Antiprismatic Configuration Research Articles

A spherical capped square antiprismatic DyIII complex encapsulated three acylhydrazone Schiff base ligands behaving field-induced single-ion magnet behaviour

One mononuclear DyIII based complex, [Dy(L)3]·0·25H2O (1) (HL= N'-(2-hydroxybenzoyl)pyridine-2-carbohydrazonamide) has been successfully synthesized and systematically characterized. Single-crystal X-ray diffraction reveals that 1 crystallizes in the orthorhombic system with space group P/21. The nine-coordinated DyIII ion in 1 adopts distorted spherical capped square antiprism configuration (C4v-CSAPR) with three tridentate coordination pockets. In addition, the alternating-current (ac) magnetic susceptibility investigations show that 1 exhibits slow magnetic relaxation behavior under an applied 1000 Oe field with effective energy barrier (Ueff) of 83.10 K. To understand the magnetic behaviour in depth, the magnetic axes and magneto-structural correlations are analyzed to reveal that the coordination of three ligands effectively enhances the axiality of the nine-coordinated mononuclear DyIII complexes, thereby exhibiting the slow magnetic relaxation behaviour. This work provides a strategy to effectively improve the performance of single-ion magnets (SIMs) by introducing more ligands around the DyIII ion, and regularizing the coordination configuration of the DyIII ion towards an axial-type structure.

Synthesis and Effects of Two Novel Rare-Earth Energetic Complexes on Thermal Decomposition of Cyclotetramethylene Tetranitramine (HMX).

In order to explore the effect of the energetic complex on the thermal decomposition HMX, two new rare-earth energetic complexes [La(tza)(NO3)2(H2O)4]n (1) and [Ce(tza)(NO3)2(H2O)4]n (2) (Htza = tetrazole-1-acetic acid) were prepared by a solvent evaporation method. The obtained products were structurally characterized by Fourier-transform infrared spectroscopy (FTIR), elemental analysis, powder X-ray diffraction (PXRD), single crystal X-ray diffraction (XRD), and thermogravimetric analysis coupled with differential scanning calorimetry (TG-DSC). In addition, the compatibility of complex 1 with cyclotetramethylene tetranitramine (HMX) was studied by DSC and FTIR, respectively. Structural analysis suggested that complex 1 exhibits an orthorhombic, P 21 21 21 space group, and the La (III) ion was 10-fold coordinated in a distorted double-capped antiprism configuration. Complex 2 featured a one-dimensional, right-handed helical infinite chain. The effect of complexes 1 and 2 on the thermal decomposition of HMX was investigated by DSC, which revealed that complex 1 showed a slightly better effect than 2 on the thermal decomposition of HMX and released more heat. Furthermore, complex 1 had good compatibility with HMX, indicating that it may act as a combustion promoter for nitrate ester plasticized polyether (NEPE) solid propellant.

Regulation of Substituent Effects on Configurations and Magnetic Performances of Mononuclear DyIII Single-Molecule Magnets.

