Stellated cuboctahedron of FeIII.

The solvothermal reaction of FeCl2·4H2O and H4TBC[4] in a basic dmf/EtOH solution affords an [FeIII18] Keplerate conforming to a stellated cuboctahedron. Magnetic measurements reveal spin frustration effects arising from the high symmetry.

A {Gd12Na6} Molecular Quadruple-Wheel with a Record Magnetocaloric Effect at Low Magnetic Fields and Temperatures.

Reaction of Gd(OAc)3·4H2O, salicylaldehyde and CH3ONa in MeCN/MeOH affords [Gd12Na6(OAc)25(HCO2)5(CO3)6(H2O)12]·9H2O.0.5MeCN (1·9H2O.0.5MeCN), whose structure describes a quadruple-wheel consisting of two {Na3} and two {Gd6} rings. The magnetic properties of 1 reveal very weak antiferromagnetic interactions between the GdIII ions, which give rise to a record magnetocaloric effect at low applied magnetic fields and low temperatures. The magnetic entropy change reaches -ΔSm= 29.3 J kg-1 K-1 for full demagnetization from B = 1 T at T = 0.5 K.

A Ferromagnetically Coupled, Bell-Shaped [Ni4Gd5] Cage.

Reaction between NiCl2·6H2O, 2-hydroxy-4-methyl-6-phenyl-pyridine-3-amidoxime (H2L), benzoic acid, and M(NO3)3·6H2O (M = Gd, Y) in MeCN under basic conditions yields the complexes [NiII4GdIII5(PhCOO)10(HL)4(HLzw)4(OH)2(NO3)2]Cl·13.6MeCN·H2O (1·13.6MeCN·H2O) and [NiII4YIII5(PhCOO)10(HL)4(HLzw)4(OH)2(NO3)1.5(H2O)0.5]0.5Cl(NO3)·3H2O (2·3H2O). Both clusters display similar structures, consisting of a bell-shaped {NiII4MIII5} unit, in which a linear "zigzag" {Ni4} subunit bisects the central {MIII5} "ring". Direct (dc) and alternating current (ac) magnetic susceptibility measurements carried out in the 2-300 K temperature range for complexes 1 and 2 revealed ferromagnetic intermolecular interactions, while heat-capacity measurements for the Gd analogue suggest that complex 1 lowers its temperature from T = 9.6 K down to 2.3 K by adiabatically demagnetizing from Bi = 7 T to Bf = 0.

An [FeIII 34 ] Molecular Metal Oxide.

The dissolution of anhydrous iron bromide in a mixture of pyridine and acetonitrile, in the presence of an organic amine, results in the formation of an [Fe34 ] metal oxide molecule, structurally characterised by alternate layers of tetrahedral and octahedral FeIII ions connected by oxide and hydroxide ions. The outer shell of the complex is capped by a combination of pyridine molecules and bromide ions. Magnetic data, measured at temperatures as low as 0.4 K and fields up to 35 T, reveal competing antiferromagnetic exchange interactions; DFT calculations showing that the magnitudes of the coupling constants are highly dependent on both the Fe-O-Fe angles and Fe-O distances. The simplicity of the synthetic methodology, and the structural similarity between [Fe34 ], bulk iron oxides, previous FeIII -oxo cages, and polyoxometalates (POMs), hints that much larger molecular FeIII oxides can be made.

Copper Keplerates: High-Symmetry Magnetic Molecules.

Keplerates are molecules that contain metal polyhedra that describe both Platonic and Archimedean solids; new copper keplerates are reported, with physical studies indicating that even where very high molecular symmetry is found, the low-temperature physics does not necessarily reflect this symmetry.

Structurally Flexible and Solution Stable [Ln4TM8(OH)8(L)8(O2CR)8(MeOH)y](ClO4)4: A Playground for Magnetic Refrigeration.

