A highly selective visual and fluorescent sensor for Pb2+ and Zn2+ and crystal structure of Cu2+ complex based-on a novel single-armed Salamo-type bisoxime

Optical Chemosensors Synthesis and Appplication for Trace Level Metal Ions Detection in Aqueous Media: A Review

In recent years, the development of optical chemosensors for the sensitive and selective detection of trace level metal ions in aqueous media has garnered significant attention within the scientific community. This review article provides a comprehensive overview of the synthesis strategies and applications of optical chemosensors dedicated to the detection of metal ions at low concentrations in water-based environments. The discussion encompasses a wide range of metal ions, including but not limited to heavy metals, transition metals, and rare earth elements, emphasizing their significance in environmental monitoring, industrial processes, and biological systems. The review explores into the synthesis methodologies employed for designing optical chemosensors, discovering diverse materials like organic dyes, nanoparticles, polymers, and hybrid materials. Special attention is given to the design principles that enable the selective recognition of specific metal ions, highlighting the role of ligand chemistry, coordination interactions, and structural modifications. Furthermore, the article thoroughly surveys the analytical performance of optical chemosensors in terms of sensitivity, selectivity, response time, and detection limits. Real-world applications, including water quality assessment, environmental monitoring, and biomedical diagnostics, are extensively covered to underscore the practical relevance of these sensing platforms. Additionally, the review sheds light on emerging trends, challenges, and future prospects in the field, providing insights into potential advancements and innovations. By synthesizing the current state of knowledge on optical chemosensors for trace level metal ions detection. The collective information presented herein not only offers a comprehensive understanding of the existing technologies but also inspires future research endeavors to address the evolving demands in the realm of trace metal ion detection.

Crystal structure of bis{2-(tert-butyl)-6-((E)-((4-((E)-1-(methoxyimino)ethyl)phenyl)imino)methyl)phenolato-κ2 N,O}zinc(II), C40H46N4O4Zn

C40H46N4O4Zn, monoclinic, P21/n (no. 14), a = 12.0198(4) Å, b = 28.0212(9) Å, c = 12.0655(4) Å, β = 110.727(2)°, V = 3800.8(2) Å3, Z = 4, R gt (F) = 0.0442, wR ref (F 2) = 0.1076, T = 173(2) K.

Two highly sensitive and efficient salamo-like copper(II) complex probes for recognition of CN. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2020;228:117775. [PMID: 31718968 DOI: 10.1016/j.saa.2019.117775]

Two salamo-like copper(II) complex probes, L¹-Cu²⁺ and L²-Cu²⁺, were designed and synthesized for sensitive and efficient identification of CN^-. UV spectroscopy, high resolution mass spectrometry, RGB analysis and naked eye recognition were performed to explore their recognition mechanisms. High resolution mass spectra indicated that the probes L¹-Cu²⁺ and L²-Cu²⁺ formed complexes with CN^-. The two probes could recognize CN^- by the naked eye and the color of the solution changed from light yellow to red. In terms of application, the contents of CN^- in the environmental water samples were tested. In addition, the optimal pH ranges for probe detection of CN^- were investigated by pH value measurement.

A selective “turn-on” sensor for recognizing In3+ and Zn2+ in respective systems based on imidazo[2,1-b]thiazole

An imidazo[2,1-b]thiazole-based compound (X) was designed and synthesized as an “off–on–off” sensor for the multiple recognition of In³⁺ and Zn²⁺ in different systems.

