Material Synthesis Solubility

2.2 EXPERIMENTAL PROCEDURE

2.2.1 Material Synthesis, Solubility and Crystal Growth

The title compound of BTPCA was synthesized from commercially available 1H-1,2,3 Benzotriazole (C6H5N3) (Spectrochem, AR grade, purity 99%) and pyridine-2-carboxylic acid (C6H5NO2) (Spectrochem, AR grade, purity 99%). The amounts of raw materials in equimolar ratio were dissolved in 100 ml of methanol and prepared solution was stirred well for 6h using a motorized magnetic stirrer to get homogeneous mixture. The chemical reaction for BTPCA compound is given in Figure 2.1. The starting material is miscible in water and it is highly soluble in methanol.

The solubility of benzotriazole pyridine-2-carboxylic acid in methanol was assessed as a function of temperature in the range 30o-50oC. The concentration of the solute at specific temperature was determined by a gravimetric method. The BTPCA compound exhibits a positive solubility gradient with moderate solubility as shown in Figure 2.2. The prepared growth solution was taken in a beaker and covered with perforated polythene sheet. Then, the saturated solution was kept in a constant temperature path (35oC) to avoid temperature fluctuation and to maintain constant temperature throughout the growth period, which gives the defect free crystals.

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The synthesized compound was further purified by repeated recrystalization process in methanol. After allowed to evaporate the mother solution, the colourless crystals of size upto 13 x 5 x 6 mm3 have been obtained in the span of 15 days and the grown crystals are shown in Figure 2.3.

Figure 2.1 Synthesis scheme for BTPCA compound

Figure 2.2 Solubility diagram of BTPCA in methanol

Figure 2.3 Photograph of as grown of BTPCA by slow evaporation

2.3 RESULTS AND DISCUSSION

2.3.1 Single Crystal and Powder X-ray Diffraction Studies

The crystal system and lattice parameters were determined from single-crystal X-ray diffraction data. Bruker Kappa Apex II single crystal X-ray diffractometer with MoK? (? = 0.71013 ? ) radiation was used to measure cell parameters of BTPCA crystal with typical cell dimension of 0.28 x 0.24 x 0.18 mm3. The structure was solved and refined by the direct method and the full matrix least-squares technique respectively on F2 employing the SHELXL-97 program package (Bruker et al 2004, Sheldrick et al 2008). The cell parameters were obtained from the least square refinement of the setting angle of all the observed reflections. The molecular structure of the title compound, BTPCA (C12H10N4O2) is illustrated as ORTEP diagram in Figure 2.4. The asymmetric unit of the title compound comprises of 1H-1,2,3-benzotriazole and pyridine-2-carboxylic acid (Picolinc acid). The BTPCA crystallizes in orthorhombic crystal system with space group Pna21 is a non-centrosymmetric. The cell parameters are a = 22.691(3) ?, b = 3.9030(5)?, c = 12.7562(13)?, ? = ? = ? = 90° and volume V = 1129.7(2) ?3. The crystal data and structure refinement of BTPCA crystal are listed in Table 2.1. In compound of BTPCA, all the bond lengths and angles are within normal ranges (Allen et al, 1987, Cremer et al 1975). The benzotriazole ring is mostly planar with a dihedral angle of 0.31(2)o between the N1 N3/C1/C6 triazole and C1 C6 benzene rings. The N N bonds within the triazole ring clearly maintain their localized character (cf. N1 N2 = 1.304(3) ?, N3 N2 = 1.346(3) ?), which is, however, not reflected in the adjacent bonds. The lengths of the remaining in-ring bonds, N1 C6, C1 C6 and C1 N3 differ by less than 0.006 ? along chain axis, while all in-ring angles span in a range of 104.2(2) 110.7(2)o. On the other hand, the variation in the analogous parameters describing the geometry of the annealating benzene ring is less pronounced (cf.C C = 1.357(3) 1.404(3) ?, C C C = 115.9(2) 122.5(2)o).

The pyridine ring is essentially planar with the maximum deviation from planarity being 0.005(2) ? for atom C8. The picolinc acid is also planar with the maximum deviation from planarity being 0.031(2) ? for atom O2. The atom O2 is typical double bond character (C7-O2 = 1.200(3) ?). The molecules are linked by O H···N, N H···O and N H···N (Table 2) hydrogen bonds, forming a two-dimensional zig-zag chain along the b-axis and the crystal packing diagram is shown in Figure 2.5. The crystal structure is further stabilized by ?-? interactions involving the benzene (C1-C6) and triazole (N1-N3/C1/C6) rings, with centroid-to-centroid distance of 3.5547 (14) ? (symmetry code: X, -1+Y, Z).

Full crystallographic data of the crystal structure have been deposited with the Cambridge Crystallographic Data Centre as CCDC-1498882. The copies of this information can be obtained at free of charge from the Cambridge Crystallographic Data Centre, Cambridge CB2 1EZ, UK.

Powder X-ray diffraction pattern of the grown crystal of BTPCA is shown in the Figure 2.6. Powder X-ray diffraction pattern for the grown crystal was recorded by using BRUKER AXS CAD 4 with 1.5406 ? CuK? radiations. Data were obtained over 2? range of 10-70o using step scan of 0.04o. The measured reflections were completely indexed using the program of powder-X software. From the powder pattern, miller indices of reciprocal lattice values are indexed with help of the JCPDS. The high intensity peaks appeared at (401), (411) and (211), shows that the grown crystal of BTPCA exhibits good crystallinity in nature.

Figure 2.4 ORTEP diagrams of BTPCA crystal (or) Molecular configuration and atom numbering scheme for the title compound. Displacement ellipsoids are drawn at the 50% probability level

Figure 2.5 Crystal packing diagram of BTPCA (or) Packing diagram of the title compound shows O H···N, N H···O and N H···N hydrogen bonds link the molecules into a zig-zag chain