The family of compounds of general formula [LnIII4TMII8(OH)8(L)8(O2CR)8(MeOH)y](ClO4)4 {[Gd4Zn8(OH)8(hmp)8(O2CiPr)8](ClO4)4 (1a); [Y4Zn8(OH)8(hmp)8(O2CiPr)8](ClO4)4 (1b); [Gd4Cu8(OH)8(hmp)8(O2CiPr)8](ClO4)4 (2a); [Y4Cu8(OH)8(hmp)8(O2CiPr)8](ClO4)4 (2b); [Gd4Cu8(OH)8(hep)8(O2CiPr)8](ClO4)4 (3a); [Gd4Cu8(OH)8(Hpdm)8(O2CtBu)8](ClO4)4 (4a); [Gd4Cu8(OH)8(ea)8(O2CMe)8](ClO4)4 (5a); [Gd4Ni8(OH)8(hmp)8(O2CEt)8(MeOH)6](ClO4)4 (6a); [Y4Ni8(OH)8(hmp)8(O2CEt)8(MeOH)6](ClO4)4 (6b); [Gd4Co8(OH)8(hmp)8(O2CEt)8(MeOH)6](ClO4)4 (7a); [Y4Co8(OH)8(hmp)8(O2CEt)8(MeOH)6](ClO4)4 (7b)} can be formed very simply and in high yields from the reaction of Ln(NO3)3·6H2O and TM(ClO4)2·6H2O and the appropriate ligand blend in a mixture of CH2Cl2 and MeOH in the presence of a suitable base. Remarkably, almost all the constituent parts, namely the lanthanide (or rare earth) ions LnIII (here Ln = Gd or Y), the transition metal ions TMII (here TM = Zn, Cu, Ni, Co), the bridging ligand L (Hhmp = 2-(hydroxymethyl)pyridine; Hhep = 2-(hydroxyethyl)pyridine; H2pdm = pyridine-2,6-dimethanol; Hea = 2-ethanolamine), and the carboxylates can be exchanged while maintaining the structural integrity of the molecule. NMR spectroscopy of diamagnetic complex 1b reveals the complex to be fully intact in solution with all signals from the hydroxide, ligand L, and the carboxylates equivalent on the NMR time scale, suggesting the complex possesses greater symmetry in solution than in the solid state. High resolution nano-ESI mass spectrometry on dichloromethane solutions of 2a and 2b shows both complexes are present in two charge states with little fragmentation; with the most intense peak in each spectrum corresponding to [Ln4Cu8(OH)8(hmp)8(O2CiPr)8](ClO4)22+. This family of compounds offers an excellent playground for probing how the magnetocaloric effect evolves by introducing either antiferromagnetic or ferromagnetic interactions, or magnetic anisotropy, by substituting the nonmagnetic ZnII (1a) with CuII (2a), NiII (6a) or CoII (7a), respectively. The largest magnetocaloric effect is found for the ferromagnetically coupled complex 6a, while the predominant antiferromagnetic interactions in 2a yield an inverse magnetocaloric effect; that is, the temperature increases on lowering the applied field, under the proper experimental conditions. In spite of increasing the magnetic density by adding ions that bring in antiferromagnetic interactions (2a) or magnetic anisotropy (7a), the magnetocaloric effect is overall smaller in 2a and 7a than in 1a, where only four GdIII spins per molecule contribute to the magnetocaloric properties.

Rotating Magnetocaloric Effect in an Anisotropic Molecular Dimer.

In contrast to the mainstream research on molecular refrigerants that seeks magnetically isotropic molecules, we show that the magnetic anisotropy of dysprosium acetate tetrahydrate, [{Dy(OAc)3 (H2 O)2}2]⋅4 H2O (1), can be efficiently used for cooling below liquid-helium temperature. This is attained by rotating aligned single-crystal samples in a constant applied magnetic field. The envisioned advantages are fast cooling cycles and potentially compact refrigerators.

Magnetic "Molecular Oligomers" Based on Decametallic Supertetrahedra: A Giant Mn49 Cuboctahedron and its Mn25Na4 Fragment.

