A Dissertation Submitted to the

The importance of self-assembly in biology and applications of chiral tridentate ligands is also reviewed in this chapter. Overall, the self-assembly observed in this thesis will boost the understanding of the self-sorting process of chiral tridentate imine and amine ligands around the dimetallic core.

Introduction, Materials and Methods

Chirality
Schiff bases having chiral center(s)

Self-assembly of racemic Schiff base(s)
Self-assembly of racemic amine/amide ligands
Self-assembly of macrocyclic ligand

One of the enantiomers has a dextrorotatory (P) and the other a levorotatory (M) form. Schematic representation of dimerization of two [Cu(R-7)]+ units (top) and [Cu(S-7)]+ and [Cu(R-7)]+ units (bottom left) and mediates AgClO4 self-assembly.

Structure of SS-11 and RR-11

Self-assembly of box ligand(s)
Self-assembly in Biology
Application of chiral Schiff base complexes
Definition of the Problem
Materials and Methods .1 Materials

Instrumentation and Methods
EPR Measurements
X-ray Crystallography
Thermal Measurements

Metal-directed multicomponent self-assembly for the formation of chiral, heteroleptic complexes in the design of novel heterobimetallic asymmetric catalyst systems is an active area of research. The pairing of binary hydrogen bonds, such as A···T and G···C in a DNA double helix, plays an important role in generating supramolecular self-assembly and processing genetic information [93, 199].

Molecular Structures of Nickel(II) Monochelates of a Racemic Tridentate Ligand and Co-ligand Induced

Structural Variations †

Molecular structures of racemic tridentate ligand and co-ligand induced nickel(II) monochelates.

Structural Variations

Experimental .1 Syntheses
Molecular structures
Magnetism
Conclusion

Continuously from 1 to 2, due to the effective increase in coordination number, elongation of all Ni-N and Ni-O bonds is observable. Due to the effective increase in coordination number, going from 1 to 3, a systematic elongation of all Ni-N and Ni-OP bonds is observable.

Diastereoselectivity in Dinuclear Complexes of Chiral Tridentate Ligands †

Diastereoselectivity in Dinuclear Complexes of Chiral Tridentate Ligands

Chirality selective dimetallic core (B = bridging ligand)

Results and discussion

After standing overnight, the pale pink crystals deposited were filtered, washed with water and dried in desiccators. The mixture was filtered to remove undissolved zinc and washed with sufficient amount of ethanol. The combined ether portions were dried over Na2SO4 and the solvent was removed in vacuo.

The yellow precipitate of the deposited L2H was collected by suction filtration, washed with cold methanol and dried over CaCl. Single crystals of 1 suitable for X-ray diffraction studies were obtained by slow evaporation of the methanol solution. The green solution was kept at room temperature and after a week green crystals of 2 suitable for X-ray diffraction studies were obtained and washed with cold methanol.

The green solution was kept at room temperature and after a week green crystals of 3 suitable for X-ray diffraction study were isolated and washed with cold methanol. Dark green crystals of 4 were formed from the green solution on standing for several days. Single crystals of 5 suitable for X-ray diffraction study were obtained by slow diffusion of methanolic solution of the crude 5 in dichloromethane.

Structure of L1H and synthesis of L2H

Schematic representation of bridging ligand dependent chirality selectivity in dimetallic core

Molecular Structures
Conclusion

13.8%) was observed in the temperature range 37 – 196 °C corresponding to the loss of all seven water molecules. Whereas, in the 3-5 inversion center they do not extend to the dimetallic core and are homochiral. The ligand has a slight bowl shape and the copper center has a distorted square pyramidal geometry, with the bridged OP being in the axial site.

In the packing diagram of 3, dimers having RR and SS combinations are packed alternately along the c-axis generated by the inversion center, but identical RR or SS combinations are packed on top of each other along the a-axis. In the packing diagram of 4 , the RR and SS combinations form discrete dimeric units linked by hydrogen bonding interactions involving solute water and methanol. Coordination by L2, the acetate ion, and the OP overshoot result in the same penta-coordinating environment around the two nickel centers, but differ in the sixth coordination site, which is filled by the methanol oxygen atom in Ni1 and the cyanide nitrogen atom of the ligand dicyanamide to Ni2.

In the packing diagram, the RR and SS dimers are arranged alternately in chains (Figure 11), in which the two dimers are connected by a hydrogen bond interaction between the coordinated methanol, the methanol in the lattice (O3···O Å) and the uncoordinated end of the dicyanamide group (O6· ··N Å). The yield reported here refers only to the isolated yields of the compounds in the crystalline state. To verify the nature of the compound in the eluates, the solvent was removed and the overall recovery of this compound from eluates and crystals was around 90–95%.

Molecular Structures of Isostructural Dinuclear M(II) (M=Ni, Cu, Zn) Complexes of Chiral Tridentate Ligand

Molecular structures
Thermal analyses
Luminescence properties
Conclusion

These bands originate from the coordinated dca ion, and since the frequencies of these bands are shifted to higher values than those observed in the free dca, the presence of the µ-1.5 bridging state can be inferred [315–320]. Presence of coordinated L3H in these complexes can be deduced from the bands due to νC=N and νC=C stretches in the cm-1 range. One end of dca is connected to the metal ion in the square plane and the other end occupies the axial site of the other metal center.

