The compounds [Cp(2)M(S(2)C(2)(H)R)] (M = Mo or W; R = phenyl, pyridin-2-yl, pyridin-3-yl, pyridin-4-yl or quinoxalin-2-yl) and [Cp(2)Mo(S(2)C(2)(Me)(pyridin-2-yl)] have been prepared by a facile and general route for the synthesis of dithiolene complexes, viz. the reaction of [Cp(2)MCl(2)] (M = Mo or W) with the dithiolene pro-ligand generated by reacting the corresponding 4-(R)-1,3-dithiol-2-one with CsOH. These Mo compounds were reported previously (Hsu et al., Inorg. Chem. 1996, 35, 4743); however, the preparative method employed herein is more versatile and generates the compounds in good yield and all of the W compounds are new. Electrochemical investigations have shown that each compound undergoes a diffusion controlled one-electron oxidation (OX(I)) and a one-electron reduction (RED(I)) process; each redox change occurs at a more positive potential for a Mo compound than for its W counterpart. The mono-cations generated by chemical or electrochemical oxidation are stable and the structures of both components of the [Cp(2)Mo(S(2)C(2)(H)R)](+)/[Cp(2)Mo(S(2)C(2)(H)R)] (R = Ph or pyridin-3-yl) redox couples have been determined by X-ray crystallography. For each redox related pair, the changes in the Mo-S, S-C and C-C bond lengths of the {MoSCCS} moiety are generally consistent with OX(I) involving the loss of an electron from a π-orbital that is Mo-S and C-S antibonding and C-C bonding in character. These results have been interpreted successfully within the framework provided by DFT calculations accomplished for [Cp(2)M(S(2)C(2)(H)Ph)](n) (M = Mo or W; n = +1, 0 or -1). The HOMO of the neutral compounds is derived mainly from the dithiolene π(3) orbital (65%); therefore, OX(I) is essentially a dithiolene-based process. The similarity of the potentials for OX(I) (ca. 30 mV) for analogous Mo and W compounds is consistent with this interpretation and the EPR spectra of each of the Mo cations show that the unpaired electron is coupled to the dithiolene proton but relatively weakly to (95,97)Mo. The DFT calculations indicate that the unpaired electron is more localised on the metal in the mono-anions than in the mono-cations. In agreement with this, the EPR spectrum of each of the Mo-containing mono-anions manifests a larger (95,97)Mo coupling (A(iso)) than observed for the corresponding mono-cation and RED(I) for a W compound is significantly (ca. 300 mV) more negative than that of its Mo counterpart. [Cp(2)W(S(2)C(2)(H)(quinoxalin-2-yl))] is anomalous; RED(I) occurs at a potential ca. 230 mV more positive than expected from that of its Mo counterpart and the EPR spectrum of the mono-anion is typical of an organic radical. DFT calculations indicate that these properties arise because the electron is added to a quinoxalin-2-yl π-orbital.

