Stellated cuboctahedron of FeIII

The solvothermal reaction of FeCl2 ⋅ 4H2O and H4TBC[4] in a basic dmf/EtOH solution affords an [FeIII 18] Keplerate conforming to a stellated cuboctahedron. Magnetic and heat capacity measurements reveal spin frustration effects arising from the high symmetry. A crossover between inverse and direct magnetocaloric effects is observed at ~10 K for applied-field changes lower than 3 T.

Elucidating the exchange interactions in a {GdIIICuII4} propellor

The multinucleating ligand 2,2'-(propane-1,3-diyldiimino)bis[2-(hydroxymethyl)-propane-1,3-diol] (bis-tris propane, H₆L) is used in the design of a new family of 3d-4f complexes that display an unusual {LnCu₄} four-blade propeller topology. We report the synthesis, structure and magnetic characterisation of [LnCu₄(H₄L)₄](Cl)₂(ClO₄)·6CH₃OH, where Ln = Gd (1), Tb (2), Dy (3), La (4). Previously we have used CH₃COO^- and NO₃^- as co-ligands with bis-tris propane, but here the use of Cl^- and ClO₄^- leads to coordination of four {Cu(H₄L)} units around the central Ln ion. A magneto-structural analysis reveals that the geometrical arrangement of the Cu(II) centres defined by the H₄L^2- ligands controls the magnetic communication between the different metal centres. DFT calculations performed on the isotropic (Gd) and diamagnetic (La) systems 1 and 4 help to unravel the intriguing exchange interactions.

Synergistic Experimental and Theoretical Studies of Luminescent-Magnetic Ln2Zn6 Clusters

The present work is part of our ongoing quest for developing functional inorganic complexes using unorthodox pyridyl-pyrazolyl-based ligands. Accordingly, we report herein the synthesis, characterization, and luminescence and magnetic properties of four 3d-4f mixed-metal complexes with a general core of Ln₂Zn₆ (Ln = Dy, Gd, Tb, and Eu). In stark contrast to the popular wisdom of using a compartmental ligand with separate islands of hard and soft coordinating sites for selective coordination, we have vindicated our approach of using a ligand with overcrowded N-coordinating sites that show equal efficiency with both 4f and 3d metals toward multinuclear cage-cluster formation. The encouraging red and green photolumiscent features of noncytotoxic Eu₂Zn₆ and Tb₂Zn₆ complexes along with their existence in nanoscale dimension have been exploited with live-cell confocal microscopy imaging of human breast adenocarcinoma (MCF7) cells. The magnetic features of the Dy₂Zn₆ complex confirm the single-molecule-magnet behavior with befitting frequency- and temperature-dependent out-of-phase signals along with an U_eff value of ∼5 K and a relaxation time of 8.52 × 10^-6 s. The Gd₂Zn₆ complex, on the other hand, shows cryogenic magnetic refrigeration with an entropy change of 11.25 J kg^-1 K^-1 at a magnetic field of 7 T and at 2 K. Another important aspect of this work reflects the excellent agreement between the experimental results and theoretical calculations. The theoretical studies carried out using the broken-symmetry density functional theory, ORCA suite of programs, and MOLCAS calculations using the complete-active-space self-consistent-field method show an excellent synergism with the experimentally measured magnetic and spectroscopic data.

Two new calix[4]resorcinarene-based coordination cages adjusted by metal ions for the Knoevenagel condensation reaction

Two new calix[4]resorcinarene-based coordination cages, namely, [Zn4(TPC4R)(PDC)4]·2DMF·6H2O (1-Zn) and [In11(TPC4R)2(PDC)16(μ2-OH)2(H2O)2]·[(CH3)2NH2]·8DMF·20H2O·EtOH (2-In), have been synthesized via solvothermal reactions (TPC4R = tetra(2-(4H-pyrazol-3-yl)pyridine)calix[4]resorcinarene, H2PDC = 3,5-pyridinedicarboxylic acid, DMF = N,N'-dimethylformamide). By carefully tuning different metal ions, two structurally different cages 1-Zn and 2-In were achieved. The former shows a bowl-shaped structure, while the latter features a dumbbell-like structure. After activation, they exhibited unsaturated Zn(ii) or In(iii) Lewis acid sites and the free nitrogen Lewis base sites of the PDC2-. Therefore, they were employed as catalysts for the Knoevenagel condensation reaction in the absence of a solvent. Particularly, 1-Zn featured high structural stability and enhanced the catalytic activity.

