DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2197–2203 2197 Oxygenation of heterodinuclear di(Ï-phenoxo) CoIIMII (M 5 Mn, Fe or Co) complexes having a “Co(salen)” entity in a macrocyclic framework † Hideki Furutachi,*a Shuhei Fujinami,a Masatatsu Suzuki a and Hisashi O— kawa*b a Department of Chemistry, Faculty of Science, Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan b Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan Received 19th April 1999, Accepted 18th May 1999 Heterodinuclear di(m-phenoxo) CoIIMII complexes [CoM(L)(AcO)]ClO4 (M = Mn 1, Fe 2 or Co 3) and [CoM(L)(NCS)]ClO4 (M = Mn 4, Fe 5 or Co 6) have been obtained where L22 is a heterodinucleating macrocycle derived by the 2:1:1 condensation of 2,6-diformyl-4-methylphenol, ethylenediamine and diethylenetriamine and has a “salen”-like N2O2 metal-binding site and a “saldien”-like N3O2 site sharing the phenolic oxygens.The CoM(AcO) complexes 1 and 3 show reversible oxygenation at 0 8C in dmf, whereas 2 is irreversibly oxidized under the same conditions.The structures of the dioxygen adducts of 1 and 3 have been determined by X-ray crystallography. In that of 1, [{CoMn(L)(AcO)}2(O2)][ClO4]2?4CH3CN oxy-1, the Co resides in the “salen” site and the Mn in the “saldien” site. An exogenous acetate group bridges the two metal ions in the h1 :h1 mode together with the two phenolic oxygens. The peroxo group bridges two {CoMn(L)(AcO)} molecules at the Co forming a Co–O–O–Co linkage.The peroxo O(1)–O(2) bond distance is 1.416(5) Å and the Co(1) ? ? ? Co(2) intermetallic separation is 4.359(1) Å. The geometry about the Co is pseudo octahedral with a peroxo oxygen and an acetate oxygen at the axial sites and the Mn has a distorted six-co-ordination. The dioxygen adduct of 3, [{Co2(L)(AcO)}2(O2)][ClO4]2? 4CH3CN oxy-3, is isomorphous with oxy-1: the peroxo O(1)–O(2) bond distance is 1.415(4) Å and the Co(1) ? ? ? Co(3) intermetallic separation is 4.3527(8) Å.Within the CoM(NCS) complexes 4–6, 4 shows reversible oxygenation at 230 8C, whereas irreversible oxidation is observed for 5 and 6. Introduction Dioxygen binding and activation on dinuclear metal complexes are of current interest relating to the physiological metabolism of dioxygen at bimetallic biosites.1–5 Oxygenation of homodinuclear metal complexes like CuICuI 4 and FeIIFeII 5 have been extensively studied with the aim of providing models for hemocyanin and hemerythrin, but less attention has been paid to oxygenation of heterodinuclear complexes.6–9 It is well known that dioxygen reduction in cytochrome c oxidase is promoted by a CuFe pair in close proximity,10,11 and this has stimulated studies of the oxygenation behaviour of heterodinuclear complexes having diVerent combinations of metal ions.Recently some CuFe and CoCu complexes have been prepared and their oxygenation behaviour examined,8,9 but such studies are still limited because of the diYculty in preparing suitable heterodinuclear core complexes. The phenol-based compartmental ligand L22, having a “salen”-like N2O2 metal-binding site and a “saldien”-like N3O2 site sharing the phenolic oxygen, was developed in our laboratory for the study of heterodinuclear complexes (H2salen = N,N9-bis(salicylidene)ethylenediamine; H2saldien = N,N0-bis- (salicylidene)diethylenetriamine).12–21 Since [Co(salen)] is well known for its reactivity toward dioxygen,22,23 the dinuclear CoIIMII complexes with CoII in the “salen”-like site of the macrocycle are of great interest for studying oxygenation at the “Co(salen)” center with respect to the participation of the adjacent metal(II) ion.† Supplementary data available: ORTEP drawing of part of oxy-3, electronic spectra of 1–5. For direct electronic access see http : // www.rsc.org/suppdata/dt/1999/2197/, otherwise available from BLDSC (No.SUP 57560, 9 pp.) or the RSC Library. See Instructions for Authors, 1999, Issue 1 (http://www.rsc.org/dalton). Previously we reported the synthesis and the structures of the CoIIMII complexes [CoM(L)(AcO)]ClO4 (M = Mn 1, Fe 2 or Co 3) and [CoM(L)(NCS)]ClO4 (M = Mn 4, Fe 5 or Co 6).16 They have a di(m-phenoxo) CoIIMII core with the CoII in the “salen” site and the MII in the “saldien” site. The MII in the “saldien” site largely deviates from the mean molecular plane, leaving the “closed” and the “open” faces for dioxygen.In complexes 1–3 an acetate group is involved in an additional bridge at the closed face (Scheme 1, (a)), leaving only the open face of “Co(salen)” for oxygenation. Complexes 4–6 assume a chain structure extended by a thiocyanate bridge in the solid but a discrete dinuclear core structure with isothiocyanato donation to the MII in solution. Thus, both the closed and open faces of “Co(salen)” are available for oxygenation of 4–6 (Scheme 1, (b)).The oxygenation behaviour of 1–6 has now been