Anion–Cation Recognition Pattern, Thermal Stability and DFT-Calculations in the Crystal Structure of H2dap[Cd(HEDTA)(H2O)] Salt (H2dap = H2(N3,N7)-2,6-Diaminopurinium Cation)

Abstract

The proton transfer between equimolar amounts of [Cd(H 2 EDTA)(H 2 O)] and 2,6-diaminopurine (Hdap) yielded crystals of the out-of-sphere metal complex H 2 (N3,N7)dap [Cd(HEDTA)(H 2 O)]·H 2 O (1) that was studied by single-crystal X-ray diffraction, thermogravimetry, FT-IR spectroscopy, density functional theory (DFT) and quantum theory of "atoms-in-molecules" (QTAIM) methods. The crystal was mainly dominated by H-bonds, favored by the observed tautomer of the 2,6-diaminopurinium(1+) cation. Each chelate anion was H-bonded to three neighboring cations; two of them were also connected by a symmetry-related anti-parallel π,π-staking interaction. Our results are in clear contrast with that previously reported for H 2 (N1,N9)ade [Cu(HEDTA) (H 2 O)]·2H 2 O (EGOWIG in Cambridge Structural Database (CSD), Hade = adenine), in which H-bonds and π,π-stacking played relevant roles in the anion-cation interaction and the recognition between two pairs of ions, respectively. Factors contributing in such remarkable differences are discussed on the basis of the additional presence of the exocyclic 2-amino group in 2,6-diaminopurinium(1+) ion. Crystals 2020, 10, 304 2 of 15 reported analog of adenine, [Cu(HEDTA)(H 2 O)]·2H 2 O [5,32], was also performed. The H-bonding networks that are established at both faces of H 2 dap were also studied using DFT calculations and the relative strength of each H-bond was estimated using the QTAIM theory. The antiparallel π,π-stacking interactions that were formed between the cations were also studied, focusing on the effect of the counter-ions. Materials and Methods ReagentsH 4 EDTA acid (TCI), Hdap (Alfa Aesar) and CdCO 3 (Alfa Aesar) were used as received. CrystallographyA colorless needle crystal of H 2 dap[Cd(HEDTA)(H 2 O)]·H 2 O (1) was mounted on a glass fiber and used for data collection. Crystal data were collected at 100(2) K, using a Bruker D8 VENTURE PHOTON III-14 diffractometer. Graphite-monochromated MoK(α) radiation (λ = 0.71073 Å) was used throughout. The data were processed with APEX2 [33] and corrected for absorption using SADABS (transmissions factors: 1.000-0.962) [34]. The structure was solved by direct methods using the program SHELXS-2013 [35] and refined by full-matrix least-squares techniques against F 2 using SHELXL-2013 [35]. Positional and anisotropic atomic displacement parameters were refined for all non-hydrogen atoms. Hydrogen atoms were located in difference maps and included as fixed contributions riding on attached atoms with isotropic thermal parameters 1.2/1.5 times those of their carrier atoms. Criteria of a satisfactory complete analysis were the ratios of 'rms' shift to standard deviation less than 0.001 and no significant features in final difference maps. Atomic scattering factors were taken from the International Tables for Crystallography [36]. Molecular graphics were plotted with PLATON [37]. A summary of the crystal data, experimental details and refinement results are listed in Table 1. Crystallographic data for 1 has been deposited in the Cambridg...

Аминоацетатные, Аминодиацетатные, Аминотриацетатные И Этилендиаминтетраацетатные Электролиты Кадмирования

“…В системе Cd 2+ − H2NCH2COOH -H2O наблюдаются следующие равновесия комплексообразования: [18,19]. По дан-ным [20] [32]. Во всех известных этилендиаминтетраацетатах катион кадмия(+2) проявляет к. ч.…”

Novel Cd (II) Coordination Polymers Afforded with EDTA or Trans-1,2-Cdta Chelators and Imidazole, Adenine, or 9-(2-Hydroxyethyl) Adenine Coligands

“…A bond path and bond critical point (CP) interconnecting two atoms can be used as an unambiguous indication of interaction [26]. Moreover, this type of analysis has been recently used in similar systems [27][28][29][30][31]. The distribution of bond CPs and bond paths of the two motifs analyzed above are shown in Figure 14.…”

σ- and π-Hole Interactions

“…In reference [24], Belmont-Sanchez et al reported the synthesis and X-ray characterization of several out-of-sphere cadmium complexes with 2,6-diaminopurine. The crystal packing of these compounds is mostly dominated by H-bonds, which were analyzed by using DFT calculations.…”