Spin-Phonon Coupling and Slow-Magnetic Relaxation in Pristine Ferrocenium.

We report the spin dynamic properties of non-substituted ferrocenium complexes. Ferrocenium shows a field-induced single-molecule magnet behaviour in DMF solution while cobaltocene lacks slow spin relaxation neither in powder nor in solution. Multireference quantum mechanical calculations give a non-Aufbau orbital occupation for ferrocenium with small first excitation energy that agrees with the relatively large measured magnetic anisotropy for a transition metal S=1/2 system. The analysis of the spin relaxation shows an important participation of quantum tunnelling, Raman, direct and local-mode mechanisms which depend on temperature and the external field conditions. The calculation of spin-phonon coupling constants for the vibrational modes shows that the first vibrational mode, despite having a low spin-phonon constant, is the most efficient process for the spin relaxation at low temperatures. In such conditions, vibrational modes with higher spin-phonon coupling constants are not populated. Additionally, the vibrational energy of this first mode is in excellent agreement with the experimental fitted value obtained from the local-mode mechanism.

Metal-Organic Nanocapsules with Functionalized s-Heptazine Ligands.

A metalloorganic capsule was synthesized where the ligand is a derivative of heptazine with three carboxylic groups that are coordinated to CuII cations, forming paddle-wheel motifs. Each nanocapsule is neutral, with 12 CuII centers and 8 ligands adopting a rhombicuboctahedron shape. It has almost 3 nm diameter, and the main intermolecular interactions in the solid are π··· π stacking between the C6N7 heptazine moieties. The nanocapsules can form monolayers deposited on graphite as observed by atomic force microscopy, which confirms their stability in solution.

Mononuclear Lanthanide Complexes with 18-Crown-6 Ether: Synthesis, Characterization, Magnetic Properties, and Theoretical Studies.

A family of lanthanide metal complexes with the general formula [Ln(H2O)3(18-crown-6)](ClO4)3 (Ln = TbIII, DyIII, ErIII, and YbIII) has been synthesized. Their magnetic properties have been characterized by direct- and alternating-current SQUID measurements and analyzed with the help of CASSCF-type calculations. The DyIII and YbIII compounds show slow relaxation of magnetization under an external magnetic field. Analysis of the dependence of the relaxation time with the temperature and external magnetic field reveals that the main contributions are the quantum tunneling and Raman relaxation terms, respectively. Analysis of the ß electron density and electrostatic potentials indicates that the axial ligands (three water molecules) generate a relatively small repulsion, with the lanthanide electron density being the reason for the moderate magnetic anisotropy found in these systems.

Slow-spin relaxation of a low-spin S = 1/2 FeIII carborane complex.

In this communication, we report the first evidence of slow-spin relaxation of a low-spin FeIII carborane complex. Iron S = 1/2 complexes showing such behaviour are particularly appealing as qubit candidates because they fulfil some of the main requirements to reach long decoherence times, such as moderate magnetic anisotropy, small spin, metal element mainly with zero-nuclear spin and furthermore, large versatility to introduce chemical modifications.

A trinuclear Cu(II) complex with functionalized s-heptazine N-ligands: molecular chemistry from a g-C3N4 fragment.

A new kind of N-ligand based on heptazine derivatives is presented. A trinuclear Cu(II) complex, [(L)2CuCl3](ClO4)3·3CH2Cl2 (L = 2,4,6-tris(di-2-pyridylamino)heptazine), utilizing a pyridine derivative of heptazine has been synthesized and characterized avoiding the inherent solubility problems of heptazine compounds. Thus, this work opens the application of such ligands either in supramolecular chemistry as a larger ligand of the widely used s-triazine derivatives or to provide molecular systems for photocatalysis as heptazine is the fundamental unit of the very promising g-C3N4 2D compound.

Different topologies in three manganese-µ-azido 1D compounds: magnetic behavior and DFT-quantum Monte Carlo calculations.

The syntheses and structural characterization of three new monodimensional azido-bridged manganese(ii) complexes with empirical formulae [Mn(N3)2(aminopyz)2]n (1), [Mn(N3)2(4-azpy)2]n (2) and [Mn(N3)2(4-Bzpy)2]n (3) (pyz = pyrazine (1,4-diazine)), 4-azpy = 4-azidopyridine and 4-Bzpy = 4-benzoylpyridine) are reported. 1 is a monodimensional compound with double EO azido bridges, 2 is an alternating monodimensional compound with double end-on and double end-to-end azido bridges in the sequence di-EO-di-EE and 3 is a monodimensional compound with double end-on and double end-to-end azido bridges in the sequence di-EO-di-EO-diEO-di-EO-di-EE. The magnetic properties of 1-3 are reported. Periodic DFT calculations were performed to estimate the J values and quantum Monte Carlo simulations were carried out using the calculated J values to check their accuracy in comparison with the experimental magnetic measurements. From this theoretical analysis, two appealing features of the di-EO Mn(ii) compounds can be extracted: first, the exchange coupling becomes more ferromagnetic when the Mn-N-Mn bridging angle becomes larger and the spin density of the bridging nitrogen atoms has an opposite sign to that of the Mn(II) centers.