Trigonal Prismatic Coordination Geometry Research Articles

Structures, photoluminescence, and magnetism of 1D lanthanide coordination polymers dominated on 3,5‐dichlorobenzoate

AbstractTwo series of novel coordination polymers (CPs), namely, Ln3(3,5‐DCB)9(bipy) (H2O)2·(bipy) [Ln = Nd (1), Sm (2)] and Ln2(3,5‐DCB)6(bipy)H2O [Ln = Eu (3), Gd (4), Tb (5) and Dy (6)], have been synthesized by hydrothermal reaction of a bridging ligand, 3,5‐dichlorobenzoic acid (3,5‐HDCB), with LnCl3·nH2O and N‐donor neutral ligand, 2,2′‐bipyridine (bipy). Single‐crystal x‐ray diffraction, elemental analysis, IR spectroscopy, thermogravimetric analysis (TGA), and powder x‐ray diffraction (PXRD) for 1–6 are presented. CPs 1 and 2 exhibit trinuclear lanthanide architectures, in which the center Ln(III) are seven‐coordinated and eight‐coordinated adopting monocapped triangular prismatic, distorted square antiprism and bicapped trigonal prismatic coordination geometry, respectively, whereas CPs 3–6 are isostructural dinuclear structures. The center Ln(III) ions are also seven‐coordinated and eight‐coordinated with different coordinate modes adopting distorted monocapped triangular prismatic and square antiprism coordination geometry. Trinuclear CPs 1 and 2 are packed together via hydrogen‐bonding interaction to form the two‐dimensional (2D) supramolecular layers. CPs 3–6 exhibit 2D layers by the π–π interaction. CPs 2, 3, 5, and 6 display the characteristic fluorescent emissions of Sm(III), Eu(III), Tb(III), and Dy(III), respectively. CPs 1 and 4–6 exhibit corresponding weak anti‐ferromagnetic and ferromagnetic interactions of Nd(III), Gd(III), Tb(III), and Dy(III) in the low‐temperature range.

A novel style of 2D Hofmann-type coordination polymer incorporated trigonal prismatic coordination geometry with bidentate co-ligands.

A novel 2D Hofmann-type framework was prepared with a bidentate co-ligand, 5,5'-dimethyl-2,2'-bipyridyl (dmbpy), which forces the curvature of the layer. X-ray diffraction analysis demonstrated that the coordination polymers, MnII(dmbpy)[MVN(CN)4] (MV = Mn (1) and Cr (2)), formed a considerably corrugated 2D cyanide-bridged network with a quasi C4v symmetric building unit, [CrVN(CN)4]2-, and trigonal prismatic coordination geometry around MnII. Compound 2 demonstrated a metamagnetic-like ordering at 14.4 K, caused by the intra- and inter-layer antiferromagnetic interactions between CrV (S = 1/2) and MnII (S = 5/2), and a weak ferromagnetic behaviour at 2 K reflecting the single-ion anisotropy of CrV and structural anisotropy.

Alkyl Chains Modulated Magnetization Dynamics of Mononuclear Trigonal Prismatic CoII Complexes.

Four benzeneboron-capped mononuclear CoII complexes with different alkyl substitutions on the fourth position of phenylboronic acid were obtained. The CoII ions are all wrapped by the pocket-like ligands and located in trigonal prismatic coordination geometries. Alternating-current magnetic susceptibility measurements reveal that they show different magnetization dynamics, such as distinct relaxation rates at the same temperature, the faster QTM rates for the ethyl and propyl substituted complexes, as well as different relaxation processes. Magneto-structural correlation study reveals that the various deviations of coordination geometry of CoII ion, diverse crystal packings and possible different vibration modes of substituents caused by modifying alkyl chains are the key factors affecting the magnetization dynamics. This work demonstrates that the alkyl chains even locating far away from the metal center can have a large impact on the magnetic behavior of the CoII complex with a very rigid coordination geometry, offering a new perspective towards transition metal based single-molecule magnets.