Two nanosized Mn49 and Mn25Na4 clusters based on analogues of the high-spin (S=22) [Mn(III)6Mn(II)4(µ4-O)4](18+) supertetrahedral core are reported. Mn49 and Mn25Na4 complexes consist of eight and four decametallic supertetrahedral subunits, respectively, display high virtual symmetry (O(h)), and are unique examples of clusters based on a large number of tightly linked high nuclearity magnetic units. The complexes also have large spin ground-state values (Mn49: S=61/2; Mn25Na4: S=51/2) with the Mn49  cluster displaying single-molecule magnet (SMM) behavior and being the second largest reported homometallic SMM.

Decanuclear Ln10 Wheels and Vertex-Shared Spirocyclic Ln5 Cores: Synthesis, Structure, SMM Behavior, and MCE Properties.

The reaction of a Schiff base ligand (LH3) with lanthanide salts, pivalic acid and triethylamine in 1:1:1:3 and 4:5:8:20 stoichiometric ratios results in the formation of decanuclear Ln10 (Ln = Dy (1), Tb (2), and Gd (3)) and pentanuclear Ln5 complexes (Ln = Gd (4), Tb (5), and Dy (6)), respectively. The formation of Ln10 and Ln5 complexes are fully governed by the stoichiometry of the reagents used. Detailed magnetic studies on these complexes (1-6) have been carried out. Complex 1 shows a SMM behavior with an effective energy barrier for the reversal of the magnetization (Ueff) = 16.12(8) K and relaxation time (τo) = 3.3×10(-5) s under 4000 Oe direct current (dc) field. Complex 6 shows the frequency dependent maxima in the out-of-phase signal under zero dc field, without achieving maxima above 2 K. Complexes 3 and 4 show a large magnetocaloric effect with the following characteristic values: -ΔSm = 26.6 J kg(-1) K(-1) at T = 2.2 K for 3 and -ΔSm = 27.1 J kg(-1) K(-1) at T = 2.4 K for 4, both for an applied field change of 7 T.

Theoretical studies on polynuclear {Cu(II)5Gd(III)n} clusters (n = 4, 2): towards understanding their large magnetocaloric effect.

Density functional theory (DFT) studies on two polynuclear clusters, [Cu(II)5Gd(III)4O2(OMe)4(teaH)4(O2CC(CH3)3)2(NO3)4] (1) and [Cu5Gd2(OH)4(Br)2-(H2L)2(H3L)2(NO3)2(OH2)4] (2), have been carried out to probe the origin of the large magnetocaloric effect (MCE). The magnetic exchange interactions for 1 and 2 via multiple pathways are estimated using DFT calculations. While the calculated exchange parameters deviate from previous experimental estimates obtained by fitting the magnetic data, the DFT parameter set is found to offer a striking match to the magnetic data for both complexes, highlighting the problem of overparameterization. Magnetostructural correlations for {Cu-Gd} pairs have been developed where both the Cu-O-Gd angles and Cu-O-Gd-O dihedral angles are found to significantly influence the magnitude and sign of the exchange constants. The magnitude of the MCE has been examined as a function of the exchange interactions, and clues on how the effect can be enhanced are discussed.

Low temperature magnetic properties and spin dynamics in single crystals of Cr8Zn antiferromagnetic molecular rings.

