Reaction of ethylidenepyridyl-functionalized bisphosphonates with vanadium containing oxo compounds has afforded three different bisphosphonate-polyoxovanadate derivatives, viz. 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,Polyanions 1 and 2 crystallize in the non-centrosymmetric space group P21212 and have an Sshaped assembly containing two different sets of vanadium atoms, based upon their oxidationstate and different coordination environments. Polyanion 3 crystallizes in the centrosymmetric trigonal space group R𝟑 ̅ c and is observed to have a highly symmetric trinuclear structure. The polyanions have been characterized in solution with 1 H and 31 P 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 3 possibilities of other side effects. Isostructural derivatives of compounds 1a and 2a with L3, viz. 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(V IV O)3(O){O3P-C(OH)(CH2-3-C5NH4)-PO3}3]•21H2O (5a), has also been identified using infrared spectroscopy, and characterized with elemental analysis.

No abstract

Due to their potential future applications in high-density data storage devices, single-ion magnets (SIMs) have become one of the most exciting classes of materials for research at present. Vanadium complexes, with their unique multiple oxidation states and coordination geometries, are excellent candidates for investigating such properties. In the present study, we have explored the SIM properties of two mixed-valent organo-polyoxovanadyl complexes, viz. (NH 4 ) 4 [H 6 , each of which contains four vanadium(V) atoms and one vanadium(IV) atom. One unpaired electron on the central Kramers vanadium(IV) (S = 1/2) atom gives the molecule its magnetic moment, which is responsible for the reversal of its magnetization/spin at low temperatures. As such, the investigation of these complexes has involved a combination of experimental techniques, including superconducting quantum interference device (SQUID) magnetometry, electron paramagnetic resonance (EPR) spectroscopy, and a computational technique that used the CASSCF-based wave function theory and included relativistic effects by considering NEVPT2 for more accurate results. AC magnetic susceptibility measurements have revealed the single ion magnet (SIM) behaviors of both the complexes under the application of an external DC magnetic field, which were characterized by maxima in the plots of the "out-of-phase" magnetic susceptibility against the AC frequency (χ″ vs ν) at different temperatures. The spin relaxation time (τ) has been determined to be in the range of 2−10 K. From the fitting of the plot of relaxation time (τ) versus temperature to different models, we have tried to understand the type of slow relaxation process present in the system under a particular applied DC magnetic field. Finally, the ab initio method, viz. the CASSCF-based computational methods, has been employed to justify/ rationalize and correlate the experimental results.

No abstract