Assembly of Silver(I) Complexes of Isomeric NS₂-Macrocycles Displaying Cyclic Oligomer, Helix, and Zigzag Structures

An isomeric series of NS₂-macrocycles, incorporating <i>ortho</i>- (<i><b>o</b></i><b>-L</b>), <i>meta</i>- (<i><b>m</b></i><b>-L</b>), and <i>para</i>-xylyl (<i><b>p</b></i><b>-L</b>) groups in their backbones between the sulfur donors, have been synthesized. A comparative investigation of the coordination behavior of these macrocyclic ligands with silver­(I) salts is reported. The X-ray structures of six complexes (<b>1</b>–<b>6</b>) were determined, and a variety of structural types that range from cyclic oligomers to zigzag or helical chains is shown to occur. Reactions of <i><b>o</b></i><b>-L</b> with silver nitrate and perchlorate afforded three complexes with different topologies: the cyclic hexamer [Ag₆(<i><b>o</b></i><b>-L</b>)₆]­(NO₃)₆·0.5DMF·7H₂O (<b>1</b>), the cyclic hexamer with two terminal complex units [Ag₈(<i><b>o</b></i><b>-L</b>)₈]­(ClO₄)₈ (<b>2</b>), and a one-dimensional (1D) zigzag coordination polymer of type {[Ag₂(<i><b>o</b></i>-<b>L</b>)₂]­(ClO₄)₂·2CH₃CN·CHCl₃}_<i>n</i> (<b>3</b>). Reaction of <i><b>m</b></i>-<b>L</b> with silver­(I) perchlorate gave the 1D zigzag coordination polymer, {[Ag­(<i><b>m</b></i><b>-L</b>)]­ClO₄·CH₂Cl₂}_<i>n</i> (<b>4</b>). Reaction of <i><b>p</b></i><b>-L</b> with silver perchlorate yielded a crystalline product whose X-ray analysis confirmed it to be a mixture of two different species: the discrete helical complex {[Ag₃(<i><b>p</b></i><b>-L</b>)₃]­(ClO₄)₃}_<i>n</i> (<b>5</b>) and the cyclic tetramer [Ag₄(<i><b>p</b></i><b>-L</b>)₄(ClO₄)₄]·3DMF (<b>6</b>). The influence of macrocyclic ring flexibility and sulfur donor atom spacing on the topologies adopted by the respective complexes is discussed

Assembly of Silver(I) Complexes of Isomeric NS₂-Macrocycles Displaying Cyclic Oligomer, Helix, and Zigzag Structures

An isomeric series of NS₂-macrocycles, incorporating <i>ortho</i>- (<i><b>o</b></i><b>-L</b>), <i>meta</i>- (<i><b>m</b></i><b>-L</b>), and <i>para</i>-xylyl (<i><b>p</b></i><b>-L</b>) groups in their backbones between the sulfur donors, have been synthesized. A comparative investigation of the coordination behavior of these macrocyclic ligands with silver­(I) salts is reported. The X-ray structures of six complexes (<b>1</b>–<b>6</b>) were determined, and a variety of structural types that range from cyclic oligomers to zigzag or helical chains is shown to occur. Reactions of <i><b>o</b></i><b>-L</b> with silver nitrate and perchlorate afforded three complexes with different topologies: the cyclic hexamer [Ag₆(<i><b>o</b></i><b>-L</b>)₆]­(NO₃)₆·0.5DMF·7H₂O (<b>1</b>), the cyclic hexamer with two terminal complex units [Ag₈(<i><b>o</b></i><b>-L</b>)₈]­(ClO₄)₈ (<b>2</b>), and a one-dimensional (1D) zigzag coordination polymer of type {[Ag₂(<i><b>o</b></i>-<b>L</b>)₂]­(ClO₄)₂·2CH₃CN·CHCl₃}_<i>n</i> (<b>3</b>). Reaction of <i><b>m</b></i>-<b>L</b> with silver­(I) perchlorate gave the 1D zigzag coordination polymer, {[Ag­(<i><b>m</b></i><b>-L</b>)]­ClO₄·CH₂Cl₂}_<i>n</i> (<b>4</b>). Reaction of <i><b>p</b></i><b>-L</b> with silver perchlorate yielded a crystalline product whose X-ray analysis confirmed it to be a mixture of two different species: the discrete helical complex {[Ag₃(<i><b>p</b></i><b>-L</b>)₃]­(ClO₄)₃}_<i>n</i> (<b>5</b>) and the cyclic tetramer [Ag₄(<i><b>p</b></i><b>-L</b>)₄(ClO₄)₄]·3DMF (<b>6</b>). The influence of macrocyclic ring flexibility and sulfur donor atom spacing on the topologies adopted by the respective complexes is discussed

