Alfonso Castiñeiras

A 2-naphthyl functionalized thiosemicarbazone has been synthesized in high yield by means of a Schiff base condensation reaction. The 2-(naphthalen-2-ylmethylene)hydrazinecarbothioamide (Hnatsc, 1) reacts with zinc(II) and cadmium(II) chlorides and acetates to obtain neutral complexes of formulae: [ZnCl2(Hnatsc)2]·H2O (2·H2O), [Zn(natsc)2]·3H2O (3·3H2O), [Zn(natsc)2(Hnatsc)2]·3H2O (4·3H2O), [Zn(OAc)(natsc)(Hnatsc)]·2H2O (5·2H2O), [CdCl2(Hnatsc)2] (6), [Cd(natsc)2] (7), and [Cd(OAc)(natsc)(MeOH)] (8), in which the thiosemicarbazone functions as a monodentate thione ligand or as a deprotonated bidentate chelating ligand coordinating to the metal ions via the imine nitrogen and thiolate sulfur atoms. The characterization of all compounds was through a combination of analytical techniques, including elemental analysis, nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, and electrospray ionization (ESI) mass spectrometry. The molecular and crystal structures of Hnatsc and complexes 2 and 6 were determined by means of single-crystal X-ray diffraction. Furthermore, a fluorescence study was conducted on the thiosemicarbazone and the complexes. A density functional theory (DFT) study using MEP, QTAIM, and NCIplot analyzed the supramolecular architecture, revealing that metal coordination significantly strengthens hydrogen-bonded synthons. Furthermore, TD-DFT calculations provided insight into the photophysical properties, confirming the ligand-centered nature of the electronic transitions and identifying high internal conversion rates as the primary quenching mechanism in the zinc complex 2.

The reaction of the thiazolidinone-based ligands HAm4DHotaz, Am4Motaz, and Am4Eotaz with AgClO₄ in a 1:1 molar ratio yields complexes of varying nuclearities depending on the N_{thiazolidinone} R-substituent. The unsubstituted HAm4DHotaz (R = H) affords the coordination polymer {[Ag­(HAm4DHotaz)]­(ClO₄)} _n (1) whereas Am4Motaz (R = Me) and Am4Eotaz (R = Et) lead to the discrete mononuclear complexes [Ag­(Am4Motaz)₂]­(ClO₄) (2) and [Ag­(Am4Eotaz)₂]­(ClO₄)] (3), respectively, as the main products. From the corresponding mother liquors, small amounts of the coordination polymers {[Ag­(Am4Motaz)­(ClO₄)]} _n (4) and {[Ag₂(Am4Eotaz)₂(H₂O)­(ClO₄)]­(ClO₄)·H₂O} _n (5·H₂O) were also obtained. In addition, the reaction of AgNO₃ with Am4Eotaz in 1:1 or 0.5:1 molar ratio leads to [Ag­(Am4Motaz)₂]­(NO₃)·H₂O (6·H₂O), while the mother liquors of the 0.5:1 experiment produced small amounts of the coordination polymer {[Ag₂(Am4Motaz)₃]­(NO₃)₂·H₂O} _n (7·H₂O). X-ray diffraction analyses of all the complexes highlight the remarkable coordination versatility of these ligands, revealing five distinct binding modes, including the unprecedented tridentate μ₂-κ²NN′:κ¹N″ and μ₂-κ¹N:κ²N′S bridging motifs, as well as the two rarely reported modes μ₂-κ²NN′:κ¹S and μ₂-κ³NN′S:κ¹. In addition, photophysical studies also highlight a pronounced dependence of the emission properties on the N_{thiazolidinone} R-substituent. Notably, although Ag⁺ coordination quenches ligand-centered emission in all cases, [Ag­(Am4Eotaz)₂]­(ClO₄)] (3) stands out as the only complex that remains emissive.

