Alkali Metal Directed Assembly of Heterometallic V^v/M (M = Na, K, Cs) Coordination Polymers: Structures, Topological Analysis, and Oxidation Catalytic Properties

The reactions of [VO­(acac)₂] with bis­(salicylaldehyde)-oxaloyldihydrazone (H₄L) and an alkali metal carbonate M₂CO₃ (M = K, Na, Cs), in EtOH/H₂O medium upon reflux, resulted in the generation of three new heterometallic V^V/M materials, namely the 1D [(VO₂)₂(μ₄-L)­{Na₂(μ-H₂O)₂(H₂O)₂}]_<i>n</i> (<b>1</b>), 2D [{V­(μ-O)₂}₂(μ₄-L)­{K₂(μ-H₂O)₂(H₂O)₂}]_<i>n</i> (<b>2</b>), and 3D [{V­(μ-O)­(μ₃-O)}₂(μ₈-L)­{Cs₂(μ-H₂O)₂(H₂O)₂}]_<i>n</i> (<b>3</b>) coordination polymers. They were isolated as air-stable solids and fully characterized by IR, UV–vis, ¹H, and ⁵¹V NMR spectroscopy, ESI–MS(±), elemental, thermal, and single-crystal X-ray diffraction analyses, the latter showing that <b>1</b>–<b>3</b> are constructed from the resembling [(VO₂)₂(μ_4/8-L)]^2– blocks assembled by the differently bound aqua-metal [M₂(μ-H₂O)₂(H₂O)₂]²⁺ moieties (M = Na, K, Cs). The main distinctive features of <b>1</b>–<b>3</b> arise from the different coordination numbers of Na (5), K (7), and Cs (9) atoms, thus increasing the complexity of the resulting networks from the ladder-like 1D chains in <b>1</b> to double 2D layers in <b>2</b>, and layer-pillared 3D framework in <b>3</b>. The topological analysis of <b>2</b> disclosed a uninodal 4-connected underlying net with a rare <b>kgm</b> [Shubnikov plane net (3.6.3.6)/kagome pattern] topology, while <b>3</b> features a trinodal 4,7,8-connected underlying net with an unprecedented topology. Compounds <b>1</b>–<b>3</b> also show solubility in water (<i>S</i>_25 °C ≈ 4–7 mg mL^–1) and were applied as efficient precatalysts for the homogeneous oxidation of cyclohexane by aqueous H₂O₂, under mild conditions (50 °C) in MeCN/H₂O medium and in the presence of an acid promoter. Total yields (based on substrate) of cyclohexanol and cyclohexanone up to 36% and turnover numbers (TONs) up to 5700 were achieved

Alkali Metal Directed Assembly of Heterometallic V^v/M (M = Na, K, Cs) Coordination Polymers: Structures, Topological Analysis, and Oxidation Catalytic Properties

The reactions of [VO­(acac)₂] with bis­(salicylaldehyde)-oxaloyldihydrazone (H₄L) and an alkali metal carbonate M₂CO₃ (M = K, Na, Cs), in EtOH/H₂O medium upon reflux, resulted in the generation of three new heterometallic V^V/M materials, namely the 1D [(VO₂)₂(μ₄-L)­{Na₂(μ-H₂O)₂(H₂O)₂}]_<i>n</i> (<b>1</b>), 2D [{V­(μ-O)₂}₂(μ₄-L)­{K₂(μ-H₂O)₂(H₂O)₂}]_<i>n</i> (<b>2</b>), and 3D [{V­(μ-O)­(μ₃-O)}₂(μ₈-L)­{Cs₂(μ-H₂O)₂(H₂O)₂}]_<i>n</i> (<b>3</b>) coordination polymers. They were isolated as air-stable solids and fully characterized by IR, UV–vis, ¹H, and ⁵¹V NMR spectroscopy, ESI–MS(±), elemental, thermal, and single-crystal X-ray diffraction analyses, the latter showing that <b>1</b>–<b>3</b> are constructed from the resembling [(VO₂)₂(μ_4/8-L)]^2– blocks assembled by the differently bound aqua-metal [M₂(μ-H₂O)₂(H₂O)₂]²⁺ moieties (M = Na, K, Cs). The main distinctive features of <b>1</b>–<b>3</b> arise from the different coordination numbers of Na (5), K (7), and Cs (9) atoms, thus increasing the complexity of the resulting networks from the ladder-like 1D chains in <b>1</b> to double 2D layers in <b>2</b>, and layer-pillared 3D framework in <b>3</b>. The topological analysis of <b>2</b> disclosed a uninodal 4-connected underlying net with a rare <b>kgm</b> [Shubnikov plane net (3.6.3.6)/kagome pattern] topology, while <b>3</b> features a trinodal 4,7,8-connected underlying net with an unprecedented topology. Compounds <b>1</b>–<b>3</b> also show solubility in water (<i>S</i>_25 °C ≈ 4–7 mg mL^–1) and were applied as efficient precatalysts for the homogeneous oxidation of cyclohexane by aqueous H₂O₂, under mild conditions (50 °C) in MeCN/H₂O medium and in the presence of an acid promoter. Total yields (based on substrate) of cyclohexanol and cyclohexanone up to 36% and turnover numbers (TONs) up to 5700 were achieved

