LA TRANSICION DEL CAPITALISMO AL COMUNISMO

A family of novel Schiff base ligands (Figure 5.3), N,N’,N’’-tris-(1-H- imidazol-2-ylmethylene)-1-3-5-triphenyl benzene (L8), N,N’,N’’-tris-(1-methyl-1-H- imidazol-2-ylmethylene)-1-3-5-triphenyl benzene (L9), N,N’,N’’-tris-(4-pyridin-2- ylmethylene)-1-3-5-triphenyl benzene (L10), N,N’,N’’-tris-(4-phen-2-ol-2- ylmethylene)-1-3-5-triphenyl benzene (L11) and N,N’,N’’-tris-(2-benzoic acid-2- ylmethylene)-1-3-5-triphenyl benzene (L12) were successfully synthesised. These ligands were prepared from the reaction of 1,3,5-tri(4-aminophenyl)benzene with three equivalents of the relevant aldehyde in methanol. The synthetic routes for the formation of the L8 - L12 ligands are summarised in Figure 5.3.

1_{H NMR spectroscopy (Table 5.1) was employed to confirm the formation of}

L8 - L12. The spectrum of each ligand shows a highly deshielded chemical shift at ca.

Figure 5.3: Schematic representation of the formation of the extended Schiff base ligands L8 - L12. L10

L11

L8 L12

124 9 ppm which arises from hydrogen atoms of the the imine functionalities. Each spectrum also shows proton signals that arise from the aromatic hydrogen atoms of the triphenyl-benzene backbone. The remaining signals observed in the spectra can be assigned to the various head groups of the extended ligands. These assignments are summarised in Table 5.1.

The compounds were also characterised by FT-IR spectroscopy (Table 5.2) which confirms the formation of the imine bonds, as the spectra show a characteristic asymmetric C═N bond stretch at ca. 1630 cm-1 in each case.164 The relevant

molecular ion peak is also observed in the ESI mass spectrum of each ligand (Table 5.2) and elemental analysis (CHN) also confirms the composition of each ligand.

Table 5.1: 400 MHz 1H NMR data for L8 - L12

Ligand Chemical Shift and Assignment

L8 δ = 13.1 (s, 3H, HNH), 8.6 (s, 3H, H4), 7.9 (m, 6H, H5+H6), 7.6 (s, 3H, H1), 7.3 (m, 12H, H2+H3) ppm. L9 δ = 8.7 (s, 3H, H4), 8.0 (m, 6H, H5+H6), 7.9 (s, 3H, H1), 7.7 (d, J = 7.6 Hz, 6H, H2), 7.5 (d, J = 7.6 Hz, 6H, H3), 4.0 (s, 9H, HMe) ppm. L10 δ = 9.5 (s, 3H, H4), 8.9 (d, J = 5.2 Hz, 3H, H5), 8.85 (d, J = 7.6 Hz, 3H, H8), 8.8 (dd, J = 7.6 Hz, 5.4 Hz, 3H, H7), 8.6 (dd, J = 5.2 Hz, 5.4 Hz, 3H, H6), 8.1 (d, J = 8 Hz, 6H, H3), 8.0 (d, J = 8 Hz, 6H, H2), 7.9 (s, 3H, H1) ppm. L11 δ = 12.1 (s, 3H, HOH), 9.1 (s, 3H, H4), 8.0 (m, 6H, H5+H7), 7.7 (d, J = 8 Hz, 6H, H3), 7.6 (d, J = 8 Hz, 6H, H2), 7.5 (s, 3H, H1), 7.0 (m, 6H, H6+H8) ppm. L12 δ = 8.7 (s, 3H, H4), 7.6 (m, 6H, H5+H7), 7.4 (m, 6H, H2+H3), 7.3 (s, 3H, H1), 7.2 (m, 6H, H6+H8) ppm.

