Antiprismatic Geometry Research Articles

Supramolecular structures, thermal decomposition mechanism and heat capacity of the novel binuclear Tb(III) and Dy(III) complexes with 2,3-dimethoxybenzoic acid and 5,5′-dimety-2,2′-bipyridine

Two novel binuclear lanthanide complexes [Tb(2,3-DMOBA)3(5,5′-DM-2,2′-bipy)]2·C2H5OH (1) and [Dy(2,3-DMOBA)3(5,5′-DM-2,2′-bipy)]2·C2H5OH (2) (2,3-DMOBA = 2,3-dimethoxybenzoate, 5,5′-DM-2,2′-bipy = 5,5′-dimety-2,2′-bipyridine) have been successfully synthesized and structurally validated by single-crystal diffraction. The results of single-crystal analyses indicate the complexes contains one free ethanol molecule, and each center Ln(III) is nine-coordinated, exhibiting a distorted monocapped square anti-prismatic coordination geometry. The two center Ln(III) are bound by four 2,3-DMOBA ligands, two of which are bridging bidentate and the other two are bridging–chelating. The adjacent binuclear complexes can form 1D supramolecular structure by a pair of alternating identical C–H···O hydrogen bonding interactions, which further form 2D sheet structures. The thermal behavior of these complexes is investigated by TG-DSC/FTIR. What is more, the heat capacities of the complexes 1–2 are measured by DSC at 259.15–346.15 K, and the result indicates that the heat capacity values of the complexes gradually increased with the increase in temperature. In addition, the thermodynamic functions values (HT − H298.15K) and (ST − S298.15K) of the complexes 1–2 are calculated according to the fitted polynomial equations and the thermodynamic equation. The luminescence property of complex 1 is studied.

Dehydration–Hydration Switching of Single-Molecule Magnet Behavior and Visible Photoluminescence in a Cyanido-Bridged DyIIICoIII Framework

Microporous magnets compose a class of multifunctional molecule-based materials where desolvation-driven structural transformation leads to the switching of magnetic properties. Herein, we present a special type of microporous magnet where a dehydration-hydration process within a bimetal coordination framework results in the switching of emissive DyIII single-molecule magnets (SMMs). We report a three-dimensional (3-D) cyanido-bridged coordination polymer, {[DyIII(H2O)2][CoIII(CN)6]}·2.2H2O (1), and its dehydrated form of {DyIII[CoIII(CN)6]} (2), which was obtained through a reversible single-crystal-to-single-crystal transformation. Both phases are composed of paramagnetic DyIII centers alternately arranged with diamagnetic hexacyanidocobaltates(III). The hydrated phase contains eight-coordinated [DyIII(μ-NC)6(H2O)2]3- complexes of a square antiprism geometry, while the dehydrated form contains six-coordinated [DyIII(μ-NC)6]3- moieties of a trigonal prism geometry. This change in coordination geometry results in the generation of DyIII single-molecule magnets in 2, whereas slow magnetic relaxation effect is not observed for DyIII sites in 1. The D4d-to-D3h symmetry change of DyIII complexes produces also the shift of photoluminescent color from nearly white to deep yellow thanks to the modulation of emission bands of f-f electronic transitions. A combined approach utilizing dc magnetic data and low-temperature emission spectra confirmed an axial crystal field of trigonal prismatic DyIII complexes in 2, which produces an Orbach type of slow magnetic relaxation. Therefore, we present a unique route to the efficient switching of SMM behavior and photoluminescence of DyIII complexes embedded in a 3-D cyanido-bridged framework.

