J.A. Güida

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.

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.

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.

Infrared evidence of NO linkage photoisomerization in Na2[Fe(CN)5NO]·2H2O at low temperature: experimental and theoretical (DFT) isotopic shifts from 15N(O), 18O and 54Fe species

Infrared spectra of the metastable state I (MSI) of normal and 15NO, N18O and 54Fe isotopically substituted sodium nitroprusside dihydrate (Na2[Fe(CN)5NO].2H2O) have been obtained at 77 K. A comparison of the isotopic shifts measured for the vibrational modes of the FeXY (XY = NO or ON) moiety with those calculated by means of quantum chemistry (DFT) procedures supports the linear Fe-O = N arrangement for the MSI state.

Low temperature polarized infrared spectra of the nitroprusside anion in the electronic ground and metastable excited states in (001) plates of Ba[Fe(CN)5NO].3H2O

Abstract The polarized IR spectra of the nitroprusside ion in thin (001) single crystal plates of Ba[Fe(CN) 5 NO]. 3H 2 O were obtained in the range 4000-250 cm -1 , at room temperature and at about 10 K, before and after irradiation with the 514.5 nm line of an Ar + - laser. The IR behavior of the electronically excited metastable state of the anion was similar to the previously reported behavior in Na 2 [Fe(CN) 5 NO].2H 2 O and confirmed a finding not detected by Raman spectroscopy in this latter substance. The splitting of some bands and the appearance of new features in the spectrum of unirradiated Ba[Fe(CN) 5 NO].3H 2 O upon cooling, not seen previously due to instrumental limitations, seem to support a phase change at low temperature.

Infrared spectra of K2[RuCl5NO] in two excited metastable states and the evidence for the NO linkage photoisomerization of metastable state I (MSI) in [RuX5NO]2− (X=Cl, CN)

Abstract Low temperature IR vibrational spectra of light induced metastable states I and II (MSI and MSII) of K 2 [RuCl 5 NO] are presented and discussed here. MSII bands and some MSI features are reported for the first time. Some of the MSI bands confirm Raman spectroscopic observations. The thermal deactivation of MSI and MSII states occur at temperatures T MSI > T MSII . This is the same ordering observed for Na 2 [Fe(CN) 5 NO]·2H 2 O and certain other RuNO complexes but opposite to that found for Na 2 [M(CN) 5 NO]·2H 2 O (M=Ru, Os). Evidence for the RuON structure of MSI is provided for [RuL 5 NO] 2− (L=CN, Cl) as results of the analysis of ν (NO) differences between 15/14 N( 16 O) and 18/16 O( 14 N) pairs of natural isotopic compositions.

Low temperature infrared spectra of photoexcited (η-cyclopentadienyl)nitrosylnickel, [Ni(C5H5)NO]

Abstract A new metastable excited state (metastable state I, MSI) was detected when (η-cyclopentadienyl)nitrosylnickel, Ni(C5H5)NO, was irradiated at 77 K with 488.0 and 514.5 nm Ar+-laser lines. The infrared spectra of metastable states I (MSI) and metastable state II (MSII) are characterized by down-shifts of the ν(NO) bands (260 cm−1 for MSI, and 460 cm−1 for MSII). Upon heating the irradiated samples, MSII bands vanished at a lower temperature than that occuring for the MSI bands. Irradiation with the 514.5 nm line generated half of the ν(NO) bands produced after illumination with the 488.0 nm line and upon further irradiation with the 632.8 nm HeNe laser line the ν(NO)MSI band completely disappeared. Results are compared with recent X-ray diffraction and DFT studies on excited Cp*NiNO and with infrared behavior of metastable excited states of [Fe(CN)5NO]2− and [Ru(NO2)4(OH)NO]2−.

Infrared and Raman studies on renal stones: the use of second derivative infrared spectra

Urolithiasis is a very frequent illness found in Argentina; however, stone analysis is not routinely performed. In this work, 86 renal calculi (from cities of Luján and San Antonio de Areco, State of Buenos Aires, Argentina) have been analyzed by infrared and Raman spectroscopies, and the results correlated with the main possible pathological conditions. Calcium oxalate monohydrate (whewellite) and mixtures of calcium oxalate monohydrate and carbonate apatite were the most frequent compounds found in our samples. In order to improve the identification of different phases present in calculi [particularly whewellite and weddellite (calcium oxalate dihydrate)], the second derivative spectra were used. The FTIR spectroscopy together with the second derivative analysis provides the urologist with a good method for calculi component determinations.

Crystal structure of tetrabutylammonium nitroprusside dihydrate, [(C4H9)4N]2[Fe(CN)5NO].2H2O, and vibrational spectra of ground and metastable excited states of the dihydrate and the anhydrate

The crystal structure of tetrabutylammonium nitroprusside dihydrate (TBANPDH, [(C4H9)4N]2[Fe(CN)5NO]·2H2O) was determined by single crystal X-ray diffraction (XRD) and the compound was also studied, as well as the anhydrous salt (TBANP), by room and low temperature Fourier Transform Infra-Red (FTIR) and room temperature Fourier Transform Near Infra-Red Raman (FTNIRR) spectroscopies. In addition to the ground states (GS), the metastable excited states (MSI and MSII) generated by laser excitation (488 nm) at low temperature were IR studied, both of the dihydrate and the anhydrate. TBANPDH crystallizes in the trigonal space group P3221, D63, with a = b = 13.777(2), c = 22.039(2) Å, and Z = 3. The structure was solved employing 1273 independent XR reflections, with I > 2σ(I), by Patterson and Fourier methods and refined by full-matrix least-squares to R1 = 0.054.