A highly sensitive and selective fluorescent "off-on-off" relay chemosensor based on a new bis(salamo)-type tetraoxime for detecting Zn2+ and CN. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2019;222:117209. [PMID: 31200268 DOI: 10.1016/j.saa.2019.117209]

A new naphthalenediol-based bis(salamo)-type fluorescent probe H₄L for Zn²⁺ and CN^- was reported. Probe H₄L showed a highly selective fluorescence enhancement toward Zn²⁺ over other metal ions including Cd²⁺, and obtained the L-Zn²⁺complex can only detect CN^- in various anions. Their recognition mechanisms were explained by Job plots, fluorescent and UV-vis titrations, and theoretical calculations. The L-Zn²⁺complex has been synthesized and structurally characterized using Hirshfeld surface analysis, elemental analyses, IR, UV-Vis and fluorescent spectra. Additionally, the relay probe with the wide adaptability of pH range and excellent stability showed highly selectivity for CN^- recognition.

Crystal structure of bis{μ2-bis{(((((1-methoxyimino)ethyl)phenyl)imino)methyl)-2-phenolato-κ3 N,O:O}copper(II)}, C68H68Cu2N8O8

C68H68Cu2N8O8, monoclinic, P21/c, a = 16.241(3) Å, b = 12.1604(19) Å, c = 15.531(3) Å, β = 96.364(3)°, Z = 2, V = 3048.3(9) Å3, R gt(F) = 0.0497, wR ref(F 2) = 0.1263, T = 296(2)K.

Synthesis and crystal structure of bis{4-methyl-2-((E)-((4-((E)-1-(benzyloxyimino)ethyl)phenyl)imino)methyl)phenolato-κ3 N,O,O}copper(II), C92H84Cu2N8O8

C92H84Cu2N8O8, monoclinic, P21/c (no. 14), a = 18.315(2) Å, b = 12.1533(12) Å, c = 17.518(2) Å, β = 105.289(4)°, Z = 2, V = 3761.3(7) Å3, R gt(F) = 0.0658, wR ref(F 2) = 0.1809, T = 173(2)K.

Synthesis and crystal structure of bis{((E)-((4-((E)-1-(benzyloxyimino)ethyl)phenyl)imino)methyl)-2-phenolato-κ2 N,O}copper(II), C44H38CuN4O4

C44H38CuN4O4, monoclinic, P21/n (no. 14), a = 8.0172(13) Å, b = 10.9003(17) Å, c = 42.154(8) Å, β = 94.749(6)°, Z = 4, V = 3671.2(11) Å3, R gt(F) = 0.0483, wR ref(F 2) = 0.1072, T = 173(2)K.

Crystal structure of 1-(4-{2,5-dichloro-3-hydroxy-4-[4-(1-methoxyimino-ethyl)-phenylamino]-6-methyl-phenylamino}-phenyl)-ethanone O-methyl-oxime, C24H22Cl2N4O4

C24H22Cl2N4O4, triclinic, P1̄ (no. 2), a = 9.7533(6) Å, b = 10.2969(8) Å, c = 17.9128(12) Å, α = 104.131(2)°, β = 99.242(2)°, γ = 91.106(2)°, V = 1718.7(2) Å3, Z = 3, R gt(F) = 0.0502, wR ref(F 2) = 0.1256, T = 153(2) K.

A New Half-Salamo-Based Homo-Trinuclear Nickel(II) Complex: Crystal Structure, Hirshfeld Surface Analysis, and Fluorescence Properties

A new homo-trinuclear Ni(II) half-salamo-based complex [Ni3(L)2(μ-OAc)2(OAc)2(CH3OH)2]·2CH3OH was synthesized via the reaction of a tridentate ligand HL (2-[O-(1-ethyloxyamide)]oxime-4-bromophenol) and Ni(OAc)2·4H2O, and characterized using elemental analyses, IR spectra, UV-Vis absorption spectra, X-ray crystallography, and Hirshfeld analysis. Interestingly, single-crystal X-ray analysis showed that the two acetate molecules were bonded simultaneously with the Ni(II) atoms by mono-dentate chelating and bidentate bridging coordination modes, respectively, and the resulting hexa-coordinate geometries were ultimately formed. Furthermore, the Hirshfeld analysis of the complex was studied. Compared with HL, the complex fluorescence intensity was significantly lowered, indicating that the Ni(II) ions have fluorescence quenching characteristics.

