H2O Ligands Research Articles

Exploring Aqueous Coordination Chemistry of Highly Lewis Acidic Metals with Emerging Isotopes for Nuclear Medicine.

Nuclear medicine harnesses radioisotopes for the diagnosis and treatment of disease. While the isotopes 99mTc and 111In have enabled the clinical diagnosis of millions of patients over the past 3 decades, more recent clinical translation of numerous 68Ga/177Lu-based radiopharmaceuticals for diagnostic imaging and therapy underscores the clinical utility of metal-based radiopharmaceuticals in mainstream cancer treatment. In addition to such established radionuclides, advancements in radioisotope production have enabled the production of radionuclides with a broad range of half-lives and emission properties of interest for nuclear medicine. Chemical means to form kinetically inert, in vivo-compatible species that can be modified with disease-targeting vectors is imperative. This presents a challenge for radiosiotopes of elements where the aqueous chemistry is still underdeveloped and poorly understood. Here, we discuss our efforts to date in exploring the aqueous, radioactive coordination chemistry of highly Lewis acidic metal ions and how our discoveries apply to the diagnosis and treatment of cancer in preclinical models of disease. The scope of this Account includes approaches to aqueous coordination of to-date understudied highly Lewis acidic metal ions with radioisotopes of emerging interest and the modulation of well-understood coordination environments of radio-coordination complexes to induce metal-catalyzed reactivity for separation and pro-drug applications.First, we discuss the development of seven-coordinate, small-cavity macrocyclic chelator platform mpatcn/picaga as an exemplary case study, which forms robust complexes with 44Sc/47Sc isotopes. Due to the high chemical hardness and pronounced Lewis acidity of the Sc3+ ion, the displacement of ternary ligand H2O by 18/natF- can be achieved to form an inert Sc-18/natF bond. Corresponding coordination complex natSc-18F is in vivo compatible and forms a theranostic tetrad with corresponding 44Sc/47Sc, 177Lu complexes all exhibiting homologous biodistribution profiles. Another exceptionally hard, highly Lewis acidic ion with underdeveloped aqueous chemistry and emerging interest in nuclear medicine is 45Ti4+. To develop de novo approaches to the mononuclear chelation of this ion under aqueous conditions, we employed a fragment-based bidentate ligand screening approach which identified two leads. The screen successfully predicted the formation of [45Ti][Ti(TREN-CAM)], a Ti-triscatechol complex that exhibits remarkable in vivo stability. Furthermore, the fragment-based screen also identified approaches that enabled solid-phase separation of Ti4+ and Sc3+ of interest in streamlining the isotope production of 45Ti and accessing new ways to separate 44Ti/44Sc for the development of a long-lived generator system. In addition to establishing the inert chelation of Ti4+ and Sc3+, we introduce controlled, metal-induced reactivity of corresponding coordination complexes on macroscopic and radiotracer scales. Metal-mediated autolytic amide bond cleavage (MMAAC) enables the temperature-dependent release of high-molar-activity, ready-to-inject radiopharmaceuticals; cleavage is selectively triggered by coordinated trivalent Lewis acid nat/68Ga3+ or Sc3+. Following the scope of reactivity and mechanistic studies, we validated MMAAC for the synthesis of high-molar-activity radiopharmaceuticals to image molecular targets with low expression and metal-mediated prodrug hydrolysis in vivo.This Account summarizes how developing the aqueous coordination chemistry and tuning the chemical reactivity of metal ions with high Lewis acidity at the macroscopic and tracer scales directly apply to the radiopharmaceutical synthesis with clinical potential.

N^N^C-Cyclometalated rhodium(III) complexes with isomeric pyrimidine-based ligands: unveiling the impact of isomerism on structural motifs, luminescence and cytotoxicity.

