Antiprismatic Geometry Research Articles

Hydrothermal syntheses, structures and photophysical properties of two lanthanide isonicotinic acid complexes

Two rare earth isonicotinic acid compounds [Y(HIA)2(H2O)4(NO3)](2NO3) ((1); HIA = isonicotinic acid) and [LaHg3Cl8(HIA)4] nnCl (2) were reported. Compound one features an isolated (0-D) structure, while compound two has a two-dimensional (2-D) structure. The rare earth ions are coordinated by eight oxygen atoms to display a square antiprismatic REO8 geometry. Compound one shows blue photoluminescence and it has CIE chromaticity coordinates of 0.2332 and 0.3104. The CCT of compound 1 is 13755 K. Compound two exhibits green photoluminescence and it has CIE chromaticity coordinates of 0.3663 and 0.6184. The CCT is 4997 K. Their band gaps are 2.86 and 3.12 eV.

Tb and Er dimers based on an asymmetric anilato ligand with slow magnetic relaxation

We report the synthesis, structure and magnetic properties of two dimers prepared with the asymmetric chloronitranilato ligand: 3-chloro-6-nitro-2,5-dihydroxy-1,4-benzo-quinone (C6O4(NO2)Cl)2- and two lanthanoid ions as TbIII and ErIII. The two compounds, formulated as: [Tb2(C6O4Cl(NO2))3(H2O)10]·6H2O (1) and [Er2(C6O4Cl(NO2))3(H2O)10]·6H2O (2) are isostructural and present a dimeric structure where the LnIII ions are connected by a bridging bis-bidentate chloronitranilato ligand. Each metal completes its nona-coordination environment with a terminal bidentate chloronitranilato ligand and five water molecules in a slightly distorted capped square antiprismatic geometry. In addition, these dimers exhibit field-induced slow magnetic relaxation with energy barriers of ca. 5 and 24 K, respectively.

Preparation, Structures, Photoluminescence and Semiconductive Properties of Two Novel Lanthanide Mercury Materials with a 3-D Framework Structure.

Two novel lanthanide mercury materials, [Gd(IA)3(H3O)2Hg3Br6]n·2nCl (1) and [La(IA)3(H3O)2Hg3Br6]n·2nCl (2) (IA = isonicotinic anion), have been prepared under solvothermal conditions and characterized by single-crystal X-ray diffraction techniques. They are isomorphic and characterized by a three-dimensional (3-D) framework structure. The lanthanide ions are bound by eight oxygen atoms to exhibit a square antiprismatic geometry. The solid-state photoluminescence experiment discovers that compound 1 shows a strong emission in the red region. Compound 1 possesses CIE (Commission Internationale de I'Éclairage) chromaticity coordinates of 0.7347 and 0.2653. Its CCT (correlated color temperature) is 6514 K. Compound 2 displays yellow photoluminescence and it has CIE chromaticity coordinates of 0.4411 and 0.5151. The CCT of compound 2 is 3633 K. Solid-state UV/Vis diffuse reflectance spectra revealed that their semiconductor band gaps are 2.16 eV and 2.85 eV, respectively.

Using Chiral Auxiliaries to Mimic the Effect of Chiral Media on the Structure of Lanthanide(III) Complexes Common in Bioimaging and Diagnostic MRI.

[Ln·DOTA]- complexes and systems derived therefrom are commonly used in MRI and optical bioimaging. These lanthanide(III) complexes are chiral, and, in solution, they are present in four forms, with two sets of enantiomers, with the ligand donors arranged in either a square antiprismatic, SAP, or twisted square antiprismatic geometry, TSAP. This complicated speciation is found in laboratory samples. To investigate speciation in biological media, when Ln·DOTA-like complexes interact with chiral biomolecules, six Eu·DOTA-monoamide complexes were prepared and investigated by using 1D and 2D 1H NMR. To emulate the chirality of biological media, the amide pendant arm was modified with one or two chiral centers. It is known that a chiral center on the DOTA scaffold significantly influences the properties of the system. Here, it was found that chirality much further away from the metal center changes the available conformational space and that both chiral centers and amide cis/trans isomerism may need to be considered─a fact that, for the optically enriched materials, led to the conclusion that eight chemically different forms may need to be considered, instead of the four forms necessary for DOTA. The results reported here clearly demonstrate the diverse speciation that must be considered when correlating an observation to a structure of a lanthanide(III) complex.

