper-containing proteins,3 iron oxo-proteins4 or the manganese-water oxidation centre (W.O.C.) of Photosystem II.’ It was felt that incorporation of chelating amido fragments of the type shown, especially in deprotonated forms could potentially stabilize high oxidation state metal ion combinations such as Cul’-Cul”, Cu”‘-Cu”‘, Mn”‘-Mn”‘, Mn”‘-Mn”‘, etc., some of which have been postulated to be important in the biological systems mentioned above. Studies by other groupsG8 and our own’ on related mononuclear amido-chelate species have shown that these oxidation states can be obtained. It was also felt that the planar-deprotonated -CON--
groups might impose geometric features at the metal ions and the endogenous bridging moiety different to those observed in the Schiff-base and tripodal-pyridyl analogues.
L’H,
The ligands LH3 and L’H 5 were synthesized by reaction of 1,3-diaminopropan-2-01 with the corresponding ester of the 2-carboxypyridine or 2-carboxyphenol precursor, and were fully characterized by analytical and spectroscopic methods. Variations have been made, for instance, in the length * Author to whom correspondence should be addressed. and symmetry of the diamine backbone. Macro2867
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Table 1. Mononuclear and binuclear complexes of amido-pyridyl and amido-phenol (L’H,) ligands
Complex Ligand LH, Mn(LH,)Cl, Cu(LH,)(ClO& Cu(LH) - 2H,O Ni(LH).H,O Cu,L(OAc).2.5H,O Cu2L(CF,C02)*4H,0*MeOH
(LH,)
Colour
pe,R(BM) at 295 K (per M ion)
Colourless Pale blue Violet Orange Blue Blue
5.81 1.63 1.92 0 1.61” 1.61
Dark green Dark green
4.82 4.63
Ligand L’H,
[MG’(OAc)m41w - Hz0 Mn,L’(OAc)(MeOH),
“A value of 1.70 BM was obtained on a sample obtained by heating, in vucuo, the sample used for crystallography, viz. Cu,L(H,O) (OAc)*OSDMF. The DMF is easily lost at 295 K.
cyclic analogues of these open-chain amido ligands are also currently being explored. There is an early report of a related macrocyclic system based on the 4-methylphenol-2,6-dicarboxy backbone. ‘O Transition metal ions can readily be incorporated into these ligands and some results were noted which did not always accord with preconceived
* Crystal data on Cu(LH) *2Hz0 : Cl ,H, &uN,O,, fw = 397.9, monoclinic, a = 7.998(2), b = 22.696(6), c = 9.463(3) A, /3 = 109.94(2)“. Space group: P2,/a, Z= 4, D, = 1.64 g cme3, D, = 1.64(l) g cmp3, F(OOO)= 820, ~(Mo-K,) = 1.39 mm-‘, I(Mo-K,) = 0.71073 A, T = 2O(l)“C. Structure solved by Patterson and Fourier methods and refined by full-matrix leastsquares (positional and anisotropic thermal parameters for Cu, 0, N and isotropic thermal parameters for all other atoms). R =0.061, R, = 0.072 for 152 parameters and 1905 observed [F> 60(F)] data from 3716 measured. The limits of data collection were 3.5 < 20 < 55”. t Crystal data on Cu,L(H,O)(OAc) *0.5DMF : C, 8.5 fw = 538.0, triclinic, a = 8.662(l), HmCu,N,.,O,.,, b = 10.010(l), c = 12.833(2) A, tl = 83.27(l), /I = 73.61(l), y = 79.35(l)“. Space group: Pi, Z = 2, D, = 1.71 g cmm3, F(OOO)= 548, ~(Mo-K,) = 2.08 mm-‘, Structure I(Mo-K,) = 0.7107 A, T = - lOO(l)C. solved by Patterson and Fourier methods and refined by full-matrix least-squares (positional and anisotropic thermal parameters for Cu and isotropic thermal parameters for all other atoms). R = 0.045, R, = 0.052 for 147 parameters and 2716 observed [F > 60(F)] data from 3680 measured. The limits of data collection were 3.5 < 20 < 50”. DMF is disordered about the origin. C(8) is also disordered above and below the C(7), C(9), O(2) plane.