Differentially Selective Chemosensor with Fluorescence <i>Off–On</i> Responses on Cu²⁺ and Zn²⁺ Ions in Aqueous Media and Applications in Pyrophosphate Sensing, Live Cell Imaging, and Cytotoxicity

A new benzoyl hydrazone based chemosensor <b>R</b> is synthesized by Schiff base condensation of 2,6-diformyl-4-methylphenol and phenyl carbohydrazide and acts as a highly selective fluorescence sensor for Cu²⁺ and Zn²⁺ ions in aqueous media. The reaction of <b>R</b> with CuCl₂ or ZnCl₂ forms the corresponding dimeric dicopper­(II) [Cu₂(R)­(CH₃O)­(NO₃)]₂(CH₃O)₂ (<b>R-Cu</b>^<b>2+</b>) and dizinc­(II) [Zn₂(R)₂]­(NO₃)₂ (<b>R-Zn</b>^<b>2+</b>) complexes, which are characterized, as <b>R</b>, by conventional techniques including single-crystal X-ray analysis. Electronic absorption and fluorescence titration studies of <b>R</b> with different metal cations in a CH₃CN/0.02 M HEPES buffer medium (pH = 7.3) show a highly selective binding affinity only toward Cu²⁺and Zn²⁺ ions even in the presence of other commonly coexisting ions such as Na⁺, K⁺, Mg²⁺, Ca²⁺, Mn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cd²⁺, and Hg²⁺. Quantification of the fluorescence titration analysis shows that the chemosensor <b>R</b> can indicate the presence of Cu²⁺and Zn²⁺ even at very low concentrations of 17.3 and 16.5 ppb, respectively. <b>R-Zn</b>^<b>2+</b> acts as a selective metal-based fluorescent sensor for inorganic pyrophosphate ion (PPi) even in the presence of other common anions such as F^–, Cl^–, Br^–, I^–, CH₃COO^–, CO₃^2–, HCO₃^–, N₃^–, SO₄^2–, PPi, AMP, ADP, and ATP in an aqueous medium. The propensity of <b>R</b> as a bioimaging fluorescent probe to detect Cu²⁺ and Zn²⁺ ions in human cervical HeLa cancer cell lines and their cytotoxicity against human cervical (HeLa), breast cancer (MCF7), and noncancer breast epithelial (MCF10a) cells have also been investigated. <b>R-Cu</b>^<b>2+</b> shows better cytotoxicity and sensitivity toward cancer cells over noncancer cells than <b>R</b> and <b>R-Zn</b>^<b>2+</b> under identical conditions, with the appearance of apoptotic bodies

Differentially Selective Chemosensor with Fluorescence <i>Off–On</i> Responses on Cu²⁺ and Zn²⁺ Ions in Aqueous Media and Applications in Pyrophosphate Sensing, Live Cell Imaging, and Cytotoxicity

