Novel 2,2′-bipyridine-modified calix[4]arenes: ratiometric fluorescent chemosensors for Zn ion

Two calix[4]arene derivatives with modified bipyridine as binding sites have been designed and synthesized. Compounds 1 and 2 are the first 2,2′-bipyridine-modified calix[4]arene-based sensors that can detect Zn²⁺ selectively with respect to ratiometric fluorescent changes and red shift. A binuclear complex structure has been demonstrated in the binding modes of 1-Zn²⁺ and 2-Zn²⁺ complexes.     

Asymmetric Bipyridine‐Terpyridine‐Copper(II) Complexes: An Approach for New Supramolecular Architectures

On the way towards novel supramolecular assemblies and polymers, several copper(II) complexes consisting of one terpyridine as well as one bipyridine ligand were synthesized in a one‐step reaction. The compounds were characterized by UV/VIS spectroscopy and MALDI‐TOF mass spectrometry. Single crystals were obtained and their structures were determined by X‐ray analyses.     

Convenient synthesis of tridentate 2,6-di(pyrazol-1-yl)-4-carboxypyridine and tetradentate 6,6′-di(pyrazol-1-yl)-4,4′-dicarboxy-2,2′-bipyridine ligands

Citrazinic acid is used as a convenient starting material for both tridentate 2,6-di(pyrazol-1-yl)-pyridine and tetradentate 6,6′-di(pyrazol-1-yl)-2,2′-bipyridine ligands containing carboxylic groups useful for further anchoring of sensitizer on TiO₂ for dye-sensitized solar cells (DSCs). Using 2,6-dichloro-4-carboxypyridine, the synthesis of the terdentate ligands was improved compared to previously used 2,6-dibromo-4-carboxypyridine or 2,6-dichloro-4-ethylcarboxylate pyridine. Controlling the reaction conditions, it is possible to efficiently obtain the monosubstituted 2-chloro-6-pyrazol-1-yl-4-carboxypyridine, a key intermediate for the preparation of tetradentate 6,6′-di(pyrazol-1-yl)-4,4′-dicarboxy-2,2′-bipyridine ligand.     

The Evolution Aspect in the Crystallization Process of [5,5′‐(HCF2CF2CH2OCH2)2‐2,2′‐bpy]MX2 (M = Pt,Pd; X = I,Br): Role of the Intramolecular CF2─H…X(─M) Hydrogen Bonds

The general species (2,2′‐bpy)MX₂ (M = Pd, Pt; X = Br, I) in a crystallization process results in an isomorphous convergence in P2₁/c. Yet, with polyfluorinated side chains, the general [5,5′‐(HCF₂CF₂CH₂OCH₂)₂‐2,2′‐bpy]MX₂ species proceeds to crystallize the isomorphous structures of 5 (M = Pt; X = I) and 6 (M = Pd; X = I) in P2₁/c only; structure 7 (M = Pt; X = Br) crystallizes in P2₁/c but is not isomorphous with 5 and 6 , and structure 8 (M = Pd; X = Br) forms differently in P–1. The causes making the system nonlinear are (1) the intramolecular CF₂─H^…X(─M) hydrogen bonds found in 5–7 but not in 8, and (2) in response to the transition from I to Br, bifurcated [C─H^…]₂ F ─C hydrogen bonds that are formed in 5 and 6 and bifurcated C─ H [^…F─C]₂ hydrogen bonds in 7 . Additionally, the intramolecular CF₂─H^…X(─M) hydrogen bonding from compounds 5–7 could be affirmed by the IR studies.     

Design of a zinc(II) ion specific fluorescence sensor

We report the synthesis of {[3-(biscarboxymethylamino)-2-methoxy-5-methylphenyl]carboxymethylamino}acetic acid, which functions as a Zn²⁺ selective fluorescence probe (sensor).     

Mixed‐Ligand Complexes of Zinc(II) with α‐Hydroxycarboxylates and Aromatic N‐N Donor Ligands: Synthesis,Crystal Structures and Effect of Weak Interactions on their Crystal Packing

Several new two‐ligand complexes of zinc(II) with the aromatic N, N‐donor ligands 2, 2′‐bipyridine or 1, 10‐phenanthroline and one of three different α‐hydroxycarboxylates (HL′) derived of the α‐hydroxycarboxylic acids (H₂L′) (2‐methyllactic, H₂mL; mandelic, H₂M or benzilic, H₂B) were prepared. The compounds of formula [Zn(HL′)₂(NN)]·nH₂O (HL′ = HM, HB) were isolated as white powders and characterized by elemental analysis, IR spectroscopy and thermogravimetric analysis. The complexes of general formula [Zn(HL′)(NN)₂](HL′)·nH₂O (HL′ = HmL, HM) and [Zn(HB)₂(NN)₂], were obtained as single crystals and were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis and X‐ray diffractometry. In all cases, the zinc atom is in a distorted octahedral environment. In [Zn(HL′)(NN)₂](HL′)·nH₂O the α‐hydroxycarboxylato ligands behave as bidentate chelating monoanion and an α‐hydroxycarboxylate as counterion is also present. In [Zn(HB)₂(NN)₂], the monoanionic benzilato ligand behaves as monodentate through one oxygen atom of the carboxylate function. The effect of the classical and no‐classical hydrogen bonding and of the π‐π and C‐H…π interactions in the 3D supramolecular arrangement of these molecular complexes is analyzed.     

