Three new ZnII sulfate complexes

The three zinc sulfate complexes presented herein display three completely different coordination modes, viz tri­aqua(1,10‐phenanthroline‐N,N′)(sulfato‐O)­zinc(II) hydrate, [Zn(SO₄)(C₁₂H₈N₂)(H₂O)₃]·H₂O (octahedral, monomeric), bis(μ‐sulfato‐O:O′)­bis[(2,9‐di­methyl‐1,10‐phenanthroline‐N,N′)­zinc(II)], [Zn₂(SO₄)₂(C₁₄H₁₂N₂)₂] (tetrahedral, dimeric), and catena‐poly­[[di­aqua(2,2′‐bipyridyl‐N,N′)­zinc(II)]‐μ‐(sul­fato‐O:O′)], [Zn(SO₄)(C₁₀H₈N₂)(H₂O)₂]_n (octahedral, polymeric, twofold crystallographic symmetry). In the first, the sulfate is monodentate, while in the other two it acts as a bidentate bridge between two different Zn centers. There is a variety of sulfate S—O bond lengths, depending on the different coordination conditions and hydrogen‐bonding interactions.     

[62]Tetradecaphyrin and Its Mono‐ and Bis‐ZnII Complexes

A coiled structure of meso‐pentafluorophenyl‐substituted [62]tetradecaphyrin 1 was revealed by X‐ray structural analysis. Synthetic protocols were devised to form mono‐ and bis‐Zn^II complexes, 1 Zn and 1 Zn₂ , selectively. The former displayed a trigonal‐bipyramidal pentacoordinated Zn^II ion as a rare case and a cyclic voltammogram exhibiting eleven reversible redox waves. The latter showed a Ci‐symmetric structure with modest Hückel aromaticity owing to a 62 π‐electronic circuit as the largest aromatic molecule to date.     

Tetraaryl ZnII Porphyrinates Substituted at β‐Pyrrolic Positions as Sensitizers in Dye‐Sensitized Solar Cells: A Comparison with meso‐Disubstituted Push–Pull ZnII Porphyrinates

A facile and fast approach, based on microwave‐enhanced Sonogashira coupling, has been employed to obtain in good yields both mono‐ and, for the first time, disubstituted push–pull Zn^II porphyrinates bearing a variety of ethynylphenyl moieties at the β‐pyrrolic position(s). Furthermore, a comparative experimental, electrochemical, and theoretical investigation has been carried out on these β‐mono‐ or disubstituted Zn^II porphyrinates and meso‐disubstituted push–pull Zn^II porphyrinates. We have obtained evidence that, although the HOMO–LUMO energy gap of the meso‐substituted push–pull dyes is lower, so that charge transfer along the push–pull system therein is easier, the β‐mono‐ or disubstituted push–pull porphyrinic dyes show comparable or better efficiencies when acting as sensitizers in DSSCs. This behavior is apparently not attributable to more intense B and Q bands, but rather to more facile charge injection. This is suggested by the DFT electron distribution in a model of a β‐monosubstituted porphyrinic dye interacting with a TiO₂ surface and by the positive effect of the β substitution on the incident photon‐to‐current conversion efficiency (IPCE) spectra, which show a significant intensity over a broad wavelength range (350–650 nm). In contrast, meso‐substitution produces IPCE spectra with two less intense and well‐separated peaks. The positive effect exerted by a cyanoacrylic acid group attached to the ethynylphenyl substituent has been analyzed by a photophysical and theoretical approach. This provided supporting evidence of a contribution from charge‐transfer transitions to both the B and Q bands, thus producing, through conjugation, excited electrons close to the carboxylic anchoring group. Finally, the straightforward and effective synthetic procedures developed, as well as the efficiencies observed by photoelectrochemical measurements, make the described β‐monosubstituted Zn^II porphyrinates extremely promising sensitizers for use in DSSCs.     

ZnII Complexes for Bioimaging and Correlated Applications

Zinc is a biocompatible element that exists as the second most abundant transition metal ion and an indispensable trace element in the human body. Compared to traditional metal‐organic complexes systems, d¹⁰ metal Zn^II complexes not only exhibit a large Stokes shift and good photon stability but also possess strong emission and low cytotoxicity with a relatively small molecular weight. The use of Zn^II complexes has emerged in the last decade as a versatile and convenient tool for numerous biological applications, including bioimaging, molecular and protein recognition, as well as photodynamic therapy. Herein, we review recent developments involving Zn^II metal complexes applied as specific subcellular compartment imaging probes and their correlated utilizations.     