Structural, stability and relaxation features of lanthanide‐complexes designed for multimodal imaging detection of enzyme activities

AbstractLanthanide complexes of DO3A‐derivative ligands bearing a pyridine‐carbamate (L1) or pyridine‐amine (L2) arm have potential interest in the design of enzymatically activated imaging probes. Solid‐state X‐ray structures for CeL1 and YbL2 both demonstrate twisted square antiprismatic geometry, with the metal ion in a nine‐ or an eight‐coordinate environment, respectively. As assessed by pH‐potentiometry, in solution lanthanide ions form more stable complexes with the nonadentate L1 than with the octadentate L2 ligand (logKML=18.7–21.1 vs. 16.7–18.6, respectively), while stability constants are similar for L1 and L2 chelates of Mg2+, Ca2+, Zn2+ or Cu2+. The kinetic inertness of GdL1 is exceptionally high, with an estimated dissociation half‐life of ~108 h at pH 7.4, while LnL2 (Ln=Ce, Gd, Yb) complexes have 3–4 orders of magnitude faster dissociation, related to the presence of the protonatable, non‐coordinating amine function. The water exchange rate determined for the monohydrated GdL2 (kex298=1.3×106 s−1) shows a threefold decrease with respect to GdDOTA, as a consequence of a reduction in the negative charge and in the steric crowding around the water binding site, both important in dissociatively activated water exchange processes.

A Genuine Trivalent Bis‐Acylphosphide (BAP) Complex of Uranium

AbstractThe genuine trivalent uranium complex, K[UIII(mesBAP)4], employing four bidentate bis(2,4,6‐trimethylbenzoyl)phosphide (mesBAP) chelating ligands, is reported and obtained by the reduction of the literature‐known tetravalent analog [UIV(mesBAP)4]. Hence, the bis(acyl)phosphide mesBAP ligand allowed to establish a fully reversible redox couple with uranium in the oxidation states +III and +IV. In both complexes [U(mesBAP)4]0/−, the uranium ions are coordinated to four mesBAP ligands in a square antiprismatic geometry. All new compounds have been characterized by single‐crystal XRD analysis, 1H and 31P NMR, and UV/Vis/NIR electronic absorption spectroscopy, as well as SQUID magnetization and electrochemical measurements, and CW X‐band EPR in the case of the trivalent complex.

Decoration of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) with N-oxides increases the T1 relaxivity of Gd-complexes.

High complex stability and longitudinal relaxivity of Gd-based contrast agents are important requirements for magnetic resonance imaging (MRI) because they ensure patient safety and contribute to measurement sensitivity. Charged and zwitterionic Gd3+-complexes of the well-known chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) provide an excellent basis for the development of safe and sensitive contrast agents. In this report, we describe the synthesis of DOTA-NOx, a DOTA derivative with four N-oxide functionalities via "click" functionalization of the tetraazide DOTAZA. The resulting complexes Gd-DOTA-NOx and Eu-DOTA-NOx are stable compounds in aqueous solution. NMR-spectroscopic characterization revealed a high excess of the twisted square antiprismatic (TSAP) coordination geometry over square antiprismatic (SAP). The longitudinal relaxivity of Gd-DOTA-NOx was found to be r1=7.7 mm-1 s-1 (1.41 T, 37 °C), an unusually high value for DOTA complexes of comparable weight. We attribute this high relaxivity to the steric influence and an ordering effect on outer sphere water molecules surrounding the complex generated by the strongly hydrated N-oxide groups. Moreover, Gd-DOTA-NOx was found to be stable against transchelation with high excess of EDTA (200 eq) over a period of 36 h, and it has a similar in vitro cell toxicity as clinically used DOTA-based GBCAs.

