Abstract:
Hybrid inorganic organic network compounds constitute an important
class of materials that have been studied extensively over the last few years due to
their potential applications in catalysis, gas separation and storage. Other
properties which draw attention to these materials include magnetic, optical and
electronic properties. An effective and widely used strategy for the design of
hybrid framework solids is based on the selection of metal and ligand geometries
to produce desired network topologies. The mode of linkage and the
dimensionality of the inorganic sub network, along with the size, geometry,
chemical functionality and various coordinating modes of the linkers, provide
excellent means of controlling and modulating the properties in these solids. In an
attempt to understand these aspects and design hybrid frameworks with novel
structural features and properties, hybrid dicarboxylates have been explored in this
thesis in terM.S. of dimensionality and extended inorganic connectivity. In pursuit of
the above understanding, benzene-, cyclohexane- and aliphatic-dicarboxylic acids
have been employed to synthesize hybrid inorganic-organic frameworks of di- and
trivalent metal ions with or without chelating amines. To understand the process of
formation of a three-dimensional zinc terephthalate, a systematic time and
temperature dependent transformation study has been carried out. Investigations
were also carried out to synthesize novel hybrid solids and nano materials by
employing ionic liquids as solvents.
After providing an brief overview on hybrid inorganic-organic frameworks
(Chapter 1), the thesis presents the results of the investigations of the hybrid
benzenedicarboxylates (BDCs) of the three isomeric (1,2-, 1,3- and 1,4-)
benzenedicarboxylic acids with divalent cations of Zn, Cd, Pb and trivalent cations
of lanthanides (in Chapter 2). Several coordination polymers and the hybrids with
extended inorganic connectivity of BDCs in different dimensionality have been
prepared under hydrothermal conditions. Few of them have been doped Eu and Tb
and they exhibit the lanthanide-centered red and green emission sensitized by the
ligands at room temperature. The studies on zinc terephthalates show that a
progressive transformation of a one-dimensional structure to a three-dimensional
structure and the possible presence of a dimensional hierarchy.
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Chapter 3 presents the results of the investigations of the hybrid
cyclohexane and cyclohexenedicarboxylates (CHDCs and CHeDCs) of the three
isomeric (1,2-, 1,3- and 1,4-) flexible cyclohexanedicarboxylic acids in different
conformation with cations of Mn, Cd, Pb and La and 1,2-
cyclohex(4)enedicarboxylic acid with Cd(II) cation. Several coordination polymers
and the hybrids with extended inorganic connectivity in different dimensionality
have been prepared under hydrothermal conditions.
Chapter 4 presents the results of the investigations of the hybrid aliphaticdicarboxylates.
These novel hybrid networks with extended inorganic connectivity,
have been synthesized hydrothermally by employing single (homoleptic) and
mixture (heteroleptic) of aliphatic dicarboxylicacids with the potentially lone pair
active, flexible coordinating Pb(II) cation with larger ionic radii.
Chapter 5 presents the results of the investigations on a hybrid
dihydroxybenzoate. A novel three-dimensional coordination network of lead 2,6-
dihydroxybenzoate with (3,6) 3D net topology, has been synthesized and
characterized.
Chapter 6 presents the results of the investigations on the exploration of
ionic liquids as solvents to synthesize novel hybrid frameworks and nano
materials. Ionic liquids are salts with low melting points (<100oC), consisting of a
bulky organic cation and an organic or inorganic anion. Two imidazolium
bromoplumbates which exhibit unusual supramolecular organization with channel
structures have been obtained by heating imidazolium bromide-based ionic liquids
with lead (II) salts under ionothermal conditions. Nanocrystals, nanorods,
nanowires and nanobelts of various elemental chalcogens and metal oxides have
been synthesized by using imidazolium [BMIM]-based ionic liquids as solvents at
100 – 200 °C.