A series of mononuclear DyIII compounds, [Dy(tmpd)3(4,4'-dmpy)] (1), [Dy(tffb)3(4,4'-dmpy)] (2), [Dy(tffb)3(5,5'-dmpy)] (3), and [Dy(tmpd)3(5,5'-dmpy)] (4) [tmpd = 4,4,4-trifluoro-1-(4-methoxyphenyl)-1,3-butanedione, tffb = 4,4,4-trifluoro-1-(4-fluorophenyl)-1,3-butanedione, 4,4'-dmpy = 4,4'-dimethyl-2,2'-bipyridyl, and 5,5'-dmpy = 5,5'-dimethyl-2,2'-bipyridyl], have been synthesized by modifying β-diketonate ligands and capping N-donor co-ligands. DyIII ions in 1-4 possess N2O6 octacoordinated environments. Compounds 1 and 2 exhibit distorted trigonal dodecahedron configurations, while 3 and 4 display distorted square antiprismatic configurations. Systematic investigations of the alternating current measurements indicate the different magnetic relaxation dynamics with energy barriers (Ueff) of 66 K (1, 45 cm-1), 189 K, (2, 131 cm-1), 115 K (3, 79 cm-1), and 205 K (4, 142 cm-1). To deeply understand their different magnetic behaviors, the magnetic anisotropies of 1-4 were studied by ab initio calculations. From ab initio calculations, the energies of the first excited state (KD1) are consistent with the experimental Ueff under zero direct current field. Compound 4 presents the largest Ueff because of the smallest gX,Y and μQTM as well as the most strong axial crystal field parameters (CFPs) among compounds 1-4. The M versus H data exhibit butterfly-shaped hysteresis loops at 2 K for 1-4. The different coordination geometries, the magnetic dynamics, the electrostatic repulsion, and CFPs result from the different substituent effects of ligands, including the electronic effect, the steric effect, and the positions of substituted groups.

Physical chemistry CeF4 complexes in organic solvents

The first complexes of cerium tetrafluoride in solutions were investigated by 19F NMR and IR spectroscopy. The temperature dependence of the 19F NMR spectra was, studied and it was concluded that mobile equilibrium exists between the molecular adduct and singly charged ionic forms, including geometric isomers. The static probability of stereoisomer formation [CeF4(dmso)4] was calculated using the square antiprism configuration and, based on the relative intensity of the 19F NMR resonance signals, they were assigned to possible stereoisomers. Quantum-chemical calculations of the structure of the isomer [CeF4(dmso)4], the isomer [CeF3(dmso)5]+ and [CeF5(dmso)3]-, showing their thermodynamic stability, were performed.

CeF4 Complexes in Organic Solvents

The first complexes of cerium tetrafluoride in solutions have been studied by 19F NMR and IR spectroscopy. The temperature dependence of the 19F NMR spectra has been explored, and conclusion has been made that dynamic equilibrium between the molecular adduct and singly charged ionic forms, including geometric isomers, exists in solution. The statistical probability for the formation of [CeF4(dmso)4] stereoisomers of square antiprism configuration has been calculated, and their assignment to possible stereoisomers have been made on the basis of relative intensities of the 19F NMR signals. Quantum-chemical calculations of the structure of one of the possible isomers have been performed for the [CeF4(dmso)4] molecular adduct, [CeF3(dmso)5]+ cation, and [CeF5(dmso)3]– anion to show their thermodynamic stability.

Photoluminescence and semiconductive properties of a 4f–5d compound

A novel 4f–5d compound [Ho(H2O)2(μ-IA)3Hg3Br6]n (1, HIA = isonicotinic acid) was prepared. It is characterized by single-crystal X-ray diffraction. The title compound crystallizes in the space group P21/n of the monoclinic system. The holmium ion is coordinated by six oxygen atoms to yield a slightly distorted tetragonal antiprism configuration. Three crystallographically independent mercury ions exhibit two different coordination environments, i.e., tetrahedron geometry and square pyramidal configuration. In the title compound, there are two types of one-dimensional (1D) chains, namely Hg–Br chains and Ho–IA chains. Both chains are interconnected by the μ3-bridging isonicotinic acid ligands to form a three-dimensional (3D) frame structure. Photoluminescence from solid samples showed that the title compound could emit up-conversion red fluorescence, and its half-peak width was about 14 nm. The emission peak comes from its characteristic emission of 5F5 → 5I8 of Ho3+. The CIE color coordinates of the title compound are (0.693, 0.307). The title compound displays a broad semiconductor gap being of 2.47 eV, as discovered by the solid-state diffuse reflection. A novel 4f–5d compound has been prepared. It features a 3D framework structure. It displays a red up-conversion photoluminescence emission band. Diffuse reflection spectrum with solid-state sample shows that it possesses a wide optical band gap of 2.47 eV.

