Studies on supramolecular assemblies, metal complexes of aromatic oxime derivatives for molecular and ions recognition

I declare that this thesis entitled "Studies on supramolecular assemblies, metal complexes of aromatic oxime derivatives for molecular and ion recognition" is the result of the research work carried out by me under the supervision of Prof. Baruah, in the Department of Chemistry. Indian Institute of Technology Guwahati, India. This is to prove that the research work presented in this thesis entitled "Studies on supramolecular assemblies, metal complexes of aromatic oxime derivatives for molecular and ion recognition" is an authentic record of the results obtained from the research work carried out by Mr. in the Department of Chemistry, Indian Institute of Technology Guwahati, India.

Doctoral Committee

Introduction
Chapter 2 (Part A): Anion Assisted Supramolecular Assemblies of Oxime Derivatives and Recognition of Fluoride ion
Chapter 2 (Part B): Anion Assisted Conformationally Guided Dendrimer-like Self- assemblies of Multi-component Cocrystals of Dioxime
Recognition of Aggregation Induced Emission Active Oxime Derivatives by Nitrogen Containing Compounds in Solid and Solution State
Synthesis of different cocrystals of oxime derivatives
Chapter 4 (Part A): Transition Metal Complexes of Hydroxyaromaticaldoximes and Their Interactions with Fluoride ion
Synthesis of transition metal complexes of 2,4-dihydroxybenzaldoxime
Chapter 4 (Part B): Inclusion of Aldehyde or Oxime in Cadmium Coordination Polymer and Conversion of Aldehyde to Oxime
Chapter 5: Supramoleular Aspects of Quinoline-4-carbaldoxime with Aliphatic Dicarboxylic or Mineral or Aromatic Carboxylic Acids
Chapter 6: Self-assemblies, Absorption and Emission Properties of Picrate Salts of Aromatic Amine or Heterocycle Linked Oxime Derivatives
Synthesis of different picrate salts of oxime derivatives with different protonation sites

Self-assembly of oxime-containing compounds is well studied, and necessary supramolecular properties of oxime derivatives to form non-covalently bonded self-assembly are presented in the introductory chapter. In this chapter we discussed the self-assembly, photophysical and thermal properties of pirate salts of aromatic amine or heterocyclic linked oxime derivatives.

Introduction
Synthesis of different cadmium coordination polymers of 1,3-di(pyridin-4-yl)propane ligand
Introduction
Introduction
Introductory aspects on supramolecular chemistry
Supramolecular assemblies formed by hydrogen bonds
Molecular recognition
Weak interactions in anion bound non-covalent assemblies
Neutral host for anion binding
Oxime molecules in biological systems
Different supramolecular synthons of oxime based molecules
Aakeröy and his coworkers described structural details of various oxime molecules and elucidated various oxime synthons. 73 They performed systematic structural and spectroscopic
a and b are explored for heavy metal cation binding study. The fluorescence properties associated with this oxime a and b are helpful to understand their sensing
Coordination chemistry of oxime derivatives
Scope of the present work
References

Crystal structure of oxime derivatives 2.1.1-2.1.3
Adducts of oximes 2.1.1-2.1.3 with tetrabutylammonium fluoride
Anion assisted supramolecular assemblies of oximes 2.1.1-2.1.3
b). Fluoride ions adopt tetrahedral hydrogen bond environment around them
UV-vis spectroscopic studies of oximes 2.1.1-2.1.3 with fluoride ion
Conclusions
References
Adducts of oxime 2.2.1 with different tetrabutylammonium salts

Based on the strengths of the hydrogen bonds, they are classified into three different categories, namely strong, moderate and weak hydrogen bonds. Different conformers can arise from the orientations of the active hydrogen atoms of this molecule (Fig. 2.2.1a).