Molecules into Materials, pp. 559-565 (2007) No AccessNew superconducting charge-transfer salts (BEDT-TTF)4[A·M(C2O4)3]·C6H5NO2 (A = H3O or NH4, M = Cr or Fe, BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene)Samina Rashid, Scott S. Turner, Peter Day, Judith A. K. Howard, Philippe Guionneau, Eric J. L. McInnes, Frank E. Mabbs, Robin J. H. Clark, Steven Firth, and Tim BiggsSamina RashidDavy–Faraday Research Laboratory, The Royal Institution of Great Britain, 21 Albemarle Street, London, UK W1X 4BS, UK, Scott S. TurnerDavy–Faraday Research Laboratory, The Royal Institution of Great Britain, 21 Albemarle Street, London, UK W1X 4BS, UK, Peter DayDavy–Faraday Research Laboratory, The Royal Institution of Great Britain, 21 Albemarle Street, London, UK W1X 4BS, UK, Judith A. K. HowardDepartment of Chemistry, University of Durham, Durham, UK DH1 3LE, UK, Philippe GuionneauDepartment of Chemistry, University of Durham, Durham, UK DH1 3LE, UK, Eric J. L. McInnesChemistry Department, University of Manchester, Oxford Road, Manchester, UK M13 9PL, UK, Frank E. MabbsChemistry Department, University of Manchester, Oxford Road, Manchester, UK M13 9PL, UK, Robin J. H. ClarkChristopher Ingold Laboratories, University College, 20 Gordon Street, London, UK WC1H 0AJ, UK, Steven FirthChristopher Ingold Laboratories, University College, 20 Gordon Street, London, UK WC1H 0AJ, UK, and Tim BiggsClarendon Laboratory, Oxford, Oxford University, Parks Road, Oxford, UK OX1 3PU, UKhttps://doi.org/10.1142/9789812706836_0043Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: The syntheses, crystal structures, and physical properties of two new crystalline charge-transfer salts of BEDT-TTF, bis(ethylenedithio)tetrathiafulvalene, containing tris(oxalato)metallate(III) anions of 3d elements are reported. Electrochemical oxidation of BEDT-TTF in the presence of (NH4)3[Fe(C2O4)3]·3H2O or (NH4)3[Cr(C2O4)3]·3H2O in C6H5NO2, yields crystals of β″-(BEDT-TTF)4[A·Fe(C2O4)3]·C6H5NO2 [1] or β″-(BEDT-TTF)4[A·Cr(C2O4)3]·C6H5NO2 [2] (A = H3O+ or NH4+). The crystal structure of [1] has been solved at 120 K in the monoclinic space group C2/c, and that of [2] in the same space group at 298 and 120 K. For [1], a = 10.273 Å, b = 19.949 Å, c = 35.030 Å, β = 92.97°, V=7169.6(2) Å3, Z=8. For [2], at 298 K: a= 10.304 Å, b = 20.091 Å, c=35.251 Å, β = 92.70°, V= 7289.3(2) Å3, Z=8, and at 120 K a= 10.283 Å, b = 19.917 Å, c = 34.939 Å, β = 93.30°, V= 7144.4(1) Å3, Z=8. The crystal structures of both compounds consist of alternating layers of BEDT-TTF cations and layers containing [M(C2O4)3]3−, H3O+ or NH4+, and PhNO2. The BEDT-TTF molecules are arranged in the β″ packing motif and the tris(oxalato)metallate(III) ions form the well-known honeycomb motif found in many molecular based magnets. SQUID magnetometry, Raman spectroscopy and electron paramagnetic resonance (EPR) measurements were performed on crystals of [1]. SQUID magnetometry, single-crystal four-probe conductivity measurements, Raman spectroscopy, EPR and polarised infrared reflectance were performed on crystals of [2]. Both compounds have metal to superconducting transitions with Tc = 6.2K for [1] and for [2], Tc = 5.8 K. FiguresReferencesRelatedDetails Molecules into MaterialsMetrics History PDF download

Crystals of the title compound (1) contain two independent, centrosymmetric half-molecules per asymmetric unit. While both of these show Jahn-Teller elongated six-coordinate geometries, the lengths of the elongated Cu-N bonds in the two molecules differ by 0.117(2) A at 30 K. The structure of one of these molecules (molecule A) does not vary with temperature below 350 K. The other molecule (molecule B) shows Cu-N bond lengths that are temperature-dependent between 225 and 375 K, but do not vary further at lower temperature. This indicates a fluxional axis of Jahn-Teller elongation in this molecule at these higher temperatures. Consideration of the thermal parameters in these structures implies that the fluxionality in molecule B is frozen out near 150 K. This conclusion is supported by a Q-band powder EPR study. The d-d transition energies of molecules A and B have been calculated by several density function (DF) methods, including a time-dependent DF calculation. The crystallographic data have been reproduced using the vibronic coupling model of Burgi and Hitchman. This has shown that the different fluxionality regimes for molecules A and B are not a consequence of their different static molecular structures, but rather reflect their different local environments in the crystal.

