Shuvankar Mandal

Syntheses, crystal structures, magnetochemistry and catechol oxidase activity of a tetracopper(II) compound and a new type of dicopper(II)-based 1D coordination polymer

This report describes the syntheses, crystal structures, electrospray ionisation mass spectra, catechol oxidase activity and magnetic properties of a tetracopper(II) cluster [CuII4L2(µ3-OH)2(NCO)4]·2H2O (1) and a one-dimensional (1D) coordination polymer [{{CuII2L(µ1,1-N3)}2(µ1,1-N3)2}(µ1,3-N3)2]n (2) derived from a Schiff base ligand (HL; 1 : 2 condensation product of 4-ethyl-2,6-diformylphenol and 3-morpholinopropylamine). Compound 1 may be considered a dimer of two µ-phenoxo-µ3-hydroxido dicopper(II) units, where the dimerisation takes place through the two µ3-hydroxido moieties. Compound 2 is a µ-phenoxo-µ1,1-azido dicopper(II)-based 1D polymer, where the dicopper(II) units are interlinked by two end-on azide bridges to form a dimer of dinuclear-type tetracopper(II) moieties, which, in turn, are self-assembled by end-to-end azide bridges. Magnetic investigations reveal a strong antiferromagnetic interaction in the dicopper(II) basic unit in both cases, with J values of −382 cm−1 for 1 and −220 cm−1 for 2. Both compounds have been found to be functional models for catechol oxidase activity in N,N-dimethylformamide (DMF) and acetonitrile, with Kcat values around 15 h−1 for 1 and 13 h−1 for 2. Interestingly, compound 2 is a unique example in which a dimer of a dinuclear metal unit is the node for a versatile and well-explored linker, azide, to generate a coordination polymer. It is also interesting that a coordination polymer, 2, has been identified as the functional model of catechol oxidase activity.

Syntheses, crystal structures, magnetic properties and ESI-MS studies of a series of trinuclear CuIIMIICuII compounds (M = Cu, Ni, Co, Fe, Mn, Zn)

Six trinuclear CuIIMIICuII compounds (M = Cu, Ni, Co, Fe, Mn, Zn) derived from the Schiff base ligand, H2L (2 + 1 condensation product of salicylaldehyde and trans-1,2-diaminocyclohexane) are reported in this investigation. The composition of the metal complexes are [{CuIIL(ClO4)}2CuII(H2O)]·2H2O (1), [{CuIIL(ClO4)}{NiII(H2O)2}{CuIIL}]ClO4·CH3COCH3 (2), [{CuIIL(ClO4)}{CoII(CH3COCH3)(H2O)}{CuIIL(CH3COCH3)}]ClO4 (3) and isomorphic [{CuIIL(ClO4)}2MII(CH3OH)2] (4, M = Fe; 5, M = Mn; 6, M = Zn). Two copper(II) ions in 1–6 occupy N2O2 compartments of two L2− ligands, while the second metal ion occupies the O(phenoxo)4 site provided by the two ligands, i.e., the two metal ions in both CuIIMII pairs are diphenoxo-bridged. Positive ESI-MS of 1–6 reveals some interesting features. Variable-temperature and variable-field magnetic studies reveal moderate or weak antiferromagnetic interactions in 1–6 with the following values of magnetic exchange integrals (H = −2JS1S2 type): J1 = −136.50 cm−1 and J = 0.00 for the CuIICuIICuII compound 1; J1 = −22.16 cm−1 and J = −1.97 cm−1 for the CuIINiIICuII compound 2; J1 = −14.78 cm−1 and J = −1.86 cm−1 for the CuIICoIICuII compound 3; J1 = −6.35 cm−1 and J = −1.17 cm−1 for the CuIIFeIICuII compound 4; J1 = −6.02 cm−1 and J = −1.70 cm−1 for the CuIIMnIICuII compound 5; J = −2.25 cm−1 for the CuIIZnIICuII compound 6 (J is between two CuII in the N2O2 compartments; J1 is between CuII and MII through a diphenoxo bridge).