A detailed experimental investigation of the effects giving rise to the magnetic energy level structure in the vicinity of the level crossing (LC) at low temperature is reported for the open antiferromagnetic molecular ring Cr8Zn. The study is conducted by means of thermodynamic techniques (torque magnetometry, magnetization and specific heat measurements) and microscopic techniques (nuclear magnetic resonance line width, nuclear spin lattice, and spin-spin relaxation measurements). The experimental results are shown to be in excellent agreement with theoretical calculations based on a minimal spin model Hamiltonian, which includes a Dzyaloshinskii-Moriya interaction. The first ground state level crossing at µ0Hc1 = 2.15 T is found to be an almost true LC while the second LC at µ0Hc2 = 6.95 T has an anti-crossing gap of Δ12 = 0.19 K. In addition, both NMR and specific heat measurements show the presence of a level anti-crossing between excited states at µ0H = 4.5 T as predicted by the theory. In all cases, the fit of the experimental data is improved by introducing a distribution of the isotropic exchange couplings (J), i.e., using a J strain model. The peaks at the first and second LCs in the nuclear spin-lattice relaxation rate are dominated by inelastic scattering and a value of Γ âˆ¼ 10(10) rad/s is inferred for the life time broadening of the excited state of the open ring, due to spin phonon interaction. A loss of NMR signal (wipe-out effect) is observed for the first time at LC and is explained by the enhancement of the spin-spin relaxation rate due to the inelastic scattering.

Rational electrostatic design of easy-axis magnetic anisotropy in a Zn(II) -Dy(III) -Zn(II) single-molecule magnet with a high energy barrier.

Two novel trinuclear complexes [ZnCl(µ-L)Ln(µ-L)ClZn][ZnCl3 (CH3 OH)]⋅3 CH3 OH (Ln(III) =Dy (1) and Er (2)) have been prepared from the compartmental ligand N,N'-dimethyl-N,N'-bis(2-hydroxy-3-formyl-5-bromo-benzyl)ethylenediamine (H2 L). X-ray studies reveal that Ln(III) ions are coordinated by two [ZnCl(L)](-) units through the phenoxo and aldehyde groups, giving rise to a LnO8 coordination sphere with square-antiprism geometry and strong easy-axis anisotropy of the ground state. Ab initio CASSCF+RASSI calculations carried out on 1 confirm that the ground state is an almost pure MJ =±15/2 Kramers doublet with a marked axial anisotropy, the magnetic moment is roughly collinear with the shortest DyO distances. This orientation of the local magnetic moment of the Dy(III) ion in 1 is adopted to reduce the electronic repulsion between the oblate electron shape of the MJ =±15/2 Kramers doublet and the phenoxo-oxygen donor atoms involved in the shortest DyO bonds. CASSCF+RASSI calculations also show that the ground and first excited states of the Dy(III) ion are separated by 129 cm(-1) . As expected for this large energy gap, compound 1 exhibits, in a zero direct-current field, thermally activated slow relaxation of the magnetization with a large Ueff =140 K. The isostructural Zn-Er-Zn species does not present significant SMM behavior as expected for the prolate electron-density distribution of the Er(III) ion leading to an easy-plane anisotropy of the ground doublet state.

A multifunctional magnetic material under pressure.

Fe(II)(Metz)6](Fe(III)Br4)2 (Metz = 1-methyltetrazole) is one of the rare systems combining spin-crossover and long-range magnetic ordering. A joint neutron and X-ray diffraction and magnetometry study allows determining its collinear antiferromagnetic structure, and shows an increase of the Néel temperature from 2.4 K at ambient pressure, to 3.9 K at 0.95 GPa. Applied pressure also enables a full high-spin to low-spin switch at ambient temperature.

Two C3 -symmetric Dy3III complexes with triple di-µ-methoxo-µ-phenoxo bridges, magnetic ground state, and single-molecule magnetic behavior.

