https://doi.org/10.3390/magnetochemistry4020024

Three new dinuclear copper(II) complexes [Cu₂(μ–HLⁿ)₂(μ-Cl)₂Cl₂]Cl₂ (1–3) have been synthesized and structurally characterized by single-crystal X-ray diffraction, where HL^x, (HL¹ = N⁶-propyladeninium, HL² = N⁶-butyladeninium and HL³ = N⁶-isobutyladeninium) are N⁶-alkyl bidentate NN donor adenine bases. Complexes 1–3 exhibit a coplanar arrangement of both N⁶-alkyladeninium moieties with UD conformation, with the terms U(up) or D(down) referring to the coordination of each pyrimidinic N³ atoms to the upper or lower metal center. In the three complexes, both copper atoms are five-coordinated (N₂Cl₃ donor set), resembling a compressed trigonal bipyramid. Each adenine moiety is protonated in N¹ and the positive charge balanced by chloride counterions. Magnetic measurements of complexes 1 and 3 in the 2–300 K temperature range indicate antiferromagnetic coupling with J = −156.1(7) and J = −151(2) cm⁻¹, respectively. Density functional theory calculations have also been performed in order to estimate the exchange coupling constants in these complexes. The theoretically calculated J values are in good agreement with the experimental values. 

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