Pentacoordinate Copper Complexes of Nitrogen-sulfur Donors: Structural Chemistry of Two Complexes of Bis(2-(2-benzimidazolyl)ethyl) Sulfide with the Sulfur Alternatively in Equatorial and Axial Coordination Modes


Simple and mixed-ligand copper(II) complexes were synthesized and characterized by crystallographic and spectroscopic techniques. The N,S- and O-donor chelating agents used include the following: 1,5-bis(benzimidazol-2-yl)-3-thiapentane, BBES; 1,5-bis(N-methylbenzimidazol-2-yl)-3-oxopentane, Me 2BBEO; 2,5,8-trimethyl-2,5,8-triazanonane, pmeta; pentane-2,4-dionate anion, acac -; 2,2′-bipyridyl, bpy; 2,2′-biimidazole, biim. The perchlorate of Cu(BBES) crystallizes from methanol as the salt [Cu(BBES)(MeOH)(OH 2)](ClO 4) 2, with the symmetry of the space group P1, Z = 2, a = 9.306 (3) Å, b = 10.072 (5) Å, c = 14.194 (5) Å, α = 92.23 (2)°, β = 96.63 (4)°, γ = 108.56 (3)°, and ρ calcd = 1.66 g·cm -3. The structure was solved with the Patterson method, incorporating 3088 of the 3884 independent reflections, to final R values of 5.6% and 6.1% (R w). The complex cation has a distorted tetragonal pentacoordinate structure (τ = 0.27) with the BBES occupying three equatorial positions, with a Cu-S linkage of 2.297 Å, and the methanol bound axially. This contrasts with the perchlorate salt of a similar ligand's complex, obtained from ethanol, which has a perchlorate coordinated at this axial position. [Cu(BBES)(acac)]PF 6·H 2O·EtOH was recrystallized from ethyl acetate to give the ester solvate, [Cu(BBES)(acac)]PF 6·C 4H 8O 2. This complex also crystallizes with symmetry P1, and Z = 2, a = 13.961 (3) Å, b = 12.892 (3) Å, c = 10.154 (3) Å, α = 101.57 (4)°, β = 104.99 (4)°, γ = 104.34 (4)°, and ρ calcd = 1.160 g·cm -3. The structure was solved by the Patterson method, using 2939 of the 3243 independent reflections, to final R values of 6.3% and 6.1% (R w). The complex cation is of regularly tetragonal pyramidal geometry (τ = 0.02) with an equatorial N 2O 2-donor set and the thioether bound axially at 2.696 Å, in contrast to the Cu(BBES) perchlorates. There are hydrogen-bonding interactions with benzimidazole and water protons in the lattices of the complexes. ESR spectroscopy shows that the Cu(BBES) 2+ and Cu(Me 2BBEO) 2+ complexes retain their distorted structures in solution; both give single-line ESR spectra in solution at ambient temperatures. The [Cu(BBES)(acac)] + salts exhibit pairwise dipolar coupling in their crystalline states. Substitution of ether by thioether as donor causes absorptivity enhancement throughout the visible-near-UV spectrum, and difference spectroscopy has been used to assign sulfur-to-copper charge-transfer transitions. Unlike [Cu(bpy)(acac)] + and [Cu-(BBES)(acac)] +, the complex cations [Cu(Me 2BBEO)(acac)] + and [Cu(biim)(acac)] + are unstable toward coordinative disproportionation in the solvents used. The Cu(BBES) 2+ cation in solution is in equilibrium between the fac-BBES and mer-BBES isomers, the latter being dominant. © 1983 American Chemical Society.



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© 1983 American Chemical Society (ACS), All rights reserved.