studied in dmf by means of visible and EPR methods and discussed in view of the dinuclear core structure and the participation of the neighboring metal(II) ion. A part of this work was briefly reported previously.19 O– CH3 O– CH3 N N N NH N (L)2–2198 J. Chem. Soc., Dalton Trans., 1999, 2197–2203 Experimental Measurements Elemental analyses of C, H and N were obtained from the Service Center of Elemental Analysis at Kyushu University.Infrared spectra were recorded on a JASCO IR-810 spectrophotometer using KBr discs, electronic spectra in dmf or acetonitrile (ª1 × 1023 M) on Shimadzu MPS-2000 and UV- 3100 spectrophotometers and X-band EPR spectra on a JEOL JEX-FE3X spectrometer at liquid nitrogen temperature. Preparation The complexes [CoM(L)(AcO)]ClO4 (M = Mn 1, Fe 2 or Co 3) and [CoM(L)(NCS)]ClO4 (M = Mn 4, Fe 5 or Co 6) were prepared by methods in our previous paper.16 Oxygenation studies A dmf solution of a CoIIMII complex was prepared in a nitrogen or argon atmosphere and the reactivity towards dioxygen examined by means of electronic and EPR spectroscopy.The oxygenated complexes of 1 and 3, [{CoMn(L)(AcO)}2(O2)]- [ClO4]2?4CH3CN (oxy-1) and [{Co2(L)(AcO)}2(O2)][ClO4]2? 4CH3CN (oxy-3), were isolated as good crystals when each oxygenated solution in acetonitrile was diVused with diethyl ether at 230 8C. Found: C, 41.83; H, 4.39; N, 9.37.Calc. for C26H34ClCoMnN5O11 oxy-1: C, 42.09; H, 4.62; N, 9.44. Found: C, 42.38; H, 4.35; N, 9.49. Calc. for C52H66Cl2Co4N10O21 oxy-3: C, 42.38; H, 4.51; N, 9.50%. The oxidized complex of 6, [Co2(L)(NCS)(OH)]ClO4?1.5H2O 69, was obtained as brown crystals when an oxygenated dmf solution of 6 in the presence of an excess of NaClO4 was diVused with 2-propanol at 230 8C. Calc. for C25H31- ClCo2N6O8.5S: C, 40.75; H, 4.24; N, 11.40. Found: C, 40.69; H, 4.29; N, 11.55%.X-Ray crystallography Single crystals of complexes oxy-1 and oxy-3 were picked up on a hand-made cold copper plate mounted inside a liquid N2 Dewar vessel and mounted on a glass rod at 280 8C. Measurements were made on a Rigaku RAXIS-IV imaging plate area detector using graphite monochromated Mo-Ka radiation (l = 0.71070 Å) at 280 8C. Crystal-to-detector distance was 120 mm. In order to determine the cell constants and the orientation matrix, three oscillation photographs were taken with oscillation angle 28 and exposure time of 8 min for oxy-1 and 6 min for oxy-3 for each frame.The accurate unit-cell parameters used for the refinement were determined by least-squares calculations on the setting angles for 25 reflections with 2q = 22.08– 24.768 for oxy-1 and 25.20–29.178 for oxy-3 collected on a Rigaku AFC7R diVractometer with graphite monochromated Mo-Ka radiation and a rotating anode generator. Intensity data were collected by taking oscillation photographs (total oscillation range 1628, 54 frames, oscillation angle 38, and exposure time 18 min for oxy-1, 1658, 55 frames, 38, and 10 min Scheme 1 Possible oxygenation sites of CoM(AcO) 1–3 and CoM- (NCS) 4–6 complexes.N O N N N M N O Co N N N M N O Co SCN N O O O open face open face closed face (a) CoMAcO core (b) CoMNCS core for oxy-3). The data were corrected for Lorentz-polarization eVects, but not for absorption. The structure was solved by direct methods and expanded using Fourier techniques.Nonhydrogen atoms were refined anisotropically. Hydrogen atoms were included but not refined. The final cycle of full-matrix least-squares refinement was based on observed reflections (I > 3.00s(I)). Crystal data and details of the structure determinations are summarized in Table 1. CCDC reference number 186/1470. See http://www.rsc.org/suppdata/dt/1999/2197/ for crystallographic files in .cif format. Results and discussion [CoMn(L)(AcO)]ClO4 1 and [Co2(L)(AcO)]ClO4 3 These complexes have similar oxygenation behaviours. Introduction of dioxygen into a dmf solution of 1 at 0 8C caused an immediate change from red to dark red, suggesting formation of an oxygenated complex.Complex 1 shows an intense absorption band at 362 nm (e 10500 M21 cm21) and weaker bands near 460 (shoulder) and 560 nm (e 990 M21 cm21) (Fig. 1a) whereas its oxygenated complex shows an intense band at 382 nm (e 11750 M21 cm21) and an enhanced band at 550 nm (e 1700 M21 cm21) (Fig. 1b). The latter band of moderate intensity is characteristic of cobalt–dioxygen complexes and can be attributed to a LMCT band.22–24 The oxygenated complex was stable at 0 8C for several days. When the oxygenated solution was purged with argon the original red solution was recovered. The reversible oxygenation/deoxygenation cycle for 1 is confirmed by observing the electronic spectral interconversion between traces a and b (Fig. 1). A similar reversible oxygenation/ deoxygenation has been established for 3 at 0 8C (UV-vis: 3, 365 (e 10000), 480 (shoulder) and 565 nm (e 