Fluorescent and Electrochemical Sensing of Polyphosphate Nucleotides by Ferrocene Functionalised with Two ZnII(TACN)(pyrene) Complexes

The [Fc? bis{Zn^II(TACN)(Py)}] complex, comprising two Zn^II(TACN) ligands (Fc=ferrocene; Py=pyrene; TACN=1,4,7‐triazacyclononane) bearing fluorescent pyrene chromophores linked by an electrochemically active ferrocene molecule has been synthesised in high yield through a multistep procedure. In the absence of the polyphosphate guest molecules, very weak excimer emission was observed, indicating that the two pyrene‐bearing Zn^II(TACN) units are arranged in a trans‐like configuration with respect to the ferrocene bridging unit. Binding of a variety of polyphosphate anionic guests (PPi and nucleotides di‐ and triphosphate) promotes the interaction between pyrene units and results in an enhancement in excimer emission. Investigations of phosphate binding by ³¹P NMR spectroscopy, fluorescence and electrochemical techniques confirmed a 1:1 stoichiometry for the binding of PPi and nucleotide polyphosphate anions to the bis(Zn^II(TACN)) moiety of [Fc? bis{Zn^II(TACN)(Py)}] and indicated that binding induces a trans to cis configuration rearrangement of the bis(Zn^II(TACN)) complexes that is responsible for the enhancement of the pyrene excimer emission. Pyrophosphate was concluded to have the strongest affinity to [Fc? bis{Zn^II(TACN)(Py)}] among the anions tested based on a six‐fold fluorescence enhancement and 0.1 V negative shift in the potential of the ferrocene/ferrocenium couple. The binding constant for a variety of polyphosphate anions was determined from the change in the intensity of pyrene excimer emission with polyphosphate concentration, measured at 475 nm in CH₃CN/Tris‐HCl (1:9) buffer solution (10.0 mM , pH 7.4). These measurements confirmed that pyrophosphate binds more strongly (K_b=(4.45±0.41)×10⁶ M ^?1) than the other nucleotide di‐ and triphosphates (K_b=1–50×10⁵ M ^?1) tested.     

Diketopyrrolopyrrole J‐Aggregates Formed by Self‐Organization with DNA

Bis(2‐thienyl)diketopyrrolopyrrole with two Zn^II‐cyclens (ZnCyc‐DPP) was designed and synthesized to evaluate the selective binding of Zn^II‐cyclen with thymine base in single‐strand DNA as a tool for the construction of a highly ordered multichromophore system on DNAs. Through UV/Vis titrations, gel filtration chromatography, and circular dichroism spectroscopy, ZnCyc‐DPP formed J‐type DPP aggregates with oligo‐dT_n DNAs. The DPP aggregates absorbed on a gold electrode exhibited good photocurrent responses. The present results show that binding Zn^II‐cyclen–chromophore conjugates and thymine bases together is a powerful tool for preparing DNA‐templated multichromophoric systems with specific functions.     

Synthesis of a Neutral Mixed‐Valence Diferrocenyl Carborane for Molecular Quantum‐Dot Cellular Automata Applications

The preparation of 7‐Fc⁺‐8‐Fc‐7,8‐nido‐[C₂B₉H₁₀]^? (Fc⁺FcC₂B₉^?) demonstrates the successful incorporation of a carborane cage as an internal counteranion bridging between ferrocene and ferrocenium units. This neutral mixed‐valence Fe^II/Fe^III complex overcomes the proximal electronic bias imposed by external counterions, a practical limitation in the use of molecular switches. A combination of UV/Vis‐NIR spectroscopic and TD‐DFT computational studies indicate that electron transfer within Fc⁺FcC₂B₉^? is achieved through a bridge‐mediated mechanism. This electronic framework therefore provides the possibility of an all‐neutral null state, a key requirement for the implementation of quantum‐dot cellular automata (QCA) molecular computing. The adhesion, ordering, and characterization of Fc⁺FcC₂B₉^? on Au(111) has been observed by scanning tunneling microscopy.     

