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The band structure of porphyrinatonickel(II). A semiempirical crystal orbital study based on the tight‐binding formalism
Author(s) -
Böhm Michael C.
Publication year - 1984
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560250506
Subject(s) - chemistry , binding energy , molecular physics , formalism (music) , tight binding , electron , lone pair , chemical physics , crystallography , ligand (biochemistry) , atomic physics , electronic structure , physics , computational chemistry , molecule , quantum mechanics , biochemistry , receptor , organic chemistry , art , musical , visual arts
The band structure of porphyrinatonickel(II) ( 2 ) has been studied by means of crystal orbital calculations that are based on the tight‐binding approximation; the computational framework is a recently developed INDO model for transition metal compounds of the 3 d series. The porphyrinato polymer has been studied in an eclipsed arrangement ( 2a ) and in a staggered conformation ( 2b ) where neighboring layers are rotated by 41°. The total energy of the metallomacrocycle has been decomposed into one‐ and two‐center contributions; the latter interaction parameters have been fragmented into physically feasible resonance, exchange, and classical electrostatic (electron–electron, electron–core, core–core) interactions. It is shown that individual two‐center potentials between atoms in neighboring layers are prevailingly determined by the electrostatic interaction energy. The NiNi coupling in the chain is highly repulsive; important stabilizing interactions are predicted between the 3 d center of one cell and the electronegative N atoms in the neighboring layers. Stabilizing and destabilizing electrostatic interaction potentials largely compensate each other; the net stabilization in the polymer comes from the accumulation of resonance and exchange increments. The unoxidized Ni(II) porphyrinato polymer is an insulator. Several ligand bands (π, σ, and lone‐pair) are predicted on top of bands with significant Ni 3 d admixtures; the conduction band of the unoxidized strand is of ligand π* character. The dense manifold of ligand states in the vicinity of the Ni 3 d states (3 d z 2, 3 d x 2 − y 2, 3 d xz /3 d yz ) prevents the formation of bands in the polymer that are strongly localized at the 3 d center. Ni 3 d z 2and 3 d x 2 − y 2interact strongly with ligand lone‐pair and σ states. Avoided crossings between ϵ( k ) curves in k space lead to compositions in the various bands that differ significantly at the bottom and the top. The INDO crystal orbital formalism predicts a partial oxidation of ligand bands in derivatives of 2 that contain oxidants (e.g., halides). The theoretical findings derived for 2 are compared with available experimental data on highly conducting porphyrinatonicke(II) polymers (tetrabenzo and octamethyltetrabenzo derivatives of 2 ).