Ab initio molecular-orbital study of the binding of ZnII with SH2 and SH−

This paper reports an ab initio molecular-orbital (MO ) study of binding of SH₂ and SH^? with Zn^II. The mechanism of binding of Zn^II with these ligands is investigated using a detailed analysis of the energy decomposition and of the electronic distribution. The dependence of the results on the choice of the basis set for sulfur (in particular the effect of incorporation of diffuses p and d orbitals) on the geometry of ligand binding, the binding energy, and the proton affinity of SH^? are investigated. Comparison made with the corresponding results concerning the binding of OH₂, OH^?, and NH₃ shows that sulfur binding is less favorable although more covalent. Both sulfur ligands show a marked preference for angular conformations for binding with the metal ion. The effect of Zn^II binding on the ease of deprotonation of H₂S is quite similar to the corresponding effect found earlier for H₂O.     

Trinuclear Cage‐Like ZnII Macrocyclic Complexes: Enantiomeric Recognition and Gas Adsorption Properties

Three zinc(II) ions in combination with two units of enantiopure [3+3] triphenolic Schiff‐base macrocycles 1 , 2 , 3 , or 4 form cage‐like chiral complexes. The formation of these complexes is accompanied by the enantioselective self‐recognition of chiral macrocyclic units. The X‐ray crystal structures of these trinuclear complexes show hollow metal–organic molecules. In some crystal forms, these barrel‐shaped complexes are arranged in a window‐to‐window fashion, which results in the formation of 1D channels and a combination of both intrinsic and extrinsic porosity. The microporous nature of the [Zn₃ 1 ₂] complex is reflected in its N₂, Ar, H₂, and CO₂ adsorption properties. The N₂ and Ar adsorption isotherms show pressure‐gating behavior, which is without precedent for any noncovalent porous material. A comparison of the structures of the [Zn₃ 1 ₂] and [Zn₃ 3 ₂] complexes with that of the free macrocycle H₃ 1 reveals a striking structural similarity. In H₃ 1 , two macrocyclic units are stitched together by hydrogen bonds to form a cage very similar to that formed by two macrocyclic units stitched together by Zn^II ions. This structural similarity is manifested also by the gas adsorption properties of the free H₃ 1 macrocycle. Recrystallization of [Zn₃ 1 ₂] in the presence of racemic 2‐butanol resulted in the enantioselective binding of (S)‐2‐butanol inside the cage through the coordination to one of the Zn^II ions.     

Coordination of ZnII,CdII, and HgII by 2‐Pyridineformamide‐3‐piperidyl‐thiosemicarbazone

Sodium in dry methanol reduces 2‐cyanopyridine in the presence of 3‐piperidylthiosemicarbazide and produces 2‐pyridine‐formamide‐3‐piperidylthiosemicarbazone, HAmpip. Complexes with zinc(II), cadmium(II), and mercury(II) have been prepared and characterized by elemental analyses and spectroscopic techniques. In addition, the crystal structures of [Zn(Ampip)₂], [Zn(Ampip)(Oac)]₂, [Cd(HAmpip)Cl₂]·(CH₃)₂SO, [Cd(HAm‐pip)Br₂] · (CH₃)₂SO, [Cd(HAmpip)I₂]·(CH₃)₂SO, [Cd(Ampip)₂] and [Hg(HAmpip)Br₂]·(CH₃)₂SO have been solved. Coordination of the anionic and neutral thiosemicarbazone ligand is via the pyridyl nitrogen, imine nitrogen and thiolato/thione sulfur atom, respectively. In [Zn(Ampip)(OAc)]₂ one of the bridging acetato ligands has monodentate coordination and the other bridges in a bidentate manner. ¹¹³Cd NMR studies were carried out on the [Cd(HAmpip)X₂](X = Cl, Br or I) and [Cd(Ampip)(OAc)]₂ complexes. The ¹¹³Cd chemical shifts are affected by the halogen and range from 411 to 301 ppm, and the spectrum of [Cd(Ampip)(OAc)]₂ shows two signals at 450 and 251 ppm. The ¹⁹⁹Hg NMR spectrum of [Hg(HAmpip)Cl₂] also is discussed.     

A Theoretical and Experimental Investigation of the Spectroscopic Properties of a DNA‐Intercalator Salphen‐Type ZnII Complex

The photophysical and DNA‐binding properties of the cationic zinc(II) complex of 5‐triethylammonium methyl salicylidene ortho‐phenylenediiminato (ZnL²⁺) were investigated by a combination of experimental and theoretical methods. DFT calculations were performed on both the ground and the first excited states of ZnL²⁺ and on its possible mono‐ and dioxidation products, both in vacuo and in selected solvents mimicked by the polarizable continuum model. Comparison of the calculated absorption and fluorescence transitions with the corresponding experimental data led to the conclusion that visible light induces a two‐electron photooxidation process located on the phenylenediiminato ligand. Kinetic measurements, performed by monitoring absorbance changes over time in several solvents, are in agreement with a slow unimolecular photooxidation process, which is faster in water and slower in less polar solvents. Moreover, structural details of ZnL–DNA binding were obtained by DFT calculations on the intercalation complexes between ZnL and the d(ApT)₂ and d(GpC)₂ dinucleoside monophosphate duplexes. Two main complementary binding interactions are proposed: 1) intercalation of the central phenyl ring of the ligand between the stacked DNA base pairs; 2) external electrostatic attraction between the negatively charged phosphate groups and the two cationic triethylammonium groups of the Schiff‐base ligand. Such suggestions are supported by fluorescence titrations performed on the ZnL/DNA system at different ionic strengths and temperatures. In particular, the values of the DNA‐binding constants obtained at different temperatures provided the enthalpic and entropic contributions to the binding and confirmed that two competitive mechanisms, namely, intercalation and external interaction, are involved. The two mechanisms are coexistent at room temperature under physiological conditions.     

Chiral detection of entecavir stereoisomeric impurities through coordination with R‐besivance and ZnII using mass spectrometry

In this study, a mass spectrometry (MS)‐based kinetic method (KM) is shown to be successful at analyzing a multichiral center drug stereoisomer, entecavir (ETV), both qualitatively and quantitatively. On the basis of the KM, the bivalent complex ion [M^II(A)(ref*)₂]²⁺ (M^II = divalent metal ion, A = analyte, and ref* = chiral reference) was set as precursor ion in MS/MS. The experiment results suggest strong chiral selectivity between ETV and its isomers when using Zn^II coordinated with the chiral reference R‐besivance (R‐B). The logarithm of the fragment ion abundance ratio and the enantiomeric percentage (%) exhibits a strong linear relation because of the competitive loss of the reference and analyte. The product ion pair [Zn^II(R‐B)A‐H]⁺ (m/z 733) and [Zn^II(R‐B)₂‐H]⁺ (m/z 849), together with [R‐B + H]⁺ (m/z 394) and [A + H]⁺ (m/z 278), can realize the identification of ETV and all of its chiral isomers. Theoretical calculation were also performed using the B3LYP functional with the 6‐31G* and LanL2DZ basis set to clarify the mechanism of structural difference of these bivalent complex ions. The results reveal that MS‐KM can be used to detect optical impurities without a chiral chromatographic column and fussy sample pretreatment. The established method has been used to determine stereoisomeric impurities of less than 0.1% in ETV crude drug, a demonstration of its simple and effective nature for rapid detection of stereoisomeric impurities.     

A two‐dimensional ZnII coordination polymer constructed by benzotriazole‐5‐carboxylate and 1,4,8,9‐tetraazatriphenylene

Poly[[(μ₃‐benzotriazole‐5‐carboxylato‐κ⁴N¹:N³:O,O′)(1,4,8,9‐tetraazatriphenylene‐κ²N⁸,N⁹)zinc(II)] 0.25‐hydrate], {[Zn(C₇H₃N₃O₂)(C₁₄H₈N₄)]·0.25H₂O}_n, exhibits a two‐dimensional layer structure in which the asymmetric unit contains one Zn^II centre, one 1,4,8,9‐tetraazatriphenylene (TATP) ligand, one benzotriazole‐5‐carboxylate (btca) ligand and 0.25 solvent water molecules. Each Zn^II ion is six‐coordinated and surrounded by four N atoms from two different btca ligands and one chelating TATP ligand, and by two O atoms from a third btca ligand, to furnish a distorted octahedral geometry. The infinite connection of the metal ions and ligands forms a two‐dimensional wave‐like (6,3) layer structure. Adjacent layers are connected by C—H...N hydrogen bonds. The solvent water molecules are located in partially occupied sites between parallel pairs of inversion‐related TATP ligands that belong to two separate layers.     

Synthesis and Structural Characterization of ZnII α‐Diimine Complexes with Chloride and Thiocyanate Co‐Ligands

The preparation and spectroscopic and structural characterization of three Zn^II complexes with bis[N‐(2,6‐dimethylphenyl)imine]acenaphthene, L¹, and with bis[N‐(2‐ethylphenyl)imine]acenaphthene, L², are decribed herein. Two of the complexes were prepared from ZnCl₂ and the third from Zn(NCS)₂. One‐pot reaction techniques were used, leading to high yields. The complexes were characterized by microanalysis, IR and ¹H NMR spectroscopy, and single‐crystal X‐ray diffraction. The structures of the complexes are significantly different, with the chloride‐containing species forming distorted tetrahedra around the metal, whereas its thiocyanate analog is dimeric, with each metal at the center of a distorted square pyramid, with bridging and terminal [SCN]^– ligands.     

