Copper(I) 1,1-dithiolate cluster transformations. Synthesis of [Bu 4N] 6[Cu 6(S, i-MNT) 6], i-MNT=[S 2CC(CN) 2] −, from [Bu 4N] 4[Cu 8( i-MNT) 6] with sulfur. Reaction of the cyclic hexanuclear complex with phosphine to give the tetrahedral [Bu 4N] 4[Cu 4( i-MNT) 4] which oxidizes in solution to give the homocubane [Bu 4N] 4[Cu 8( i-MNT) 6] and [Bu 4N]

Abstract

The novel sulfur-rich cluster anion, [Cu 6(S, i-MNT) 6] 6−, 2, is obtained from the reaction of the homocubane, [Cu 8( i-MNT) 6] 4−, 1, and powdered sulfur in acetonitrile solution under basic conditions. Compound 2 crystallizes in the R bar 3 space group with a=33.519(5) Å, b=33.519(5) Å, c=11.748(2) Å, γ=120°, and V=11431(3) Å 3. The molecule contains six trigonally coordinated copper atoms linked together into a 12 membered ring by the six sulfur atoms of the bridging sulfur-rich i-MNT ligands. Six Cu I atoms are located at the vertices of a nearly regular hexagon. The mean distance between the two planes of alternating Cu I atoms is 0.345(2) Å. When 2 reacts with triphenylphosphine, a sulfur atom is removed from the disulfide containing ligands to give [Cu 4( i-MNT) 4] 4−, isolated as the [ n B u 4N] + salt, 4. This tetranuclear species also can be synthesized directly from [Cu(CH 3CN) 4][PF 6] and [ n B u 4N] 2[ i-MNT] in acetonitrile. Compound 4 crystallizes in the C2/ c space group with a=38.351(6) Å, b=38.468(8) Å, c=32.685(5) Å, β=124.94(1)°, and V=39527(12) Å 3. The anion reveals discrete units of four copper atoms at the vertices of a distorted tetrahedron, bound to four i-MNT groups acting as “tridentate” ( μ 1, μ 2) ligands. The cluster anion also is found as [BzEt 3N][ n B u 4N] 3 [Cu 4( i-MNT) 4], 5. Compound 5 crystallizes in the C2/ c space group with a=27.306(7) Å, b=14.127(3) Å, c=27.868(6) Å, β=121.22(2)°, and V=9193(4) Å 3. In solution the tetranuclear species transforms with oxidation into the Cu 8 homocubane, 1, and the paramagnetic anion [Cu II( i-MNT) 2] 2−, isolated as the [ n B u 4N] + salt, 3. Spectroscopic evidence, including UV–Vis and 13 C−NMR , for the cluster transformation is presented. Compound 3 crystallizes in the P2 1/ n space group with a=10.036(1), b=16.724(2), c=14.234(1), β=91.37(9), and V=2388(0). The anion in 3 is planar with the copper atom located on the center of symmetry. Pertinent 13 C chemical shifts (ppm) and absorption maxima (nm) with extinction coefficients in parentheses are as follows: 1, 14, 20, 24, 59, 79.8, 116.5, 197.7; 404 ( ϵ=86 000 M −1 cm −1), 320 ( ϵ=60 000 M −1 cm −1). 2, 14, 20, 24, 59, 61.7, 118.5, 119.5, 158; 380 ( ϵ=85 000 M −1 cm −1), 350 sh ( ϵ=74 000 M −1 cm −1). 3, 450 ( ϵ=15 000 M −1 cm −1), 350 ( ϵ=80 000 M −1 cm −1), 340 sh ( ϵ=43 000 M −1 cm −1), 315 sh ( ϵ=25 000 M −1 cm −1). 4, 14, 20, 24, 59, 70.8, 120, 209.5; 380 ( ϵ=92 000 M −1 cm −1).