0D to 3D Coordination Assemblies Engineered on Silver(I) Salts and 2‐(Alkylsulfanyl)azine Ligands: Crystal Structures, Dual Luminescence, and Cytotoxic Activity

Molecular Switches Guided by a Reversible Access to Room-Temperature Phosphorescence and ESIPT Fluorescence

This work contributes to luminescent molecular switches featuring several emission pathways, which can be activated by external stimuli. We designed Zn complexes with phenylbenzothiazole-based α-aminomethylphosphine oxide (L) and isolated them as crystalline phases, α-[ZnL2Cl2], [ZnL(EtOAc)Cl2], [ZnL2Cl2]·1.5CH2Cl2, and [ZnL2Cl2]·1.5CHCl3. They feature an intramolecular hydrogen bond of medium strength, capable of excited-state intramolecular proton transfer (ESIPT), as well as able for intersystem crossing between singlet and triplet states. Since neither of these processes is predominant, one or the other can occur depending on a slight change in a molecular geometry. The crystalline phases reveal red-colored ESIPT fluorescence, while a metastable amorphous phase β-[ZnL2Cl2] with a similar structure of the coordination center reveals yellow-colored room-temperature phosphorescence. Combined experimental and quantum-chemical TD-DFT study clarified the dual emission behavior for the polymorphs α-[ZnL2Cl2] and β-[ZnL2Cl2], which is attributed to the high dependence of the probability of the excited-state processes on the geometry of the phenylbenzothiazole moiety. The reversible phase transition, accompanied by the change in the emission mechanism (ESIPT fluorescence vs phosphorescence), can be manipulated by fuming with CHCl3 and Et2O, respectively. We have demonstrated good adhesive properties of the polymer-free β-[ZnL2Cl2] film toward glass and plastic, naked-eye color response to fuming with Et2O, and easy recovery with CHCl3.

A Silver Nanocluster Assembled by a Superatomic Building Unit

A unique assembly of a two-electron superatom, [Ag10{S2P(OiPr)2}8], as a primary building unit in the construction of a supramolecule [Ag10{S2P(OiPr)2}8]2(μ-4,4'-bpy) through a 4,4'-bipyridine (4,4'-bpy) linker is reported. This approach is facilitated by an open site in the structure that allows for effective pairing. The assembled structure demonstrates a minimal solvatochromic shift across organic solvents with variable polarities, highlighting the influence of self-assembly on the photophysical properties of silver nanoclusters.

Complexes of 2-Amino-3-methylpyridine and 2-Amino-4-methylbenzothiazole with Ag(I) and Cu(II): Structure and Biological Applications

Coordination complexes (1–4) of 2-amino-4-methylbenzothiazole and 2-amino-3-methylpyridine with Cu(CH3COO)2 and AgNO3 were prepared and characterized by UV/Vis and FT-IR spectroscopy. The molecular structure for single crystals of silver complexes (2 and 4) were determined by X-ray diffraction. The coordination complex (2) is monoclinic with space group P21/c, wherein two ligands are coordinated to a metal ion, affording distorted trigonal geometry around the central Ag metal ion. The efficient nucleophilic center, i.e., the endocyclic nitrogen of the organic ligand, binds to the silver metal. Ligands are coordinated to adopt cis arrangement, predominantly due to steric reasons. The O(2) and O(3) atoms of the NO3− group further play an important role in such type of ligand arrangement by hydrogen bonding with the NH2 group of ligands. Complex (4) is orthorhombic, P212121, comprising two molecules of 2-amino-3-methylpyridine as ligand coordinated with the metal ion, affording a polymeric structure. The coordination behavior of the ligand is identical to that in complex 2, wherein ring nitrogen is coordinated to the metal center and bridged to another metal ion through an NH2 group. The resulting product is polymeric in nature with the Ag metal in the backbone and ligand as the bridge. Compounds (2–4) were found to be luminescent, while 1 did not show such activity. All compounds were screened for their preliminary biological activities such as antibacterial, antioxidant and enzyme inhibition. Compounds exhibited moderate activity in these tests.