Structurally characterized homo-trinuclear ZnII and hetero-pentanuclear [ZnII4LnIII] complexes constructed from an octadentate bis(Salamo)-based ligand: Hirshfeld surfaces, fluorescence and catalytic properties

One 3d and five 3d-4f complexes were synthesized. Complexes 1–6 were characterized via elemental analyses, FT-IR, UV-Vis spectroscopy and X-ray crystallography, and their fluorescence properties, catalytic activities and Hirshfeld surface analyses were studied.

Luminescent and electrochemical properties of four novel butterfly-shaped hetero-pentanuclear [Zn4Ln] complexes constructed from a bis(salamo)-type ligand

Four novel butterfly-shaped hetero-pentanuclear 3d-4f complexes [Zn₄(L)₂Sm(H₂O)₄]3NO₃·2EtOH (1) [Zn₄(L)₂Eu(NO₃)₂(MeOH)(EtOH)]NO₃·H₂O (2), [Zn₄(L)₂Gd(H₂O)₄]3NO₃·MeOH·EtOH (3) and [Zn₄(L)₂Tb(NO₃)(EtOH)(H₂O)₂]NO₃·MeOH·EtOH (4) were synthesized by the reactions of a bis(salamo)-type tetraoxime ligand (H₄L) with Zn(OAc)₂·2H₂O and Ln(NO₃)₃·6H₂O (Ln = Sm, Eu, Gd and Tb), respectively. The structures of complexes 1-4 were fully characterized by elemental analyses, FT-IR, UV-Vis spectroscopy and single crystal X-ray crystallography, and their luminescence properties were also discussed. In addition, cyclic voltammograms were used to characterize electrochemical properties of the Zn(II)-Ln(III) (Ln = Sm, Eu, Gd and Tb) complexes.

Synthesis and Fluorescence Properties of a Structurally Characterized Hetero-Hexanuclear Zn(II)-La(III) Salamo-Like Coordination Compound Containing Auxiliary Ligands

A hetero-hexanuclear Zn(II)-La(III) coordination compound, [{(ZnL)2La}2(bdc)2](NO3)2 (H2bdc = terephthalic acid) has been synthesized with a symmetric Salamo-like bisoxime, and characterized by elemental analyses, IR, UV-Vis, fluorescent spectroscopy, and single-crystal X-ray diffraction analysis. All of the Zn(II) ions are pentacoordinated by N2O2 donator atoms from the (L)2− unit and one oxygen atom from one terephthalate anion. The Zn(II) ions adopt trigonal bipyramidal geometries (τZn1 = 0.61, τZn2 = 0.56). The La(III) ions are decacoordinated in the Zn(II)-La(III) coordination compound and has a distorted bicapped square antiprism geometry. Meanwhile, the photophysical property of the Zn(II)-La(III) coordination compound was also measured and discussed.

Homo- and heterometallic Cu(II)-M(II) (M = Ca, Sr and Ba) bis(salamo)-based complexes: Syntheses, structures and fluorescent properties

Four homo/heterometallic complexes [Cu₃(L)(μ₂-OAc)₉(CH₃OH) ₉]·3CHCl₃ (1), [Cu₂(L)Ca(μ₂-NO₃)₉] (9), [{Cu₂(L)Sr(μ₂-NO₃)₉}₉]·CH₃CH₂OH (11) and [Cu₂(L)Ba(μ₂-OAc)₉(OAc)] (14), containing an acyclic naphthalenediol-based ligand H₄L, were synthesized and characterized by elemental analyses, IR, UV-Vis, fluorescence spectra, TG-DTA and X-ray crystallography. The complex 1 was obtained by the reaction of H₄L with 11 equivalents of Cu(OAc) ₉·2H₂O. The heterometallic complexes 9, 11, 14 were acquired by the reaction of H₄L with 9 equivalents of Cu(OAc)₉·2H₂O or Cu(NO₃)₉·2H₂O and 1 equivalent of M(OAc)₉ (M = Ca, Sr and Ba). Owing to the different coordination cavities of the N₂O₂ and O₆ of the completely deprotonated (L)^14- unit, the crystal structures showed the N₂O₂ sites were occupied by Cu(II) atoms, alkaline earth metal(II) atoms occupied the O₆ site of the ligand (L)^14- unit, respectively. Furthermore, the fluorescence properties and TG-DTA analyses were discussed.

