A Very Rare Hydrogen‐Bridged Hexanuclear Cu II Complex Containing a Triangular Cu 3 O Core Capped by an Unusual Triply Coordinated Perchlorate Anion

An unusual hexanuclear Cu II complex, [{[Cu(NHDEPO)] 3 (μ 3 ‐O)(O 3 ClO)} 2 (μ‐H)] · 7ClO 4 · 4H 2 O ( 1 ) was prepared starting from Cu(ClO 4 ) 2 · 6H 2 O 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 Cu 3 O 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 – (O 2– ) group together with three atoms (N, N, O) of the Schiff base. An unusual triply coordinated perchlorate ion (μ 3 ‐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.