Further synthetic investigation of the general lanthanoid(iii) [Ln(iii)]/copper(ii)/pyridine-2,6-dimethanol/carboxylate reaction system: {CuLn} coordination clusters (Ln = Dy, Tb, Ho) and their yttrium(iii) analogue

In addition to previously studied {CuGd₆}, {CuGd₄}, {CuLn₇} and {CuLn₈} coordination clusters (Ln = trivalent lanthanide) containing pdm^2- or Hpdm^- ligands (H₂pdm = pyridine-2,6-dimethanol) and ancillary carboxylate groups (RCO₂^-), the present work reports the synthesis and study of three new members of a fifth family of such complexes. Compounds [Cu₅Ln₄O₂(OMe)₄(NO₃)₄(O₂CCH₂Bu^t)₂(pdm)₄(MeOH)₂] (Ln = Dy, 1; Ln = Tb, 2; Ln = Ho, 3) were prepared from the reaction of Ln(NO₃)₃·xH₂O (x = 5, 6), CuX₂·yH₂O (X = ClO₄, Cl, NO₃; y = 6, 2 and 3, respectively), H₂pdm, Bu^tCH₂CO₂H and Et₃N (2 : 2.5 : 2 : 1 : 9) in MeCN/MeOH. Rather surprisingly, the copper(ii)/yttrium(iii) analogue has a slightly different composition, i.e. [Cu₅Y₄O₂(OMe)₄(NO₃)₂(O₂CCH₂Bu^t)₄(pdm)₄(MeOH)₂] (4). The structures of 1·4MeCN·1.5MeOH and 4·2MeOH were solved by single-crystal X-ray crystallography. The five Cu^II and four Dy^III centres in 1 are held together by two μ₅-O^2-, four μ-MeO^-, two syn,synη¹:η¹:μ Bu^tCH₂CO₂^-, four η²:η¹:η²:μ₃ pdm^2- (each of these groups chelates a Cu^II atom and simultaneously bridges two Dy^III atoms through its two -CH₂O^- arms) and two μ-MeOH ligands. The four terminal nitrato groups each chelate (η¹:η¹) a Dy^III centre. The five Cu^II atoms are co-planar (by symmetry) forming a bow-tie arrangement; the four outer Cu^II atoms form a rectangle with edges of 3.061(1) and 6.076(1) Å. The four Dy^III centres also form a rectangle that lies above and below the plane of the Cu^II centres, with edges of 3.739(1) and 5.328(1) Å. The two strictly planar rectangles are almost perpendicular. Two trigonal bipyramidal μ₅-O^2- groups link the perpendicular Cu₅ and Dy₄ frameworks together. The molecule 4 has a very similar structure to that of 1, differences being the replacement of the two chelating nitrato groups of 1 by two chelating Bu^tCH₂CO₂^- ligands in 4 and the coordination polyhedra of the Ln^III and Y^III atoms (Snub diphenoids in 1 and biaugmented trigonal prisms in 4). Dc magnetic susceptibility data (χ_M) on analytically pure samples of 1-3, collected in the 300-2 K range, indicate that ferromagnetic exchange interactions dominate leading to large spin ground states. The χ_MT vs. T data for 4 suggest moderately strong antiferromagnetic Cu^IICu^II exchange interactions. Studies of the dynamic magnetic properties of the {Cu₅Ln₄} clusters show that 1 behaves as a SMM at zero field and 2 is a very weak field-induced SMM, while 3 exhibits only weak tails in the χ''_Mvs. T plots at various ac frequencies at zero dc field.

Magneto-structural studies of an unusual [MnIIIMnIIGdIII(OR)4]4- partial cubane from 2,2'-bis-p-tBu-calix[4]arene

Reaction of 2,2'-bis-p-tBu-calix[4]arene (H8L) with MnCl2·4H2O, GdCl3·6H2O and 2,6-pyridinedimethanol (H2pdm) affords [MnIIIMnIIGdIII(H3L)(pdmH)(pdm)(MeOH)2(dmf)]·3MeCN·dmf (3·3MeCN·dmf) upon vapour diffusion of MeCN into the basic dmf/MeOH mother liquor. 3 crystallises in the tetragonal space group P41212 with the asymmetric unit comprising the entire cluster. The highly unusual core contains a triangular arrangement of MnIIIMnIIGdIII ions housed within a [MnIIIMnIIGdIII(OR)4]4- partial cubane. Magnetic susceptibility and magnetisation data reveal best fit parameters JMn(II)-Mn(III) = +0.415 cm-1, JMn(III)-Gd(III) = +0.221 cm-1, JMn(II)-Gd(III) = -0.258 cm-1 and DMn(III) = -4.139 cm-1. Theoretically derived magnetic exchange interactions, anisotropy parameters, and magneto-structural correlations for 3 are in excellent agreement with the experimental data.