Unusual constructions of two Salamo-based copper(II) complexes

wo unusual Cu(II) complexes [{Cu(L¹)}₂] (1) and [Cu₂(L²)] (2), with an asymmetric salamo-type bisoxime ligand H₂L¹ were synthesized and characterized by elemental analyses, UV-Vis, fluorescent spectra, Hirshfeld surface analyses and single-crystal X-ray diffraction analyses. For the complex 1, two Cu(II) ions are penta-coordinate by N₂O₂ donor atoms from the (L¹)^2- unit and one bridged phenol oxygen atom from another (L¹)^2- unit. Complex 1 does not have intermolecular hydrogen bonds, formed an isolated zero dimensional structure. Meanwhile, for the complex 2, an unexpected ligand H₄L² was synthesized by aldol condensation reaction of H₂L¹ and acetone upon coordination, then the new ligand and Cu(II) ions combined, formed a highly symmetrical structure, and two Cu(II) ions of the complex 2 have tetra-coordinate environment. With the help of intermolecular hydrogen bonding CH⋯O interactions, a self-assembled infinite 1D supramolecular structure was formed. Meanwhile, the photophysical spectra and Hirshfeld surface analyses of the complexes 1 and 2 were also measured and discussed.

Exploration and application of a highly sensitive bis(salamo)-based fluorescent sensor for B4O72- in water-containing systems and living cells

A highly selective fluorescent sensor H4L based on a bis(salamo)-type compound with two N2O2 chelating moieties as ionophore was successfully developed. Sensor H4L was found to have excellent selectivity for B4O72- over many other anions (Br-, CI-, CN-, CO32-, HCO3-, H2PO4-, HSO4-, NO3-, OAc-, S2O3-, SCN-, SO42-, Hcy (homocysteine) and H2O2), and it exhibited an approximately 150-fold enhancement of the fluorescence response to B4O72- in Tris-HCl buffer (DMF/H2O = 9:1, v/v, pH = 7) solutions. Significantly, its fluorescence intensity was enhanced in a linear fashion with increasing concentrations of B4O72-. The detection limit of sensor H4L towards B4O72- was 8.61 × 10-7 M. The test strips could conveniently, efficiently and simply detect B4O72- ions in Tris-HCl buffer (DMF/H2O = 9:1, v/v, pH = 7) solutions. Furthermore, sensor H4L showed excellent membrane permeability in living cells, and it was successfully used to monitor intracellular B4O72- by confocal luminescence imaging.

A novel colorimetric and "turn-on" fluorimetric chemosensor for selective recognition of CN- ions based on asymmetric azine derivatives in aqueous media

A novel chemosensor 2-((Z)-(((E)-quinolin-2-ylmethylene)hydrazono)methyl)phenol PX has been successfully designed and synthesized, which showed both colorimetric and "turn-on" fluorescence responses for CN^- in DMSO/H₂O (3:2, v/v; pH=7.20) solution. The sensor could respond effectively to the stimulation of CN^- ions via deprotonation and sensing mechanism of intramolecular charge transfer (ICT). Moreover, the sensor PX was successfully utilized to detect CN^- in bitter almond, and the detection limit on fluorescence response of PX towards CN^- was down to 4.5×10^-7M. Test strips containing PX were also prepared, which could act as a practical colorimetric tool to detect CN^- in aqueous media.

