Structures of a Labile Copper Redox Couple: Sterically Constrained Copper(II) and Copper(I) Complexes Formed with a Simple Cyclic Pentathia Ether, 1,4,7,10,13-Pentathiacyclopentadecane

Article abstract of DOI:10.1021/ja00294a034

Crystal structures have been resolved at room temperature for the perchlorate salts of the Cu(II) and Cu(I) complexes formed with the quinquedentate macrocycle 1,4,7,10,13-pentathiacyclopentadecane (<15>aneS5).The space groups, lattice constants, and final R factors for these two compounds are as follows.For Cu(II)(<15>aneS5)(CLO4)2: space group P2₁/c, a = 17.966 (5) Angstroem, b = 9.908 (5) Angstroem, c = 11.230 (6) Angstroem, β = 90.66 (2) deg, Z = 4, R = 0.039, and R_w = 0.051.For Cu(I)(<15>aneS5)(ClO4): space group P2₁/n, a = 11.354 (7) Angstroem, b = 14.759 (9) Angstroem, c = 11.749 (6) Angstroem, β = 113.16 deg, Z = 4, R = 0.083, and R_w = 0.092.Both of the complexes exist as 1:1 monomers in the crystalline state.The Cu(II) complex has a square-pyramidal geometry with the copper atom situated 0.41 Angstroem above the mean basal plane formed by four of the sulfur donor atoms while the fifth sulfur atom is coordinated apically but bent back by 12.8 deg from the perpendicular due to the steric constraints imposed by the ethylene bridges.The five Cu-S bond lengths are 2.331 (2), 2.315 (2), 2.289 (2), 2.338 (2), and 2.398 (2) Angstroem, with the longest bond being to the apical sulfur.The Cu(I) complex has a distorted tetrahedral geometry which closely approximates the Cu(II) geometry except that one of the Cu-S bonds in the basal plane is broken.The four Cu-S bond lengths in this complex are 2.338 (5), 2.243 (5), 2.245 (5), and 2.317 (5) Angtstroem, with the nonbonded sulfur having two alternative orientations at distances of 3.442 (12) and 3.560 (11) Angstroem from the copper atom.For both complexes the perchlorates are noncoordinating.The relatively minor change in structure which occurs on reducing Cu(II)(<15>aneS5) to Cu(I)(<15>aneS5) implies a relatively small Franck-Condon barrier for this redox couple.This is consistent with the results of kinetic studies on this system which indicate that this couple is more labile in its electron-transfer properties than any other copper-polythia ether or copper-poly(amino)thia ether complexes yet investigated.