RESUMO
Current advances in molecular magnetism are aimed at the construction of molecular nanomagnets and spin qubits for their utilization as high-density data storage materials and quantum computers. Mononuclear coordination compounds with low spin values of S = ½ are excellent candidates for this endeavour, but knowledge of their construction via rational design is limited. This particularly applies to the single copper(II) spin center, having been only recently demonstrated to exhibit slow relaxation of magnetisation in the appropriate octahedral environment. We have thus prepared a unique organic scaffold that would allow one to gain in-depth insight into how purposeful structural differences affect the slow magnetic relaxation in monometallic, transition metal complexes. As a proof-of-principle, we demonstrate how one can construct two, structurally very similar complexes with isolated Cu(II) ions in an octahedral ligand environment, the magnetic properties of which differ significantly. The differences in structural symmetry effects and in magnetic relaxation are corroborated with a series of experimental techniques and theoretical approaches, showing how symmetry distortions and crystal packing affect the relaxation behaviour in these isolated Cu(II) systems. Our unique organic platform can be efficiently utilized for the construction of various transition-metal ion systems in the future, effectively providing a model system for investigation of magnetic relaxation via targeted structural distortions.
RESUMO
The electrostatic self-assembly reaction of the [Cu(HL)]2+ cation, where HL = 2-(2-aminoethylamino) ethanol, and the N3- or [Fe(CN)6]4- anion leads to the formation of two coordination polymers with the general formula of [Cu6(µ1,1-N3)6(µ1,3-N3)2(µ1,1,3-N3)2(µ1,1,1,3-N3)2(HL)2]n (1) and {[Cu(HL)]2[Fe(CN)6]·H2O}n (2), respectively. The resulting compounds have been structurally characterized by a single-crystal X-ray diffraction technique. Compound 1 possesses a rare 3D structure. It contains centrosymmetric hexanuclear repeating units, which act as six-connected nodes in the final network and copper(ii) ions are joined together by azide anions with four different types of bridging modes, µ1,1, µ1,1,3, µ1,1,1,3, and µ1,3. The structure of compound 2 is a 2D heterometallic CuII/FeII layer in which the [Cu(HL)]2 nodes and the octahedral [Fe(CN)6]4- linkers are joined by µ2- and unusual µ3-CN bridging modes. Detailed static and dynamic magnetic analyses of 1 reveal a dominant ferromagnetic intracluster interaction and a ferromagnetic 3D ordering transition below Tc = 5 K. The variable temperature magnetic susceptibility measurements of compound 2 show a very weak ferromagnetic coupling between the nearest Cu(ii) ions. Also, EPR spectroscopy of these compounds has been investigated in the solid state. Nanocrystals of compound 2 have also been synthesized by a sonochemical process under different reaction conditions. The results show that the crystallinity degree and uniform distribution of nanosheets are inversely dependent on the irradiation time.
