Structural Studies of Vanadium Soaps in Solid State By X-Ray Diffraction Analysis

The structure of vanadium soaps (palmitate, stearate) in solid state was studie using x-ray diffraction analysis technique. The x-ray diffraction analysis confirmed that the vanadium soaps possess single layer structure and metal divalent ions are arranged in a parallel plane.


INTRODUCTION
The study of metallic soaps is becoming increasingly important in technological and academic fields. The metallic soaps have high metal contents, which lend them unique properties and make them useful for many applications in industries. The characteristic & structure of metal soaps depend largely on the method and conditions of their preparations. Therefore, studies of metal soaps are of great significance for understanding their characteristics under different conditions and for their use in industry. While majar development have taken palace in the study of alkali and alkaline earth metal and some transition metal soaps, the vanadium soaps (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) have not been thoroughly investigated.
The present work deals with the study of vanadium soap (palmitate, stearate) in solid state using x-ray diffraction analysis technique.

EXPEREMENTAL
All chemicals used were of BDH/AR grade. Vanadium soaps (Palmitate & Stearate) were prepared by direct metathesis of the corresponding potassium soap with slight excess of the solution of vanadium pentaoxide under vigorous Stirring.
The X-ray diffraction analysis of vanadium soaps were obtained with RIGAKU Geiger flex RBRU 200. The Cu -Ka radiation were used over the range of diffraction angle, 2 = 380° (where  is the Bragg's angle). The XRD curves were recorded under the applied voltage of 35 KV using scanning speed 50/minute. The readings of the diffraction angle were made up to 0.01A° and the wavelength of radiation was taken as 1.542 A°.

RESULTS AND DISCUSSION
Generally, the crystals of metal soaps do not grow up to an extent to give a large single crystal sufficient for a detailed single crystal X-ray examination and so the powder diffraction patterns of vanadium soaps (palmitate and stearate) were analysed to characterize the structure of these soaps in solid state.
The intensities of the diffracted X-rays as a function of diffraction angle 2 for vanadium soaps are measured over the range of 360° with the help of x-ray spectrophotometer and the interplanar spacing, have been calculated form the position of intense peaks using Bragg's relationship.
Where  is the wavelength of radiation. The calculated spacings together with the relative intensities with respect to the most intense peak for vanadium soaps are recorded in Table 1, 2. The Xray diffraction of stearic acid was measured as a check of apparatus and its long spacing was 39.84 A° Table 1, which was in good agreement with that (39.75 A°) reported by Francis and Tiper² for stearic acid.
The X-ray diffraction analysis of vanadium soaps (palmitate and stearate) show numerous peaks over the range of 3-60° of Diffraction angle.
The peaks are attributed to the diffraction of X-ray by planes of metal-ions known as basal plane.
The appearance of diffractions up to 20 th and 24 th order for palmitate and stearate of vanadium suggested good crystallinity for these soaps. The order of diffraction (i.e. crystallinity of soaps) increases with increasing chain length of the soap molecules.
The average planner distance i.e. long spacings for palmitate and stearate of vanadium are 44.28 and 49.07 A° respectively Table 1 and 2 differences in long spacings of vanadium palmitate and stearate is 4.79 A° corresponds to double the length of the methylene ( -CH 2 ) groups in the fatty acid radical constituent of the soap molecules. It is, therefore, suggested that he zig-zag chain of the

Hydrocarbon Chain
A number of diffraction peaks in the intermediate range are also observed in the diffraction pattern of vanadium soaps and are attributed to the diffraction of the X-ray by planes of atoms of much smaller separation than the basal planes. The calculated spacings from those peakes correspond to the shorter side spacings i.e. the lateral distance between one shop molecule and the next in a layer.
The value of long and short spacings for vanadium soaps are in agreement with those reported by Koga and Matsuura 14,16 for vanadium penta soaps.
It is therefore, suggested that the soaps posses single layer structure as proposed by Hattiangdi and vold 17,18 in which metal divalent ions are arranged is a parallel plane, i.e. a basal plane, equally spaced in a soap crystal, with fully extended zig-zag chains of fatty acid radical on both sides of each basal plane as the double layer structure for penta soap crystals would be energetically difficult due to the considerable strain of bonds in the ionized carboxyl group of soap molecules. However, the double layer structure is well established for fatty acids.
It is also therefore, concluded that these soaps posses single layer structure with molecular axes some what inclined to the basal planes.