A new β-diketonate Dy(III) single‒ion magnet featuring multiple magnetic relaxation processes

A β-diketonate mononuclear dysprosium compound, [Dy(TFNB)3(bpy)] (1) (TFNB = 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione, bpy = 2,2′-bipyridine), has been prepared and structurally and magnetically characterized. X-ray crystallographic analysis reveals that 1 contains two crystallographically equivalent Dy(III) ions of which the eight-coordinate geometries uniformly behave as distorted square antiprismatic configurations (D4d). Magnetic investigations demonstrate that 1 displays dual relaxation processes of SMMs behavior with the effective barrier (ΔE/kB) of 23.44 K under 1200 Oe DC field, corresponding to the coexistence of two metal centers in the structure of the compound. The comparative studies of some Dy(III)-based SIMs with TFNB ligand have been conducted as well. Ab initio studies demonstrate that the Kramers doublet ground state is predominantly axial with the gz tensors of two Dy(III) fragments matching the Ising-limit factor (20) anticipated for the pure MJ = ±15/2 state.

Field-induced single-molecule magnet (SMM) behavior of dinuclear DyIII system

In this context, three isomorphic compounds were obtained, namely, [Ln2(L)2(NO3)4(H2O)2]·2CH3OH (Ln=Dy (1), Tb (2) and Er (3), HL=N′-(2-Hydroxybenzoyl) pyridine-2-carbohydrazonamide). In these compounds, LnIII ion locates in N2O7 coordination environment, forming a monocapped square antiprism configuration (C4v). Furthermore, two L− ligands coordinate to two LnIII centers in an antiparallel or “head-to-tail” fashion with tridentate unit and monodentate phenol-O−, resulting in a center of symmetry with LnIII⋯LnIII distances (intramolecular) of 6.751Å for 1, 6.708Å for 2 and 6.723Å for 3, respectively. Magnetic measurement reveals that 1 shows frequency-dependent out-of-phase (χ″) signals under a direct-current (dc) field, exhibiting single-molecule magnet (SMM) behavior with the anisotropy energy barrier (Ueff) of 16.0K and the pre-exponential factor value (τ0) of 1.0×10−6s. In addition, the luminescence properties of 1 and 2 were studied. Moreover, the semiconductor behaviors of 1–3 have been investigated by experimental measurements of UV−vis spectroscopy.

Imposing high-symmetry and tuneable geometry on lanthanide centres with chelating Pt and Pd metalloligands.

Exploitation of HSAB preferences allows for high-yield, one-pot syntheses of lanthanide complexes chelated by two Pd or Pt metalloligands, [MII(SAc)4]2- (SAc- = thioacetate, M = Pd, Pt). The resulting complexes with 8 oxygen donors surrounding the lanthanides can be isolated in crystallographically tetragonal environments as either [NEt4]+ (space group: P4/mcc) or [PPh4]+ (space group: P4/n) salts. In the case of M = Pt, the complete series of lanthanide complexes has been structurally characterized as the [NEt4]+ salts (except for Ln = Pm), while the [PPh4]+ salts have been structurally characterized for Ln = Gd-Er, Y. For M = Pd, selected lanthanide complexes have been structurally characterized as both salts. The only significant structural difference between salts of the two counter ions is the resulting twist angle connecting tetragonal prismatic and tetragonal anti-prismatic configurations, with the [PPh4]+ salts approaching ideal D4d symmetry very closely (φ = 44.52-44.61°) while the [NEt4]+ salts exhibit intermediate twist angles in the interval φ = 17.28-27.41°, the twist increasing as the complete 4f series is traversed. Static magnetic properties for the latter half of the lanthanide series are found to agree well in the high temperature limit with the expected Curie behavior. Perpendicular and parallel mode EPR spectroscopy on randomly oriented powder samples and single crystals of the Gd complexes with respectively Pd- and Pt-based metalloligands demonstrate the nature of the platinum metal to strongly affect the spectra. Consistent parametrization of all of the EPR spectra reveals the main difference to stem from a large difference in the magnitude of the leading axial term, B02, this being almost four times larger for the Pt-based complexes as compared to the Pd analogues, indicating a direct Pt(5d z2 )-Ln interaction and an arguable coordination number of 10 rather than 8. The parametrization of the EPR spectra also confirms that off-diagonal operators are associated with non-zero parameters for the [NEt4]+ salts, while only contributing minimally for the [PPh4]+ salts in which lanthanide coordination approximates D4d point group symmetry closely.

