Combining single-molecule magnets (SMMs) and emergent two-dimensional substrates such as graphene may lead to device configurations that are promising for spintronics and quantum computing. However, to fully exploit the unique features of SMMs anchored to two-dimensional substrates, the choice of ligand attachments, which could affect the magnetic and electronic properties, is critical. In this work, we focus on hybrid junctions comprising CVD-grown graphene and [Mn12O12(O2CR)16(H2O)4](R=CH3,CHCl2) SMMs with different ligands. We find that [Mn12O12(O2CCH3)16(H2O)4] SMMs barely change the graphene’s conductivity, while [Mn12O12(O2CCHCl2)16(H2O)4] SMMs with more electronegative ligands, by means of charge transfer, remarkably modify the electronic transport in graphene as revealed by gate-voltage dependent magnetotransport measurements.

The synthesis, structure, and magnetic properties of three related iron(III)-oxo clusters are reported, [ F e 7 O 3 ( O 2 C P h ) 9 ( m d a ) 3 ( H 2 O ) ]( 1 ) , [Fe 2 2 O 1 4 (OH) 3 (O 2 CMe) 2 1 (mda) 6 ](ClO 4 ) 2 (2), and [Fe 24 O 15 (OH) 4 (OEt)(O 2 CMe) 21 (mda) 7 ](ClO 4 ) 2 (3), where mdaH 2 is N-methyldiethanolamine. 1 was prepared from the reaction of [Fe 3 O(O 2 CPh) 6 (H 2 O) 3 ](NO 3 ) with mdaH 2 in a 1:2 ratio in MeCN, whereas 2 and 3 were prepared from the reaction of FeCl 3 /NaO 2 CMe/mdaH 2 in a 2:∼13:2 ratio and FeCl 3 / NaO 2 CMe/mdaH 2 /pyridine in a 2:∼13:2:25 ratio, respectively, both in EtOH. The core of 1 consists of a central octahedral Fe III ion held within a nonplanar Fe 6 loop by three μ 3 -O 2− and three μ 2 -RO − arms from the three mda 2− chelates. The cores of the cations of 2 and 3 consist of an A:B:A three-layer topology, in which a central Fe 6 (2) or Fe 8 (3) layer B is sandwiched between two Fe 8 layers A. The A layers structurally resemble 1 with the additional Fe added at the center to retain virtual C 3 symmetry. The central Fe 6 layer B of 2 consists of a {Fe 4 (μ 4 -O) 2 (μ 3 -OH) 2 } 6+ cubane with an Fe on either side attached to cubane O 2− ions, whereas that of 3 has the same cubane but with an {Fe 3 (μ 3 -O)(μ-OH)} unit attached on one side and a single Fe on the other. Variable-temperature dc and ac magnetic susceptibility studies revealed dominant antiferromagnetic coupling in all complexes leading to ground-state spins of S = 5 / 2 for 1 and S = 0 for 2 and 3. All Fe 2 pairwise exchange parameters (J ij ) for 1−3 were estimated by two independent methods: density functional theory (DFT) calculations using broken symmetry methods and a magnetostructural correlation previously developed for high-nuclearity Fe III /O complexes. The two approaches gave satisfyingly similar J ij values, and the latter allowed rationalization of the experimental ground states by identification of the spin frustration effects operative and the resultant relative spin vector alignments at each Fe III ion.

In this work, we assess the potential of the Green's function approximation to predict isotropic magnetic exchange couplings and to reproduce the standard broken-symmetry energy difference approach for transition metal complexes. To this end, we have selected a variety of heterodinuclear, homodinuclear, and polynuclear systems containing 3d transition metal centers and computed the couplings using both the Green's function and energy difference methods. The Green's function approach is shown to have mixed results for the cases tested. For dinuclear complexes with large strength couplings (≳50 cm −1 ), the Green's function method is unable to reliably reproduce the energy difference values. However, for weaker dinuclear couplings, the Green's function approach acceptably reproduces broken-symmetry energy difference couplings. In polynuclear cases, the Green's function approximation worked remarkably well, especially for Fe III complexes. On the other hand, for a Ni II polynuclear complex, qualitatively wrong couplings are predicted. Overall, the evaluation of exchange couplings from local rigid magnetization rotations offers a powerful alternative to time-consuming energy differences methods for large polynuclear transition metal complexes, but to achieve a quantitative agreement, some improvements to the method are needed.

The single-molecule magnet {Mn84} is a challenge to theory because of its high nuclearity. We directly compute two experimentally accessible observables, the field-dependent magnetization up to 75 T and the temperature-dependent heat capacity, using parameter-free theory. In particular, we use first-principles calculations to derive short- and long-range exchange interactions and compute the exact partition function of the resulting classical Potts and Ising spin models for all 84 Mn S = 2 spins to obtain observables. The latter computation is made possible by using hyperoptimized tensor network contractions, a technique developed to simulate quantum supremacy circuits. We also synthesize the magnet and measure its heat capacity and magnetization, observing qualitative agreement between theory and experiment and identifying an unusual bump in the heat capacity and a plateau in the magnetization. Our work also identifies some limitations of current theoretical modeling in large magnets, such as sensitivity to small, long-range exchange couplings.