Three Novel Zinc(II) Sulfonate−Phosphonates with Tetranuclear or Hexanuclear Cluster Units

Dicyanamide-intertwined assembly of two new Zn complexes based on N2O4-type pro-ligand: Synthesis, crystal networks, spectroscopic insights, and selective nitroaromatic turn-off fluorescence sensing

Two new dicyanamide bridged multinuclear Zn complexes, [Zn₂(L¹)(µ_1,5-dca)₂(µ₁-dca)]_n (1) and [Zn₂(L²)(µ_1,5-dca)₂(µ₁-dca)]_n (2) have been synthesized using N₂O₄-based pro-ligands (H₂L¹ = N,N'-bis(5-bromo-3-methoxysalicylidenimino)-1,3-diaminopropane, H₂L² = N,N'-bis(3-ethoxysalicylidene)-2,2-dimethyl-1,3-propanediamine) and characterized by microanalytical and spectroscopic techniques. Both complexes are stable in solution and solid-state. Thermogravimetric analysis (TGA) findings showed that complexes are stable at room temperature. Single-crystal X-ray diffraction (SCXRD) has proven that complexes are identical structures where two zinc metal ions are crystallographically independent. The directional properties of dicyanamide co-ligands via µ_1,5 bridging have resulted in different connectivity of zinc metal ions leading to 1D templates. SCXRD revealed some notable non-covalent interactions (π⋯π, C-H····π, and H-bonding) in their solid-state crystal structures. 1-2 have strong fluorescence behaviour over pro-ligands, which may be quenched in the presence of various electron-deficient explosive nitroaromatic compounds (epNACs). Complex 2 fluorescence intensity is sharper than 1; hence the former retained high sensitivity and selectivity for trinitrophenol (TNP). The enhancement of fluorescence mechanism, detection limit (LOD), and the quenching constant (K_SV) have been calculated using the Stern-Volmer equation (SV), where the K_SV value for TNP is found to be 1.542 × 10⁴ M^-1. The solution phase quenching mechanism has been rationalized by (a) electrostatic interactions through charge-transfer complex, (b) photo-induced electron transfer (PET) by the HOMO-LUMO energy gap via DFT, and (c) fluorescence resonance energy transfer (FRET). Finally, complex 2 is applied as a sensor by turn-off fluorescence response to detecting TNP nitroaromatics in the DMF medium.

Syntheses, structures and properties of two one-dimensional coordination polymers constructed by phenol-sulfonate ligands and rare earth metal ions

Two new isomorphic and heterogeneous coordination polymers (CPs), namely {[RE (L) (H2O) 2] · (Hbipy) · H2O} n (RE = Yb(1), Y(2), Na2H2L = 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt, bipy = 2,2′-bipyridine) have been synthesized by hydrothermal methods and structurally characterized by elemental analyses, power X-ray diffraction (PXRD) and single crystal X-ray diffraction. Compounds 1 and 2 feature one-dimensional (1D) wavy ladder-like chain structures, which are further connected by hydrogen bonds from water molecules to result in two-dimensional (2D) layered structures. The 1H-protonated bipy molecules act as uncoordinated cations, leading to valences of zero in compounds 1 and 2. Compounds 1 and 2 emit luminescence at 382 nm and 372 nm in the ultraviolet regions, respectively. The luminescent emissions originate from the typical ligand-centered (n–π* and π–π*) transitions. In addition, compound 1 has characteristic near-infrared emission of ytterbium ion at 964 nm.

A series of trinuclear zinc(ii) complexes with reduced Schiff base ligands: turn-off fluorescent chemosensors with high selectivity for nitroaromatics

A series of trinuclear zinc(ii) complexes have been synthesized and characterized by X-ray crystallography. The ability of the complexes to act as sensors for the detection of nitroaromatics in DMF has been assessed.

Synthesis of phosphonosulfonic acid building blocks as linkers for coordination polymers

Ten benzene based linkers containing sulfonic and phosphonic acids have been synthesized. One lanthanum MOF was isolated and characterized.

