Single-molecule magnets are gaining attention in recent years with the growing focus on achieving higher barriers of magnetization reversal. Metallocenes, owing to their unique sandwiched structure, assure themselves as plausible molecular systems for the development of novel single-molecule magnets (SMMs). Here in this work, we have explicitly investigated metallocenes of firstrow transition elements, along with their one-electron-oxidized (cationic) and -reduced (anionic) analogues, for their magnetic anisotropies by adopting multireference ab initio calculations. Herein, we report a high magnetic anisotropy for 3d 2 systems among all 3d-metallocenes.

Single-molecule magnet (SMM) based quantum technology is gaining attentions in recent years with growing focus on achieving higher barrier of magnetization reversal. Metallocenes owing unique sandwiched-structure, assure themselves as plausible molecular systems for development of novel SMMs. Here in this work, we have explicitly investigated metallocenes of first row transition metal elements, along with their one electron oxidized (cationic) and reduced (anionic) analogues, for their magnetic anisotropies (D) adopting multi-reference ab initio calculations. Herein, we report the unprecedented high D values for 3d^2 systems among all the 3d-metallocenes.

Single-molecule magnets (SMMs) based on transition metals have appeared as enticing targets exploiting the magnetic anisotropy in 3d elements. Among transition metals, Co based SMMs are very prominent as they...

Single-molecule magnet (SMM) based quantum technology is gaining attentions in recent years with growing focus on achieving higher barrier of magnetization reversal. Metallocenes owing unique sandwiched-structure, assure themselves as plausible molecular systems for development of novel SMMs. Here in this work, we have explicitly investigated metallocenes of first row transition metal elements, along with their one electron oxidized (cationic) and reduced (anionic) analogues, for their magnetic anisotropies (D) adopting multi-reference ab initio calculations. Herein, we report the unprecedented high D values for 3d^2 systems among all the 3d-metallocenes.

Single-molecule magnets (SMMs) with large magnetization reversal barrier are predominated by the lanthanide systems due to their strong spin-orbit coupling (SOC). However, the transition metals have also emerged as potential contenders and the largest magnetic anisotropy has been identified for a cobalt system among any d-series based SMMs (Bunting et al. Science 2018, 362, eaat7319). In this work, we have explored the magnetic anisotropy in highly axial ligand field systems of metallocene, having different d-subshell (3d4, 4d4 and 5d4). The wavefunction based multireference methods including static and dynamic electron correlations, have been employed to investigate the zero-field splitting (ZFS) parameters. Here, we report exceptionally large magnetic anisotropy for a 5d complex of [WCp2]0 with highest energy barrier that is nearly twice as high as the previous record value for the Co complex. We have also observed that the axial ZFS parameter (D) is increasing down the group in the order of 3d < 4d < 5d, pertaining to large SOC.

Single-molecule magnets (SMMs) based on transition metals have appeared as enticing targets exploiting the magnetic anisotropy in 3d elements. Among transition elements, Co based SMMs are very prominent as they often exhibit a high spin-reversal barrier (Ueff ), owing to large unquenched orbital angular momentum. Employing the wave function-based multireference CASSCF/NEVPT2 calculations, herein we substantiate the zero-field splitting parameters of four mononuclear Co complexes and one of them has been realized as a prospective SMM. The mechanism of magnetic relaxation has been studied to underpin the molecular origin of the slow relaxation of magnetization. The combination of suppressed quantum tunnelling of magnetization (QTM) at the ground state and the high negative D value usually manifests SMM behavior at zero-applied magnetic field. However, mere fulfillment of these conditions ensure little about their SMM behavior, as spin-phonon couplings often play the role of spoilsports by lowering the spin-relaxations channels. A detailed study accounting all the 46 vibrational modes below the first-excited state for the prospective Co(II) complex reveals one of the vibrational modes, providing lower spin-relaxation pathway and hence, resulting an SMM with Ueff value of 239.30 cm−1.

Single-molecule magnets (SMMs) based on transition metals have appeared as enticing targets exploiting the magnetic anisotropy in 3d elements. Among transition elements, Co based SMMs are very prominent as they often exhibit a high spin-reversal barrier (Ueff ), owing to large unquenched orbital angular momentum. Employing the wave function-based multireference CASSCF/NEVPT2 calculations, herein we substantiate the zero-field splitting parameters of four mononuclear Co complexes and one of them has been realized as a prospective SMM. The mechanism of magnetic relaxation has been studied to underpin the molecular origin of the slow relaxation of magnetization. The combination of suppressed quantum tunnelling of magnetization (QTM) at the ground state and the high negative D value usually manifests SMM behavior at zero-applied magnetic field. However, mere fulfillment of these conditions ensure little about their SMM behavior, as spin-phonon couplings often play the role of spoilsports by lowering the spin-relaxations channels. A detailed study accounting all the 46 vibrational modes below the first-excited state, for the prospective Co(II) complex, reveals one of the vibrational modes, providing lower spin-relaxation pathway. This results an SMM with Ueff value of 239.30 cm−1, decreased by ~81 cm-1 from the value without spin-vibrational coupling.