Crystal lattice effect on the quenching of the intracluster magnetic interaction in [V₁₂B₁₈O₆₀H₆]¹⁰⁻polyoxometalate

Abstract

In the present work, the synthesis and structural characterization of four new polyoxovanadoborate (BVO) frameworks based on the [V12B18O60H6](10-) polyanion are reported: (NH4)8(1,3-diapH2)[V12B18O60H6]·5H2O (1), K8(NH4)2[V12B18O60H6]·18H2O (2), K10[V12B18O60H6]·10H2O (3) and K8Cs2[V12B18O60H6]·10H2O (4). A global antiferromagnetic behaviour is observed for these 10V(IV)/2V(V) mixed valence clusters. The magnetic data of 1, 2 and 3, which present different countercation environments, show that 1 is more coupled than 2 and 3. DFT calculations show that the positive charges strongly influence the polarization mechanism of the spin density of the vanadyl groups and the extent of the magnetic orbitals, therefore corroborating the experimental observation of the quenching effect of the magnetic coupling between vanadium centres of 2 and 3.

Structural and Electronic Properties of Polyoxovanadoborates Containing the [V12B18O60] Core in Different Mixed Valence States

“…Among all the counterbalancing alkaline ions of the [V12B18O60] polyanions, Li + is found to be five-coordinated, with a square pyramidal geometry (SPY-5) [58], while Cs + is eight-coordinated in a hexagonal bipyramidal geometry (HBPY-8) [57]. On the other hand, Na + and K + are found with more than one coordination number.…”

“…Among all the studied compounds included in this review, the magnetic properties of only (5), (11), (12), (15), (18), (19), (27), and (38) have been reported [53][54][55]57,63]. All of these systems have a mixed valence ratio of 10V IV /2V V , and present a bulk antiferromagnetic behavior.…”

“…In lattices (2) and (3), the diammonium cations do not adopt a preferential order in the lattice, whereas the (H3teta) 3+ molecules in framework (4) are defined by the authors as forming pseudo-hexagonal channels [34]. In framework (5), the (1,3-diapH2) 2+ cations are described as all oriented along the c axis [57]. Within all the crystalline lattices, each protonated diamine connects four [V12B18O60H6] 1°− clusters through unidirectional, bifurcated, and trifurcated hydrogen bonds, thus generating supramolecular structures [59].…”

“…In general, the two absorption bands in the high energy region are assigned as O→V and O→B charge transfer transitions, respectively. The less intense band in the low energy region has been assigned to Intervalence Charge Transfer Transitions (IVCT) and to d-d transitions [34,48,[52][53][54][55]57,58,63,67]. With respect to the low energy absorption bands (ca.…”

“…In 2014 we reported a new crystalline system (5) containing (1,3-diapH2) 2+ and ammonium as counterbalancing ions. The synthesis was also carried out using the hydrothermal method, in which the ammonium ions were included in the lattice by adding (NH4)2HPO4 to the reaction mixture [57].…”