Solution and Solid‐State Structure of the First NHC‐Substituted Rhenium Heptahydrides

The structure of three new bis(N‐heterocyclic carbene) heptahydride rhenium complexes ([ReH7(NHC)2] with NHC= IMes (2b) (1,3‐bis(2,4,6‐trimethyl phenyl) imidazol‐2‐ylidene), IMesCl2 (4b) (4,5‐dichloro‐1,3‐dihydro‐1,3‐bis(2,4,6‐trimethyl phenyl)‐2H‐imidazol‐2‐ylidene) BIMes (5b) (1,3‐Bis(2,4,6‐trimethylphenyl)‐benzo imidazole ylidene), and of the known complex [ReH7(PPh3)2] (1) (bis(triphenyl phosphine)‐rhenium heptahydride), and the one of their labelled counterparts 2c‐d7, 4c‐d7, and 5c‐d7, were established in solution. The compounds exchanged with HD (2 bar) at 60 °C in deuterated THF to produce statistically distributed isotopomers. This exchange pointed to the intermediacy of H2 complexes and dynamic systems with fast equilibration processes of all hydride positions. T1min measurements were run on 2b, 4b, 5b and 1 in deuterated methylcyclohexane: 2b T1min = 144 ms, 5b T1min = 127 ms, both at 203 K. For 4b two T1min values were obtained corresponding to the 1H‐NMR signals of the hydrides: T1min = 119 ms and T1min = 128 ms both at 203 K. The T1min values determined are typical of terminal rhenium polyhydrides and for 1 was reported a comparably short value of T1min (70 ms, [D8]toluene, at –73 °C), typical of complexes that contain dihydrogen ligands. D‐NMR T1min measurements were also run for the fully deuterated compounds 2c‐d7, 4c‐d7, 5c‐d7 and of 1c‐d7 allowing to calculate the ionicities of the metal hydride bonds. The Re‐D ionicity values were obtained from the Deuterium Quadrupole Coupling Constant (DQCC) determinations. They were in the range of 0.61–0.71 for the fully labelled complexes: 2c‐d7: T1min = 15 ms, i = 61 %; 4c‐d7: (A) T1min = 20 ms, i = 67 %, (B) T1min = 41 ms, i = 77 %; 5c‐d7: T1min = 24 ms, i= 70 %; and 1c‐d7: T1min = 26 ms, i = 71 %. Single crystal X‐ray diffraction studies on 4b enabled us to refine the hydride positions with only restraints in the bond lengths and thermal parameters. The X‐ray solid structure resembles a pseudo‐capped square antiprismatic geometry.

The efficient sensitization of Sm(III) ion by a macrocycle with the matched cavity and energy level

A series of mononuclear lanthanide(III) coordination compounds Ln-1a with the “lasso-type” protection have been synthesized based on the flexible [1+1] pendant-arm Schiff-base macrocyclic ligand H2L1a. X-ray structure analysis reveals that the central ten-coordinate Ln(III) ion in every compound adopts distorted bicapped square antiprism geometry which is surrounded by one macrocycle and two axial chelating nitrates. Photophysical measurements have demonstrated that the macrocyclic ligand can serve as an effective sensitizer for Sm(III) ion. The relative compound Sm-1a shows efficient luminescence. Especially, the quantum yields are as high as about 1.48 ± 0.03 and 0.24 ± 0.02% for Sm(III) ion in solid state and methanol, respectively. The fluorescence lifetime is 42.3 μs in solid state together with 24.5 μs in methanol. It is proposed that the macrocyclic ligand plays an important role in guaranteeing the effective match of energy levels for Sm(III) central ion and constructing unique cavity microenvironment to shield the Sm(III) ion emitter from possible quenching effects.

Ionic nature of cadmium polymer plays decisive role in selective dye adsorption

A new coordination polymer {[Cd3(EGTA)(H2O)5]·(NO3)2}n1 was synthesized by using cadmium nitrate salt and flexible carboxylate EGTA (ethylene bis(oxyethylenenitrilo)tetraaceticacid) ligand under hydrothermal condition. The structure of 1 was characterized by FT-IR spectroscopy, elemental analysis and single crystal X-ray diffraction techniques. Complex 1 displayed 2D structure with uninodal 4-connected underlying net of a rare kgm topology with point symbol {32.62.72}. All three Cd(II) in the complex exhibited different geometrical configuration such as distorted square antiprism geometry, distorted trigonal pyramidal and distorted square pyramidal geometry. Additionally, TGA property of complex 1 was also studied. The anionic dyes (methyl orange and congo red) were studied to examine the potential of complex 1 for removal of dyes from aqueous solution. Interestingly, ionic nature of complex 1 played decisive role in removal of anionic dye within 15 min as two nitrate ion present in the lattice could influence the adsorption performance.