Substituent and Solvent Effects on the Electrochemical Properties and Intervalence Transfer in Asymmetric Mixed‐Valent Complexes Consisting of Cyclometalated Ruthenium and Ferrocene

Four heterodimetallic complexes [Ru(Fcdpb)(L)](PF₆) (Fcdpb=2‐deprotonated form of 1,3‐di(2‐pyridyl)‐5‐ferrocenylbenzene; L=2,6‐bis‐(N‐methylbenzimidazolyl)‐pyridine (Mebip), 2,2′:6′,2′′‐terpyridine (tpy), 4‐nitro‐2,2′:6′,2′′‐terpyridine (NO₂tpy), and trimethyl‐4,4′,4′′‐tricarboxylate‐2,2′:6′,2′′‐terpyridine (Me₃tctpy)) have been prepared. The electrochemical and spectroelectrochemical properties of these complexes have been examined in CH₂Cl₂, CH₃NO₂, CH₃CN, and acetone. These complexes display two consecutive redox couples owing to the stepwise oxidation of the ferrocene (Fc) and ruthenium units, respectively. The potential difference, ΔE_1/2 (E_1/2(Ru^II/III)?E_1/2(Fc^0/+)), decreased slightly with increasing solvent donocity. The mixed‐valent states of these complexes have been generated by electrolysis and the resulting intervalence charge‐transfer (IVCT) bands have been analyzed by Hush theory. Good linear relationships exist between the energy of the IVCT band, E_op, and ΔE_1/2 of four mixed‐valent complexes in a given solvent.     

Micelles as Containers for Self‐Assembled Nanodevices: A Fluorescent Sensor for Lipophilicity

Potentiometric titrations, fluorescence versus pH titrations, dynamic light scattering and fluorescence polarization anisotropy studies demonstrate that inside the nanodimensioned Triton X‐100 micelles, 1‐pyrenecarboxylic acid, PCOO^?, forms an apical complex with the Zn²⁺ cation encircled by a lipophilic cyclen ligand and hugely increasing its fluorescence. The ability of the Zn²⁺‐cyclen‐PCOO^? complex plus its micellar container to act as a fluorescent sensor to evaluate the lipophilicity of molecular species is demonstrated on the fatty acid series CH₃(CH₂)_xCOOH (x=0–16). At pH 7.4 a decrease in fluorescence is observed on the addition of fatty acids that is directly related to their chain length, that is, to their tendency to enter the micellar containers, where they dislocate PCOO^? from the Zn²⁺ centre. The independent determination of fatty acid pK_a values in the presence of Triton X‐100 micelles confirms that our fluorescent micellar device is capable of sensing their lipophilicity.     

Photoluminescence properties of a cationic trinuclear zinc(II) complex with the tetradentate Schiff base ligand 6‐methyl‐2‐({[(pyridin‐2‐yl)methyl]imino}methyl)phenolate

Metal complexes with Schiff base ligands have been suggested as potential phosphors in electroluminescent devices. In the title complex, tetrakis[6‐methyl‐2‐({[(pyridin‐2‐yl)methyl]imino}methyl)phenolato‐1:2κ⁸N,N′,O:O;3:2κ⁸N,N′,O:O]trizinc(II) hexafluoridophosphate methanol monosolvate, [Zn₃(C₁₄H₁₃N₂O)₄](PF₆)₂·CH₃OH, the Zn^II cations adopt both six‐ and four‐coordinate geometries involving the N and O atoms of tetradentate 6‐methyl‐2‐({[(pyridin‐2‐yl)methyl]imino}methyl)phenolate ligands. Two terminal Zn^II cations adopt distorted octahedral geometries and the central Zn^II cation adopts a distorted tetrahedral geometry. The O atoms of the phenolate ligands bridge three Zn^II cations, forming a dicationic trinuclear metal cluster. The title complex exhibits a strong emission at 469 nm with a quantum yield of 15.5%.     

