Thermal behavior, powder X-ray diffraction, DFT calculations and vibrational spectra of barium bis(pentacyanonitrosylchromate) octahydrate, Ba3[Cr(CN)5NO]2.8H2O(D2O).

The cell parameters of Ba3[Cr(CN)5NO]2.8H2O were determined from powder X-ray diffraction using the autoindexing program TREOR, and refined by the Le Bail methods with the FULLPROF program. An orthorhombic cell was determined with cell parameters a = 15.0324(2) A, b = 12.9542(9) A, and c = 7.5094(5) A. Two possible space groups are consistent with the systematic absences: Pmcb (#55) and P2cb (#32). Infrared spectra are reported for the polycrystalline compound, isotopically normal and partially deuterated, at temperatures ranging between ca. 80 K and 293 K together with the room temperature Raman spectrum. The assignment of the observed bands was accomplished assuming the existence of one type of pentacyanonitrosylchromate ion in the asymmetric unit, as suggested by the single band found in the NO stretching region of the deuterated anion and in the anhydrous compound. TGA-DTA data are also reported and discussed. The assignments are supported by DFT calculations of the normal modes of vibration of the [Cr(CN)5NO](3-) structure, optimized at the same level of theory.

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.

Reaction pathways for the one- and two-electron reductions of [Fe(CN)(5)NO](2)(-) have been investigated by means of a density functional theory (DFT) approach combined with the polarized continuum model (PCM) of solvation. In addition, UV-vis spectroscopic data were obtained using ZINDO/S calculations including a point-charge model simulation of solvent effects. DFT methodologies have been used to assess the thermodynamical feasibility of protonation and cyanide-release processes for the reduced species. We conclude that [Fe(CN)(5)NO](3)(-) is a stable species in aqueous solution but may release cyanide yielding [Fe(CN)(4)NO](2)(-), consistent with experimental results. On the other hand, the [Fe(CN)(5)NO](4)(-) complex turns out to be unstable in solution, yielding the product of cyanide release, [Fe(CN)(4)NO](3)(-), and/or the protonated HNO complex. All the structural and spectroscopic (IR, UV-vis) predictions for the [Fe(CN)(5)HNO](3)(-) ion are consistent with the scarce but significant experimental evidence of its presence as an intermediate in nitrogen redox interconversion chemistry. Our computed data support an Fe(II)(LS) + NO(+) assignment for [Fe(CN)(5)NO](2)(-), an Fe(II)(LS) + NO assignment for the one-electron reduction product, but an Fe(I)(LS) + NO(+) for the one-electron product after dissociation of an axial cianide, and an Fe(II) + singlet NO(-) for the two-electron reduction species.