1100); oxygenated complex of 3, 392 (e 11200) and 560 nm (e 1500 M21 cm21)).19 In order to characterize the oxygenated complex in solution, EPR spectra of the oxygenated solution of 1 were studied (Fig. 1, insert). The observed isotropic EPR signal near g ª 2.0 has a well resolved six-line hyperfine structure attributable to isolated MnII (Aiso = 90 G).This result demonstrates that the oxygenated complex is a peroxo dimer having the MnIICoIII–O– O–CoIIIMnII linkage. This was demonstrated by X-ray crystallography for [{CoMn(L)(AcO)}2(O2)][ClO4]2?4CH3CN (oxy-1) and [{Co2(L)(AcO)}2(O2)][ClO4]2?4CH3CN (oxy-3) isolated from the oxygenated solutions of 1 and 3, respectively. An ORTEP25 drawing of the cationic part of [{CoMn(L)- (AcO)}2(O2)][ClO4]2?4CH3CN oxy-1 with 30% probability thermal ellipsoids is shown in Fig. 2 together with the atomnumbering scheme and the framework of the complex.Relevant bond distances and angles are given in Table 2. The cation Fig. 1 Electronic spectra for complex 1 in dmf: (a) in the absence of O2. (b) oxygenated at 0 8C. Insert: EPR spectrum of the oxygenated species in dmf at liquid nitrogen temperature.J. Chem. Soc., Dalton Trans., 1999, 2197–2203 2199 consists of two {CoMn(L)(AcO)} entities and a peroxo group; four acetonitrile molecules and two perchlorate ions are free from co-ordination and captured in the lattice.The {CoMn(L)(AcO)} part is very similar to the di(m-phenoxo)- (m-acetato) CoMn core of 1,16 having the Co in the “salen” site and the Mn in the “saldien” site. The acetate group bridges the metal ions at the closed face. Oxygenation occurs at the open face of “Co(salen)”, trans to the bridging acetate oxygen, forming a m-h1 :h1 peroxo dimer with a Mn(1)Co(1)–O(1)–O(2)– Co(2)Mn(2) linkage; the Co(1) ? ? ? Co(2) intermetallic separation is 4.359(1) Å.The two {CoMn(L)(AcO)} parts in oxy-1 are not equivalent; the Co(1) ? ? ? Mn(1) and Co(2) ? ? ? Mn(2) intermetallic separations are 3.124(1) and 3.123(1) Å, respectively. The peroxo O(1)–O(2) bond distance is 1.416(5) Å that is long relative to those of [{Co(salen)(dmf)}2(O2)] (1.339(6) Å)22e,26 and [{Co(salen)(pip)}2(O2)] (1.383(7) Å; pip = Fig. 2 (a) An ORTEP drawing of the [{CoMn(L)(AcO)}2(O2)]21 part of oxy-1 with the atom numbering scheme.(b) The framework of oxy-1. piperidine).22e,27 Instead, the Co(1)–O(1) and Co(2)–O(2) bond distances (1.866(4) and 1.849(4) Å, respectively) are shortened relative to those of the Co(salen) peroxo complexes (1.909(5)– Table 1 Crystallographic data for [{CoM(L)(AcO)}2(O2)][ClO4]2? 4CH3CN (M = Mn, oxy-1; Co, oxy-3) oxy-1 oxy-3 Formula M Crystal size/mm Crystal system Space group a/Å b/Å c/Å a/ 8 b/ 8 g/ 8 U/Å3 Z Dc /g cm23 m/cm21 No. reflections No of data used (I > 3.00s(I)) No.variables RR 9 C60H72Cl2Co2Mn2N14O18 1575.96 0.20 × 0.10 × 0.10 Triclinic P1� 15.296(4) 17.578(5) 14.224(3) 99.57(2) 113.00(2) 80.14(2) 3447(1) 2 1.518 9.87 10375 7271 884 0.051 0.066 C60H72Cl2Co4N14O18 1583.95 0.50 × 0.25 × 0.15 Triclinic P1� 14.833(2) 17.962(2) 13.820(3) 98.656(9) 110.540(8) 82.378(9) 3395.9(7) 2 1.549 11.19 11147 9158 884 0.058 0.083 Table 2 Selected bond distances (Å) and angles (8) of [{CoMn(L)- (AcO)}2(O2)][ClO4]2?4CH3CN oxy-1 Co(1)–O(1) Co(1)–O(4) Co(1)–N(1) Co(2)–O(2) Co(2)–O(8) Co(2)–N(6) Mn(1)–O(3) Mn(1)–O(5) Mn(1)–N(4) Mn(2)–O(7) Mn(2)–O(9) Mn(2)–N(9) O(1)–Co(1)–O(3) O(1)–Co(1)–O(6) O(1)–Co(1)–N(2) O(3)–Co(1)–O(6) O(3)–Co(1)–N(2) O(4)–Co(1)–N(1) O(6)–Co(1)–N(1) N(1)–Co(1)–N(2) O(2)–Co(2)–O(8) O(2)–Co(2)–N(6) O(7)–Co(2)–O(8) O(7)–Co(2)–N(6) O(8)–Co(2)–O(10) O(8)–Co(2)–N(7) O(10)–Co(2)–N(7) O(3)–Mn(1)–O(4) O(3)–Mn(1)–N(3) O(3)–Mn(1)–N(5) O(4)–Mn(1)–N(3) O(4)–Mn(1)–N(5) O(5)–Mn(1)–N(4) N(3)–Mn(1)–N(4) N(4)–Mn(1)–N(5) O(7)–Mn(2)–O(9) O(7)–Mn(2)–N(9) O(8)–Mn(2)–O(9) O(8)–Mn(2)–N(9) O(9)–Mn(2)–N(8) O(9)–Mn(2)–N(10) N(8)–Mn(2)–N(10) Co(1)–O(3)–Mn(1) Co(2)–O(7)–Mn(2) 1.866(4) 1.918(4) 1.881(5) 1.849(4) 1.921(4) 1.875(5) 2.189(4) 2.119(4) 2.379(4) 2.195(4) 2.109(4) 2.385(5) 89.0(2) 173.0(2) 88.7(2) 94.2(1) 177.2(2) 177.6(2) 87.9(2) 85.3(2) 90.9(2) 90.2(2) 86.6(1) 92.8(2) 90.3(2) 95.4(2) 91.0(2) 72.0(1) 147.3(1) 79.1(2) 79.9(1) 129.0(1) 84.6(1) 75.6(2) 74.1(2) 84.3(1) 132.7(2) 89.1(1) 152.9(2) 108.2(2) 133.4(2) 107.0(2) 98.8(2) 98.2(2) Co(1)–O(3) Co(1)–O(6) Co(1)–N(2) Co(2)–O(7) Co(2)–O(10) Co(2)–N(7) Mn(1)–O(4) Mn(1)–N(3) Mn(1)–N(5) Mn(2)–O(8) Mn(2)–N(8) Mn(2)–N(10) O(1)–Co(1)–O(4) O(1)–Co(1)–N(1) O(3)–Co(1)–O(4) O(3)–Co(1)–N(1) O(4)–Co(1)–O(6) O(4)–Co(1)–N(2) O(6)–Co(1)–N(2) O(2)–Co(2)–O(7) O(2)–Co(2)–O(10) O(2)–Co(2)–N(7) O(7)–Co(2)–O(10) O(7)–Co(2)–N(7) O(8)–Co(2)–N(6) O(10)–Co(2)–N(6) N(6)–Co(2)–N(7) O(3)–Mn(1)–O(5) O(3)–Mn(1)–N(4) O(4)–Mn(1)–O(5) O(4)–Mn(1)–N(4) O(5)–Mn(1)–N(3) O(5)–Mn(1)–N(5) N(3)–Mn(1)–N(5) O(7)–Mn(2)–O(8) O(7)–Mn(2)–N(8) O(7)–Mn(2)–N(10) O(8)–Mn(2)–N(8) O(8)–Mn(2)–N(10) O(9)–Mn(2)–N(9) N(8)–Mn(2)–N(9) N(9)–Mn(2)–N(10) Co(1)–O(4)–Mn(1) Co(2)–O(8)–Mn(2) 