Correlation of the redox properties and stereochemical features of copper complexes of [18]aneN2S4(1,4,10,13-tetrathia-7,16-diazacyclooctadecane) and its N,N′-dimethyl derivative Me2[18]aneN2S4. Crystal structures of [CuII([18]aneN2S4)][ClO4]2·H2O, [CuII(Me2[18]aneN2S4)][PF6]2, [CuI2([18]aneN2S4)]BPh4, [CuI(Me2[18]aneN2S4)]PF6 and [CuI2(Me2[18]aneN2S4)(NCMe)2][PF6]2

Abstract

Reaction of copper(II) salts with L =[18]aneN₂S₄(1,4,10,13-tetrathia-7,16-diazacyclooctadecane) or its 7,16-dimethyl derivative Me₂[18]aneN₂S₄ affords the cations [CuL]²⁺ in high yields. The complex [Cu([18]aneN₂S₄)][ClO₄]₂·H₂O crysatallises in the orthorhombic space group Pcab with a= 12.020(8), b= 17.733(17), c= 21.999(23)Å and Z= 8. A single-crystal structure determination has shown the Cu^II to be bound via all six macrocyclic donors atoms to give a tetragonally compressed octahedral stereochemistry, Cu–S(1) 2.577(5), Cu–S(4) 2.487(5), Cu–S(10) 2.528(5), Cu–S(13) 2.578(5), Cu–N(7) 2.007(13) and Cu–N(16) 2.036(12)Å, with the macrocycle in a rac configuration. The complex [Cu(Me₂[18]aneN₂S₄)][PF₆]₂ crystallises in the trigonal space group Pm1, a= 10.5140(4), c= 6.6604(5)Å and Z= 1. The Cu^II occupies a site of D_3d symmetry, bound to the six macrocyclic donor atoms to give a tetragonally elongated octahedral stereochemistry in a meso configuration, Cu–S 2.496(5) and Cu–N 2.191(17)Å. The ion [Cu([18]aneN₂S₄)]²⁺ shows a reversible Cu^II–Cu^I redox couple at E_½=–0.31 V vs. ferrocene–ferrocenium, while that for [Cu(Me₂[18]aneN₂S₄)]²⁺ occurs at a more anodic potential, E_½=+0.06 V. The diamagnetic copper(I) species [CuL]⁺ can be generated electochemically from the copper(II) precursors by controlled-potential electrolysis, although the direct route via reaction of [Cu(NCMe)₄]⁺ with 1 molar equivalent of L in refluxing MeOH under N₂ is better. The complex [Cu(Me₂[18]aneN₂S₄)]PF₆ crystallises in the triclinic space group P, a= 10.3386(23), b= 10.7643(25), c= 12.054(3)Å, α= 102.450(9), β= 113.951(11), γ= 102.692(10)° and Z= 2. The Cu^I is bound via three macrocyclic S- and one macrocyclic N-donor atom, Cu–S 2.2516(16), 2.2612(16), 2.3342(17), Cu–N 2.175(5)Å, giving a distorted-tetrahedral stereochemistry. The complex [Cu([18]aneN₂S₄)]BPh₄ crystallises in the orthorhombic space group P2₁2₁2₁, with a= 12.270(4), b= 14.314(8), c= 19.914(5)Å and Z= 4. The structure is very similar to that of [Cu(Me₂[18]aneN₂S₄)]⁺ with the Cu^I bound via three S- and one N-donor atom, Cu–S 2.250(3), 2.245(3), 2.357(4), Cu–N 2.121(9)Å, giving a distorted-tetrahedral stereochemistry. The differences in potentials for the Cu^II–Cu^I couples in [Cu([18]aneN₂S₄)]^2+/+ and [Cu(Me₂[18]aneN₂S₄)]^2+/+ are therefore due to the different configurations, meso and rac, in the parent copper(II) species rather than to differences in the copper(I) structure. Reaction of Me₂[18]aneN₂S₄ with 2 molar equivalents of [Cu(NCMe)₄]⁺ affords the binculear copper(I) species [Cu₂(Me₂[18]aneN₂S₄)(NCMe)₂]²⁺ the PF₆^– salt of which crystallises in the triclinic space group P, a= 7.3435(18), b= 11.0562(3), c= 11.824(3)Å, α= 62.298(10), β= 81.904(15), γ= 82.764(16)° and Z= 1. The cation lies across an inversion centre, with each Cu^I bound via two macrocyclic S- and one macrocyclic N-donor atom, Cu–S 2.317(4), 2.286(4), Cu–N 2.165(7)Å, with an NCMe solvent molecule completing the distorted-tetrahedral stereochemistry, Cu–N 1.924(9)Å.