The reactions of silver-(I) nitrate with N-substituted thiosemicarbazones derived from 5-acetylbarbituric acid (H₂Acb4R, R = NH₂, NHCH₃, N-(CH₃)₂, piperidine (Pip), or hexamethylenimine (hexim) in the presence of triphenylphosphine and triethylamine form a series of silver-(I) complexes with various structural motifs and different coordination geometries at the metal, with the composition [Ag-(PPh₃)₂(HAcb4NH₂)] (1), [Ag-(PPh₃)₃(HAcb4NH₂)]·EtOH·H₂O (2), Ag-(PPh₃)-(H₂Acb4NHM)-(NO₃)·2H₂O (3), [Ag-(PPh₃)₃(HAcb4NHM)]·2EtOH (4), Ag-(PPh₃)-(H₂Acb4NHM)₂(NO₃)·3H₂O (5), [Ag-(PPh₃)₃(HAcb4NDM)]·3EtOH (6), [Ag-(PPh₃)₃(HAcb4NDM)]·2DMSO·H₂O (7), [Ag-(PPh₃)-(HAcb4Pip)]₃·4.5H₂O (8) and [Ag-(PPh₃)₃(HAcb4Hexim)]·3EtOH·3H₂O (9), and {[Ag-(H₂O)₁₄]-(NO₃)}-n, [Ag-(PPh₃)₄]-(NO₃)·EtOH, [AgCl-(PPh₃)]₄ as byproducts. In many cases, polycrystalline samples of these compounds were characterized using elemental analysis, FT-IR, UV-Visible, ¹H, ¹³C-{¹H} and ³¹P-{¹H} NMR spectroscopy, FAB-MS, and single-crystal X-ray crystallography. The spectroscopic properties and structures of these compounds, except 1, 3, and 5, are discussed. Various hydrogen-bonding interactions, such as N-H···O, O-H···O, C-H···O, and π-π stacking interactions, contribute to the crystal packing. The influence of these weak interactions has been addressed with the help of Hirshfeld surface analyses and further analyzed using DFT calculations and Bader's theory of atoms-in-molecules.

A coordination polymer is synthesized via the reaction of a mixture of Pb(ClO₄)₂ and KCN with N'-isonicotinoylpicolinohydrazonamide (HL), leading to the formation and stabilization of a {[Pb₃L₃(OAc)(H₂O)](ClO₄)₂}_n·nH₂O (1·nH₂O) network, with the formation and trapping of the acetate anion. Using the sodium N-(amino(pyridin-2-yl)methylene)isonicotinohydrazonate (NaL) instead of HL yields complex [Pb₂L₂OH](ClO₄)·H₂O (2·H₂O) with the formation and trapping of the hydroxide anion. In 1·nH₂O, an almost linear aggregate is produced when the 4-pyridine fragments of the two [PbL]⁺ are coordinated to the metal cation of the third species, joining the three [PbL]⁺ cations. In 1·nH₂O, supramolecular stability is enhanced by Pb···O and Pb···π interactions involving the electron-rich core (Cg) of a ten-membered hydrogen-bonded ring, indicative of tetrel-type bonding. [Pb₂L₂OH]⁺ in 2·H₂O is formed, when a pair of the [PbL]⁺ cations are joined by a hydroxide anion. The Pb···N tetrel bonds bind [Pb₂L₂OH]⁺ to form a zigzag-like 1D supramolecular cationic chain. Both complexes are emissive in methanol. The emission profiles of 1·nH₂O and 2·H₂O in MeOH correspond to CIE-1931 chromaticity coordinates of (0.406, 0.492) and (0.420, 0.498), placing them within the yellow-green region of the visible spectrum. DFT studies are applied to reveal noncovalent interactions, including tetrel bonding, governing the supramolecular architectures. Electrostatic potential and QTAIM analyses confirm the presence of σ-holes at the Pb²⁺ cation in both structures.

