JJC Jordan Journal of Chemistry Vol. 5 No.3, 2010, pp. 239-252 Synthesis of VO (IV) Complexes and Study of their Liquid Crystalline Behavior Uhood J. AL Hamdani* and Maan abd Al -diem Chemistry Department, College of education, Basrah university,basrah, Iraq Received on March 2, 2010 Accepted on June 6, 2010 Abstract The synthesis and characterization of new homologous series of VO(IV) complexes derived from 4 (4 Chloro benzoyloxy) 2 hydroxyl benzylidine 4 alkoxy aniline (where the alkoxy chain is OCnH 2n+1 and n=1-7, 9,10)are reported. The liquid crystalline properties and phase transitions were studied using polarized hot stage optical microscopy and differential scanning calorimetry (DSC) for the ligands and their complexes. Keywords: Metallomesogens; Oxovanadium; Schiff base. Introduction The synthesis of new metal containing liquid crystals is of great interest at present due to the special combination of liquid crystalline properties and the presence of a transition metal in the structure which introduces unusual electro optic and magnetic properties [1]. Metal complexes of Schiff bases have played an important role in the development of metallomesogens as can be seen from the large number of publications that have appeared in the literature [2,3]. The particular advantage of the salicylaldimine ligand system is the considerable flexibility of the synthetic procedure which has allowed the preparation of a wide variety of complexes whose properties are strongly dependent on the ligand structure and on the metal used [1]. Ovchinnikov etal have carried out some systematic studies on such kinds of complexes [4] and the mesomorphic properties of several series of Cu (II), Ni (II) and VO (IV) complexes derived from N alkyl and N aryl salicyldimines have been described [5] and the relationship between mesogenic behavior and molecular structure have been studied [6]. To improve our knowledge of the relationship between molecular structure, thermal stability and mesogenic properties, we present in this paper the synthesis and mesogenic properties of new series of ligands and the VO (IV) complexes derived from these ligands. Their general structures are presented in figure1. * Corresponding author: E-mail: uhood1959@yahoo.com 239
Figure1: Structures of ligands and complexes 240
Experimental Synthesis The preparation of the ligand and their complexes were performed according to scheme 1. Schem.1: synthesis of ligands and complexes. 241
Synthesis of 4 chloro benzoyl chloride A mixture of 4 chloro benzoic acid (0.1 mole), SOCl 2 (0.15 mole) and two drops of DMF was refluxed until the evolution of SO 2 and HCl gases ceased. The excess SOCl 2 was distilled off and the product obtained as a yellow liquid which was used immediately in the following step (yield 75%). Synthesis of 4 (4 Chloro benzoyloxy) 2 hydroxy benzaldehyde A solution of 4 chloro benzoyl chloride in CH 2 Cl 2 as a solvent and triethyl amine (3 ml) was added with stirring to a cooled solution of 2, 4 dihydroxy benzaldehyde (0.1 mole) in triethylamine (3 ml). Stirring was continued (4hr) at room temperature, the mixture was filtered and acidified with diluted HCl (0.1M). The precipitate was then separated by filtration washed first with water, then with a 10% solution of Na 2 CO 3 and again with water. The product was recrystallized from ethanol (yield 45%). Synthesis of alkyloxy aniline a. Synthesis of 4- acetamido phenol A solution of (0.127 mole) acetic anhydride was added to a solution of (0.1 mole) 4- amino phenol in 30 ml of distilled water. The reaction mixture was heated at 70 0 C with continuous stirring for 10 minutes. The mixture was then cooled to room temperature. A black needle shaped crystalline precipitate was formed.it was recrystallized from