Search Results (80)

Rare earth elements (Ln: Sm, Eu, Tb, Dy) were complexed with caffeic acid (Caf), a natural phenolic compound, to synthesize novel luminescent complexes with enhanced biological activities. The complexes, formulated as Ln(Caf)₃·4H₂O, were characterized using infrared spectroscopy (IR), thermogravimetric analysis (TGA/DTA), mass spectrometry (MS), and fluorescence spectroscopy. Structural studies confirmed the coordination of caffeic acid via carboxylate and hydroxyl groups, forming stable hexacoordinate complexes. Luminescence analysis revealed intense emission bands in the visible spectrum (480–700 nm), attributed to f-f transitions of Ln³⁺ ions, with decay lifetimes ranging from 0.054 to 0.064 ms. Biological assays demonstrated significant antibacterial activity against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa, with inhibition zones up to 44 mm at 200 µg/mL. The complexes also exhibited potent anticancer activity against MCF7 breast cancer cells, with Sm(Caf)₃·4H₃O showing the lowest IC₅₀ value (15.5 µM). This study highlights the dual functionality of rare earth metal-caffeic acid complexes as promising candidates for biomedical imaging and therapeutic applications. Full article

The development of gadolinium-based magnetic resonance imaging (MRI) contrast agents (CAs) is a highly challenging and demanding research field in metal-coordination medicinal chemistry. The recognized high capacity of hydroxypyridinone (HOPO)-based compounds to coordinate Gd (III) led us to evaluate the set of physic–chemical–biological properties of a new Gd (III) complex with a hexadentate tripodal ligand (H₃L) containing three 3,4-HOPO chelating moieties attached to an anchoring cyclohexane backbone. In particular, the thermodynamic stability constants of the complex were evaluated by potentiometry, showing the formation of a highly stable (1:1) Gd-L complex (log β_GdL = 26.59), with full coordination even in an acid-neutral pH under the experimental conditions used. Molecular simulations of the Gd (III) complex revealed a minimum energy structure with somewhat-distorted octahedral geometry, involving full metal hexa-coordination by the three bidentate moieties of the ligand arms, indicating that an extra water molecule should be coordinated to the metal ion, an important feature for the CAs (and the required enhancement of water proton relaxivity). In vivo biodistribution studies with the ⁶⁷Ga complex, as a surrogate of the corresponding Gd complex, showed in vivo stability and rapid excretion from the animal body. Though deserving further investigation, these results may give an input on future perspectives towards new MRI diagnostic agents. Full article

Four mononuclear bioefficient zinc coordination complexes [Zn(NN)₃](ClO₄)₂ (A–D) involving chiral bidentate Schiff base ligands have been synthesized and characterized by IR, ¹H, and ¹³C NMR spectroscopy and mass spectrometry. X-ray crystal structures of three of the zinc complexes revealed that the zinc metal ion is hexacoordinated, exhibiting a distorted octahedral geometry where both the nitrogen atoms (NN = pyridyl and imine) of imines are coordinated to the central zinc ion. The isolated zinc complexes were evaluated for their antimicrobial activity in vitro against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus, displaying varying levels of growth inhibition. An acute toxicity test conducted using Artemia salina and Swiss albino mice showed that the zinc complexes A–D were non-toxic towards A. salina at concentrations below 414, 564, 350, and 385 µM, respectively, and did not affect liver biochemical parameters, although pyknosis was induced in hepatocytes of the treated mice. Full article

Curcuminoids are widely studied due to their well-recognized therapeutic properties. These molecules are often derivatized with metals, producing their corresponding homoleptic metal complexes. Numerous crystal structures of homoleptic symmetric curcuminoids with physiologically essential metals are known, although the literature lacks reports of homoleptic metal complexes of unsymmetric curcuminoids (or hemi-curcuminoids) as ligands. Three unknowns must be solved when an unsymmetric curcuminoid ligand is reacted with a metal ion: (a) the degree of coordination (MLn); (b) the spatial geometry; and (c) the conformational nature (syn or anti) of the complex. Herein, we report the structure of the anti-isomer of the Zn complex of the hemi-curcuminoid 5-hydroxy-1-(4-methoxyphenyl)hexa-1,4-dien-3-one. While the NMR shows only one set of signals for this homoleptic complex, the unambiguous stereochemistry was established through single-crystal X-ray diffractometry, revealing an anti-hexacoordinated octahedral ML₂ structure. Full article

