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 H₂L and its eight dinuclear zinc­(II) complexes and one cadmium­(II) complex having composition [Zn₂L­(H₂O)₂]­(ClO₄)₂·2CH₃CN (<b>1</b>), [Zn₂L­(H₂O)₂]­(ClO₄)₂·2dmf (<b>2</b>), [Zn₂L­(H₂O)₂]­(NO₃)₂·2dmf (<b>3</b>), [Zn₂LCl₂] (<b>4</b>), [Zn₂L­(N₃)₂] (<b>5</b>), [Zn₂L­(NCS)₂] (<b>6</b>), [Zn₂L­(NCO)₂] (<b>7</b>), [Zn₂L­(NCSe)₂]₂·dmf (<b>8</b>), and [Cd₂L­(OAc)₂] (<b>9</b>) with various coordinating and noncoordinating anions. The structures of all the complexes <b>1</b>–<b>9</b> 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 <b>1</b>, <b>2</b>, <b>4</b>, <b>6</b>, <b>7</b>, <b>8</b>, and <b>9</b>; three-dimensional network in <b>5</b>. Spectrophotometric and spectrofluorometric titrations of the diprotonated salt [H₄L]­(ClO₄)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 [H₄L]­(ClO₄)₂ and <b>1</b>–<b>9</b> have been studied and their quantum yields have been determined. Time resolved fluorescence behavior of [H₄L]­(ClO₄)₂ and the dizinc­(II) and dicadmium­(II) complexes <b>1</b>–<b>9</b> 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, [H₄L]­(ClO₄)₂ and <b>1</b>–<b>9</b>, 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

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 H₂L and its eight dinuclear zinc­(II) complexes and one cadmium­(II) complex having composition [Zn₂L­(H₂O)₂]­(ClO₄)₂·2CH₃CN (<b>1</b>), [Zn₂L­(H₂O)₂]­(ClO₄)₂·2dmf (<b>2</b>), [Zn₂L­(H₂O)₂]­(NO₃)₂·2dmf (<b>3</b>), [Zn₂LCl₂] (<b>4</b>), [Zn₂L­(N₃)₂] (<b>5</b>), [Zn₂L­(NCS)₂] (<b>6</b>), [Zn₂L­(NCO)₂] (<b>7</b>), [Zn₂L­(NCSe)₂]₂·dmf (<b>8</b>), and [Cd₂L­(OAc)₂] (<b>9</b>) with various coordinating and noncoordinating anions. The structures of all the complexes <b>1</b>–<b>9</b> 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 <b>1</b>, <b>2</b>, <b>4</b>, <b>6</b>, <b>7</b>, <b>8</b>, and <b>9</b>; three-dimensional network in <b>5</b>. Spectrophotometric and spectrofluorometric titrations of the diprotonated salt [H₄L]­(ClO₄)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 [H₄L]­(ClO₄)₂ and <b>1</b>–<b>9</b> have been studied and their quantum yields have been determined. Time resolved fluorescence behavior of [H₄L]­(ClO₄)₂ and the dizinc­(II) and dicadmium­(II) complexes <b>1</b>–<b>9</b> 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, [H₄L]­(ClO₄)₂ and <b>1</b>–<b>9</b>, 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

Structures, Magnetochemistry, Spectroscopy, Theoretical Study, and Catechol Oxidase Activity of Dinuclear and Dimer-of-Dinuclear Mixed-Valence Mn^IIIMn^II Complexes Derived from a Macrocyclic Ligand

