P. J. Aymonino

Polarized infrared absorption spectra of Na2 [Fe (CN) 5NO] · 2H2O with part of the anions in the electronically excited metastable state

Abstract IR spectra of the nitroprusside ion in Na2[Fe (CN) 5NO]. 2H2O in the metastable electronic state produced by irradiation at boiling air temperature with the 514.5 nm line of an Ar+ LASER were obtained for thin (100) single crystal plates in the ranges 4000-430 cm-1 and 4000-550 cm-1 for polarizations along the 1b and c -axes, respectively. The spectra showed that the suggested bending of the FeNO group upon excitation occurs in the (a,b) mirror plane of the ground state crystal. In addition to bands corresponding to Raman lines reported as due to excited nitroprusside, new bands appeared in the infrared spectra. Some of them showed a strong dichroic behavior. On heating the samples some of the new bands disappeared earlier than the bands correspon d ing to the Raman lines. No explanation is still available for those bands.

Infrared absorption spectra of electronically excited long-lived metastable states in Na2[Ru(CN)5NO]·2H2O

Abstract [Ru(CN)5NO]2− can be excited selectively by two very long-lived electronic metastable states (MSI and MSII) by irradiation at low temperature with blue-near UV light. Upon excitation to MSI and MSII states, CN and NO modes suffer frequency down-shifts, a fact which implies softening of the named bonds. Shifts of vibrational modes of the RuNO group are far larger than shifts of CN modes, a fact that indicates that the metastable states involve electronic transitions mainly located at that group. The MSI and MSII states decay when heating at two different onset temperatures TI T > TI shows that MSII is energetically below MSI.

Spectroscopic evidence of vibrational dipole-dipole coupling between nitrosyl groups in some nitroprussides

The nature and magnitude of the intermolecular vibrational coupling between nitrosyl groups in Sr[Fe(CN)5NO]⋅4H2O and Ba[Fe(CN)5NO]⋅2H2O have been studied quantitatively by IR spectroscopy. The isotopic dilution technique has been used by incorporating in the first compound up to 40% of 18O as N18O ligand in the crystal. The results can be interpreted by postulating a dynamic electric dipole–dipole interaction which operates between the polar NO stretching vibrations. The main features of the fine structure displayed by the NO stretching band in the infrared spectra of polycrystalline Sr[Fe(CN)5N(16O/18O)]⋅4H2O, and in single crystals of Ba[Fe(CN)5NO]⋅2H2O can be explained in terms of a linear‐chain model of nitrosyls vibrationally coupled through transition dipole–dipole forces, with interactions between nearest neighbors. The value ‖(∂m/∂S)0‖=13 D/A calculated on the basis of this model for the NO dipole‐moment derivative agrees satisfactorily with the value reported from integrated IR absorption intens...

TGA-DTA, infrared and x-ray powder diffraction studies on strontium nitroprusside and its hydrates

Abstract Dehydration data for the tetra-, di- and monohydrate of strontium nitroprusside and the vibrational behaviour of the water molecules in normal and deuterated samples agree with crystal data previously reported (for the di- and tetrahydrate as single crystals) and in this paper (monohydrate as a powder). Four distinct types of water molecules are present in the three hydrates with one type (oxygen bonded to Sr 2+ ) in common. Other types are a non hydrogen-bonded molecule (dihydrate), a molecule bonded by a single hydrogen atom to the nitrogen atom of a cyanide group and a set of two molecules similarly bonded to the oxygen atom of the previous type (tetrahydrate). The spatial orientation of the NO groups of the nitroprusside ions in the tetrahydrate is confirmed by the observed dichroism of the corresponding stretching band.