An Fe(III)-carbonato six-coordinate picket fence porphyrin complex with the formula [K(2,2,2-crypt)][Fe^III(TpivPP)(CO₃)]·C₆H₅Cl·3H₂O (I) has been synthesized and characterized by UV-Vis and FT-IR spectra. The structure of (carbonato)(α,α,α,α-tetrakis(o-pivalamidophenyl)porphinato)ferrate(III) was also established by XRD. The iron atom is hexa-coordinated by the four nitrogen atoms of the pyrrol rings and the two oxygen atoms of the CO₃²⁻ group. Complex I, characterized as a ferric high-spin complex (S = 5/2), presented higher Fe-Np (2.105(6) Å) and Fe-P_C (0.654(2) Å) distances. Both X-ray molecular structure and Hirshfeld surface analysis results show that the crystal packing of I is made by C-H⋯O and C-H⋯Cg weak intermolecular hydrogen interactions involving neighboring [Fe^III(TpivPP)(CO₃)]⁻ ion complexes. Computational studies were carried out at DFT/B3LYP-D3/LanL2DZ to investigate the HOMO and LUMO molecular frontier orbitals and the reactivity within the studied compound. The stability of compound I was investigated by analyzing both intra- and inter-molecular interactions using the 2D and 3DHirshfeld surface (HS) analyses. Additionally, the frontier molecular orbital (FMO) calculations and the molecular electronic potential (MEP) analyses were conducted to determine the electron localizations, electrophilic, and nucleophilic regions, as well as charge transfer (ECT) within the studied system. Full article

Reactions of copper(II) sulfate with 2,2′-bipyridine (bipy) and amino acids with nonpolar side chains (l-alanine (HAla), l-valine (HVal), or l-phenylalanine (HPhe)) were investigated under different solution-based and mechanochemical methods. Five new ternary coordination compounds were obtained by a solution-based synthesis and three of them additionally by the liquid-assisted mechanochemical method: {[Cu(μ-l-Ala)(H₂O)(bipy)]₂SO₄·2H₂O}_n (1a·2H₂O), {[Cu(μ-l-Ala)(H₂O)(bipy)][Cu(l-Ala)(H₂O)(bipy)]SO₄·2.5H₂O}_n (1b·2.5H₂O), {[Cu(μ-l-Val)(H₂O)(bipy)][Cu(l-Val)(H₂O)(bipy)]₃(SO₄)₂·4H₂O}_n (2·4H₂O), [Cu(l-Phe)(H₂O)(bipy)][Cu(l-Phe)(SO₄)(bipy)]∙8H₂O (3·8H₂O), and [Cu(l-Phe)(H₂O)(bipy)][Cu(l-Phe)(SO₄)(bipy)]∙9H₂O (3·9H₂O). The compounds were characterized by single-crystal and powder X-ray diffraction, infrared spectroscopy, and a thermal analysis. Structural studies revealed two structural types, monomeric in 3·8H₂O and 3·9H₂O, polymeric architectures in 1a·2H₂O, and mixed structures (monomeric and polymeric) in 1b·2.5H₂O and 2·4H₂O. The copper(II) ion is either pentacoordinated or hexacoordinated, with an observed Jahn–Teller effect. The crystal structures are based on an intensive network of hydrogen bonds and π interactions. 1a·2H₂O and 2·4H₂O showed substantial in vitro antiproliferative activity toward human hepatocellular carcinoma (HepG2) and moderate activity toward human acute monocytic leukemia cell lines (THP-1). Full article

Hell’s Gate globin-I (HGb-I) is a thermally stable globin from the aerobic methanotroph Methylacidiphilium infernorum. Here we report that HGb-I interacts with lipids stoichiometrically to induce structural changes in the heme pocket, changing the heme iron distal ligation coordination from hexacoordinate to pentacoordinate. Such changes in heme geometry have only been previously reported for cytochrome c and cytoglobin, linked to apoptosis regulation and enhanced lipid peroxidation activity, respectively. However, unlike cytoglobin and cytochrome c, the heme iron of HGb-I is altered by lipids in ferrous as well as ferric oxidation states. The apparent affinity for lipids in this thermally stable globin is highly pH-dependent but essentially temperature-independent within the range of 20–60 °C. We propose a mechanism to explain these observations, in which lipid binding and stability of the distal endogenous ligand are juxtaposed as a function of temperature. Additionally, we propose that these coupled equilibria may constitute a mechanism through which this acidophilic thermophile senses the pH of its environment. Full article

The present paper deals with a new two-in-one zero-dimensional (0D) organic–inorganic hybrid compound namely (C₆H₁₀N₂)₄[CdBr₆][CdBr₄]₂. This molecular crystal structure contains isolated CdBr₄ tetrahedra and CdBr₆ octahedra. The optical characterization by UV–Vis–NIR spectroscopy shows that the (C₆H₁₀N₂)₄[CdBr₆][CdBr₄]₂ exhibits a large gap energy of 4.97 eV. Under UV excitation, this hybrid material shows a bright cold white light emission (WLE) at room temperature. The photoluminescence (PL) analysis suggests that the WLE originates from the organic molecules. Density of states (DOS) analysis using the density functional theory (DFT) demonstrates that the calculated HOMO(Br)→LUMO(organic) absorption transition (4.1 eV) does not have significant intensity, while, the transition involving the valence band (VB) and the second and third conduction bands (CB) around 5 eV are allowed, which is in good agreement with the experimental gap value. The interesting theoretical result is that the LUMO(organic)→HOMO(Br) emission is allowed, which confirms the important role of the organic molecule in the emission mechanism, in good agreement with the experimental PL analysis. Full article