Multi-frequency EPR spectroscopy on 61Ni-labelled samples of [Ni2(L)]3+ confirms extensive charge-delocalisation between the Ni(III) centre and thiolate donors in the Ni(II)Ni(III) complex.

Two hydroxo-bridged Cu(II) complexes of the trimacrocyclic ligand, 1,3,5-tris(1,4,7-triazacyclonon-1-ylmethyl)-benzene (L-mes), have been prepared and characterized. The trinuclear complex, [Cu3Lmes(mu-OH)(2)(H2O)(2)](ClO4)(4).3.2H(2)O (1), formed when the pH of an aqueous solution of [Cu3Lmes(H2O)(6)](ClO4)(6).6H(2)O, was adjusted to ca. 6. X-Ray structural analysis confirmed the presence of a binuclear [Cu-2(mu-OH)(2)](2+) core and an isolated Cu(II) centre. The "roof-shaped" [Cu-2(mu-OH)(2)](2+) core has a dihedral angle (delta) of 152degrees between the CuO2 planes and exhibits a relatively short Cu . . . Cu distance of 2.9041(8) Angstrom. An increase in pH to 9.5 generates the hexanuclear complex, [Cu-6(L-mes)(2)(mu-OH)(6)](ClO4)(6).2H(2)O(2), by linking two [Cu3Lmes(mu-OH)(2)](4+) trinuclear units via two mu-hydroxo bridges. The structure of 2 features three [Cu-2(mu-OH)(2)](2+) units, two with bent geometries, similar to that observed in 1 [delta = 153degrees, Cu . . . Cu = 2.8757(8) Angstrom], and one with planar geometry [Cu . . . Cu = 2.961(1) Angstrom]. A variable temperature magnetic susceptibility study on 1 has identified an S = 1/2 ground state, consistent with a system composed of an antiferromagnetically coupled Cu(II) pair (J = -24 cm(-1)) and a magnetically isolated Cu(II) centre. Variable temperature Q-band EPR spectra confirmed this interpretation. Comparisons to the Q-band EPR spectra of the previously reported trinuclear complex, {[Cu3Lmes(mu-OH)(mu(3)-HPO4)(H2O)](PF6)(3).3H(2)O}(n,) were made, the latter also shows a S = 1/2 ground state but with the unpaired electron delocalised between two Cu(II) ions. The susceptibility data for 2 were interpreted in terms of the presence of three independent Cu(II) binuclear units with weak antiferromagnetic coupling observed in both the bent and planar [Cu-2(mu-OH)(2)](2+) cores (J = -61 and -29 cm(-1), respectively).

Multifrequency continuous wave EPR spectra (4-34 GHz) on a powder of the title compound are consistent with a spin-triplet state. This arises from interaction between centrosymmetrically related pairs of copper(II) ions in the solid. The spectra at all frequencies have been simulated with a single set of spin-Hamiltonian parameters. The results show that there is noncoincidence between the principal axes of the g-matrices on each copper center and those of the zero-field splitting (D) tensor. This noncoincidence is a single rotation of 33 degrees +/- 2 degrees. The parameters from the powder spectra have been verified by a subsequent single-crystal EPR study which yielded the spin-Hamiltonian parameters g(XX) = 2.074, g(YY) = 2.093, g(ZZ) = 2.385, D(XX) = +/-0.0228 cm(-1), D(YY) = +/-0.0211 cm(-1), D(ZZ) = -/+0.0439 cm(-1) with Euler angles of alpha = 179 degrees, chi = 33.4 degrees, and gamma = 328 degrees. Analysis of the zero-field splitting tensor in terms of exchange indicates that the interaction between the pairs of copper(II) ions is almost entirely dipolar in origin. This study shows that multifrequency EPR spectroscopy on powders, coupled with spectrum simulation, can detect and measure noncoincidence between the principal axes of the g-matrix and zero-field splitting tensor, and does not necessarily require the presence of metal hyperfine interactions.