Slow relaxation in doped coordination polymers and dimers based on lanthanoids and anilato ligands

In this work we report the synthesis, structure and magnetic properties of two lanthanoid based coordination polymers (CP) and two dimers prepared with two derivatives of the 2,5-dihydroxy-1,4-benzoquinone (C6O4X2)2− as ligands. Using the bromanilato ligand: (C6O4Br2)2− we have prepared the CP [Eu1.96Dy0.04(C6O4Br2)3(DMSO)6]·2DMSO (1) (DMSO = dimethylsulfoxide) and with the chlorocyananilato ligand: (C6O4(CN)Cl)2−) we have prepared one CP formulated as [Eu1.96Dy0.04(C6O4(CN)Cl)3(DMSO)6] (2) and two isostructural dimers: [Eu1.96Dy0.04(C6O4(CN)Cl)3(H2O)10]·6H2O (3) and [Eu2(C6O4(CN)Cl)3(H2O)10]·6H2O (4). Compounds 1, 2 and 3 are Eu(III) compounds doped with 2.0 % of Dy(III), whereas compound 4 is a pure phase of Eu(III). The X-ray structure of these CPs shows that compounds 1 and 2 present neutral (6,3)-2D networks with rectangular cavities in 1 and very distorted hexagonal cavities in 2, while 3 and 4 are isostructural and present a dimeric structure where the Ln(III) ions are connected by a bis-bidentate chlorocyananilato ligand. Each metal completes its nonacoordination environment with a terminal bidentate chlorocyananilato ligand and five water molecules in a slightly distorted capped square antiprismatic geometry. In addition, these coordination complexes have very interesting magnetic properties. Compounds 1 and 3 behave as single-molecule magnets (SMM) with energy barriers of 40.9 and 25.3 K, respectively. In contrast, compound 2 does not present any SMM behaviour.

Construction of lanthanide complexes based on 3,4-dichlorobenzoic acid and 5,5′-dimethyl-2,2′-bipyridine: Supramolecular structures, thermodynamic properties and luminescent behaviors

Two novel lanthanide complexes, [Ln2(3,4-DClBA)6(5,5′-DM-2,2′-bipy)2(C2H5OH)(H2O)] (Ln = Gd(1), Tb(2)); 3,4-DClBA: 3,4-dichlorobenzoate; 5,5′-DM-2,2′-bipy: 5,5′-dimethyl-2,2′-bipyridine) have been hydrothermally synthesized and structurally characterized by elemental analysis, IR spectrum, thermal analysis and single X-ray diffraction techniques. The binuclear complexes 1–2 are isomorphous and crystallize in the triclinic crystal system and P1¯ space group, and each metal center is eight-coordinated with distorted square antiprismatic molecular geometry. The structure of this type of complex is unique in that the solvent ethanol molecule participates in the coordination. Complexes 1–2 are stitched together via π–π stacking interactions and hydrogen bonding interactions to form the 1D, 2D supramolecular structures. The thermal decomposition mechanisms of two complexes were obtained by TG-DSC/FTIR techniques. The molar heat capacities of the complexes 1 and 2 are measured by a DSC instrument over the temperature range from 255.15 to 323.15 K and thermodynamic functions were calculated by fitted polynomial and thermodynamic equations. The luminescence studies demonstrate that complex 2 exhibits the characteristic emission of Tb3+ ion (5D4 → 7F6-3).

Differences in the Relaxometric Properties of Regioisomeric Benzyl-DOTA Bifunctional Chelators: Implications for Molecular Imaging.

