Crystal structure of bis(η5-6,6-dimethylcyclohexadienyl)chromium, Cr(C8H11)2
Zeitschrift für Kristallographie - New Crystal Structures
C 16H 22Cr, orthorhombic, P 2 1 2 1 2 1 (no. 19), a =7.6112(2) Å, b =9.2521(4) Å, c =20.2174(9) Å, V =1423.7 Å 3 , Z =4, Source of material The compound wasprepared asdescribed in the literature , and single crystals were obtained by slow sublimation at50°Cunder vacuum. Discussion Cr(6,6-dmch) 2 (dmch =dimethylcyclohexadienyl) adopts aconformation consistent with expectations . The conformation angle, defined asthe relative twist between the two dienyl ligands awayf rom asyn-eclipsedo
... asyn-eclipsedo rientation,i sf ound to be 83.8°, as compared to very similarv alues of 82.2°and 84.0°for its 2,4dimethylpentadienyl and cyclooctadienyl analogues  . The value is intermediate between those found for Fe(6,6-dmch) 2 (47.5°) and V(6,6-dmch) 2 (96.2°) [5, 6] . The average M -Cbond distances ( M =t ransition metal) for these three M (6,6-dmch) 2 complexes decrease from Vto Fe, being2.194 Å,2.166 Å,and 2.068 Å.These values mayb ec ompared with those for the respective metallocenes, at2.280(5) Å,2.169(4) Å,and 2.064(3)Å . Consistent with the intermediate size of chromium, the average C1-C5s eparation for Cr(6,6-dmch)2 is intermediate between those of its vanadium and iron analogues,at2.380 Åvs.