A photochromic complex with disulfur and dimethyl-ethylene-1,2-dithiolate ligands, [Mo-2(mu-S-2)(mu-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) Angstrom, b = 14.287(3) Angstrom, c = 14.685(4) Angstrom, beta = 105.30(1)degrees, V = 3074(1) Angstrom(3), Z = 4; 3', monoclinic, space group C2/c, a = 21.5400(8) Angstrom, b = 9.5232(5) Angstrom, c = 13.9828(2) Angstrom, beta = 11 8.924(1)degrees, V = 2510.5(2) Angstrom(3), Z = 4. H-1 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.