1.916(4) 2.003(4) 1.872(4) 1.931(4) 2.046(4) 1.866(4) 2.243(3) 2.222(5) 2.223(4) 2.233(3) 2.223(5) 2.207(5) 96.2(2) 85.8(2) 85.6(1) 92.9(2) 90.3(2) 96.3(2) 87.8(2) 81.2(2) 172.8(2) 96.0(2) 91.8(1) 176.6(2) 178.6(2) 88.4(2) 85.3(2) 88.6(1) 131) 87.8(1) 151.0(2) 107.1(2) 133.0(2) 107.4(2) 73.3(1) 151.3(2) 79.1(2) 81.0(2) 125.9(1) 86.8(2) 75.0(2) 74.0(2) 97.0(1) 97.2(2)2200 J.Chem. Soc., Dalton Trans., 1999, 2197–2203 1.914(5) Å).22e,26,27 This fact suggests that the axial acetate coordination is strong compared with dmf or pip co-ordination, aVording a high aYnity towards dioxygen for the CoII in the “salen” site. The Co(1)–O(1)–O(2) and Co(2)–O(2)–O(1) angles are 109.1(3) and 116.3(3)8, respectively, typical for Co(salen) peroxo complexes.22e,26,27 The Co(1), Co(2), O(1), and O(2) are not coplanar and the Co(1)–O(1)–O(2)–Co(2) torsion angle with respect to the O(1)–O(2) edge is 149.5(2)8.In each {CoMn(L)(AcO)} unit the Co assumes a pseudo octahedral geometry with the N2O2 donor atoms of the macrocycle on the equatorial plane and the bridging acetate oxygen and the peroxo oxygen at the axial positions. The in-plane Co– N and Co–O bond distances fall in the range 1.866(4)–1.931(4) Å, slightly longer than those of 1 (1.864(6)–1.916(4) Å).The axial Co–O (acetate) bond distance in oxy-1 (Co(1)–O(6) 2.003(4), Co(2)–O(10) 2.046(4) Å), on the other hand, is considerably short relative to that of 1 (2.129(4) Å). The {CoN2O2} part forms a good coplane; the sum of the bite angles about the Co is 360.18 (mean value for the two units). The O (acetate)– Co–O (peroxo) angle is 172.98 (mean). The Mn in the “saldien” site is not involved in the oxygenation and retains a distorted trigonal-prismatic geometry as found for complex 1, but some geometric changes occur upon oxygenation. The Mn–O (phenolate) and Mn–N (imine) bond distances of oxy-1 (2.189(4)–2.243(3) Å) are slightly shortened relative to the corresponding bond distances of 1 (2.221(5)– 2.258(4) Å).The Mn–N (amine) bond distances of oxy-1 Table 3 Selected bond distances (Å) and angles (8) of [{Co2(L)- (AcO)}2(O2)][ClO4]2?4CH3CN oxy-3 Co(1)–O(1) Co(1)–O(4) Co(1)–N(1) Co(2)–O(3) Co(2)–O(5) Co(2)–N(4) Co(3)–O(2) Co(3)–O(8) Co(3)–N(6) Co(4)–O(7) Co(4)–O(9) Co(4)–N(9) O(1)–Co(1)–O(3) O(1)–Co(1)–O(6) O(1)–Co(1)–N(2) O(3)–Co(1)–O(6) O(3)–Co(1)–N(2) O(4)–Co(1)–N(1) O(6)–Co(1)–N(1) N(1)–Co(1)–N(2) O(3)–Co(2)–O(5) O(3)–Co(2)–N(4) O(4)–Co(2)–O(5) O(4)–Co(2)–N(4) O(5)–Co(2)–N(3) O(5)–Co(2)–N(5) N(3)–Co(2)–N(5) O(2)–Co(3)–O(7) O(2)–Co(3)–O(10) O(2)–Co(3)–N(7) O(7)–Co(3)–O(10) O(7)–Co(3)–N(7) O(8)–Co(3)–N(6) O(10)–Co(3)–N(6) N(6)–Co(3)–N(7) O(7)–Co(4)–O(9) O(7)–Co(4)–N(9) O(8)–Co(4)–O(9) O(8)–Co(4)–N(9) O(9)–Co(4)–N(8) O(9)–Co(4)–N(10) N(8)–Co(4)–N(10) Co(1)–O(3)–Co(2) Co(3)–O(7)–Co(4) 1.878(3) 1.895(3) 1.866(4) 2.168(3) 2.056(3) 2.297(4) 1.854(3) 1.917(3) 1.870(4) 2.161(3) 2.053(3) 2.281(4) 90.5(1) 173.3(1) 88.0(2) 92.8(1) 178.0(2) 176.8(1) 88.2(2) 85.4(2) 85.9(1) 128.4(1) 89.2(1) 155.3(1) 103.1(2) 133.1(1) 108.9(2) 83.1(1) 175.3(1) 95.5(1) 92.2(1) 177.0(2) 177.1(1) 88.9(2) 84.9(2) 84.8(1) 123.2(1) 88.2(1) 158.2(1) 98.2(1) 138.0(1) 109.4(2) 99.5(1) 98.0(1) Co(1)–O(3) Co(1)–O(6) Co(1)–N(2) Co(2)–O(4) Co(2)–N(3) Co(2)–N(5) Co(3)–O(7) Co(3)–O(10) Co(3)–N(7) Co(4)–O(8) Co(4)–N(8) Co(4)–N(10) O(1)–Co(1)–O(4) O(1)–Co(1)–N(1) O(3)–Co(1)–O(4) O(3)–Co(1)–N(1) O(4)–Co(1)–O(6) O(4)–Co(1)–N(2) O(6)–Co(1)–N(2) O(3)–Co(2)–O(4) O(3)–Co(2)–N(3) O(3)–Co(2)–N(5) O(4)–Co(2)–N(3) O(4)–Co(2)–N(5) O(5)–Co(2)–N(4) N(3)–Co(2)–N(4) N(4)–Co(2)–N(5) O(2)–Co(3)–O(8) O(2)–Co(3)–N(6) O(7)–Co(3)–O(8) O(7)–Co(3)–N(6) O(8)–Co(3)–O(10) O(8)–Co(3)–N(7) O(10)–Co(3)–N(7) O(7)–Co(4)–O(8) O(7)–Co(4)–N(8) O(7)–Co(4)–N(10) O(8)–Co(4)–N(8) O(8)–Co(4)–N(10) O(9)–Co(4)–N(9) N(8)–Co(4)–N(9) N(9)–Co(4)–N(10) Co(1)–O(4)–Co(2) Co(3)–O(8)–Co(4) 1.895(3) 2.002(4) 1.856(4) 2.174(3) 2.074(4) 2.111(4) 1.913(3) 2.003(3) 1.854(4) 2.148(3) 2.100(4) 2.104(4) 95.7(1) 85.8(2) 84.0(1) 93.1(1) 90.4(1) 97.5(1) 88.6(1) 71.5(1) 153.8(1) 80.3(1) 83.9(1) 127.0(1) 79.1(1) 77.8(1) 75.3(1) 90.6(1) 91.1(2) 85.4(1) 92.5(2) 89.2(1) 97.2(2) 89.2(1) 74.2(1) 158.8(1) 80.5(1) 84.9(1) 124.3(1) 81.1(1) 77.9(1) 74.8(2) 99.3(1) 98.3(1) (Mn(1)–N(4) 2.379(4); Mn(2)–N(9) 2.385(4) Å) are also shortened relative to that of 1 (2.407(5) Å).Instead, the Mn–O (acetate) bond distances (Mn(1)–O(5) 2.119(4); Mn(2)–O(9) 2.109(4) Å) are slightly elongated relative to that of 1 (2.099(4) Å). The least-squares plane of the “salen” site and that defined by the two phenolic oxygens and two iminic nitrogens of the “saldien” site are bent at the O(3)–O(4) (O(7)–O(8)) edge.The dihedral angle between the two least-squares planes is 10.38 (mean for the two units) which is large compared with 4.68 for 1. The {CoMn(L)(AcO)} unit also shows a distortion with respect to the