Towards multifunctional magnetic systems through molecular-programmed self assembly of Re(IV) metalloligands

Synthesis, Crystal Structure and Magnetic Properties of Heteropolynuclear ReIVMII Complexes Based on the Robust [ReCl5(pyzCOO)]2– Unit (pyzCOO = 2‐pyrazinecarboxylate)

“…In the structure of compound 3, the best model was reached by refining one acetonitrile molecule, even if large voids [50] of 622 Å 3 account for a second acetonitrile molecule, which, due to statistic disorder, was neither found nor located in the model. The final fullmatrix least-squares refinements on F 2 , minimizing the function Σw(|F o | -|F c |) 2 , reached convergence with values of the discrepancy indices given in Table 6. The high residual density in 2 and 4 are located near the Re atom.…”

“…[8] The high value of the spin-orbit coupling constant of around 1000 cm -1 for the free ion [9] is the main factor responsible for its large magnetic anisotropy. In fact, the combination of spin-orbit coupling and low molecular symmetry explains the SMM behaviour of even mononuclear Re IV compounds, as in the case of the recently reported (NBu 4 ) 2 [ReBr 4 (ox)]. [10] Also, the diffuse character of 5d orbitals allows a significant degree of spin delocalization onto the ligands, which accounts for the strength of the magnetic interactions between Re IV centres or between Re IV and other paramagnetic ions at large distances.…”

“…The appropriate phenomenological spin Hamiltonian, taking into account the Zeeman perturbation in axially distorted surroundings, is given by Equation (2): (2) in which Ŝ x , Ŝ y and Ŝ z are the spin operators, H x , H y and H z are the components of the magnetic field along the coordinate axes x, y and z, g s and g ⊥ are the parallel and perpendicular components of the g tensor, μ B is the Bohr magneton and 2D is the energy gap between ±3/2 and ±1/2 Kramer doublets in the absence of a magnetic field. The experimental data, at temperatures above that giving the maximum susceptibility value, were analysed by means of Equations (3a, 3b, 3c) derived from the Hamiltonian shown in Equation (2): (3a) (3b) (3c) in which the term θ has been added to account for the magnetic coupling between the mononuclear units and g is supposed to be isotropic to avoid overparametrization, while N is the Avogadro number and k the Boltzmann constant.…”

“…[2] Indeed, some of them were found to exhibit slow relaxation of the magnetization, for example, (NBu 4 ) 4 [Ni{ReCl 4 (ox)} 3 ] (NBu 4 = tetra-nbutylammonium cation, ox = oxalate dianion) [3] and [M(dmf ) 4 {ReCl 4 (CN) 2 }] n (M = Mn, Fe, Co, Ni; dmf = dimethylformamide), [4,5] being new examples of SMMs [6] and singlechain magnets (SCMs), [7] respectively. Rhenium(IV) is a 5d 3 ion that usually forms inert, relatively stable, octahedral complexes.…”

“…Besides the two examples mentioned in the first paragraph, several other di-, [15][16][17] tri- [18] and tetranuclear complexes [15b] as well as one-dimensional (1D) compounds [12,16,19,20] have also been described. Up to now, two heterobimetallic Re IV compounds with heavier 4d or 4f metals have also been synthesized, namely (PPh 4 ) 2 [21] and the pentanuclear (NBu 4 ) 5 [Gd III {Re IV Br 4 (μ-ox)} 4 (H 2 O)]·H 2 O. [22] Both ferro-and antiferromagnetic interactions have been observed, depending on the electronic structure of the M II/III ion and the coordination mode and bond lengths and angles of the bridge between the cations.…”