Different cocrystals of oxime 2.2.1 with different tetrabutylammonium salts

a). Each chloride ion form three hydrogen bonds with hydroxy groups of oximes
Gas phase DFT calculation and 1 H-NMR studies
FT-IR and Raman spectroscopic studies
Conclusions
Experimental section
References

Asymmetric unit of the cocrystal 2.2.2 contains a tetrabutylammonium cation, a mono-deprotonated oxime anion and a neutral oxime molecule. Two oxime molecules of the cocrystal 2.2.4 consist of different conformers; one of them is H-out-out and another is H-out-in. Inclusion of water in co-crystal 2.2.4 apparently modifies the uniform dendrimer-like assembly present in co-crystal 2.2.3.

In the self-assemblies of cocrystal 2.2.3 and cocrystal 2.2.4, the coordination environment of the anions is similar (Fig. 2.2.3a and Fig. 2.2.4b), each has a distorted trigonal geometry. Because cocrystal 2.2.3 is in a 2:1 ratio between oxime 2.2.1 and TBAF, even this experiment could not distinguish the conformational change in solution. In the fluoride-assisted self-assembly of the 2.2.3 co-crystal, there are robust dimeric subassemblies formed by O-H···O interactions between two oxime molecules, while in the chloride-assisted assembly of the 2.2.4 R22 co-crystal.

Strong cyclic sub-assemblies within the self-assembly guided by strong O-H···F bonds in cocrystal 2.2.3 add value to the utility to stabilize cyclic hydrogen-bonded motifs of rigid molecules.

Emission changes through photo-induced electron transfer (PET) mechanism

Aggregation induced emission (AIE) of 2-hydroxynaphthaldoxime (2.1.1)
b). The intensity of the new emission peak at 446 nm was increased with amounts of added water to the solution and it continuously increased till the volume of water was 80%

Among various spectroscopic instruments, fluorescence spectroscopy is a very sensitive process.3 The benefit of the fluorescence emission is reflected on large intensity or wavelength shifts due to changes in weak interactions between hosts, guests, host-guest and solute-solvent interactions .4 The changes in emission on host-guest binding go through different mechanisms such as photo-induced electron transfer (PET),5 excited state intramolecular proton transfer (ESIPT),6 forster resonance energy transfer (FRET),2 internal charge transfer (ICT) ,7 chelation enhanced fluorescence (CHEF)8 etc. Among them, photoelectron transfer mechanisms are one of the many conventional mechanisms leading to enhancement or quenching of emission.5 On the other hand, exciplex and excimer formation are also common for changes in the emission of aromatic molecules.9 The conventional fluorescence processes that contribute to emission changes is shown in scheme 3.1. Interaction of the weak interactions involving hydroxy groups on hydroxyaromatic aldoximes, as seen in chapter 2, changes the hydrogen bonding patterns of oxime counterparts.

There was also drastic increase in intensity of the new peak at 446 nm with addition of water in each case. But in each case, aggregation-induced emission occurred at 446 nm, regardless of the solvents considered. The images were indicative of the changes in the sizes of the particles in DMSO and in mixed solvent of water and DMSO.

This was attributed to solvent interactions with labile OHs, which slightly change the C=N character.

Synthesis of different cocrystals of oxime derivatives 2.1.1 and 2.1.2

Structural descriptions of cocrystals 3.1-3.4
Recognition of oxime 2.1.1 or 2.1.2 in solid and solution state by nitrogen containing compounds
Conclusions

The structures of the cocrystal 3.1 of oxime 2.1.1 with 4,4'-bipyridine or HMTA possess similar O-H…N interactions as shown in Fig. 3.6a-6b; but the packing patterns of both cocrystals differ widely. 3.7, the dimeric subassemblies that were present in the packing pattern of the parent structure of oxime 2.1.2 were disrupted. The caffeine molecules in the cocrystal 3.3 are positioned on top of the oxime 2.1.1 molecule, and the internuclear distance is 3.718 Å.

