Conformational variability in π-complexes of hexaethylbenzene. Crystal and molecular structure of [(C₆Et₆)(C₅H₅)Fe]BPh₄

[(Hexaethylbenzene)Fe(C₅H₅)][BPh₄], [1BPh₄], crystallizes in the monoclinic space group, P2₁/C, with a 15.7288(23), b 15.4411(14), c 16.3356(20)Å, β 107.972(10)° and D_calc 1.208 g cm^-3 for Z = 4. Least-squares refinement gave a conventional R value of 0.047 for 2881 independent observed reflections. The structure reveals that the complexed hexaethylbenzene moiety in 1 adopts a conformation such that five ethyl groups point away from the iron atom (distal) and only one is directed towards the iron atom (proximal). This observation contrasts with an earlier crystallographic study conducted (1PF₆), in which the hexaethylbenzene ligand was shown to adopt a four distal/two proximal conformation. In other ways the cations in 1BPh₄ and 1PF₆ are almost identical, thereby suggesting that even subtle packing effects may influence the conformation adopted by sterically crowded ligands such as hexaethylbenzene.