The bifunctional chelator S-2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane- N, N', N″, N‴-1,4,7,10-tetraacetate (IB-DOTA) is on paper the most attractive of the commercially available bifunctional chelators for magnetic resonance imaging (MRI) applications. The preserved DOTA scaffold is known to produce extremely kinetically and thermodynamically robust chelates with the Gd3+ ion. Also, ligation through four acetate pendant arms should ensure that the rapid water exchange kinetics so, crucial to the function of an MRI contrast agent are retained. However, upon ligation of the Gd3+ ion, IB-DOTA differentiates into two distinct isomers defined by the positions of the benzylic substituent (corner or side). A relaxometric analysis of these two isomers revealed marked differences in the property and behavior of the two chelates. Most notably the side isomer is found to be substantially more likely to aggregate in aqueous solution than its corner counterpart. This aggregation results in higher relaxivity for the side isomer versus the corner isomer, an observation that potentially obscures the impact of differences in water exchange kinetics between the two isomers. The side isomer is composed of a significant fraction of a twisted square antiprismatic coordination geometry that exchanges water more rapidly than optimal (τM = 7 ns) for maximizing relaxivity. The impact of this excessively fast exchange is not observed in the relaxivity of the side isomer only because in isolation this chelate tumbles much more slowly than the corner isomer. However, this situation is not expected to persist when the chelate is employed in a typical bioconjugate. These results imply that the corner isomer of IB-DOTA may represent a better choice of bifunctional chelator for bioconjugation applications in which a large macromolecule is to be tagged for MRI applications.

Synthesis, Thermal, Structural Analyses, and Photoluminescent Properties of a New Family of Malonate-Containing Lanthanide(III) Coordination Polymers.

Five new Lanthanide(III) complexes of malonic acid (HOOC-CH2-COOH); {[Gd(C3H2O4)(H2O)4]·NO3}n (1), {[Tb(C3H2O4)(H2O)4]·NO3}n (2), {[Ho(C3H2O4)(H2O)4]·NO3}n (3), [Er(C3H2O4)(C3H3O4)(H2O)2]n (4), and {[Eu2(C3H2O4)2(C3H3O4)2(H2O)6]·4H2O}n (5) were synthesized and characterized by elemental, infrared spectral, and thermal analyses. The structures of compounds 1–5 were determined by single crystal X-ray diffraction technique. The X-ray analysis reveals that compounds 1, 2, and 3 are isostructural and crystallized in the orthorhombic space group Pmn21. The lanthanide(III) ions are coordinated by four carboxylate and four water oxygen atoms adopting a distorted square antiprism geometry. The LnO8 square antiprisms are linked into infinite layers by malonate (C3H2) dianions sandwiching sheets of nitrate counter ions. Compound 4 contains ErO8 square antiprisms linked into a two-dimensional network by hydrogen malonate (C3H3) anions and malonate dianions. The europium complex, 5 is dinuclear having the two europium(III) ions (Eu1 and Eu2) bridged by carboxylate groups of hydrogen malonate ligands. The europium ions in 5 are nine-coordinate and exhibit a distorted monocapped square antiprism geometry. All the structures are consolidated by O–H⋯ O hydrogen bonds. The photoluminescence spectra of 1–5 exhibit characteristic emissions in the visible region. The IR spectra and thermal data are consistent with the structural results. The room-temperature effective magnetic moments for 1–4 are in good agreement with those expected for the free ions, while the data for 5 indicates that low-lying excited states contribute to the observed moment. The compound 1 was further subjected to quantum computational calculations to explore its optoelectronic properties including; density of states (DOS), dielectric function, refractive index, extinction coefficient, and absorption spectrum, to highlight the possible applications of such materials in the optoelectronics.

5×1 + 1×1] Hexanuclear Lanthanide(III) Cocrystal Complexes: Syntheses, Structures, and Magnetic Properties

Syntheses, structures, and magnetic properties of two hexanuclear [5×1 + 1×1] lanthanide cocrystal complexes [Ln5(L)4(LH2)2(tfa)4]·[Ln(tfa)4]·2CH3OH [Ln = Dy(1) and Tb(2)] derived from the polyhydroxy ligand 2‐(hydroxymethyl)‐6‐carbaldehyde‐4‐methylphenol (LH2) are reported. Compounds 1 and 2 crystallize in the triclinic system with space group P1. X‐ray crystallography reveals that 1 and 2 are cocrystals comprising one cationic pentanuclear [Ln5(L)4(LH2)2(tfa)4]+ unit and one anionic mononuclear [Ln(tfa)4]–unit as well as two molecules of methanol as solvent of crystallization. Both complexes form a [2.2] spirocyclic topology fashioned core due to merging of two triangular geometries composed of Ln(III) ions through a common vertex. The central Ln(III) ion in the spirocyclic pentanuclear assembly is eight‐coordinate with distorted square antiprism geometry. On the other hand, the peripheral eight‐coordinate Ln(III) ions are in a distorted trigonal dodecahedron geometry. The comprehensive magnetic study reveals that compound 1 displays slow relaxation of magnetism.

Eu(III) and Tb(III) complexes of 1,3-bis(4-chlorophenyl)-1,3-propanedione combined with phenanthroline ligand: synthesis, structural characterization, and thermogravimetric studies

β-Diketone lanthanide complexes are used mainly in lighting, telecommunication, screens, safety inks, and marking as well as in the field of luminescent materials for probes in biosciences. Two new lanthanide ternary complexes, the general formula Eu(BCPP)3(Phen) and Tb(BCPP)3(Phen), combined 1,3-bis(4-chlorophenyl)-1,3-propanedione (BCPP) with 1,10-phenanthroline as a secondary ligand, were synthesized and structurally characterized by single crystal X-ray diffraction, elemental analysis, FT-IR, and MALDI-TOF MS. Single crystal X-ray diffraction analysis revealed that these Eu(III) and Tb(III) complexes displayed bidentate ligands and a square antiprism geometry for the metal center. Also, the absorption and thermal behavior of these lanthanide complexes were investigated. When the maximum absorption of the lanthanide complexes was compared, it was observed that the absorption wavelength of the lanthanide complexes were red shifted in DMSO, DMF, and DCM, depending on the polarity of the solvent.

Structure and properties of a novel bimetallic praseodymium(III)-manganese(II) compound with a two-dimensional layer-like structure

A novel compound [Pr2(IA)6(H2O)4MnCl2(H2O)4]n (1; HIA is isonicotinic acid) was prepared. The praseodymium(III) cation is surrounded by eight oxygen atoms and exhibits a square antiprismatic PrO8 geometry. The manganese(II) ion shows a hexagonal bipyramid. Adjacent Pr3+ cations are interconnected by IA groups to give a one-dimensional (1-D) chain. The chains are further connected by the MnCl2(H2O)4 moieties to give a two-dimensional (2-D) layer. Complex 1 shows red photoluminescence, which comes from the 1D2 → 3H4, 3P0 → 3H6, 3P0 → 3F2 and 3P1 → 3F3 transitions of praseodymium(III) ions. It possesses a band gap of 1.98 eV.

Syntheses, luminescences and Hirshfeld surfaces analyses of structurally characterized homo-trinuclear ZnII and hetero-pentanuclear ZnII-LnIII (Ln = Eu, Nd) bis(salamo)-like complexes

Homo-trinuclear [Zn3(L)(μ2-OAc)2(H2O)].CH2Cl2 (1) and hetero-pentanuclear [Zn4(L)2Eu(NO3)3(H2O)] (2) and [Zn4(L)2Nd(NO3)3(H2O)]·CH3CH2OH (3) complexes containing a coumarin-skeleton bis(salamo) ligand H4L, were successfully prepared and characterized via the means of elemental analyses, single crystal X-ray crystallography, FT-IR, UV–Vis absorption spectroscopy and Hirshfeld surfaces analyses. Complex 1 is a 1:3 ((L)4−:ZnII) structure, and complexes 2 and 3 are 2:4:1 ((L)4−:ZnII:LnIII) structure. All ZnII atoms in complexes 1–3 occupied the N2O2 sites are five-coordinated with geometries of slightly distorted tetragonal pyramid and trigonal bipyramid. Rare earth metal (EuIII and NdIII) atoms are both coordinated with phenolic oxygen atoms, and eight-coordinated with the square antiprism geometries in complexes 2 and 3. Water molecules as coordinating solvents participate in the coordination. Supra-molecular structures are built by CH…π and hydrogen bonding interactions in complexes 1–3. Moreover, Hirshfeld surfaces analyses of complexes 1–3 were also analysed in detail. Most important of all, luminescences of complexes 1–3 were discussed.

Structural effect on the central cavity of a pendent 12N3 macrocycle on bonding and photophysical properties of Eu3+ and Tb3+ complexes: Experimental and theoretical study

The effect of the ring size of the central cavity of a triaza macrocycle on coordination, bonding and properties is described through synthesis, characterization and detailed DFT studies. For this, two new Eu3+ and Tb3+ neutral complexes based on new 12N3 macrocyclic chelator bearing three 8-hydroxyquinoline pendants, [Ln(12N3Me5Ox)(H2O)n].xH2O (Ln = Eu3+ and Tb3+; 12N3Me5Ox = 1,5,9-tris-{(5-methylene-8-hydroxyquinoline)-1,5,9-triazacyclononane} (x = 4 for Eu and x = 5.3 for Tb; n = 2, 3) were synthesized and characterized by elemental analysis, FT-IR, FT-NMR, ESI-mass spectrometry, molar conductance and thermal analysis data. The spectral and analytical data reveal that both the complexes have different coordination number and geometry as compared to its lower homologue. The europium complex is eight coordinate with stoichiometry [Eu(12N3Me5Ox)(H2O)2].4H2O with twist square antiprismatic geometry while [Tb(12N3Me5Ox)(H2O)3].5.3H2O has nine coordination with distorted mono-capped square antiprismatic geometry. The FTIR and TGA analyses confirmed the presence of coordinated waters. The molecular modeling studies suggest that the metal ion can be easily encapsulated in the central cavity of the ligand. The geometries of the complexes are distorted due to parallel π−π and parallel-displaced π−π stacking arrangement between three pendants of 8HQ with inter planner distance are 3.318 and 3.821 Å. The 1HNMR spectra of Eu3+ complex spectra were much sharper than that of Tb3+ complex. The photoluminescence spectra showed different behaviour in solid as compared to solution state. In the solid state, and at 77 K, the complexes showed characteristic lanthanide emission in addition to the ligand emission peaks. However, in solution, the lanthanide-centred emissions of the complexes were overlapped with the ligand emissions. A weak antenna effect was observed only in the powder form of the complexes. The vibrational data calculated from the DFT [GGA (B3LY-D3)] optimized structures showed good agreement with the experimental results. The excitation and emission behaviour of the ligand and the complexes were established by molecular orbital analysis of the ground state as well as on the excited state optimized geometry at DFT level. The nature of bonding between the lanthanide ions and the 12N3Me5Ox3−, interpreted by means of the natural bond orbital (NBO) and Morokuma Ziegler energy decomposition analysis (ETS-NOCV) scheme, suggest that the Ln-L bonds are more electrostatic (∼73%) than covalent (∼27%). The covalent character of the complexes increases in the order Tb > Eu. The Slater Condon parameters and spin-orbital coupling constants were calculated from LF-DFT (ligand field density functional theory) calculation. The theoretical Nephelauxetic parameter was also compared with experimental data.

Solvent-tuned magnetic exchange interactions in Dy2 systems ligated by a μ-phenolato heptadentate Schiff base.

A series of binuclear dysprosium compounds, namely, [Dy(api)]2 (1), [Dy(api)]2·2CH2Cl2 (2), [Dy(Clapi)]2·2C4H8O (3), and [Dy(Clapi)]2·2C3H6O (4) (H3api = 2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazoline; H3Clapi = 2-(2′-hydroxy-5′-chlorophenyl)-1,3-bis[3′-aza-4′-(2′′-hydroxy-5′′-chlorophenyl)prop-4′-en-1′-yl]-1,3-imidazolidine), have been isolated by the reactions of salen-type ligands H3api/H3Clapi with DyCl3·6H2O in different solvent systems. Structural analysis reveals that each salen-type ligand provides a heptadentate coordination pocket (N4O3) to encapsulate a DyIII ion and all of the DyIII centers in 1–4 adopt a distorted square antiprism geometry with D4d symmetry. Magnetic studies showed that compound 1 did not exhibit single-molecule magnetic (SMMs) behavior. With the introduction of different lattice solvents, compounds 2–4 showed filed-induced slow magnetic relaxation with barriers Ueff of 18.2 K (2), 28.0 K (3) and 16.4 K (4), respectively. Ab initio calculations were employed to interpret the magnetization behavior of 1–4. The combination of experimental and theoretical data reveal the importance of the weak exchange interaction between the DyIII ions in the observation of slow magnetic relaxation, and a relaxation mechanism has been developed to rationalize the observed difference in the Ueff values. The different lattice solvents influence Dy–O–Dy bond angles and thus alter the torsion of the square antiprism geometry, consequently resulting in distinct magnetic interactions and the magnetic behavior.