A heterotrimetallic Ni(II)–Dy(III) bis(salamo)-based complex: synthesis, structure and fluorescent property

A discrete heterotrinuclear complex [{Ni2LDy(OAc)3(CH3OH)}2] · 2CH3OH · 3CH2Cl2, with a naphthalenediol-based acyclic bis(salamo) ligand H4L, has been synthesized and structurally characterized using elemental analyses, IR, UV/Vis and fluorescence spectra and single crystal X-ray diffraction. The crystal structure shows two crystallographically independent but chemically identical molecules (moleculesIandII). All the Ni(II) atoms are hexa-coordinated with slightly distorted octahedral geometries. The central Dy atoms are nona-coordinated with slightly distorted tricapped trigonal prism geometries. An infinite 3D supramolecular structure is formed via intermolecular hydrogen bonding and C–H…π interactions.

Unprecedented Fluorescent Dinuclear CoII and ZnII Coordination Compounds with a Symmetric Bis(salamo)-Like Tetraoxime

Two unprecedented homometallic Co^II and Zn^II coordination compounds, [M₂(L)(OCH₃)][M₂(L)(OAc)] (M^II = Co^II (1) and Zn^II (2)), with a novel symmetric bis(salamo)-like tetraoxime ligand H₃L were synthesized and characterized by elemental analyses, infrafred (IR), ultraviolet–visible spectroscopy (UV-Vis), fluorescent spectra and single-crystal X-ray diffraction analyses. The unit cell of the two coordination compounds contains two crystallographically and chemically independent dinuclear coordination compounds. In the two coordination compounds, three metal ions are five-coordinated, formed two square pyramidal and a trigonal bipyramidal geometries, and the other metal ion is a hexacoordinate octahedral configuration. In addition, the coordination compound 1 forms a 3D supramolecular structure, and the coordination compound 2 forms a 0D dimer structure by the inter-molecular hydrogen bond interactions. Meanwhile, the fluorescence spectra of the coordination compounds 1 and 2 were also measured and discussed.

Synthesis and Fluorescence Properties of Structurally Characterized Heterobimetalic Cu(II)⁻Na(I) Bis(salamo)-Based Complex Bearing Square Planar, Square Pyramid and Triangular Prism Geometries of Metal Centers

A novel heterotrinuclear complex [Cu₂(L)Na(µ-NO₃)]∙CH₃OH∙CHCl₃ derived from a symmetric bis(salamo)-type tetraoxime H₄L having a naphthalenediol unit, was prepared and structurally characterized via means of elemental analyses, UV-Vis, FT-IR, fluorescent spectra and single-crystal X-ray diffraction. The heterobimetallic Cu(II)–Na(I) complex was acquired via the reaction of H₄L with 2 equivalents of Cu(NO₃)₂·2H₂O and 1 equivalent of NaOAc. Clearly, the heterotrinuclear Cu(II)–Na(I) complex has a 1:2:1 ligand-to-metal (Cu(II) and Na(I)) ratio. X-ray diffraction results exhibited the different geometric behaviors of the Na(I) and Cu(II) atoms in the heterotrinuclear complex; the both Cu(II) atoms are sited in the N₂O₂ coordination environments of fully deprotonated (L)⁴⁻ unit. One Cu(II) atom (Cu1) is five-coordinated and possesses a geometry of slightly distorted square pyramid, while another Cu(II) atom (Cu2) is four-coordination possessing a square planar coordination geometry. Moreover, the Na(I) atom is in the O₆ cavity and adopts seven-coordination with a geometry of slightly distorted single triangular prism. In addition, there are abundant supramolecular interactions in the Cu(II)–Na(I) complex. The fluorescence spectra showed the Cu(II)–Na(I) complex possesses a significant fluorescent quenching and exhibited a hypsochromic-shift compared with the ligand H₄L.

