Coordination and supramolecular chemistry of aromatic N-oxides

Aromatic N-oxides are a special class of heterocyclic aromatic compounds containing exo-cyclic N-oxo functionality. They are a class of useful ligands for the generation of coordination complexes as well as supramolecular architectures, especially coordination polymers. This thesis deals with the studies on synthesis, characterization and structural aspects of a number of coordination polymers and molecular complexes of aromatic N-oxides.

Introduction

Furthermore, suitable conditions for synthesizing metal-containing molecular complexes of aromatic N-oxides are investigated and presented.

Chapter 2: Synthesis, characterization and properties of manganese(II), copper(II) and zinc(II)

Based on the versatile coordination possibility, various coordination polymers of cadmium(II) are prepared and reported from time to time although report on mercury(II) complex is rare. A schematic representation for the synthesis of the coordination polymers of Tb(III) is shown in scheme 3.

Chapter 5: Supramolecular aspects of multi containing aromatic N-oxide

Supramolecular aspects of molecular complexes of aromatic with phenyl boronic acid: syntheses,

The common point in each of these structures is the strong hydrogen bonding interactions between. Weak interactions are related to theoretical ones by different model assemblies of the molecule.

In addition to the direct substitution reactions, various metallizations followed by electrophilic substitution reactions of pyridine N-oxide are also studied. The addition of one equivalent of pyridine N-oxide to a toluene solution of the U(IV)-bis(alkyl) complexes [(C5Me5)2An(R)2] (R=CH3, CH2Ph; An= U, Th) results in activation of an sp2-hybridized C-H bond with loss of alkane and formation of the new cyclometalated pyridine-N-oxide complexes [(C5Me5)2An(R)(2-(O,C)-).

Coordination complexes of The coordination chemistry

Furthermore, the magnetic moments of the Mn(II) complexes suggest a possible spin-spin interaction. Based on the infrared spectrum and the dipole moments of the compounds, they suggested the.

Coordination modes of aromatic N-oxides

Due to the orientation of the lone pair on the N bridge, it can be a trans (E) or cis (F) conformation. To simplify distinguishing these coordination modes from each other with a simple terminology based on the bridging pattern (µ) and density ( ) of the ligand.

Aromatic N-oxides based coordination polymers

One dimensional coordination polymers
Three dimensional coordination polymers

The perchlorate anions remain embedded within the pores of the three-dimensional hydrogen-bonded networks formed by the 2D coordination polymers (Figure 1.27).56. Three-Dimensional Coordination Polymer of Mn(II) with Pyridine Introduction Two-dimensional mental chains of cross-linked two-dimensional networks of axially bonded cations further linked through Ln(III) anions remain embedded within the pores of three-dimensional hydrogen-bonded networks formed by 2D.

Molecular complexes of

Molecular complexes of aromatic N-oxides

The remaining coordination sites are occupied by the oxo, O3, pyridine N-oxide ligand. In addition, the presence of the hydroxyl group gives the coordination polymer 2.3 somewhat more supramolecular properties. One-dimensional coordination polymer chain 2.2 and hydrogen bonding interactions between one-dimensional coordination chains.

One-dimensional chain of the coordination polymer 2.4 The reaction of benzoic acid, manganese(II) acetate tetrahydrate and 4,4' . BPNO) in methanol (MeOH) leads to the formation of 2.5 with the composition [{Mn3(C6H5COO). This ligand, being a bidentate ligand, resulted in the formation of the 1D coordination polymer 2.8 with the composition BPNO)]n. There are a few reports available on the 2,2' chelating coordination state. However, in the case of the coordination polymer 2.8, the dioxide coordinates in the trans fashion to bridge two paddle wheels.

Conclusion

The structure of the two-dimensional coordination polymer is shown in Figure 2.3.4b with the different types of zinc centers and ligand connectivity in Figure 2.3.4a. PXRD analysis of bulk samples of coordination polymers 2.11-2.13 was performed and found to be in good agreement with the simulated samples. We study the thermal stability of complexes 2.11-2.13 and thermograms show that all coordination polymers are thermally stable up to ~200 oC.