Binuclear and chain‐structure zinc(II) complexes constructed from 3,4‐dimethoxy‐trans‐cinnamic acid and N‐donor coligands 4‐(1H‐pyrazol‐3‐yl)pyridine and 4,4′‐bipyridine

3,4‐Dimethoxy‐trans‐cinnamic acid (Dmca) reacts with zinc sulfate in the presence of 4‐(1H‐pyrazol‐3‐yl)pyridine (L₁) or 4,4′‐bipyridine (L₂) under hydrothermal conditions to afford two mixed‐ligand coordination complexes, namely tetrakis(μ‐3,4‐dimethoxy‐trans‐cinnamato‐κ²O:O′)bis[[4‐(1H‐pyrazol‐3‐yl)pyridine]zinc(II)] heptahydrate, [Zn₂(C₁₁H₁₁O₄)₄(C₈H₇N₃)₂]·7H₂O or [Zn₂(Dmca)₄(L₁)₂]·7H₂O, (I), and catena‐poly[[bis(3,4‐dimethoxy‐trans‐cinnamato‐κO)zinc(II)]‐μ‐4,4′‐bipyridine‐κ²N:N′], [Zn(C₁₁H₁₁O₄)₂(C₁₀H₈N₂)]_n or [Zn(Dmca)₂(L₂)]_n, (II). The Zn^II centres in the two compounds display different coordination polyhedra. In complex (I), the Zn^II cation is five‐coordinated with a pseudo‐square‐pyramidal geometry, while in complex (II) the Zn^II cation sits on a twofold axis and adopts a distorted tetrahedral coordination environment. Complex (I) features a centrosymmetric binuclear paddle‐wheel‐like structure, while complex (II) shows a chain structure. This study emphasizes the significant effect of the coordination mode of both carboxylate‐group and N‐donor coligands on the formation of complex structures.     

Three Polymorphic CdII Coordination Polymers Obtained from the Solution and Mechanochemical Reactions of 3‐Cyanopentane‐2,4‐dione with CdII Acetate

We previously reported that monomeric and polymeric metal complexes are obtained from solution and mechanochemical reactions of 3‐cyano‐pentane‐2,4‐dione (CNacacH) with 3d metal acetates (M=Mn^II, Fe^II, Co^II, Ni^II, Cu^II, and Zn^II). A common feature found in all complexes was that their structural base is trans‐[M(CNacac)₂]. Here, we report that the reactions of CNacacH with Cd^II acetate in the solution and solid states afford different coordination polymers composed of trans‐[Cd(CNacac)₂] and cis‐[Cd(CNacac)₂] units, respectively. From a methanol solution containing CNacacH (L) and Cd(OAc)₂ ? 2 H₂O (M), a coordination polymer ( Cd‐1 ) in which trans‐[Cd(CNacac)₂] units are three‐dimensionally linked was obtained. In contrast, two different coordination polymers, Cd‐2 and Cd‐3 , were obtained from mechanochemical reactions of CNacacH with Cd(OAc)₂ ? 2 H₂O at M/L ratios of 1:1 and 1:2, respectively. In Cd‐2 , cis‐[Cd(CNacac)₂] units are two‐dimensionally linked, whereas the units are linked three‐dimensionally in Cd‐3 . Furthermore, Cd‐1 and Cd‐2 converted to Cd‐3 by applying an annealing treatment and grinding with a small amount of liquid, respectively, in spite of the polymeric structures. These phenomena, 1) different structures are formed from solution and mechanochemical reactions, 2) two polymorphs are formed depending on the M/L ratio, and 3) structural transformation of resulting polymeric structures, indicate the usability of mechanochemical method in the syntheses of coordination polymers as well as the peculiar structural flexibility of cadmium‐CNacac polymers.     