Two new coordination compounds comprising Mn(II) and Cu(II) viz. [Mn(bz)₂(Hdmpz)₂(H₂O)] (1) and [Cu(crot)₂(Hdmpz)₂] (2) (where, bz = benzoate; crot = crotonate; Hdmpz = 3, 5-dimethyl pyrazole) were synthesized and characterized. The characterization involved a single crystal X-ray diffraction technique, FT-IR spectroscopy, electronic spectroscopy, TGA, and elemental analyses. Compounds 1 and 2 crystallize as mononuclear entities of Hdmpz with penta-coordinated Mn(II) and hexa-coordinated Cu(II), respectively. These complexes exhibit distorted trigonal bipyramidal and distorted octahedral geometries, respectively. A crystal structure analysis of compound 1 elucidates the existence of C–H⋯π and π-stacking interactions alongside O–H⋯O, N–H⋯O, and C–H⋯O H-bonding interactions contributing to the stabilization of the compound’s layered assembly. Similarly, in compound 2, the crystal structure stability is attributed to the presence of hydrogen bonding in conjugation with π-stacking interactions. We conducted theoretical investigations to analyze π⋯π, H-bonding, and antiparallel CH···π non-covalent interactions observed in compounds 1 and 2. DFT calculations were performed to find out the strength of these interactions energetically. Moreover, QTAIM and non-covalent interaction (NCI) plot index theoretical tools were employed to characterize them and evaluate the contribution of the H-bonds. Full article

The structures and bonding of selected neutral M(CO)₆ complexes (M = Sc, Y, La, Lu, Ac and U) have been studied by density functional theory calculations. The calculations revealed the preference for C_2v symmetry and low-spin electronic state for most of these complexes. The relative stability of the low-symmetry species increases gradually with the size of the metal atom. While the characteristic O_h hexa-coordinated structure is favored in the high-spin electronic state of the smaller metals, for heavier metals, important advantages of the C_2v vs. O_h structures include larger charge transfer interactions in terms of transferred electrons as well as better steric conditions. Our joint experimental–theoretical analysis detected and confirmed the O_h structure of the Sc(CO)₆ complex in cryogenic CO/Ar matrices. Full article

4-Azidopyridine (1) and SiCl₄ react with the formation of the hexacoordinate silicon complex SiCl₄(4-azidopyridine)₂ (2). Upon dissolving in warm chloroform, the complex dissociates into the constituents 1 and SiCl₄ and forms back upon cooling. Depending on the cooling, two different crystalline modifications of 2 were obtained, which feature two different trans-conformers. Slow cooling to room temperature afforded conformer 2′, which features coplanar pyridine rings. Rapid cooling to −39 °C afforded crystals of conformer 2″, in which the planes of the pyridine ligands are nearly orthogonal to one another. Whereas 2′ resembles the molecular arrangement of various other known SiX₄(pyridine)₂ (X = halide) complexes, 2″ represents the first crystallographically confirmed example of a SiX₄(pyridine)₂ complex in this conformation. Conformers 2′ and 2″ were studied with ¹³C and ²⁹Si solid state NMR spectroscopy. Their differences in ²⁹Si chemical shift anisotropy, as well as energetic differences, were further investigated with computational analyses. In spite of the similar stabilities of the two conformers as isolated molecules, the crystal packing of 2″ is less stable, and its crystallization is interpreted as a kinetically controlled effect of seed formation. (3+2)-cycloaddition of 1 and phenylacetylene in toluene at 110 °C yields a mixture of 1-(4-pyridyl)-4-phenyl-1,2,3-triazole (1,4-3) and 1-(4-pyridyl)-5-phenyl-1,2,3-triazole (1,5-3) in approximate 1:2 molar ratio. The crystal structures of the two isomers were determined via X-ray diffraction. In chloroform (at 60 °C), this reaction is slow (less than 2% conversion within 4 h), but the presence of SiCl₄ enhanced the rate of the reaction slightly, and it shifted the triazole isomer ratio to ca. 1:6 in favor of 1,5-3. Full article