The work in this paper presents syntheses, characterization, magnetic properties (experimental and density functional theoretical), catecholase activity, and electrospray ionization mass spectroscopic (ESI-MS positive) studies of two mixed-valence dinuclear Mn^IIIMn^II complexes, [Mn^IIIMn^IIL­(μ-O₂CMe)­(H₂O)₂]­(ClO₄)₂·H₂O·MeCN (<b>1</b>) and [Mn^IIIMn^IIL­(μ-O₂CPh)­(MeOH)­(ClO₄)]­(ClO₄) (<b>2</b>), and a Mn^IIIMn^IIMn^IIMn^III complex, [{Mn^IIIMn^IIL­(μ-O₂CEt)­(EtOH)}₂(μ-O₂CEt)]­(ClO₄)₃ (<b>3</b>), derived from the Robson-type macrocycle H₂L, which is the [2 + 2] condensation product of 2,6-diformyl-4-methylphenol and 2,2-dimethyl-1,3-diaminopropane. In <b>1</b> and <b>2</b> and in two Mn^IIIMn^II units in <b>3</b>, the two metal centers are bridged by a bis­(μ-phenoxo)-μ-carboxylate moiety. The two Mn^II centers of the two Mn^IIIMn^II units in <b>3</b> are bridged by a propionate moiety, and therefore this compound is a dimer of two dinuclear units. The coordination geometry of the Mn^III and Mn^II centers are Jahn–Teller distorted octahedral and distorted trigonal prism, respectively. Magnetic studies reveal weak ferro- or antiferromagnetic interactions between the Mn^III and Mn^II centers in <b>1</b> (<i>J</i> = +0.08 cm^–1), <b>2</b> (<i>J</i> = −0.095 cm^–1), and <b>3</b> (<i>J</i>₁ = +0.015 cm^–1). A weak antiferromagnetic interaction (<i>J</i>₂ = −0.20 cm^–1) also exists between the Mn^II centers in <b>3</b>. DFT methods properly reproduce the nature of the exchange interactions present in such systems. A magneto-structural correlation based on Mn–O bridging distances has been proposed to explain the different sign of the exchange coupling constants. Utilizing 3,5-di-<i>tert</i>-butyl catechol (3,5-DTBCH₂) as the substrate, catecholase activity of all the three complexes has been checked in MeCN and MeOH, revealing that all three are active catalysts with <i>K</i>_cat values lying in the range 7.5–64.7 h^–1. Electrospray ionization mass (ESI-MS positive) spectra of the complexes <b>1</b>–<b>3</b> have been recorded in MeCN solutions, and the positive ions have been well characterized. ESI-MS positive spectrum of complex <b>1</b> in presence of 3,5-DTBCH₂ has also been recorded, and a positive ion, [Mn^IIIMn^IIL­(μ-3,5-DTBC^2–)]⁺, having most probably a bridging catecholate moiety has been identified

Synthesis and crystal structure of a triple-decker Cu^II₃Tl^I₂ complex: first example of a thallium(I) system in the imino-phenolate Schiff base ligand family

<div><p>This report deals with the synthesis, characterization, and crystal structure of a heteropentanuclear Cu^II₃Tl^I₂ compound [(Cu^IIL)₃Tl^I₂](NO₃)₂ (<b>1</b>), where H₂L=<i>N</i>,<i>N</i>′-ethylenebis(3-ethoxysalicylaldimine). This compound crystallizes in the monoclinic crystal system within space group <i>C2</i>/<i>c</i>. Each of the two symmetry related thallium(I) centers is located between a terminal and a common, central [Cu^IIL] by forming bonds with four phenoxo and three ethoxy oxygens. The three [Cu^IIL] moieties are parallel and hence <b>1</b> is a triple-decker system. Neighboring triple-decker moieties are interlinked by π⋯π stacking interaction and weak hydrogen bonds to generate 3-D self-assembly in <b>1</b>. Salient features in the composition and structure of the title compound are discussed; the title compound is the first example of a thallium(I) system in imino-phenolate Schiff base family.</p></div

A Series of M^IICu^II₃ Stars (M = Mn, Ni, Cu, Zn) Exhibiting Unusual Magnetic Properties