Mixed Tb/Dy coordination ladders based on tetra(carboxymethyl)thiacalix[4]arene: a new avenue towards luminescent molecular nanomagnets

The macrocyclic ligand calix[4]arene (L1) and its sulphur-containing analogue thia[4]calixarene (L2) are promising precursors for functional molecular materials as they offer rational functionalization with various organic groups. Here, we present the first example of lanthanide-based coordination polymers built from the macrocyclic thiacalix[4]arene backbone bearing four carboxylic moieties, namely, ligand H₄L3. The combination of H₄L3 with the Tb³⁺ and Dy³⁺ cations led to the formation of 1D ladder-type coordination polymers with the formula [Ln^IIIHL3DMF₃]·(DMF) (where DMF = dimethylformamide and Ln = Tb or Dy, denoted as HL3–Tb and HL3–Dy), which resulted from the coordination of the lanthanide cations with the partially deprotonated ligand HL3³⁻ that behaved as a T-shape connector. The coordination sphere around the metal was completed by the coordinated DMF solvent molecules. By combining both Tb³⁺ and Dy³⁺ cations, isostructural heterobimetallic solid solutions HL3–Tb_1−xDy_x were also prepared. HL3–Tb and HL3–Dy showed visible light photoluminescence originating from the f–f electronic transitions of pale green emissive Tb³⁺ and pale yellow emissive Dy³⁺ with efficient sensitization by the functionalized thia[4]calixarene ligand HL3. In the HL3–Tb_1−xDy_x solid solutions, the Tb/Dy ratio governed both the emission colour as well as the emission quantum yield, which reached even 28% at room temperature for HL3–Tb. Moreover, HL3–Dy exhibited a slow magnetic relaxation effect related to the magnetic anisotropy of the dodecahedral Dy³⁺ complexes, which were well isolated in the crystal lattice by expanded organic spacers.

The single crystals of the two isostructural Tb³⁺- and Dy³⁺-based coordination polymers (HL3–Tb and HL3–Dy) were structurally characterized, and their photophysical properties were investigated, together with their corresponding solid solutions.

With complements of the ligands: an unusual S-shaped [Mn7]2 assembly from tethered calixarenes

A large S-shaped [MnIII5MnII2]₂ assembly (∼40 Å top to tail) has been formed with bis-p-^tBu-calix[4]arene and 2-(hydroxymethyl)pyridine as a co-ligand, with the former existing unusually in both syn and anti-conformations (as shown).

Hybrid Rare-Earth(III)/Bismuth(III) Clusters Assembled with Phosphonates

tert-Butylphosphonic acid and rare-earth precursors are employed to construct four trinuclear rare-earth phosphonate clusters, RE₃( ^tBuPO₃)₂(hfac)₅(CH₃OH)₈]·2CH₃OH (RE = Eu, Y, Pr, and Sm; hfac = hexafluoroacetylacetonate), which are composed of three RE³⁺ ions alternately bridged by two phosphonates. With the introduction of bismuth oxido diketonate, [Bi₉O₇(hfac)₁₃], three different types of rare-earth/bismuth phosphonate clusters, Bi₁₂RE₂ (RE = Pr and Sm), Bi₆Eu₇, and Bi₆Y₉, are successfully obtained via variation of the reaction conditions, and they are the first reported examples of bismuth-oxo clusters encapsulated by cyclic rare-earth-oxo or rare-earth/bismuth-oxo phosphonate clusters, respectively. These clusters show obvious absorption in the UV region, and the Eu-containing clusters exhibit bright-red fluorescence.

The remarkable influence of N,O-ligands in the assembly of a bis-calix[4]arene-supported [MnIV2MnIII10MnII8] cluster

Bis-calix[4]arene is a highly versatile ligand that is capable of forming a range of polymetallic clusters. Use of an N,O-chelating co-ligand affords a very high nuclearity mixed-valence Mn cluster (shown here) that displays coordination modes relative to each ligand type.