Synthesis and characterisation of unsymmetrical Schiff bases derived from 3,4-diaminopyridine. Crystal and molecular structure of hydrogen-bonded dimers of 3-{[(4-aminopyridin-3-yl)amino]methylene}pentane-2,4-dione

Synthesis, characterization, and thermodynamics of some new unsymmetrical Schiff bases of salicylaldehyde with 3,4-diaminopyridine and their cobalt(III) complexes

Some new Schiff bases derived from 3,4-diaminopyridine (3,4-DAP) and their new unsymmetrical Co(III) five coordinate complexes described as [Co(Chel)(L)]ClO4⋅H2O where (Chel) is the deprotonated form of a series of unsymmetric ligands containing 3,4-diaminopyridine (3,4-DAP) and substituted salicylaldehyde moieties and a new Co(III) six coordinate Co(III) complex, were synthesized and characterized by (1)H NMR, IR, UV-Vis, and elemental analysis. For the new synthesized five coordinate complexes, the formation constants of the interaction of the Co(III) Schiff bases with various donors were measured spectrophotometrically. The trend of the formation constants of the five coordinate Co(III) Schiff base complexes toward a given phosphine is as follow: 5-H>5-Br and the formation constants trend of these donors are as follow: PBu3>PPh2Me. Furthermore the adduct formation of the five coordinate [Co(3,4-Salpyr)(PBu3)] ClO4⋅H2O, with aromatic amines shows the following binding trend: Im>2-MeIm>2-EtIm>BzIm. The trend of the formation constants of Co(III) Schiff base complexes toward a given donor according to the phosphine axial ligand is as follow: PBu3>PPh2Me.

3,4-Diamino-pyridinium 4-nitro-benzoate-4-nitro-benzoic acid (1/1)

In the title compound, C₅H₈N₃⁺·C₇H₄NO₄⁻·C₇H₅NO₄, the non-H atoms of the 3,4-diamino­pyridinium cation are coplanar, with a maximum deviation of 0.022 (1) Å. The carboxyl­ate and nitro groups of the 4-nitro­benzoate anion are twisted out of the attached ring planes by dihedral angles of 15.89 (8) and 10.20 (8)°, respectively. In the 4-nitro­benzoic acid mol­ecule, the carboxyl and nitro groups form dihedral angles of 18.25 (8) and 6.55 (8)°, respectively, with the benzene ring. In the crystal, the constituent units form two-dimensional networks parallel to (001) by O—H⋯O, N—-H⋯O and C—H⋯O hydrogen bonds. Weak π–π inter­actions involving inversion-related 4-nitro­benzoic acid mol­ecules [centroid–centroid distance = 3.7325 (8) Å] and inversion-related 4-nitro­benzoate mol­ecules [centroid–centroid distance = 3.7124 (8) Å] are also observed.

3,4-Diamino-pyridinium hydrogen succinate

In the title compound, C₅H₈N₃⁺·C₄H₅O₄⁻, the pyridine N atom of the 3,4-diamino­pyridine mol­ecule is protonated. The protonated N atom participates in an N—H⋯O hydrogen bond to a succinate O atom of the singly deprotonated succinate anion. Each of the two amino groups are hydrogen-bonded to the O atoms of two different sets of succinate groups.. The crystal structure is further stabilized by O—H⋯O and C—H⋯O hydrogen bonds.

The molecular structure and vibrational spectra of 3-acetyl-4-[N-(2'-aminopyridinyl)-3-amino]-3-buten-2-one by Hartree-Fock and density functional theory calculations

The molecular structure and vibrational spectra of 3-acetyl-4-[N-(2'-aminopyridinyl)-3-amino]-3-buten-2-one (C(11)H(13)N(3)O(2)) in the ground state have been investigated by Hartree-Fock and density functional method (B3LYP and BLYP) with 6-31G(d) basis set. The optimized geometric bond lengths and bond angles obtained by using HF and DFT show the best agreement with the experimental data. Comparison of the observed fundamental vibrational frequencies of title compound and calculated results by HF and DFT methods indicate that B3LYP is superior to the scaled HF approach for molecular problems.