Construction of Pendant‐Armed Schiff‐Base Macrocyclic Dinuclear Zinc Complexes and Their Selective Recognition of Acetate Ions

Two new flexible extended dialdehydes (H₂hpdd and H₂pdd) with different functional pendant arms (? CH₂CH₂PhOH and ? CH₂CH₂Ph) have been synthesized and reacted with 1,2‐bis(2‐aminoethoxy)ethane to prepare Schiff‐base macrocyclic complexes in the presence of a Zn^II‐ion template. As a result, two preorganized dinuclear Zn^II intermediates ( 1 and 2 ), as well as two 42‐membered folded [2+2] macrocyclic dinuclear Zn^II complexes ( 3 and 4 ), were produced. The central zinc ions in compounds 1 – 4 showed distinguishable coordination patterns with the dialdehydes and the [2+2] macrocyclic ligands, in which a subtle pH‐adjustment function of the two pendant arms (with or without the phenolic hydroxy group) was believed to play a vital role. Furthermore, cation‐ and anion‐recognition experiments for complexes 3 and 4 revealed that they could selectively recognize acetate ions by the formation of 1:1 stoichiometric complexes, as verified by changes in their UV/Vis and MS (ESI) spectra and even by the naked eye.     

二茂铁取代卟啉的合成表征及电化学性质

通过吡咯与二茂铁甲醛和对甲基苯甲醛的直接交叉缩合反应,合成并成功分离了6个含有0~4个二茂铁取代基的卟啉化合物:5,10,15,20-四(4-甲苯基)卟啉[(CH3Ph)4PH2]、5-(二茂铁基)-10,15,20-三(4-甲苯基)卟啉[Fc(CH3Ph)3PH2]、cis-5,10-二(二茂铁基)-15,20-二(4-甲苯基)卟啉[cis-Fc2(CH3Ph)2PH2]、trans-5,15-二(二茂铁基)-10,20-二(4-甲苯基)卟啉[trans-Fc2(CH3Ph)2PH2]、5,10,15-三(二茂铁基)-20-(4-甲苯基)卟啉[Fc3(CH3Ph)PH2]、5,10,15,20-四(二茂铁基)卟啉[Fc4PH2]。用紫外-可见和红外光谱、核磁共振及质谱等技术对卟啉化合物进行了表征,用微量光谱滴定法测定了化合物在非水溶剂中的质子化反应常数,研究了它们的电化学和光谱电化学性质。结果表明,二茂铁取代基对化合物的光谱及氧化还原电位有较大的影响。     

Voltammetric Studies of the Interactions Between Ferrocene‐Labeled Glutathione and Proteins in Solution or Immobilized onto Surface

Glutathione (GSH) tagged with a ferrocene (Fc) label at its C‐terminal was synthesized via coupling ferrocenyl amine to glutathione using o‐(benzotriazol‐1‐yl)‐N,N,N′,N′‐tetramethyluronium (HBTU)/1‐hydroxybenzotrizole (HOBt). The presence of Fc yielded well defined voltammetric signals, rendering the Fc‐tagged GSH (GSH‐Fc) suitable for electrochemical studies of GSH binding to other biological species. The interaction of GSH‐Fc with bovine serum albumin (BSA) was investigated, and a binding ratio of 1.41±0.06 (GSH‐Fc/BSA) and an affinity constant K_a of 6.53±2.01×10⁶ M^?1 were determined. These results compare well with those measured by fluorescence using untagged GSH, suggesting that the attachment of Fc to GSH does not significantly perturb the GSH structure and binding behavior. By contrasting the binding behavior to several compounds that are known to conjugate to different domains of BSA, the voltammetric study confirmed that GSH‐Fc binds at subdomain IIA of BSA with high affinity. The versatility of GSH‐Fc for studying GSH binding to surface‐confined proteins was also demonstrated with the GSH binding to electroinactive Zn‐metallothionein (Zn₇‐MT) through hydrogen binding at the region between the Zn₇‐MT α and β domains.     

Metal(II) Ion Complexes with 5‐(Pyrazin‐2‐yl)‐2,4‐dihydro‐3H‐1,2,4‐triazole‐3‐thione; Synthesis,Structural Characterization,Acid‐base,and Complexing Properties in Solution

The study reports the synthesis of complexes Co(HL)Cl₂ ( 1 ), Ni(HL)Cl₂ ( 2 ), Cu(HL)Cl₂ ( 3 ), and Zn(HL)₃Cl₂ ( 4 ) with the title ligand, 5‐(pyrazin‐2‐yl)‐1,2,4‐triazole‐5‐thione (HL), and their characterization by elemental analyses, ESI‐MS (m/z), FT‐IR and UV/Vis spectroscopy, as well as EPR in the case of the Cu^II complex. The comparative analysis of IR spectra of the metal ion complexes with HL and HL alone indicated that the metal ions in 1 , 2 , and 3 are chelated by two nitrogen atoms, N(4) of pyrazine and N(5) of triazole in the thiol tautomeric form, whereas the Zn^II ion in 4 is coordinated by the non‐protonated N(2) nitrogen atom of triazole in the thione form. pH potentiometry and UV/Vis spectroscopy were used to examine Co^II, Ni^II, and Zn^II complexes in 10/90 (v/v) DMSO/water solution, whereas the Cu^II complex was examined in 40/60 (v/v) DMSO/water solution. Monodeprotonation of the thione triazole in solution enables the formation of the L:M = 1:1 species with Co^II, Ni^II and Zn^II, the 2:1 species with Co^II and Zn^II, and the 3:1 species with Zn^II. A distorted tetrahedral arrangement of the Cu^II complex was suggested on the basis of EPR and Vis/NIR spectra.     

A three‐dimensional zinc‐based coordination polymer built from 5‐carboxylato‐1‐carboxylatomethyl‐2‐oxidopyridinium with a 4‐connected sra topology

A novel three‐dimensional Zn^II complex, poly[aqua(μ₄‐5‐carboxylato‐1‐carboxylatomethyl‐2‐oxidopyridinium)zinc(II)], [Zn(C₈H₅NO₄)(H₂O)]_n, has been prepared by hydrothermal assembly of Zn(CH₃COO)₂·2H₂O and 5‐carboxy‐1‐(carboxymethyl)pyridin‐1‐ium‐2‐olate (H₂ccop). The ccop²⁻ anions bridge the Zn^II cations in a head‐to‐tail fashion via monodentate aromatic carboxylate and phenolate O atoms to form an extended zigzag chain which runs parallel to the [011] direction. One O atom of the aliphatic carboxylate group of the ccop²⁻ ligand coordinates to the Zn^II atom of a neighbouring chain thereby producing undulating layers which lie parallel to the (01) plane. A similar parallel undulating planar structure can be obtained if a path involving the other O atom of the aliphatic carboxylate group is considered. Thus, the aliphatic carboxylate group acts in a bridging bidentate mode to give extended –Zn–O–C–O–Zn– sequences running parallel to [001] which link the layers into an overall three‐dimensional framework. The three‐dimensional framework can be simplified as a 4‐connected sra topology with a Schläfli symbol of 4².6³.8 if all the Zn^II centres and ccop²⁻ anions are regarded as tetrahedral 4‐connected nodes. The three‐dimensional luminescence spectrum was measured at room temperature with excitation and emission wavelengths of 344–354 and 360–630 nm, respectively, at intervals of 0.15 and 2 nm, respectively.     

Organotin–Oxido Cluster‐Based Multiferrocenyl Complexes Obtained by Hydrolysis of Ferrocenyl‐Functionalized Organotin Chlorides

Three organotin–oxido clusters were formed by hydrolysis of ferrocenyl‐functionalized organotin chloride precursors in the presence of NaEPh (E=S, Se). [R^FcSnCl₃?HCl] ( C ; R^Fc = CMe₂CH₂C(Me)?N?N?C(Me)Fc) and [SnCl₆]^2? formed {(R^FcSnCl₂)₃[Sn(OH)₆]}[SnCl₃] ( 3 a ) and {(R^FcSnCl₂)₃[Sn(OH)₆]}[PhSeO₃] ( 3 b ), bearing an unprecedented [Sn₄O₆] unit, in a one‐pot synthesis or stepwise through [(R^FcSnCl₂)₂Se] ( 1 ) plus [(R^FcSnCl₂)SePh] ( 2 ). A one‐pot reaction starting out from FcSnCl₃ gave [(FcSn)₉(OH)₆O₈Cl₅] ( 4 ), which represents the largest Fc‐decorated Sn/O cluster reported to date.     

