I am forwarding his thesis entitled "Study on Aromatic Carboxylic Acids as Ligands and Receptors" submitted for Ph.D.). This certifies that Anirban Karmakar has successfully completed all courses required for the Ph.D.
Acknowledgements
- Introduction
- Synthesis, structure and polymorphism in cobalt carboxylate complexes
- Synthesis and structures of dinuclear nickel carboxylate complexes
- Synthesis and characterization of zinc carboxylate complexes through solid state reactions
- Structural studies and metal complexation of flexible carboxylic acid and its derivative
- Structural aspects and acid/anion recognition properties of carboxylic acid derivatives
This chapter of the thesis discusses the synthesis, characterization and structural features of various aqua-bridged dinuclear nickel(II) carboxylate complexes. This chapter describes the synthesis and structure of zinc carboxylate complexes obtained via the solid-state strategy.
Contents
Introduction
General features of carboxylic acids
In the solid state or in concentrated solution, carboxylic acids assume a dimeric structure due to strong hydrogen bonding 5-6. The extremely strong hydrogen bonding in carboxylic acids can be explained by the large contribution of the ionic canonical form II.
Coordination modes of carboxylic acids
Yaghi and co-workers showed that the secondary building units can be used as molecular building blocks to construct well-defined orientations16. The secondary building units are sufficiently rigid because the metal ions are locked in their positions by the carboxylates.
Mono and multinuclear carboxylate complexes of first row transition metals
- Mononuclear metal carboxylates
- Dinuclear metal carboxylates
- Trinuclear metal carboxylates
- Tetranuclear metal carboxylates
- Pentanuclear metal carboxylates
- Hexanuclear metal carboxylates
- Heptanuclear metal carboxylates
- Higher nuclearity metal clusters
- Mixed-metal carboxylate complexes
In this complex manganese ion, the octahedral geometry62 is disturbed, as shown in Figure 1.13B. The complex with [Mn4O3] core with halogen is also known in the literature63. Hexanuclear cobalt complex with the composition [Co6(OH)2(PhCOO)10(PhCOOH)4].3PhCH3 (1.25) is prepared by the reaction of cobalt(II) nitrate with benzaldehyde53. The structure of the complex consists of a centrosymmetric hexametallic unit.
Carboxylate based coordination polymers
- One dimensional coordination polymers
- Linear chain
- Zig-zag chain
- Double chain
- Ladder
- Helix
- Two dimensional coordination polymers
- Square grid
- Rhomboid grid
- Rectangular Grid
- Honeycomb
- Herringbone
- Brickwall
- Three dimensional coordination polymers
- Diamondoid net
- Octahedral net
Helical, multinuclear assemblies mediated by metal–ligand coordination are well documented in the literature142. The double-stranded helix of copper(II) with 4,4'-oxybis(benzenecarboxylic acid) and phenanthroline has also been reported in the literature143. The effective cavity size of the two-dimensional complex is 6.7 x 13 Å. The cavities are filled with guest molecules.
Biological role of carboxylic acids and carboxylates
- Nickel containing metalloenzyme: Urease
- Cobalt and zinc containing Metalloenzymes: Aminopeptidases
- Heterodinuclear metalloenzyme: Purple Acid Phosphatases
A schematic representation of the active site of methionine aminopeptidase from Escherichia coli is shown in Figure 1.53. A schematic representation of the active site of aminopeptidase from Aeromonas proteolytica is shown in Figure 1.54.
Porous carboxylate networks
- Gas separation by carboxylate frameworks
- Selective guest binding in carboxylate networks
- Carboxylate frameworks for enantioselective transformations
The organometallic skeleton obtained by reacting zinc(II) salt with 1,4-benzenedicarboxylate has a cubic three-dimensional expanded porous structure and capable of adsorbing hydrogen (Figure 1.56). Some of the metal-organic frameworks based on Zn4O network topology are shown in Figure 1.57. The zinc ions are also bonded to two hydroxy groups to give two tetrahedral and one octahedral zinc center arranged in coplanar fashion. The infinite Zn–O–C columns are stacked in parallel and linked in the [110] direction by the biphenyl linkages to give one-dimensional (1D) rhombic channels of 12.2 Å along one edge and 16.6 Å along the diagonal (Figure 1.58A).
A mixed metal framework of Cu(II) and Hg(II) constructed from [(Cu(2-pyrazinecarboxylato)2] building block and HgI2 as linkers (Figure 1.60B).
Carboxylic acids and its derivatives as receptors
Scope of the present work
One of the most challenging aspects of carboxylate chemistry is to design multifunctional materials with predictable structures and properties260. Robson developed and extrapolated Wells' work to the area of metal-organic compounds and coordination supramolecular chemistry118. This leads to loss of information about the formation and the nucleation process of carboxylate complexes.
With this background, we study the synthesis, characterization of metal carboxylate complexes by ligand exchange reaction and their ability to bind to organic substrates.
