Unconventional Heisenberg spin triangle in magnetic molecule {V15}: A proton nuclear magnetic resonance study

Abstract

We present results of H1 nuclear magnetic resonance (NMR) and relaxation in polyoxovanadate cluster {V15} with formula K6[V15As6O42]⋅9(H2O). The data in {V15} are compared with the published data in {V6} with the formula [CN3H6]4Na2[H4{V3L}2P4O4]⋅14H2O, which contains two independent spin triangles. Temperature T and field H dependence of the NMR linewidth are well explained by the magnetic dipolar interaction between the proton nuclei and vanadium ion spins in both compounds. T and H dependence of proton relaxation rate T1−1 show great differences in the two compounds. The difference indicates a completely different spin dynamics for the two Heisenberg spin-triangle systems whereby in {V15} the fluctuations of the VIV (s=1/2) in the central triangle are dominated by the interlayer coupling with the VIV spins in the two upper and lower hexagons.