Enhanced magnetic spin-spin interactions observed between porphyrazine derivatives on Au(111)

Recycling e-waste into gold-loaded covalent organic framework catalysts for terminal alkyne carboxylation

The rising demand for gold requires innovative methods for its recovery from e-waste. Here we present the synthesis of two tetrazine-based vinyl-linked covalent organic frameworks: TTF-COF and TPE-COF that adsorb gold ions and nanoparticles and catalyze the carboxylation of terminal alkynes. These covalent organic frameworks have low band gaps and high photocurrent responses. TTF-COF has an adsorption capacity toward aqueous Au(III) of 2440 mg g-1, and TPE-COF's Au(III) adsorption capacity is 1639 mg g-1. The gold source is metal flakes isolated from waste computer processing units. Of the gold present, > 99% is selectively captured by TTF-COF whereas only 5% of the Ni and 2% of the Cu in the solution is adsorbed. The Au-loaded covalent organic frameworks catalyze the carboxylation of terminal alkynes and are stable and reusable for six reuse cycles. Our covalent organic frameworks convert e-waste into a valuable catalyst for a useful green organic transformation.

Manipulation of the Magnetic State of a Porphyrin-Based Molecule on Gold: From Kondo to Quantum Nanomagnet via the Charge Fluctuation Regime

By moving individual Fe-porphyrin-based molecules with the tip of a scanning tunneling microscope in the vicinity of the elbow of the herringbone-reconstructed Au(111) containing a Br atom, we reversibly and continuously control their magnetic state. Several regimes are obtained experimentally and explored theoretically: from the integer spin limit, through intermediate magnetic states with renormalized magnetic anisotropy, until the Kondo-screened regime, corresponding to a progressive increase of charge fluctuations and mixed valency due to an increase in the interaction of the molecular Fe states with the substrate Fermi sea. Our study demonstrates the potential of utilizing charge fluctuations to generate and tune quantum magnetic states in molecule-surface hybrids.

Probing Vibrational Symmetry Effects and Nuclear Spin Economy Principles in Molecular Spin Qubits

The selection of molecular spin qubits with a long coherence time, Tm, is a central task for implementing molecule-based quantum technologies. Even if a sufficiently long Tm can be achieved through an efficient synthetic strategy and ad hoc experimental measurement procedures, many factors contributing to the loss of coherence still need to be thoroughly investigated and understood. Vibrational properties and nuclear spins of hydrogens are two of them. The former plays a paramount role, but a detailed theoretical investigation aimed at studying their effects on the spin dynamics of molecular complexes such as the benchmark phthalocyanine (Pc) is still missing, whereas the effect of the latter deserves to be examined in detail for such a class of compounds. In this work, we adopted a combined theoretical and experimental approach to investigate the relaxation properties of classical [Cu(Pc)] and a CuII complex based on the ligand tetrakis(thiadiazole)porphyrazine (H2TTDPz), characterized by a hydrogen-free molecular structure. Systematic calculations of molecular vibrations exemplify the effect of normal modes on the spin-lattice relaxation process, unveiling a different contribution to T1 depending on the symmetry of normal modes. Moreover, we observed that an appreciable Tm enhancement could be achieved by removing hydrogens from the ligand.