Synthesis, structure and polymorphism in cobalt carboxylate complexes
Synthesis and characterisation of dinuclear aqua bridged cobalt carboxylates
The effective magnetic moment of complex 2.1 (per dimer) at room temperature is found to be 6.54 BM. Cobalt carboxylate complexes In the thermogram for the cobalt complex (2.1) it is observed that the complex is lost in three steps (figure 2.2). The magnetic moment of complex 2.2 at room temperature is found to be 6.52 BM, ie.
This weight loss is due to the FTIR spectrum of complex 2.4 showing an absorption band at 3395 cm-1 due to O–H stretching.
Polymorphism in an aqua bridged dinuclear cobalt(II) carboxylate
The orientations of the nitro benzoate groups in the three polymorphs are plotted in Figure 2.9. The torsion angles (Table 2.8) are different for the different orientations of the nitrobenzoate groups in the three polymorphs. The polymorphism originates due to the different orientations of the nitro groups in the three polymorphs.
Each of the polymorphs (I-III) shows a broad signal around 3433 cm-1 (O-H stretching) in their solid-state FT-IR spectra.
Synthesis and structure of mononuclear cobalt(II) carboxylate complexes
The structure of complex 2.6 shows that the two carboxylates are coordinated to the cobalt center in opposite directions. Analogous reaction of cobalt(II) salts with 2-nitrobenzoic acid and sodium hydroxide in the presence of excess pyridine in methanol gave the complex (2.7) as orange prisms (Scheme 2.8). The O−H····O, C−H····O and π····· π interactions in complex 2.7 are responsible for the construction of a three-dimensional hydrogen-bonded network.
For the complex 2.6, the C=O stretching frequency of monodentate carboxylate appears at 1593 cm-1 and the asymmetric C-O stretching frequency of chelating carboxylate appears at 1540 cm-1.
Synthesis and characterisation of tetranuclear cobalt(III) carboxylates
- Materials
- Physical Measurement
The diamagnetic nature of complex 2.8 is evident from its 1H NMR spectrum where the aromatic protons belonging to the benzoate and pyridine ligands appear at expected positions. The cyclic voltammetry analysis of the complex 2.8 in acetonitrile solution shows an almost reversible reduction with E versus saturated calomel electrode. In conclusion, we have described a solid-state synthetic route for the synthesis of aqua-bridged dinuclear cobalt(II) carboxylate complexes.
The aqua-bridged cobalt(II) benzoate complex prone to oxidation and such oxidation provides a method for the preparation of tetranuclear cobalt(III) carboxylate complex.
Then the reaction mixture was transferred to a round bottom flask and 20 ml of benzene was added.
- Synthesis of polymorphs of aqua bridged dinuclear cobalt(II) carboxylate complex of 2-nitro benzoic acid
Cobalt carboxylate complexes were added and the heterogeneous mixture was stirred at room temperature for 5 min, followed by the addition of pyridine (0.16 g, 2 mmol).
Synthesis of mononuclear cobalt(II) carboxylate complex
The heterogeneous mixture was then stirred for 5 minutes at room temperature, followed by the addition of pyridine (0.16 m. To a well-stirred solution of benzoic acid (0.24g, 2mmol) in methanol (20ml) cobalt (II) acetate tetrahydrate ( 0.25) g, 1 mmol) was added and stirred at room temperature for 12 hours.
Synthesis and structures of dinuclear nickel
Synthesis and characterisation of aqua bridged dinuclear nickel(II) benzoate complex
- Synthesis of aqua bridged dinuclear nickel(II) benzoate complexes with substituted aromatic acids
- Synthesis and characterisation of mixed chloro and aqua bridged nickel(II) carboxylate complex
- Ni 2 (µ-H 2 O)(µ-L) 2 (L) 2 (Pyridine) 4 ].(C 7 H 8 )(LH)
- Ni 2 (µ-H 2 O)(µ-L) 2 (L) 2 (Pyridine) 4 ].1.5(C 6 H 6 )
- Ni 2 (µ-H 2 O)(µ-L) 2 (L) 2 (Pyridine) 4 ].H 2 O
- Ni 2 (µ-H 2 O)(µ-L) 2 (L) 2 (Pyridine) 4 ]
- Ni 2 (µ-H 2 O)(µ-L) 2 (L) 2 (Pyridine) 4 ] OH
Thermogravimetric analysis of complex 3.2 shows the loss of benzene and bridging water molecule in the temperature range 90-170°C. The crystal structure of the complex shows similar type of aqua-bridged dinuclear nickel(II) core. In the case of complex 3.6, the bond angle is the smallest compared to 3.1–3.5 due to the presence of both chlorine and aqua bridges (Table 3.7).
A mixture of benzoic acid (0.73 g, 6 mmol), sodium hydroxide (0.34 g, 6 mmol) and anhydrous nickel(II) chloride (0.39 g, 3 mmol) were mixed together in a mortar pestle and the mixture was heated to 100ºC for 45 min. The mixture was transferred to a round bottom 1) was added to this mixture.