Synthesis of (E)-diethyl 6,6′-(diazene-1,2-diyl)bis(5-cyano-2-methyl-4-phenylnicotinates), a new type of 2,2′-azopyridine dyes

An unexpected, but simple method for the efficient synthesis of new 2.2′-azopyridine dyes, such as (E)-diethyl 6,6′-(diazene-1,2-diyl)bis(5-cyano-2-methyl-4-phenylnicotinates) (2, 4, 6, 8, 10, and 12), based on the treatment of ethyl 6-amino-5-cyano-2-methyl-4-arylnicotinates (1, 3, 5, 7, 9, and 11) with NBS/benzoyl peroxide, is described. The X-ray diffraction analysis and the UV-vis absorption spectra of dye 2 are reported and discussed.     

Synthesis, characterization, and electrochemistry of tetracarbonyl(6-ferrocenyl-2,2′-bipyridine)tungsten(0)

6-Ferrocenyl-2,2′-bipyridine (fcbpy) was prepared by the reaction of lithiated ferrocene with bipyridine and employed as a bidentate ligand for the formation of tetracarbonyl(6-ferrocenyl-2,2′-bipyridine)tungsten(0). The labile complex pentacarbonyl[η²-bis(trimethylsilyl)ethyne]tungsten(0) reacts with fcbpy in CH₂Cl₂ to yield the disubstitution product, W(CO)₄(fcbpy), which was isolated as analytically pure substance and characterized by elemental analysis, IR, UV-Vis, MS, ¹H and ¹³C NMR spectroscopies. Electrochemistry of the fcbpy molecule and its complex W(CO)₄(fcbpy) was studied by cyclic voltammetry and controlled potential electrolysis combined with UV-Vis spectrometer. In the cyclic voltammogram of both the fcbyp molecule and its complex, an irreversible reduction and a reversible oxidation are assigned to the bipyridine and ferrocene moieties, respectively. The W(CO)₄(fcbpy) complex exhibits additionally two irreversible oxidations due to the tungsten centered electron transfer reactions.     

(R)-6,6′-Bis(trifluoromethanesulfonyl)-2,2′-dihydroxy-1,1′-binaphthyl: a new ligand for asymmetric synthesis

The new (R)-6,6′-bis(trifluoromethanesulfonyl)-2,2′-dihydroxy-1,1′-binaphthyl (1) has been synthesized and proved to generate highly active zirconium-based catalysts for asymmetric Mannich-type reactions.     

Diastereoselective Ion Pairing of TRISPHAT Anions and Tris(4,4′-dimethyl-2,2′-bipyridine)iron(II)

Two configurationally stable, chiral anions (TRISPHAT, 1 ) behave as efficient hosts that control the configuration of a configurationally labile iron(II ) complex as the guest with high diastereoselectivity (>96 % de) upon ion pairing. The diastereoselectivity increases with decreasing solvent polarity.     

Hydrogen‐Bond‐Based Magnetic Exchange Between μ‐Diethylnicotinamide(aqua)bis(X‐salicylato)copper(II) Polymeric Chains

Polymeric salicylatocopper(II) complexes of unusual composition [C u(X‐ sal)₂( μ‐denia)(H₂O)]_n [denia = diethylnicotinamide, and X‐sal = 5‐methylsalicylate ( 1 ), 3‐methylsalicylate ( 2 ), 4‐methoxysalicylate ( 3 ), 3,5‐dichlorosalicylate ( 4 ) and 3,5‐dibromosalicylate ( 5 )] were synthesized and characterized. Magnetic measurements were performed in the temperature range 1.8–300 K. The structural unit of all complexes consists of a Cu^II atom, which is monodentately coordinated by the pair of X‐salicylate anions in trans positions. Water and the diethylnicotinamide ligand occupy the other two basal plane positions of the tetragonal pyramid. The axial positions are occupied by a diethylnicotinamide oxygen atom of neighboring structural units, thus forming a spiral polymeric structure parallel to b axis. Magnetic measurements showed that all complexes 1 – 5 exhibit a susceptibility maximum at about 6–8 K. The obtained data fit to Bleaney–Bowers equation gave singlet‐triplet energy gaps 2J = –8.60 cm^–1 for 1 , 2J = –6.57 cm^–1 for 2 , 2J = –8.57 cm^–1 for 3 , 2J = –6.82 cm^–1 for 4 , and 2J = –6.45 cm^–1 for 5 . The supramolecular structure based on hydrogen bonds [described by supramolecular synthons R₂²(10) and R₂²(12)] is the pathway for antiferromagnetic interactions of the magnetically coupled pairs of copper atoms of neighboring chains within the 2D supramolecular layers. The results of the magnetic measurements suggest involvement of the COO groups in the magnetic interaction pathway for all five complexes.     

