Crystalline Peroxosolvates: Nature of the Coformer, Hydrogen-Bonded Networks and Clusters, Intermolecular Interactions

Abstract

Despite the technological importance of urea perhydrate (percarbamide) and sodium percarbonate, and the growing technological attention to solid forms of peroxide, fewer than 45 peroxosolvates were known by 2000. However, recent advances in X-ray diffractometers more than tripled the number of structurally characterized peroxosolvates over the last 20 years, and even more so, allowed energetic interpretation and gleaning deeper insight into peroxosolvate stability. To date, 134 crystalline peroxosolvates have been structurally resolved providing sufficient insight to justify a first review article on the subject. In the first chapter of the review, a comprehensive analysis of the structural databases is carried out revealing the nature of the co-former in crystalline peroxosolvates. In the majority of cases, the coformers can be classified into three groups: (1) salts of inorganic and carboxylic acids; (2) amino acids, peptides, and related zwitterions; and (3) molecular compounds with a lone electron pair on nitrogen and/or oxygen atoms. The second chapter of the review is devoted to H-bonding in peroxosolvates. The database search and energy statistics revealed the importance of intermolecular hydrogen bonds (H-bonds) which play a structure-directing role in the considered crystals. H2O2 always forms two H-bonds as a proton donor, the energy of which is higher than the energy of analogous H-bonds existing in isostructural crystalline hydrates. This phenomenon is due to the higher acidity of H2O2 compared to water and the conformational mobility of H2O2. The dihedral angle H-O-O-H varies from 20 to 180° in crystalline peroxosolvates. As a result, infinite H-bonded 1D chain clusters are formed, consisting of H2O2 molecules, H2O2 and water molecules, and H2O2 and halogen anions. H2O2 can form up to four H-bonds as a proton acceptor. The third chapter of the review is devoted to energetic computations and in particular density functional theory with periodic boundary conditions. The approaches are considered in detail, allowing one to obtain the H-bond energies in crystals. DFT computations provide deeper insight into the stability of peroxosolvates and explain why percarbamide and sodium percarbonate are stable to H2O2/H2O isomorphic transformations. The review ends with a description of the main modern trends in the synthesis of crystalline peroxosolvates, in particular, the production of peroxosolvates of high-energy compounds and mixed pharmaceutical forms with antiseptic and analgesic effects.

Comparison of Proton Acceptor and Proton Donor Properties of H2O and H2O2 in Organic Crystals of Drug-like Compounds: Peroxosolvates vs. Crystallohydrates

“…The detailed analysis of these crystals’ structures is given in Tables S1 and S2 of Ref. [ 28 ]. After excluding structures with structurally disordered H 2 O 2 molecules and structures with non-alkaline metals, the number of peroxosolvates decreased to 56.…”

“…More universal approaches use the frequency shifts of the O-H stretching vibrations [ 24 ], the H∙∙∙O distance [ 25 , 26 ] and the electron density at the bond critical point [ 27 ]. The pros and cons of various schemes for E HB /Δ H HB estimating are given elsewhere [ 28 ]. In the present study, the Δ H HB values were evaluated using the Rozenberg equation [ 25 ]: –Δ H HB [kJ mol −1 ] = 0.134· R (H∙∙∙O) −3.05 , where the R (H∙∙∙O) is the H∙∙∙O distance (nm).…”

Molecular Dynamics Simulation of Association Processes in Aqueous Solutions of Maleate Salts of Drug-like Compounds: The Role of Counterion

“…Various approaches can be used to estimate the enthalpy and energy of intermolecular H-bonds, for example, see [ 80 ]. In the present work, we used approaches that explore the metric [ 81 ] and spectroscopic [ 82 ] characteristics of this bond, calculated using the B3LYP/6-31G** level in the PCM approximation ( Section 3.2 ).…”

Solid State NMR for Nonexperts: An Overview of Simple but General Practical Methods

“…This review includes only a very limited number of examples of simple static calculations of NMR parameters using the density functional theory (DFT). More detailed descriptions of these and advanced methods can be found elsewhere [19][20][21][22][23].…”