Functional dependence of the axial zero-field splitting parameter D with respect to a properly chosen geometrical parameter (D_str) in metal complexes is termed the magnetostructural D-correlation. In mononuclear hexacoordinate Ni(II) complexes with the ground electronic term ³B_1g (³A_2g in the regular octahedron), it proceeds along two intercepting straight lines, allowing for predicting the sign and magnitude of the D-parameter by knowing the X-ray structure alone; D_str is constructed from the metal–ligand bond lengths. In hexacoordinate Co(II) complexes, it is applicable only in the segment of the compressed bipyramid where the ground electronic term ⁴B_1g is orbitally non-degenerate so that the spin Hamiltonian formalism holds true. The D vs. D_str correlation is strongly non-linear, and it is represented by a set of decreasing exponentials. In tetracoordinate Co(II) complexes, on the contrary, the angular distortion from the regular tetrahedron is crucial so that the appropriate structural parameter D_str is constructed of bond angles. The most complex case is represented by pentacoordinated Co(II) systems, for which it is not yet possible to define a statistically significant correlation. All of these empirical correlations originate in the electronic structure of metal complexes that can be modelled using generalized crystal-field theory. As the barrier to spin reversal in single-molecule magnets is proportional to the D-value, for rational tuning and/or prediction of the single-molecule magnetic behaviour, knowledge/prediction of the D-parameter is beneficial. In this review, we present the statistical processing of an extensive set of structural and magnetic data on Co(II) and Ni(II) complexes, which were published over the past 15 years. Magnetostructural D-correlations defined for this data set are reviewed in detail. Full article

The hexacoordinate Co(II) complex [Co(neo)₂(cin)][BPh₄]·½Me₂CO (1·½Me₂CO) containing trans-cinnamic acid (Hcin) and neocuproine (neo) was prepared. The compound 1·½Me₂CO was characterized via single-crystal X-ray analysis, FT-IR spectroscopy, and magnetic measurements. The coordination polyhedron of the complex cation adopts a deformed octahedron shape, and cinnamate exhibits a bidentate mode of coordination, which is unusual for mononuclear Co(II) cinnamate complexes. The analysis of DC magnetic measurements with zero-field splitting (ZFS) spin Hamiltonian revealed large magnetic anisotropy defined by the axial ZFS parameter D = +53.2 cm⁻¹. AC susceptibility measurements revealed the slow relaxation of magnetization under the applied field; thus, 1·½Me₂CO behaves as a field-induced single-molecule magnet. The analysis of magnetic properties was also supported by CASSCF/NEVPT2 calculations. Full article

In this work, the synthesis and structure of an antimony complex with an aromatic, asymmetric tridentate ligand without an Sb-C bond were studied. Ethoxy(2-salicylidenaminophenolato)antimony(III) was studied with NMR, UV-Vis, and IR spectroscopy and the molecular structure was determined by single crystal X-ray diffraction. The antimony atom is formally tetracoordinate in this molecule. Coordinative unsaturation becomes visible in the solid-state structure where intermolecular Sb…O interactions supplement the coordination sphere of the antimony atom to be hexacoordinated. Quantum chemical calculations were performed in order to obtain a better understanding of the bond properties in the antimony complex. These show a spherical distribution of the lone pair at antimony and polar shared bonds from antimony to the heteroatoms of the tridentate ligand. Full article

The two dinuclear Cd(II) complexes [Cd(BPMST)(SCN)]₂ (1) and [Cd(BPMST)(N₃)Cl]₂ (2) of a s-triazine/pyrazolo ligand (BPMST) were synthesized. The preparation of both complexes was performed in a water–ethanol solvent mixture and involved the mixing of the functional ligand BPMST with CdCl₂ in the presence of thiocyanate or azide as linkers, respectively. The dinuclear formula of both complexes and the involvement of the pesudohalide as a linker between the Cd(II) centers were approved by single crystal X-ray structures. The Cd(II) was hexa-coordinated and the CdN₅S (1) and CdN₅Cl (2) coordination environments had distorted octahedral geometry. In the [Cd(BPMST)(SCN)]₂ and [Cd(BPMST)(N₃)Cl]₂, the BPMST acted as a pincer tridentate N-chelate. In the case of 1, the SCN¯ acted as a μ(1,3) bridging ligand between the Cd(II) centers, while the N₃¯ had a μ(1,1) bridging mode in 2. As a result, the Cd…Cd distance was significantly longer in 1 (5.8033(5) Å) than in 2 (3.796(2) Å). In both complexes, the Cd(II) had distorted octahedral coordination geometry. Hirshfeld surface analysis was performed to inspect the supramolecular aspects of the two Cd(II) complexes. The C…H, N…H and S…H contacts were important in the case of [Cd(BPMST)(SCN)]₂ (1). Their percentages were calculated to be 14.7, 17.0 and 13.4%, respectively. In the case of [Cd(BPMST)(N₃)Cl]₂ (2), the most significant contacts were the Cl…H, C…H and N…H contacts. Their contributions in the molecular packing were 16.5, 9.7 and 25.3%, respectively. The propensity of atom pairs of elements to form contacts in the crystal structure was analyzed using enrichment ratio (E_XY). Full article