Leena Mandal

Syntheses, structures, and steady state and time resolved photophysical properties of a tetraiminodiphenol macrocyclic ligand and its dinuclear zinc(II)/cadmium(II) complexes with coordinating and noncoordinating anions.

The work in the present investigation reports the syntheses, structures, steady state, and time-resolved photophysical properties of a tetraiminodiphenol macrocyclic ligand H(2)L and its eight dinuclear zinc(II) complexes and one cadmium(II) complex having composition [Zn(2)L(H(2)O)(2)](ClO(4))(2)·2CH(3)CN (1), [Zn(2)L(H(2)O)(2)](ClO(4))(2)·2dmf (2), [Zn(2)L(H(2)O)(2)](NO(3))(2)·2dmf (3), [Zn(2)LCl(2)] (4), [Zn(2)L(N(3))(2)] (5), [Zn(2)L(NCS)(2)] (6), [Zn(2)L(NCO)(2)] (7), [Zn(2)L(NCSe)(2)](2)·dmf (8), and [Cd(2)L(OAc)(2)] (9) with various coordinating and noncoordinating anions. The structures of all the complexes 1-9 have been determined by single-crystal X-ray diffraction. The noncovalent interactions in the complexes result in the generation of the following topologies: two-dimensional network in 1, 2, 4, 6, 7, 8, and 9; three-dimensional network in 5. Spectrophotometric and spectrofluorometric titrations of the diprotonated salt [H(4)L](ClO(4))(2) with triethylamine as well as with zinc(II) acetate and cadmium(II) acetate have been carried out, revealing fluorescence enhancement of the macrocyclic system by the base and the metal ions. Steady state fluorescence properties of [H(4)L](ClO(4))(2) and 1-9 have been studied and their quantum yields have been determined. Time resolved fluorescence behavior of [H(4)L](ClO(4))(2) and the dizinc(II) and dicadmium(II) complexes 1-9 have also been studied, and their lifetimes and radiative and nonradiative rate constants have been determined. The induced fluorescence enhancement of the macrocycle by zinc(II) and cadmium(II) is in line with the greater rate of increase of the radiative rate constants in comparison to the smaller rate of increase of nonradiative rate constants for the metal complexes. The fluorescence decay profiles of all the systems, being investigated here, that is, [H(4)L](ClO(4))(2) and 1-9, follow triexponential patterns, revealing that at least three conformers/components are responsible to exhibit the fluorescence decay behavior. The systems and studies in this report have been compared with those in the reports of the previously published similar systems, revealing some interesting aspects.

More surprising differences between two closely similar compartmental ligand families and another dinuclear synthon to stabilize dinuclear–mononuclear cocrystals

This paper presents syntheses, characterization, crystal structures and magnetic properties of two diphenoxo-bridged heterodinuclear CuIIMnII/CuIIFeII compounds [CuIIL1MnII(H2O)3](ClO4)2 (1) and [CuIIL1FeII(H2O)3](ClO4)2 (2) and two tetranuclear CuII3MnII/CuII3FeII compounds [{CuIIL2MnII(H2O)(MeOH)2}(CuIIL2)2](ClO4)2·MeOH (3) and [{CuIIL2FeII(H2O)(MeOH)2}(CuIIL2)2](ClO4)2·MeOH (4) derived from two 3-methoxysalicylaldehyde-diamine Schiff base compartmental ligands H2L1 and H2L2, in which the diamine counterpart comes from 1,3-diaminopropane and o-phenylenediamine, respectively. The two compounds 1 and 2 crystallize in the same space group (monoclinic P21/n) with practically identical unit cell parameters and are isomorphous. Similarly, the two compounds 3 and 4 crystallize in the same space group (monoclinic P21/c) with practically identical unit cell parameters and are isomorphous. The tetranuclear [{CuIIL2MII(H2O)(MeOH)2}(CuIIL2)2]2+ dication in 3 (M = Mn) and 4 (M = Fe) is a self-assembly of one diphenoxo-bridged dinuclear [CuIIL2MII(H2O)(MeOH)2]2+ dication and two mononuclear [CuIIL2] units. One mononuclear unit is self-assembled with the dinuclear unit by four bifurcated water⋯phenoxo/methoxy (O–H⋯O) hydrogen bonds and three π⋯π stacking interactions, while the second mononuclear unit is interlinked with the dinuclear unit by one methanol⋯phenoxo (O–H⋯O) hydrogen bond only. Clearly, compounds 3 and 4 are [2 × 1 + 1 × 2] cocrystals of one dinuclear and two mononuclear units. Variable-temperature magnetic susceptibility measurements of all the four compounds have been carried out, revealing moderate antiferromagnetic interaction between the copper(II) and manganese(II)/iron(II) in the dinuclear cores with J values (H = −2JS1S2) −29.1, −36.9, −15.9 and −20.2 cm−1, respectively. The magnetic properties are in line with those of previous related examples. Unique features in the structures of 1–4 have been discussed.

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 and steady state and time-resolved fluorescence properties of a PET based macrocycle and its dinuclear ZnII/CdII/HgII complexes

The work in the present investigation reports the syntheses, crystal structures, ESI-MS (positive) and steady state and time resolved photophysical properties of a tetraaminodiphenol macrocyclic ligand H2L (saturated analogue of a tetraiminodiphenol macrocycle obtained on 2 + 2 condensation of 4-ethyl-2,6-diformylphenol and 2,2-dimethyl-1,3-diaminopropane) and its three dinuclear d10 metal ion (ZnII, CdII and HgII) complexes having compositions [ZnLCl2]·2CH3OH (1), [CdL(μ-H2O)(H2O)2](NO3)2·4H2O (2) and [HgLCl2] (3). H2L is colorless and weakly fluorescent, Cd compound 2 is colorless and more weakly fluorescent, Zn compound 1 is colorless and highly fluorescent and Hg compound 3 is yellow and nonemissive. The order of the radiative rate constant (Kr), obtained from time-resolved studies, corroborates the order of quantum yields, obtained from steady state studies: 1 (φ = 0.12; Kr = 116.6 × 106 s-1) ≫ H2L (φ = 0.005; Kr = 7.726 × 106 s-1) > Cd compound 2 (φ = 0.0014; Kr = 0.675 × 106 s-1). Spectrophotometric and steady state/time-resolved spectrofluorimetric titrations of H2L with ZnII, CdII and HgII have been performed. The relative fluorescence efficiencies of H2L, H2L + various single metal ions (ZnII, CdII, HgII, CuII, NiII, CoII, FeII, MnII) and H2L + ZnII + another metal ion (metal ion competition study) have been studied. Relative fluorescence efficiency can be well rationalized in terms of photoinduced electron transfer (PET), perturbation of PET by metal coordination (chelation enhanced fluorescence, CHEF), heavy metal ion effect (spin-orbit coupling) and fluorescence quenching mechanism. It has been established from comparative fluorescence spectra of 4-ethylphenol, H2L and 1 that H2L can be reasonably considered as a PET species in which the fluorophore is 4-ethylphenol. The binding constants, as determined from titration experiments, qualitatively corroborate the results of metal ion competition studies. The modulation of the absorption spectra and color of the H2L-HgII solution in the presence of various diamagnetic metal ions has been explored. Significant aspects of structures and spectroscopic properties have been discussed.