The First Crystallographic Evidence for Side-On Coordination of N 2 to a Single Metal Center in a Photoinduced Metastable State (original) (raw)
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Tetrahedron, 2000
AbstractÐNew metastable species are formed by low-temperature irradiation of crystals of transition metal nitrosyl complexes. In the work described, photocrystallographic techniques, in which crystals are exposed in situ, are combined with differential scanning calorimetry measurements, IR spectroscopy and theoretical calculations. The new species are identi®ed as isonitrosyl and h 2 -NO linkage isomers, which revert to the ground state on subsequent warming. The stability of the linkage isomers increases with increasing p-withdrawing ability of the ligand trans to NO, indicating the crucial role of electronic factors in determining relative stability of the isomers of different complexes. Isomers with decay temperatures up to ,08C have been prepared. Solid state effects are evident from comparison of the behavior of different salts of the same ion, of sodiumnitroprusside in the neat crystal and in a co-crystal with 18-crown-6 ether, and from the observation of different photochemical behavior when [Ru(NO)(NH 3 ) 5 ](NO 3 ) 3 is absorbed in a sol±gel glass. The two independent molecules in the asymmetric unit of [Ni(NO)(h 5 -Cp p )] show different orientations of the h 2 -NO ligand after irradiation, the difference being related to the shape of the reaction cavities at the two sites. A previously unknown side-on binding mode, similar to that occurring for NO, has been discovered for the dinitrogen ligand in [Os(NH 3 ) 5 (N 2 )][PF 6 ] 2 , indicating the potential of the techniques used in the search for new species and novel binding modes of transition metal atoms. q
Inorganic Chemistry, 1998
The crystal structure of [Ni(NO)(η 5-Cp*)] in the light-induced metastable state was determined by X-ray diffraction at 25 K of a crystal with a 47% metastable-state population. The most significant geometrical change is the formation of a side (η 2) bound structure with an Ni-NO angle of 92(1)°, compared with 179.2(2)°in the most stable configuration, and a corresponding Ni-O distance of 2.09 Å. An elongation of the Ni-N bond by 0.08(1) Å and local distortions in the pentamethylcyclopentadienyl ring are also observed. Geometry optimizations, carried out using density functional theory, confirm that the [Ni(η 2-NO)(η 5-Cp*)] structure corresponds to a local minimum with energy 0.99 eV above that of the stable isomer and predict a second local minimum at 1.85 eV for the isonitrosyl, [Ni(ON)(η 5-Cp*)], structure. Geometrical parameters obtained from the theoretical calculation for [Ni(η 2-NO)(η 5-Cp*)] agree reasonably well with the experimental findings. This is the first example of a sidebound nitrosyl complex generated by photoirradiation of an {M(NO)} 10 ground-state configuration. Its geometry is comparable with that of the photoinduced metastable state (MS 2) of sodium nitroprusside, which in its ground state has the {M(NO)} 6 configuration.
Inorganic Chemistry, 2000
Low-temperature IR experiments on crystalline samples of trans-[Ru(NH 3 ) 4 (NO) nicotinamide] 3+ salts show a light-induced absorption band typical for MS1 NO linkage isomers upon exposure to 300-500 nm light from a Xe source. The formation of a metastable species is confirmed by DSC measurement on a sample irradiated at low temperature with 457 nm light from an Ar + laser. The light-induced species decays between 250 and 260 K according to both IR and DSC results. This decay temperature (T d ) is somewhat below that observed for other high-T d linkage isomers, even though the NO-stretching frequency of the of [Ru(NH 3 ) 4 (NO) nicotinamide] 3+ ion is above that of the other isomers, demonstrating a lack of precise correlation between the two physical properties. The 90 K crystal structure of trans-[Ru(NH 3 ) 4 (NO)nicotinamide](SiF 6 )(NO 3 )‚H 2 O is reported. The geometry from theoretical DFT calculations of the ground-state structure agrees well with the experimental results, except for the orientation of the CONH 2 substituent in the pyridine ring, which is rotated by 180°in the crystal due to packing effects. The MS1 and MS2 linkage isomers are found to correspond to local minima on the ground-state potential energy surface, and their geometries and energies are reported.
