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Published on: February 10, 2023
Tri‑, Tetra‑, Octa-Nuclear Copper Complexes Including the First Mode Cubane-like {Cu4O3N} Core: Synthesis, Structure,
Cándida Pastor-Ramírez1, Sylvain Bernès2, Rafael Zamorano-Ulloa3
1Benemérita Universidad Autónoma de Puebla, Instituto de Ciencias Químicas BUAP, Av. San Claudio y 24 sur S/N, Col San Manuel, C. P., 72570 Puebla, Puebla, Mexico.
Abstract:
In this study, the synthesis and characterization of three Cu-(II) complexes employing the Schiff base ligand 2-[(2-hydroxy-benzylidene)-amino]-2-hydroxymethylpropane-1,3-diol (H4L), sodium azide (NaN3), and Cu-(II) salts were investigated. This research led to the formation of [Cu4(H2L)4(H2O)] 1, previously reported, the first octa-nuclear cubane-like compound based on the {Cu4O3N} core, [Cu4(μ3-N3)-(H2L)2(HL)-(H2O)]2 2, and a polymeric compound [Cu3(H2L)2(μ2-N3)2]n 3. Single-crystal X-ray diffraction analysis revealed that 1·CH3OH possesses a '4 + 2' cubane-type core, 2 is a double cubane of eight Cu-(II) ions including μ3-alkoxido and μ3-azido bridges, while 3 is a polymeric structure with three Cu-(II) ions conforming the monomeric unit. Temperature-dependent (2.9-300 K) magnetic susceptibility measurements demonstrate the coexistence of ferromagnetic and antiferromagnetic spin exchange interactions in 1, associated with Cu-O-Cu bridging angles ranging from 77.81(6)° to 112.77(8)°. Compounds 2 and 3 exhibited antiferromagnetic exchange coupling, attributed to their large Cu-O-Cu bond angles, the largest of which was 108.92°. The ESR spectra of 1-3 at 300 and 90 K are axial, accompanied by hyperfine splitting in g ∥ and coupling constants A Cu in the range 169 × 10-4 cm-1 to 197 × 10-4 cm-1. In accordance with g ⊥ values >2.0023, the unpaired electron ground state is , consistent with a Cu-(II) ion. Furthermore, for 2, a forbidden half-field transition was observed, which is characteristic of ΔM S = ± 2 for antiferromagnetic exchange interaction of dimers of Cu-(II). These affirmations align with the ESR spectra area ratio and line width as the temperature decreases. The IR, absorption spectra, and magnetic studies of 1-3 were analyzed and compared to those of analogous complexes with the same geometry.
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