Three Zinc(II) Phosphonates: Syntheses, Structures and Sensing of Copper(II) Ions

Three zinc(II) phosphonocarboxylates, [Zn₃ (m-bpc)₂ (OH)]⋅(CH₃ )₂ NH₂ ⋅H₂ O (1), [Zn₂ (m-bpc)(m-Hbpc)(4,4'-bpy)]⋅(CH₃ )₂ NH₂ ⋅H₂ O (2) and [Zn₃ (m-bpc)₂ (4,4'-bpy)(CH₃ )₂ NH]⋅H₂ O (3) (m-H₃ bpc=3-phosphonobenzoic acid, 4,4'-bpy=4,4'-bipyridine), have been solvothermally synthesised to generate unique topologies, as characterised by single-crystal XRD. Compound 1 possesses a diamond topology, which has rarely been found among phosphonate-based metal-organic frameworks. Compound 2 shows a 2D layered structure with pendant m-Hbpc and 4, 4'-bpy ligands, in which the layers feature as a zeolite-like network. Compound 3 has a 3D sandwich pillared-layer framework with an interesting double-helix structure. Only 1 shows an adsorption capacity for CO₂ of 28.5 cm³  g^-1 at 273 K. Luminescence studies revealed that both 1 and 2 could be potential sensors to copper(II) ions.

Structural variation in cation-assisted assembly of high-nuclearity Mn arsonate and phosphonate wheels

The use of arsonate or phosphonate ligands in related reaction systems afforded the K⁺-assisted assembly of high nuclearity {Mn₈} arsonate and {Mn₂₄} phosphonate complexes.

New thorium(iv)-arsonates with a [Th8O13]6+ octanuclear core

Three new octanuclear Th(iv) arsonates, namely [Th(8)(O)(L)(6)(HL)(6)(H(2)O)(12)]·19.5H(2)O (1) (H(3)L = o-HO(3)S-C(6)H(4)-AsO(3)H(2)), [Th(8)(O)(L)(6)(HL)(6)(H(2)O)(10)]·17H(2)O (2) and [Th(8)(O)(L)(6)(HL)(6)(H(2)O)(5)]·0.5H(2)O (3), with o-sulfophenylarsonic acid as the bridging ligand, have been prepared under hydrothermal conditions. Each complex contains [Th(8)O(13)](6+) octanuclear cluster cores composed of two [Th(4)O(6)](4+) units bridged by a μ(2)-oxo anion. The structure of compound features a 0D highly symmetric polynuclear cluster encapsulating the octanuclear core of [Th(8)O(13)](6+) which is further decorated by six L(3-) and six HL(2-) ligands. Compound 2 features one-dimensional chains along the b-axis in which the neighboring clusters similar to are bridged by a pair of sulfophenylarsonate ligands via M-O-S-O-M bridges. Compound 3 with chiral P2(1)2(1)2(1) features two-dimensional cluster layers, in which each cluster connects with four neighbors via four M-O-S-O-M linkages. Compounds 2 and 3 display unusual broad green light emission bands at 523 nm (λ(ex) = 320 nm) and 517 nm (λ(ex) = 312 nm), respectively, which originate from the ligand-to-metal charge transfer (LMCT) transition.

Molecular and polymeric zinc(II) phosphonates: isolation of an octanuclear ellipsoidal ensemble

The reaction of zinc(II) perchlorate with trichloromethyl phosphonic acid at room temperature afforded, upon crystallization, a two-dimensional layered coordination polymer possessing a dinuclear repeat unit, [{Zn2(Cl3CPO3)2(H2O)3}·1.5H2O]n (1). Modification of the above reaction by involving a co-ligand afforded the tetranuclear complex, [{Zn4(η(1)-DMPzH)6(Cl3C-PO3)2}(μ-OH)2(ClO4)2] (2). The molecular structure of 2 reveals that the tetranuclear core is non-planar and consists of three contiguous inorganic rings which include one 8-membered Zn2P2O4 ring and two six-membered Zn2PO3 rings. Replacement of Zn(ClO4)2·6H2O with ZnCl2 under the same reaction conditions that afforded 2 allowed the formation of the dinuclear complex [{(ZnCl)2(η(2)-Pz)2(Cl3CPO3)}(Et3NH)2] (3). 3 possesses a bicyclic core containing a seven-membered Zn2N2O2P ring. In 3, the phosphoryl oxygen atom (P=O) is involved in a bifurcated hydrogen bonding interaction with the triethylammonium cation. The reaction of ZnCl2 and 2,3,5,6-(Me)4C6HCH2PO3H2 afforded the octanuclear complex [Zn8(Cl)6{2,3,5,6-(Me)4C6HCH2PO3}6(Et3N)2](Et3NH)2]·2n-hexane·3H2O (4). The core of 4 is ellipsoid-shaped with the end-end polar distance (C-C) being ~20 Å.

Di-, tri- and tetranuclear molecular vanadium phosphonates: a chloride encapsulated tetranuclear bowl

Synthesis and characterization of three dinuclear, two dinuclear and one tetranuclear vanadium phosphonates is being reported. These include a chloride encapsulated tetranuclear bowl-shaped complex.