Two series of isostructural C(3)-symmetric Ln(3) complexes Ln(3)⋅[BPh(4)] and Ln(3)⋅0.33[Ln(NO(3))(6)] (in which Ln(III) =Gd and Dy) have been prepared from an amino-bis(phenol) ligand. X-ray studies reveal that Ln(III) ions are connected by one µ(2)-phenoxo and two µ(3)-methoxo bridges, thus leading to a hexagonal bipyramidal Ln(3)O(5) bridging core in which Ln(III) ions exhibit a biaugmented trigonal-prismatic geometry. Magnetic susceptibility studies and ab initio complete active space self-consistent field (CASSCF) calculations indicate that the magnetic coupling between the Dy(III) ions, which possess a high axial anisotropy in the ground state, is very weakly antiferromagnetic and mainly dipolar in nature. To reduce the electronic repulsion from the coordinating oxygen atom with the shortest Dy-O distance, the local magnetic moments are oriented almost perpendicular to the Dy(3) plane, thus leading to a paramagnetic ground state. CASSCF plus restricted active space state interaction (RASSI) calculations also show that the ground and first excited state of the Dy(III) ions are separated by approximately 150 and 177 cm(-1), for Dy(3)⋅[BPh(4)] and Dy(3)⋅0.33[Dy(NO(3))(6)], respectively. As expected for these large energy gaps, Dy(3)⋅[BPh(4)] and Dy(3)⋅0.33[Dy(NO(3)(6)] exhibit, under zero direct-current (dc) field, thermally activated slow relaxation of the magnetization, which overlap with a quantum tunneling relaxation process. Under an applied Hdc field of 1000 Oe, Dy(3)⋅[BPh(4)] exhibits two thermally activated processes with U(eff) values of 34.7 and 19.5 cm(-1), whereas Dy(3)⋅0.33[Dy(NO(3))(6)] shows only one activated process with Ueff =19.5 cm(-1).

Synthesis, structure, and magnetism of a family of heterometallic {Cu2Ln7} and {Cu4Ln12} (Ln = Gd, Tb, and Dy) complexes: the Gd analogues exhibiting a large magnetocaloric effect.

The syntheses, structures, and magnetic properties of two heterometallic Cu(II)-Ln(III) (Ln(III) = Gd, Tb, and Dy) families, utilizing triethanolamine and carboxylate ligands, are reported. The first structural motif displays a nonanuclear {Cu(II)2Ln(III)7} metallic core, while the second reveals a hexadecanuclear {Cu(II)4Ln(III)12} core. The differing nuclearities of the two families stem from the choice of carboxylic acid used in the synthesis. Magnetic studies show that the most impressive features are displayed by the {Cu(II)2Gd(III)7} and {Cu(II)4Gd(III)12} complexes, which display a large magnetocaloric effect, with entropy changes -ΔSm = 34.6 and 33.0 J kg(-1) K(-1) at T = 2.7 and 2.9 K, respectively, for a 9 T applied field change. It is also found that the {Cu(II)4Dy(III)12} complex displays single-molecule magnet behavior, with an anisotropy barrier to magnetization reversal of 10.1 K.

Closely-related Zn(II)2Ln(III)2 complexes (Ln(III) = Gd, Yb) with either magnetic refrigerant or luminescent single-molecule magnet properties.