Paramagnetic Phospholipid-Based Micelles Targeting VCAM-1 Receptors for MRI Visualization of Inflammation.

Inflammation is signaled by the overexpression of epitopes on the vascular endothelium that primarily aim at recruiting immune cells into the inflamed area. The intravascular localization of these biomarkers makes them suitable targets for the MRI visualization of inflammation. Phospholipid-based nanosystems appear excellent candidates in virtue of their good biocompatibility, ability to deliver a high number of imaging units at the target site, and for the easy functionalization with targeting vectors. In this work, phospholipid-based micelles (hydrodynamic diameter of 20 nm) loaded with the amphiphilic Gd(III)-complex Gd-DOTAMA(C18)2 were vectorized with a small peptide able to specifically bind VCAM-1 receptors. The micelles displayed a high longitudinal relaxivity (36.4 s(-1)mmolGd(-1) at 25 °C and 0.7 T). A (1)H- and (17)O-water relaxometry study indicated that the paramagnetic complex embedded in the nanoparticles adopted two isomeric conformations, likely reflecting the well-known square antiprismatic (SAP) and twisted square antiprismatic (TSAP) configurations typically observed in DOTA-like lanthanide complexes. Interestingly, the TSAP structure, showing a much faster exchange rate for the water molecule coordinated to the metal ion, was the most abundant, thus explaining the high relaxivity of the micellar agent. The systemic administration of the micelles into a lipopolysaccharide-induced murine model of acute inflammation successfully demonstrated the ability of the targeting agents to detect the diseased area by T1 contrast enhanced MRI.

Rare single-molecule magnets with six-coordinate Ln(III) ions exhibiting a trigonal antiprism configuration.

Four Ni-Ln-Ni heterometallic complexes, [Ni2LnL2]NO3·3H2O (H3L = tri(((3-methoxysalicylidene)amino)ethyl)amine, Ln = Gd for , Tb for and Dy for , respectively) and [Ni2DyL2]ClO4·MTBE·0.65H2O (, MTBE = methyl tert-butyl ether) have been synthesized by diffusion of methyl tert-butyl ether vapor into the reaction solution. The X-ray analyses demonstrated that the Gd(III) ion in exhibits rare seven-coordination, the Tb(III) and Dy(III) ions in display unusual six-coordination, and two Ni(II) ions and one Ln(III) ion are bridged by six phenolato atoms to form linear Ni-Ln-Ni heterotrinuclear complexes for . All complexes exhibit weak ferromagnetic interactions between Ni(II) and Ln(III) ions. Alternating current susceptibility measurements demonstrated that compounds and behave as single-molecule magnets with the effective energy barriers of 14.17 and 11.13 K under zero direct current field. They are rare single-molecule magnets containing six-coordinate Dy(III) ions.

Labile capping bonds in lanthanide(III) complexes: shorter and weaker.

For a wide range of trivalent lanthanide ion coordination complexes of tricapped trigonal prism or monocapped square antiprism configurations, the bonds between the central lanthanide ions and the capping ligands are found to violate Badger's rule: they can get weaker as they get shorter. We demonstrate that this observation originates from the screening and repulsion effect of the prism ligands. Both effects enhance as the electric field of the central ion or the softness of the prism ligands increases. Thus, for heavier lanthanides, despite the fact that the capping bond could be shorter, it is more efficient to be weakened by the prism ligands, being inherently labile. This concept of "labile capping bonds phenomenon" is then successfully used to interpret many problems in lanthanide(III) hydration, e.g., why the water exchange rate of a lanthanide(III) complex is much higher in a twisted square antiprism than in square antiprism configuration. Thus, the theory proposed in this paper offers new insights in understanding chemical problems.