Synthesis and characterisation of zinc carboxylate complexes through solid state
Study on the effect of different salts on solid sate synthesis of zinc carboxylate
- Study the substituent and solvent effect on solid state synthesis
- Synthesis and structure of mononuclear zinc carboxylate complexes
- Zn 3 (µ-L) 6 (Py) 2 ][Zn 2 (µ-L) 4 (pyridine) 2 ]
- Zn 2 (µ-L) 4 (pyridine) 2 ]
- Zn 4 (μ-L) 6 (μ-O)(DMSO) 2 ]
- Zn 5 (μ-L) 6 (L) 2 (μ-OH) 2 (pyridine) 2 ] OH
In the temperature range 125-225°C, the complex 4.2 also loses two pyridine molecules, corresponding to 18.65% of the total weight. A careful look at the geometry of the complexes shows that in complex 4.3 the two pyridine rings lie in one plane, while in 4.4 the two rings are perpendicular to each other. The crystal structure of complex 4.6 shows that it is a pentanuclear zinc carboxylate complex in which the zinc centers are linked by six bridging benzoate groups and two hydoxo ligands.
The structures of each of these complexes are shown in Figure 4.8A and 4.8B. The complexes are further two zinc centers have fulfilled its coordination sites by three carboxylate oxygens and a hydroxyl group.. characterized by 1H-NMR and FT-IR spectroscopy.
Structural studies and metal complexation behaviour of flexible carboxylic acids and
The combination of metal ions and bridging ligands containing different flexible carboxylates can the. The carboxylate metallo-organic frameworks are of special interest as they can be easily synthesized with diverse structures314. Various options for various binding modes in metal carboxylate complexes make them versatile315. Metal carboxylates with flexible ligands are being studied to improve selectivity in molecular recognition and much work in this direction is needed to have control over the construction of voids in a predictable manner316.
Amino acids and its derivatives with flexible coordination modes have been investigated in generating various coordination frameworks with potential application in materials science.
Metal complexation and structural study of flexible mono-carboxylic acid Urea derivatives are very useful for selective guest 318 and anion recognition 319 . A
The symmetry-non-equivalence arises due to the self-assembly of the two molecules in such. The urea part of the ligand in the sodium complex has an anti-syn conformation. Such an anti-syn conformation arises due to puckering of the ligand upon coordination to metal centers.
The organic part bound to the carboxylate group of the ligand are placed parallel to each other and m.
B) Packing dia com 4B
- Metal complexation of fl
- Experimental Section
- Synthesis of flexible mono-carboxylic acid and its metal complex
- Synthesis of flexible di-carboxylic acid and its metal complex
The crystal structure of complex 5.6 shows that it is a network of metallacycles formed by the ligand L1 with zinc ions. The symmetry nonequivalence in the complex arises from the location of the solvent molecules in the crystal lattice. After completion of the reaction, the reaction mixture was filtered off (to remove unreacted K2CO3). The solvent was removed under reduced pressure and a white solid was obtained.
The isolated product was washed with NaOH (5%) solution and water and then the product was extracted with dichloromethane. The organic extracts were collected over anhydrous sodium sulfate. 3-Methoxycarbonylmethoxy-naphthalen-2-yloxy)-acetic acid methyl ester (0.34 g, 1 mmol) was dissolved in methanol (10 mL) and kept for crystallization.
Zn(L 1 )(Pyridine) 2 (H 2 O)(CH 3 OH)].H 2 O} n
The solution was cooled to room temperature and zinc(II) acetate dihydrate (0.219 g, 1 mmol) was added. After that, the solution was kept for crystallization and after 10 days colorless crystals appeared. The resulting solution was filtered to discard any insoluble material if any, and the filtrate was kept for crystallization.
Yield: 63 %,
Yield: 6 %
Structural aspects and acid/anion recognition properties of carboxylic acid
Structural study of receptors
The water molecules are assembled by hydrogen bonding interaction and lead to the formation of infinite 2D hydrogen bonded networks parallel to [110]. When we crystallized, the anhydrous ained. the compound 6.3 was crystallized nt If ize. th l acetate or l-wa crystallizes as mo ate and. In the dimeric structure, two amide molecules are arranged in a head-to-tail orientation (Figure 6.7B).
The extended structure in the dihydrate is formed by the interaction of this hydrogen-bonded water molecule.
Salt and gel formation study of receptors
It is observed that two protonated molecules of 6.1 self-assemble into hydrogen-bonded dimeric cavity-like structures, which are stabilized by the template effect of the hydrogen sulfate anions (Figure 6.11). It can be noted that the hydrogen bonding interactions involving the two nitrate anions in the lattice are quite different, one of the anions. protonated bond. A representative SEM image of the hydrogel formed from 6.2 in aqueous sulfuric acid is shown in Figure 6.13B.
The intermolecular self-association 1H-NMR spectra of compound 6.3 in benzene-d6 and methanol-d4 (Figure 6.18A and 6.19A) showed this aromatic region in the spectral record.
