Three Polymorphic Forms of the Co‐Crystal 4,4′‐Bipyridine/Pimelic Acid and their Structural, Thermal, and Spectroscopic Characterization

Abstract

Three crystal forms of the co-crystal 4,4'-bipy/pimelic acid (bipy: bipyridine), [NH(4)C(5)-C(5)H(4)N][HOOC(CH(2))(5)COOH], have been prepared and their relationship investigated by single-crystal X-ray diffraction, variable-temperature X-ray powder diffraction, differential scanning calorimetry and solid-state NMR spectroscopy. Both X-ray and NMR spectroscopic results indicate that no proton transfer takes place, that is, the three crystal forms are true co-crystals of neutral molecules. Forms I and II both convert into Form III at high temperature, Forms II and III being the thermodynamically stable forms at room and high temperature, respectively.

A Molecular Antenna Coordination Polymer from Cadmium(II) and 4,4’-Bipyridine Featuring Three Distinct Polymer Strands in the Crystal

“…As expected, the spectrum exhibits three groups of lines, which are assigned according to Osborne [51] (solution NMR) and Braga et al [52] (solid-state NMR). The spectrum of 4,4'-bipy in 1 is well-resolved, in stark contrast to that obtained for co-crystals containing 4,4'-bipy [52], pure solid anhydrous 4,4'-bipy (Figure 7(b)) and 4,4'-bipy dihydrate (Figure 7(c)).…”

“…As expected, the spectrum exhibits three groups of lines, which are assigned according to Osborne [51] (solution NMR) and Braga et al [52] (solid-state NMR). The spectrum of 4,4'-bipy in 1 is well-resolved, in stark contrast to that obtained for co-crystals containing 4,4'-bipy [52], pure solid anhydrous 4,4'-bipy (Figure 7(b)) and 4,4'-bipy dihydrate (Figure 7(c)). The ill-resolved lines observed for pure solid anhydrous 4,4'-bipy and 4,4'-bipy dihydrate cannot be due to the formation of amorphous phases, since samples from the same batches were shown to be crystalline by independent PXRD and single-crystal diffraction investigations.…”

Solid‐State NMR Studies on Supramolecular Chemistry

“…44 In the HB characterization 1D spectra give information concerning the HB presence, the hydrogen-bonded atom position, and the strengh of the interaction, while 2D 1 H DQ MAS experiments provide elucidation of HB geometries and networks. This is the case of the three crystal forms of the cocrystal 4,4 -bipy/pimelic acid (bipy = bipyridine), [NH 4 C 5 -C 5 H 4 N]-[HOOC(CH 2 ) 5 COOH], where their relationship have been investigated by comparing single-crystal X-ray diffraction and 1 H DQ MAS SSNMR experiments. 5 Xray diffraction supplied packing and conformation of the molecules while 1 H DQ MAS spectra provided new parameters for differencing the polymorphs and for elucidating the HB network.…”

“…By fitting the experimental data with a twofold flipping model (180 • rotation), the Arrhenius analysis of the exchange rate affords an activation energy of 11.3 ± 2.0 Kcal mol −1 . distinct motions, ranging from simple C 6 -rotations of benzene-d 6 at low temperatures to rather ill-defined 180 • phenyl flips of fluorobenzene-d 5 . 67 The large CSA associated with the carbonyl resonances in the 13 C cross polarization magic angle spinning (CPMAS) spectrum at room temperature of crystalline Cr(CO) 3 (η 6 -C 6 H 6 ) indicates that the carbonyl moieties are rigid due to crystalline packing constraints.…”

“…and heteronuclear ( 1 H- 13 C and 1 H-31 P, 13 C-15 N, etc.) proximities or distances from 2D spectra 4,5 or from redor-like experiments 6 ; 4. the wide range of the timescale of motions that can be investigated at variable temperature (VT) with a large set of different NMR parameters. 7 Owing to all these possibilities the NMR techniques have been used in many aspects of supramolecular chemistry: from biological (protein, polypeptide, etc.)…”