Intramolecular ferromagnetic coupling in bis-oxoverdazyl and bis-thioxoverdazyl diradicals with polyacene spacers

Orchestration of ferro- and anti-ferromagnetic ordering in gold nanoclusters

The unpaired electron in the gold clusters (Aun, n = no. of Au atoms) with an odd number of total electrons is solely responsible for the magnetic properties in the small-sized Au nano-clusters. However, no such unpaired electron is available due to pairing in the even number of atom gold clusters and behaving as a diamagnetic entity similar to bulk gold. In this work, we unveiled the spin-density distribution of odd Aun clusters with n = 1 to 19 that reveals that a single unpaired electron gets distributed non-uniformly among all Au-atoms depending on the cluster size and morphology. The delocalization of the unpaired electron leads to the spin dilution approaching a value of ∼1/n spin moments on each atom for the higher clusters. Interestingly, small odd-numbered gold clusters possess spin-magnetic moments similar to the delocalized spin moments as of organic radicals. Can cooperative magnetic properties be obtained by coupling these individual magnetic gold nanoparticles? In this work, by applying state-of-the-art computational methodologies, we have demonstrated ferromagnetic or anti-ferromagnetic couplings between such magnetic nanoclusters upon designing suitable organic spacers. These findings will open up a new avenue of nanoscale magnetic materials combining organic spacers and odd-electron nano-clusters.

Antiaromatic Molecules as Magnetic Couplers: A Computational Quest

In this study, we investigate a set of organic diradical structures in which two oxo-verdazyl radicals are selected as radical spin centers that are connected (coupled) via six coupler molecules (CM), resulting in various magnetic (ferromagnetic (FM) or antiferromagnetic (AFM)) characteristics, as reflected by their exchange coupling constants (J). We have designed 12 diradicals with 6-antiaromatic couplers coupled with bis-oxo-verdazyl diradicals with meta-meta (m-m) and para-meta (p-m) positional connectivities. The nature of the magnetic coupling (ferromagnetic, nonmagnetic, or antiferromagnetic) and the magnitude of the exchange constant J depend on the type of coupler, the connecting point between each radical center and CM, the degree of aromaticity of the coupler, and the length of the through-bond distance between radical centers. The computed magnetic exchange coupling constants J for these diradicals at the B3LYP/6-311++G(d,p) and MN12SX/6-311++G(d,p) levels of theory are large for many of these structures, indicating strong ferromagnetic coupling (with positive J values). In some cases, magnetic couplings are observed with J > 1000 cm-1 (B3LYP/6-311++G(d,p)) and strong antiferromagnetic coupling (with negative J values) with J < -1000 cm-1 (B3LYP/6-311++G(d,p)). Similarly, in some cases, magnetic couplings are observed with J > 289 cm-1 (MN12SX/6-311++G(d,p)) and strong antiferromagnetic coupling (with negative J values) with J < -568 cm-1 (MN12SX/6-311++G(d,p)). Furthermore, while numerous studies have reported that the degree of aromaticity of molecular couplers often favors strong ferromagnetic coupling, displaying the high-spin character of diradicals in their ground states, the couplers chosen in this study are characterized as antiaromatic or nonaromatic. The current investigation provides evidence that, remarkably, antiaromatic couplers are able to enhance stability by favoring electronic diradical structures with very strong ferromagnetic coupling when the length of the through-bond distance and connectivity pattern between radical centers are selected in such a way that the FM coupling is optimized. The findings in this study offer new strategies in the design of novel organic materials with interesting magnetic properties for practical applications.

Magnetic and transport properties of conjugated and cumulated molecules: the π-system enlightens part of the story

We have investigated the intramolecular magnetic exchange coupling constants (J) for a series of nitronyl nitroxide diradicals connected by a range of linear conjugated and cumulene couplers focusing on the unusual π-interaction properties within the couplers.

Diradicalized biphenyl derivative carbon-based material molecules: exploring the tuning effects on magnetic couplings

While the conductance behavior of carbon-based couplers has been successfully investigated, insight into the magnetic properties of such carbon-based molecule coupled diradical systems is still scarce, and especially the structural effect of such couplers on the magnetic properties is poorly understood. The present work reports three different interference effects on the magnetic properties of carbon-based molecule coupled nitroxide diradicals: twisting, sideways group, and position effects. DFT calculations reveal that (i) torsion does not change their broken-symmetry singlet ground state and antiferromagnetic coupling, but decreases their magnetism; (ii) different linkages of two radical moieties result in different ground states and thus different magnetisms, depending on a combination of meta-sites and para-sites; (iii) the antiferromagnetic coupling with a broken-symmetry singlet ground state is not changed by adding sideways groups, but the coupling magnitude can be tuned by modifying the side-bridge. Discussions on geometries, magnetic properties, SOMO-SOMO splittings, and spin density distributions are made to clarify relevant magnetic behaviors. Clearly, the findings concerning the regulation of the diradicalized material molecules through modifying the carbon-based bridges provide a comprehensive understanding of the magnetism of such carbon-based diradicals and new prospects for the design of building blocks of magnetic functional molecular materials.

Theoretical design of magnetic wires from acene and nanocorone derivatives

A theoretical design of molecular magnetic wires based on linear and cyclic oligoacene-bridged dicopper(ii) model complexes is highlighted in the present contribution.

Borazine: spin blocker or not?

Spin-blocker capacity of borazine is investigated formeta-BB,meta-NN andpara-BN structures highlighting the correlation between magnetic properties and aromaticity.

Role of the coupler to design organic magnetic molecules: LUMO plays an important role in magnetic exchange

The occupation number and spatial position of the LUMO play an important role in magnetic exchange in diradicals.