Anion−Anion Assembly in Crystal of Sodium Nitroprusside

Abstract

The experimental charge density in the crystal of disodium pentacyanonitrosoferrate (sodium nitroprusside) dihydrate was analyzed in detail by means of Bader's atoms in molecules theory. It was shown that nitroprusside anion is involved in relatively strong self-interactions through the nitroso group. The obtained results agree well with the spectroscopic data, indicating the tendency of the corresponding moiety to the formation of anion-anion association both in solutions and in the crystalline phase.

Anion–anion interactions: their nature, energy and role in crystal formation

“…As it has been shown earlier by the EAS analysis, 11 the AA association involving the nitroso group of the nitroprusside moiety is common for the systems [FeNO(CN) 5 ] 27 ± X (X is an anion acting as a reducing agent) in solution. 129,130 The possibility of the anions to approach each other in the crystal was also proven by the potentiometric data 128 indicating that the CA bonding involve only the interactions with the cyano groups. The latter is apparently caused by the electrostatic reasons, i.e., by the pronounced concentration of the charge density on the CN fragments the charge of which varied from 70.64 to 70.30 e in the crystal.…”

“…This was accomplished in the study of disodium pentacyanonitrosoferrate dihydrate (sodium nitroprusside). 128 In its crystal, the shortened [2.6423(5) # A] contacts O_O (Fig. 20) were found between the neighbouring anions, which is common for the most of the nitroso-containing compounds (137 ordered structures were found in CCDC with the distance O_O in the range of 2.5 ± 3.1 # A).…”

“…Indeed, the energy of the CA bonds and the interactions of the cation with water molecules in the crystal were estimated to be less than 3.9 kcal mol 71 , while for the AA association this value approached 3.0 kcal mol 71 . The strengthening of the interactions O_O in the crystal of sodium nitroprusside 128 as compared with those in urea nitrate 126 was explained by the decrease in the interatomic distance while the charge on the oxygen atoms is practically the same (70.32 e in sodium nitroprusside 128 and 70.33 e on average in urea nitrate 126 ), which provides more effective overlap of valence shells of the oxygen atoms. The contribution of the AA association in the crystal of sodium nitroprusside is 17% of the total interaction energy; this is probably sufficient for it to persist in solution.…”

“…132,133 The total charge of the anion in the crystal of sodium nitroprusside appeared to be 71.75 e. On the one hand, the high negative charge should cause the strong electrostatic repulsion between the species and the significant weakening of the bonding AA interactions, the occurrence of which in sodium nitroprusside followed from the presence of the corresponding CP (3,71) along the line O_O. 128 On the other hand, the obtained value of the charge transfer from the anion (0.25 e) indicated the relative weakness of the CA bonds. Indeed, the energy of the CA bonds and the interactions of the cation with water molecules in the crystal were estimated to be less than 3.9 kcal mol 71 , while for the AA association this value approached 3.0 kcal mol 71 .…”

XPAD X-ray hybrid pixel detector for charge density quality diffracted intensities on laboratory equipment

“…We describe below the experimental setup and evaluate the quality of the measurement using a sodium nitroprusside (Na 2 [Fe(CN) 5-NO]Á2H 2 O, SNP) single crystal. It is not a usual charge density paper but a report on a new way to collect accurate data; therefore we did not analyse our data via topological analysis but compared our deformation densities with the existing excellent published data respectively collected with CCD APEXII and CAD4 diffractometers (Nelyubina et al, 2008;Pressprich et al, 1994).…”