The reaction of the compartmental ligand N,N',N″-trimethyl-N,N″-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H2L) with Zn(NO3)2·6H2O and subsequently with Ln(NO3)3·5H2O (Ln(III) = Gd and Yb) and triethylamine in MeOH using a 1:1:1:1 molar ratio leads to the formation of the tetranuclear complexes {(µ3-CO3)2[Zn(µ-L)Gd(NO3)]2}·4CH3OH (1) and{(µ3-CO3)2[Zn(µ-L)Yb(H2O)]2}(NO3)2·4CH3OH (2). When the reaction was performed in the absence of triethylamine, the dinuclear compound [Zn(µ-L)(µ-NO3)Yb(NO3)2] (3) is obtained. The structures of 1 and 2 consist of two diphenoxo-bridged Zn(II)-Ln(III) units connected by two carbonate bridging ligands. Within the dinuclear units, Zn(II) and Ln(III) ions occupy the N3O2 inner and the O4 outer sites of the compartmental ligand, respectively. The remaining positions on the Ln(III) ions are occupied by oxygen atoms belonging to the carbonate bridging groups, by a bidentate nitrate ion in 1, and by a coordinated water molecule in 2, leading to rather asymmetric GdO9 and trigonal dodecahedron YbO8 coordination spheres, respectively. Complex 3 is made of acetate-diphenoxo triply bridged Zn(II)Yb(III) dinuclear units, where the Yb(III) exhibits a YbO9 coordination environment. Variable-temperature magnetization measurements and heat capacity data demonstrate that 1 has a significant magneto-caloric effect, with a maximum value of -ΔSm = 18.5 J kg(-1) K(-1) at T = 1.9 K and B = 7 T. Complexes 2 and 3 show slow relaxation of the magnetization and single-molecule magnet (SMM) behavior under an applied direct-current field of 1000 Oe. The fit of the high-temperature data to the Arrhenius equation affords an effective energy barrier for the reversal of the magnetization of 19.4(7) K with τo = 3.1 × 10(-6) s and 27.0(9) K with τo = 8.8 × 10(-7) s for 2 and 3, respectively. However, the fit of the full range of temperature data indicates that the relaxation process could take place through a Raman-like process rather than through an activated Orbach process. The chromophoric L(2-) ligand is able to act as an "antenna" group, sensitizing the near-infrared (NIR) Yb(III)-based luminescence in complexes 2 and 3 through an intramolecular energy transfer to the excited states of the accepting Yb(III) ion. These complexes show several bands in the 945-1050 nm region, corresponding to (2)F5/2→(2)F7/2 transitions arising from the ligand field splitting of both multiplets. The observed luminescence lifetimes τobs are 0.515 and 10 µs for 2 and 3, respectively. The shorter lifetime for 2 is due to the presence of one coordinated water molecule on the Yb(III) center (and to a lesser extent noncoordinated water molecules), facilitating vibrational quenching via O-H oscillators. Therefore, complexes 2 and 3, combining field-induced SMM behavior and NIR luminescence, can be considered to be dual magneto-luminescent materials.

Thiocyanate complexes of uranium in multiple oxidation states: a combined structural, magnetic, spectroscopic, spectroelectrochemical, and theoretical study.

A comprehensive study of the complexes A4[U(NCS)8] (A = Cs, Et4N, (n)Bu4N) and A3[UO2(NCS)5] (A = Cs, Et4N) is described, with the crystal structures of [(n)Bu4N]4[U(NCS)8]·2MeCN and Cs3[UO2(NCS)5]·O0.5 reported. The magnetic properties of square antiprismatic Cs4[U(NCS)8] and cubic [Et4N]4[U(NCS)8] have been probed by SQUID magnetometry. The geometry has an important impact on the low-temperature magnetic moments: at 2 K, µeff = 1.21 µB and 0.53 µB, respectively. Electronic absorption and photoluminescence spectra of the uranium(IV) compounds have been measured. The redox chemistry of [Et4N]4[U(NCS)8] has been explored using IR and UV-vis spectroelectrochemical methods. Reversible 1-electron oxidation of one of the coordinated thiocyanate ligands occurs at +0.22 V vs Fc/Fc(+), followed by an irreversible oxidation to form dithiocyanogen (NCS)2 which upon back reduction regenerates thiocyanate anions coordinating to UO2(2+). NBO calculations agree with the experimental spectra, suggesting that the initial electron loss of [U(NCS)8](4-) is delocalized over all NCS(-) ligands. Reduction of the uranyl(VI) complex [Et4N]3[UO2(NCS)5] to uranyl(V) is accompanied by immediate disproportionation and has only been studied by DFT methods. The bonding in [An(NCS)8](4-) (An = Th, U) and [UO2(NCS)5](3-) has been explored by a combination of DFT and QTAIM analysis, and the U-N bonds are predominantly ionic, with the uranyl(V) species more ionic that the uranyl(VI) ion. Additionally, the U(IV)-NCS ion is more ionic than what was found for U(IV)-Cl complexes.

