Metallocenium salts of perhalophenylplatinate anions: ion shape, charge and solvation effects on crystal structure

Abstract

The [ML2]+ [M = Co, L = Cp (η-C5H5), Cp* (η-C5Me5) or Ind (η-C9H7); M = Fe, L = Cp*] salts of the complex anions [Pt(C6F5)4]2−, [Pt(C6Cl5)4]2−, [Pt(C6Cl5)4]− and [PtCl2(C6Cl5)2]2− were synthesised by solution phase stoichiometric reactions of the [NBun4]+ salt of the anion with either a [BF4]− or [PF6]− salt of the appropriate organometallic cation. The crystal structures of 12 salts have been determined: [CoCp2]2[Pt(C6F5)4] 1, [CoCp2]2[Pt(C6Cl5)4]·Et2O·Me2CO 2, [CoCp2][Pt(C6Cl5)4] 3, [FeCp*2]2[Pt(C6F5)4]·2CH2Cl25, [FeCp*2]2[Pt(C6Cl5)4]·2CH2Cl26, [FeCp*2][Pt(C6Cl5)4] 7, [FeCp*2]2[PtCl2(C6Cl5)2]·MeCN 8, [CoCp*2]2[Pt(C6F5)4]·2CH2Cl29, [CoCp*2]2[Pt(C6Cl5)4] 10, [CoCp*2][Pt(C6Cl5)4] 11, [CoInd2]2[Pt(C6F5)4]·2MeCN 13, [CoInd2]2[Pt(C6Cl5)4]·2Me2CO 14. All of these structures show aromatic interactions between Cp (or Cp*) and perhalophenyl groups, as well as weak C–H⋯X interactions. Comparison between the structures of 3 and 11 shows the effect of cation size on the crystal structure. Both structures appear dominated by the larger [Pt(C6Cl5)4]− anions, with the metallocenium cations sandwiched between the perchlorophenyl rings. The structures containing [CoInd2]+ cations (13 and 14) show π⋯π interactions between the extended π-systems of the indenyl ligands. The perchloro structures show larger solvent-occupied volumes and lower symmetry anions (approximately D4vs.D4h) than their fluoro analogues. The less symmetric [PtCl2(C6Cl5)2]2− dianions of 8 also form π⋯π interactions, with the [FeCp*2]+ cations sandwiched between two perchlorophenyl rings. The crystal structures of 5, 6 and 9 are each solvated by dichloromethane, with the solvent occupying notably different volumes in the structures of 5cf.6, and 5cf.9.