The reactions of Cu2(O2CMe)4(H2O)2 with 2,2′-bipyridine (bpy): Influence of the Cu: bpy ratio, and the structure of a linear polymer comprising two alternating types of Cu2 units

Abstract Further investigation of the Cu2(O2CMe)4(H2O)2/bpy reaction system is described, including the determination of the influence of the CuII: bpy ratio (x) on the identity of the reaction products. Values of x in the 1-2 range have been employed. Reaction of Cu2(O2CMe)4(H2O)2 with two equivalents of bpy (x = 1) in MeCN yields [Cu2(O2CMe)4(bpy)2]·2H2O (1) in 79% yield. Treatment of Cu2(O2CMe)4(H2O)2 with 1.33 equivalent of bpy (x = 1.5) in MeCN leads to precipitation of the polymeric compound [—Cu2(O2CMe)2(bpy)2—O2CMe—Cu2(O2 CMe)4—O2CMe—]n (2); from the filtrate 1 slowly crystallizes in 15% yield. A high yield (89%) of pure 2 can be obtained by increasing x from 1.5 to 2. Treatment of 1 with Cu2(O2CMe)4(H2O)2 in MeCN provides an additional route to 2. Compound 2 reacts with equimolar bpy in EtOH to yield complex 1. Complex 1 undergoes facile carboxylate substitution in MeCN with an excess of PhCOOH, leading to reasonable yields (40-65%) of [Cu2(O2CPh)4(bpy)2]· MeCN (3a) or [Cu2(O2 CPh)4(bpy)2]· 2H2O (3b), depending on the rate of crystallization. Complex 2 is converted to the known compound Cu2(O2CPh)4(EtOH)2 (4) or 3b by treatment with excess PhCOOH in EtOH or MeCN, respectively. Complexes 1 and 2 undergo a variety of additional reactions that lead to the dinuclear complexes [Cu2(O2CMe)3(bpy)2](ClO4) (5), [Cu2(OH)(H2O)(O2CMe)(bpy)2](ClO4)2 (6), Cu2(OH)2(bpy)2(ClO4)2 (7), [Cu2(O2CMe)2 (H2O)2(bpy)2](ClO4)2· H2O (8) and Cu2(O2CMe)2(ClO4)2(bpy)2 (9). Complex 1 crystallizes in the triclinic space group P 1 with (at — 143°C) a = 8.842(2), b = 12.266(2), c = 7.708(1) A, α = 98.72(1), β = 106.35, γ = 109.68(1)°, Z = 1 and V = 726.68 A3. A total of 2318 unique reflections with F > 3.00σ(F) were refined to values of R and Rw of 2.67 and 2.87%, respectively. Compound 2 crystallizes in the triclinic space group P 1 with (at — 155°C) a = 9.272(2), b = 14.718(3), c = 8.023(1) A α = 102.66(1), β = 103.89(1), γ = 94.00(1)°, Z = 1 and V = 1028.21 A3. A total of 2319 unique reflections with F > 3.00σ(F) were refined to values of R and Rw of 3.68 and 3.96%, respectively. The structure of 1 consists of a [Cu2(O2CMe)4(bpy)2] molecule located at a centre of symmetry with two syn,anti acetate bridges. The molecules of 1 form infinite ladder-like chains as a result of hydrogen-bonding interactions with the water molecules. The structure of 2 is composed of one-dimensional, well-separated polymeric chains and contains two different types of copper(II) dinuclear units, each at a crystallographic centre of symmetry. The chains are formed by alternating Cu2(O2CMe)4 and [Cu2(O2CMe)2(bpy)2]2+ units which are linked by syn,anti bridging acetates. The Cu2(O2CMe)4 unit has a tetra-bridged structure with four syn,syn bridging acetates and two oxygens from the two syn,anti acetates occupying the axial positions. The other dinuclear unit has a structure with two acetate groups forming mono-atomic bridges. From the IR and UV-vis solution spectra, it is concluded that the polymeric structure of 2 is not retained in MeCN. A cyclic voltammetric study of 1 in MeCN reveals a quasi-reversible reduction at −0.82 V vs ferrocene, and an irreversible reduction at −1.82 V yielding copper metal which deposits on the electrode. Complex 3b displays almost identical processes. Compound 2 displays two reduction processes at −0.84 and −1.82 V.