Modulation of Nuclearity in Cu II −Mn II Complexes of a N 2 O 2 Donor Ligand Depending upon Carboxylate Anions: Structures, Magnetic Properties and Catalytic Oxidase Activities

Three new hetero‐metallic copper(II)‐manganese(II) complexes, [(CuL) 2 Mn 3 (C 6 H 5 CO 2 ) 6 ] ( 1 ), [(CuL) 2 Mn(CH 3 CO 2 ) 2 ] ( 2 ), and {[(CuL) 2 Mn(C 6 H 5 CH 2 CO 2 ) 2 ] ⋅ 2CH 3 CN} ( 3 ), have been synthesized using [CuL] as ‘‘metalloligand’’ (where H 2 L=N,N′‐bis(2‐hydroxynaphthyl‐methylidene)‐1,3‐propanediamine). Single‐crystal structural analyses show an almost linear penta‐nuclear structure for complex 1 where a square planar [CuL] unit is connected to each of the two terminal Mn II ions of a linear, centrosymmetric [Mn 3 (benzoate) 6 ] unit through the double phenoxido bridges. Both complexes 2 and 3 possess a linear tri‐nuclear structure where two terminal square‐pyramidal [CuL] units are bonded to the central Mn II ion through double phenoxido oxygen atoms along with a syn‐syn bridging acetate (for 2 )/phenyl acetate (for 3 ). All three complexes exhibit catecholase, and phenoxazinone synthase‐like activities under aerial conditions. For catecholase like activity, the turnover numbers ( k cat ) are 595, 40, and 205 h −1 whereas, for phenoxazinone synthase like activity, the turnover numbers are 25, 4, and 11 h −1 for complexes 1–3 , respectively. The mechanism of both catalytic oxidase activities is proposed on the basis of mass spectral evidences. Variable‐temperature (2–300 K) dc molar magnetic susceptibility measurements of 1 reveal antiferromagnetic interactions between the Cu−Mn centres ( J 1 =−29.3 cm −1 ), and also between the Mn−Mn centres of the [Mn 3 (benzoate) 6 ] unit ( J 2 =−0.68 cm −1 ). On increasing the magnetic field at 2 K, its ground spin state changes from S =3/2 to S =5/2 at 4 T, attributable to the low value of J 2 which makes the excited spin states close in energy with the ground spin state. Complexes 2 and 3 show antiferromagnetic coupling interactions between the Cu−Mn pairs with J values of −9.51, and −5.32 cm −1 , respectively.