notions of the relative pK, values of the various donor groups on the ligand, and probably relate to a subtle interplay of acidity, stability, solubility, hydrogen bonding and nature of solvent. Thus, reaction of LH, with metal salts in methanol in the ratio 1: 2, in the absence of base, yielded crystalline 1 : 1 “adducts” such as Cu”(LHJ(ClO& and Mn” (LH3)C12 (Table 1). Similar adducts were obtained by Vagg and co-workers ’ ’ using related non-binucleating pyridyl-amide ligands and polymeric structures were postulated for such species in the solid state. Addition of a base such as NaOH, to a 1: 1 or 1 : 2 mixture of LH, and Cu(CF3C0J2, yielded the violet-coloured complex Cu(LH) - 2H20, in which the ligand acted as a tetradentate chelate and still retained the protonated, non-bonded alcohol moiety but had undergone deprotonation of the amido NH groups. A crystal structure determination* confirmed the planar CuN, coordination imposed by LH2- on copper [Fig. 1(a)] and showed hydrogen-bonded lattice interactions involving water molecules and amide-oxygen or alcoholoxygen atoms. The Cu-N(amido) and Cu-N (pyridyl) distances are normal. I2 The analogous square-planar Ni(LH) - Hz0 complex was likewise obtained and displayed IR, ‘H NMR and mass spectral data compatible with the copper(I1) structure. Binuclear p-carboxylate copper(H) complexes of LH3 were obtained using a 2 : 1 copper carboxylateto-ligand ratio with DMF or MeCN as preferred solvents. FAB mass spectral measurements clearly show the Cu,L(RCO,) parent ion. A low temperature crystal structure determinationt of Cu2L
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a
Fig. 1. (a) ORTEP drawing of Cu(LH)*2H,O. The solvated Hz0 molecules are not shown. Selected bond lengths (A) : Cu( l)--N( 1) = 2.064(5) ; Cu( 1)-N(2) = 1.956(S) ; Cu( 1)-N(3) = 1.949(5) ; Cu(l)-N(4) = 2.026(6); Cu(l)-O(l) = 2.533; C(6)-O(1) = 1.257(8); C(6)-N(2) = 1.291(g); C( 10)-O(3) = 1.259(g) ; C( 10)-N(3) = 1.309(g). Hydrogen-bonded contacts : 0( 1). . .0(5) = 2.78 ; O(2). . .0(5) = 2.69; O(3). . .0(4) = 2.80; O(3). . .0(4’) = 2.82; O(4). (5) = 2.72 [where O(4) and O(5) are water oxygens]. (b) ORTEP drawing of Cu,L(H,O)(OAc)O.SDMF. The solvated DMF molecules not shown. C(8) is disordered, only the site above the C(7), C(9), O(2) plane is shown. Selected bond lengths (A) : Cu( 1)--N(3) = 1.913(4) ; Cu(l)--N(4) = 2.003(4) ; Cu(l)-O(2) = 1.907(4) ; Cu( 1)-O(4) = 1.963(3) ; Cu( 1)-O(6) = 2.344(4) ; Cu(2)-N( 1) = 1.992(4) ; Cu(2)-N(2) = 1.899(5) ; Cu(2)-O(2) = 1.874(3) ; Cu(2)-O(5) = 1.923(4) ; C(6)-0( 1) = 1.250(6) ; C(6)-N(2) = 1.317(6); C(lO)-O(3) = 1.258(6); C(lO)-N(3) = 1.312(6). Cu(1). . Cu(2) = 3.416. Selected bond angle (“) : Cu(l)-0(2)-Cu(2) = 129.2(2).
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Communication C(311( ) ) Cl321
Fig. 2. ORTEP drawing of [MnzL’(OAc)py,]py *H20. The solvated py and H,O molecules are not shown. Selected bond lengths (A) and angles (“) : Mn( l)-0( 1) = 1.938(5) ; Mn( 1)-O(6) = 1.995(5) ; Mn(l)-O(2) = 1.848(5); Mn(l)-N(1) = 1.919(6); Mn(l)-N(3) = 2.362(6); Mn(l)-N(4) = 2.389(7); Mn(2)-0( 1) = 1.942(4) ; Mn(2)-O(7) = 1.977(5) ; Mn(2)-O(5) = 1.851(5); Mn(2)-N(2) = 1.927(6); Mn(2)-N(5) = 2.410(6) ; Mn.. .Mn = Mn(2)-N(6) = 2.389(7). 3.552(2); Mn(l)-O(l)--Mn(2) = 132.5(2).