This paper reports a crystallographic and EPR study of pseudo-Jahn–Teller fluxionality in [Cu(L1)2][BF4]2 (1; L1 = 2,6-dipyrazol-1-ylpyridine). For 50 ≤ T ≤ 350 K, the Cu(II) ion in crystalline 1 is fluxional, with its axis of pseudo-Jahn–Teller elongation being disordered about the two N{pyrazole}–Cu–N{pyrazole} axes. The crystallographic data for 1 at these temperatures are well reproduced by a two-state model that neglects intermolecular interactions, but which yields an unusually small pseudo-Jahn–Teller radius (SpJT) for the compound. This was confirmed by measuring SpJT independently from the mean-square displacement amplitudes (MSDAs) in 1 and [Zn(L1)2][BF4]2 (2). At 41 K, 1 undergoes a phase transformation to a new polymorph containing three molecules per asymmetric unit, which have static structures and exhibit more normal SpJT values. Q-band EPR data show that the proportion of static spins in a powdered sample of 1 grows in relatively slowly as the temperature is lowered below 40 K.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Reactions of [MoO2 (acetylacetonate)(2)] with the proligands (N-hydroxyimino)diacetic acid (H(3)hidpa), R, R-2,2'-(N-hydroxyimino)dipropionic acid (R,R-H(3)hidpa) or R,S-2,2'-(N-hydroxyimino) dibutyric acid (R,S-H(3)hidba) yielded the compounds [PPh4][Delta,Lambda -Mo(hida)(2)]. CH2Cl2 1, [H5O2][Delta -Mo(R,R-hidpa)(2)] 2, [PPh4][Mo(R,S-hidba)(2)]. 2H(2)O 3a and Na[Delta,Lambda -Mo(R,S-hidba)(2)]. 1/4 Pr-i(2) O 3b, respectively. Reactions of H(3)hida with a methanolic solution of [PPh4][MoOCl4 (H2O)] in the presence of NaOH (ca. pH 8) provided an alternative synthesis for 1. The complex of 1 when transferred into CH2Cl2 using [PPh4]Br yielded brown block-like crystals from a CH2Cl2-EtOH solution, however, 2 and 3b were crystallised from H2O and MeCN solutions with [H5O2](+) and [Na](+) counter cations, respectively. X-Ray crystallography confirmed the same distinctive eight-co-ordinate geometry of the complex anions of 1, 2 and 3b as identified for Amavadin, the form in which vanadium(IV) is bound in Amanita muscaria mushrooms. EPR and UV/vis spectra recorded for 1, 2 and 3a are consistent with the presence of molybdenum(V). Cyclic voltammetric studies using a glassy carbon working electrode in CH2Cl2 for 1 exhibited a reversible Mo-VI/Mo-V and a quasi-reversible Mo-V/Mo-IV redox couple at E-1/2 = +0.96 and -0.99 V (vs. a saturated calomel electrode), respectively. Complex 3a also displayed a reversible Mo-VI/Mo-V redox couple at E-1/2 = +0.77 V, whereas the Mo-V/Mo-IV couple was irreversible (E-pc = -1.28 V). Additional electrochemical studies with 2 recorded a reversible Mo-VI/Mo-V redox couple in Me2SO (E-1/2 = +0.77 V), however in H2O this one-electron oxidation process is irreversible.

The complex [Cu(L-4)(2)](BF4)(2) (3 L-4=2-[pyrazol-1-yl]-6-[3-{2,4,6-trimethylphenyl}pyrazol-1-yl]pyridine) has been synthesised. Complex 3 crystallises in two crystal forms from MeNO2/Et2O. The monoclinic alpha -form contains crystallographically ordered, pseudo-Jahn-Teller elongated {d(y)(2)-z(2)}(1) Cu(II) ions that are structurally very similar to [Cu(L-2)(2)](BF4)(2) (1; L-2=2,6-dipyrazol-1-ylpyridine). The Cu ion in the orthorhombic beta -polymorph at 180 K exhibits Cu-N bond lengths that are rather different from the alpha -form, and which could correspond to a disordered {d(y)(2)-z(2)}(1) Cu(II) centre; or, to a static, rhombically compressed ion with a {d(z)(2)}(1) ground state. Variable temperature EPR data favour the former interpretation. A crystal structure at 31 K of [Cu(L-3)(2)](BF4)(2) (2; L-3=2,6-bis-[3-{2,4,6-trimethylphenyl}pyrazol-1-yl]pyridine), a genuine {d(z)(2)}(1) ion, is also described. Comparison of the crystallographic data of 1-3 shows that the {d(y)(2)-z(2)}(1)-to-{d(z)(2)}(1) ground state change occurs concomitantly with only a small z-axis compression.