Non-covalent interactions orchestrated distinct molecular arrangements along different axes within the novel mixed ligand thorium metal complex: Experimental and theoretical insights

This study presents the crystallographic analysis of a defect-free single crystal of a novel thorium metal complex, revealing its intricate three-dimensional molecular structure. The crystal was found to belong to space group C2/c, containing six mononuclear complexes in each unit cell. The central metal atom exhibited a ten-coordinated distorted sphenocoronal capped square antiprismatic geometry, forming bidendate bonds with 4,4,4-trifluoro-1-(thiophen-2-yl)butane-1,3‑dione) (TFTBD) and a 1,10 phenanthrene (Phe) ligand groups. Intriguingly, the crystal displayed a nonplanar geometry and featured various non-covalent interactions within its structure, both intra and intermolecular, enhancing its overall stability. Notably, intramolecular interactions involving CH⋯F/S/O bonds led to the formation of unique synthons, further substantiated by NCI analysis. Intermolecular interactions, such as CH⋯F, CH⋯Cg, and π⋯π interactions, played a crucial role in the crystal packing, resulting in the formation of two-dimensional molecular zig-zag chains, linear layers and hexagonal arrangements on the crystallographic ab-, bc-, and ca-planes respectively.

Heteroleptic samarium complexes with high quantum yields for temperature sensing applications.

Two new crystallographically characterized samarium complexes, [Sm(fod)3(L1)] (1) and [Sm(fod)3(L2)] (2) {L1 = 4,7-diphenyl-1,10-phenanthroline (bath), L2 = 2,2':6',2''-terpyridine and fod = anion of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione (Hfod)}, were synthesized and thoroughly characterized. Single-crystal (SC) analysis shows that complex 1 is an eight-coordinate structure with a distorted square antiprism geometry (D4d), whereas complex 2 possesses a nine-coordinate structure with distorted muffin geometry (Cs). The NMR results are in line with SC-XRD analysis, which further validate that the complexes remain intact in solutions. The photophysical characteristics of the complexes were studied in both visible and near infra-red (NIR) regions. The PLQY values of the present complexes were found to be higher than those reported in the literature except for a tetrakis Sm complex. This result indicates that both the ligands act as effective antennas for the present systems. A comparison of PLQY and emission lifetime values within the present complexes (in solid state) reveals that energy transfer from terpy to Sm3+ is more effective than that from the bath ligand. Various color parameters of the complexes were calculated, and the determined CCT values suggest that the complexes may be used as warm light sources. The determined band gap values for the complexes are in the range of those for semiconductors, which suggest the application of present systems in the field of optoelectronics. The curve between the emission intensity and temperature for complex 1 shows a perfect linearity (χ2 = 0.99), which suggests that this complex can have potential application as a temperature sensor in the range 60-350 K.

Transition metal complexes of the (2,2,2-trifluoroethyl)phosphinate NOTA analogue as potential contrast agents for 19F magnetic resonance imaging.

