Four new heterometallic Cu(ii)–Mn(ii) complexes have been synthesised by using a Cu(ii) complex of an unsymmetrical Schiff base as O3 donor ligand; one of which is catalytically active towards catecholase and phenoxazinone synthase activities.

Five new heterometallic Cu(II)-Mn(II) discrete trinuclear complexes, [(CuL)2Mn(CH3COO)2] (1), [(CuL)2Mn(NO3)2] (2), [(CuL)2Mn(C6H5COO)(H2O)]Cl (3), [(CuL)2Mn((p-OH)C6H5COO)(H2O)]ClO4 (4) and [(CuL)2Mn(HCOO)(H2O)]ClO4 (5) have been synthesized using a metalloligand, CuL derived from an N2O2 donor...

Among the four one-dimensional coordination polymers obtained by joining (CuL)2M (M = MnII and CdII) nodes with 1,3- and 1,4-benzenedicarboxylate linkers, the chains derived from 1,3-benzenedicarboxylate are co-crystallized with dimeric CuII units.

The joining of bimetallic trinuclear nodes, [(CuL1)2Cd] (where H2L1 = N,N′-bis(α-methylsalicylidene)-1,3-propanediamine) by a spacer, 4,4′-benzenedicarboxylic acid (H2L2), produced two isomeric one-dimensional coordination polymers, having molecular formula {[(CuL1)2CdL2]·H2O} n . Structural characterization revealed that, in complex 1, one of the oxygen atoms of each carboxylate group of the linker [L2]2– coordinates only to the central Cd­(II) atom of the node in η1 fashion. However, in complex 2, both the oxygen atoms of each carboxylate group coordinate to the metal centers, one to Cd­(II) and the other to a terminal Cu­(II) via η2 syn–syn bridging mode. Moreover, the two bridging carboxylate O atoms are mutually cis in 1 while these are trans in 2. These differences resulted in the novel isomeric zigzag (or cis) and linear (or trans) chains of the coordination polymer. DFT calculations revealed that complex 2 is thermodynamically more stable than complex 1 by 4.3 kcal/mol in the gas phase. The electrical characterizations, i.e., impedance, capacitance, and current–voltage (I–V) studies, reveal substantive electrical conductivity for both complexes, but the charge transport properties are higher for 2 in comparison to 1. Both the materials exhibit photoswitching properties as they show increased electrical conductivity under illuminated conditions than under dark conditions. However, complex 2 shows significantly higher photosensitivity (P S = 571.50) compared to 1 (P S = 201.40) and thus has more potentiality toward fabrication of photosensitive devices.

In the present work, four new heterometallic coordination complexes, {[(CuL) 2 Mn(nic and [(CuL) 2 Cd(nic) 2 ]•2CH 3 OH (4) (where H 2 L = N,N′-bis(α-methylsalicylidene)-1,3-propanediamine and nic = nicotinate ion), have been synthesized and characterized by single-crystal X-ray crystallography. In complexes 1 and 2, the nicotinate ion acts as a bifunctional linker (N,O donor) and joins the linear trinuclear nodes to form 1D polymeric chains. However, in complexes 3 and 4, the nicotinate ion uses only the oxygen atoms of the carboxylic acid (O donor) to bind to the metal centers, forming discrete linear trinuclear units, while the pyridyl nitrogen (N donor atom) remains free. The dc magnetic susceptibility measurements show that the Cu II and Mn II ions are antiferromagnetically coupled in both 1 and 3, with exchange coupling constants (J Mn−Cu ) of −20.57 ± 0.08 and −9.38 ± 0.08 cm −1 , respectively. Among the four complexes, 1 and 3 show catechol oxidase and phenoxazinone synthase like catalytic activities. The turnover numbers (k cat ) of complexes 1 and 3 for catecholase activity are 1121 and 720 h −1 , respectively, at an optimum pH of 8.0 and for phenoxazinone synthase activity are 429 and 398 h −1 , respectively, at an optimum pH of 9.7. The higher k cat values of 1 for both reactions are attributable to a water molecule coordinated to the central Mn II atom that facilitates the substrate−catalyst binding. An ESI-mass spectral analysis indicates that trinuclear heterometallic species, e.g., [(CuL) 2 Mn(nic)(H 2 O)] + for 1 and [(CuL) 2 Mn-(nic)] + for 3, are the active species that bind to the substrate, and on that basis, probable mechanisms through the formation of radical intermediates have been proposed.

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