This weight loss is explained by the loss of the pyridine N-oxide molecule (theoretical weight loss 23.6). The structure of each such coordination polymer is determined by the nature of the metal ions and the spatial orientation of the auxiliary ligands. Moreover, different architectures of the coordination polymers with repeating mononuclear, dinuclear or trinuclear M(II) (M=Mn, Cu, Zn) units can be observed.

Experimental section

It appears that 4,4'-bipyridyl-N,N'-dioxide prefers a 2-2 coordination mode, either cis or trans, rather than a 2-2:0 coordination mode. We obtained a preferred transbidentate bridging mode of binding of 2,2'-bipyridyl-N,N'-dioxide to form a copper(II) coordination polymer instead of the commonly occurring chelate mode. In the case of copper(II) and zinc(II) coordination polymers, the paddle-wheel benzoate units act as secondary building blocks linked by 4,4'-bipyridyl-N,N'-dioxide, which acts as a bidentate spacer ligand, assuming a coordination mode trans 2-2. The copper(II) blade structures, separated by different N-oxide spacers, control their structural features.

Manganese(II) N-oxide coordination polymers 2.1-2.4 exhibit weak antiferromagnetic interactions between the nearest Mn(II) centers. Interactions between the metal centers within the paddlewheel moieties of 2.7-2.9 were found to be strongly antiferromagnetic, with values typical of copper(II) carboxylates. However, inter-dinuclear interactions between these moieties were too weak to be detected, or non-existent.

Mn(C 6 H 5 COO) 2 (PNO)] n

Complex 2.2 was synthesized through a similar method as for 2.1; only difference being the use of 4-nitrobenzoic acid in place of benzoic acid

Mn(4-OHC 6 H 4 COO) 2 (PNO)] n

Complex 2.3 was synthesized through a similar method as for 2.1; only difference being the use of 4-hydroxybenzoic acid in place of benzoic acid

Precipitation occurred and a small amount (3 mL) of pyridine was added to dissolve the precipitate that appeared after the addition of pyridine N-oxide. The thus obtained clear solution after one week gave yellow crystals of coordination polymer 2.4 (70% yield).

To this reaction mixture was added pyridine-N-oxide (1 mmol, 0.095 g) with constant stirring at room temperature. A small amount of toluene (5 mL) was added to this reaction mixture and kept for crystallization.

slowly gets converted to a new coordination polymer NO 2 C 6 H 4 COO) 2 (PNO)] n
has its characteristic IR absorptions at 1555 cm bound to metal ion and at 1216 cm -1 due to N-ox
Conclusion
Experimental section

It is worth mentioning that the one-dimensional chains of the coordination polymer 3.5 adopt a spiral shape (figure). The coordination polymer 3.5 crystallizes in the monoclinic space group. Each mercury(II) ion of the polymeric chain is associated with one chelating benzoate ligand and one monodentate benzoate ligand along with two bridging 4,4''. This is confirmed by the index of 0.11 (calculated as the difference between the two largest angles divided by 60).

H19···O6, 164) together with - interactions (centroid-centroid ) between the aromatic rings of 4,4'-bipyridyl dioxide of two neighboring one-dimensional chains of the coordination polymer. The single crystal analysis of the coordination polymer 3.6 suggests that the crystals must be of the monoclinic P21/c space group. The coordination polymer 3.9 has a three-dimensional structure built from the aggregation of the asymmetric [Pb2(C6H5COO)3(4,4'-BPNO)2.5] units.

Cd(C 6 H 5 COO) 2 (PNO)] n

4,4'-bipyridyl-N,N'-dioxide binds through the 2-µ2 coordination mode with both Cd(II) and Hg(II) metal ions, while in the case of Pb(II) coordination through both . In addition to the syntheses of coordination polymers with different architectures, the isolation and characterization of a pair of mixed anionic coordination polymers of lead(II) formed as intermediate species is demonstrated. The linear polymer with trinuclear block in the case of 3.2, which has a width of about 9 Å, is a significant observation in the preparation of rod-like polymeric structures.