Trigonal prismatic coordination geometry imparted by a macrocyclic ligand: an approach to large axial magnetic anisotropy for Co(II).

Large uniaxial magnetic anisotropy, expressed by a negative value of the axial zero-field splitting parameter D, has been achieved in a series of trigonal prismatic Co(II) complexes with the general formula [Co(L)X]Y, where L = 1,5,13,17,22-pentaazatricyclo[15.2.2.17,11]docosa-7,9,11(22)-triene, X = Cl-(1a,b), Br-(2), N3-(3), NCO-(4), NCS-(5), NCSe-(6), and Y = Cl-(1), Br-(2), NCS-(4), NCSe-(5), ClO4-(3,6). Complexes 1-6 are six-coordinate with the distorted trigonal prismatic geometry imparted by the pentadentate pyridine-/piperazine-based macrocyclic ligand L and by one monovalent coligand X-. Based on magnetic studies, all complexes 1-6 exhibit strong magnetic anisotropy with negative D-values ranging from about -20 to -41 cm-1. This variation in D (i.e. the increase of magnetic anisotropy) parallels the trend obtained by theoretical calculations and the lesser distortion of the coordination sphere with respect to the trigonal prismatic reference geometry. AC magnetic susceptibility investigations revealed field-induced single-molecule magnet behaviour for all complexes except Cl- derivative 1. The series investigated represents a rare example of Co(II) complexes with a robust trigonal prismatic geometry.

Ideal trigonal prismatic coordination geometry of Co(II) in a honeycomb MOF with a triptycene-based ligand.

A metal-organic framework (MOF) comprised of cobalt ions and triptycene-based 3-fold symmetric bridging ligands 9,10-[1,2]benzenoanthracene-2,3,6,7,14,15(9H,10H)-hexaone (o-TT) was prepared. Single-crystal structure analysis revealed a 2D honeycomb network structure and the ideal trigonal prismatic geometry of the Co(II) ion. The magnetic anisotropy of the Co(II) ion in the trigonal prism coordination geometry was analyzed via magnetic measurements and model calculations.

An investigation into the coordination chemistry of tripodal “click” triazole ligands with Mn, Ni, Co and Zn ions

The steric influences of the triazole side chains in two tripodal chelating ligands tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (TBTA) and tris[(1-phenyl-1H-1,2,3-triazol-4-yl)methyl]amine (TPTA) are explored through structural studies of four new mononuclear d-block metal complexes. The manganese(II) complex [Mn(TPTA)2](ClO4)2·H2O 1 includes two TPTA ligands each coordinated in a tridentate fashion to give an unusual trigonal prismatic coordination geometry with two non-coordinated pendant triazole groups which engage in weak hydrogen bonding interactions. [Ni(TBTA)(OH2)Cl]Cl·3H2O·MeCN 2 contains an octahedral nickel(II) centre bound by a tetradentate TBTA ligand along with aqua and chloride ligands, where the significant degree of lattice solvation leads to an extensive hydrogen bonding network linking complexes through hexa-aqua water clusters. The mononuclear copper(II) complex [Cu(TPTA)Cl2]·MeCN 3 contains no classical hydrogen bond donors but instead intermolecular aggregation takes place through chelating CH···Cl hydrogen bonds involving the acidic triazole CH groups which leads to close association of adjacent complexes. The zinc complex [Zn(TPTA)Cl]2[ZnCl4]·MeOH 4, in which cationic [Zn(TPTA)Cl]+ species are accompanied by tetrachlorozincate anions, exhibits a tris-triazole chelating coordination geometry for the TPTA ligand and associates through tetrameric π···π stacking interactions despite the positive charge present on each species. Structural analysis of these complexes, supported by solution-state mass spectrometry, NMR spectroscopic and magnetic susceptibility measurements, where applicable, provides new insights into the breadth of coordination geometries and intermolecular packing modes available to this important class of chelating ligand.

A Dicobalt(II) Single-Molecule Magnet via a Well-Designed Dual-Capping Tetrazine Radical Ligand

The recent years have witnessed the glory development for the construction of high-performance mononuclear single molecule magnets (SMMs) within a specific coordination geometry, which, however, is not well applied in cluster-based SMMs due to the synthetic challenges. Given that the monocobalt(II) complexes within a trigonal-prismatic (TPR) coordination geometry have been classified as excellent SMMs with huge axial anisotropy (D ≈ -100 cm-1), here we designed and synthesized a new dual-capping tetrazine ligand, 3,6-bis(6-(di(1H-pyrazol-1-yl)methyl)pyridin-2-yl)-1,2,4,5-tetrazine (bpptz), and prepared a novel dicobalt(II) complex, [Cp2CoIII][{(hfac)CoII}2(bpptz•-)][hfac]2·2Et2O (1, hfac = hexafluoroacetylacetonate). In the structure of 1, the bpptz•- radical ligand enwraps two Co(II) centers within quasi-TPR geometries, which are further bridged by the tetrazine radical in the trans mode. The magnetic study revealed that the interaction between the Co centers and the tetrazine radical is strongly antiferromagnetic with a coupling constant (J) of -65.8 cm-1 (in the -2J formalism). Remarkably, 1 exhibited the typical SMM behavior with an effective energy barrier of 69 cm-1 under a 1.5 kOe dc field, among the largest for polynuclear transition metal SMMs. In addition, DFT and ab initio calculations suggested that the presence of a strong Co(II)-radical magnetic interaction effectively quenches the QTM effect and enhances the barrier height for the magnetization reversal.

A capped trigonal prismatic cobalt(ii) complex as a structural archetype for single-ion magnets.

Two mononuclear, seven-coordinate Co(ii) and Fe(ii) complexes [CoII(BPA-TPA)](BF4)2 (1-Co) and [FeII(BPA-TPA)](ClO4)2 (2-Fe) with a capped trigonal prismatic coordination geometry have been synthesized from the pentapyridyldiamine (BPA-TPA) ligand. 1-Co exhibits easy plane anisotropy in which slow magnetic relaxation is observed under a 1.0 kOe dc field. It is the first example of a single-ion magnet (SIM) of a 3d transition metal ion with a capped trigonal prismatic configuration. 2-Fe is not a SIM at 1.8 K.

Synthesis, Crystal Structures and Photoluminescent Properties of One-Dimensional Europium(III)- and Terbium(III)-Glutarate Coordination Polymers, and Their Applications for the Sensing of Fe3+ and Nitroaromatics

Two lanthanide–glutarate coordination polymers, viz. : {[Eu(C5H6O4)(H2O)4]Cl}n, (1) and [Tb(C5H7O4)(C5H6O4)(H2O)2]n, (2) have been synthesized and characterized by IR spectroscopy, thermogravimetric analysis, and X-ray crystallography. In 1, the Eu(III) ions are coordinated by four O atoms from two bidentate chelating carboxylate groups, one O atom from a bridging carboxylate group and four O atoms from water molecules adopting an EuO9 distorted tri-capped trigonal prismatic coordination geometry. In 2, the Tb(III) ions are coordinated by six O atoms from three bidentate chelating carboxylates, one O atom from a bridging carboxylate and two O atoms from water molecules to generate distorted tri-capped trigonal prismatic TbO9 polyhedron. In both compounds, the metal polyhedra share edges, producing centrosymmetric Ln2O2 diamonds, and are linked into [001] chains by bridging glutarate di-anions. The crystal structures are consolidated by O–H···O and O–H···Cl hydrogen bonds in 1, and O–H···O hydrogen bonds in 2. Compound 1 exhibits a red emission attributed to the 5D0 → 7FJ (J = 1–4) transitions of the Eu(III) ion, whereas 2 displays green emission corresponding to the 5D4 → 7FJ (J = 0–6) transitions of the Tb(III) ion. Both the compounds exhibit high sensitivity and selectivity for Fe3+ ions due to luminescence quenching compared with other metal ions, which include; Na+, Mg2+, Al3+, Cr3+, Mn2+, Fe2+, Co2+, Ni2+, Zn2+ and Cd2+. Compounds 1 and 2 also show high luminescence quenching sensitivity for 4-nitrophenol over the other aromatic and nitroaromatic compounds, namely; bromobenzene, 1,3-dimethylbenzene, nitrobenzene, 4-nitrotolune, 4-nitrophenol, 2,6-dinitrophenol and 2,4,6-trinitrophenol.

Structural Systematics of Lanthanide(III) Picrate Solvates: Adducts of the Carboxamide Ligands Dimethylacetamide and N-Methylpyrrolidinone

The carboxamide-O donor ligands dimethylacetamide (dma) and N-methylpyrrolidinone (nmp) form complexes of lanthanide picrates, Ln(pic)3, of stoichiometry Ln(pic)3(carboxamide)3 in a remarkable variety of phases. Complexes [Ln(pic)3(dma)3], Ln=La, Ce, Nd, Sm, Gd, Yb, Lu, and Y, adopt the 9-coordinate molecular form of tricapped trigonal-prismatic coordination geometry seen to predominate, as two stereoisomers, in related species involving dimethylsulfoxide (dmso), trimethylphosphate (tmp), and hexamethylphosphoramide (hmpa) but as four different phases (depending on Ln), none of which is the same as for the previously known La complex. For Ln=Pr, 9-coordinate species of composition [Pr(pic)3(dma)2(alcohol)] (alcohol=ethanol and propan-2-ol) have been characterised and a low quality determination indicates that a similar species (with propan-2-ol) is formed by Y. For nmp, the composition [Ln(pic)3(nmp)3] is maintained across the series for Ln=La, Ce, Pr, Nd, Gd, Er, Tm, Yb, and Lu but 9-coordination is not for Ln=Er, Tm, Yb, and Lu. A decreased coordination there is a result of one or two picrate ligands acting as phenoxide-O donors only, a marked contrast with the analogous Ln(pic)3 complexes with dmso, tmp, hmpa, and dma, where picrate chelation is universal, but with some parallel to related ScIII complexes. Several polymorph pairs can be identified among the nmp complexes.

Structural Systematics of Lanthanide(III) Picrate Solvates: Hexamethylphosphoramide and Octamethylpyrophosphoramide Adducts

Crystalline products of the reactions of lanthanide picrates, Ln(pic)3 (pic=2,4,6-trinitrophenoxide), with hexamethylphosphoramide (hmpa) and octamethylpyrophosphoramide (ompa) have been characterised by single-crystal X-ray diffraction studies. With hmpa and lighter lanthanides (La, Sm, Eu), isomorphous species (monoclinic, P21/c, Z 4) of stoichiometry [Ln(pic)3(hmpa)3]·0.5H2O, have been defined where the molecular units in the lattice contain 9-coordinate Ln with tricapped trigonal-prismatic coordination geometry. The picrate ligands are bidentate through phenoxide-O and 2-nitro-O, with the latter occupying the capping positions, while the hmpa ligands are singly O-bound to one trigonal face. Heavier lanthanides (Gd, Lu) and Y have been found to give isomorphous (monoclinic, P21/n, Z 4) species of stoichiometry [Ln(pic)3(hmpa)2], with 8-coordinate Ln of an irregular geometry best considered as close to that of a bicapped trigonal-prism. The picrate ligands chelate in the same manner as in the lighter Ln complexes but with one spanning a trigonal edge, and the hmpa-O donors occuping two apices of the other trigonal face. The ligand ompa has been found to act as a bidentate chelate in all isolated species, displacing one picrate from the metal ion coordination sphere to give ionic complexes. For La, Nd, and Gd, isomorphous (monoclinic, P21/n, Z 4) complexes of stoichiometry [Ln(pic)2(ompa)2(OH2)](pic)·0.5H2O containing 9-coordinate, tricapped trigonal-prismatic Ln with a single aqua ligand have been defined, while for Er, Yb, Lu, and Y, both the coordinated and lattice water molecules are lost in isomorphous (monoclininc, P21/c, Z 8) 8-coordinate, square-antiprismatic species of stoichiometry [Ln(pic)2(ompa)2](pic). For Er, further polymorphs, one monoclinic, P21/c, and the other triclinic, , have also been characterised.