A new benzoyl hydrazone based chemosensor <b>R</b> is synthesized by Schiff base condensation of 2,6-diformyl-4-methylphenol and phenyl carbohydrazide and acts as a highly selective fluorescence sensor for Cu²⁺ and Zn²⁺ ions in aqueous media. The reaction of <b>R</b> with CuCl₂ or ZnCl₂ forms the corresponding dimeric dicopper­(II) [Cu₂(R)­(CH₃O)­(NO₃)]₂(CH₃O)₂ (<b>R-Cu</b>^<b>2+</b>) and dizinc­(II) [Zn₂(R)₂]­(NO₃)₂ (<b>R-Zn</b>^<b>2+</b>) complexes, which are characterized, as <b>R</b>, by conventional techniques including single-crystal X-ray analysis. Electronic absorption and fluorescence titration studies of <b>R</b> with different metal cations in a CH₃CN/0.02 M HEPES buffer medium (pH = 7.3) show a highly selective binding affinity only toward Cu²⁺and Zn²⁺ ions even in the presence of other commonly coexisting ions such as Na⁺, K⁺, Mg²⁺, Ca²⁺, Mn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cd²⁺, and Hg²⁺. Quantification of the fluorescence titration analysis shows that the chemosensor <b>R</b> can indicate the presence of Cu²⁺and Zn²⁺ even at very low concentrations of 17.3 and 16.5 ppb, respectively. <b>R-Zn</b>^<b>2+</b> acts as a selective metal-based fluorescent sensor for inorganic pyrophosphate ion (PPi) even in the presence of other common anions such as F^–, Cl^–, Br^–, I^–, CH₃COO^–, CO₃^2–, HCO₃^–, N₃^–, SO₄^2–, PPi, AMP, ADP, and ATP in an aqueous medium. The propensity of <b>R</b> as a bioimaging fluorescent probe to detect Cu²⁺ and Zn²⁺ ions in human cervical HeLa cancer cell lines and their cytotoxicity against human cervical (HeLa), breast cancer (MCF7), and noncancer breast epithelial (MCF10a) cells have also been investigated. <b>R-Cu</b>^<b>2+</b> shows better cytotoxicity and sensitivity toward cancer cells over noncancer cells than <b>R</b> and <b>R-Zn</b>^<b>2+</b> under identical conditions, with the appearance of apoptotic bodies

A Hexanuclear Mixed-Valence Oxovanadium(IV,V) Complex as a Highly Efficient Alkane Oxidation Catalyst

The new hexanuclear mixed-valence vanadium complex [V₃O₃(OEt)­(ashz)₂(μ-OEt)]₂ (<b>1</b>) with an N,O-donor ligand is reported. It acts as a highly efficient catalyst toward alkane oxidations by aqueous H₂O₂. Remarkably, high turnover numbers up to 25000 with product yields of up to 27% (based on alkane) stand for one of the most active systems for such reactions

Silver(I) 1,3,5-Triaza-7-phosphaadamantane Coordination Polymers Driven by Substituted Glutarate and Malonate Building Blocks: Self-Assembly Synthesis, Structural Features, and Antimicrobial Properties

Three new bioactive silver­(I) coordination polymers formulated as [Ag₂(μ₂-PTA)­(μ₃-PTA)­(μ₂-pga)­(H₂O)]_<i>n</i>·6H₂O (<b>1</b>), [Ag₂(μ₂-PTA)­(μ₃-PTA)<i>(</i>Hpmal)₂]<i><i>_n</i></i>·2H₂O (<b>2</b>), and [Ag­(μ₃-PTA) (Hdmga)]<i>_n</i> (<b>3</b>) were self-assembled from Ag₂O, 1,3,5-triaza-7-phosphaadamantane (PTA), and a substituted dicarboxylic acid (3-phenylglutaric acid (H₂pga), phenylmalonic acid (H₂pmal), or 3,3-dimethylglutaric acid (H₂dmga)) as an ancillary ligand. Compounds <b>1</b>–<b>3</b> were fully characterized by IR and NMR spectroscopy, ESI-MS(±), elemental analysis, and single-crystal X-ray diffraction, revealing that their architectural and topological diversity is governed by structural modulation of a dicarboxylate building block. The structures vary from a 1D cyclic chain with the SP 1-periodic net (4,4)­(0,2) topology in <b>2</b> to distinct 2D metal–organic layers with the <b>cem-d</b> and <b>hcb</b> topologies in <b>1</b> and <b>3</b>, respectively. In addition, compounds <b>1</b>–<b>3</b> exhibit a notable antimicrobial efficiency against a panel of common Gram-negative (E. coli and P. aeruginosa) and Gram-positive (S. aureus) bacteria and yeast (C. albicans). The best normalized minimum inhibitory concentrations (normalized MIC) of 11–23 nmol mL^–1 (for bacterial strains) or 68 nmol mL^–1 (for a yeast strain) are shown by compound <b>2</b>, and the eventual structure–bioactivity correlations are discussed

Bioactive Silver–Organic Networks Assembled from 1,3,5-Triaza-7-phosphaadamantane and Flexible Cyclohexanecarboxylate Blocks