Symmetry argument of cyano-bridged copper-molybdenum complexes

Motivated by photoinduced magnetism in the mixed-valent bimetallic compounds with the general formula Cu2II [MoIV(CN)8]·xH2O, we investigate their ground-state properties, in comparison with those of nickel-molybdenum analogs, by employing a group-theoretical technique. These bimetallic assemblies consist of octacyanomolybdenum complexes with a square antiprism configuration and crystallize in the I4/m tetragonal symmetry. We set up a relevant three-band extended Hubbard Hamiltonian and systematically calculate its broken-symmetry solutions. An itinerant ferromagnetism extending over both the Cu and the Mo sublattices closely competes with the localized paramagnetism in Cu2[Mo(CN)8] whereas spins are rather localized in the Ni sublattice and an antiferromagnetism is likely to predominate in the ground-state phase diagram in Ni2[Mo(CN)8].

A novel LaIII-based metal–organic framework (MOF) with a new topology: poly[diaquabis(μ5-2,5-dioxopiperazine-1,4-diacetato)(μ2-oxalato)dilanthanum(III)

In the title metal-organic framework (MOF), [La(C(8)H(8)N(2)O(6))(C(2)O(4))(0.5)(H(2)O)](n), the La(III) cation is coordinated by eight O atoms in a square antiprismatic configuration. Each La(III) cation is connected to adjacent La(III) cations by bridging 2,5-dioxopiperazine-1,4-diacetate (PODC(2-)) and oxalate (lying about an inversion centre) ligands, generating two-dimensional grid layers. The layers are further linked via the carboxylate groups of the PODC(2-) ligands in syn-syn and syn-anti modes, resulting in a three-dimensional framework with a short Schläfli vertex notation of {4(7).6(3)}{4(7).6(7).8}.

Phase competition and photomagnetism in supramolecular assemblies based on octacyanomolybdates of square antiprism configuration

AbstractWe construct a microscopic theory on the photomagnetism in the cyano‐bridged bimetallic assemblies Cu2[Mo(CN)8]·��H2O. Going through a grouptheoretical analysis on the ground‐state properties, we simulate photoirradiation and the resultant magnetization dynamics with a time‐dependent Hartree‐Fock method.It is not c‐axis‐polarized photons but those polarized in the ab plane that induce a macroscopic magnetization. Absorption of the photon energy is double‐stepped and the occurrence of a significant magnetization is simultaneous with the second stage (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

An Unusual Bismuth Ethanedisulfonate Network

The three dimensional bismuth ethanedisulfonate framework Bi(O3SC2H4SO3)1.5(H2O)2 was synthesized under hydrothermal conditions using the bidentate ligand 1,2-ethanedisulfonate and then characterized through X-ray diffraction and elemental analyses. The bismuth cation coordinates at three different ethanedisulfonate ligands and has a coordination number of eight, which is accompanied by a distorted square antiprismatic configuration. Here, we report on the crystal structure of this bismuth metal–organic framework and its coordination behavior, which has thus far not been reported in heavier main group elements.

New chelate complexes of trivalent Y and lanthanides (Eu, Ho, Yb) with a triazene N-oxide: Synthesis, structural characterization and luminescence properties

Deprotonated 3-(4-nitrophenyl)-1-phenyltriazene N-oxide reacts with YCl3·6H2O and LnCl3·6H2O (Ln=Eu, Ho, Yb) to give the monoclinic chelate complexes [Y{O2N(C6H4)NNN(O)Ph}4](Et3NH)·H2O (1) (Ph=C6H5; Et=C2H5) and [LnIII{O2N(C6H4)NNN(O)Ph}4](Et3NH)·H2O·{CH3OH∗} {LnIII=Eu (2), Ho (3), Yb∗ (4), in which the metal centers present a square antiprismatic configuration. As already observed for hydrated ammonium complexes of triazene-oxides ligands with (C6H4)−NO2 groups, multiple, effective O···H and N···H interactions hold the species in supramolecular 3D assemblies. The optical and the luminescent properties of the triazene-oxide europium complex 2 are also presented and fully discussed.

