The synthesis, crystal structure, and magnetic properties of two trinuclear oxo-centered carboxylate complexes are reported and discussed: [Cr 3(μ3-O)(μ2-PhCOO)6(H 2O)3]NO3·4H2O·2CH 3OH (1) and [Cr3(μ3-O)(μ2- PhCOO)2(μ2-OCH2CH3) 2(bpy)2(NCS)3] (2). For both complexes the crystal system is monoclinic, with space group C2/c for 1 and P1/n for 2. The structure of complex 1 consists of discrete trinuclear cations, associated NO3- anions, and lattice methanol and water molecules. The structure of complex 2 is built only by neutral discrete trinuclear entities. The most important feature of 2 is the unusual skeleton of the [Cr3O] core due to the lack of peripheral bridging ligands along one side of the triangular core, which is unique among the structurally characterized (μ3-oxo)-trichromium(III) complexes. Magnetic measurements were performed in the 2-300 K temperature range. For complex 1, in the high-temperature region (T > 8 K), experimental data could be satisfactorily reproduced by using an isotropic exchange model, H = -2J 12S1S2 - 2J13S1S 3 - 2J23S2S3 (J12 = J13 = J23) with Jij = -10.1 cm-1, g = 1.97, and TIP = 550 × 10-6 emu mol-1. The antisymmetric exchange interaction plays an important role in the magnetic behavior of the system, so in order to fit the experimental magnetic data at low temperature, a new magnetic model was used where this kind of interaction was also considered. The resulting fitting parameters are the following: G zz = 0.25 cm-1, δ = 2.5 cm-1, and TIP = 550 × 10-6 emu mol-1. For complex 2, the experimental data could be satisfactorily reproduced by using an isotropic exchange model, H = -2J1(S1S2 + S 1S3) - 2J2(S2S3) with J1 = -7.44 cm-1, J2 = -51.98 cm-1, and g = 1.99. The magnetization data allows us to deduce the ground term of S = 1/2, characteristic of equilateral triangular chromium(III) for complex 1 and S = 3/2 for complex 2, which is confirmed by EPR measurements.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry