With the ongoing effort to obtain mononuclear 3d-transitionmetal complexes that manifest slow relaxation of magnetization and, hence, can behave as single-molecule magnets (SMMs), we have modeled 14 Fe(III) complexes based on an experimentally synthesized (PMe 3 ) 2 FeCl 3 complex [J. Am. Chem. Soc. 2017, 139 (46), 16474−16477], by varying the axial ligands with group XV elements (N, P, and As) and equatorial halide ligands from F, Cl, Br, and I. Out of these, nine complexes possess large zero field splitting (ZFS) parameter D in the range of −40 to −60 cm −1 . The first-principles investigation of the ground-spin state applying density functional theory (DFT) and wave function-based multiconfigurations methods, e.g., SA-CASSCF/NEVPT2, are found to be quite consistent except for few delicate cases with near-degenerate spin states. In such cases, the hybrid B3LYP functional is found to be biased toward high-spin (HS) state. Altering the percentage of exact exchange admixed in the B3LYP functional leads to intermediate-spin (IS) ground state consistent with the multireference calculations. The origin of large zero field splitting (ZFS) in the Fe(III)-based trigonal bipyramidal (TBP) complexes is investigated. Furthermore, a number of complexes are identified with very small ΔG HS−IS adia. values indicating the possible spin-crossover phenomenon between the bistable spin states.

The development of stimuli responsive systems that can switch between two distinct spin states under the application of an external stimuli has always remained an illusory challenge. Here, we report...

With ongoing efforts to synthesize super-stable Blatter's diradicals having strong ferromagnetic exchange interactions, all the ten possible isomers of di-Blatter diradical coupled through the fused benzene rings are investigated. A variety of electronic structure theory such as broken-symmetry methods in density functional theory (DFT), spin-constraint DFT (CDFT), and wave function-based multi-configurational methods e.g. CASSCF/NEVPT2 are applied to compute the magnetic exchange interactions. Surprisingly, anti-ferromagnetic interactions are revealed for all the stable isomers of di-Blatter diradicals. Indeed it commensurates with the experimental observations for the only available synthesized isomer. However, the other nine isomeric diradicals in the series are yet to synthesize. Despite a good match between theory and experiment, the anti-ferromagnetic exchange interactions could not be explained based on the spin alternation rule due to unique spin-distributions in the triazinyl ring. Thus, we propose the zonal spin-alternation rule which explains the observed ground spin-state for the conjugated di-Blatter diradicals quite accurately. Further, the fractional spin-moment localization on the N-atoms activates multiple exchange pathways and the dominating exchange interactions render anti-ferromagnetic interactions in the conjugated isomers. The study further reveals that due to strong steric hindrance in certain coupled isomers, the exchange interaction switches from anti-ferromagnetic to weak ferromagnetic interactions with the cost of stabilization energy of the radicals. Thus it questions the possibility of synthesizing ferromagnetic di-Blatter diradicals.

In the quest of obtaining organic molecular magnets based on stable diradicals, we have tuned the inherent zwitterionic ground state of tetraphenylhexaazaanthracene (TPHA), the molecule embraced with two Blatter’s moieties,...

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.

The recent accomplishments in obtaining strong ferromagnetic exchange interactions in organic diradicals have made the field quite fascinating and even more promising toward its technological applications. In this context, herein, we report a unique combination of remarkably strong ferromagnetic exchange interactions coupled with molecular rigidity, utilizing superstable Blatter's radical as a spin source. The planar analogues of the parent Blatter's radical obtained by annulation with a chalcogen coupled to nitronyl nitroxide (NN) are investigated using density functional theory along with the wave function-based multiconfigurational self-consistent field methods, for example, complete active space self-consistent field (CASSCF)−Nelectron valence state perturbation theory (NEVPT2). The calculations reveal phenomenal modulation in exchange couplings upon annulation such that remarkably strong ferromagnetic interactions are realized especially for a certain class of the Blatter-NN diradicals. The modulation of spin−spin interactions is rationalized by variation in spin density distribution and molecular torsional angles. We demonstrate that annulation in OMMs opens an additional coupling pathway via auxiliary X-atom acting as the atomic relay center which strongly manipulates the magnitude of exchange couplings.

In an effort to obtain superior magnetic properties, all the possible isomers of di-Blatter diradical coupled through its fused benzene ring are investigated employing numerous density and wave function-based<i> </i>methods. It reveals that the energetically stable and also experimentally reported diradicals are anti-ferromagnetic in nature due to dominant coexisting exchange interactions between the strongly localized micro-magnetic radical centers. However, due to strong steric hindrance in certain cases, the exchange interaction switches from anti-ferromagnetic to weak ferromagnetic interactions. Moreover, we propose the modified version of <i>spin alternation</i> rule, called here as <i>zonal spin alternation</i> rule, which can be applied successfully to predict exchange interactions in such diradicals.<br>

<div>With the ongoing efforts to obtain mononuclear 3d-transition metal complexes that manifest slow relaxation of magnetization and hence, can behave as single molecule magnets (SMMs), we have modelled 14 novel Fe(III) complexes out of which nine behave as potential SMMs. These complexes possess large zero-field splitting (ZFS)</div><div>parameter D in the range of -40 to -60 cm^-1. The first-principles investigation of the ground-spin state applying density functional theory (DFT) and wave-function based</div><div>multi-configurations methods e.g. SA-CASSCF/NEVPT2 are found to be quite consistent except for few delicate cases with near degenerate spin-states. In such cases, the</div><div>hybrid B3LYP functional is found to be biased towards high-spin (HS) state. Altering the percentage of exact exchange admixed in B3LYP functional leads to intermediate spin</div><div>(IS) ground state consistent with the multireference calculations. The origin of large zero field splitting (ZFS) in the Fe(III)-based trigonal bipyramidal (TBP) complexes</div><div>is investigated and the D-values are further tuned by varying the axial ligands with group XV elements (N, P and As) and equatorial halide ligands from F, Cl, Br and I. Furthermore, a number of complexes are identified with very small Gibbs free energy values indicating the possible spin-crossover phenomenon between the bi-stable spin-states.</div>