This work presents an efficient and straightforward method for obtaining two previously described thiazolidinone-based ligands, HAm4DHotaz (N'-(4-oxothiazolidin-2-ylidene)picolino-hydrazonamide) and Am4Eotaz (N'-(3-ethyl-4-oxothiazol-idin-2-ylidene)picolinohydrazonamide), with high yield and purity. Moreover, the reactivity of these ligands toward different Ag⁺ salts has been explored, resulting in the isolation of four novel coordination complexes: two mononuclear species, [Ag(HAm4DHotaz)₂](NO₃)·H₂O (1·H₂O) and [Ag(Am4Eotaz)₂](NO₃) (2), and two tetranuclear compounds, [Ag₄(Am4DHotaz)₄]·8H₂O (3·8H₂O) and [Ag₄(Am4Eotaz)₄(NO₃)₂(H₂O)](NO₃)₂·1.18H₂O (4·1.18H₂O). The crystal structures of 1·H₂O, 2, 4·1.18H₂O, and 3·3DMF, the latter obtained by recrystallization of [Ag₄(Am4DHotaz)₄]·8H₂O in dimethylformamide, have been determined. Notably, in 4·1.18H₂O, the thiazolidinone moiety shows the unprecedented bridging mode μ₂-κ¹S:κ¹S. In addition, 3·3DMF represents a rare example of a thiazolidinone-containing complex featuring a μ₂-κ¹N:κ¹S bridge. Moreover, across these complexes, the Am4Rotaz (R = DH or E) ligands display five hitherto unknown coordination modes. These ligands, and the auxiliary donors (present in 4·1.18H₂O), provide different Ag⁺ coordination environments: AgN₄ cores with a seesaw geometry in the mononuclear complexes, and AgN₂, AgN₂S, AgN₄, AgN₂OS, AgN₂S₃ or AgN₂O₂S₃ cores with varied geometries in the tetranuclear ones. Furthermore, structures of the polynuclear species reveal significant argentophilic Ag···Ag interactions, which play a key role in directing the formation of the multinuclear frameworks.

Inspired by the reported crystal structure of compound 1, we aimed to synthesize and determine the structure of compound 2, where two imidazolium (H₂im⁺) ions serve as diamagnetic countercations. Here, we report the thermal stabilities, FT–IR, visible, and RSE spectra, as well as the magnetic properties of both compounds. In these structures, µ-EDTA acts as a pentadentate chelator for both terminal Cu centers within the centrosymmetric linear trinuclear anion. The Cu(µ-EDTA) chelates bind to the central Cu(Him)₄ unit in subtly different ways: in compound 1, µ-EDTA has a free acetate arm and binds the central Cu(II) center through a syn,anti-carboxylate group. In contrast, in compound 2, the non-chelating acetate arm serves as a monodentate O-donor to the central Cu(II) atom, increasing the Cu(terminal)···Cu(central) distance from 6.08 Å in 1 to 6.80 Å in 2. Additionally, pairs of H₂im⁺ ions in compound 2 display antiparallel π-stacking interactions. We conclude that the H₂im⁺ counterions in compound 2 enable the magnetic isolation of the nearly identical trinuclear anion present in both compounds. DFT calculations further support the role of different interactions in stabilizing each crystal structure. In compound 2, dominant contributions from N–H···O hydrogen bonds and π-stacking interactions are accompanied by other, less conventional interactions, such as multiple C–H···O contacts and an O···CO(π-hole) interaction within the trinuclear anion.

Inspired by the reported crystal structure of compound 1, we aimed to synthesize and determine the structure of compound 2, where two imidazolium (H₂im⁺) ions serve as diamagnetic counter cations. Here, we report the thermal stabilities, FT-IR, visible, and RSE spectra, as well as the magnetic properties of both compounds. In these structures, µ-EDTA acts as a pentadentate chelator for both terminal Cu centers within the centrosymmetric linear trinuclear anion. The Cu(µ-EDTA) chelates bind to the central Cu(Him)₄ unit in subtly different ways: in compound 1, µ-EDTA has a free acetate arm and binds the central Cu(II) center through a syn,anti-carboxylate group. In contrast, in compound 2, the non-chelating acetate arm serves as a monodentate O-donor to the central Cu(II) atom, increasing the Cu(terminal)···Cu(central) distance from 6.08 Å in 1 to 6.80 Å in 2. Additionally, pairs of H₂im⁺ ions in compound 2 display antiparallel π-stacking interactions. We conclude that the H₂im⁺ counterions in compound 2 enable the magnetic isolation of the nearly identical trinuclear anion present in both compounds. DFT calculations further support the role of different interactions in stabilizing each crystal structure. In compound 2, dominant contributions from N–H···O hydrogen bonds and π-stacking interactions are accompanied by other, less conventional interactions, such as multiple C–H···O contacts and an O···CO(π-hole) interaction within the trinuclear anion.