Table 5.2: Summary of FT-IR spectroscopic and ESI mass spectrometric data Ligand Asymmetric C=N vibration Molecular ion peak

L8 1628 cm-1 [NaC36H27N9]+ at 608.2 m/z

L9 1627 cm-1 [NaC39H33N9]+ at 650.3 m/z

L10 1629 cm-1 [NaC42H30N6]+ at 641.1 m/z

L11 1627 cm-1 [C45H34N3O3]+ at 664.2 m/z

L12 1630 cm-1 [C48H34N3O6]+ at 748.2 m/z

5.2.3 The crystal structure of L11·2H

O

The re-crystallisation of L11 in acetonitrile yielded colourless single crystals suitable for single crystals X-ray diffraction. L11·2H2O crystallises in the

125 (Figure 5.4) consists of a planar triphenyl-benzene unit to which three coordinating imine ‘arms’ are attached. The phenol ring of each ‘arm’ is twisted relative to the plane of the tri-phenyl benzene core in a propeller-like arrangement. The imine ‘arms’ display dihedral angles of 40.01(2)°, 31.41(2)° and 30.23(2)° with respect to the central benzene ring.

The most notable feature of the molecule is the orientation of the OH groups, which face in the direction of the imino-nitrogen atoms. This arrangement enables the phenol groups to engage in intramolecular hydrogen bonding with the imine nitrogen atoms. The N-O distances for this H-bonding interactions range from 2.546(1) Å to 2.630(1) Å. These distances and other characteristic bond lengths for L11 are summarised in Table 5.3.

In the solid state, the L11 molecules are linked by very weak π-π interactions

and van der Vaals forces resulting in a repeating abab stacking arrangement in the

direction of the crystallographic c-axis (Figure 5.5a). Figure 5.5b highlights the

repeating abab motif viewed in the crystallographic ab-plane. Figure 5.5c reveals the

overall packing structure of L11·2H2O, with the constitutional water molecules

residing in the void spaces between the neighbouring stacks of L11 molecules.

Figure 5.4: The crystal structure of L11. (All hydrogen atoms except phenolic H-atoms and

constitutional water molecules have been removed for clarity.) C black, O red, N blue and H white. Dashed lines indicate intramolecular hydrogen bonding.

126 Table 5.3: Selected bond lengths for L11·2H2O

Bond Bond Length Bond Bond Length

N(1)-C(32) 1.252(1) Å O(3)-C(37) 1.312(1) Å

N(2)-C(39) 1.242(1) Å O(1)-N(2) 2.613(1) Å

N(3)-C(25) 1.162(1) Å O(2)-N(3) 2.630 (1) Å

O(1)-C(45) 1.317(1) Å O(3)-N(1) 2.546(1) Å

O(2)-C(31) 1.416(1) Å

Figure 5.5: The packing arrangement adopted by the L11 molecules as viewed along a) the

crystallographic a-axis and b) the crystallographic c-axis. Alternate L11 molecules coloured red and

blue, respectively.c) The packing structure of L11·2H2O as viewed along the crystallographic c-axis.

C black, O red, N blue and H white.

c)

127 Table 5.4: Crystal data and structure refinement for L11·2H2O

Identification code L11·2H2O

Empirical formula C45H38N3O5

Formula weight 700.80 g mol-1

Temperature 150(2) K

Wavelength 0.71073 Å

Crystal system Orthorhombic

Space group Aba2

Unit cell dimensions a = 31.576(12) Å α= 90°

b = 33.022(13) Å β= 90° c = 7.190(3) Å γ = 90° Volume 7497(5) Å3 Z 2 Density (calculated) 1.233 Mg/m3 Absorption coefficient 0.081 mm-1 F(000) 1580 Crystal size 0.02 x 0.05 x 0.2 mm3 Theta range for data collection 1.23 to 25.00°

Index ranges -27<=h<=30, -31<=k<=31, -6<=l<=6 Reflections collected 12994

Independent reflections 3476 [R(int) = 0.1461] Completeness to theta = 25.00° 99.9 %

Absorption correction None

Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 3476 / 1 / 544

Goodness-of-fit on F2 1.208

Final R indices [I>2sigma(I)] R1 = 0.0894, wR2 = 0.2304 R indices (all data) R1 = 0.1197, wR2 = 0.2512 Largest diff. peak and hole 0.862 and -0.304 e.Å-3

128