The impact of isomerism of pyrimidine-based ligands and their rhodium(III) complexes with regard to their structures and properties was investigated. Two isomeric ligands, 4-(3,5-dimethyl-1H-pyrazol-1-yl)-2,5-diphenylpyrimidine (HL2,5) and 4-(3,5-dimethyl-1H-pyrazol-1-yl)-2,6-diphenylpyrimidine (HL2,6), were synthesized. The ligands differ by the degree of steric bulk: the molecular structure of HL2,5 is more distorted due to presence of pyrazolyl and phenyl groups in the neighbouring positions 4 and 5 of the pyrimidine ring. The complexation of HL2,5 and HL2,6 with RhCl3 leads to the sp2 C-H bond activation, resulting in the isolation of two complexes, [RhL2,5(Solv)Cl2]·nEtOH and [RhL2,6(Solv)Cl2]·nEtOH (Solv = H2O, EtOH), with the deprotonated forms of the pyrazolylpyrimidine molecules which coordinate the Rh3+ ion as N^N^C-tridentate ligands. According to DFT modelling, the mechanism of the deprotonation involves (i) the C-H bond breaking in the 2-phenyl group followed by the coordination of the C atom to the Rh atom, (ii) the protonation of coordinated chlorido ligand, (iii) the ejection of the HCl molecule and (iv) the coordination of the H2O molecule. The ligand isomerism has an impact on emission properties and cytotoxicity of the complexes. Although the excited states of the complexes effectively deactivate through S0/T1 and S0/S1 crossings associated with the cleavage of the weak H2O ligands upon excitation, the [RhL2,5(Solv)Cl2]·nEtOH complex appeared to be emissive in the solid state, while [RhL2,6(Solv)Cl2]·nEtOH is non-emissive at all. The complexes show significant cytotoxic activity against cancerous HepG2 and Hep2 cell lines, with the [RhL2,6(Solv)Cl2]·nEtOH complex being more active than its isomer [RhL2,5(Solv)Cl2]·nEtOH. On the other hand, noticeable cytotoxicity of the latter against HepG2 is supplemented by its non-toxicity against non-cancerous MRC-5 cells.

Direct evidence for ligand-enhanced activity of Cu(i) sites.

Little is known about the strong mediating effect of the ligand sphere and the coordination geometry on the strength and isotopologue selectivity of hydrogen adsorption on the undercoordinated copper(i) site. Here, we explore this effect using gas-phase complexes Cu+(H2O)(H2) n (with n ≤ 3) as model systems. Cu+(H2O) attracts dihydrogen (82 kJ mol -1) more strongly than bare Cu+ (64 kJ mol -1) does. Combining experimental and computational methods, we demonstrate a high isotopologue selectivity in dihydrogen binding to Cu+(H2O), which results from a large difference in the adsorption zero-point energies (2.8 kJ mol-1 between D2 and H2, including an anharmonic contribution of 0.4 kJ mol-1). We investigate its origins and the bond strengthening between Cu+ and H2 upon addition of a single H2O ligand. We discuss the role of the environment and the coordination geometry of the adsorption site in achieving a high selectivity and the ramifications for identifying and designing future materials for adsorptive dihydrogen isotopologue separation.

Complexation of Zr and Hf in fluoride-rich hydrothermal aqueous fluids and its significance for high field strength element fractionation

Zirconium and hafnium behave nearly identically in most geological processes due to their identical nominal ionic charge and similar radius. Some of the most pronounced exceptions from this rule are observed in fluoride-rich aqueous systems, suggesting that aqueous fluoride complexation may be involved in Zr/Hf fractionation. To understand the mechanisms causing this phenomenon, we investigated complexation of Zr4+ and Hf4+ in fluoride-rich (1.0 mol/kg HF) aqueous solutions at 40 MPa and 100–400 °C, using synchrotron X-ray absorption spectroscopy (X-ray absorption near edge structure and extended X-ray absorption fine structure) combined with classical and ab initio molecular dynamics simulations. The dominant experimentally observed complexes are [Zr(F,OH)4·2H2O]0 and [Hf(F,OH)4·2H2O]0, respectively. The first coordination shell comprises a distorted octahedron, with fluoride and hydroxide ligands at a similar mean radial distance (1.9–2.0 Å) from the central cation, and H2O ligands at a slightly greater distance (>2.1 Å). With increasing temperature, the H2O ligands move further out, causing first an increasing distortion of the octahedron and subsequently a partial transition to less hydrated complexes as a certain fraction of the H2O molecules move to the second shell at > 3 Å. As a consequence, the radial distance of the F- and OH– anions from the central cation, as well as the overall average radial distance of the first shell decreases due to decreased steric repulsion from the H2O ligands. Both experiments and simulations agree in that Hf forms slightly shorter bonds to its nearest neighbors than Zr. The results suggest two hypotheses for the mechanism of Zr/Hf fractionation during precipitation of minerals from fluoride-rich hydrothermal solutions: 1) The heavy twin (Hf) prefers the lower coordination (shorter bonds) and is thus less likely to enter into the higher coordination found in the solids. This mechanism would be analogous to equilibrium isotope fractionation. 2) The change of Hf into a higher coordination environment (e.g., from solution to solid) is slower because it forms stronger ligand-bonds than Zr. This would be analogous to reactive kinetic isotope fractionation. In either case mass dependent fractionation qualitatively matches the observations but mass independent effects on bond strength may also be significant. Quantitative investigations of these effects are needed and may also shed light on the currently still somewhat enigmatic fractionation behavior of Zr isotopes.

