Investigation of Guest-Dependent Dielectric Behavior of Chiral Metal-Organic Frameworks and Supramolecular Compounds
Date Issued
2014
Date
2014
Author(s)
Mendiratta, Shruti
Abstract
A series of chiral metal-organic frameworks (MOFs) and supramolecular compounds were synthesized by reacting nitrogen containing ligands with transition metal salts and their dielectric behavior was investigated. The structures of these compounds range from one dimensional zig-zag chains to three dimensional structures. Compounds 1~4 were found to be chiral, with two dimensional structures. Compounds {[Zn2(L-trp)2(bpe)2(H2O)2]‧2H2O‧2NO3}n (1), {[Co(L-trp)(bpe)(H2O)]‧H2O‧NO3}n (2) and {[Co(L-trp)(bpa)(H2O)]‧H2O‧NO3}n (3) displayed a common framework with a rectangle- like (4,4) topology, whereas compound [Zn2(Hbbim)2(bbim)]n (4) has a honeycomb structure with a (6,3) connected net. Compound {{[Mn(bbim)(H2bbim)]‧CH3OH}{[Mn(bbim)(H2bbim)]‧ H2O}}n (5) was found to be a one dimensional coordination polymer with a zig-zag chain structure. Compound [Mg(phen)(bdc)]n (6) was a guest free 3D compound and serves as a rare example of a cds-type framework. Compounds {[Ni2(bbim)(H2bbim)4]‧2CH3COO‧CH3CN}2 (7), {[Ni(H2bbim)3]‧2Cl‧2H2O} (8) and D/L-{[Cr(Hbbim)3]‧3H2O} (9), were supramolecular compounds forming extended structures via extensive hydrogen-bonding with the guest molecules. The racemic compound D/L-{[Cr(Hbbim)3]‧3H2O} (9) had a very unique molecular-propeller structure, in which the D/L-molecular propellers were glued together by rare water tetrahedrons. Astonishingly, the packing arrays formed by the enantiomeric propellers of one chirality were interpenetrated with those of the opposite chirality to form specific 3D supramolecular arrays with 103 nets and srs topology. This chiral discrimination and self-assembly between enantiomers of the same chirality on a supramolecular level has never been reported to date.
We investigated the dielectric properties of the compounds prepared in this thesis. Compounds 1 and 4 were found to be third generation low-κ dielectric materials. The dielectric constant (κ = 2.53 at 1 MHz) of 1 was found to be comparable to zeolitic imidazolate frameworks (ZIFs). Its unique anion controlled dielectric behavior is demonstrated for the first time, in which the dielectric constant increases with increasing polarization of the anion. In addition, compound 1 was found to be a good luminescent material (with a green emission at 546 nm) and a modest non-linear optical material in which the second harmonic generation (SHG) efficiency was about twice that of SiO2. Remarkably, the κ value of compound 4 was found to be even lower than the reported ZIFs, owing to the presence of an interlayer free space and the absence of guest molecules. It is a very useful low-κ dielectric material which is highly thermally stable. Frequency dependent dielectric studies for compounds 7 and 8 revealed a significant difference in the value of dielectric constant (κ) and dielectric loss for the two compounds owing to differences in structure and the type of solvent molecules. This fundamental, structure-based study provides insights into the creation of both high and low-κ materials with the judicious selection of guest molecules.
Subjects
有機配位化合物
蜂巢
Type
thesis
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