A HF/CI-SD study of the low-lying states of nitroprusside ion

Abstract

Desde a descoberta de dois estado meta-estáveis gerados por excitação ótica do nitroprussiato de sódio cristalino, Na2[Fe(CN)5NO].2H2O (SNP), exibindo longa meia-vida a temperaturas abaixo de 160 K, grande esforço vem sendo realizado no sentido de entender a estrutura eletrônica de sistemas correlatos. Apesar deste esforço, a natureza dos orbitais de fronteira e dos processos de excitação eletrônica de baixa energia são, ainda hoje, controversos. Cálculos iniciais EHT mostram que o HOMO possuia caráter do orbital 3d metálico, enquanto o LUMO possuia uma contribuição dominantemente π* (NO). Entretanto, cálculos INDO definiram o orbital metálido d como orbital de valência interna com vários elétron-volts em energia de Koopmans. O espectro vertical foi estimado através de cálculos HF/Cl-SD com bases de qualidade double-zeta e potenciais de caroço. As energias de Koopmans para os resultados ab initio estão de acordo com os resultados de Bottomley e Grein, e atribuem as primeiras excitações a processos de transferência de carga (TC) do trans-cyano para os ligantes nitrosila. Forças de oscilador foram calculadas e os resultados mostraram intensidades comparáveis com os resultados experimentais. A energia de excitação para o processo de transferência de carga metal → NO, 8e → 13e (dxz,dyz → π* NO) foi estimada em 4.52 eV e exibindo intensa banda de absorção. A segunda excitação de transferência de carga, 1b 2 → 13e (dxy → π* NO), apontada por trabalhos prévios como uma típica banda de transferência de carga (TC) mostra uma pequena intensidade em 5.04 eV. Nos cálculos foi observado que o ordenamento SCF é muito independente do conjunto de base utilizado para o metal. Bases metálicas de caráter mínimo mostram resultados em grande concordância com os resultados EHT, enquanto as bases double-zeta empurram os orbitais d metálicos para os orbitais de valência interna. O ordenamento das energias HF foi empregado no sentido de interpretar resultados de experimentos fotoquímicos e de termoanálise do SNP e os resultados parecem mostrar boa concordância com as propriedades calculadas.Since the discovering of two photoexcited metastable states of crystalline sodium nitroprusside, Na2[Fe(CN)5NO].2H2O (SNP), showing rather long lifetimes at temperatures below 160 K, much effort has been devoted toward the study of its electronic structure. Despite this tremendous effort the nature of the frontier orbitals and the related low energy excitations remains controversial. Early calculations, EHT, showed the HOMO as mainly the metallic 3d orbital while the LUMO had a major π* (NO) contribution. However INDO calculations, clearly set the metal d orbital many electron-volts deep in core. The vertical electronic spectrum have been estimated through ab initio HF/CI-SD with a double-zeta quality basis set. The ab initio results support Bottomley and Grein's interpretations and assign the first electronic transitions to ligand-to-ligand charge-transfer excitation from trans-cyano to nitrosyl ligands. The corresponding oscillator strengths have b...

Photoinduced Linkage Isomers of Transition-Metal Nitrosyl Compounds and Related Complexes

“…Fenske-Hall-type calculations 27 of SNP and other first-row transition-metal nitrosylpentacyanides similarly indicated the HOMO to be a b 2 orbital of mostly metal d xy character with some π(CN cis ) contribution. The assignment was compatible with the interpretation of a variety of experimental results obtained with the ESR, 28 XPS, 26 XANES, 18 polarized absorption, 9,26 and Mo ¨ssbauer 28 techniques.…”

“…They were set aside by the authors because of the disagreement with the experimental results listed above, though they are supported by subsequent HF results. The HF/CI-SD calculations 28 of Hollauer and Olabe assign the first electronic transition to ligand-to-ligand charge transfer from axial-cyano to the nitrosyl ligand, the e-type HOMO being composed of CN orbitals with about 70% axial-CN character. The excitation energy of d xz,yz f π*-(NO) and d xy f π*(NO) transitions were calculated with the ∆SCF method (including CI) as 4.52 and 5.04 eV, which is in good agreement with the spectroscopic observations.…”

Theoretical Investigation on the Electronic Structure of Pentacyano(L)ferrate(II) Complexes with NO+, NO, and NO-Ligands. Redox Interconversion, Protonation, and Cyanide-Releasing Reactions

“…NO orbitals also mix with those of Fe to define the LUMOs. This description resembles several ones previously given, which have been obtained by means of different methodologies with no consideration of the solvent − and also with the DFT calculations performed in this work for isolated [Fe(CN) 5 NO] 2- . In this way, lack of modeling the solvent seems to be the origin of the controversy among the related data.…”

PEO−[M(CN)5NO]x- (M = Fe, Mn, or Cr) Interaction as a Driving Force in the Partitioning of the Pentacyanonitrosylmetallate Anion in ATPS: Strong Effect of the Central Atom

“…This alteration reflects the loss of electron density of the CNgroup and accumulation of electron density of the NO + upon complex formation. 29 Appropriate calculations, which make use of a Mulliken population analysis, 30 found that for both the cyanide and the nitrosyl ligands the electronic structures of the 3σ, 4σ, and 1π orbitals were unchanged as compared with those of the free ions. Only the 5σ and 2π orbital occupancies appear to be affected by complex formation.…”

“…However, It is well known that there are intramolecular environmental effects, caused by the central atom, in the energy levels and electronic distributions, as illustrated by the fact that the magnitudes of the separations are not nearly as large as those in the isolated ligands (CN − and NO + ). This alteration reflects the loss of electron density of the CN − group and accumulation of electron density of the NO + upon complex formation . Appropriate calculations, which make use of a Mulliken population analysis, found that for both the cyanide and the nitrosyl ligands the electronic structures of the 3σ, 4σ, and 1π orbitals were unchanged as compared with those of the free ions.…”