The interactions between the phthalocyanine macrocycle Pc2- and the metal ions Co2+, Ni2+ and Cu2+ are analyzed in detail. It is concluded that u bonding is by far dominant, mostly due to strong charge donation from the pyrrolic nitrogen lone pairs into the empty or singly occupied (in Cu) 3d,, with additional effects from donation into the 4p,, and 4s. The a bonds, consisting of back-donation from 3d, into empty ring P orbitals and donation from occupied ring P orbitals into the metal 4p, are rather weak, but there is a sizable contribution from polarization of the Pc2- system. In CoPc and NiPc the total orbital interaction contribution (the covalent component) is about equal to the ionic component of the bond, the latter being identified as the sum of the Pauli repulsion and the attractive electrostatic interaction between M2+ and Pc2-. In CuPc the electron in the 3d,acceptor orbital diminishes the orbital interaction contribution, making this the least strongly bound system. Comparison with Mg2+ shows that the ionic contribution is about the same but the covalent component of the bond drops by ca. 50% due mostly to the absence of the TM 3d AO's. Comparison of phthalocyanine (Pcz-) to porphyrin (P2-) shows that the larger hole size of P2- has the following effects: (a) the orbital interactions are somewhat less effective due to smaller overlap; (b) the Pauli repulsion is diminished; (c) the electrostatic attraction is larger in spite of the larger hole size due to higher negative electron density on the smaller ring system of P2-. The net effect is stronger bonding to Pzthan to Pc2-. The photoelectron and optical spectra of CoPc, NiPc and CuPc have been calculated and compared to gas phase and condensed phase spectra.

Metal-Macrocycle Interaction in Phthalocyanines: Density Functional Calculations of Ground and Excited States

ROSA, Angela Maria;
1994

Abstract

The interactions between the phthalocyanine macrocycle Pc2- and the metal ions Co2+, Ni2+ and Cu2+ are analyzed in detail. It is concluded that u bonding is by far dominant, mostly due to strong charge donation from the pyrrolic nitrogen lone pairs into the empty or singly occupied (in Cu) 3d,, with additional effects from donation into the 4p,, and 4s. The a bonds, consisting of back-donation from 3d, into empty ring P orbitals and donation from occupied ring P orbitals into the metal 4p, are rather weak, but there is a sizable contribution from polarization of the Pc2- system. In CoPc and NiPc the total orbital interaction contribution (the covalent component) is about equal to the ionic component of the bond, the latter being identified as the sum of the Pauli repulsion and the attractive electrostatic interaction between M2+ and Pc2-. In CuPc the electron in the 3d,acceptor orbital diminishes the orbital interaction contribution, making this the least strongly bound system. Comparison with Mg2+ shows that the ionic contribution is about the same but the covalent component of the bond drops by ca. 50% due mostly to the absence of the TM 3d AO's. Comparison of phthalocyanine (Pcz-) to porphyrin (P2-) shows that the larger hole size of P2- has the following effects: (a) the orbital interactions are somewhat less effective due to smaller overlap; (b) the Pauli repulsion is diminished; (c) the electrostatic attraction is larger in spite of the larger hole size due to higher negative electron density on the smaller ring system of P2-. The net effect is stronger bonding to Pzthan to Pc2-. The photoelectron and optical spectra of CoPc, NiPc and CuPc have been calculated and compared to gas phase and condensed phase spectra.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11563/3353
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