ChemInform Abstract: A Novel-Type Mixed-Ligand Polyoxotungstolanthanoate, [Ln(BW11O39)(W5O18)] 12- (Ln: Ce3+ and Eu3+).

Two isostructural anions, [Ln(BW11O39)(W5O18)]12- (Ln = Ce and Eu), were isolated as K+ salts from aqueous solutions containing tungstate, Ln3+, and BO33-, at pH = 7. An X-ray crystallographic analysis showed that the Ln3+ center in the anion is chelated by two kinds of tetradentate polyoxotungstate ligands, [W5O18]6- and α-[BW11O39]9- with a square antiprismatic LnO8 configuration, which are monovacant derivatives of [W6O19]2- and α-[BW12O40]5-, respectively. The anion is of approximate Cs symmetry, and the observable asymmetry of K-O bonding between two different K+ cations and the anion causes the two mirror planes within [(W5O18)Ln]3- and [(BW11O39)Ln]6- moieties to be canted to each other by 5.2° for Ln = Ce and 4.1° for Ln = Eu.

Stabilization of substituted triazene oxides by lanthanides chelation: Synthesis, TGA evaluations and X-ray structural features of [M III{O 2NPhNNN(O)Ph} 4](Et 3NH)·H 2O (M = La 3+, Dy 3+; Et = C 2H 5)

Deprotonated 3-(4-nitrophenyl)-1-phenyltriazene N-oxide reacts with La(NO 3) 3·6H 2O and DyCl 3 · 6H 2O to give [M III{O 2NPhNNN(O)Ph} 4](Et 3NH)·H 2O (M = La 3+ ( 1), Dy 3+ ( 2); Et = C 2H 5). In both complexes the metal centers present the coordination number 8, with a square antiprismatic configuration. As already expected for triazene oxides with PhNO 2 groups, multiple, effective O···H interactions hold the species in two-dimensional layers in the bc plane. TGA and IR data of both compounds are also presented and discussed.

Synthesis, structure and magnetic behaviour of dinuclear uranium(iv) complexes with a ‘calixsalophen’ type macrocycle

Treatment of UCl4 with the octadentate tricompartmental ‘calixsalophen’ type macrocycle H4L1 [N,N:N′,N′-bis(2,2′-dihydroxy-3,3′-dimethylidene-5,5′-di-tert-butylbiphenyl)benzene-1,2-diamine] in THF or pyridine gave the complexes [U2L1Cl4] (1) and [U2L1Cl4(py)2] (2), respectively. The crystal structures of 1·4THF and 2·3py are centrosymmetric, the metal atoms occupying the N2O2 cavities with either a pentagonal bipyramidal environment in 1, two Cl atoms being in apical positions, or a dodecahedral environment in 2. Reaction of U(acac)4 (acac = MeCOCHCOMe) with H4L1 in THF did not afford the corresponding acetylacetonate product but gave instead the isomeric complex [U2L1(acac)4] (3), in which one of the two N2O2 cavities is empty, one of the uranium atoms occupying the central O4 site. The dinuclear complex [U2(HL3)(acac)5] (4) was obtained by treating U(acac)4 with H4L1 in pyridine; in this case, the macrocyclic ligand L1 was transformed into its mono(benzimidazole) derivative L3. The eight-coordinate uranium atoms in 3·5THF and 4·2py adopt a distorted square antiprismatic configuration. The magnetic properties of compounds 1 and 3 were investigated.