Co–Mn edge, aVording a saddle-like shape for the molecule. The dihedral angle between the two aromatic rings is 29.38 (mean) that is slightly smaller than the corresponding dihedral angle for 1 (31.38). Complex oxy-3 (M = Co) is isomorphous with oxy-1.19 Relevant bond distances and angles are given in Table 3.Some geometrical features for oxy-1 and oxy-3 are summarized in Table 4. The peroxo O(1)–O(2) bond distance (1.415(4) Å), the Co(1)–O(1)–O(2), Co(3)–O(2)–O(1) angles (110.0(2) and 117.0(2)8, respectively), and the Co(1) ? ? ? Co(3) intermetallic separation (4.3527(8) Å) for oxy-3 are comparable to the respective values for oxy-1. The Co(1)–O(1)–O(2)–Co(3) torsion angle of oxy-3 (143.7(2)8) is smaller than that of oxy-1 (149.5(2)8). The “Mn(saldien)” part of oxy-1 and the “Co(saldien)” part of oxy-3 diVer from each other because of the different ionic radii of MnII and CoII.The Mn-to-ligand bond distances in the former (2.217 Å, mean) are evidently longer than the Co-to-ligand bond distances in the latter (2.130 Å, mean). The distortions in the {CoM(L)(AcO)} core with respect to the O (phenolate)–O (phenolate) edge (t) and the Co–M edge (f) are both larger in oxy-3. The above X-ray crystallographic studies indicate that the acetate bridge is retained in the oxygenation process to allow oxygenation at the open face of “Co(salen)”.The initial oxygenation product must be the superoxo complex [CoIIIMII(L)- (AcO)(O2 2)]1 that then reacts with another CoIIMII complex (1 or 3) to form the peroxo dimer (oxy-1 or oxy-3); eqns. (1) and (2). [CoIIMII(L)(AcO)]1 1 O2 [CoIIIMII(L)(AcO)(O2 2)]1 (1) [CoIIMII(L)(AcO)]1 1 [CoIIIMII(L)(AcO)(O2 2)]1 [{CoIIIMII(L)(AcO)}2(O2 22)]21 (2) Table 4 Structural parameters of [{CoM(L)(AcO)}2(O2)][ClO4]2? 4CH3CN (M = Mn, oxy-1; Co, oxy-3) oxy-1 oxy-3 O(1)–O(2)/Å Co–O(1)–O(2)/8 Co–O(2)–O(1)/8 Co–O(1)–O(2)–Co/8 Co(1) ? ? ? M(1) (unit 1)/Å (unit 2)/Å Co(1) ? ? ? Co(2) (unit 1–unit 2)/Å Co(1) ? ? ? M(2) (unit 1–unit 2)/Å Co(2) ? ? ? M(1) (unit 1–unit 2)/Å M(1) ? ? ? M(2) (unit 1–unit 2)/Å d(Co) a/Å d(M)b/Å (unit 1) (unit 2) t c/8 (unit 1) (unit 2) fd/8 (unit 1) (unit 2) 1.416(5) 109.1(3) 116.3(3) 149.5(2) 3.124(1) 3.123(1) 4.359(1) 6.143(1) 5.617(1) 7.160(1) 0 0.70 0.69 9.30 11.37 27.21 31.41 1.415(4) 110.0(2) 117.0(2) 143.7(2) 3.105(8) 3.0785(8) 4.3527(8) 6.0776(8) 5.5295(9) 7.0428(1) 0 0.61 0.57 12.27 14.52 34.14 31.81 a Deviation from the least-squares plane defined by the basal donor atoms at the “salen” site.b Deviation from the least-squares plane defined by the basal donor atoms at the “saldien” site. c The bending at O (phenolate)–O (phenolate) edge between the plane defined by the basal donor atoms at the “salen” site and the plane defined by the basal donor atoms at the “saldien” site. d Dihedral angle between the two aromatic rings.J.Chem. Soc., Dalton Trans., 1999, 2197–2203 2201 Such a stepwise formation of a peroxo dimer through a superoxo complex has been demonstrated for Co(salen) and related SchiV base complexes.22,23 It must be noted that Co(salen) itself predominantly forms the superoxo complex [Co(salen)(O2 2)] in dmf22,23 whereas 1 and 3 form the peroxo dimer.The X-ray crystallographic results for oxy-1 and oxy-3 indicate that the peroxo O–O bond is elongated whereas the Co–O (peroxo) bond is shortened relative to the corresponding bonds of the Co(salen) peroxo complexes. As discussed above the axial acetate oxygen is a strong enough donor to cause an eYcient electron transfer from the CoII to dioxygen in oxy-1 and oxy-3. Such axial ligation of an acetate group is diYcult for mononuclear Co(salen) and analogs. Thus, the MII in the “saldien” site contributes to the axial acetate ligation to the “Co(salen)” through the acetate bridge formation.When a solution of complex oxy-1 was warmed to room temperature the spectrum changed with the decrease of the absorption bands at 382 and 550 nm, forming a yellow solution within 2 h, probably due to decomposition of oxy-1. Similarly the solution of oxy-3 faded within 2 h when warmed to room temperature. [CoFe(L)(AcO)]ClO4 2 This complex was very sensitive toward molecular dioxygen so as to be oxidized even at 230 8C with a change from red to yellow.Complex 2 shows an intense absorption band at 358 nm (e 10900 M21 cm21) and weaker bands near 460 (shoulder) and 560 nm (e 1400 M21 cm21), whereas its oxidized yellow solution shows an intense band at 385 nm (e 11200 M21 cm21) but no distinct absorption in the visible region. The resulting yellow solution showed EPR signals at g = 4.26 and 2.01 that are attributable to isolated high-spin FeIII (in frozen solution at liquid nitrogen).This result indicates that a CoIIIFeIII species is formed. The mechanism for the conversion of 2 into the CoIIIFeIII complex is not straightforward because the facile oxidation of FeII in the “saldien” site is recognized for analogous [CuIIFeII( L)]21 and [NiIIFeII(L)]21 complexes.13,14 [CoMn(L)(NCS)]ClO4 4 Complex 4 in dmf formed a dioxygen adduct at 230 8C with a change from red to dark red. Purging to the oxygenated solution with argon at 230 8C resulted in the recovery of the original red colour of 4.The reversible oxygenation/deoxygenation was confirmed by the interconversion of the electronic spectra of 4 and its dioxygen adduct. Complex 4 shows an intense absorption band at 370 (e 11000 M21 cm21) and a weaker band at 540 nm (e 500 M21 cm21). The oxygenated solution of 4 (oxy-4) has an intense absorption band at 377 nm (e 11400 M21 cm21) and a moderately intense band at 595 nm (e 2700 M21 cm21).The latter band in the visible region (LMCT band) is located at longer wavelength relative to the corresponding bands for oxy-1 and oxy-3 (ca. 560 nm). The red-shift of the peroxide-to-CoIII charge transfer band for oxy-4 can be explained by no axial donation to “Co(salen)”. That is, the cobalt d orbitals of oxy-4 are low-lying relative to those of oxy- 1 and oxy-3. The EPR spectrum of the oxygenated solution of 4 (in frozen dmf solution) shows an isotropic signal with six-line hyperfine structure near g ª 2.0 (Aiso = 93 G) typical of isolated MnII as observed for oxy-1.The EPR result is in harmony with the formulation MnIICoIII–O–O–CoIIIMnII for the oxygenated complex. As mentioned in the Introduction, both the open and closed faces of the “Co(salen)” can be available for oxygenation of complex 4. A peroxo dimer formed at the closed face of “Co(salen)” is ruled out because this would give rise to a severe steric repulsion between two {CoMn(L)(NCS)} entities.Thus, the oxygenation of 4 to form the peroxo dimer (oxy-4) occurs at the open face of “Co(salen)” as provided for oxy-1 and oxy-3 (see Scheme 2, left). When the oxygenated solution of complex 4 was warmed to 0 8C the spectrum of the peroxo dimer changed with a decrease of the bands at 377 and 595 nm, forming a yellow solution due to decomposition of oxy-4 as observed for oxy-1 and oxy-3. [CoFe(L)(NCS)]ClO4 5 Complex 5 was very sensitive to dioxygen like 2 and instantaneously oxidized at 230 8C when exposed. The oxidized solution showed an absorption spectrum very similar to that of the oxidized solution of 2.Further, it showed EPR signals (g = 4.24 and 2.01) very similar to those of 2. Evidently both the CoII and FeII are oxidized with dioxygen to form a CoIIIFeIII species. [Co2(L)(NCS)]ClO4 6 Complex 6 was also sensitive to dioxygen and irreversibly oxidized even at 230 8C within 20 min and the formation of a peroxo complex was not confirmed.Thus, 6 and 3 diVer in oxygenation behaviour in spite of the same Co2 pair. Fig. 3 shows the electronic spectral changes of 6 upon oxidation at 230 8C. The absorption spectrum of 6 has two bands near 360 and 550 nm which are replaced by one at 393 nm on oxidation. The facile oxidation of 6 even at 230 8C may proceed by a mechanism involving a neighbouring CoII in the “saldien” site. We have noticed that the lifetime of the oxygenated solution of 6 varies with the complex concentration; the higher the concentration the longer is the lifetime.This fact suggests that a peroxo dimer and superoxo complex exist in an equilibrium in solution and the superoxo complex as a minor species is associated with the high sensitivity of 6. As mentioned above the oxygenation can occur either at the open or the closed face of “Co(salen)”. Oxygenation at the open face forms the peroxo dimer [{CoIIICoII(L)(NCS)}2- (O2 22)]21 as a dominant species.If oxygenation occurs at the closed face of “Co(salen)” a superoxo complex [CoIIICoII( L)(NCS)(O2 2)]1 is formed because of steric reasons as Scheme 2 A possible oxygenation mechanism for complexes 4 and 6. N O N N N M N O Co SCN N O N N N M N O Co SCN N N N M N O Co SCN O N O O O– O– N N N Mn N O Co SCN O N O N N NCS N O Co O N O N Mn N O N N N Co N O Co O O intramolecular peroxo complex O2 irreversible oxidation for CoMn (4) for CoCo (6) intermolecular peroxo complex2202 J.Chem. Soc., Dalton Trans., 1999, 2197–2203 discussed above. The terminal superoxo oxygen can make a bridge to the adjacent CoII in the “saldien” site, by kicking out the thiocyanate ion, forming an intramolecular peroxo complex [CoIIICoIII(L)(O2 22)]21 (see Scheme 2, right). The intramolecular peroxo complex must be formed as a minor species in the equilibrium, but 6 is oxidized to a CoIIICoII species through this complex at 230 8C. In our preliminary study the final product was shown to be the CoIIICoII complex [Co2(L)(NCS)(OH)]ClO4?1.5H2O 69.It appears that the resulting “CoIII(saldien)” center may act as a strong oxidant of the oxidized complex 6 as in eqn. (3). {CoIIICoIII(L)} 1 {CoIICoII(L)} 2{CoIIICoII(L)} (3) It must be noted that complexes 4 (CoMn) and 