A new hexadentate 1,4,7-triazacyclononane-based ligand bearing three coordinating methylene-(2,2,2-trifluoroethyl)phosphinate pendant arms was synthesized and its coordination behaviour towards selected divalent (Mg2+, Ca2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+) and trivalent (Cr3+, Fe3+, Co3+) transition metal ions was studied. The ligand forms stable complexes with late divalent transition metal ions (from Co2+ to Zn2+) and the complexes of these metal ions are formed above pH ∼3. A number of complexes with divalent metal ions were structurally characterized by means of single-crystal X-ray diffraction. The complex of the larger Mn2+ ion adopts a twisted trigonally antiprismatic geometry with a larger coordination cavity and smaller torsion of the pendant arms, whereas the smaller ions Ni2+, Cu2+ and Zn2+ form octahedral species with a smaller cavity and larger pendant arm torsion. In the case of the Co2+ complexes, both coordination arrangements were observed. The complexes with paramagnetic metal ions were studied from the point of view of potential utilization in 19F magnetic resonance imaging. A significant shortening of the 19F NMR longitudinal relaxation times was observed: a sub-millisecond range for complexes of Cr3+, Mn2+ and Fe3+ with symmetric electronic states (t2g3 and HS-d5), the millisecond range for the Ni2+ and Cu2+ complexes and tens of milliseconds for the Co2+ complex. Such short relaxation times are consistent with a short distance between the paramagnetic metal ion and the fluorine atoms (∼5.5-6.5 Å). Among the redox-active complexes (Mn3+/Mn2+, Fe3+/Fe2+, Co3+/Co2+, Cu2+/Cu+), the cobalt complexes show sufficient stability and a paramagnetic-diamagnetic changeover with the redox potential lying in a physiologically relevant range. Thus, the Co3+/Co2+ complex pair can be potentially used as a smart redox-responsive contrast agent for 19F MRI.

Two mononuclear chromophore coumarin-based Dy(III) complexes with magnetic relaxation and luminescent properties

Lanthanide luminescent single-molecule magnets (SMMs) serve as a kind of multifunctional molecular materials that have attracted extensive attention. Herein, a novel chromophore coumarin ligand 7-(diethylamino)-(2‑hydroxy-3-methoxybenzylidene)-2-oxo-2-chromene-3-carbohydrazide (Hvalcoumarin) is designed to construct the luminescent Dy(III) complexes. Two Dy complexes 1 ([Dy(valcoumarin)(DMF)2Cl2]·(CHCl3)) and 2 [Dy(valcoumarin)(DMF)2(NO3)2] were synthesized based on the luminescent chromophore coumarin ligand (Hvalcoumarin). X-ray crystallography reveals that the Dy(III) center in complex 1 adopts a hepta-coordinated arrangement by a distorted pentagonal bipyramidal geometry. In contrast, complex 2 exhibits a nine-coordinate arrangement by a spherical capped square antiprism geometry. Magnetic investigations reveal that 1 and 2 exhibit a slow magnetic relaxation phenomenon. Furthermore, the luminescent spectra of 1 and 2 display the characteristic emission profiles associated with Dy(III) spectra. Moreover, theoretical calculations also demonstrated the relaxation dynamics of 1 and 2. The results furnish a potent avenue for the acquisition of multifunctional molecular materials with magnetic and luminescent properties.

1D-photosensitized lanthanide polymers with flexible 4, 4′-bipyridyl linker

Three new ternary lanthanide complexes, [Ln(fod)3(4,4′-bpy)]n (Ln = Nd, Sm and Tb) were synthesized using asymmetric fluorinated β-diketone, 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione, as first sensitizer and 4, 4′-bipyridyl, the linker. The structural characterizations were carried out through various techniques viz., 1H NMR, FT-IR, single crystal X-ray diffraction (SC-XRD) and thermal analysis. Single crystal X-ray diffraction (SC-XRD) analysis demonstrates a 1D-polymeric chain structure of [Nd(fod)3(4,4′-bpy)]n in which Nd (III) ions are octa-coordinate with distorted square antiprismatic geometry. The structure of samarium and terbium complexes were optimized by the sparkle PM7 model using MOPAC implemented in LUMPAC and found to be distorted triangular dodecahedron The thermal studies shows that the complexes are thermally stable and acquire volatility without decomposition. The 1H NMR of these complexes are similar. The protons of 4, 4ʹ-bpy are largely shifted upfield in the Tb complex followed by Nd and Sm. The detailed photoluminescence and decay curves of these polymeric complexes have been discussed in solution and solid state. The emission spectra obtained for all the complexes display their characteristic emission peaks. The terbium complex shows pure green luminescence and exhibits a longer lifetime of 406 µs. The [Sm(fod)3(4,4′-bpy)]n displays color tuning during interphase and also with a change in excitation wavelength from turquoise to pure yellow via green. All the synthesized complexes exhibiting remarkable photophysical properties ensures their importance in various fields.

A mono-aquated di-pyridine-based Gd(III) complex as T1-weighted MRI probe with high relaxivity and stability

This study reports a new octadentate tricarboxylate appended ligand (H4dphta) with enhanced relaxivity and high stability towards Gd(III) complex as an MRI probe. The designed ligand was synthesized in multiple steps. Both, the ligand and its complex were characterized by spectroscopic techniques. Structural analysis of Gd(III) complex by single crystal XRD confirms its mono-hydrated form adopting distorted capped square antiprism geometry. Protonation constants of the ligand and the thermodynamic stability constant of the [Gd(Hdphta)] and [Gd(H2dphta)]+ species have been found as log K110 = 18.6(1) and log K111 = 24.8(1) at 25.0 °C, and I = 0.15 mol·L−1 NaClO4 by potentiometric method. The r1 relaxivity of the complex was found to be 4.63 mM−1s−1 at 1.41 T, 25 °C, and pH 7.4 in the HEPES buffer, which remained unaltered in the pH range of 4–10. The complex sustained its stability in the presence of different physiological anions (F−, HCO3−, HPO42−, C2O42−, CH3COO− and CH2(COO−)2) as supported by insignificant changes in longitudinal relaxivity (r1) at 1.41 T, 25 °C. The concentration-dependent contrast ability of [Gd(Hdphta)] is investigated by T1–weighted phantom images in a 3 T MRI scanner at 20 °C and pH 7.4. The cell viability has been evaluated using tissue culture in HEK cells.

Fluorescent and electronic properties of Dysprosium acylpyrazolone complexes along with their synthesis and structural features

Six distorted square antiprismatic eight coordinated Dysprosium acylpyrazolone complexes were synthesized having the compositions [Dy(L1)3(EtOH)(H2O)] (DyL1), [Dy(L2)3(EtOH)(H2O)] (DyL2), [Dy(L3)3(EtOH)(H2O)] (DyL3), [Dy(L4)3(EtOH)(H2O)] (DyL4), [Dy(L5)3(EtOH)(H2O)] (DyL5), and [Dy(L6)3(H2O)(EtOH)] (DyL6). The structure of all six complexes was examined using ESI-mass, FT-IR, UV–Vis, powder XRD, and thermogravimetric methods. According to the single crystal analysis of DyL4A, the complex was found eight coordinated (DyO8) with a distorted square antiprismatic geometry. The comparison of stimulated powder pattern of DyL4A crystal and experimental powder x-ray data helps to confirm the geometry of other complexes. In the solid-state emission spectra, the transition 4F9/2→6H13/2, which is close to the yellow region of the visible spectrum (∼510–530 nm), exhibits hypersensitivity. The variance in intensity between electric-dipole and magnetic-dipole transition suggests a less asymmetric environment. The solvent effect has been thoroughly investigated through a comparative analysis of electronic spectra in different solvents. The intensity of emission spectra, Y/B ratio, and antenna effect energy diagram were examined from solid-state emission spectra.

Crystal structure and photocatalytic activity of luminescent 3D-Supramolecular metal organic framework of dysprosium

A 3D supramolecular metal organic framework of dysprosium has been fabricated through a facile hydrothermal procedure with the ligand, 2,6-naphthalene disulphonic acid and the co-ligand, 4,4′-bipyridine. The MOF has been characterized as [C60H81DyN8O30S4] by routine analytical procedures. SXRD studies of the MOF show the existence of a hydrogen-bonded 3D supramolecular structure with high porosity. It crystallizes in monoclinic space group P21/n with unit cell parameters, a = 16.5424(6) Å, b = 37.0052(14) Å, c = 24.4361(9) Å, β = 100.7410°, α = γ = 90°. The Dy-MOF has eight coordinated water molecules around the metal centre and exhibits square anti-prismatic geometry. The band gap is 3.11 eV. The degradation experiments under visible light confirmed that Dy-MOF can act as a photocatalyst. Addition of hydrogen peroxide remarkably increases the degradation efficiency of the MOF through an advanced oxidation process. The newly synthesized MOF produced sharp emission peaks characteristic of dysprosium ion.

