Bis(arylisocyanide) complexes of tungsten containing bulky bidentate aryl phosphine ligands adopt either cis or trans conformations, depending on the nature of the pam-substituent group on the aryl isocyanide ligand. Ab initio calculations on a series of ligands, p-RC6H4NC, indicate that the energy of the LUMO is determined by the electron-withdrawing/donating capabilities of the substituent group, which determine the relative pi -acidity of the ligand. Strong pi acids, which contain electron-withdrawing groups, tend to polarize sufficient charge density away from the metal center to effect the formation of the sterically less favorable, but electronically stabilized, cis conformer. Weaker pi acids, containing donor substituents, do not provide enough electronic stabilization to overcome steric repulsion, resulting in the adoption of trans geometry. (CNC6H4NC)W(dppe)(2) exists as the cia conformer, as does (CNC6H2(CH3)(2)NC)W(dppc)(2), while (CNC6(CH3)(4)-NC)W(dppe)(2), with increased steric built coupled with decreased pi -acidity, exists as the trans conformer. Theoretical and experimental studies indicate that the energy match between isocyanide ligands and the metal center can be modified significantly by the selection of various substituents and that relatively subtle variations in the electronic structure of the ligands can have dramatic effects on the structures of the resulting complexes.