Three new Zn(ii) coordination polymers for highly selective and sensitive detection of Fe3+

In this work, three novel Zn(ii)-CPs with diverse structures and fascinating topologies can be highly selective and sensitive luminescent sensors for detection of Fe3+.

Computational Study on the Nature of Bonding between Silver Ions and Nitrogen Ligands

In this paper, the nature of silver ion-nitrogen atom bonding in the complexation with ammonia, azomethine, pyridine, and hydrogen cyanide from one to four coordinations is studied at the B97-1 level of density functional theory. The results indicate that the two-coordinated complex of the silver ion with different nitrogen ligands representing sp, sp², and sp³ orbital hybridizations is the most stable form having the shortest Ag⁺-N bond distance, highest vibrational frequencies, largest bond order, and favorable Gibbs free energy of formation. Natural bond orbital analyses further show that σ-donation from the nitrogen lone pair to the silver empty 5s orbital is dominant in the dative metal-ligand bonding character with N-sp³ having the largest contribution among the different N atomic orbital hybridizations. Natural energy decomposition analyses further show that the two-coordinated complexes have enhanced electrostatic interaction and charge transfer energies over other coordination types leading them to be more stable. For this reason, the two-coordinated complexes would be a better representation for studying bonding and interaction in silver ion complexes.

Trapping of Ag+ into a Perfect Six-Coordinated Environment: Structural Analysis, Quantum Chemical Calculations and Electrochemistry

Self-assembly of (Bu4N)4[β-Mo8O26], AgNO3, and 2-bis[(2,6-diisopropylphenyl)-imino]acenaphthene (dpp-bian) in DMF solution resulted in the (Bu4N)2[β-{Ag(dpp-bian)}2Mo8O26] (1) complex. The complex was characterized by single crystal X-ray diffraction (SCXRD), X-ray powder diffraction (XRPD), diffuse reflectance (DR), infrared spectroscopy (IR), and elemental analysis. Comprehensive SCXRD studies of the crystal structure show the presence of Ag+ in an uncommon coordination environment without a clear preference for Ag-N over Ag-O bonding. Quantum chemical calculations were performed to qualify the nature of the Ag-N/Ag-O interactions and to assign the electronic transitions observed in the UV-Vis absorption spectra. The electrochemical behavior of the complex combines POM and redox ligand signatures. Complex 1 demonstrates catalytic activity in the electrochemical reduction of CO2.

Iodine(i) complexes incorporating sterically bulky 2-substituted pyridines

The silver(i) and iodine(i) complexes of the 2-substituted pyridines 2-(diphenylmethyl)pyridine (1) and 2-(1,1-diphenylethyl)pyridine (2), along with their potential protonated side products, were synthesised to investigate the steric limitations of iodine(i) complex formation. The complexes were characterised by ¹H and ¹H–¹⁵N HMBC NMR, X-ray crystallography, and DFT calculations. The solid-state structures for the silver(i) and iodine(i) complexes were extensively compared to the literature and analysed by DFT to examine the influence of the sterically bulky pyridines and their anions.

The silver(i) and iodine(i) complexes of two sterically bulky 2-substituted pyridines, along with their potential protonated side products, were synthesised to investigate the steric limitations of iodine(i) ion formation.

Anion-controlled Zn(II) coordination polymers with 1-(tetrazo-5-yl)-3-(triazo-1-yl) benzene as an assembling ligand: synthesis, characterization, and efficient detection of tryptophan in water