N^N^C platinum(II) and palladium(II) cyclometallates of 6,6′-diphenyl-2,2′-bipyridine, L: Crystal and molecular structure of [Pd(L-H)Cl]

Reaction of K₂[PtCl₄] or Na₂[PdCl₄] with 6,6′-diphenyl-2,2′-bipyridine, L, gives the cyclometallated species [Pt(L-H)Cl], 1, and [Pd(L-H)Cl], 2, respectively, where L-H is a terdentate N^N^C anionic ligand originated by direct activation of a C(sp²)-H bond. The crystal structure of 2 has been solved by X-ray diffraction and compared to that of the analogous complex [Pd(L′-H)Cl] L′ = 6-phenyl-2,2′-bipyridine. The second phenyl ring in 2 entails a considerable distortion of the coordination around the metal. A similar distortion is also to be expected in the analogous compound 1, due to the almost equal covalent radii of palladium(II) and platinum(II).From the complexes 1 and 2 the chloride can be displaced with AgBF₄ and substituted by CO or PPh₃ to give the corresponding cationic species. By reaction of 1 with Na[BH₄] substitution of H⁻ for Cl⁻ can be achieved: the rare hydrido complex [Pt(L-H)H], stabilized only by nitrogen ligands, was isolated in the solid state and fully characterized in solution. It is noteworthy that in the case of the 6-phenyl-2,2′-bipyridine the analogous terminal hydride [Pd(L′-H)H] is unstable. In platinum chemistry the reaction of 6-substituted 2,2′-bipyridines is known to give either N^N^C or N′^C(3) rollover cyclometallation, depending on the nature of the metal precursor. In the case of 6,6′-Ph₂-2,2′-bipy cyclometallation was also shown to undergo multiple C-H activation giving the C^N^C pincer complex [Pt(L-2H)(DMSO)]. The latter species can be related to complex 1: indeed its reaction with HCl produces complex 1 and [Pt(L-H)(DMSO)Cl], a rollover species with a pendant phenyl substituent.     

Synthesis,crystal structure and thermal analysis of supramolecular architectures of copper(II)(2,2′-biimidazole) complexes using dicarboxylate as a coligand

Two new copper(II) complexes {[Cu(H₂biim)(H₂O)(suc)](H₂O)}_n (1) and {[Cu(H₂biim)₂(H₂O)][Cu(H₂biim)₂(glut)](glutH)(NO₃) · 2.5H₂O}_n (2) (H₂biim, 2,2′-biimidazole; suc, succinate dianion; glut, glutarate dianion) have been synthesized and characterized by single crystal X-ray diffraction study and thermal analysis. Complex 1 comprises of 1D zigzag coordination polymers, elongated along the crystallographic b-axis, connected through H-bonding and face-to-face π–π interactions to form a robust 3D network. Whereas complex 2 is built up of bischelated [Cu(II)(H₂biim)₂]²⁺ units, glutarate and nitrate anions and water molecules, held together through an extensive H-bonded system. The resulting 3D supramolecular architecture defines channels which are filled by lattice water molecules and disordered nitrate anions.     

A novel dinuclear double-stranded helical complexes of bis(terdentate) N4O2 donor ligand with silver(I) and zinc(II) d metal ions

Reaction of the hexadentate N₄O₂-donor ligand 6,6′-bis(3-hydrazonobutan-2-one)-2,2′-bipyridine (L) with Ag^(I) and Zn^(II) affords a dinuclear double stranded helicate species [Ag₂L₂]²⁺ (1a) and [Zn₂L₂]²⁺ (1b), in which partitioning of the ligand into two bis-tridentate pyridyl-ketoimine chelating units allow each ligand to bridge both metal centres. X-ray crystallography, ESI-MS and UV–Vis spectrophotometric titration experiments reveal that the complex (1a) retains its solid-state structure in solution. The crystal structure of (1a) provides the first example of dinuclear silver(I) complex in which both of the metal centres can be approximated as a seven coordinate distorted mono-capped trigonal prism in which the Ag?Ag close contact of 3.034(4) Å is taken into account and forms the cap. The counter-ions do not interact with metal centres but hydrogen bond to N–H protons of the hydrazonic arms from the separate strands. The adjacent helical units are cross-linked together via NH?O_keto hydrogen bonding to maintain the supramolecular structure.     

