An experimental and theoretical charge density study, based on Bader’s Quantum Theory: Atoms in Molecule (QTAIM), on a trichromium metal string complex, Cr3(dpa)4Cl2(C2H5OC2H5)x(CH2Cl2)1-x (1, dpa- = bis(2-pyridyl)amido)) is performed. The structure and multipole model of 1 are performed by using experimental X-ray diffraction data which are collected at both 100 K using conventional X-ray source (DS1) and 15 K using synchrotron source (DS2). The three chromium metal string is bridged by four dpa- ligands. These tri-chromium metal ions are bonded to each other and terminated by two Cl- ions on the both ends, forming a [Cl(1)Cr(1)Cr(2)Cr(3)Cl(2)] linear string. Each Cr atoms are coordinated by four N atoms of each dpa- ligand. This metal string is slightly unsymmetrical at both data sets. The bond distance, from DS1 (DS2), of Cr(1)Cr(2), 2.3480(2) (2.3669(1)) Å, is 0.03 (0.003) Å shorter than Cr(2)Cr(3), 2.3773(2) (2.3689(1)) Å. Furthermore, the Cr(1)Cl(1) is 0.04 (0.04) Å longer than Cr(3)Cl(2) (2.5481(2) (2.5335(2)) and 2.5065(2) (2.4947(2)), respectively). The bond characterization of CrCr bonds indicate that the (3,-1) bond critical points are located at the center of CrCr bonds with small value of electron density, ρb ~ 0.25 e/Å3 and small positive value of total energy density, Hb ~ 0.03 H/Å3. The Laplacian density maps of Cr atoms show obviously local valence shell charge concentration (VSCC) along the bisection of CrN bonds. The total d-orbital populations of Cr atoms have similar value of 4.76 e for Cr(1) and Cr(3) but has slightly larger value of 4.8 e for Cr(2). The charge difference becomes larger at 15 K (4.61 for Cr(2) and 4.3 for Cr(1) and Cr(3). The electron populations of each five d-orbitals are populated unevenly. The dx2-y2 orbital which points to CrN bonds has smallest population in all three Cr atoms. This is consistent to the observation of Laplacian density of Cr atoms. The theoretical charge density analyses show good agreement with experimental one. A detailed analysis of the electron density will be given.
Charge density; Molecular wire; Linear metal-string; Synchrotron radiation
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Gordon Research Conferences : Electron Distribution & Chemical Bonding, 2013