The work in this report describes the syntheses, electrospray ionization mass spectromtery, structures, and experimental and density functional theoretical (DFT) magnetic properties of four tetrametallic stars of composition [M^II(Cu^IIL)₃]­(ClO₄)₂ (<b>1</b>, M = Mn; <b>2</b>, M = Ni; <b>3</b>, M = Cu; <b>4</b>, M = Zn) derived from a single-compartment Schiff base ligand, <i>N</i>,<i>N</i>′-bis­(salicylidene)-1,4-butanediamine (H₂L), which is the [2 + 1] condensation product of salicylaldehyde and 1,4-diaminobutane. The central metal ion (Mn^II, Ni^II, Cu^II, or Zn^II) is linked with two μ₂-phenoxo bridges of each of the three [Cu^IIL] moieties, and thus the central metal ion is encapsulated in between three [Cu^IIL] units. The title compounds are rare or sole examples of stars having these metal-ion combinations. In the cases of <b>1</b>, <b>3</b>, and <b>4</b>, the four metal ions form a centered isosceles triangle, while the four metal ions in <b>2</b> form a centered equilateral triangle. Both the variable-temperature magnetic susceptibility and variable-field magnetization (at 2–10 K) of <b>1</b>–<b>3</b> have been measured and simulated contemporaneously. While the Mn^IICu^II₃ compound <b>1</b> exhibits ferromagnetic interaction with <i>J</i> = 1.02 cm^–1, the Ni^IICu^II₃ compound <b>2</b> and Cu^IICu^II₃ compound <b>3</b> exhibit antiferromagnetic interaction with <i>J</i> = −3.53 and −35.5 cm^–1, respectively. Variable-temperature magnetic susceptibility data of the Zn^IICu^II₃ compound <b>4</b> indicate very weak antiferromagnetic interaction of −1.4 cm^–1, as expected. On the basis of known correlations, the magnetic properties of <b>1</b>–<b>3</b> are unusual; it seems that ferromagnetic interaction in <b>1</b> and weak/moderate antiferromagnetic interaction in <b>2</b> and <b>3</b> are possibly related to the distorted coordination environment of the peripheral copper­(II) centers (intermediate between square-planar and tetrahedral). DFT calculations have been done to elucidate the magnetic properties. The DFT-computed <i>J</i> values are quantitatively (for <b>1</b>) or qualitatively (for <b>2</b> and <b>3</b>) matched well with the experimental values. Spin densities and magnetic orbitals (natural bond orbitals) correspond well with the trend of observed/computed magnetic exchange interactions

Syntheses, Structures, Magnetic Properties, and Density Functional Theory Magneto-Structural Correlations of Bis(μ-phenoxo) and Bis(μ-phenoxo)-μ-acetate/Bis(μ-phenoxo)-bis(μ-acetate) Dinuclear Fe^IIINi^II Compounds

The bis­(μ-phenoxo) Fe^IIINi^II compound [Fe^III(N₃)₂LNi^II(H₂O)­(CH₃CN)]­(ClO₄) (<b>1</b>) and the bis­(μ-phenoxo)-μ-acetate/bis­(μ-phenoxo)-bis­(μ-acetate) Fe^IIINi^II compound {[Fe^III(OAc)­LNi^II(H₂O)­(μ-OAc)]_0.6·[Fe^IIILNi^II(μ-OAc)₂]_0.4}­(ClO₄)·1.1H₂O (<b>2</b>) have been synthesized from the Robson type tetraiminodiphenol macrocyclic ligand H₂L, which is the [2 + 2] condensation product of 4-methyl-2,6-diformylphenol and 2,2′-dimethyl-1,3-diaminopropane. Single-crystal X-ray structures of both compounds have been determined. The cationic part of the dinuclear compound <b>2</b> is a cocrystal of the two species [Fe^III(OAc)­LNi^II(H₂O)­(μ-OAc)]⁺ (<b>2A</b>) and [Fe^IIILNi^II(μ-OAc)₂]⁺ (<b>2B</b>) with weights of 60% of the former and 40% of the latter. While <b>2A</b> is a triply bridged bis­(μ-phenoxo)-μ-acetate system, <b>2B</b> is a quadruply bridged bis­(μ-phenoxo)-bis­(μ-acetate) system. Variable-temperature (2–300 K) magnetic studies reveal antiferromagnetic interaction in <b>1</b> and ferromagnetic interaction in <b>2</b> with <i>J</i> values of −3.14 and 7.36 cm^–1, respectively (<i>H</i> = −2<i>JS</i>₁·<i>S</i>₂). Broken-symmetry density functional calculations of exchange interaction have been performed on complexes <b>1</b> and <b>2</b> and also on previously published related compounds, providing good numerical estimates of <i>J</i> values in comparison to experiments. The electronic origin of the difference in magnetic behavior of <b>1</b> and <b>2</b> has been well understood from MO analyses and computed overlap integrals of BS empty orbitals. The role of acetate and thus its complementarity/countercomplementarity effect on the magnetic properties of diphenoxo-bridged Fe^IIINi^II compounds have been determined on computing <i>J</i> values of model compounds by replacing bridging acetate and nonbridging acetate ligand(s) by water ligands in the model compounds derived from <b>2A</b>,<b>B</b>. The DFT calculations have also been extended to develop several magneto-structural correlations in these types of complexes, and the correlations focus on the role of Fe–O–Ni bridge angle, average Fe/Ni–O bridge distance, Fe–O–Ni–O dihedral angle, and out-of-plane shift of the phenoxo group

