Photochromic Isomerization of a Dinuclear Molybdenum Complex with Ethylene-1,2-Dithiolate and Disulfur Ligands: X-ray Structures of the Two Isomers

A photochromic complex with disulfur and dimethyl-ethylene-1,2-dithiolate ligands, [Mo2(μ-S2)(μ-S2C2Me2)2(S2C2Me2)2] (3), was
synthesized and characterized. Photoirradiation of 3 with visible
light resulted in the formation of the isomer (3‘). The electronic
spectrum of 3‘ has a new intense peak in the near infrared region,
and in the dark, the spectrum returns to that of 3. X-ray structural
analyses of 3·C6H6 and 3‘ revealed a large conformational change
of the bridging dithiolate ligands:  the two ligands in 3‘ come very
close to each other compared to those in 3·C6H6. Crystal data: 
3·C6H6, monoclinic, space group C2/c, a = 15.193(4) Å, b =
14.287(3) Å, c = 14.685(4) Å, β = 105.30(1)°, V = 3074(1) Å3,
Z = 4; 3‘, monoclinic, space group C2/c, a = 21.5400(8) Å, b =
9.5232(5) Å, c = 13.9828(2) Å, β = 118.924(1)°, V = 2510.5(2)
Å3, Z = 4. 1H NMR spectra of 3 (3.06, 3.05, 1.66, and 1.31 ppm)
and 3‘ (2.90, 2.75, 2.14, and 1.97 ppm) are also reported:  each
spectrum has four signals due to methyl groups, which accords
well with the fact that each of the molecules, 3·C6H6 and 3‘, has
a crystallographic 2-fold axis.