A novel one‐dimensional double‐chain‐like ZnII coordination polymer: poly[bis(1‐benzyl‐1H‐imidazole‐κN3)tris(μ‐cyanido‐κ2C:N)(cyanido‐κC)disilver(I)zinc(II)]

One of most interesting systems of coordination polymers constructed from the first‐row transition metals is the porous Zn^II coordination polymer system, but the numbers of such polymers containing N‐donor linkers are still limited. The title double‐chain‐like Zn^II coordination polymer, [Ag₂Zn(CN)₄(C₁₀H₁₀N₂)₂]_n, presents a one‐dimensional linear coordination polymer structure in which Zn^II ions are linked by bridging anionic dicyanidoargentate(I) units along the crystallographic b axis and each Zn^II ion is additionally coordinated by a terminal dicyanidoargentate(I) unit and two terminal 1‐benzyl‐1H‐imidazole (BZI) ligands, giving a five‐coordinated Zn^II ion. Interestingly, there are strong intermolecular Ag^I…Ag^I interactions between terminal and bridging dicyanidoargentate(I) units and C—H…π interactions between the phenyl rings of BZI ligands of adjacent one‐dimensional linear chains, providing a one‐dimensional linear double‐chain‐like structure. The supramolecular three‐dimensional framework is stabilized by C—H…π interactions between the phenyl rings of BZI ligands and by Ag^I…Ag^I interactions between adjacent double chains. The photoluminescence properties have been studied.     

A one‐dimensional zinc(II) coordination polymer based on mixed multidentate N‐ and O‐donor ligands

In the title coordination polymer, catena‐poly[[bis[{1‐[(1H‐benzimidazol‐2‐yl‐κN³)methyl]‐1H‐tetrazole}zinc(II)]‐bis(μ₄‐pentane‐1,5‐dioato‐1:2:1′:2′κ⁴O¹:O^1′:O⁵:O^5′)] methanol disolvate], {[Zn(C₅H₆O₄)(C₉H₈N₆)]·CH₃OH}_n, each Zn^II ion is five‐coordinated by four O atoms from four glutarate ligands and by one N atom from a 1‐[(1H‐benzimidazol‐2‐yl)methyl]‐1H‐tetrazole (bimt) ligand, leading to a slightly distorted square‐pyramidal coordination environment. Two Zn^II ions are linked by four bridging glutarate carboxylate groups to generate a dinuclear [Zn₂(CO₂)₄] paddle‐wheel unit. The dinuclear units are further connected into a one‐dimensional chain via the glutarate ligands. The bimt ligands coordinate to the Zn^II ions in a monodentate mode and are pendant on both sides of the main chain. In the crystal, the chains are linked by O—H...O and N—H...O hydrogen bonds into a two‐dimensional layered structure. Adjacent layers are further packed into a three‐dimensional network through van der Waals forces. A thermogravimetric analysis was carried out and the photoluminescent behaviour of the polymer was investigated.     

Fine‐Tuning of Saponification‐Triggered Gelation by Strategic Modification of Peripheral Substituents: Gelation Regulators

A pioneering approach towards controlling the efficiency of saponification assisted gelation in ethyl ester based Zn^II‐complexes have been described. Using four new ester containing bis‐salen Zn^II complexes ( C1–C4 ) involving different para‐azo phenyl substituted ligands it has been clearly shown that gelation efficiency is greatly influenced by the electronic effects of the substituents (‐H ( C1 ), ‐CH₃ ( C2 ), ‐NO₂ ( C3 ), and ‐OCH₃ ( C4 )). Morphological, photophysical, and rheological investigations corroborated the experimental observations well and established that gelation efficiency was enhanced with electron‐withdrawing characteristics of substituents ( C4 < C2 < C1 < C3 ). This conclusion was also supported by DFT studies.     