Slow Magnetization Relaxation in a Family of Triangular {CoIII 2 LnIII } Clusters: The Effect of Diamagnetic CoIII Ions on the LnIII Magnetic Dynamics.

The first use of the Schiff base chelate N-naphthalidene-o-aminophenol (naphH2 ) in Co/Ln chemistry has afforded a family of isostructural [CoIII 2 LnIII (OMe)2 (naph)2 (O2 CMe)3 (MeOH)2 ] (Ln=Tb, Dy and Er) complexes, revealing a rare {CoIII 2 Ln(μ3 -OMe)}8+ triangular core composed of two diamagnetic CoIII ions and a 4f-ion with slightly distorted square antiprismatic geometry. Alternating current (ac) magnetic susceptibility studies revealed that {Co2 Dy}, and its magnetic diluted analogue {Co2 Dy0.05 Y0.95 }, behave as mononuclear single-molecule magnets (SMMs) with similar energy barriers for the magnetization reversal, Ueff , of ~85-90 K. SMM properties were also detected for {Co2 Er}, with the compound exhibiting a Ueff of 18.7 K under an applied magnetic field of 800 Oe. To interpret the experimental magnetic results, ab initio CASSCF/RASSI-SO and DFT calculations were performed as a means of exploring the single-ion characteristics of LnIII ions and comprehend the role of the diamagnetic CoIII ions in the magnetization relaxation of the three heterometallic compounds.

Structure, slow magnetic relaxation behavior and bacteriostatic activity of a novel Dy4 cluster

A novel tetranuclear Dy(III)-based cluster, namely [Dy4(CO3)L4 (acac)2(CH3OH)2(CH2OH)2]·2CH3OH (1) (where H2L is 2-(hydroxyimino)-2-[(5-bromo-2-hydroxyphenyl)methylene]hydrazide and Hacacis acetylacetonate) has been constructed by employing a newly prepared Schiff based ligand H2L. X-ray diffraction data reveal that 1 is mainly consist of a rhombic Dy4core, in which the four Dy3+ ions are bridged by six μ-O atoms from four ligands H2L and two μ2-O atoms from thein situformed CO32−via spontaneous fixation of atmospheric CO2.The crystalstructure of 1 possesses two distinct Dy3+ ions coordinationcenter, and the nine-coordinated Dy73+ionscenter presenting a distorted spherical capped square antiprism geometry and eight-coordinated Dy43+ionscenter presenting a distorted triangular dodecahedron geometry.Magnetic study indicates that 1displays slow magnetic relaxation behavior under Hdc = 0 Oe filed. Furthermore, the fluorescence property investigation reveals that 1shows DyIIIcharacteristic emission peaks. Moreover, theantibacterial activity and mechanism of 1 have been systemically studied, and cluster 1 possesses well antibacterial activity on five common bacteria (Escherichia coli, Staphylococcus aureus, Staphylococcus albus, Bacillus subtilis, and Micrococcus luteus). Inaddition,the interaction between 1 and DNA have been studied.

Neodymium based acylpyrazolone complexes: Synthesis and physicochemical characterizations

