A new Cu(II) complex of an asymmetrically dicondensed Schiff base (HL = N-(2-hydroxyacetophenylidene)-N'-salicylidene-1,3-propanediamine) derived from 1,3-propanediamine, salicylaldehyde, and o-hydroxyacetophenone has been synthesized. Using this complex, [CuL] (1), as a metalloligand, two new trinuclear Cu-Mn complexes, [(CuL)Mn(N)(HO)](ClO)·HO (2) and [(CuL)Mn(NCS)] (3), have been prepared. Single-crystal structural analyses reveal that complexes 2 and 3 both have the same bent trinuclear {(CuL)Mn} structural unit in which two terminal bidentate square-planar (CuL) units are chelated to the central octahedral Mn(II) ion. This structural similarity is also evident from the variable-temperature magnetic susceptibility measurements, which suggest that compounds 2 and 3 are both antiferromagnetically coupled with comparable exchange coupling constants (-21.8 and -22.3 cm, respectively). The only difference between 2 and 3 lies in the coordination around the central Mn(II) ion; in 3, two SCN groups are coordinated to the Mn(II), leaving a neutral complex, but in 2, one N group and one HO molecule are coordinated to give a positively charged species. The presence of such a labile HO coligand makes 2 catalytically active in mimicking two well-known polynuclear copper proteins, catecholase and phenoxazinone synthase. The turnover numbers (k) for the aerial oxidation of 3,5-di-tert-butylcatechol and o-aminophenol are 1118 and 6581 h, respectively, values which reflect the facility of the heterometallic catalyst in terms of both efficiency and catalytic promiscuity for aerial dioxygen activation. The mechanisms of these biomimetic oxidase reactions are proposed for the first time involving any heterometallic catalyst on the basis of mass spectral analysis, EPR spectroscopy, and cyclic voltammetry. The evidence of the intermediates indicates possible heterometallic cooperative activity where the substrates bind to a Mn(II) center and Cu(II) plays the role of an electron carrier for transformation of the phenolic substrates to their respective products with the reduction of aerial dioxygen.

Three new heterometallic Cu­(II)–Mn­(II) complexes, [{(CuL)2Mn}2­(μ1,5-N­(CN)2)­(CH3CN)2]­(ClO4)3 (1), [(CuL)2Mn­(N­(CN)2)2]­·(H2O) (2), and [(CuL)2Mn­(μ1,5-N­(CN)2)2] n (3), have been synthesized using a Cu­(II)-metalloligand of an asymmetrically dicondensed Schiff base ligand (where H2L = N-α-methylsalicylidene-N′-salicylidene-1,3-propanediamine). Complex 1 was formed when the ratio of [CuL]/Mn­(ClO4)2/NaN­(CN)2 was 2:1:1, whereas complexes 2 and 3 were obtained with a 2:1:2 ratio of the same reactants on varying the reaction conditions. Single-crystal structural analyses reveal that complex 1 possesses a hexanuclear structure in which two (CuII)2MnII units are connected by one μ1,5-N­(CN)2 – bridge, 2 is a discrete trinuclear species with two terminally coordinated N­(CN)2 – ions to the Mn­(II), whereas complex 3 is a polymeric form of 2 with μ1,5-N­(CN)2 – bridges between Cu­(II) and Mn­(II) centers. The thermal variations of dc magnetic susceptibilities suggest that all three complexes (1–3) are antiferromagnetically coupled with comparable exchange coupling constants (−25.4, −22.8, and −22.0 cm–1, respectively) which are expected from the Cu–O–Mn angles. All the complexes show biomemitic phenoxazinone synthase-like activity for the aerial oxidation of o-aminophenol to amino phenoxazinone. The turnover numbers (k cat) for the process are 4966, 2021, and 1107 h–1 for complexes 1–3 respectively. The mass spectral evidence on intermediates suggests that the cooperative activity of the two different metal ions, i.e., coordination of substrate to Mn­(II) and shuttling of oxidation state of Cu between I and II, is possibly operative in the oxidation process. The highest catalytic activity of 1 is attributed to the presence of one coordinating solvent molecule to Mn­(II).

Twom ononuclear uranyl complexes, [UO 2 L 1 ]( 1) and [UO 2 L 2 ]·0.5 CH 3 CN·0.25 CH 3 OH (2), have been synthesized from two multidentate N 3 O 4 donor ligands, N,N'-bis(5-methoxysalicylidene)diethylenetriamine (H 2 L 1 )a nd N,N'-bis(3methoxysalicylidene)diethylenetriamine (H 2 L 2 ), respectively, and have been structurally characterized. Both complexes 1 and 2 showedareversible U VI /U V couple at À1.571 and À1.519 V, respectively,i nc yclic voltammetry.T he reduction potential of the U VI /U V couple shifted towards more positive potential on addition of Li + ,N a + ,K + ,a nd Ag + metal ions to acetonitrile solutions of complex 2,a nd the resulting potential was correlated with the Lewis acidity of the metal ions and wasa lso justified by theoretical DFT calculations. No such shift in reduction potentialw as observed for complex 1.A ll four bimetallic products,[ UO 2 L 2 Li 0.5 ](ClO 4 ) 0.5 (3), [UO 2 L 2 Na(ClO 4 )] 2 (4), [UO 2 L 2 Ag(NO 3 )(H 2 O)] (5), and [(UO 2 L 2 ) 2 K(H 2 O) 2 ]PF 6 (6), formed on addition of the Li + ,N a + , Ag + ,a nd K + metal ions, respectively,t oa cetonitrile solutions of complex 2,w ere isolated in the solid state and structurally characterized by single-crystal X-ray diffraction. In all the species, the inner N 3 O 2 donor set of the ligand encompasses the equatorial plane of the uranyl ion and the outero pen compartment with O 2 O' 2 donors ites hosts the secondm etal ion.[a] T.

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Among four isostructural heterometallic CuII–LnIII complexes (Ln = Tb, Dy, Ho or Er) of an N2O3 donor asymmetric ligand, only the CuII–TbIII complex shows SMM behavior at zero bias field but at applied bias field both the CuII–TbIII and CuII–DyIII complexes show SMM behavior.