Luminescent Pr(III)-Based Coordination Polymer: Syntheses, Structures, N2 and CO2 Adsorption Properties

A new Pr(III)-based metal organic framework with formula {[Pr2(C8H3O6N)(SO4)2]·5H2O}n was hydrothermally synthesized and characterized by techniques of single crystal X-ray diffraction, infrared spectra (IR), thermogravimetric analysis (TGA), elemental analysis, powder X-ray diffraction (PXRD), and luminescent measurements. X-ray crystal structure analyses reveal that complex 1 is binuclear structure and all Pr(III) atoms show a coordination number of nine with a tricapped trigonal prismatic coordination geometry. Throughout the molecular structure, this lanthanide metal–organic frameworks exhibits a 3D architecture built by the 1D double-stranded chains of Pr ions linked by the 5-nitroisophthalic acid ligand and 2D Pr–SO42− grid. In addition, the fluorescence, nitrogen adsorption properties and carbon dioxide adsorption properties of complex 1 were also investigated. The results indicate that the complex is not only a luminescent and mesoporous material, but also a potential material for selective absorption of carbon dioxide.

Dynamic solution behaviour of metal complexes of the hexaamine cage ligand Me8tricosane

The solid state structures of the hexaamine cage complexes [M(Me8tricosane)]2+ (M = Zn, Cd, Hg) were previously shown to feature highly symmetric octahedral or trigonal prismatic coordination geometries. Here we show that the solution NMR spectra of each of these three complexes are far more complex than what would be expected if the solid state structures were retained after dissolution. The large numbers of resonances observed in the solution NMR spectra reflects establishment of equilibria involving multiple diastereoisomers with different nitrogen atom configurations. Support for this explanation was provided by the 15N HSQC spectrum of the Zn complex, and by variable temperature 1H and 13C NMR spectra of each of the three metal complexes. In addition, the results of calculations performed using DFT methods showed that the differences in energy between diastereoisomers were sometimes very small, and therefore unlikely to present a significant barrier to isomerisation processes.

Synthesis and structural, redox and photophysical properties of tris-(2,5-di(2-pyridyl)pyrrolide) lanthanide complexes.

A first series of lanthanide complexes of tris(dipyridyl)pyrrolide ligands has been prepared. The [Ln(dppR1,R2)3] complexes (Ln = La(iii), Sm(iii), Eu(iii), Gd(iii) and Yb(iii); and dppR1,R2 = 2,5-di(2-pyridyl-3-(R1)-4-(R2)) pyrrolide) have been isolated and their structures and photophysical and redox properties characterised, both in the solid-state and in solution. In the complexes, the three dpp- ligands form a distorted tricapped trigonal prismatic coordination geometry about the lanthanide ions, with the antiparallel isomer observed in the solid state for non-symmetric (dppCO2Me,Me)-. However, 1H NMR spectroscopy of the diamagnetic and paramagnetic [Ln(dppR1,R2)3] complexes in d6-benzene solution reveal evidence for a statistical distribution of all possible isomers. Time-resolved luminescence studies suggest that the dpp- ligand (with triplet excited state T1 energy at 18 622 cm-1) sensitises red emission from [Eu(dppCO2Me,Me)3] and near-infrared emission from [Yb(dppCO2Me,Me)3] through the antenna effect. Cyclic voltammetry reveals three consecutive, reversible, one-electron oxidation processes for each [Ln(dppR1,R2)3] complex, corresponding to oxidations of each dpp- ligand between 0.3-0.8 V vs. E1/2 (Fc+/0), and for [Eu(dppCO2Me,Me)3] the EuIII/II couple was -2.099 V vs. E1/2 (Fc+/0).