(H,O)(OAc) *OSDMF confirmed that the binucleating ligand had been fully deprotonated and that the two CuN202 planar moieties were coplanar and were bridged, as desired, by the endogenous p-alkoxo-oxygen atom and the exogenous q ’ : q ’ : p,-bridging acetate group. One of the copper atoms has an axially-bonded water molecule [Fig. l(b)]. A Cu-Cu distance of 3.416 A and Cu-O(R)-Cu angle of 129.2(2)’ were generally in accord with the observed magnetic moment of 1.70 BM (at 295 K), which in turn is indicative of weak antiferromagnetic coupling. Interestingly, * Crystal data on [Mn,L’(OAc)py,]py - H,O : C,, H,,Mn,N,O*, fw = 907.7, triclinic, a = 9.218(3), b = 13.637(4), c = 17.291(5) A, u = 99.50(2), p = 91&I(2), y = 100.14(3)“. Space group: PT, Z= 2, D,= 1.43 g cm- 3, F(OOO) = 940, ~(Mo-K,) = 0.63 mm-‘, ~(MoK,) = 0.71073 & T = 2O(l)“C. Structure solved by Patterson and Fourier methods and refined by full-matrix least-squares [positional and anisotropic thermal parameters for Mn, 0, N and C(7) through C(11) and isotropic thermal parameters for all other atoms]. R = 0.062, R, = 0.079 for 355 parameters and 3456 observed [F> 60(F)] data from 5489 measured. The limits of data collection were 4.0 < 28 < 45”. The stereochemistry around C(9) is trigonal but should be tetrahedral and is, therefore, disordered. An attempt to refine C(9) as occupying two sites, above and below the C(8), C( lo), 0( 1) plane, was unsuccessful.
Okawa and co-workers13 have recently observed weak ferromagnetic coupling in a p-acetate-bridged Cu’*--Cu*’ complex of another binucleating amido ligand system which contains a p-pyrazolato endogenous bridging group. Unfortunately, no structural data were obtainable which could be compared with those for Cu,L(H,O)(OAc) 0.5DMF. Crystalline CL-pyrazolate-bridged complexes such as [Cu2L(3,5-Me2-pyz)] were obtained using Cu(ClO& in the presence of NaOH and ligand. Na+ and Clod- ions were incorporated into the lattice of some of these derivatives. This is a feature sometimes observed in metal-amid0 chelate compound&’ and is related to the ability of amide oxygen atoms to bind to Na+ as well as to the chelated metal. One of the most interesting groups of binuclear complexes is that formed from manganese(II1) and the ligand L’H,. These complexes are of general formula Mn,L’(OAc)(B)4, where B = pyridine, ypicoline and methanol, and are formed by reacting [Mn,0(OAC),py,](C10,)‘4 or Mn(OAc),, in air, with L’HS using the neat pyridine base or methanol as solvent. Such conditions are basic enough to cause removal of five protons from L’HS. The molecular structure* of the pyridine derivative, shown in Fig. 2, consists of two octahedrally-coordinated manganese(II1) ions bridged by both
Communication the p-alkoxo-oxygen atom of (L’)‘-, with a Mn-0-Mn angle of 132.5(2)“, and by a q’ : q’ : p,-bridging acetate group. The Mn-Mn distance is 3.552(2) A. A doubly-bridged Mn’nz structure of this, or any other type, is quite rare in the general context of models for the polynuclear manganese site in the W.O.C. or in manganese catalase enzymes.5 The whole of the binucleating (L’)5ligand moiety is remarkably planar, presumably through a combination of favourable geometry around the manganese atoms and incorporation of deprotonated amide fragments along the backbone. It is interesting to note that the Mn-0 and Mn-N distances provided by (L’)5- are similar to those recently deduced from EXAFS for the W.O.C. of Photosystem II, whereas the Mn-N(pyridine) and Mn*. .Mn distances are longer than those obtained from fits of the first and second shell EXAFS peaks. ” The room temperature magnetic moment, per manganese, of [Mn&‘(OAc)py,]py * Hz0 is 4.82 BM, which is close to the uncoupled S = 2 value. Similar weak coupling has been observed recently in other doubly- and triply-bridged Mn”‘-Mn”’ systems.’ An irreversible oxidation wave, observed in the cyclic voltammogram of DMF solutions of this complex at + l.lV (reference to SCE), is assigned to Mnin -+ Mn’“. Thus, in contrast to other recently reported mononuclear amidomanganese chelates,7,8 a stronger oxidant than air is required to obtain Mn’” or Mn” species. Studies of reactivity, electrochemistry and variable temperature susceptibility are in progress on the various compounds described here. Supplementary data. Tables of atomic coordinates, thermal parameters, bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre.
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