Crystal structure of bis{2-((E)-((4-((E)-1-(methoxyimino)ethyl)phenyl)imino)methyl)phenolato-κ2 N,O}zinc(II), C32H30N4O4Zn

C32H30N4O4Zn, triclinic, P1̅ (no. 2), a = 8.6632(8) Å, b = 12.7133(10) Å, c = 14.2719(12) Å, α = 98.585(3)°, β = 94.985(3)°, γ = 92.916(3)°, Z = 2, V = 1545.1(2) Å3, R gt(F) = 0.0714, wR ref(F 2) = 0.1740, T = 296(2) K.

Structural and Luminescent Properties of Heterobimetallic Zinc(II)-Europium(III) Dimer Constructed from N2O2-Type Bisoxime and Terephthalic Acid

A new heterohexanuclear ZnII–EuIII dimer [{(ZnL)2Eu}2(bdc)2]·2Cl constructed from a N2O2-type chelating ligand H2L (6,6′-Dimethoxy-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol), Zn(OAc)2·2H2O, EuCl3·6H2O and H2bdc (terephthalic acid) was synthesized, and characterized using elemental analyses, IR (Infrared), UV-Vis (Ultraviolet–visible) spectra and X-ray single crystal diffraction method. There are two crystallographically equivalent [(ZnL)2Eu] moieties in the ZnII–EuIII complex, the two [(ZnL)2Eu] moieties are linked by two bdc2– ligand leading to a heterohexanuclear dimer, in which the carboxylato groups bridge the ZnII and EuIII atoms. Furthermore, the luminescence properties of H2L and its ZnII–EuIII complex have been studied.

Synthesis and Fluorescence Properties of a New Heterotrinuclear Co(II)-Ce(III)Complex Constructed from a bis(salamo)-Type Tetraoxime Ligand

[Co₂(L)Ce(OAc)₃(CH₃CH₂OH)]·1.5CH₃OH∙0.5CH₂Cl₂, a heterotrinuclear Co(II)-Ce(III) bis(salamo)-type complex with a symmetric bi(salamo)-type ligand H₄L and an acyclic naphthalenediol moiety, was designed, synthesized and characterized by elemental analyses, FT-IR, UV-Vis and fluorescence spectroscopy and X-ray crystallography. The X-ray crystallographic investigation revealed the heterotrinuclear complex consisted of two Co(II) atoms, one Ce(III) atom, one (L)^4‒ unit, three μ₂-acetate ions, one coordinated ethanol molecule, one and half crystallization methanol molecule and half crystallization dichloromethane molecule. Two Co(II) atoms located in the N₂O₂ coordination spheres, are both hexacoordinated, with slightly distorted octahedral geometries. The Ce(III) atom is nine-coordinated and located in the O₆ cavity possesses a single square antiprismatic geometry. In addition, supramolecular interactions exist in the Co(II)-Ce(III) complex. Two infinite 2D supramolecular structures are built via intermolecular O-H···O, C-H···O and C-H···π interactions, respectively.

A Reversible Bis(Salamo)-Based Fluorescence Sensor for Selective Detection of Cd2+ in Water-Containing Systems and Food Samples

A novel, simple, highly selective, and sensitive fluorescence chemosensor for detecting Cd2+ that was constructed from a bis(salamo)-type compound (H₄L) with two N₂O₂ chelating moieties as ionophore was successfully developed. Sensor H₄L could show fluorescence turn-on response rapidly and significant selectivity to Cd2+ over many other metallic ions (Cu2+, Ba2+, Ca2+, K⁺, Cr3+, Mn2+, Sr2+, Co2+, Na⁺, Li⁺, Ni2+, Ag⁺, and Zn2+), and a clear change in color from colorless to yellow that can be very easily observed via the naked eyes in the existence of Cd2+, while other metallic ions do not induce such a change. Interestingly, its fluorescent intensity was increased sharply with the increased concentration of Cd2+. The detection limit of sensor H₄L towards Cd2+ was down to 8.61 × 10-7 M.