The electronic spectra of three neodymium acylpyrazolone complexes with the compositions [Nd(DMBPMP)3(H2O)(EtOH)] (Nd1), [Nd(DMMCPMP)3(H2O)(EtOH)] (Nd2), and [Nd(DMBPTMP)3(H2O)(EtOH)] (Nd3) have been analyzed. Utilizing ESI-mass, FT-IR, thermogravimetric, and single crystal X-ray diffraction methods, the structure of the DMBPTMP ligand and all three complexes were investigated. According to the single crystal analysis of Nd2, the complex is mononuclear and eight-coordinate (NdO8) with a distorted square antiprismatic geometry. A powder XRD pattern confirmed a similar structural arrangement of the other two complexes. The transition 4G5/2 ← 4I9/2, which is close to the centre of the visible spectrum (∼17,500 cm−1), exhibits hypersensitivity, which stands out in stark contrast to the behaviour of many other typically weak and reliably unchanging, typical 4f-4f transitions. Through a comparative analysis of calculated oscillator strength, Judd-Ofelt parameters, and covalency parameters in various solvents, hypersensitivity, symmetry characteristics, and covalency have been thoroughly investigated. The promotion of 4f-4f electric-dipole intensity has been found to be particularly successful with DMF, DMSO, pyridine and ethanol. Utilizing Judd-Ofelt parameter Ω4 values and Hirshfeld analysis, long-range secondary π⋯π stacking or H-bonding interactions were investigated. Using solid-state emission spectra, intensity of emission spectra and antenna effect energy diagram was examined.

Structural Features, Emission Analysis, and Covalency Comparison of Neodymium Acylpyrazolone Complexes using Oscillator Strengths, Covalency and Judd‐Ofelt Parameters**

AbstractThree distorted square antiprismatic eight coordinated neodymium acylpyrazolone complexes were synthesized having the compositions [Nd(L1)3(H2O)(EtOH)] (NdL1), [Nd(L2)3(H2O)(EtOH)] (NdL2), and [Nd(L3)3(H2O)(EtOH)] (NdL3). The structure of all three complexes was examined using ESI‐mass, FT‐IR, and thermogravimetric methods. According to the single crystal analysis of NdL1, the complex was found eight‐coordinated (NdO8) with a distorted square antiprismatic geometry. A powder XRD pattern confirmed a similar structural arrangement of the other two complexes. In electronic absorption spectra, the transition 4G5/2←4I9/2, which is close to the centre of the visible spectrum (~17,500 cm−1), exhibits hypersensitivity, which stands out in stark contrast to the behaviour of many other typically weak and reliably unchanging, typical 4f–4f transitions. Through a comparative analysis of calculated oscillator strength, Judd‐Ofelt parameters, root mean square deviation, radiative lifetime and covalency parameters in various solvents, hypersensitivity, symmetry characteristics, and covalency have been thoroughly investigated. The promotion of 4f–4f electric‐dipole intensity has been found to be particularly successful with ethanol, pyridine, DMF, and DMSO. Utilizing Judd‐Ofelt Ω4 values and Hirshfeld analysis, long‐range secondary π⋅⋅⋅π stacking or H‐bonding interactions were investigated. The intensity of emission spectra, quantum yield, stokes shift, and antenna effect energy diagram was examined using solid‐state emission spectra.

Evolution of the La(III) ion coordination sphere in ethylammonium nitrate solution upon water addition

A thorough structural study of La(NO3)3 salt solutions in mixtures of the ethylammonium nitrate (EAN) ionic liquid (IL) and water with EAN molar fraction (χEAN) ranging from 0 to 1 has been carried out by means of X-ray absorption spectroscopy (XAS) measurements at the La K-edge and molecular dynamics (MD) simulations. Both the XAS and MD outcomes agree in finding that the composition of the La3+ ion first solvation shell undergoes steadily changes when moving from pure water to pure EAN. Upon increasing of the IL concentration, the La3+ solvation complexes progressively lose water molecules to accommodate more and more nitrate anions, and the ratio between the two ligands continuously changes across the explored composition range. The nitrate ligands coordinate the metal ion only in a monodentate fashion for the lower EAN contents, while the percentage of bidentate nitrates becomes more and more predominant as the EAN concentration increases. When moving from pure water to pure EAN, the La3+ ion coordination passes from a 9-fold tricapped trigonal prismatic geometry to a 12-fold icosahedral one, while a 10-fold coordination with bicapped square antiprism geometry is the dominant species for the mixed compositions. The remarkable flexibility of this solvation complex in accommodating a variable amount of water molecules and nitrate ligands at dependence of the system composition is key for its predominance in all the EAN/water mixtures.