distilled water yield (60%). b. Synthesis of 4- alkoxy acetamido benzene A solution of (1.75g ) sodium hydroxide dissolved in 2 ml of water was added to the solution of 4-acetamido phenol (0.025 mol) in 20 ml of hot ethanol slowly with stirring, then added portion wise to the above mixture a solution of (0.0275 mole) appropriate alkyl bromide (C 2 C 10 ) with continuous stirring. The reaction mixture was refluxed for one hour. The mixture was allowed to cool, a white precipitate was separated by filtration and finally the product was washed with enough amount of distilled water until the washing water became neutral. The solid product was recrystalized from ethanol / water (3:1). (yield 65%) C.Synthesis of 4- alkoxy aniline Asolution of (4ml) 2M sodium hydroxide was added to the solution of (0.012 mol) 4- acetamidoalkoxy benzene (C 2 C 10 ) in ethanol. The reaction mixture was refluxed with stirring for five hours. The product was extracted twice with benzene. The extract was then washed with water and dried with anhydrous magnesium sulphate. After evaporation a thick oily red liquid (n = 2 8) or a solid for (n = 9 and 10) was produced. Yield (75%). Synthesis of ligands The respective ligands were synthesized using the known method [7] by mixing an ethanolic solution of (1 mol) 4 (4 Chloro benzoyloxy) 2 hydroxy 242
benzaldehyde with(1 mol) of appropriate amine and 2 drops of acetic acid as catalyst. The reaction mixture was heated under reflux for 2h, the solution was allowed to cool, the yellow precipitate was separated by filtration and finally the product was recrystallized several times from heptan to yield the pure Schiff bases(yield 65%). Synthesis of VO (IV) complex: Oxovanadium (IV)complexes were synthesized by addition of methanolic solution (20 ml) containing vanadium (IV) oxide sulfate (VOSO 4.5H 2 O) (0.33 mole) in the presence of 1ml of triethyl amine to a hot solution of the appropriate ligands (0.7 mol) in 40 ml methanol. The solution was refluxed for 3h. After cooling the precipitate was collected by filtration and recrystallized from ethyl acetate (yield 60%). Instruments The 1 HNMR was carried out by (NMR 400MHz Bruker). IR spectra were recorded on FTIR 8400S spectrophotometer using KBr discs. UV spectra were recorded on apye unicame UL 1500 spectrophotometer and the elemental analysis were done by elemental Micro analysis. The phase transitions were observed with a leitz Laborlux 12 POl optical microscope with polarized light in conjunction with a leitz 350 hot stage equipped with a vario orthomat camera. Measurements of transition temperature were made using a perkin Elmer DSC 7 differential scanning calorimeter with heating rate 10 o C min -1. Results and discussion Characterization The new ligands presented here were characterized by elemental analysis and various spectroscopic methods, 1 H NMR, IR and UV- Visible.The proposed structures are in full agreement with these spectroscopic data. The complexes were characterized by elemental analysis and and IR and UV- Visible spectroscopy. The elemental analysis of the ligands and the complexes are consistent with their proposed structures (table.1 and 3). Table 1: Elemental analytical data (calculated values in parentheses) the most relevant IR data for ligands Molecular Compound %C % N % H (C=O),cm -1 (C=N),cm -1 formula SB 1 C 21 H 16 O 4 NCl 66.05(66.5 ) 3.66(3.87) 4.19(4.20) 1740 1635 SB 3 C 23 H 20 O 4 NCl 67.39(66.97) 3.41(3.18) 4.88(4.92) 1740 1638 SB 4 C 24 H 22 O 4 NCl 68.00(67.60) 3.30(3.43) 5.19(5.21) 1742 1637 SB 6 C 26 H 26 O 4 NCl 69.10(68.61) 3.10(3.21) 5.75(5.79) 1740 1638 SB 7 C 27 H 28 O 4 NCl 69.60(69.28) 3.00(3.09) 6.01(6.04) 1742 1635 SB 9 C 29 H 32 O 4 NCl 70.51(70.21) 2.83(2.96) 6.48(6.52) 1740 1635 SB 10 C 30 H 34 O 4 NCl 70.93(70.50) 2.75(3.00) 6.69(6.72) 1740 1635 243