6 (Co2) have essentially the same core structure but diVer in oxygenation behaviour; 4 forms a stable peroxo dimer at 230 8C whereas 6 is oxidized at this temperature through an intramolecular peroxo intermediate.This can be explained by the participation of the adjacent metal in oxygenation. In the case of 4, the adjacent MnII cannot be involved in two-electron reduction of dioxygen to form an intramolecular CoIII–O–O–MnIII peroxo bond because of the preferred d5 electronic configuration of MnII. In the case of 6, the Co in the “saldien” site can be involved in such a two-electron reduction forming the intramolecular peroxo complex. Further, it should be noted that oxygenation of 3 significantly diVers from that of 6 in spite of the same Co2 pair.In the case of 3, the formation of the peroxo bridge over the Co2(AcO) core at the open face is diYcult as judged from the core structure. Thus, the core structure bridged by an acetate group at the closed face suppresses a neighbouring eVect of the adjacent metal(II) ion. Conclusion The CoIIMII complexes of the macrocyclic ligand L22 show diVerent oxygenation behaviours at the “Co(salen)” center, depending upon the dinuclear core structure and the nature of the MII in the adjacent “saldien” site.Complexes [CoMn(L)- (AcO)]ClO4 1 and [Co2(L)(AcO)]ClO4 3 have an acetatebridged core in solution leaving the open face of “Co(salen)” for oxygenation. The resulting peroxo dimers [{CoM(L)- (AcO)}2(O2)][ClO4]2 (M = Mn, oxy-1; Co, oxy-3) were stable at 0 8C and deoxygenated by purging with argon at this temperature. The complexes [CoFe(L)(AcO)]ClO4 2 and [CoFe(L)- (NCS)]ClO4 5 were immediately oxidized to CoIIIFeIII species at 230 8C.The mechanism for the oxidation was complicated because the FeII in the “saldien” site is air-sensitive. Complex [CoMn(L)(NCS)]ClO4 4 showed reversible oxygenation at Fig. 3 Electronic spectral changes of complex 6 in dmf upon oxygenation at 230 8C. 230 8C forming the peroxo dimer [{CoMn(L)(NCS)}2(O2)]21, whereas [Co2(L)(NCS)]ClO4 6 showed a high sensitivity toward dioxygen and was oxidized even at 230 8C. The marked sensitivity of 6 is explained by a participation of the adjacent CoII in the oxidation; the CoII in the “saldien” site can be involved in two-electron reduction of dioxygen to form an intramolecular peroxo intermediate [Co2(L)(O2)]21. Thus, the present study illustrates that the oxygenation of the “Co(salen)” center can be drastically changed not only by the metal ion in the “saldien” site but also by the stereochemistry of the core structure constructed by the exogenous anionic donor AcO2 or NCS2.Acknowledgements This work was supported by Grants-in-Aid for Scientific Research (No. 09440231), Scientific Research on Priority Area “Metal-assembled Complexes” (No. 10149106) and an International Scientific Research Program (No. 09044093) from the Ministry of Education, Science and Culture, Japan and by the JSPS Research Fellowships for Young Scientists (H. F.). References 1 Chem. Rev., 1994, 94, 567; 1996, 96, 2237. 2 K. D.Karlin and Y. Gultneh, Prog. Inorg. Chem., 1987, 35, 219; N. Kitajima, Adv. Inorg. Chem., 1992, 39, 1; W. B. Tolman, Acc. Chem. Rev., 1997, 30, 227. 3 S. J. Lippard, Angew. Chem., Int. Ed. Engl., 1988, 27, 344; L. Que, Jr. and A. E. True, Prog. Inorg. Chem., 1990, 38, 97; L. Que, Jr. and Y. Dong, Acc. Chem. Rev., 1996, 29, 190; A. M. Valentine and S. J. Lippard, J. Chem. Soc., Dalton Trans., 1997, 3295; L. Que, Jr., J. Chem. Soc., Dalton Trans., 1997, 3933. 4 N. Kitajima, K.Fujisawa, C. Fujimoto, Y. Moro-oka, S. Hashimoto, T. Kitagawa, K. Toriumi, K. Tatsumi and A. Nakamura, J. Am. Chem. Soc., 1992, 114, 1277; Z. Tyeklar, R. R. Jacobson, N. Wei, N. N. Murthy, J. Zubieta and K. D. Karlin, J. Am. Chem. Soc., 1993, 115, 2677; K. Fujisawa, M. Tanaka, Y. Moro-oka and N. Kitajima, J. Am. Chem. Soc., 1994, 116, 12079; J. Reim and B. Krebs, Angew. Chem., Int. Ed. Engl., 1994, 33, 1969; J. A. Halfen, S. Mahapatra, E. C. Wilkinson, S. Kaderli, V. G. Young, Jr., L.Que, Jr., A. D. Zuberbuhler and W. D. Tolman, Science, 1996, 271, 1397; S. Mahapatra, J. A. Halfen, E. C. Wilkinson, G. Pan, X. Wang, V. G. Young, Jr., C. J. Cramer, L. Que, Jr. and W. D. Tolman, J. Am. Chem. Soc., 1996, 118, 11555; S. Mahapatra, J. A. Halfen and W. D. Tolman, J. Am. Chem. Soc., 1996, 118, 11575; A. Cole, D. E. Root, P. Mukherjee, E. I. Solomon and T. D. P. Stark, Science, 1996, 273, 1848. 