Syntheses, Structures, Magnetic Properties, and Density Functional Theory Magneto-Structural Correlations of Bis(μ-phenoxo) and Bis(μ-phenoxo)-μ-acetate/Bis(μ-phenoxo)-bis(μ-acetate) Dinuclear Fe^IIINi^II Compounds

The bis­(μ-phenoxo) Fe^IIINi^II compound [Fe^III(N₃)₂LNi^II(H₂O)­(CH₃CN)]­(ClO₄) (<b>1</b>) and the bis­(μ-phenoxo)-μ-acetate/bis­(μ-phenoxo)-bis­(μ-acetate) Fe^IIINi^II compound {[Fe^III(OAc)­LNi^II(H₂O)­(μ-OAc)]_0.6·[Fe^IIILNi^II(μ-OAc)₂]_0.4}­(ClO₄)·1.1H₂O (<b>2</b>) have been synthesized from the Robson type tetraiminodiphenol macrocyclic ligand H₂L, which is the [2 + 2] condensation product of 4-methyl-2,6-diformylphenol and 2,2′-dimethyl-1,3-diaminopropane. Single-crystal X-ray structures of both compounds have been determined. The cationic part of the dinuclear compound <b>2</b> is a cocrystal of the two species [Fe^III(OAc)­LNi^II(H₂O)­(μ-OAc)]⁺ (<b>2A</b>) and [Fe^IIILNi^II(μ-OAc)₂]⁺ (<b>2B</b>) with weights of 60% of the former and 40% of the latter. While <b>2A</b> is a triply bridged bis­(μ-phenoxo)-μ-acetate system, <b>2B</b> is a quadruply bridged bis­(μ-phenoxo)-bis­(μ-acetate) system. Variable-temperature (2–300 K) magnetic studies reveal antiferromagnetic interaction in <b>1</b> and ferromagnetic interaction in <b>2</b> with <i>J</i> values of −3.14 and 7.36 cm^–1, respectively (<i>H</i> = −2<i>JS</i>₁·<i>S</i>₂). Broken-symmetry density functional calculations of exchange interaction have been performed on complexes <b>1</b> and <b>2</b> and also on previously published related compounds, providing good numerical estimates of <i>J</i> values in comparison to experiments. The electronic origin of the difference in magnetic behavior of <b>1</b> and <b>2</b> has been well understood from MO analyses and computed overlap integrals of BS empty orbitals. The role of acetate and thus its complementarity/countercomplementarity effect on the magnetic properties of diphenoxo-bridged Fe^IIINi^II compounds have been determined on computing <i>J</i> values of model compounds by replacing bridging acetate and nonbridging acetate ligand(s) by water ligands in the model compounds derived from <b>2A</b>,<b>B</b>. The DFT calculations have also been extended to develop several magneto-structural correlations in these types of complexes, and the correlations focus on the role of Fe–O–Ni bridge angle, average Fe/Ni–O bridge distance, Fe–O–Ni–O dihedral angle, and out-of-plane shift of the phenoxo group