Three Dy(iii) single-ion magnets bearing the tropolone ligand: structure, magnetic properties and theoretical elucidation.

The reactions of dysprosium nitrate with the main ligand of tropolone (HL) in the presence of ancillary ligands of phenanthroline (phen) or 1,3,5-benzenetricarboxylic acid (H3BTC) gave three mononuclear complexes, [Dy(phen)2(L)(NO3)2] (1), [Dy(phen)(L)3]·H2O (2) and [Dy(H3BTC)(H2O)(L)3]2·3H2O (3). They present different sets of mixed ligands. The Dy(iii) ions are ten-coordinated to build a bicapped square anti-prismatic geometry for complex 1 and eight-coordinated in dodecahedral geometries for complexes 2 and 3. Their magnetic properties were investigated in detail. Complexes 1 and 2 are single ion magnets under an external field, and complex 3 is a single ion magnet under zero field. This revealed a tuning effect on the performances of single ion magnets from ancillary ligands. These experimental magnetic behaviours are supported by the results from ab initio calculations, including g-tensors, averaged transition magnetic moments, magnetic easy axes, and crystal field parameters.

Near-infrared excited cooperative upconversion in luminescent Ytterbium(ΙΙΙ) bioprobes as light-responsive theranostic agents

Near-infrared (NIR) Ytterbium(ΙΙΙ) complexes namely [Yb(dpq)(DMF)2Cl3] (1), [Yb(dppz)(DMF)2Cl3] (2), [Yb(dpq)(ttfa)3] (3) and [Yb(dppz)(ttfa)3] (4) based on photosensitizing antenna: dipyrido-[3,2-d:2′,3′-f]-quinoxaline (dpq), dipyrido-[3,2-a:2′,3′-c]-phenazine (dppz) and 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (Httfa), were designed as NIR bioimaging agents utilizing cooperative upconversion luminescence (CUCL) of Yb(III). Their structures, detailed photophysical properties, biological interactions, photo-induced DNA cleavage, NIR photocytotoxicity and cellular internalization and bioimaging properties were examined. Discrete mononuclear complexes adopt a seven-coordinated {LnN2O2Cl3} mono-capped octahedron (1, 2) and eight-coordinated {LnN2O6} distorted square antiprism geometry (3, 4) with bidentate N, N-donor dpq, dppz and O,O-donor ttfa ligands. The designed Yb(III) probes (3, 4) having advantages of dual sensitizing antennae (dpq/dppz and Httfa) to modulate the desirable optical properties in NIR region for bioimaging in biologically transparent window and light-responsive intracellular damage with spatiotemporal control. The lack of inner-sphere water (q = 0), remarkable photostability, large Stokes' shifts, presence of energetically rightly poised ligand 3T states allows efficient energy transfer (ET) to the emissive 2F5/2 state of Yb(ΙΙΙ). The unique cooperative upconversion luminescence (CUCL) of Yb(III) was observed in 1–4 in the visible blue region (λem = 490 nm) upon NIR excitation at 980 nm, makes them special candidates for NIR-to-visible or NIR-to-NIR cellular imaging probes. The CUCL property of Yb(III) were observed in the discrete mononuclear complexes both in solid state and solution. We elegantly utilized this remarkable property of Yb(III) for cellular imaging application for the first time to the our knowledge including potential uses in CUC/multiphoton excitation microscopy. The complexes exhibit significant binding propensity to DNA, HSA and BSA (K ∼ 105 M−1). They effectively cleave supercoiled (SC) DNA to its nicked circular (NC) form at 365 nm via photoredox pathways. The cellular uptake studies evidently displayed cytosolic and nuclear localization of the complexes. Finally, the capability of Yb(III) complexes usage for PDT were demonstrated through significant near-IR photocytotoxicity at 980 nm CW laser. The results depicted here offers an intelligent strategy towards developing light-responsive highly photostable Yb(III) probes for NIR theranostic application in the biologically transparent phototherapeutic window.