A pyrazolyl-terminated 2,2′:6′,2″-terpyridine ligand: Iron(II), ruthenium(II) and palladium(II) complexes of 4′-(3,5-dimethylpyrazol-1-yl)-2,2′:6′,2″-terpyridine

The preparation of 4′-(3,5-dimethylpyrazol-1-yl)-2,2′:6′,2″-terpyridine (2) under acidic conditions results in the formation of the salts [H₂2][MeOSO₃]₂ and [H₂2][EtOSO₃]₂, treatment of which with base leads to neutral 2. The structure of [H₂2][EtOSO₃]₂ · H₂O has been established by single crystal X-ray diffraction. The complexes [Fe(2)₂][PF₆]₂ and [Ru(2)₂][PF₆]₂ have been prepared and characterized, and the single crystal structure determination of [Ru(2)₂][PF₆]₂ is reported; [Fe(2)₂][PF₆]₂ is isostructural with [Ru(2)₂][PF₆]₂. Treatment of [Fe(2)₂]²⁺ with PdCl₂ produces [Pd(2)Cl]⁺, isolated and structurally characterized as the hexafluoridophosphate salt, illustrating that metal exchange within the tpy-binding domain occurs in preference to palladium(II) coordination by the N-donor atom of the pendant 3,5-dimethylpyrazol-1-yl unit in 2. [Pd(2)Cl]²⁺ can also be prepared from PdCl₂ and [H₂2][MeOSO₃]₂ in refluxing methanol.     

Attempted synthesis of axial-equatorial pyrazine-bridged copper(II) complexes toward homometallic ferromagnetic compounds

The introduction of a relatively bulky alkyl group at 2-position of pyrazine afforded unique μ-pyz complexes, namely, dinuclear [{Cu(hfac)₂}₂(μ-2-isobutylpyrazine)], trinuclear [{Cu(hfac)₂}₃(μ-2-isopropylpyrazine)₂], and polymeric [Cu(hfac)₂(μ-ibupyz)]_n (Hhfac stands for 1,1,1,5,5,5-hexafluoropentane-2,4-dione). These compounds have an axial-equatorial dinuclear moiety, which is expected to show ferromagnetic interaction. However, they exhibited practically negligible or very weak antiferromagnetic interaction. This may be due to violation of orthogonality because of the steric hindrance of the isobutyl or isopropyl groups. We analyzed the relationship between the structural deformation parameter defined as the N(eq)?N(ax)-Cu angle and the exchange coupling parameter. A critical angle, at which the sign of the magnetic coupling changes from positive to negative, is estimated to be 165(2)°. The present results are reasonably explained in this relation.     

Construction of a Ytterbium Supramolecular Compound from 5,5＇-（Buta-diyne- 1,4-diyl）diisophthalic Acid

A novel 3D ytterbium supramolecular compound, [Yb（HBDDC）（H20）4]·2H2O（1）, was synthesized via 5,5＇-（buta-diyne-1,4-diyl）diisophthalic acid ligand（HaBDDC） under solvothermal conditions. Single-crystal X-ray diffraction analysis reveals that compound 1 crystallizes in triclinic system, PT space group with a=0.71372（14） nm, b=1.0566（2） nm, c=1.7969（4） nm, a=101.01（3）°, β=98.15（3）°, γ=99.17（3）° and V=1.2922（4） nm3. Compound 1 exhi- bits a special infinite 1D chain, which stacks parallel each other in an ABAB sequence, leading to the formation of a 3D supramolecular structure owing to the strong π-π interactions between adjacent phenyl ring groups. Moreover, compound 1 manifests excellent luminescent property.     

Synthesis of bis(2,2′:6′,2″-terpyridine)-terminated telechelic polymers by RAFT polymerization and ruthenium-polymer complexation thereof

Well-defined polystyrenes and poly(n-butyl acrylate)s of the two ends being functionalized with terpyridine groups were synthesized via addition-fragmentation chain transfer (RAFT) polymerization using a symmetric bisterpyridine-functionalized trithiocarbonate as a chain transfer agent (CTA). Kinetic studies on RAFT mediated thermal polymerization of styrene indicated the controlled polymerization. Corresponding triblock copolymers of styrene and n-butyl acrylate were obtained by utilizing the bisterpyridine-functionalized homopolymers as the macro-CTAs. Supramolecular metallo-polystyrenes with different repeat blocks were prepared by the chelating interaction between the terpyridine ends and Ru(II) ions. The formation of the metallo-polymers was proven by UV-vis spectra and dynamic light scattering (DLS).