Unprecedented Hexanuclear Cobalt(II) Nonsymmetrical Salamo-Based Coordination Compound: Synthesis, Crystal Structure, and Photophysical Properties

A novel hexanuclear Co(II) coordination compound with a nonsymmetrical Salamo-type bisoxime ligandH4L, namely [{Co3(HL)(MeO)(MeOH)2(OAc)2}2]·2MeOH, was prepared and characterized by elemental analyses, UV–vis, IR and fluorescence spectra, and X-ray single-crystal diffraction analysis. Each Co(II) is hexacoordinated, and possesses a distorted CoO6 or CoO4N2 octahedrons. The Co(II) coordination compound possesses a self-assembled infinite 2D supramolecular structure with the help of the intermolecular C–H···O interactions. Meanwhile, the photophysical properties of the Co(II) coordination compound were studied.

Synthesis, crystal structure, luminescence and electrochemical properties of a Salamo-type trinuclear cobalt(II) complex

A trinuclear Co(II) complex, [{CoL(C4H9OH)}2-(OAc)2Co]·C3H7NO, was synthesized by the reaction of a Salamo-type chelating ligand (H2L=4,42′-dinitro-2,2′-[1,2-ethylenedioxybis(nitrilomethylidyne)]diphenol) with cobalt(II) acetate tetrahydrate in n-butanol, and characterized by elemental analyses, X-ray crystallography, FT-IR and UV/Vis spectra. In the Co(II) complex, there are two ligand L2− units, two μ 2-acetate ions, two coordinated n-butanol molecules and one non-coordinated N,N-dimethylformamide molecule. The Co(II) atoms in the structure of the Co(II) complex adopt slightly distorted octahedra geometries. Furthermore, through intermolecular C–H···O, O–H···O and C–H···π interactions, infinite layer-like, plane-like and 3D supramolecular structures are constructed. The fluorescence and electrochemical properties of the Co(II) complex have also been investigated.

A highly selective fluorescent chemosensor for CN- based on a novel bis(salamo)-type tetraoxime ligand

The optical properties of a novel chemosensor for cyanide anions based on a symmetric bis(salamo)-type ligand (H₃L) were investigated by UV-Vis and fluorescence spectroscopy in MeOH/H₂O (1:1 v/v) solution. Sensor H₃L can selectively sense CN^- based on prominent color changes among other anions. The chemosensor exhibits an apparent fluorescence enhancement at 482nm to CN^- which because cyanide ions interact with CN bonds. Combining the corrected Benesi-Hildebrand formula, the binding constant of the formed host-guest complex was calculated as 2.42×10⁵M^-1. Meanwhile, the detection limit of the sensor toward CN^- was 8.91×10^-7M. It is worth noting that the designed sensor can be used for rapid detection of cyanide anions in basic pH range, and has great practical value.

A supramolecular tetranuclear zinc(II) complex constructed from an asymmetrical Salamo-type ligand: synthesis, structure and fluorescence properties

The tetranuclear Zn(II) complex, [{ZnL(μ-OAc)Zn(CH3CH2CH2OH)}2], derived from an asymmetrical Salamo-type chelate ligand H3L (5-methoxy-6′-hydroxy-2,2′-[ethanedioxybis(nitrilomethylidyne)]diphenol) has been synthesized and structurally characterized by elemental analysis, IR spectrum, X-ray crystallography, UV/Vis and fluorescence spectra. The structure is made up of four Zn(II) atoms, μ 2-coordinated acetate ions and two coordinated n-propanol molecules, and forms an infinite one-dimensional supramolecular structure via intermolecular C–H···π interactions. The four Zn(II) atoms are penta-coordinated and show slightly distorted trigonal bipyramidal and tetragonal pyramidal symmetries.

