Polyoxovanadates with Ethylidene-Pyridine Functionalized Bisphosphonate Ligands: Synthesis, Structure, Spectroscopic Characterization, Magnetic, and Antibacterial Studies
Dewendra Thakre, Sk Rajab Ali, Sakshi Mehta, Noohul Alam, Masooma Ibrahim, Debajit Sarma, Abhishake Mondal, Mrinmoy De, Abhishek Banerjee
Abstract
Reaction of ethylidene-pyridyl functionalized bisphosphonates with vanadium containing oxo compounds has afforded three different bisphosphonate–polyoxovanadate derivatives, viz., [(VIVO2)(VV2O5)2{O3P-C(O)(CH2-2-C5NH4)-PO3}2]10– (1), [(VIVO2)(VV2O5)2{O3P-C(O)(CH2-3-C5NH4)-PO3}2]10– (2), [(VIVO)3(O){O3P-C(OH)(CH2-4-C5NH4)-PO3}3]8– (3), obtained in aqueous ammonium acetate buffer solutions (pH 4.7). Polyanions 1 and 2 were synthesized by the reaction of V2O5 with 1-hydroxy-2-(2-pyridyl) ethylidene-1,1-bisphosphonic acid (L1) and 1-hydroxy-2-(3-pyridyl) ethylidene-1,1-bisphosphonic acid (L2), respectively. Polyanion 3 was obtained by the reaction of VOSO4 with 1-hydroxy-2-(4-pyridyl) ethylidene-1,1-bisphosphonic acid (L3), in the presence of pyrazine. Single-crystal X-ray diffraction and elemental analysis reveal that all the polyanions are crystallized as ammonium salts, (NH4)4[H6(VIVO2)(VV2O5)2{O3P-C(O)(CH2-2-C5NH4)-PO3}2]·9H2O (1a), (NH4)4[H6(VIVO2)(VV2O5)2{O3P-C(O)(CH2-3-C5NH4)-PO3}2]·8H2O (2a), and (NH4)2[H6(VIVO)3(O){O3P-C(OH)(CH2-4-C5NH4)-PO3}3]·26H2O (3a), respectively. Polyanions 1 and 2 crystallize in the non-centrosymmetric space group P21212 and have an S-shaped assembly containing two different sets of vanadium atoms, based upon their oxidation state and different coordination environments. Polyanion 3 crystallizes in the centrosymmetric trigonal space group R3c and is observed to have a highly symmetric trinuclear structure. The polyanions have been characterized in solution with 1H and 31P NMR and optical spectroscopy, and in the solid state with detailed magnetic analysis. The magnetic studies under an external dc field showed paramagnetic behavior in agreement with the presence of V(IV) ions for 1a–3a. Furthermore, in vitro studies of the synthesized bisphosphonate–polyoxovanadate compounds were observed to exhibit peroxidase-like activity, and hence were employed to enhance the antibacterial activity of H2O2 solution at very low concentrations, thereby minimizing the possibilities of other side effects. Isostructural derivatives of compounds 1a and 2a with L3, viz., (NH4)4[H6(VIVO2)(VV2O5)2{O3P-C(O)(CH2-4-C5NH4)-PO3}2]·11H2O(4a), has been identified using infrared spectroscopy and characterized with NMR spectroscopy and elemental analysis. Similarly, an isostructural derivative of 3a with L2, viz., (NH4)2[H6(VIVO)3(O){O3P-C(OH)(CH2-3-C5NH4)-PO3}3]·21H2O (5a), has also been identified using infrared spectroscopy and characterized with elemental analysis.