AbstractA penta‐coordinated Cu(II) complex with 1,4‐diazacydoheptane(DACH), [Cu(DACH)2(H2O)]Cl2(1), has been synthesized and characterized by X‐ray diffraction, IR spectra, elemental analyses, thermal analyses, UV‐Vis and ESR techniques. Complex 1 crystallizes in orthorhombic crystal system,Pbcnspace group witha= 1.6075(4),b =1.0539(3),c= 0.9195(3) nm,V=l.5578(7) nm3,Mr= 352.79,Z= 4,Dc=1.487 g/cm3, finalR =0.0451 and wR= 0.1294. The structure of 1 indicates that the central Cu(II) atom is penta‐coordinated by four nitrogen atoms of two DACH moieties at the equatorial positions and a water molecule at the axis position. The coordination geometry of Cu(II) could be considered as an approximately ideal square‐pyramidal environment. Both DACH rings arrange incis‐form and are predominantly in the boat‐boat conformation (80%) with some disorder to the chair‐chair conformation (20%). The Cl−anions are hydrogen bonded with the nitrogen donors of the DACH rings and the oxygen donor of the coordinated H2O molecule to form a one‐dimensional zigzag linear structure. The solution behaviors of 1 are also discussed in detail by Uv