The 1 H NMR data of the ligands give definite evidence for the molecular structure (figure.2 and table.2). The (HC =N) value of ~ 8.60 ppm for the ligands is well within the range expected for imine compounds [8]. Table 2: 1 H- NMR data for ligands (ppm) Compound OH CH =N Aromatic protons Aliphatic protons SB 1 13.90 8.60 6.86 8.06 OCH 3 (S,3.38) SB 3 13.90 8.60 6.86 8.06 OCH 2 (t, 3.95), CH 2 (H, 1.85) CH 3 (t, 1.08) SB 4 13.90 8.59 6.86 8.06 OCH 2 (t, 4.00), CH 2 (P, 1.76) CH 2 (P,1.45)CH 3 (t, 0.90) SB 6 13.89 8.60 6.86 8.06 OCH 2 (t, 4.06), CH 2 (P, 1.76) CH 2 (P,1.43), (CH 2 ) 2 (m,1.29 1.31), CH 3 (t, 0.88) SB 7 13.88 8.60 6.86 8.06 OCH 2 (t, 4.00), CH 2 (P, 1.76) CH 2 (P,1.45), (CH 2 ) 3 (m,1.29 1.31) CH 3 (t, 0.95) SB 9 13.90 8.60 6.86 8.06 OCH 2 (t, 4.00), CH 2 (P, 1.76) CH 2 (P,1.45), (CH 2 ) 5 (m,1.29 1.31) CH 3 (t, 0.95) SB 10 13.90 8.60 6.86 8.06 OCH 2 (t, 4.06), CH 2 (P, 1.76) CH 2 (P,1.43), (CH 2 ) 6 (m,1.29 1.31)CH 3 (t, 0.88) 244
Figure 2: 1 H-NMR Spectra for the Ligand (SB 3 ) 245
The IR spectra of both the ligand and the complexes show the C =N stretching frequency at expected values (table.1 and 3), the C = N stretching vibration in the ligands is located in the 1635 1638cm -1 region and is shifted to lower wavenumbers (approximately 5-8 cm -1 ) upon chelation, indicating that the azomethine N is involved in metal nitrogen bond formation [9]. The oxovanadium complexes also exhibit a stretching band around 880 cm -1 assigned to V O. Table 3: Elemental analytical data (calculated values in parentheses) the most relevant IR data for complexes Compound Molecular formula %C % N % H (C=O),cm -1 (C=N),cm -1 VO(SB 1) 2 VC 42 H 30 O 9 N 2 Cl 2 60.88(60.51) 3.64(3.68) 3.38(3.40) 1735 1630 VO(SB 3) 2 VC 46 H 38 O 9 N 2 Cl 2 62.45(62.01) 4.32(4.35) 3.16(3.19) 1738 1630 VO(SB 4) 2 VC 48 H 42 O 9 N 2 Cl 2 63.16(62.70) 4.63(4.87) 3.06(3.11) 1735 1628 VO(SB 6) 2 VC 52 H 50 O 9 N 2 Cl 2 64.46(64.81) 5.20(5.47) 2.89(2.91) 1735 1630 VO(SB 7) 2 VC 54 H 54 O 9 N 2 Cl 2 65.06(64.55) 5.46(5.71) 2.81(2.69) 1735 1628 VO(SB 9) 2 VC 58 H 62 O 9 N 2 Cl 2 66.15(65.69) 5.93(5.90) 2.66(2.55) 1738 1630 VO(SB 10) 2 VC 60 H 66 O 9 N 2 Cl 2 66.66(66.20) 6.15(6.18) 2.59(2.71) 1735 1629 The electronic spectra (in CHCl 3 ) of the ligands show amost identical the absorption bands at 239, 275, 352, nm, whereas the absorption bands of the complexes shift to 265, 303, 379 nm (figure.3) as well as a broad absorption band in 670 nm is assigned for d-d transition (figure.4). Length (nm) Figure 3: UV spectrum for SB 9 and VOSB 9 in 1x10-5 M 246
Length (nm) Figure 4: Visible spectrum for SB 9 and VOSB 9 in 1x10-3 Mesogenic behavior The optical microscope and thermal data of the ligands and its VO(IV) complexes are summarized in table 4 and 5 respectively. The ligands and its complexes show two phases (figures5 and 6) nematic (N) phase and Smectic C (Sc). All members of the ligands show Nematic phase with Smectic C (Sc) phase appearing at SB 5, but in the VO complex show Nematic phase at VO(SB 1 ) 2 until VO(SB 7 ) 2 with Smectic C phase appearing at VO (SB 6 ) 2 to the last member studied VO(SB 10 ) 2. Table 4: Phase transition temperatures ( o C) ligands Compound C Sc C N S C - N N I T S T N SB 1-170 - 282 112 SB 2-173 - 277 104 SB 3-168 - 269 101 SB 4-170 - 260 90 SB 5 151-185 251 34 66 SB 6 160-261 248 41 47 SB 7 150-214 240 64 26 SB 9 131-222 234 90 12 SB 10 125-228 231 103 3 C : Solid N : Nematic S : Smectic I : Isotropic T S : Smectic thermal range T N : Nematic thermal range 247