The naphthalene unit of oxime 2.1.1 in cocrystal 3.3 is involved in a C-H···π interaction with the adjacent naphthalene unit present in the lattice. In each case, the angle between the 2.1.1 oxime planes is shown in the third bracket. Complete segregation of the oxime 2.1.1 molecules in cocrystal 3.3 with caffeine leads to monomer-type arrangements that show the emission.

On the other hand, the cocrystals of oxime 2.1.1 with 4,4'-bipyridine or HMTA or caffeine were easily formed.

Synthesis of transition metal complexes of oxime 2.1.3

Structural descriptions of metal(II) complexes 4.1.1-4.1.7
DMF molecules are responsible to hold the layered packing structure of the complex 4.1.5, whereas the layered packing of the complex 4.1.6 is held by intermolecular hydrogen
UV-vis and fluorescence spectroscopic studies of metal complexes of oxime with fluoride ion

But these complexes have differences in the apparent parameters of the metal-ligand bond; due to nickel ion instead of copper. Fluorescent sensors based on the high chemical affinity of fluoride ions to silicon15 or boron16 atoms have been reported in the literature. However, the position of the new peak generated by interactions with fluoride ions depends on the central metal ions.

In addition to these, we have investigated the fluorescence emission of the zinc complex 4.1.7 in different pH (Fig. 4.1.17e-f). As the concentration of fluoride ions was increased, proton transfer occurred, showing the prominent peak at 415 nm originating from the anionic form of the complex. A number of anions were tested for changes in fluorescence emission with the solution of complex 4.1.7, and also the relative sensitivity of the complexes was tested.

Thus, the basic behavior of the fluoride ion deprotonates all these complexes to form the resonance-stabilized anions shown in Scheme 4.1.2.

Tautomeric structures generated from the complexes by the interactions of fluoride ion

Conclusions
b). In this part of this chapter the association ability of an aldehyde and corresponding aldoxime with cadmium coordination polymer having identical linker is described
Synthesis of different cadmium coordination polymers of 1,3-bis(4- pyridyl)propane ligand

The nickel complexes and the zinc complex have large differences in the directional arrangement of the molecules, while the zinc complex 4.1.7 showed an extension of the network structures with the coordination of one nitrogen atom of 1,3-bis(4 pyridyl)propane to zinc and phenol-pyridine hydrogen bonds. These examples showed that, in addition to changes in packing due to the presence and absence of guests or solvent molecules, directional hydrogen bonding is crucial in creating the overall architecture of a single noncovalent assembly in each case. Depending on the metal ions, as in the zinc complex 4.1.7, fluorescence emission can be a tool to detect fluoride ions, even though the parent ligand lacks such ability.

Interesting aspect of the zinc complex 4.1.7 is that it has a very weak fluorescent counterpart, but the zinc complex 4.1.7 upon the interactions with the fluoride ions becomes strongly fluorescent to show an emission at longer wavelength. Incorporation of the basic aromatic heterocyclic compounds as ligands or solvent of crystallization does not interfere with the fluoride detection. For studying interactions with fluoride ions, separate solutions of the complexes and M solution) as well as the solutions of different tetrabutylammonium ions (10-3 M solution) in dimethylsufoxide or water or DMSO-water mixture (1:1 v/) were prepared. f).

To record UV-vis spectra or fluorescence spectra, 3 ml of complex solution was placed in 10 mm path length quartz cell at room temperature.

Synthesis of cadmium coordination polymer and guest encapsulation

Structural descriptions of cadmium coordination polymers 4.2.1-4.2.3
a. The dissimilarity between the structures of the two guest included coordination polymer arises from the hydrogen bonds between the nitrate ions with the oxime molecules
Conversion of aldehyde to oxime transformation studied by the help of isothermal calorimetric titration (ICT) and FT-IR

Hydrogen bonds of coordinated water molecules with nitrate anions make 2-dimensional sheet-like structure of CP-4.2.1 (Fig. 4.2.3). Gas-enclosed coordination polymers require 1:2 metal to 1,3-bis(4-pyridyl)propane stoichiometry; while CP-4.2.1 has about 1:1 ratio. The coordination polymer 4.2.3 has 2,4-dihydroxybenzaldoxime (oxime 2.1.3) as inclusion complex; it has exactly the same self-assembly as that of the CP-4.2.2 as in Fig.

