Ferromagnetic Coupling and Single-Ion Magnet Phenomenon in Mononuclear Ruthenium(III) Complexes Based on Guanine Nucleobase

Abstract

Two mononuclear RuIII complexes of formula trans-[RuCl4(Hgua)(dmso)]·2H2O (1) and trans-[RuCl4(Hgua)(gua)]·3H2O (2) [Hgua = protonated guanine (gua), dmso = dimethyl sulfoxide] have been synthesized and characterized magnetostructurally. 1 and 2 crystallize in the monoclinic system with space groups P21/n and Pc, respectively. Each RuIII ion in 1 and 2 is bonded to four chloride ions and one (1) or two (2) nitrogen atoms from guanine molecules and one sulfur atom (1) of a dmso solvent molecule, generating axially compressed octahedral geometries in both cases. In their crystal packing, the RuIII complexes are connected through an extended network of N-H⋯Cl hydrogen bonds and π⋯Cl intermolecular interactions, forming novel supramolecular structures of this paramagnetic 4d ion. Variable-temperature dc magnetic susceptibility data were obtained from polycrystalline samples of 1 and 2 and their plots show a different magnetic behavior. While 1 is a ferromagnetic compound at low temperature, 2 exhibits a behavior of magnetically isolated mononuclear RuIII complexes with S = 1/2. The study on ac magnetic susceptibility data reveal slow relaxation of the magnetization, when external dc fields are applied, only for 2. These results highlight the presence of field-induced single-ion magnet (SIM) behavior for this mononuclear guanine-based RuIII complex.

Enantiomeric Complexes Based on Ruthenium(III) and 2,2′-Biimidazole: X-ray Structure and Magnetic Properties

“…This magnetization fitting process was not possible for 2, given the strong correlation with antiferromagnetically coupling and the S = 0 of the system (Figure S1). All these findings are consistent with the few magnetic parameters previously reported for some mononuclear Ru(III) complexes [22,23,[49][50][51]. Finally, the results of the computed θ values would support the presence of antiferromagnetic exchange couplings for these compounds, with these being comparatively much more significant in the case of compound 2, as expected, because of the magnetic susceptibility maximum observed All these findings are consistent with the few magnetic parameters previously reported for some mononuclear Ru(III) complexes [22,23,[49][50][51].…”

“…Taking these facts into consideration and in order to analyze the magnetic behavior of 1 and 2, we have used the Hamiltonian of Equation ( 1) and its derived theoretical expression for magnetic susceptibility [52], including a θ term, to account for the detected intermolecular interactions. Furthermore, the three parameters in Equation ( 1), namely, energy gap (∆), orbital reduction factor (κ) and the spin-orbit coupling constant (λ), are strongly correlated with each other (considering L = 1, S = 1/2 and g = g ⊥ = g for both 1 and 2), as previously reported [22,52].…”

“…For 2, χMT values continuously decrease with decreasing temperature to a value of approximately 0.53 cm 3 mol -1 K at 40 K. They subsequently continue decreasing faster, reaching a final value much lower than that of 1: 0.18 cm 3 mol -1 K at 2.0 K (Figure 6). This decrease in the χMT values observed in both compounds at a medium-high range of temperature would account for the 2 T2g ground term of this paramagnetic metal ion, which exhibits spin-orbit coupling (SOC) and an important orbital contribution, as previously observed for mononuclear Ru(III) complexes [22,23]. Furthermore, a maximum of the magnetic susceptibility occurs at For 2, χ M T values continuously decrease with decreasing temperature to a value of approximately 0.53 cm 3 mol −1 K at 40 K. They subsequently continue decreasing faster, reaching a final value much lower than that of 1: 0.18 cm 3 mol −1 K at 2.0 K (Figure 6).…”

“…Nevertheless, investigation of the magnetic properties of most of the mononuclear Ru(III) complexes remains scarcely explored. Indeed, there exists an important complexity to treating and investigating the experimental magnetic data of complexes based on this paramagnetic 4d metal ion, given that it exhibits a 2 T 2g ground term with an important orbital contribution [22,23]. Nevertheless, the investigation of magnetic materials based on this 4d metal ion is ultimately very appealing given that the Ru(III) pealing given that the Ru(III) ion also displays more diffuse magnetic orbitals than th of 3d analogue compounds, which allow for intermolecular magnetic interactions can also be conducted through space via weak forces in their crystal lattices and, in so cases, afford magnetic orderings in this way [24].…”

“…On the other hand, the study of pr much isolated complexes of this paramagnetic 4d metal ion is also very appealing. In only two mononuclear Ru(III) complexes displaying Single-Ion Magnet (SIM) beha have been reported so far, which is fundamental to understanding the dynamics of slow relaxation of the magnetization in Ru(III) complexes [22,23].…”