Molecular and Electronic Structures by Design:  Tuning Symmetrical and Unsymmetrical Linear Trichromium Chains

Abstract

The preparation, properties, and crystal structures of 12 trichromium extended metal atom chain (EMAC) compounds of the type Cr(3)(L)(4)X(2) (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 (D(4)) molecular structure, while more weakly donating ligands give rise to unsymmetrical (C(4)) 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.

Excited‐State Dynamics of the Metal String Complex Co3(dpa)4(NCS)2 from Femtosecond Transient Absorption Spectra

“…[10] Under these conditions, the complex is assumed to have no constraints of the crystal lattice and might thus exhibit a structure similar to that observed in solution phase. The spectra measured in solution phase display a single pyridyl line similar to that reported for the crystalline form, [12] consistent with a prediction of Berry et al [13] that trimetal string complexes with strong s-donating axial ligands have a symmetric structure.…”

Do Metal–Metal Multiply‐Bonded “Ligands” Have a trans Influence? Structural and Magnetic Comparisons of Heterometallic CrCr···Co and MoMo···Co Interactions

“…While the change in Co-N bond lengths from low-spin . [9] We note that the axial distortion of the octahedral geometry of the low-spin Co 2+ ion in 1 may partially be attributed to a Jahn-Teller effect, but this effect cannot account for the very short Cr···Co distance. Since this difference is significantly greater than the difference in ionic radii (0.085 Å) [10] for low-spin vs. high-spin Co 2+ , this result is a clear indication that direct bonding between Cr and Co must be considered.…”

“…Both structures are isomorphous in the space group Pnn2, and a crystallographic twofold axis passes through the center of the molecule normal to the CrєCr···Co axis, resulting in disorder in the positions of the metal atoms, as has been previously discussed. [9] The changes in the coordination sphere of the Co 2+ ion from 100 K (low-spin) to room temperature (high-spin) are somewhat unusual and deserve some discussion. While the change in Co-N bond lengths from low-spin .…”

Towards Selective Ethylene Tetramerization

“…[1p] Alkylation of the central nitrogen atom was also expected to diminish the established tendency of the ligand to form multiply bonded dimers or higher aggregates, [5] because of sterically induced deformation of the ligand backbone. [6] A range of substituted (2-C 5 3 ] with the ligand.…”