Since the [M2(L3)2(µ–1,5–dca)2] unit is centrosymmetric, RS combination (heterochiral dimerization) of Schiff base is present in the dimeric unit. The M–NC distances in the equatorial plane are marginally shorter by 0.023(2) Å than the axial bond in Ni, but more pronounced in Cu by 0.404(3) Å, which results from Jahn–Teller distortion. But in 3 the M–NC distances in the equatorial plane are marginally longer by 0.046(5) Å than the axial bond.

The pictorial representation of various weak interactions present between methanol and [M2(L3)2(µ–1,5-dca)2] in 1 is shown in Fig. The emission spectra of compounds 1–3 and L3H obtained using excitation wavelength (λex) in the range 390 – 410 nm are depicted in Fig. These complexes are particularly interesting because of their bimetallic core with a long dca bridge; specifically 1 and 2 from a magnetic point of view, whereas 3 due to its solid state luminescence properties.

Structural Variations in Copper Complexes Containing a Chiral Tridentate Ligand and Dicyanamide Ion

Conclusion

Three higher energy bands around 295 – 220 nm correspond to the n→π* and π→π* transitions of the Schiff base ligand (ILCT). As a consequence of the OP bridge, the coordinated ligand is non-planar and the two aromatic rings are bent away from the metal center having a butterfly shape. The basal plane of the copper (II) ion is occupied by N2O donor atoms of the L1 tridentate ligand group and the terminal nitrogen atom of the dca ligand.

The OP atom in L1 is slightly asymmetric bridging to Cu(II) center with Cu-OP distances of 1.925(3) and 2.418(3) Å and makes the ligand non-planar. A view of the zipper as a 1D coordination polymer as well as its schematic representation is shown in Fig. The ORTEP diagram of one of the [Cu2(L1)2(dca)2] units with the atomic numbering scheme is shown in Fig.

The trend in coordination bond lengths Cu–NY > Cu–ND > Cu–NI is also observed at the copper centers. In 4, the dca ion acts as a terminal ligand in a fenoxo-bridged dimer with the R and S isomers of the racemic Schiff base. The compositions of the isolated complex depend on the nature of the copper(II) salt and the amount of sodium dicyanamide used in the reaction.

Molecular Structures of Dinuclear Zinc(II) Complexes of Chiral Tridentate Imine and Amine Ligands: Effect

Molecular structures of dinuclear zinc(II) complexes of chiral tridentate imine and amine ligands: Effect. Molecular Structures of Dinuclear Zinc(II) Complexes of Chiral Tridentathimine and Amine Ligands: Effect of Chiral Tridentathimine and Amine Ligands: Effect.

Chiral tridentate imine and amine ligands used in this Chapter

Phenyl(2-pyridyl)methanamine and (R,S) 2-((phenyl(2-pyridyl)methylimino)methyl)phenol (L2H) are prepared using the same procedure as described in Chapter 3. The volatiles were removed in vacuo and the residue was dissolved in water (50 mL), extracted with CH2Cl2 (3 × 20 mL), dried over anhydrous Na2SO4 and L1'H was obtained as a colorless oil after removal of the solvent. The same procedure was followed for the synthesis of 2–3 and 1′–3′ using appropriate ligand and co-ligand in the same molar ratio.

Imine function is flat because of the sp2 hybridization for the nitrogen atom, hence ligands L1H and L2H bind to the metal ion in a meridional fashion, while amine function is pyramidal because of the sp3 hybridization for the nitrogen atom and because of that ligands L1'H and L2′ H spans the face positions around the metal center. However, in L1′H, the νN–H peak is obscured by a broad band of νO–H, probably due to the involvement of O–H and N–H groups in hydrogen bonding interactions. Thus penta-coordination around zinc centers can be described as distorted square pyramidal geometry based on the calculated τ value of 0.38 [269].

The cyanate ion is slightly bent at the carbon atom, the angle under C13 being 177.6(3)° and coordinating through the nitrogen atom in a bent manner with an angle of 137.0(2)° at N3. The asymmetric-C6 atom lies in flap at a distance of 0.32 Å from the slightly twisted plane containing other four atoms N2Zn1N1C5. In the six-membered ring, the Zn1 atom lies at a distance of 0.51Å from the slightly twisted plane containing the atoms N2C8C9C14O1.

Schematic representation for the synthesis of 1–3 and 1′–3′

Thermal analyses
Conclusion

ORTEP diagram (30%) and atom labeling scheme in 1′ (all H-atoms except H6 and H20 are omitted for clarity). The Zn2O2 unit in 1' lacks a center of symmetry within the dimeric form and therefore leads to the formation of a homochiral dimer having either a RR or SS combination for the asymmetric carbon atom. As noted in 1', if the absolute configurations of both NA centers are RR, then the C–centers are SS and vice versa.

Compound 3'·DMF crystallized in space group P–1 and ORTEP diagram with the atom labeling scheme 3' is shown in Fig. As observed in 1' and 2', if the absolute configurations of both NA centers are RR, then C centers are SS and vice versa. The hexa-coordinated zinc centers in 2′ and 3′ are intrinsically asymmetric due to the orientation of the chelate rings.

–H···O interactions of DMF with RR and SS bis-chelates in 3′. 6.3.1 Role of Ligand Geometry, Coligands and Weak Interactions:. Amine ligands span facial positions and form a noncentrosymmetric Zn2O2 unit in 1′, resulting in an RR or SS combination of amine. Where as in 1′, the Zn2O2 unit has no center of symmetry in it and has an RR(SS) combination of amine ligand.

Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part B, Fifth Edition, John Wiley & Sons, New Jersey, 2009.

Journals

141 ~ Conferences