Three novel bioactive silver–organic networks, namely, the 2D polymer [Ag­(μ₃-PTA)­(chc)]_<i>n</i>·<i>n</i>(Hchc)·2<i>n</i>H₂O (<b>1</b>), the 3D bioMOF [Ag₂(μ₃-PTA)₂(μ₂-chdc)]_<i>n</i>·5nH₂O (<b>2</b>), and the 2D polymer [Ag₂(μ₂-PTA)₂(μ₄-H₂chtc)]_<i>n</i>·6<i>n</i>H₂O (<b>3</b>), were constructed from 1,3,5-triaza-7-phosphaadamantane (PTA) and various flexible cyclohexanecarboxylic acids as building blocks {cyclohexanecarboxylic (Hchc), 1,4-cyclohexanedicarboxylic (H₂chdc), and 1,2,4,5-cyclohexanetetracarboxylic (H₄chtc) acid, respectively}. The obtained products <b>1</b>–<b>3</b> were fully characterized by IR and NMR spectroscopy, ESI-MS(±) spectrometry, elemental and thermogravimetric (TGA) analyses, and single-crystal and powder X-ray diffraction. Their structural diversity originates from distinct coordination modes of cyclohexanecarboxylate moieties as well as from the presence of unconventional <i>N,N,P</i>-tridentate or <i>N,P</i>-bidentate PTA spacers. Topological classification of underlying metal–organic networks was performed, disclosing the <b>hcb</b>, <b>4,4L28</b>, and a rare <b>fsc-3,4-<i>Pbcn</i>-3</b> topology in <b>1</b>, <b>2</b>, and <b>3</b>, respectively. Moreover, combination of aqueous solubility (<i>S</i>_25°C ≈ 4–6 mg mL^–1), air stability, and appropriate coordination environments around silver centers favors a release of bioactive Ag⁺ ions by <b>1</b>–<b>3</b>, which thus act as potent antibacterial and antifungal agents against Gram-positive (<i>S. aureus</i>) and Gram-negative (<i>E. coli</i> and <i>P. aeruginosa</i>) bacteria as well as a yeast (<i>C. albicans</i>). The best normalized minimum inhibitory concentrations (normalized MIC) of 10–18 (for bacterial strains) or 57 nmol mL^–1 (for a yeast strain) were achieved. Detailed ESI-MS studies were performed, confirming the relative stability of <b>1</b>–<b>3</b> in solution and giving additional insight on the self-assembly formation of polycarboxylate Ag–PTA derivatives and their crystal growth process

1,3-Dipolar Cycloaddition of Nitrones to Gold(III)-Bound Isocyanides

Treatment of gold­(III)-isocyanides [AuCl₃(CNR¹)] (R¹ = Xyl <b>1</b>, Cy <b>2</b>, Bu^<i>t</i> <b>3</b>) with an equimolar amount of 5,5-dimethyl-1-pyrroline-<i>N</i>-oxide (<b>4</b>) in CH₂Cl₂ at −74 °C leads to the generation of the heterocyclic aminocarbene species [AuCl₃{C­(ON^<i>a</i>CMe₂CH₂CH₂C^<i>b</i>H)N^<i>e</i>R¹}­(N^<i>a</i>–C^<i>b</i>)­(C^<i>b</i>–N^<i>e</i>)] <b>8</b> (for R¹ = Bu^<i>t</i>) or gold­(III) complexes <i>cis</i>-[AuCl₂{N^<i>a</i>(CMe₂CH₂CH₂C^<i>b</i>N^<i>e</i>R¹)­C^<i>d</i>O}­(N^<i>a</i>C^<i>b</i>)­(N^<i>e</i>–C^<i>d</i>)] <b>9</b> and <b>10</b> (for R¹ = Xyl and Cy) in good isolated yields (75–87%). DFT calculations show that deprotonation of the endocyclic CH group in the carbene ligand leads to spontaneous N–O bond cleavage, and acidity of this group is a factor controlling the different chemical behavior of <b>1</b>–<b>3</b> depending on the nature of substituent R¹. The reaction of equimolar amounts of the aldonitrone <i>p</i>-TolCHN⁺(Me)­O^– (<b>5</b>) or the ketonitrones Ph₂CN⁺(R²)­O^– (R² = Ph <b>6</b>, CH₂Ph <b>7</b>) with <b>1</b>–<b>3</b> in CD₂Cl₂ at −70 °C in air (or under N₂) revealed the formation of the carbene complexes [AuCl₃{C­(ONMeC^<i>a</i>H-<i>p</i>-Tol)N^<i>b</i>R¹}­(C^<i>a</i>–N^<i>b</i>)] (R¹ = Cy <b>11</b>, Xyl <b>12</b>, Bu^<i>t</i> <b>13</b>), [AuCl₃{C­(ONPhC^<i>a</i>Ph₂)N^<i>b</i>R¹}­(C^<i>a</i>–N^<i>b</i>)] (R¹ = Cy <b>14</b>, Bu^<i>t</i> <b>15</b>), or [AuCl₃{C­(ON­(CH₂Ph)­C^<i>a</i>Ph₂)N^<i>b</i>R¹}­(C^<i>a</i>–N^<i>b</i>)] (R¹ = Cy <b>16</b>, Xyl <b>17</b>), as studied by ¹H NMR. The reaction of <b>6</b> with <b>1</b> and of <b>7</b> with <b>3</b> did not furnish carbene products. Compounds <b>8</b>–<b>10</b> were characterized by ESI-MS, IR, 1D (¹H, ¹³C­{H}) and 2D (¹H,¹H–COSY, ¹H,¹³C-HSQC, ¹H,¹³C-HMBC) NMR spectroscopic techniques, and, only for <b>8</b>, elemental analyses (C, H, N), while compounds <b>11</b>–<b>17</b> were characterized by 1D (¹H, ¹³C­{H}) and 2D (¹H,¹³C-HSQC) NMR. Structures of compounds <b>8</b>, <b>9</b>, and <b>13</b> were additionally established by single-crystal X-ray diffraction