Tri- and Mono-Nuclear Zinc(II) Complexes Based on Half- and Mono-Salamo Chelating Ligands

Two newly designed complexes, [Zn(L1)(EtOH)] (1) and [{Zn(L2)(OAc)2}2Zn]·CHCl3 (2) derived from salamo and half-salamo chelating ligands (H2L1 and HL2) have been synthesized and characterized by elemental analyses, IR and UV-VIS spectra, fluorescence spectra, and X-ray crystallography. Complex 1 shows a slightly distorted tetragonal pyramid and forms an infinite 3D supramolecular structure. All of the Zn(II) ions in complex 2 are hexa-coordinated with slightly distorted octahedral geometries. Complex 2 possesses an infinite 2D space structure. The fluorescence titration experiments were used to characterize fluorescence properties of complexes 1 and 2. And the normalized fluorescent spectra exhibit that complexes 1 and 2 have favourable fluorescent emissions in different solvents.

Two Supramolecular Cobalt(II) Complexes: Syntheses, Crystal Structures, Spectroscopic Behaviors, and Counter Anion Effects

Two new Co(II) complexes, [{Co(L)}2{Co(Pic)2(CH3OH)2}] (1) and [{CoL(μ-OAc)}2Co] (2), where H2L = 2,2′-[Ethylenedioxybis(nitrilomethylidyne)]dinaphthol, were designed, synthesized and characterized by elemental analysis, FT-IR spectra, UV-Vis spectra, and X-ray crystallography. Complex 1 consists of two [CoL] and one [Co(Pic)2(CH3OH)2] (Pic = picrate) units and in the [CoL] unit, the Co(II) atom is tetra-coordinated with a slightly distorted square-planar geometry. In the [Co(Pic)2(CH3OH)2] unit, the Co(II) atom is hexa-coordinated with a slightly distorted octahedral geometry. Meanwhile in complex 2, two acetate ions coordinate to three Co(II) atoms through Co-O-C-O-Co bridges and four μ-naphthoxo oxygen atoms from two [CoL] units also coordinated to the central Co(II) atom. Thus, complex 2 has two distorted square pyramidal coordination geometries around the terminal Co(II) atom and an octahedral geometry around the central Co(II) atom. The supramolecular structures of complex 1 is a 3D-network supramolecular structure linked by C-H···O hydrogen bonds and π···π stacking interaction, but complex 2 possesses a self-assembled 2D-layer supramolecular structure linked by C-H···π and π···π stacking interactions. The structure determinations show that the coordination anions are important factors influencing the crystalline array.

Syntheses, Crystal Structures and Thermal Behaviors of Two Supramolecular Salamo-Type Cobalt(II) and Zinc(II) Complexes

This paper reports the syntheses of two new complexes, [Co(L1)(H2O)2] (1) and [{Zn(L2)(μ-OAc)Zn(n-PrOH)}2] (2), from asymmetric halogen-substituted Salamo-type ligands H2L1 and H3L2, respectively. Investigation of the crystal structure of complex 1 reveals that the complex includes one Co(II) ion, one (L1)2− unit and two coordinated water molecules. Complex 1 shows slightly distorted octahedral coordination geometry, forming an infinite 2D supramolecular structure by intermolecular hydrogen bond and π–π stacking interactions. Complex 2 contains four Zn(II)ions, two completely deprotonated (L2)3− moieties, two coordinated μ-OAc− ions and n-propanol molecules. The Zn(II) ions in complex 2 display slightly distorted trigonal bipyramidal or square pyramidal geometries.

Tri- and hexanuclear heterometallic Ni(ii)–M(ii) (M = Ca, Sr and Ba) bis(salamo)-type complexes: synthesis, structure and fluorescence properties

Tri- and hexanuclear Ni(ii)–M(ii) (M = Ca, Sr and Ba) complexes have been synthesized and characterized structurally. Fluorescence titration experiments show that the coordinating capabilities in the central O₆ site are in the order of Ca(ii) > Sr(ii) > Ba(ii).