Cucurbit[7]uril-improved recognition by a fluorescent sensor for cadmium and zinc cations

<p>The host–guest interaction of cucurbit[7]uril (Q[7]) with the new fluorescent sensor guest molecule (<b>BIBPAH</b>^<b>+</b>), formed by alkylation of the secondary amine site in <i>N,N</i>-bis(2-pyridylmethyl)amine with 2-(bromomethyl)benzimidazole, was investigated by fluorescence and ¹H NMR spectroscopy. The results indicate the formation of an inclusion complex in a 1:1 ratio with an association constant of <i>K</i>_a = (2.9 ± 0.7) × 10⁵ L ∙ mol⁻¹. There is minimal difference in the fluorescence intensities upon the introduction of each of Mn²⁺, Ni²⁺, Co²⁺, Cr³⁺, Ho³⁺ and Lu³⁺. However, the emission was slightly quenched on the addition of Cu²⁺ or Fe³⁺ whether Q[7] is present or not. Further investigation showed that encapsulation of <b>BIBPAH</b>^<b>+</b> in Q[7] improves Cd²⁺ and Zn²⁺ recognition by enhancing the fluorescence intensity, leading to an improvement in the limits of detection. In contrast, comparative parallel experiments in which Cu²⁺, Mn²⁺, Ni²⁺, Co²⁺, Fe³⁺, Cr³⁺, Ho³⁺ or Lu³⁺ were substituted for Zn²⁺ or Cd²⁺ resulted in minimal changes in the fluorescence that occurs for the corresponding metal-free system. The natures of the encapsulated Zn²⁺ and Cd²⁺ complexes have been investigated using fluorescence and ¹H NMR spectroscopy as well as by quantum chemistry.</p> <p>The selectivity of a fluorescent sensor for Cd²⁺ and Zn²⁺ was improved by its encapsulation within the cavity of cucurbit[7]uril.</p

Anion-controlled assembly of Ag(I) coordination polymers based on cis/trans-bis(acetylacetone)-1,4-cyclohexanediimine ligands: syntheses, structures, and solid-state luminescence

<p>Two isomorphic acetylacetone-based complexes: <i>trans</i>-bis(acetylacetone)-1,4cyclohexanediimine (TBAC) and <i>cis</i>-bis(acetylacetone)-1,4-cyclohexanediimine (CBAC) were designed to promote complex formation on reaction with AgX (X = , , , , and ) and were employed to generate nine silver coordination polymers (CPs), {[Ag(TBAC)]·2H₂O·BF₄}_n (<b>1</b>), [Ag(TBAC)_0.5(NO₃)]_n (<b>2</b>), [Ag₂(TBAC)₂(ClO₄)₂]_n (<b>3</b>), [Ag(TBAC)(CF₃SO₃)(H₂O)]_n (<b>4</b>), {[Ag(TBAC)₂]·SbF₆}_n (<b>5</b>), {[Ag(CBAC)]·BF₄}_n (<b>6</b>), {[Ag(CBAC)(H₂O)]·ClO₄}_n (<b>7</b>), {[Ag(CBAC)(H₂O)]·CF₃SO₃}_n (<b>8</b>), and {[Ag(CBAC)(H₂O)]·SbF₆}_n (<b>9</b>) that exhibit structural and topological diversity as determined by single-crystal X-ray diffraction analyses. The complexes were further characterized by elemental analyses, IR spectra, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. Complex <b>1</b> exhibited a 3-D (4,4)-connected pts topology with the Schläfli symbol of (4²·8⁴). The anions in <b>2</b> are <i>μ</i>₂-bridging linkers, connecting the 1-D [Ag(TBAC)_0.5]_n chains to 2-D (3,4)-connected nets. In <b>3</b>, TBAC is a tridentate ligand to bind Ag(I) ions to form a 1-D ladder-like supramolecular structure. Complex <b>4</b> has 2-D (3,3)-connected nets where both Ag(I) ions and TBAC ligands are 3-connected nodes. Complex <b>5</b> has a 1-D fishbone chain structure where some of the TBAC moieties are bidentate. The <i>cis</i>-isomer, CBAC, gives similar (3,3)-connected networks where the Ag(I) ions and CBAC ligands are 3-connected nodes in the resultant <b>6</b>–<b>9</b>. Although the host networks in <b>6</b>–<b>9</b> are supramolecular isomers, structural comparisons revealed that use of <i>cis-</i> and <i>trans</i>-isomers of the ligand and different counterions significantly influence the structures. The luminescent properties of all complexes and ligands were investigated.</p