The fundamental difference of the self-assemblies of CP-4.2.1 from the other two coordination polymers is in terms of their respective hydrogen bonds. Therefore, a disproportionation reaction of CP-4.2.3 will require a change in the stoichiometry of ligands and free cadmium ions. The thermodynamic parameters for the association of CP-4.2.1 with 2,4-dihydroxybenzaldehyde or 2,4-dihydroxybenzaldoxime (oxime 2.1.3) in solution are determined by the studied isothermal calorimetric titrations.

Accordingly, the conversion of aldehyde to oxime is facilitated by CP-4.2.1; this is evident from the reaction between 2,4-dihydroxybenzaldehyde and hydroxylamine in methanol.

Competitive equilibrium for formation hydrogen bonded assemblies

Conclusions
References
Synthesis of cocrystals and salts of quinoline-4-carbaldoxime (5.1)

Among the functional groups, hydroxy, carboxylic acid, amide and oxime are common functional groups for the construction of various co-crystal self-assembly.8 Different types of carboxylic acid motifs with hydrogen bonds9 form intermolecular hydrogen bonds (Fig. 5.1a-b). Oxime is a typical organic functional group used in various organic reactions, oximes form various non-covalently linked dimers and catemers by interaction between two same types of oximes or two different oximes.12 However, oxime has a lower affinity for complex formation with carboxylic acids and phenols. Due to the limited study of direct interactions between oximes and carboxylic acids; we investigate the interactions of quinoline-4-carbaldoxime oxime (5.1) based on quinoline with various carboxylic acids.

Oxime 5.1 is observed to form cocrystals or crystalline salts with aliphatic-dicarboxylic or mineral or aromatic-carboxylic acids (Fig. 5.3). Due to the two prominent sites for hydrogen bonds in oxime 5.1, it can select a partner molecule by using one functional unit or by using both functional units to form hydrogen bonds. It is observed that oxime 5.1 readily forms cocrystals or crystalline salts with aliphatic dicarboxylic acids or mineral acids or aromatic carboxylic acids (listed in Fig. 5.3).

But crystals, either as cocrystals or as salts of oxime 5.1 with nitrogen-containing compounds such as imidazole, pyrazole, picoline and pyridine, could not be prepared from a solution of these compounds with oxime 5.1 in different solvents (methanol, DMF, THF, acetone etc. .).

Synthesis of cocrystals and salts of quinoline-4-carbaldoxime with (a) aliphatic dicarboxylic or mineral and (b) aromatic carboxylic acids

Structural description of oxime 5.1 and cocrystals or salts of oxime 5.1 with aliphatic dicarboxylic or mineral acids
Structural studies of cocrystal or salts of oxime 5.1 with aromatic carboxylic acids A cocrystal and a series of salts of oxime 5.1 with different aromatic carboxylic acids listed
Conclusions

The hydrogen-bonded self-assembly of cocrystals formed by interactions of the oxime 5.1 with adipic acid is shown in Fig. The self-assembly of the chloride salt 5.7 consists of protonated oxime 5.1 molecules held on the channel by strong +N-H⋯Cl interactions. This may also be one of the reasons that carboxylic acid-oxime interactions are observed in the salts.

Self-assembly of the cocrystal 5.9 of oxime 5.1 with 2-HMBA consists of quaternary subassemblies formed by O-H⋯N and O-H⋯O hydrogen bonds (Fig. 5.13a). However, the hydrogen bonds of the two carboxylic acids in the respective subassembly show differences. Thus, the powder

Homosynthons formed between protonated oxime molecules in individual salt self-assemblies are influenced by anions.