Two ZnII coordination complexes assembled by trithiocyanuric acid and two different N‐donor auxiliary ligands

The dipyridyl‐type building blocks 4‐amino‐3,5‐bis(pyridin‐3‐yl)‐1,2,4‐triazole (3‐bpt) and 4,4′‐bipyridine (bpy) have been used to assemble with Zn^II in the presence of trithiocyanuric acid (ttcH₃) to afford two coordination compounds, namely bis[4‐amino‐3,5‐bis(pyridin‐3‐yl)‐1,2,4‐triazole‐κN³]bis(trithiocyanurato‐κ²N,S)zinc(II), [Zn(C₃H₂N₃S₃)₂(C₁₂H₁₀N₆)₂]·2H₂O, (1), and catena‐poly[[[bis(trithiocyanurato‐κ²N,S)zinc(II)]‐μ‐4,4′‐bipyridine‐κ²N:N′] 4,4′‐bipyridine monosolvate], {[Zn₂(C₃H₂N₃S₃)₄(C₁₀H₈N₂)₃]·C₁₀H₈N₂}_n, (2). Single‐crystal X‐ray analysis indicates that complex (1) is a mononuclear structure, while complex (2) presents a one‐dimensional chain coordination motif. In both complexes, the central Zn^II cation adopts an octahedral geometry, coordinated by four N‐ and two S‐donor atoms. Notably, trithiocyanurate (ttcH₂⁻) adopts the same bidentate chelating coordination mode in each complex and exists in the thione tautomeric form. The 3‐bpt co‐ligand in (1) adopts a monodentate coordination mode and serves as a terminal pendant ligand, whereas the 4,4′‐bipyridine (bpy) ligand in (2) adopts a bidentate–bridging coordination mode. The different coordination characters of the different N‐donor auxiliary ligands lead to structural diversity for complexes (1) and (2). Further analysis indicates that the resultant three‐dimensional supramolecular networks for (1) and (2) arise through intermolecular N—H...S and N—H...N hydrogen bonds. Both complexes have been further characterized by FT–IR spectroscopy and elemental analyses.     

Versatile Tailoring of Paddle‐Wheel ZnII Metal–Organic Frameworks through Single‐Crystal‐to‐Single‐Crystal Transformations

A new tetracarboxylate ligand having short and long arms formed 2D layer Zn^II coordination polymer 1 with paddle‐wheel secondary building units under solvothermal conditions. The framework undergoes solvent‐specific single crystal‐to‐single crystal (SC‐SC) transmetalation to produce 1_Cu . With a sterically encumbered dipyridyl linker, the same ligand forms non‐interpenetrated, 3D, pillared‐layer Zn^II metal–organic framework (MOF) 2 , which takes part in SC‐SC linker‐exchange reactions to produce three daughter frameworks. The parent MOF 2 shows preferential incorporation of the longest linker in competitive linker‐exchange experiments. All the 3D MOFs undergo complete SC‐SC transmetalation with Cu^II, whereby metal exchange in different solvents and monitoring of X‐ray structures revealed that bulky solvated metal ions lead to ordering of the shortest linker in the framework, which confirms that the solvated metal ions enter through the pores along the linker axis.     

Complexes of Crown Ether‐Containing N‐Phosphorylated Thioamides and Thioureas with CoII,ZnII and PdII Cations

The reaction of the potassium salts of N‐phosphorylated thioureas [4′‐benzo‐15‐crown‐5]NHC(S)NHP(Y)(OiPr)₂ (Y = S, HL^I ; Y = O, HL^II ) with Zn^II and Co^II cations in aqueous EtOH leads to complexes of formulae Zn(L^I,II‐S,Y)₂ (Y = S, 1 ; Y = O, 2 ) and Co(L^I‐S,S′)₂ ( 3 ), while interaction of the potassium salt of N‐phosphorylated thioamide [4′‐benzo‐15‐crown‐5]C(S)NHP(O)(OiPr)₂ ( HL^III ) with Zn^II in the same conditions leads to the complex Zn(HL^III)(L^III‐S,O)₂ ( 4 ). The reaction of the potassium salt of crown ether‐containing N‐phosphorylated bis‐thiourea N,N′‐[C(S)NHP(O)(OiPr)₂]₂‐1,10‐diaza‐18‐crown‐6 ( H₂L ) with Co^II, Zn^II and Pd^II cations in anhydrous CH₃OH leads to complexes M₂(L‐O,S)₂ (M = Co, 5 ; Zn, 6 ; M = Pd, 7 ). Thioamide HL^III was investigated by single‐crystal X‐ray diffraction.