A systematic investigation of the reactions between Cu2(O2CMe)4(H2O)2with 2, 2′-bipyridine (bpy) has been initiated, and initial results are described. Treatment of Cu2(O2CMe)4(H2O)2with 2 equiv of bpy and NaClO4in EtOH yields [Cu2(O2CMe)3-(bpy)2](ClO4) (la) in 95% yield. The PF6−salt (lb) can be prepared similarly. Treatment of the reaction solution to la with 1 equiv of NaOH prior to addition of NaClO4leads to the high-yield precipitation of the known compound Cu2(OH)2(bpy)2(ClO4)2(2); from the filtrate slowly crystallized la in 32% yield. If the amount of NaOH is doubled, essentially quantitative formation of complex 2 results. The same Cu2(O2CMe)4(H2O)2/bpy/NaClO4reaction mixture in hot H2O yields instead [Cu2-(OH)(H2O)(O2CMe)(bpy)2](C1O4)2(3) in ~70% yield. Complex 1a has been found to undergo facile carboxylate substitution when the more acidic PhCOOH is added; addition of excess PhCOOH to la in MeCN or MeOH leads to essentially quantitative yields of [Cu2(O2CPh)3(bpy)2](ClO4) (4). Complex la crystallizes in triclinic space group Pl with, at −154 °C, a = 11.973 (2) Å, b = 18.576 (4) Å, c = 7.745 (1) Å, α = 103.96 (1)°, β = 65.92 (1)°, γ = 119.58 (0)°, and Z = 2. A total of 3271 unique data with F > 2.33σ(F) were refined to values of R and Rwof 2.57 and 2.21%, respectively. Complex 3 crystallizes in triclinic space group Pl with, at −160 °C, a = 11.286 (2) Å, b = 16.414 (4) Å, c = 8.047 (2) Å, α = 97.31 (1)°, β = 103.78 (1)°, γ = 72.59 (1)°, and Z = 2. A total of 3079 unique data with F > 3.00σ(F) were refined to values of R and Rwof 4.67 and 4.86%, respectively. The structure of la consists of a dinuclear [Cu2(O2CMe)3(bpy)2]+cation with three acetate bridges and a well-separated anion. Two of the acetates are in the familiar bidentate η1:η1:μ2bridging mode, and the third is in the rarer monoatomic bridging mode; a terminal bpy molecule completes five-coordination at each metal atom. There is evidence for an additional weak interaction between one of the Cu11atoms and the uncoordinated oxygen of the monoatomic bridging acetate group (Cu…O = 2.716 (2) Å). The coordination geometries of the two Cu11atoms are significantly different. One Cu11possesses square-pyramidal geometry, while the other is closer to being trigonal bipyramidal. The structure of the cation of complex 3 consists of a triply (OH−, H2O, MeCO2−) bridged pair of five-coordinate copper atoms. The acetate group is in the bidentate η1:η1:μ2bridging mode; a terminal bpy molecule completes five-coordination at each metal. The metal coordination geometries are best described as square pyramidal with the water oxygen occupying the apical positions of both metals. The cations of 3 form infinite chains as a result of H-bonding interactions with the C1O4−anions. The results of solid-state magnetic susceptibility studies are described for complexes la and 3 in the temperature range 5–300 K. The results reveal intramolecular ferromagnetic coupling in both complexes. Fitting parameters are J = +3.6 cm−1, g = 2.1, and θ = 0.20 K for 1a and J = +19.3 cm−1, g = 2.1, and θ = 4.5 K for 3. The magnetic properties can be explained by considering the orbital pathways that are available for exchange, the symmetry of the copper magnetic orbitals, and noncomplementary orbital effects. An electrochemical study of la in MeCN reveals a quasi-reversible two-electron reduction at −0.74 V vs ferrocene and an irreversible two-electron reduction at Ep= −1.80 V, yielding Cu metal that deposits on the electrode. Controlled-potential coulometry shows that the two-electron-reduced (Cu12) form slowly disproportionates to Cu112and Cu metal. Complex 4 displays similar two-electron processes. Complex 3 gave only a very irreversible and poorly defined electrochemical response. © 1990, American Chemical Society. All rights reserved.