Formation of a Dicopper Platform Based Polyrotaxane Whose “<i>String</i>” and “<i>Bead</i>” Are Constructed from the Same Components

The combination of the dicopper platform [Cu₂(<b>L</b>)₂(THF)₂] (<b>1</b>·2THF), where H_<b>2</b><b>L</b> is 1,1′-(1,3-phenylene)-bis-4,4-dimethylpentane-1,3-dione, and 1,4-bis­(4-pyridyl)­piperazine (bpp), afforded the first example of a one-dimensional polyrotaxane {[(<b>1</b>)­(μ₂-bpp)]­[(<b>1</b>)₂(bpp)₂]}_<i>n</i> whose “<i>string</i>” and “<i>bead</i>” are constructed from the same components. The <i>bead</i> of stoichiometry [(<b>1</b>)₂(bpp)₂] has a large rectangular cavity of dimensions 7.40 × 15.64 Å and is threaded onto a stair-like <i>string</i> of composition [(<b>1</b>)­(μ₂-bpp)]_<i>n</i>. The formation of the polyrotaxane is driven by π–π stacking between the <i>string</i> and the <i>beads</i> with precise electronic and steric complementarity between these components. A pathway for the formation of the polyrotaxane is proposed

Metal Dilution Effects on the Reverse Spin Transition in Mixed Crystals of Type [Co_1–<i>x</i>Zn_<i>x</i>(C₁₆-terpy)₂](BF₄)₂ (<i>x</i> = 0.1–0.7)

Metal dilution effects on reverse spin transition (rST) in mixed crystals of type [Co_1–<i>x</i>Zn_<i>x</i>­(C₁₆-terpy)₂]­(BF₄)₂ (<i>x</i> = 0.1–0.7) were investigated by comparison with behavior of [Co_1–<i>x</i>Fe_<i>x</i>­(C₁₆-terpy)₂]­(BF₄)₂ (<i>x</i> = 0.1–0.4). In the mixed crystals, the Zn complexes increased rST temperatures linearly with increasing values of <i>x</i>, without changing the hysteresis width, while the Fe complexes decreased rST temperatures. Moreover, the strength of the metal dilution effects in the CoZn mixed crystals is weaker than what occurs in the CoFe mixed crystals

Metal Dilution Effects on the Reverse Spin Transition in Mixed Crystals of Type [Co_1–<i>x</i>Zn_<i>x</i>(C₁₆-terpy)₂](BF₄)₂ (<i>x</i> = 0.1–0.7)

Metal dilution effects on reverse spin transition (rST) in mixed crystals of type [Co_1–<i>x</i>Zn_<i>x</i>­(C₁₆-terpy)₂]­(BF₄)₂ (<i>x</i> = 0.1–0.7) were investigated by comparison with behavior of [Co_1–<i>x</i>Fe_<i>x</i>­(C₁₆-terpy)₂]­(BF₄)₂ (<i>x</i> = 0.1–0.4). In the mixed crystals, the Zn complexes increased rST temperatures linearly with increasing values of <i>x</i>, without changing the hysteresis width, while the Fe complexes decreased rST temperatures. Moreover, the strength of the metal dilution effects in the CoZn mixed crystals is weaker than what occurs in the CoFe mixed crystals

