Tri-, Tetra-, Octa-Nuclear Copper Complexes Including the First Mode Cubane-like {Cu ₄ O ₃ N} Core: Synthesis, Structure, and Magnetic Properties

High Resolution Image Download MS PowerPoint Slide 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 (H 4 L), sodium azide (NaN 3 ), and Cu(II) salts were investigated. This research led to the formation of [Cu 4 (H 2 L) 4 (H 2 O)] 1, previously reported, the first octa-nuclear cubane-like compound based on the {Cu 4 O 3 N} core, [Cu 4 (μ 3 -N 3 )(H 2 L) 2 (HL)(H 2 O)] 2 2, and a polymeric compound [Cu 3 (H 2 L) 2 (μ 2 -N 3 ) 2 ] n 3 . Single-crystal X-ray diffraction analysis revealed that 1· CH 3 OH possesses a ‘4 + 2’ cubane-type core, 2 is a double cubane of eight Cu(II) ions including μ 3 -alkoxido and μ 3 -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 d x 2 − y 2, consistent with a Cu(II) ion. Furthermore, for 2, a forbidden half-field transition was observed, which is characteristic of Δ M 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.