Correlation between proton transfer and (35)Cl NQR frequency as well as molecular geometry of chloranilic acid in co-crystals with some organic bases

Crystal structures of two hydrogen-bonded compounds of chloranilic acid-ethyl-eneurea (1/1) and chloranilic acid-hydantoin (1/2)

The structures of the hydrogen-bonded 1:1 co-crystal of chloranilic acid (systematic name: 2,5-di-chloro-3,6-dihy-droxy-1,4-benzo-quinone) with ethyl-eneurea (systematic name: imidazolidin-2-one), C6H2Cl2O4·C3H6N2O, (I), and the 1:2 co-crystal of chloranilic acid with hydantoin (systematic name: imidazolidine-2,4-dione), C6H2Cl2O4·2C3H4N2O2, (II), have been determined at 180 K. In the crystals of both compounds, the base mol-ecules are in the lactam form and no acid-base inter-action involving H-atom transfer is observed. The asymmetric unit of (I) consists of two independent half-mol-ecules of chloranilic acid, with each of the acid mol-ecules lying about an inversion centre, and one ethyl-eneurea mol-ecule. The asymmetric unit of (II) consists of one half-mol-ecule of chloranilic acid, which lies about an inversion centre, and one hydantoin mol-ecule. In the crystal of (I), the acid and base mol-ecules are linked via O-H⋯O and N-H⋯O hydrogen bonds, forming an undulating sheet structure parallel to the ab plane. In (II), the base mol-ecules form an inversion dimer via a pair of N-H⋯O hydrogen bonds, and the base dimers are further linked through another N-H⋯O hydrogen bond into a layer structure parallel to (01). The acid mol-ecule and the base mol-ecule are linked via an O-H⋯O hydrogen bond.

Crystal structures of two 1:2 dihydrate compounds of chloranilic acid with 2-carb-oxy-pyridine and 2-carb-oxy-quinoline

The crystal structure of the 1:2 dihydrate compound of chloranilic acid (systematic name: 2,5-di-chloro-3,6-dihy-droxy-1,4-benzo-quinone) with 2-carb-oxy-pyridine (another common name: picolinic acid; systematic name: pyridine-2-carb-oxy-lic acid), namely, 2C6H5.5NO20.5+·C6HCl2O4-·2H2O, (I), has been determined at 180 K, and the structure of the 1:2 dihydrate compound of chloranilic acid with 2-carb-oxy-quinoline (another common name: quinaldic acid; systematic name: quinoline-2-carb-oxy-lic acid), namely, 2C10H7NO2·C6H2Cl2O4·2H2O, (II), has been redetermined at 200 K. This determination presents a higher precision crystal structure than the previously published structure [Marfo-Owusu & Thompson (2014 ▸). X-ray Struct. Anal. Online, 30, 55-56]. Compound (I) was analysed as a disordered structure over two states, viz. salt and co-crystal. The salt is bis-(2-carb-oxy-pyridinium) chloranilate dihydrate, 2C6H6NO2+·C6Cl2O42-·2H2O, and the co-crystal is bis-(pyridinium-2-carboxyl-ate) chloranilic acid dihydrate, 2C6H5NO2·C6H2Cl2O4·2H2O, including zwitterionic 2-carb-oxy-pyridine. In both salt and co-crystal, the water mol-ecule links the chloranilic acid and 2-carb-oxy-pyridine mol-ecules through O-H⋯O and N-H⋯O hydrogen bonds. The 2-carb-oxy-pyridine mol-ecules are connected into a head-to-head inversion dimer by a short O-H⋯O hydrogen bond, in which the H atom is disordered over two positions. Compound (II) is a 1:2 dihydrate co-crystal of chloranilic acid and zwitterionic 2-carb-oxy-quinoline. The water mol-ecule links the chloranilic acid and 2-carb-oxy-quinoline mol-ecules through O-H⋯O hydrogen bonds. The 2-carb-oxy-quinoline mol-ecules are connected into a head-to-tail inversion dimer by a pair of N-H⋯O hydrogen bonds.

Crystal structures of three hydrogen-bonded 1:2 compounds of chloranilic acid with 2-pyridone, 3-hy-droxy-pyridine and 4-hyroxypyridine

The crystal structures of the 1:2 compounds of chloranilic acid (systematic name: 2,5-di-chloro-3,6-dihy-droxy-1,4-benzo-quinone) with 2-pyridone, 3-hy-droxy-pyridine and 4-hyroxypyridine, namely, bis-(2-pyridone) chloranilic acid, 2C5H5NO·C6H2Cl2O4, (I), bis-(3-hy-droxy-pyridinium) chloranilate, 2C5H6NO+·C6Cl2O42-, (II), and bis-(4-hy-droxy-pyridinium) chloranilate, 2C5H6NO+·C6Cl2O42-, (III), have been determined at 120 K. In the crystal of (I), the base mol-ecule is in the lactam form and no acid-base inter-action involving H-atom transfer is observed. The acid mol-ecule lies on an inversion centre and the asymmetric unit consists of one half-mol-ecule of chloranilic acid and one 2-pyridone mol-ecule, which are linked via a short O-H⋯O hydrogen bond. 2-Pyridone mol-ecules form a head-to-head dimer via a pair of N-H⋯O hydrogen bonds, resulting in a tape structure along [201]. In the crystals of (II) and (III), acid-base inter-actions involving H-atom transfer are observed and the divalent cations lie on an inversion centre. The asymmetric unit of (II) consists of one half of a chloranilate anion and one 3-hy-droxy-pyridinium cation, while that of (III) comprises two independent halves of anions and two 4-hy-droxy-pyridinium cations. The primary inter-molecular inter-action in (II) is a bifurcated O-H⋯(O,O) hydrogen bond between the cation and the anion. The hydrogen-bonded units are further linked via N-H⋯O hydrogen bonds, forming a layer parallel to the bc plane. In (III), one anion is surrounded by four cations via O-H⋯O and C-H⋯O hydrogen bonds, while the other is surrounded by four cations via N-H⋯O and C-H⋯Cl hydrogen bonds. These inter-actions link the cations and the anions into a layer parallel to (301).

Temperature dependence of one-dimensional hydrogen bonding in morpholinium hydrogen chloranilate studied by 35Cl nuclear quadrupole resonance and multi-temperature X-ray diffraction

The temperature dependence of (35)Cl NQR frequencies and the spin-lattice relaxation times T(1) has been measured in the wide temperature range of 4.2-420 K for morpholinium hydrogen chloranilate in which a one-dimensional O-HO hydrogen-bonded molecular chain of hydrogen chloranilate ions is formed. An anomalous temperature dependence of the NQR frequencies was analyzed to deduce a drastic temperature variation of the electronic state of the hydrogen-bonded molecular chain. The hydrogen atom distribution in the OHO hydrogen bond is discussed from the results of NQR as well as multi-temperature X-ray diffraction. Above ca. 330 K, the T(1) showed a steep decrease with an activation energy of ca. 70 kJ mol(-1) and with an isotope ratio (37)Cl T(1)/(35)Cl T(1) = 0.97 ± 0.2. The orientational change of the z axis of electric field gradient tensor in conjunction with the hydrogen transfer between adjacent hydrogen chloranilate ions is suggested as a possible relaxation mechanism.