Quantum Rotations and Chiral Polarization of Qubit Prototype Molecules in a Highly Porous Metal-Organic Framework: 1H NMR T1 Study

Rotations of bistable diazabicyclooctane (dabco) molecules N-2(C2H4)(3) in a layered highly porous metal-organic framework [Zn-2(C8H4O4)(2)center dot N-2(C2H4)(3)] have been studied at 310-8 K by the H-1 NMR spin-lattice relaxation method. Above 165 K, the relaxation is characterized by a single longitudinal relaxation time, T-1, related to the hindered rotation of the dabco molecules. Below 165 K, the quantum tunneling mechanism was found to be responsible for dabco reorientation and spin relaxation. At 165-25 K, the system is characterized by two different spin-lattice relaxation times, T-1_1 and T-1_2, related to two separate states of dabco in the ratio of similar to 1:2. The first state is related to the conformation of point symmetry D-3/v and the second to the sum of right- and left-twisted D-3 forms. At 25 K, a transition to a low-temperature phase occurs. The transition is characterized by three different spin-lattice relaxation times, T-1_1, T-1_2, and T-1_3, related to three conformation states of dabco in the ratio of similar to 2:3:5. The observed relationship of state populations indicates an inequality of right- and left-twisted forms and a chiral polarization of the system because of the break in its right/left symmetry.