A Very Rare Hydrogen-Bridged Hexanuclear CuII Complex Containing a Triangular Cu3O Core Capped by an Unusual Triply Coordinated Perchlorate Anion

An unusual hexanuclear CuII complex, [{[Cu(NHDEPO)]3(μ3‐O)(O3ClO)}2(μ‐H)]·7ClO4·4H2O (1) was prepared starting from Cu(ClO4)2·6H2O and the oxime‐based Schiff base ligand NHDEPO (= 3‐[3‐(diethylamino)propylimino]butan‐2‐one oxime). Structural characterization of the complex reveals that it consists of two triangular Cu3O units, the copper ions being at the corners of an equilateral triangle, separated by an O···O distance of 2.447(5) Å, held together solely by a proton. In each triangle, the copper atoms are in square‐pyramid environments. The equatorial plane consists of the bridging oxygen of the central OH– (O2–) group together with three atoms (N, N, O) of the Schiff base. An unusual triply coordinated perchlorate ion (μ3‐κO:κO′:κO″) interacts in axial position with the three copper ions. Variable‐temperature (2–300 K) magnetic susceptibility measurements show that complex 1 is antiferromagnetically coupled (J = –148 cm–1). The EPR data at low temperature clearly indicates the presence of spin frustration phenomenon in the complex. An unusual antiferromagnetically coupled hexanuclear CuII complex of an oxime‐based Schiff base ligand, consisting of two triangular Cu3O units which are held together solely by a proton shows the presence of spin frustration.