Six-Coordinate Ln(III) Complexes with Various Coordination Geometries Showing Distinct Magnetic Properties

The syntheses, structural characterization, and magnetic properties of three lanthanide complexes with formulas [Ln(L1)3] (Ln = Dy (1Dy); Er (1Er)); and [Dy(L2)2] (2Dy) were reported. Complexes 1Dy and 1Er are isostructural with the metal ion in distorted trigonal-prismatic coordination geometry, but exhibit distinct magnetic properties due to the different shapes of electron density for DyIII (oblate) and ErIII (prolate) ions. Complex 1Dy shows obvious SMM behavior under a zero direct current (dc) field with an effective energy barrier of 31.4 K, while complex 1Er only features SMM behavior under a 400 Oe external field with an effective energy barrier of 23.96 K. In stark contrast, complex 2Dy with the octahedral geometry only exhibits the frequency dependence of alternating current (ac) susceptibility signals without χ″ peaks under a zero dc field.

A Six-Coordinate Dysprosium Single-Ion Magnet with Trigonal-Prismatic Geometry.

A mononuclar six-coordinate dysprosium complex was synthesized and structurally and magnetically characterized. X-ray structural analyses show trigonal-prismatic coordination geometry of the DyIII center. Slow relaxation of magnetization in the absence of a direct-current field and magnetic hysteresis up to 3.0 K could be observed, indicating its single-ion-magnet behavior. Arrhenius fitting and ab initio calculations suggest that the magnetic relaxation process may not occur through the Orbach process at high temperatures under the experimental conditions.

Field-Induced Co(II) Single-Ion Magnets with mer-Directing Ligands but Ambiguous Coordination Geometry.

Three air-stable Co(II) mononuclear complexes with different aromatic substituents have been prepared and structurally characterized by single-crystal X-ray diffraction. The mononuclear complexes [Co(H2L1)2]·2THF (1), [Co(HL2)2] (2), and [Co(H2L3)2]·CH2Cl2 (3) (where H3L1, H2L2, and H3L3 represent 3-hydroxy-naphthalene-2-carboxylic acid (6-hydroxymethyl-pyridin-2-ylmethylene) hydrazide, nicotinic acid (6-hydroxymethyl-pyridin-2-ylmethylene) hydrazide, and 2-hydroxy-benzoic acid (6-hydroxymethyl-pyridin-2-ylmethylene) hydrazide, respectively) feature a distorted mer octahedral coordination geometry. Detailed magnetic studies of 1-3 have been conducted using direct and alternating current magnetic susceptibility data. Field-induced slow magnetic relaxation was observed for these three complexes. There are few examples of such behavior in (distorted) octahedral coordination geometry (OC) Co(II) mononuclear complexes with uniaxial anisotropy. Analysis of the six-coordinate Co(II) mononuclear single-ion magnets (SIMs) in the literature using the SHAPE program revealed that they all show what is best described as distorted trigonal prismatic (TRP) coordination geometry, and in general, these show negative D zero-field splitting (ZFS) values. On the other hand, all the Co(II) mononuclear complexes displaying what is best approximated as distorted octahedral (OC) coordination geometry show positive D values. In the new Co(II) mononuclear complexes we describe here, there is an ambiguity, since the rigid tridentate ligands confer what is best described for an octahedral complex as a mer coordination geometry, but the actual shape of the first coordination sphere is between octahedral and trigonal prismatic. The negative D values observed experimentally and supported by high-level electronic structure calculations are thus in line with a trigonal prismatic geometry. However, a consideration of the rhombicity as indicated by the E value of the ZFS in conjunction with the SHAPE analysis shows that in this case it is difficult to distinguish between the OC and TRP descriptions.