Post-Assembly Covalent Di- and Tetracapping of a Dinuclear [Fe₂L₃]⁴⁺ Triple Helicate and Two [Fe₄L₆]⁸⁺ Tetrahedra Using Sequential Reductive Aminations

The use of a highly efficient reductive amination procedure for the postsynthetic end-capping of metal-templated helicate and tetrahedral supramolecular structures bearing terminal aldehyde groups is reported. Metal template formation of a [Fe₂L₃]⁴⁺ dinuclear helicate and two [Fe₄L₆]⁸⁺ tetrahedra (where L is a linear ligand incorporating two bipyridine domains separated by one or two 1,4-(2,5-dimethoxyaryl) linkers and terminated by salicylaldehyde functions is described. Postassembly reaction of each of these “open” di- and tetranuclear species with excess ammonium acetate (as a source of ammonia) and sodium cyanoborohydride results in a remarkable reaction sequence whereby the three aldehyde groups terminating each end of the helicate, or each of the four vertices of the respective tetrahedra, react with ammonia then undergo successive reductive amination to yield corresponding fully tertiary-amine capped cryptate and tetrahedral covalent cages

Silver(I) Coordination Polymers Incorporating Neutral γ-Carbon Bound <i>N</i>,<i>N</i>′-Bis(acetylacetone)alkanediimine Units

Five new silver(I) coordination polymers of types [Ag₂L¹(NO₃)₂]_<i>n</i> (<b>1</b>), [Ag₂L²(NO₃)₂]_<i>n</i> (<b>2</b>), [Ag₂L³(NO₃)₂]_<i>n</i> (<b>3</b>), [Ag₂L⁴(NO₃)₂]_<i>n</i> (<b>4</b>), and [AgL⁵(NO₃)]_<i>n</i> (<b>5</b>) have been synthesized, where L¹–L⁵ are the Schiff base ligands formed from 2:1 condensation of acetylacetone with the symmetrical diamines H₂N(CH₂)_<i>n</i>NH₂, with <i>n</i> = 2 and 6 to give L¹ and L², 1,2-bis(2-aminophenoxy)ethane to give L³, 1,4-bis(2-aminophenoxy)butane to give L⁴, and 1,6-bis(4-aminophenoxy)butane to give L⁵. The single crystal X-ray structures of the Ag(I) complexes <b>1</b>–<b>5</b> have been determined. Both <b>1</b> and <b>2</b> adopt three-dimensional polymeric network structures, while <b>3</b>–<b>5</b> adopt two-dimensional-layered framework structures. In <b>1</b> and <b>2</b>, the terminal O and γ-C atoms of two acacH-imine domains of the same ligand bind to different silver ions, while in each of <b>3</b>–<b>5</b> a γ-C from one or both acacH-imine domains binds to a silver ion, with the remaining coordination sites occupied by bridging monodentate or bidentate nitrato groups and/or a Schiff base ligand oxygen donor

Super Dielectric Materials of Two-Dimensional TiO₂ or Ca₂Nb₃O₁₀ Nanosheet Hybrids with Reduced Graphene Oxide

High dielectric constants (ε_r) were observed in two-dimensional composites obtained from stacking of reduced graphene oxide (RGO) with Ca₂Nb₃O₁₀ and with TiO₂ nanosheets. The relative dielectric permittivity values of the composites were found to be higher than 10⁵, an amazingly high value compared to that of similar GO composites and other common dielectric materials. As a consequence, we considered application of the hybrids as super dielectric materials in high capacitance supercapacitors. The route to high capacitance involves the variation of oxygen vacancies within the surface and in the closest bulk interior of the hybrids. The effective charges generated throughout the metal oxide and carbon–oxygen polar bonding systems within the graphene skeleton appear to highly influence dielectric polarization. Moreover, the replenishment of oxygen vacancies at the RGO and metal oxide interface also contributes to polarizability