Molecular and electronic structures by design: Tuning symmetrical and unsymmetrical linear trichromium chains

The preparation, properties, and crystal structures of 12 trichromium extended metal atom chain (EMAC) compounds of the type Cr₃(L) ₄X₂ (L = equatorial ligands dipyridylamide (dpa) or di-4,4′-ethyl-2,2′-pyridylamide (depa), and X = axial ligands, e.g., halide or pseudohalide ions) with large variations in metal-metal distances are reported here. These complexes, which belong to a broad class of fundamentally interesting trinuclear molecules over which the electrons may or may not be delocalized, pose significant theoretical and experimental challenges which are dealt with in this report. Complexes with strongly donating axial or equatorial ligands tend to favor a symmetrical (D₄) molecular structure, while more weakly donating ligands give rise to unsymmetrical (C₄) structures; the physical properties of these two classes of compounds are discussed fully, and important comparisons with a reported DFT model of the electronic structures of the compounds are made.