Computational study of the interaction of DNA bases with vanadium(IV) and (V) complexes derived from the anticancer VCp2Cl2

We present a computational study on derivatives of the anticancer VCp2Cl2 and their interaction with bases of DNA. The derivatives were obtained by substituting the cyclopentadiene of VCp2Cl2 by ligands H2O, NH3, C2O42−, OH−, Cl− and O2−. Oxidation states IV and V of vanadium were considered, a total of 20 complexes are included. This study addresses the role of ligands in the interaction of vanadium complexes with nucleophilic sites of guanine, adenine, cytosine and thymine. The methodology M06-2X/cc-pVTZ was employed, and the effects of the solvent were considered. Results suggest that there is a high affinity for guanine and cytosine, particularly when H2O and NH3 ligands are considered. These findings are confirmed by the bond lengths, bond orders and charge analysis. Our results provide a clue about the ligands that favor the interaction of vanadium with DNA bases and may help the future design of vanadium-based anticancer drugs.

Trace Water Changes Metal Ion Speciation in Deep Eutectic Solvents: Ce3+ Solvation and Nanoscale Water Clustering in Choline Chloride-Urea-Water Mixtures.

Eutectic mixtures of choline chloride, urea, and water in deep eutectic solvent (DES)/water molar hydration ratios (w) of 2, 5, and 10, with dissolved cerium salt, were measured using neutron diffraction with isotopic substitution. Structures were modeled using empirical potential structure refinement (EPSR). Ce3+ was found to form highly charged complexes with a mean coordination number between 7 and 8, with the shell containing mostly chloride, followed by water. The shell composition is strongly affected by the molar ratio of dilution, as opposed to the mass or volume fraction, due to the high affinity of Cl- and H2O ligands that displace less favorable interactions with ligands such as urea and choline. The presence of Ce3+ salt disrupted the bulk DES structure slightly, making it more electrolyte-like. The measured coordination shell of choline showed significant discrepancies from the statistical noninteracting distribution, highlighting the nonideality of the blend. Cluster analysis revealed the trace presence of percolating water clusters (25 ≥ n ≥ 2) in solvent compositions of 5 and 10w for the first time.

Understanding the unique geochemical behavior of Sc in the interaction with clay minerals

Abstract Regolith-hosted rare earth elements (REEs) deposits received great attention due to the increasing incorporation of REEs in modern technologies. In lateritic Sc deposits and ion-adsorption deposits (IADs), Sc behaves quite differently from REEs: REEs adsorb as outer-sphere complexes on clay surface in IADs, while Sc could enter the lattice of clay minerals in lateritic Sc deposits. The unique behavior of Sc has not been well understood yet. Here, by using first-principles molecular dynamics techniques, we show that the complexation mechanisms of Y3+ and Sc3+ on clay edge surfaces are distinctly different. Y3+ preferentially adsorbs on Al(OH)2SiO site with its coordination water protonated. Sc3+ is found to behave similarly to other first-row transition metals (e.g., Ni2+) due to its smaller ionic radius and prefers adsorbing on the vacancy site, from where Sc3+ can be readily incorporated in the clay lattice. The H2O ligands of Sc3+ get deprotonated upon complexation, providing new binding sites for further enrichment of Sc3+. These processes prevent Sc3+ from being leached during weathering and lead to the formation of Sc-rich clay minerals found in lateritic deposits. Based on these results, it is revealed that the small ionic radius and high affinity to enter the vacancy on edge surfaces make Sc compatible with clay minerals and are the origin of its unique geochemical behavior.