Hydroxo- and methoxo-bridged tetranuclear copper(II) complexes of the tetramacrocyclic ligand 1,2,4,5-tetrakis(1,4,7-triazacyclonon-1-ylmethyl)benzene (Ldur), have been prepared from [Cu4Ldur(H2O)8](ClO4)8.9H2O (1). Addition of base to an aqueous solution of 1 gave [Cu4Ldur(mu2-OH)4](ClO4)4 (2). Diffusion of MeOH into a DMF solution of 2 produces [Cu4Ldur(mu2-OMe)4](ClO4)4.HClO4.2/3MeOH (3), a complex which hydrolyzes on exposure to moisture regenerating 2. The structurally related azido-bridged complex, [Cu4Ldur(mu2-N3)4](PF6)4.4H2O.6CH3CN (4), was produced by reaction of Ldur with 4 molar equiv of Cu(OAc)2.H2O and NaN3 in the presence of excess KPF6. Compounds 2-4 crystallize in the triclinic space group P1 (No. 2) with a = 10.248(1) A, b = 12.130(2) A, c = 14.353(2) A, alpha = 82.23(1) degrees, beta = 80.79(1) degrees, gamma = 65.71(1) degrees, and Z = 1 for 2, a = 10.2985(4) A, b = 12.1182(4) A, c = 13.9705(3) A, alpha = 89.978(2) degrees, beta = 82.038(2) degrees, gamma = 65.095(2) degrees, and Z = 1 for 3, and a = 12.059(2) A, b = 12.554(2) A, c = 14.051(2) A, alpha = 91.85(1) degrees, beta = 98.22(1) degrees, gamma = 105.62(1) degrees, and Z = 1 for 4. The complexes feature pairs of isolated dibridged copper(II) dimers with "roof-shaped" Cu2(mu2-X)2 cores (X = OH-, OMe-, N3-), as indicated by the dihedral angle between the two CuX2 planes (159 degrees for 2, 161 degrees for 3, and 153 degrees for 4). This leads to Cu.Cu distances of 2.940(4) A for 2, 2.962(1) A for 3, and 3.006(5) A for 4. Variable-temperature magnetic susceptibility measurements indicate weak antiferromagnetic coupling (J = -27 cm(-1)) for the hydroxo-bridged copper(II) centers in 2 and very strong antiferromagnetic coupling (J = -269 cm(-1)) for the methoxo-bridged copper(II) centers in 3. Pairs of copper(II) centers in 4 display the strongest ferromagnetic interaction (J = 94 cm(-1)) reported thus far for bis(mu2-1,1-azido)-bridged dicopper units. Spectral measurements on a neat powdered sample of 4 at 33.9 GHz or 90 Ghz confirm the spin-triplet ground state for the azido-bridged copper(II) pairs.

