**Acknowledgements**

The authors are thankful to the Departmental Special Assistance Scheme, under the University Grants Commission, New Delhi (SAP-DRS-III, NO.540/12/ DRS/2013) and SAIF, NEHU, Guwahati, India for 1 H NMR, 13C NMR, ESI-MS and elemental analysis. Again authors are grateful to Annamalai University, Tamil Nadu, India for PXRD analysis.