New dicyanide-salen based chromium(III) complexes: Synthesis, crystal structures, electrochemical and thermal investigations

Two compounds with formulas [K(H2O)(CH3OH)CrIII(valen)(CN)2]2 (1) and PPh4[CrIII(valen)(CN)2]·8.5H2O (2) were synthesized and structurally characterized (H2valen is the Schiff base resulted from the condensation of o-vanillin with ethylenediamine). For compound 1, a solid-state transformation (130 °C), consisting in the elimination of CH3OH and H2O ligands, was observed. The exposure of the resulting crystal to the humidity from air led to [K(H2O)2CrIII(valen)(CN)2]2 (3). The single-crystal X-ray diffraction analysis of 1 and 3 revealed that they are isostructural, their structure consisting of a tetranuclear centrosymmetric complex, {Cr2K2}, with the CrIII ions located into the (N2O2) coordination sites and the potassium ions located into the open (O2O’2) compartments of the two organic ligands. For compound 2, the crystal structure consists of discrete anionic mononuclear species, [CrIII(valen)(CN)2]−, and tetraphenylphosphonium counter cations. Thermal (TG-DTG-DSC) and electrochemical investigations of the newly synthesized complexes were performed.

Brønsted Acids Promote Olefin Oxidations by Bioinspired Nonheme CoIII(PhIO)(OH) Complexes: A Role for Low-Barrier Hydrogen Bonds.

Introduction of Brønsted acids into biomimetic nonheme reactions promotes the oxidative ability of metal-oxygen complexes significantly. However, the molecular machinery of the promoted effects is missing. Herein, a comprehensive investigation of styrene oxidation by a cobalt(III)-iodosylbenzene complex, [(TQA)CoIII(OIPh)(OH)]2+ (1, TQA = tris(2-quinolylmethyl)amine), in the presence and absence of triflic acid (HOTf) was performed using density functional theory calculations. Results revealed for the first time that there is a low-barrier hydrogen bond (LBHB) between HOTf and the hydroxyl ligand of 1, which forms two valence-resonance structures [(TQA)CoIII(OIPh)(HO---HOTf)]2+ (1LBHB) and [(TQA)CoIII(OIPh)(H2O--OTf-)]2+ (1'LBHB). Due to the oxo-wall, these complexes (1LBHB and 1'LBHB) cannot convert to high-valent cobalt-oxyl species. Instead, styrene oxidation by these oxidants (1LBHB and 1'LBHB) shows novel spin-state selectivity, i.e., on the ground closed-shell singlet state, styrene is oxidized to an epoxide, whereas on the excited triplet and quintet states, an aldehyde product, phenylacetaldehyde, is formed. The preferred pathway is styrene oxidation by 1'LBHB, which is initiated by a rate-limiting bond-formation-coupled electron transfer process with an energy barrier of 12.2 kcal mol-1. The nascent PhIO-styrene-radical-cation intermediate undergoes an intramolecular rearrangement to produce an aldehyde. The halogen bond between the OH-/H2O ligand and the iodine of PhIO modulates the activity of the cobalt-iodosylarene complexes 1LBHB and 1'LBHB. These new mechanistic findings enrich our knowledge of nonheme chemistry and hypervalent iodine chemistry and will play a positive role in the rational design of new catalysts.

Thermal, structural, and spectroscopic characterization of an ionic [Cu(H2O)4](ReO4)2 compound in a wide temperature range

AbstractWe present complementary investigations of water and anion dynamics in an ionic [Cu(H2O)4](ReO4)2. This compound has one reversible phase transition in the solid state upon heating and cooling at 247 and 224 K, respectively. The value of entropy change indicates a moderate degree of molecular dynamical disorder. At room temperature, tetraaquacopper(II) rhenate(VII) crystallizes in a triclinic crystal system, within the space group No. 2 = P‐1, with one molecule in the unit cell. X‐ray single crystal diffraction measurements indicate that the crystal structure does not change significantly at the phase transition. However, neutron diffraction experiments performed on the powdered sample revealed some subtle changes in the registered patterns. Vibrational–reorientational dynamics of H2O ligands in the high (I) and low‐temperature (II) phases of [Cu(H2O)4](ReO4)2 was probed by a set of complementary spectroscopy techniques in a wide temperature range. The dynamics of the H2O molecules in both phases was investigated by means of band shape analysis performed for infrared bands. The H2O ligands perform fast (τR ≈ 10−11 to 10−12 s) stochastic reorientational motions in the phases I and II with a mean value of activation energy: 6.13 kJ⋅mol−1. However, a continuous change of bands connected with hydrogen bonds is observed. The Raman measurements revealed that in the phase transition region the intensity of bands connected with perrhenate anion significantly increases. Using vibrational spectroscopy methods all characteristic wavenumbers of the H2O and ReO4− vibrations were detected.

