A new trinuclear Cu^II compound {[Cu₃(HL′)₂(H₂O)₂](ClO₄)₄}·(H₂O)₄ (1) was obtained and presented a trapped chiral hemiaminal (HL_2′ = [(5-amino-4H-1,2,4-triazol-3-yl)amino](1H-imidazol-4-yl)methanol)). Compound 1 shows an almost flat cationic structure [Cu₃(HL′)₂(H₂O)₂]⁴⁺ with a Cu₃ linear core reached by the double Cu-OR/NN-Cu triazole/alkoxo bridge of the hemiaminal molecule. The Cu^II spin carriers are antiferromagnetically coupled, presenting a spin doublet ground state (S = 1/2) with a magnetic coupling constant of −179 cm⁻¹. Moreover, DTF calculations show that the planarity of the compound permits a sigma-type overlapping between the unpaired electrons of the spin carriers and the p-type orbitals of the coordinated N and O atoms producing an electronic delocalization through the bridging ligand responsible for the strong antiferromagnetic interactions observed experimentally.