Single-molecule magnet behavior and magnetocaloric effect in ferromagnetically coupled Ln(III)-Ni(II)-Ni(II)-Ln(III) (Ln(III) = Dy(III) and Gd(III)) linear complexes.

New types of linear tetranuclear Ln(III)-Ni(II)-Ni(II)-Ln(III) (Ln(III) = Dy (1), Gd (2)) complexes have been prepared using the multidentate ligand N,N'-bis(3-methoxysalicylidene)-1,3-diaminobenzene, which has two sets of NO and OO' coordination pockets that are able to selectively accommodate Ni(II) and Ln(III) ions, respectively. The X-ray structure analysis reveals that the Ni(II) ions are bridged by phenylenediimine groups forming a 12-membered metallacycle in the central body of the complex, whereas the Ln(III) ions are located at both sides of the metallacycle and linked to the Ni(II) ions by diphenoxo bridging groups. Phenylenediimine and diphenoxo bridging groups transmit ferromagnetic exchange interactions between the two Ni(II) ions and between the Ni(II) and the Ln(III) ions, respectively. Complex 1 shows slow relaxation of the magnetization at zero field and a thermal energy barrier Ueff = 7.4 K with HDC = 1000 Oe, whereas complex 2 exhibits an S = 9 ground state and significant magnetocaloric effect (-ΔSm = 18.5 J kg(-1) K(-1) at T = 3 K and ΔB = 5 T).

Fluoride-bridged {Gd(III)3M(III)2} (M = Cr, Fe, Ga) molecular magnetic refrigerants.

The reaction of fac-[M(III)F3(Me3tacn)]⋅x H2O with Gd(NO3)3⋅5H2O affords a series of fluoride-bridged, trigonal bipyramidal {Gd(III)3M(III)2} (M = Cr (1), Fe (2), Ga (3)) complexes without signs of concomitant GdF3 formation, thereby demonstrating the applicability even of labile fluoride-complexes as precursors for 3d-4f systems. Molecular geometry enforces weak exchange interactions, which is rationalized computationally. This, in conjunction with a lightweight ligand sphere, gives rise to large magnetic entropy changes of 38.3 J kg(-1) K(-1) (1) and 33.1 J kg(-1) K(-1) (2) for the field change 7 T→0 T. Interestingly, the entropy change, and the magnetocaloric effect, are smaller in 2 than in 1 despite the larger spin ground state of the former secured by intramolecular Fe-Gd ferromagnetic interactions. This observation underlines the necessity of controlling not only the ground state but also close-lying excited states for successful design of molecular refrigerants.

Tandem templating strategies facilitate the assembly of calix[8]arene-supported Ln18 clusters.

Calix[n]arenes offer ideal chemical functionality through the polyphenolic lower rim to construct nano-sized coordination clusters with lanthanide (Ln) metal ions (e.g., NdIII10, GdIII8). However, the number of metal centers they can accommodate is still limited compared to that achievable with smaller ligands (e.g., GdIII140, GdIII104). Here, we exploit a combination of the "anion template strategy" and "templating ligands" to synthesise three highly symmetric (D3h, trigonal planar) LnIII18 (Ln = La, Nd, and Gd) systems, representing the largest calix[n]arene-based coordination clusters yet. The LnIII18 fragment is templated by a chloride anion located at the center of the cluster, wherefrom twelve µ3-OH- ligands bind 'internally' to the eighteen LnIII ions. 'Externally' the metallic skeleton is connected by p-tert-butylcalix[8]arene, oxo, chloro and carbonate ligands. The crystal packing in the lattice reveals large cylindrical channels of ∼26 Å in diameter, whose pore volume corresponds to ∼50% of the unit cell volume (using a 1.2 Å spherical probe radius). Magnetic measurements reveal the predominance of weak antiferromagnetic exchange in the Gd analog. Heat capacity data of GdIII18 reveal a high magnetic entropy with -ΔSm = 23.7 J K-1 kg-1, indicating potential for engineering magnetic refrigerant materials with calix[8]arenes.