Supramolecular Recognition within a Nanosized "Buckytrap" That Exhibits Substantial Photoconductivity.

We report here a nanosized "buckytrap", 1, constructed from two bis-zinc(II) expanded-TTF (exTTF) porphyrin subunits. Two forms, 1a and 1b, differing in the axial ligands, H2O vs tetrahydrofuran (THF), were isolated and characterized. Discrete host-guest inclusion complexes are formed upon treatment with fullerenes as inferred from a single-crystal X-ray structural analyses of 1a with C70. The fullerene is found to be encapsulated within the inner pseudohexagonal cavity of 1a. In contrast, the corresponding free-base derivative (2) was found to form infinite ball-and-socket type supramolecular organic frameworks (3D-SOFs) with fullerenes, (2•C60)n or (2•C70)n. This difference is ascribed to the fact that in 1a and 1b the axial positions are blocked by a H2O or THF ligand. Emission spectroscopic studies supported a 1:1 host-guest binding stoichiometry, allowing association constants of (2.0 ± 0.5) × 104 M-1 and (4.3 ± 0.9) × 104 M-1 to be calculated for C60 and C70, respectively. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) studies of solid films of the Zn-complex 1a revealed that the intrinsic charge carrier transport, i.e., pseudo-photoconductivity (ϕ∑μ), increases upon fullerene inclusion (e.g., ϕ∑μ = 1.53 × 10-4 cm2 V-1 s-1 for C60⊂(1a)2 and ϕ∑μ = 1.45 × 10-4 cm2 V-1 s-1 for C70⊂(1a)2 vs ϕ∑μ = 2.49 × 10-5 cm2 V-1 s-1 for 1a) at 298 K. These findings provide support for the notion that controlling the nature of self-assembly supramolecular constructs formed from exTTF-porphyrin dimers through metalation or choice of fullerene can be used to regulate key functional features, including photoconductivity.

The origin of anode–electrolyte interfacial passivation in rechargeable Mg-metal batteries

The formation of H2O molecules competitively solvating Mg-ion solvation structures and their decomposition in electrochemical and/or chemical reaction pathways with inherent H2O ligands result in dendritic and passivated electrodeposition.

Electrospray droplet impact/secondary ion mass spectrometry (EDI/SIMS) applied to the analysis of explosives

Electrospray droplet impact/secondary ion mass spectrometry (EDI/SIMS) was applied to the analyses of explosives including HMTD (hexamethylenetriperoxidediamine), RDX (cyclotrimethylene trinitroamine), HMX (cyclotetramethylenetetranitroamine), PETN (pentaerythritol tetranitrate), and TNT (2,4,6-trinitrotoluene) in positive- and negative-mode of operation. A mixture of H2O/CH3OH (9/1) containing 0.01 M trifluoroacetic acid (TFA) was used as a solvent for vacuum electrospray. For all explosives described above, intact molecules were detected by EDI/SIMS. HMX which is the least volatile compound tested could be readily detected in both positive- and negative-mode of operations. Nitramines of RDX and HMX were detected as proton- and Na+-bound cluster ions with H2O and CH3OH ligands. TNT and the nitrate ester PETN were not detected in positive mode. In negative mode, RDX, HMX and PETN were detected as adduct ions with NO2−, NO3−, and CF3COO−. TNT gave TNT−• and fragment ions similar to those detected in atmospheric-pressure chemical ionization. The characteristic difference in reactivity between the nitramine compounds (RDX and HMX) and the nitrate ester compound (PETN) is likely to be due to the more diffused negative charge in nitrate ester groups than in nitro groups.

Theoretical Study of Complexes of Tetravalent Actinides with DOTA

1,4,7,10-Tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid (H4DOTA) is a prominent chelating ligand with potential applications in various fields, from radiotherapy to the separation of fission products. The present study explores the stability, structure, and bonding properties of its complexes with tetravalent actinides (An = Th, U, Np, Pu) using density functional theory and relativistic multireference calculations. Neutral complexes prefer to form symmetric (C4) structures with DOTA. The first coordination sphere of the actinide ions is readily saturated by a weakly bonded H2O ligand. The latter ligand reduces the molecular symmetry while exerting only marginal effects on the properties of the parent complex. An-ligand bonding is mainly electrostatic, but there are also significant charge-transfer contributions from DOTA to the An 6d/5f orbitals. The charge-transfer interactions and the covalent character of bonding increase gradually in the order of Th < U < Np < Pu, as indicated by analysis of the electron density distribution using the Quantum Theory of Atoms in Molecules.