Tryptophan regulates and participates in various physiological systems in the human body, and its excessive intake has harmful effects. Therefore, detecting and monitoring tryptophan in water and distinguishing it from other amino acids are necessary. In addition to their excellent luminescence, coordination polymer-based sensors have good stability and high sensitivity and selectivity for sensing applications. In this work, two luminescent coordination polymers (CPs), [Zn(ttb)Cl]_n (1) and [Zn₂(ttb)₂(OH)(NO₃)]_n (2), were obtained through the solvothermal reaction of different Zn(II) salts with a rarely studied multidentate N-donor ligand, 1-(tetrazo-5-yl)-3-(triazo-1-yl) benzene (Httb). Crystallographic investigations revealed that the structure of 1 exhibits a 2D fes net with Cl^- anions acting as terminal charge balancers, and that of 2 features a 3D ant net with NO₃^- anions in a rare monodentate bridging (μ₂-O-η¹:η¹) mode. In terms of stability tests, 2 has better thermal and water stability than 1. Although both show good fluorescence performance, specific tryptophan detection, and excellent anti-interference ability, 2 has higher K_SV (111 852.6 M^-1), a lower limit of detection (LOD = 23.6 nM), and a better recovery rate than 1. Cytotoxicity experiments proved that 2 has extremely low toxicity and thus has great potential for in vivo detection. Therefore, CP 2 is a suitable candidate for advanced practical applications for the efficient sensing of tryptophan in water. The luminescence of the ligands was also calculated using DFT theory and further discussed through experiments. The quenching mechanism that occurs after tryptophan addition was explored through Hirshfeld surface analysis.

Coordination-induced emission enhancement in copper(I) iodide coordination polymers supported by 2-(alkylsulfanyl)pyrimidines

First examples of copper(i) complexes with 2-(alkylsulfanyl)pyrimidine ligands have been synthesized. Reactions of copper(i) iodide with 2-(methylsulfanyl)pyrimidine (L1) in various metal-to-ligand molar ratios in MeCN afford a ladder-type coordination polymer [Cu2L1I2]n with polymeric chains built from double-stranded (Cu2I2)n ribbons supported on both sides by μ2-N,S-L1 molecules. Although the second ligand, 2-(ethylsulfanyl)pyrimidine (L2), differs from L1 only by a methylene group, its reactions with copper(i) iodide in MeCN yield not only a congenerous coordination polymer, [Cu2L2I2]n, but also [CuL2I]n, in which a similar (Cu2I2)n ribbon is decorated by N-monodentate L2 molecules. Absorption spectra of all compounds represent an interplay of metal + iodine-to-ligand charge transfer (XMLCT) and ligand-centered (LC) and cluster-centered (CC) transitions, while the emission occurs from the excited states of XMLCT nature. The luminescence of [Cu2L1I2]n and [Cu2L2I2]n is blue-shifted and greatly enhanced in comparison with that of [CuL2I]n (quantum yields: 89% and 68% for [Cu2L1I2]n and [Cu2L2I2]nvs. 23% for [CuL2I]n at 77 K), which can be associated with a more rigid μ2-N,S coordination of 2-(alkylsulfanyl)pyrimidine ligands in [Cu2L1I2]n and [Cu2L2I2]n leading to a less distorted T1 state.

Synthesis and Thermochromic Luminescence of Ag(I) Complexes Based on 4,6-Bis(diphenylphosphino)-Pyrimidine

Two Ag(I)-based metal-organic compounds have been synthesized exploiting 4,6-bis(diphenylphosphino)pyrimidine (L). The reaction of this ligand with AgNO3 and AgBF4 in acetonitrile produces dinuclear complex, [Ag2L2(MeCN)2(NO3)2] (1) and 1D coordination polymer, [Ag2L(MeCN)3]n(BF4)2n (2), respectively. In complex 1, µ2-P,P′-bridging coordination pattern of the ligand L is observed, whereas its µ4-P,N,N′,P′-coordination mode appears in 2. Both compounds exhibit pronounced thermochromic luminescence expressed by reversible changing of the emission chromaticity from a yellow at 300 K to an orange at 77 K. At room temperature, the emission lifetimes of 1 and 2 are 15.5 and 9.4 µs, the quantum efficiency being 18 and 56%, respectively. On account of temperature-dependent experimental data, the phenomenon was tentatively ascribed to alteration of the emission nature from thermally activated delayed fluorescence at 300 K to phosphoresce at 77 K.