Chemistry of chromium-selenium complexes. Thermolytic degradation of Cp2Cr2(CO)4Se, and the crystal structures of the cubane-like clusters Cp4Cr4(μ3-CO)2(μ3-Se)2 and Cp4Cr4(μ3-O)2(μ3-Se)2

Thermolysis of Cp 2 Cr 2 (CO) 4 Se ( 1 ) solution gave initially Cp 4 Cr 4 (CO) 2 Se 3 ( 3 ), and a thermally labile unidentified species, which on further degradation afforded a mixture of products, from which more of 3 , and the cubane-like complexes Cp 4 Cr 4 (CO) 2 Se 2 ( 2 ) and Cp 4 Cr 4 O 2 Se 2 ( 4 ) were isolated. A more prolonged thermolysis in THF yielded Cp 4 Cr 4 Se 4 ( 5 ) as the main product. Crystal data: 2 , monoclinic, space group C 2/ c , a 17.656(5), b 8.232(1), c 18.079(6) A, β 126.15(2)°, Z = 4, R = 0.075 for 1499 observed Mo- K α data; 4 , monoclinic, space group P 2 1 / c , α 14.08(1), b 10.306(8), c 15.212(6) A, β 103.55(2)°, Z = 4, R = 0.082 for 1711 observed Mo- K α data. Both complexes possess a cubane-like structure with triply bridging Se and CO or O ligands at alternating corners of the cuboid.