Adsorption of Hydrated Pr3+ and NH4+/Mg2+ Ions onto the (001) Surface of Montmorillonite: A DFT Analysis with Experimental Verification

Montmorillonite is a major mineral present in ion-adsorption rare earth ores, and the microscopic adsorption states of rare earth ions on its surface are of a great significance for the efficient exploitation of ion-adsorption rare earth ores. In this article, density functional theory calculations were used to investigate the adsorption mechanisms and bonding characteristics of hydrated Pr, Mg and NH4 ions on the (001) surface of montmorillonite. Pr3+ exhibited a directed tendency geometry with Pr(H2O)103+, which was adsorbed onto montmorillonite by hydrogen bonding with an adsorption energy of −1182 kJ/mol, and one coordinated H2O ligand was separated from the first hydration layer of Pr. Both hydrated Mg and NH4 ions were adsorbed onto the montmorillonite surface through hydrogen bonds, and the adsorption energies were −206 and −188 kJ/mol, respectively, indicating that the adsorption stability of the hydrated Mg ion was slightly higher than that of the hydrated NH4 ion, but both were lower than that of hydrated Pr (−1182 kJ/mol). Hence, higher concentrations of Mg and NH4 ions than rare earth ions would be necessary in the leaching process of ion-adsorption rare earth ores. Additionally, desorption experiments revealed that the recovery of Pr3+ by Mg2+ with a concentration of 38 mmol/L is 80%, while it is only 65% with the same concentration of NH4+, and the concentrations of Mg2+ and NH4+ were much higher than that of Pr3+ in lixivium, which is consistent with the DFT calculations.

Single-Ion Behavior in New 2-D and 3-D Gadolinium 4f7 Materials: CsGd(SO4)2 and Cs[Gd(H2O)3(SO4)2]·H2O.

The recent creation of 4f7 gadolinium materials has enabled vital studies of the free-ion properties of the Gd(III) cations. While the 8 S ground state in a trivalent Gd compound is, in principle, isotropic, it has been demonstrated that there is a residual orbital angular momentum affected by the crystal field and structural distortion in certain systems. By exploiting the atomistic control innate to material growth, we address a fundamental question of how the isotropic nature of Gd(III) is preserved in different dimensionalities of crystal structures. To achieve this, we designed two new trivalent Gd materials possessing two structurally distinct features, a 2-D CsGd(SO4)2 and a 3-D Cs[Gd(H2O)3(SO4)2]·H2O. The tunability of the structural dimension is facilitated by O-H---O hydrogen bonds. The structural divergence between the two compounds allows us to investigate each material individually and make a comparison between them regarding their physical properties as a function of lattice dimension. Our results demonstrate that structural dimensions have a negligible effect on the single-ion behavior of the materials. Magnetization measurements for the Gd(III) complexes yielded paramagnetic states with the isotropic spin-only nature. Specific heat data suggest that there is a lack of magnetic phase transition down to T = 1.8 K, and coupled lattice vibrations in the materials are attributable to strong covalent bonding characters of the (SO4)2- and H2O ligands. This work offers a pathway for retaining the single-ion property of Gd(III) while constructing the large spin magnetic moment S = 7/2 in large-scale extended frameworks.

Architecture of a dinuclear Co(II) complex based on 3-amino-1,2,4-triazole-5-carboxylic acid: molecular structure, thermal behavior, optical properties, and DFT calculations

The dinuclear compound [Co2(Hatzc)2(H2O)6](NO3)2·4H2O containing the polytopic ligand Hatzc‒ = 3-amino-4H-1,2,4-triazole-5-carboxylate was synthesized and characterized. Single-crystal X-ray diffraction showed that two monoanionic N,O-chelating Hatzc‒ ligands bridge two Co(II) ions in a µ-N1,N2 fashion. Both Co(II) centers are further coordinated by three H2O ligands making up an octahedral coordination. A complex network of intra- and intermolecular O‒H···O and N‒H···O hydrogen bonding interactions characterize the structure. Hirshfeld surface analysis, ATR–FTIR, and FT-Raman spectroscopy in combination with density functional theory (DFT) calculation of vibrational modes confirm this multitude of H bonds. Thermogravimetric and differential thermal analysis experiments under an argon atmosphere in the temperature range of 25–900 °C showed thermal stability till about 100 °C and multi-step decomposition yielding Co2O3 at about 280 °C. The octahedral environment of Co(II) was confirmed by UV–vis absorption spectroscopy, which shows weak absorption bands at around 520 nm assignable to electronic d‒d transitions alongside with π‒π* transitions dominating the 250–350 nm range. Time-dependent DFT calculated excited states agree very well in terms of energy match with the observed transitions. The direct and indirect optical band gap values were determined using the Tauc plot method to 3.33 eV and 2.75 eV, respectively, indicating semiconducting properties.