Table 5: Phase transition temperatures ( o C) for complexes Compound C Sc C N S C N S I N I T s T N VO(SB 1) 2 208 308-100 VO(SB 2) 2 211 301-90 VO(SB 3) 2 209 298-89 VO(SB 4) 2 220 295-75 VO(SB 5) 2 238 293-55 VO(SB 6) 2 217-252 290 35 38 VO(SB 7) 2 222-269 288 47 19 VO(SB 9) 2 228-282 - 54 - VO(SB 10) 2 216-276 - 60 - C : Solid N : Nematic S : Smectic I : Isotropic T s : Smectic thermal range T N : Nematic thermal range Figure 5: DSC thermogram for the ligand (SB 9 ) Figure 6: DSC thermogram for the complex VO(SB 9 ) 2 This is to be expected since these ligands have long molecular lengths coupled with extension of the conjugation through the linking ester and azomethine groups (this means an increase of the electronic polarizability of the molecule), the introduction of a 248
hydroxyl group in the 2 position (ortho) to the azomethine group leads to a strong chelation ring [10] by means of an intrahydrogen bond. This hydrogen bonding is reported [11, 12] to favor mesomorphism due to the increase in molecular planarity, the appearance of local permanent dipole moments. These factors cause an increase in the anisotropy of of the polarizability for molecules with three aromatic rings, which promotes molecular interactions and liquid crystal properties. The nematic and smectic phases exhibited by these ligands and complexes, show textures that are typical of these types of mesophases.the nematic phase reflected the marbled texture on heating and schlieren texture on cooling (figure 7). The smectic C phase displayed typical schlieren texture (figure 8). a Figure 7 : Optical texture of the nematic phase a- Marble Texture on heating at 157 0 C for SB 1 b-schlieren Texture on cooling at 240 0 C for SB 6 b 249
a b Figure 8: Optical texture of the Smectic phase a- Schlieren Texture on heating at 230 0 C for VO(SB 7 ) 2 b- Schlieren Texture on cooling at 255 0 C for VO(SB 7 ) 2 A plot of the transition temperatures against the number of carbon atoms (n) in the alkoxy chain for the studied SBn, VOSBn compounds are given in figures 9 and 10 respectively. 250
n(carbon number of terminal alkyl groups) Figure 9: phase transition temperatures as afunction of the alkyloxy chain length for the ligands n(carbon number of terminal alkyl groups) Figure 10: Phase transition temperatures as a function of the a lkyloxy chain length for the complexes The nematic isotropic transition temperature curve is a falling one as the length of the chain increases, the nematic phase stability range decreases, while that of the smectic phase increases. The (VO) complexes melt at higher temperatures than the ligands and the clearing temperatures are also higher. However, the mesophase ranges are wider in the ligands than in the VO complexes. The steric effect of the (VO) group decrease the 251
stability of the mesophase (figure 11). The oxovanadium (IV) complex a square - pyramidal geometry (dsp 3, 2 D 3/2 ) [13,14]. References Figure 11: Structure of a-ligand SB 3 ; b-complex VO(SB 3 ) 2 [1] Campillos,E.; Marcose,M.; Serano, J. L.,Chem.Mater.,1993, 5(10), 1518-1525. [2] Giroud, A.; Maitlis, P, Angew. Chem. Int. Ed. Engl., 1991, 30, 375. [3] Espinet,P.; Esteruelas, M, Chem.Rev., 1992, 117, 215. [4] Ovchinnikov,I.; Galyametdinov, Yu.; Galyametdinov, G., Doki. Akad. Nauk SSSR., 1984, 276, 126. [5] Marcose, M.; Serano, J. L.; Romero, P, Chem.Mater., 1990, 2, 495. [6] Marcose, M.; Serano, J. L.; Romero, P, Mol. Cryst. Liq. Cryst.,1989, 167, 123. [7] Singh, A.; Kumar.S.; Kumar, K, Polyhedron, 2008, 27, 181-186. [8] Ghedini,M.; Morrone, S, Chem.Mater., 1991,3,752. [9] Campillos, E.; Marcose, M.; Omenat, A., J. Mater. Chem., 1996, 6(3), 349 355. [10] Prajapati, A.; Bonde, L., J. Chem. Sci., 2006, 2, 203 210. [11] Vora, R.; Prajapti, A., Bull. Mater. Sci., 2002, 25(4), 355 358. [12] Haase, W.; Wrobel, S, J. Phys., 2003, 61(2), 189 198. [13] Alonso, P.; Serano, J. L.; Marcose, M, Adv. Mater., 1995, 7, 173-176. [14] Iglesias, R.; Marcose, M., Chem.Mater., 1996,8, 2611-2617. 252