Temperature-Dependant Assemblies of Cu(II) Coordination Polymers and In Situ Ligand Reaction Based on 2,2′-Bipyridine-3,3′,6,6′-Tetracarboxylic acid

Three Cu(II) coordination polymers (CPs), namely, Cu(hbpdc)0.5(H2O)2 (1), [Cu2(hbpdc)(H2O)2]n (2), {[Cu3(hbpdc)(OH)2(H2O)]·H2O}n (3) (H4hbpdc = 3,3′-dihydroxy-2,2′-bipyridine-6,6′-dicarboxylic acid) have been obtained based on 2,2′-bipyridine-3,3′,6,6′-tetracarboxylic acid ligand (H4bptc) under hydro(solvo)thermal condition, and interestingly, the H4hbpdc ligand is in situ generated from H4bptc ligand during the synthetic process owing to the high temperature and pressure of the reaction system. Among the three complexes, 1 displays a discrete dinuclear copper building block, 2 possesses a 2D sheet, while 3 exhibits a porous 3D structure, and there exist Cu(II) centers in 3 showing an unprecedented one-capped trigonal prismatic coordination geometry. Structural comparisons indicate that the high reaction temperature is crucial factor for the in situ ligand reaction, and the solvent system and pH value play important roles in the coordination modes of H4nbtc ligand to produce various dimensional coordination polymers.

Large Energy Barrier and Magnetization Hysteresis at 5 K for a Symmetric {Dy2} Complex with Spherical Tricapped Trigonal Prismatic DyIII Ions.

The introduction of the Schiff base ligand N-salicylidene-2-amino-5-chlorobenzoic acid (sacbH2) in 4f-metal chemistry has afforded a new dinuclear complex, [Dy2(NO3)4(sacbH)2(H2O)2(MeCN)2] (1), with the metal ions adopting a rare spherical tricapped trigonal prismatic coordination geometry. The deprotonated phenoxido O atoms of the organic chelate occupy the axial triangular faces of the prism and were found to be very close to the main anisotropy axes of the two DyIII ions. As a result, the {DyIII2} compound exhibits frequency- and temperature-dependent out-of-phase ac signals below ∼25 K in the absence of a static dc field, yielding an energy barrier of 109.3(1) K for the reversal of magnetization. Fast and efficient quantum tunneling of magnetization, attributed to the strong tails of signals below ∼15 K, was suppressed through the application of a small dc field, yielding entirely visible χM″ signals below 27 K. Single-crystal magnetic hysteresis studies confirmed the single-molecule magnet (SMM) behavior of 1; the hysteresis loops appear at temperatures below ∼5 K, which is one of the highest blocking temperatures in the field of 4f-SMMs to date. This joint magneto-structural and ab initio study demonstrates the ability of more common coordination numbers (i.e., 9), but with rare coordination geometries (i.e., spherical tricapped trigonal prismatic), to promote axiality that enhances the molecular anisotropy and subsequently the magnetization dynamics of the system.

Structural elucidation, EPR and magnetic interpretation of lanthanide (Ln = La, Nd, Sm) compounds with 4,4′-bipyridine and 2-sulfoterephthalate

A series of three lanthanide compounds, namely, {[La(stp)(bipy)(H2O)]·H2O}n (1), {[Nd(stp)(bipy)(H2O)]·2H2O}n (2), and {[Sm(stp)(bipy)(H2O)]·H2O}n (3) has been synthesized through the reaction of 2-sulfoterephthalic acid monosodium salt Na(H2stp), trivalent lanthanide nitrate [Ln(NO3)3·6H2O] and N-donor ancillary co-ligand, 4,4′-bipyridine (bipy). As a result of the potential coordination modes of the stp ligand and the bipy co-ligand, the aforementioned compounds are arranged in a 2-D network, as evidenced by single-crystal X-ray diffraction technique. In all the three compounds, the Ln ion presents a distorted tricapped trigonal-prismatic coordination geometry. The EPR measurements evidence a diamagnetic behaviour of compound 1 (La3+) whereas there exhibits a weak antiferromagnetic coupling between paramagnetic Ln3+ ions (Nd3+ and Sm3+) for compounds 2 and 3. This is also supported by the magnetic data obtained for compounds 1–3. The encapsulation of the lanthanide coordination polymers displays a moderate luminescent property.