Furthermore, the interpenetrating structure and helical structure obtained in the case of coordination polymers 3.3 and 3.5 are of added value for the chemistry of coordination polymers as new advanced materials. Analytical data as well as spectroscopic data are also listed along with each of the complexes.

Hg(C 6 H 5 COO) 2 (4,4'-BPNO)] n

Pb(C 6 H 5 COO)(NO

Conclusion

A schematic presentation of the synthesis of the coordination polymers of Tb(III) is depicted in Scheme 4.1.1. This generates the zig-zag one-dimensional coordination polymer extended along the ab diagonal of the unit cell. In the structure, each of the La(III) ions is coordinated by four benzoate oxygen atoms.

These one-dimensional chains are then linked together via the 4,4'-BPNO ligands that spread the dimensionality of the complex into the three dimensions. Thermogravimetric analysis of the coordination polymer 4.1 shows weight loss of 4,4'-bipyridyl-N,N'-dioxide, DMF and benzoic acid molecules in different steps. In the third step, continuous degradation occurs due to the loss of the coordinated molecules.

Ce(C 6 H 5 COO) 3 (4,4'-BPNO)(H 2 O) 2 }.DMF] n

Pure block crystals suitable for X-ray analysis were collected after 6 days and dried in air. PXRD pattern of the complex 4,2 (4,4'-BPNO)0,5(H2O)]n. was synthesized in a similar procedure to complex 4.1 except III) acetate hydrate as the metal source.

Synthesis and characterisation of molecular complexes of pyridine N-oxide
Synthesis and characterisation of
Synthesis and characterisation of molecular complexes of quinoline N-oxide
Synthesis and characterisation of dioxide
Synthesis and characterisation of molecular complex of 4,4'-bipyridyl-
Conclusion

The same reaction, performed in aqueous methanol, results in the formation of the molecular complex of pyridine-N-oxide that co-crystallizes with hexa aquo manganese(II) and 4-nitrobenzoate ions (Scheme 5.1.1). These short-range interactions make the molecular complexes stable enough and prevent the formation of coordination. The reaction of benzoic acid, manganese(II) acetate and 4,4'-bipyridyl-N,N'-dioxide in methanol (MeOH) leads to the formation of the coordination polymer with the.

The dioxide in methanol (MeOH) leads to the formation of the coordination polymer with. However, the same reaction when carried out in aqueous methanol leads to the formation of However, there is a significant difference in the stretching frequency in the IR spectrum of the molecular complex 5.8.

Synthesis and characterisation of the molecular complexes
Theoretical study on the weak interactions in the molecular complexes 6.1-6.4

Energy optimized structures of the molecular complexes 6.1-6.4
Strength of the type-1 and type-2 interactions

The molecular complexes exhibit characteristic IR absorptions in the range 1211–1253 cm-1 due to N–O stretching of the aromatic N-oxides. In the case of the molecular complex 6.3, C-H··· and - interactions are important for the formation of assemblies, together with the O-H···O and C-H···O interactions. Interactions between the HOMO of the aromatic N-oxides and LUMO of the acid to determine the feasibility of B interactions.

We have performed similar calculations in the case of the molecular complex of BDBA with QNO (6.2). The optimized structure of the 1:1 molecular complex of BDBA and QNO is shown in Figure 6.2.1b. The optimized structure of the 1:1 molecular complexes of BDBA and IQNO is shown in Figure 6.2.1c.

The comparative energies of the 1:1 molecular complexes in their type-1 and type-2 orientations are shown in table 6.4. This symmetrical arrangement of the HOMO of PNO and BPNO interactions of PNO or BPNO with BDBA molecule. The perspective interaction in the case the BDBA-PNO.