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The syntheses, crystal structures, and physical properties of two new crystalline charge-transfer salts of BEDT-TTF, bis(ethylenedithio)tetrathiafulvalene, containing tris(oxalato)metallate(iii) anions of 3d elements are reported. Electrochemical oxidation of BEDT-TTF in the presence of (NH4)(3)[Fe(C2O4)(3)]. 3H(2)O or (NH4)(3)[Cr(C2O4)(3)]. 3H(2)O in C6H5NO2, yields crystals of beta"-(BEDT-TTF)(4)[A . Fe(C2O4)(3)].C6H5NO2 [1] or beta"-(BEDT-TTF)(4)[A . Cr(C2O4)(3)].C6H5NO2 [2] (A=H3O+ or NH4+). The crystal structure of [1] has been solved at 120 K in the monoclinic space group C2/c, and that of [2] in the same space group at 298 and 120 K. For [1], a = 10.273 Angstrom, b = 19.949 Angstrom, c = 35.030 Angstrom, beta = 92.97 degrees, V = 7169.6(2) Angstrom (3), Z = 8. For [2], at 298 K: a = 10.304 Angstrom, b = 20.091 Angstrom, c = 35.251 Angstrom, beta = 92.70 degrees, V = 7289.3(2) Angstrom (3). Z = 8, and at 120 K a = 10.283 Angstrom, b = 19.917 Angstrom, c = 34.939 Angstrom, beta = 93.30 degrees, V = 7144.4(1) Angstrom (3), Z = 8. The crystal structures of both. compounds consist of alternating layers of BEDT-TTF cations and layers containing [M(C2O4)(3)](3-), H3O+ or NH4+, and PhNO2. The BEDT-TTF molecules are arranged in the beta" packing motif and the tris(oxalato)metallate(III) ions form the well-known honeycomb motif found in many molecular based magnets. SQUID magnetometry, Raman spectroscopy and electron paramagnetic resonance (EPR) measurements were performed on crystals of [1]. SQUID magnetometry, single-crystal four-probe conductivity measurements, Raman spectroscopy, EPR and polarised infrared reflectance were performed on crystals of [2]. Both compounds have metal to superconducting transitions with T-c = 6.2 K for [1] and for [2], T-c = 5.8 K.

Four highly crystalline, cobalt-containing microporous aluminophosphates (CoAPO-5, CoAPO-11, CoAPO-44, and CoAPO-46) have been investigated by using liquid He X- and/or Q-band electron spin resonance (ESR) spectroscopy in order to investigate the coordination of high-spin cobalt before and after calcination. The ESR spectra of the four zeolite structures are characterized by an axial signal with an effective g⊥ ≈ 5.80−5.44 and g|| ≈ 2.00. Quantitative temperature dependence measurements of this axial signal in the temperature range 4−30 K reveal a Curie−Weiss behavior for both as-synthesized and calcined samples confirming (a) the ms = ± 1/2 ground state of magnetically isolated high-spin cobalt and (b) a zero field splitting Δ > 0 cm-1. Quantitation of the ESR signals indicated that most of the Co2+ is ESR active and that only about 30% of this Co2+ can be oxidized to the ESR-inactive Co3+ after calcination. The spin Hamiltonian parameters of as-synthesized and calcined CoAPO-5 material, as determined by...

The mixed sandwich complexes [M(eta -arene)(eta -C7H6R')](+) (M=Cr, R'=H, arene=C6H4Me2-1,4, 1a; or C6H3Me3-1,3,5, 2a; R'=C6H4Me-4, arene=C6H5Me, 3a; M=Mo, R'=H, arene=C6H3Me3-1,3,5, 4a) were prepared by reflux of [M(CO)(3)(eta -C7H6R')](+) in the appropriate arene solvent. Reflux of [Mo(eta -C6H5Me)(eta -C7H7)](+) with an excess of HC=CBut in acetone affords [Mo(eta -C6H3Bu3t-1,3,5)(eta -C7H7)](+), 5a. Cyclic voltammetric studies in NCMe reveal that each of 1a, 2a, 3a and 5a undergoes reversible one-electron oxidation processes to give the corresponding, isolable 17-electron radical dications, 1b, 2b, 3b and 5b which have been characterised by EPR spectroscopy. NMR data for the 18-electron monocations suggest an enhanced electron density at the arene ring in the chromium derivatives by comparison with molybdenum analogues and this is reflected in the stability of complexes 1a, 2a and 3a towards arene displacement reactions. The crystal structure of 3a reveals only a small asymmetry in the average chromium-to-ring carbon bond lengths for the arene and cycloheptatrienyl rings. One-electron oxidation of 3a to give 3b results in a small increase in metal-to-ring distances (ca. 0.02 Angstrom) consistent with a HOMO which is essentially non-bonding with respect to the metal-ring interaction.