New Coordination Polymers and Porous Supramolecular Metal Organic Network Based on the Trinuclear Triangular Secondary Building Unit [Cu₃(μ₃‑OH)(μ-pz)₃]²⁺ and 4,4′-Bypiridine. 1°

The trinuclear triangular Cu^II complex [Cu₃(μ₃-OH)­(μ-pz)₃(HCOO)₂(Hpz)₂] (Hpz = pyrazole) reacts with 4,4′-bipyridine (bpy) yielding a two-dimensional (2D) waved sheets, two three-dimensional (3D) coordination polymers (CPs), as well as a hexanuclear Cu^II cluster, depending on the reagent ratios and reaction conditions. Single crystal X-ray diffraction (XRD) determinations point out that, while CPs crystal structures are not porous, the hexanuclear Cu^II clusters are packed in the solid state generating a stable porous 3D supramolecular network, where two kinds of perpendicular, hydrophobic channels (ca. 4.83 × 5.86 Ų and 4.99 × 4.79 Ų, corresponding to the 24.7% of the total crystal volume) are present. In the “as-synthesized” compound, channels of one kind are empty, while the other ones are occupied by guest bpy molecules which can be removed by soaking the crystals in suitable solvents (benzene, toluene, <i>c</i>-hexane) maintaining intact the crystal skeleton. Moreover, two of the above complexes act as catalysts (or catalyst precursors) in the peroxidative oxidation of cyclohexane

New Coordination Polymers and Porous Supramolecular Metal Organic Network Based on the Trinuclear Triangular Secondary Building Unit [Cu₃(μ₃‑OH)(μ-pz)₃]²⁺ and 4,4′-Bypiridine. 1°

The trinuclear triangular Cu^II complex [Cu₃(μ₃-OH)­(μ-pz)₃(HCOO)₂(Hpz)₂] (Hpz = pyrazole) reacts with 4,4′-bipyridine (bpy) yielding a two-dimensional (2D) waved sheets, two three-dimensional (3D) coordination polymers (CPs), as well as a hexanuclear Cu^II cluster, depending on the reagent ratios and reaction conditions. Single crystal X-ray diffraction (XRD) determinations point out that, while CPs crystal structures are not porous, the hexanuclear Cu^II clusters are packed in the solid state generating a stable porous 3D supramolecular network, where two kinds of perpendicular, hydrophobic channels (ca. 4.83 × 5.86 Ų and 4.99 × 4.79 Ų, corresponding to the 24.7% of the total crystal volume) are present. In the “as-synthesized” compound, channels of one kind are empty, while the other ones are occupied by guest bpy molecules which can be removed by soaking the crystals in suitable solvents (benzene, toluene, <i>c</i>-hexane) maintaining intact the crystal skeleton. Moreover, two of the above complexes act as catalysts (or catalyst precursors) in the peroxidative oxidation of cyclohexane