Synthesis and Fluorescence Properties of a Structurally Characterized Hetero-Hexanuclear Zn(II)-La(III) Salamo-Like Coordination Compound Containing Auxiliary Ligands

A hetero-hexanuclear Zn(II)-La(III) coordination compound, [{(ZnL)2La}2(bdc)2](NO3)2 (H2bdc = terephthalic acid) has been synthesized with a symmetric Salamo-like bisoxime, and characterized by elemental analyses, IR, UV-Vis, fluorescent spectroscopy, and single-crystal X-ray diffraction analysis. All of the Zn(II) ions are pentacoordinated by N2O2 donator atoms from the (L)2− unit and one oxygen atom from one terephthalate anion. The Zn(II) ions adopt trigonal bipyramidal geometries (τZn1 = 0.61, τZn2 = 0.56). The La(III) ions are decacoordinated in the Zn(II)-La(III) coordination compound and has a distorted bicapped square antiprism geometry. Meanwhile, the photophysical property of the Zn(II)-La(III) coordination compound was also measured and discussed.

Synthesis, structure, photoluminescent, optical and magnetic properties of a novel thulium p-hydroxybenzenesulfonate complex

Abstract A novel thulium p-hydroxybenzenesulfonate complex [Tm(C6H5O4S)2(H2O)6](C6H5O4S)·3H2O (1) was solvothermally synthesized and characterized by elemental analyses, photoluminescence, solid-state UV/vis diffuse reflectance, magnetic measurements and single-crystal X-ray diffraction. Complex 1 features an ionic structure with the thulium ion possessing a square antiprismatic geometry. Complex 1 crystallized in the monoclinic system with space group P21. Photoluminescent measurements with solid-state sample demonstrate that the anti-Stokes emission bands in the red/NIR spectral region 710 and 812 nm are observed from the Tm3+ 4f intrashell transitions from the 3F2,3 excited states to the 3H6 and 1G4 excited state to the 3H5 state, respectively. Solid-state UV/vis diffuse reflectance spectra of complex 1 show the existence of a wide optical band gap of 3.56 eV. Variable-temperature magnetic susceptibility and field dependence magnetization measurements are also studied and the magnetic susceptibility obeys the Curie-Weiss law (χ m =c/(T−θ)) with the value C being of 8.6 K and a negative Weiss constant θ being of −0.2 K.

Two Novel Binuclear Lanthanide Complexes with 2,5‐Dichlorobenzoic Acid and 5,5’‐Dimethyl‐2,2’‐bipyridine: Crystal Structures, Luminescence and Thermal Properties

AbstractTwo novel binuclear lanthanide complexes [Ln(2, 5‐DClBA)3(5,5’‐DM‐2,2’‐bipy)(H2O)]2(5,5’‐DM‐2,2’‐bipy) (Ln=Eu(1), Tb(2)); 2,5‐DClBA=2,5‐dichlorobenzoate; 5,5’‐DM‐2,2’‐bipy=5,5’‐dimethyl‐2,2’‐bipyridine) have been successfully synthesized via conventional solution method and then characterized by single‐crystal X‐ray diffraction and elemental analysis. These two binuclear complexes differ from other reported binuclear complexes, because the free neutral ligands are not common in crystal structure. The complexes are isomorphic, which have the same coordination number of eight with a distorted square antiprismatic molecular geometry. The binuclear units feature hydrogen bonding (O−H⋅⋅⋅N and C−H⋅⋅⋅Cl) and π‐π stacking interactions assemble the adjacent molecular units into 1D, 2D and 3D supramolecular novel structures. It is worth noting that the novel 1D supramolecular structure is formed by the hydrogen bonding interaction between the nitrogen atoms of free 5,5’‐DM‐2,2’‐bipy ligand and the oxygen atom of the coordination water molecule. The thermal decomposition mechanism of the two complexes were studied by TG/DSC‐FTIR techniques. Additionally, the luminescence spectra and lifetime have been studied in detail. The results indicate that Eu3+ ion and Tb3+ ion could be sensitized by ligands and thus emitted intense characteristic red and green luminescence, respectively.