1H NMR study of dodecanuclear polyoxovanadate cluster {V12}

We report 1H nuclear spin-lattice relaxation rates T 1-1 in the magnetic cluster {V12}. While no critical enhancement in 1H T1-1 was found at T∼|J| contrary to other antiferromagnetic molecules, the T1ρ was observed to exhibit a peak at 19 K. The different behavior is discussed in terms of critical effects in classical spins (s = 5/2) vs. quantum spins (s = 1/2). From the exponential drop of the proton T1-1 at low T, we obtained the gap values between the ST = 0 ground state to the excited states: δ1 ≅ 17 K, δ2 ≅ 35 K, and δ3 ≅ 52K