Structural Diversity, Thermal Studies, and Luminescent
Properties of Metal Complexes of Dinitrobenzoates: A Single Crystal
to Single Crystal Transformation from Dimeric to Polymeric Complex
of Copper(II)
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Abstract
Seventeen
complexes of 3,5- and 2,4-dinitrobenzoates (<b>L1</b>–<b>L2</b>) with alkali, alkaline, and transition metals have been
synthesized and characterized by the single crystal X-ray diffraction,
IR spectroscopy, elemental analysis, and thermal studies. Diverse
structural topologies have been achieved due to various coordination
modes of the benzoates, resulting in five new topologies. Interesting
architectures such as zero-dimensional (0D) monomers and paddle-wheel
dimers; pseudocubane, double helices, ladders and linear one-dimensional
(1D) tapes; pseudodiamondoid and brick-wall type two-dimensional (2D);
and chiral three-dimensional (3D) networks were generated. The latter
three are formed by the coparticipation of −NO<sub>2</sub> groups
in the coordination, while 1D complexes are formed by the coordination
of water/solvent. Thermogravimetric analysis studies show that the
3D complexes are more stable than 2D; however, 1D complexes become
more stable than 2D after the loss of the solvent. The effects of
positional isomerism and
the nature of the metal ions on the topology also have been observed.
The ligands are nonemissive but nine complexes have shown a moderate
amount of photoluminescence, owing to the rigidity conferred by the
crystal structure of the complex, which largely reduces the radiation
less decay and results in enhancement of the intensity of the ligand
to ligand charge transfer (LLCT) band. A relatively much larger photoluminescence
in the polymeric complex (<b>VIII</b>) of copper(II), however,
is a combination of enhanced LLCT due to the double helical 1D crystal
structure and chelation enhanced fluorescence (CHEF) phenomenon. A
single crystal to single crystal supramolecular transformation of
a paddle-wheel complex of copper(II) with guest solvent molecules
in the lattice to a desolvated 1D polymer is achieved for the Cu<b>L1</b> complex. Because of self-assembly, six of these complexes
crystallize as homochiral, single, double, or triple helical conglomerates,
which constitute the most active expression of chirality