Complexation of hydrated Cu(BF4)(2) by 2 molar equivalents of (LR)-R-2 ((LMe)-Me-2 = 2,6-bis{methyliminomethyl}pyridine, (LCy)-Cy-2 = 2,6-bis{cyclohexyliminomethyl}pyridine, (LBut)-Bu-2 = 2,6-bis{tert-butyliminomethyl}pyridine) afforded [Cu((LR)-R-2)(2)][BF4](2) (R = Me, 1; Cy, 2; or Bu-t, 3) in moderate yields. EPR spectroscopy in solution and the solid state demonstrates that 1 and 2 adopt the expected {d(y2 - z2)}(1) electronic ground state, and that the pseudo-Jahn-Teller elongation axis is fluxional in solid 1 and static in solid 2. In contrast, 3 exhibits a {d(z2)}(1) ground state by EPR. The crystal structures of 2.MeNO2 and 3.1/2Me(2)CO contain rhombic six-co-ordinate copper(II) ions, which differ principally in the length of the Cu-N bonds close to the molecular y axis. Treatment of [Cu(NCMe)(4)]BF4 with varying ratios of (LR)-R-2 yields [Cu((LR)-R-2)(2)]BF4 (R = Me, 4; Mes, 5; or Cy, 6: L(2)Mes = 2,6-bis{2,4,6-trimethylphenyliminomethyl}pyridine) or [{Cu((LBut)-Bu-2)}(2)][BF4](2) 7. The single crystal structure of 5.MeCN shows a flattened tetrahedral copper(I) centre with two bidentate L(2)Mes ligands. Reaction of hydrated Cu(ClO4)(2) with 2 molar equivalents of L-3 (1,3-bis{pyridin-2-yl}pyrazole) yields [Cu(L-3)(2)][ClO4](2) 8, whose crystal structure demonstrates a six-co-ordinate copper(II) ion with long Cu-N{pyridine} bonds. Powder EPR spectroscopy demonstrates a {d(z2)}(1) ground state for 8 in the solid.

2-Hydroxy-5-methyl-3-methylsulfanylbenzaldehyde (HL2) and 2-hydroxy-5-methyl-3-methylselanylbenzaldehyde (HL3) have been synthesized from 2-hydroxy-5-methylbenzaldehyde (HL1), as have Schiff bases (HLR)-R-4 and (HLR)-R-5 (R = Me or Ph) derived from RNH2 and HL1 or HL2 respectively. The complexes [Cu(L)(Tp(Ph))] ([L](-) = [L-1](-), 1; [L-2](-), 2; [L-3](-), 3; [(LMe)-Me-4](-), 4; or [(LPh)-Ph-4](-), 5) have been prepared. Single crystal structure determinations of 1, 2, 4 and 5 show copper(II) centres with square pyramidal [CuN3O2] (1, 2) or [CuN4O] (4, 5) co-ordination spheres; for 4 and 5 the basal plane of the complex is twisted by 20-25 degrees because of the steric properties of the Schiff base Me or Ph substituent. The UV/vis and EPR spectra of 1-5 in CH2Cl2 show the presence of tetragonal copper(II) centres. Cyclic voltammograms of 1-5 and the uncomplexed phenols in CH2Cl2-0.5 M (Bu4NPF6)-N-n exhibit an irreversible or (for 2) reversible l-electron oxidation to a phenoxyl radical. The oxidation potentials of HL2 and HL3, and of 2 and 3, are barely distinguishable. However, the irreversibility of this process for 3 compared to that of 2 suggests that a selenoether substituent kinetically stabilises the phenoxyl unpaired spin less efficiently than a thioether one; this is borne out by EHMO calculations on L-1 .-L-3 .. Spectroelectrochemical characterisation of [2](+), whose UV/vis/NIR spectrum is very similar to that of galactose oxidase, confirms its formulation as the antiferromagnetically coupled species [Cu-II(L-2 .)(Tp(Ph))](+).