Polyhedron, 2002
18 / Abstract / 19 / / 20 / The crystal structure of nitropentaamminecobalt(III) nitroprusside sesquihydrate, [Co(NH 3 ) 5 NO 2 ][Fe(CN) 5 NO] ×/1.5H 2 O has / 21 / been determined by Patterson and Fourier methods employing 3881 independent X-ray reflections with I /2s (I ) and refined by / 22 / full-matrix least-squares to R 1 0/0.032. The substance crystallizes in the monoclinic C 2/c (C 2h 6 ) space group No. 15, with a 0/ / 23 / 28.408(3), b 0/6.422(1), c 0/22.401(3) Å , b 0/123.55(1)8 and Z0/8. The metastable state I (MSI) of the nitroprusside anion and the / 24 / photochemical isomerization reaction of the nitropentaamminecobalt(III) cation to the nitrito isomer were produced by irradiation / 25 / with Ar ' laser light of 488 nm wavelength at 77 K. TGA and DTA of the non-excited substance were performed under nitrogen / 26 / atmosphere. # 2002 Published by Elsevier Science Ltd. / 27 / Keywords: PPPPentacyanonitrosylferrate(2(/) ion; Metastable excited states; X-ray diffraction; FIRRS; TGA; DTA / 28 / 1. Introduction / 29 / An extensive work on nitroprussides, which includes / 30 / alkaline, alkaline-earth, and transition metals salts has / 31 / been previously performed ([1 Á/10] and references / 32 / therein). These studies provided interesting results, / 33 / especially about the vibrational and photophysical NO / 34 / behavior. The strongly polar NO stretching vibration / 35 / proved to be largely affected by the environment, as / 36 / suggested by resonant (interanionic) ([10] and references / 37 / therein) and non-resonant (lattice) effects experienced / 38 / by this stretching mode in salts containing the / 39 / [Fe(CN) 5 NO] 2( (NP) anion. [9,11] The MNO group, / 40 / in this and other pentaligandnitrosyl anions, [12 Á/17] / 41 / seems to be the site of the generation of two very long-/ 42 / lived metastable states (MSI and MSII) by irradiation at / 43 / low temperature with light in the 300 Á/550 nm wave-/ 44 / length range. A geometrical interpretation has been / 45 / proposed for MSI and MSII with a nearly linear / 46 / structure (FeON) for MSI and T-shaped Fe N O for MSII / 47 / [18] as results of very refined single crystal X-ray / 48 / diffraction studies. Recently, additional information / 49 / was obtained in favor of the linear, isonitrosyl structure / 50 / of MSI from the IR studies of 15 NO, N 18 O and 54 Fe-/ 51 / substituted excited sodium nitroprusside dihydrate / 52 / (SNP) and a DFT vibrational calculation [19].
CrystEngComm, 2014
The known complex [Ni(medpt)(η 1-NO2)(η 2-ONO)] 1 (medpt = 3,3'-Diamino-N-methyldipropylamine) crystallises in the monoclinic space group P21/m with 1.5 molecules in the asymmetric unit with two different η 1-NO2 ligand environments in the crystal structure. At 298 K the molecule (A) sitting in a general crystallographic site displays a mixture of isomers, 78% of the 1-NO2 isomer and 22% of an endo-nitrito-(η 1-ONO) form. The molecule (B) sitting on a crystallographic mirror plane adopts the 1-NO2 isomeric form exclusively. However, a variable temperature crystallographic study showed that the two isomers were in equilibrium and upon cooling to 150 K the η 1-ONO isomer converted completely to the 1-NO2 isomer, so that both independent molecules in the asymmetric unit were 100% in the 1-NO2 form. A kinetic analysis of the equilibrium afforded values of ΔH =-9.6 (± 0.4) kJ mol-1 , ΔS =-21.5 (± 1.8) J K-1 mol-1 and EA =-1.6 (± 0.05) kJ mol-1. Photoirradiation of single crystals of 1 with 400 nm light, at 100 K, resulted in partial isomerisation of the 1-NO2 isomer to the metastable η 1-ONO isomer, with 89% for molecule (A), and 32% for molecule (B). The crystallographic space group also reduced in symmetry to P21 with Z' = 3. The metastable state existed up to a temperature of 150 K above which temperature it reverted to the ground state. An analysis of the crystal packing in the ground and metastable states suggests that hydrogen-bonding is responsible for the difference in the conversion between molecules (A) and (B).
Reversible photoswitching between nitrito-N and nitrito-O isomers in trans-[Ru(py)4(NO2)2]
Physical Chemistry Chemical Physics, 2010
Nitro-nitrito photoisomerisation is investigated in solid samples and solutions of trans-[Ru(py) 4 (NO 2 ) 2 ]. Using light of wavelength 325 nm 50% of the N-bound Ru-NO 2 ligands can be switched to the O-bound Ru-ONO configuration (nitrito-N to nitrito-O isomerisation) at temperatures below T = 250 K in solids. The population of the isomeric configurations is determined with infrared spectroscopy from the decrease of the area of the n(NO) stretching and d(NO) deformation modes. In a frozen methanol-ethanol solution nearly 100% can be converted to the nitrito-O configuration. Upon heating above T = 250 K the Ru-NO 2 configuration is restored. The nitrito-O RuÀONO configuration can be partially transferred back to the nitrito-N configuration by irradiation with light in the spectral range 405-442 nm. Using absorption spectroscopy on a frozen methanol-ethanol solution, two new bands at 447 and 380 nm are observed in the nitrito-O configuration compared to one at 334 nm of the nitrito-N ground state configuration. The photoconversion is initiated by the metal-to ligand charge transfer transition Ru(d)p*(NO 2 ,py) as shown by the calculated partial density of states using Density Functional Theory. The calculations yield also the structure of the nitrito-N and nitrito-O isomer as well as the corresponding vibrational densities. The experimental structure of the ground state is determined using powder diffraction.
Photodissociation spectroscopy and ab initio calculations for the Sr+-N2 complex
Chemical Physics Letters, 2010
Electronic vibrationally resolved spectra of the Sr + -N 2 complex have been recorded in two energy regions 20 284-22 988 cm À1 and 15 576-16 380 cm À1 . In the high energy region, two progressions are present and they are attributed to the (2) 2 P 3/2,1/2 X 2 R þ transitions assuming a linear molecule. This linear configuration is supported from the observed spin-orbit splitting of these excited states as well as from electronic structure calculations. The lower energy spectrum shows a structure, which ends up to a continuum. Considering the complex as an anharmonic oscillator, the spectroscopic constants and the dissociation energies of the corresponding states are determined.