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.