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Three new coordination polymers, [NaI(H2L)(H2O)3]n (1), {[KI(H2L)(H2O)]8·13H2O}n (2), and {[NiIINaI2(HL)2(H2O)8]·6H2O}n (3), were assembled from 1,3-dimethyl-5-(p-sulfonic-phenylazo)-6-aminouracil (H3L) as a versatile building block. Although azo-coupling reactions generally result in simple azo-compounds, the presence of the sulfonate (–SO3−) group at the ligand frame led to the formation of the NaI-1D (1) or KI-3D (2) homometallic coordination polymer with different ligand coordination modes. Moreover, the heterometallic NiII/NaI-1D (3) coordination polymer was obtained while carrying the reaction of 2 with NiCl2·6H2O. The structures of the obtained products were fully established by single crystal X-ray diffraction and confirmed by standard methods. Compounds 1 and 3 possess 1D metal–organic chains with the 2C1 topology, whereas 2 features a very complex 3D metal–organic architecture with an unprecedented topology. The computational study for molecular electrostatic potential (MEP) surface energies revealed an important finding, namely a decrease of the π-acidity of the uracil ring upon coordination and a consequent increase of the π-basicity of the phenyl-sulfonate ring, resulting in effective anti-parallel π–π stacking interactions in 1 and 2. Finally, a semi-conductive behavior of the obtained compounds was explored using impedance spectroscopy, revealing the very remarkable conductive properties of 1 (2.2 × 10−4 S cm−1), which is a far better conductive material than 2 (7.2 × 10−6 S cm−1) and 3 (4.8 × 10−7 S cm−1). The obtained products represent the first coordination compounds derived from H3L. This study contributes to the design of functional coordination polymers driven by still poorly explored 6-aminouracil building blocks. [ABSTRACT FROM AUTHOR]

In this research paper we report synthesis of two planar ligands, namely 1,3-dimethyl-5-(4ʹ/3ʹ-pyridylazo)-6-aminouracil: HL1 (1 ) for 4ʹ-pyridyazo- and HL2 ( 2 ) for 3ʹ-pyridyazo-group and, moreover, their nickel (II) square planar complexes ([Ni II (L1) 2 ] ( 3 ) and ([Ni II (L2) 2 ] ( 4 )). The report is also included solid and solution state structure of the compounds and study of noncovalent stacking interactions. Crystal structures of the ligands, 1 and 2 are monoclinic with alike space group P 2 1 / c and the complex 3 is also monoclinic with space group C 2/ c . The molecular electrostatic potential (MEP) analysis shows that the ligands possess both π-basic and π-acid character in the same framework over the center of the pyridine and the pyrimidine rings, respectively, favoring electrostatically enhanced π-π stacking interaction among the molecular units. Upon complexation, π-acidity of the pyrimidine ring increases, and the complex 3 exhibits lone pair (lp)-π stacking interaction involving lone pair of the pyridine N-atom and π-acid pyrimidine plane. The study evidences that the ligands exist in azo-enamine-keto tautomer in solid and hydrazone-imine-keto in solution state and get coordinated with nickel (II) via azo- N and uracil-6- N H , to form a distorted square planar complex. Electronic absorption bands/energies obtained from experimental and theoretical (TDDFT) study are indeed alike, giving reliability to the level of theory and the absorption band assignments. Moreover, the synthesized compounds containing uracil and pyridine fragments exhibit π-π/lp-π interactions with considerable energy for stabilization of their assemblies in the solid state. [ABSTRACT FROM AUTHOR]

Some of our group recently demonstrated combining theory and a statistical survey of the Cambridge Structural Database (CSD) that the interaction between the π-holes of nitro groups and electron-rich atoms is somewhat directional (Chem. Commun., 2015, 51, 1491–1493). In this communication, we present a joint experimental and theoretical study on a novel cadmium(ii) complex, [Cd(C7H3N2O6)2(C12H8N2)2]·H2O·DMF (1) [where C7H4N2O6 = 3,5-dinitrobenzoic acid and C12H8N2 = 1,10-phenanthroline] to unravel the important role of this π-hole interaction. [ABSTRACT FROM AUTHOR]