Polarized and low temperature infrared spectra of barium nitroprusside dihydrate, Ba[Fe(CN)5NOl.2H2O

Abstract The infrared spectra of barium nitroprusside dihydrate were studied and the observed bands were assigned either to the internal modes of the nitroprusside ion or to the intornal and librational modes of the hydration water. The data were obtained from monocrystals (measuring in this case the polarized light) and from the polycrystalline substance (both normal and deuterated). The existence of two kinds of hydration water was evident from the infrared spectra, in good accordance with X-ray studies. The water molecules seem to form weak hydrogen bonds with neighbor nitroprusside ions; an orientation for these bonds in the lattice is proposed.

3-and 4-cyanopyridine complexes of pentacyanoferrate(II) and pentacyanocobaltate(III)☆☆☆

Abstract The preparation and some properties of complexes of 3- and 4-cyanopyridine with the Fe(CN) 3− 5 and Co(CN) 2− 5 groups are described. Visible, IR and NMR spectra indicate a coordination through the pyridine nitrogen.

On the electronic structure of metastable nitroprusside ion in Na2[Fe(CN)5NO].2H2O. A comparative single crystal esr study

Abstract Laser irradiation of Na2[Fe(CN)5NO].2H2O at low temperature produces two long-living nitroprusside metastable states which, upon heating, decay at two different temperatures. In addition, laser illumination of previously X-ray irradiated crystals generates traces of the closely related [Fe(CN)5NO]3- species with linear (axial) NCFeNO geometry where the unpaired electron is localized on a dz2 orbital as detected by ESR spectroscopy [g|=2.0055(6), g∥=2.0348(4); A|=16.9(1)G, A|=14.8(1)G]. There also exists another stable form of [Fe(CN)5NO]3- with bent FeNO group and the odd electron located in a π∗NO orbital. The comparison of metastable [Fe(CN)5NO]2- and the [Fe(CN)5NO]3- (dz2) species suggest that the electronic structure of the high-temperature metastable state should be described as 1B2: 6e(dxz,dyz)4 2b2(dxy)1 5a1(dz2)1. This assignment is consistent with reported optical absorption, Mossbauer, Raman, and IR data.

Das Schwingungsspektrum von Sr2V2O7 und die Schwingungseigenschaften des Divanadat-Ions

The infrared and laser-Raman spectra of Sr2V2O7 are reported and discussed by means of a “Site Symmetry” analysis. The principal force constants as well as the mean amplitudes of vibration for the V2O74− ion have been calculated using a simplified molecular model. Some aspects of the vibrational behaviour of the V−O−V bridge in this ion are also discussed.

The vibrational spectra of strontium and barium diarsenates

Abstract The infrared and laser-Raman spectra of crystalline Sr 2 As 2 O 7 and Ba 2 As 2 O 7 are reported and discussed. The principal force constants for the As 2 O 7 4− ion are calculated using a simplified molecular model.

Infrared spectra and molecular structure of excited electronic metastable states of the nitroprusside anion, [Fe(CN)5NO]2−

Abstract Na 2 [Fe(CN) 5 NO].2H 2 O (SNP) and Ba[Fe(CN) 5 NO].3H 2 O (BNP) irradiated at low temperature with light in the green—blue region exhibit two new sets of infrared (IR) bands. These can be assigned to two, long-lived, electronically excited metastable states of the [Fe(CN) 5 NO] 2− (NP) ion. Upon heating, these states depopulate following decay processes with different onset temperatures. We considerably extend here previous polarized IR data on irradiated SNP (100) plates to include the other basal planes. All IR-active CN, NO and FeN stretching modes and FENO bending modes of NP in both metastable states exhibit frequency down shifts This points to a softening of the corresponding bonds upon excitation. Relative frequency shift values observed for modes associated with the FeNO group are about one order of magnitude larger than the corresponding values for CN stretching modes. This supports the conclusion that the metastable states are reached through an electronic transition involving mainly the metal( nd )-NO bonding. We employ dichroic measurements in SNP to estimate the orientation in the lattice of the transition dipole moment vector corresponding to the NO mode of NP in both metastable states. Results show that the FeNO group is not appreciably bent upon excitation of NP to either of these states.