Theoretical study of heptadentate bispidine ligands for radiopharmaceutic applications

The complexes of radiopharmaceutically relevant trivalent metals (MIII = InIII, BiIII, LaIII, LuIII, AcIII) with two heptadentate bispidine-based ligands (L) have been investigated by DFT calculations. The main questions included the encapsulation efficiency of the ligands for the different-size metals, the differences in bonding, the possibility and characteristics of octa- and nonacoordination achieved by attachment of H2O ligands to the ML complexes as well as the thermodynamic stabilities under isolated and aqueous solution conditions. The results supported high efficiencies of the ligands resulting in very good stabilities of the complexes. The bonding analysis revealed small differences based on a gentle interplay of the sizes and electronic structures of the MIII ions as well as on the difference in two donor groups of the ligands. The present heptadentate ligands form tighter interactions with the metals as compared to the octadentate derivative, and leave less space for coordination of additional ligands.

Mechanism insights into the hydrated Al ion adsorption on talc (001) basal surface: A DFT study

Al ion was reported to have an enhanced depression of Carboxymethyl cellulose (CMC) on talc flotation. However, how Al ion is adsorbed on talc surface remains unclear. Herein, the hydrated Al ion adsorption on talc (001) basal surface was creatively studied by DFT calculations. The effective number of H2O ligands in hydrated Al ion was probed and the optimal adsorption structure was investigated. We found that Al(OH)3(H2O) was the preferred hydrate structure, and the top O site was its optimal adsorption position on talc surface. Furthermore, Al-O chemical bond was not formed, and H2O was found to act as a bridge to connect the Al(OH)3(H2O) to talc surface by H-bond between H of H2O ligand and surface O instead of H-bond between H of Al(OH)3 in Al(OH)3(H2O) and surface O. However, [Al(OH)4]− cannot form the H2O bridge due to the electrostatic repulsion, and its adsorption on talc surface was energetically unsupportive. Moreover, we found that the formation of H-bond was due to the hybridization reaction between O 2p and H 1s orbitals, and slight electron transfers between O and H atoms were also observed. Finally, the Al(OH)3(H2O) was adsorbed on talc surface, which is consistent with the performed experimental result.

Experimental and theoretical approaches on structural, spectroscopic (FT‐IR and UV‐Vis), nonlinear optical, and molecular docking analyses for Zn (II) and Cu (II) complexes of 6‐chloropyridine‐2‐carboxylic acid

AbstractNovel transition metal‐based complexes that may be of value as biological agents and/or nonlinear optical materials, Zn (II) and Cu (II) transition metal complexes of 6‐chloropyridine‐2‐carboxylic acid (LH), were successfully synthesized. The chemical structure of each complex was characterized using X‐ray diffraction (XRD) method and FT‐IR spectroscopy. XRD and FT‐IR demonstrated that L ligand coordinate to central metal ions through the donor N and O atoms. By coordinating two H2O ligand to Zn (II) ion, a distorted octahedral complex geometry was constructed for 1. As for 2, a distorted trigonal bipyramidal coordination geometry was obtained by a H2O ligand coordination to Cu (II) ion. Theoretical studies using B3LYP/6‐311++G(d,p)‐LanL2DZ were performed to further validate the proposed structures. The molecular docking of 1 to SARS‐CoV‐2 main protease (PDB: 6LU7) gives a binding energy of −5.24 kcal/mol and inhibition constant of 144.6 μM, demonstrating that 1 is a more promising candidate to biologically active complexes than 2. The first‐order hyperpolarizability (β) parameter for 1 and 2 was calculated as 0.88 × 10−30 and 10.40 × 10−30 esu, respectively. These β values also demonstrated that 2 exhibits more effective NLO character than 1 due to the electronic configuration and coordination geometry.