Electronic Properties of Mono‐Substituted Tetraferrocenyl Porphyrins in Solution and on a Gold Surface: Assessment of the Influencing Factors for Photoelectrochemical Applications

Two unsymmetric meso‐tetraferrocenyl‐containing porphyrins of general formula Fc₃(FcCOR)Por (Fc=ferrocenyl, R=CH₃ or (CH₂)₅Br, Por=porphyrin) were prepared and characterized by a variety of spectroscopic methods, whereas their redox properties were investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) approaches. The mixed‐valence [Fc₃(FcCOR)Por]ⁿ⁺ (n=1,3) were investigated using spectroelectrochemical as well as chemical oxidation methods and corroborated with density functional theory (DFT) calculations. Inter‐valence charge‐transfer (IVCT) transitions in [Fc₃(FcCOR)Por]⁺ were analyzed, and the resulting data matched closely previously reported complexes and were assigned as Robin–Day class II mixed‐valence compounds. Self‐assembled monolayers (SAMs) of a thioacetyl derivative (Fc₃(FcCO(CH₂)₅SCOCH₃)Por) were also prepared and characterized. Photoelectrochemical properties of SAMs in different electrolyte systems were investigated by electrochemical techniques and photocurrent generation experiments, showing that the choice of electrolyte is critical for efficiency of redox‐active SAMs.     

The Crystal Structures of Trimethylphosphane supported Nickel‐ and Cobalt‐Methyl Complexes: Octahedral mer‐cis‐[CoIIII(CH3)2(PMe3)3] and Square Planar trans‐[NiIICl(CH3)(PMe3)2]

Single crystals of octahedral mer‐cis‐[Co^IIII(CH₃)₂(PMe₃)₃] ( 1 ) and square planar trans‐[Ni^IICl(CH₃)(PMe₃)₂] ( 2 ), were obtained from solvent mixtures (methylcylohexane / pentane 1:1) and have been analyzed by X‐ray crystallography for the first time.     

A bipyridine‐ligated zinc(II) complex with bridging flavonolate ligation: synthesis,characterization, and visible‐light‐induced CO release reactivity

Metal–flavonolate compounds are of significant current interest as synthetic models for quercetinase enzymes and as bioactive compounds of importance to human health. Zinc–3‐hydroxyflavonolate compounds, including those of quercetin, kampferol, and morin, generally exhibit bidentate coordination to a single Zn^II center. The bipyridine‐ligated zinc–flavonolate compound reported herein, namely bis(μ‐4‐oxo‐2‐phenyl‐4H‐chromen‐3‐olato)‐κ³O ³:O ³,O ⁴;κ³O ³,O ⁴:O³‐bis[(2,2′‐bipyridine‐κ²N ,N ′)zinc(II)] bis(perchlorate), {[Zn₂(C₁₅H₉O₃)₂(C₁₀H₈N₂)₂](ClO₄)₂}_n , ( 1 ), provides an unusual example of bridging 3‐hydroxyflavonolate ligation in a dinuclear metal complex. The symmetry‐related Zn^II centers of ( 1 ) exhibit a distorted octahedral geometry, with weak coordination of a perchlorate anion trans to the bridging deprotonated O atom of the flavonolate ligand. Variable‐concentration conductivity measurements provide evidence that, when ( 1 ) is dissolved in CH₃CN, the complex dissociates into monomers. ¹H NMR resonances for ( 1 ) dissolved in d₆‐DMSO were assigned via HMQC to the H atoms of the flavonolate and bipyridine ligands. In CH₃CN, ( 1 ) undergoes quantitative visible‐light‐induced CO release with a quantum yield [0.004 (1)] similar to that exhibited by other mononuclear zinc–3‐hydroxyflavonolate complexes. Mass spectroscopic identification of the [(bpy)₂Zn(O‐benzoylsalicylate)]⁺ ion provides evidence of CO release from the flavonol and of ligand exchange at the Zn^II center.