ABSTRACT
(1)H NMR studies on di-2-pyridyl ketone p-aminobenzoylhydrazone hydrate (dpkabh.H(2)O) in non-aqueous solvents show high sensitivity to its surrounding. In protophilic solvents (d(6)-dmso or d(7)-dmf), the amine protons are equivalent, while in CDCl(3) they are not. Variable temperature analysis in CDCL(3) show the NH proton to exhibit high temperature dependence due to strong intra-molecular hydrogen bonding of the type N-H...N between the amide (NH) and N atom of a pyridine ring. The temperature dependence for the same proton in d(6)-dmso and d(7)-dmf is due to hydrogen bonding of the type N-H...O between the amide proton and oxygen atom of the solvent. Optical measurements on dpkabh.H(2)O show one intra-ligand charge transfer (ILCT) transition in CH(2)Cl(2) and in protophilic solvents, two ILCT of the donor-acceptor type due to dpkabh.H(2)O and its conjugate base appeared. Variable temperature studies on protophilic solution of dpkabh.H(2)O confirm the sensitivity of dpkabh.H(2)O to its surroundings and show facile reversible inter-conversion between dpkabh.H(2)O and its conjugate base. Changes in enthalpy (DeltaH(phi)) of -5.2+/-0.4 and -24.2+/-1.20 kJ mol(-1), entropy (DeltaS(phi)) of +9.6+/-0.5 and -63.0+/-2.0 JK(-1) mol(-1), and free energy (DeltaG(phi)) of +2.3+/-0.2 and +5.4+/-0.2 kJ mol(-1) were calculated for dpkabh.H(2)O at 298 K in dmso and dmf, respectively. When stoichiometric amounts of NaBH(4) or MCl(2) (M=Zn, Cd or Hg) were added to protophilic solution of dpkanh.H(2)O conversion from the high to low energy electronic transition was observed and show that substrates in low concentrations can be detected and determined using protophilic solution of dpkabh.H(2)O.
Subject(s)
Hydrazones/chemistry , Pyridines/chemistry , Solvents/chemistry , Acids/chemistry , Alkalies/chemistry , Magnetic Resonance Spectroscopy , Models, Molecular , Spectrum Analysis , Temperature , ThermodynamicsABSTRACT
A new polymorph of di-2-pyridyl ketone 4-nitrophenylhydrazone [alternative name: N-(dipyridin-2-ylmethylene)-N'-(4-nitrophenyl)hydrazine], C17H13N5O2, isolated from the filtrate of a sonicated acetonitrile solution of dpknph and CdCl2, was found to crystallize in the monoclinic space group P21/c, in contrast to the known form which crystallizes in P21/n. The non-coplanar molecules pack in parallel stacks without any intermolecular hydrogen-bonding interactions. This packing pattern contrasts with the interlocked interdigitated packing seen in the previously known polymorph.
ABSTRACT
The compound di-2-thienyl ketone p-nitrophenylhydrazone (DSKNPH) melting point 168-170 degrees C was isolated in good yield from the reaction between di-2-thienyl ketone (DSK) and p-nitrophenylhydrazine in refluxing ethanol containing a few drop of concentrated HCl. Nuclear magnetic resonance studies on DSKNPH in non-aqueous solvents revealed strong solvent and temperature dependence due to solvent-solute interactions. Optical measurements on DSKNPH in DMSO in the presence and absence of KPF(6) gave extinction coefficients of 83,300+/-2000 and 25,600+/-2000M(-1)cm(-1) at 612 and 427nm at 295K. In CH(2)Cl(2), extinction coefficient of 34,000+/-2000M(-1)cm(-1) was calculated at 422nm. When DMSO solutions of DSKNPH were allowed to interact with DMSO solutions of NaBH(4) the low energy electronic state becomes favorable and when DMSO solutions of DSPKNPH where allowed to interact with DMSO solutions of KPF(6) or NaBF(4), the high energy electronic state becomes favorable. The reversible BH(4)(-)/BF(4)(-) interconversion points to physical interactions between these species and DSKNPH and hints to the possible use of DSKNPH as a spectrophotometric sensor for a variety of physical and chemical stimuli. Thermo-optical measurements on DSKNPH in DMSO confirmed the reversible interconversion between the high and low energy electronic states of DSKNPH and allowed for the calculations of the thermodynamic activation parameters of DSKNPH. Changes in enthalpy (DeltaH(slashed circle)) of +57.67+/-4.20; 27.15+/-0.90kJmol(-1), entropy (DeltaS(slashed circle)) of +160+/-12.88; 83+/-2.91Jmol(-1) and free energy (DeltaG(slashed circle)) of -8.52+/-0.40; 2.66+/-0.25kJmol(-1) were calculated at 295K in the absence and presence of NaBH(4), respectively. Manipulation of the equilibrium distribution of the high and low energy electronic states of DSKNPH allowed for the use of these systems (DSKNPH and surrounding solvent molecules) as molecular sensors for group I and II metal ions. Group I and II metal ions in concentrations as low as 1.00x10(-5) M can be detected and determined using DSKNPH in DMSO.
ABSTRACT
The title compound [systematic name: 4-amino-2'-(di-2-pyridylmethylene)benzohydrazide hydrate], C(18)H(15)N(5)O.H(2)O, crystallizes in the triclinic space group P-1. Structural analysis shows one pyridine ring and the p-aminobenzoylhydrazone moiety to be coplanar and orthogonal to the second pyridine ring. The packing reveals infinite molecular units interlocked via a network of hydrogen bonds.