5 B. A. Brennan, Q. Chen, C. Juarez-Garcia, A. E. True, C. J.O’Connor and L. Que, Jr., Inorg. Chem., 1991, 30, 1937; Y. Dong, S. Menage, B. A. Brennan, T. E. Elgren, H. G. Jang, L. L. Pearce and L. Que, Jr., J. Am. Chem. Soc., 1993, 115, 1851; N. Kitajima, N. Tamura, H. Amagami, H. Fukui, Y. Moro-oka, Y. Mizutani, T. Kitagawa, R. Mathur, K. Heerwegh, C. A. Reed, C. R. Randall, L. Que, Jr. and K. Tatsumi, J. Am. Chem. Soc., 1994, 116, 9071; Y. Hayashi, T. Kayatani, H. Sugimoto, M. Suzuki, K. Inomata, A. Uehara, Y. Mizutani, T. Kitagawa and Y.Maeda, J. Am. Chem. Soc., 1995, 117, 11220; T. Ookubo, H. Sugimoto, T. Nagayama, H. Masuda, T. Sato, K. Tanaka, Y. Maeda, H. O—kawa, Y. Hayashi, A. Uehara and M. Suzuki, J. Am. Chem. Soc., 1996, 118, 701; Y. Dong, S. Yan, V. G. Young, Jr. and L. Que, Jr., Angew. Chem., Int. Ed. Engl., 1996, 35, 618; K. Kim and S. J. Lippard, J. Am. Chem. Soc., 1996, 118, 4914; I. Shweky, L. E. Pence, G. C. Papaefthymiou, R. Sessoli, J. W. Yun, A. Bino and S. J. Lippard, J. Am. Chem. Soc., 1997, 119, 1037; H.Sugimoto, T. Nagayama, S. Maruyama, S. Fujinami, Y. Yasuda, M. Suzuki and A. Uehara, Bull. Chem. Soc. Jpn., 1998, 71, 2267. 6 K. E. KauVmann, C. A. Goddard, Y. Zang, R. H. Holm and E. Munck, Inorg. Chem., 1997, 36, 985; S. C. Lee and R. H. Holm, J. Am. Chem. Soc., 1993, 115, 5833; 11789; M. J. Scott and R. H. Holm, J. Am. Chem. Soc., 1994, 116, 11357; M. J. Scott, H. H. Zhang, S. C. Lee, B. Hedman, K. O. Hodgson and R. H. Holm, J. Am. Chem. Soc., 1995, 117, 568. 7 A. Nanthakumar, M. S. Nasir, K. D. Karlin, N. Ravi and B. H. Huynh, J. Am. Chem. Soc., 1992, 114, 6564; A. Nanthakumar, S. Fox, N. N. Murthy, K. D. Karlin, N. Ravi, B. H. Huynh, R. D. Orosz, E. P. Day and K. S. Hagen, J. Am. Chem. Soc., 1993, 115, 8513; K. D. Karlin, A. Nanthakumar, S. Fox, N. N. Murthy,J. Chem. Soc., Dalton Trans., 1999, 2197–2203 2203 N. Ravi, B. H. Huynh, R. D. Orosz and E. P. Day, J. Am. Chem. Soc., 1994, 116, 4753; A. Nanthakumar, S. Fox, N. N.Murthy and K. D. Karlin, J. Am. Chem. Soc., 1997, 119, 3898; H. V. Obias, G. P. F. van Strijdonck, D.-H. Lee, M. Ralle, N. J. Blackburn and K. D. Karlin, J. Am. Chem. Soc., 1998, 120, 9696. 8 T. Sasaki, N. Nakamura and Y. Naruta, Chem. Lett., 1998, 351; F. Tani, Y. Matsumoto, Y. Tachi, T. Sasaki and Y. Naruta, Chem. Commun., 1998, 1731. 9 J. P. Collman, L. Fu, P. C. Herrmann and X. Zhang, Science, 1997, 275, 949; J. P. Collman, Inorg. Chem., 1997, 36, 5145; J. P. Collman, R.Schwenninger, M. Rapta, M. Broring and L. Fu, Chem. Commun., 1999, 137; J. P. Collman, L. Fu, P. C. Herrmann, Z. Wang, M. Rapta, M. Broring, R. Schwenninger and B. Boitrel, Angew. Chem., Int. Ed., 1998, 37, 3397. 10 T. Kitagawa and T. Ogura, Prog. Inorg. Chem., 1997, 45, 431. 11 T. Tsukihara, H. Aoyama, E. Yamashita, T. Tomizaki, H. Yamaguchi, K. Shinzawa-Itoh, R. Nakashima, R. Yaono and S. Yoshikawa, Science, 1995, 269, 1069; 1996, 272, 1136; S. Iwata, C. Ostermeier, B. Ludwig and H.Michel, Nature (London), 1995, 376, 660. 12 H. O—kawa, H. Furutachi and D. E. Fenton, Coord. Chem. Rev., 1998, 174, 51 and refs. therein. 13 H. O—kawa, J. Nishio, M. Ohba, M. Tadokoro, N. Matsumoto, M. Koikawa, S. Kida and D. E. Fenton, Inorg. Chem., 1993, 32, 2949. 14 J. Nishio, H. O—kawa, S. Ohtsuka and M. Tomono, Inorg.Chim. Acta, 1994, 218, 27. 15 J. Shimoda, H. Furutachi, M. Yonemura, M. Ohba, N. Matsumoto and H. O—kawa, Chem. Lett., 1996, 979. 16 H. Furutachi and H. O—kawa, Inorg. Chem., 1997, 36, 3911. 17 H. Furutachi and H. O—kawa, Bull. Chem. Soc. Jpn., 1998, 71, 671. 18 M. Yamami, H. Furutachi, T. Yokoyama and H. O—kawa, Chem. Lett., 1998, 211. 19 H. Furutachi, S. Fujinami, M. Suzuki and H. O—kawa, Chem. Lett., 1998, 779. 20 M. Yamami, H. Furutachi, T. Yokoyama and H. O—kawa, Inorg. Chem., 1998, 37, 6832. 21 H. Furutachi, A. Ishida, H. Miyasaka, N. Fukita, M. Ohba, H. O—kawa and M. Koikawa, J. Chem. Soc., Dalton Trans., 1999, 367. 22 (a) R. D. Jones, D. A. Summerville and F. Basolo, Chem. Rev., 1979, 79, 139; (b) C. Floriani and F. Calderazzo, Coord. Chem. Rev., 1972, 8, 57; (c) T. D. Smith and J. R. Pilbow, Coord. Chem. Rev., 1981, 39, 295; G. McLendon and A. E. Martell, Coord. Chem. Rev., 1976, 19, 1; (e) E. C. NiederhoVer, J. H. Timmons and A. E. Martell, Chem. Rev., 1984, 84, 137. 23 T. Tsumaki, Bull. Chem. Soc. Jpn., 1938, 13, 252; D. Chen and A. E. Martell, Inorg. Chem., 1987, 26, 1026; D. Chen, A. E. Martell and Y. Sun, Inorg. Chem., 1989, 28, 2647; K. Nakamoto, Y. Nonaka, T. Ishiguro, M. W. Urban, M. Suzuki, M. Kozuka, Y. Nishida and S. Kida, J. Am. Chem. Soc., 1982, 104, 3386; W. Kanda, H. O—kawa, S. Kida, J. Goral and K. Nakamoto, Inorg. Chim. Acta, 1988, 146, 193; E. Ochiai, J. Inorg. Nucl. Chem., 1973, 35, 1727; C. Floriani and F. Calderazzo, J. Chem. Soc. A, 1969, 946. 24 D. H. Busch and N. W. Alcock, Chem. Rev., 1994, 94, 585; T. Kayatani, Y. Hayashi, M. Suzuki and A. Uehara, Bull. Chem. Soc. Jpn., 1994, 67, 2980. 25 C. K. Johnson, Report 3794, Oak Ridge National Laboratory, Oak Ridge, TN, 1965. 26 M. Calligaris, G. Nardin and L. Randaccio, Chem. Commun., 1969, 763; M. Calligaris, G. Nardin, L. Randaccio and A. Ripamonti, J. Chem. Soc. A, 1970, 1069. 27 A. Audeef and W. P. Schaefer, Inorg. Chem., 1976, 15, 1432. Paper 9/03099I