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Gd complexes have been studied as magnetic coolants due to their large magneto-caloric effect. In this work we present a Gd 2D metal–organic framework (MOF) of formula [Gd(MeCOO)(PhCOO)2] (1). We characterize the magnetic properties of 1, showing that it displays slow relaxation of the magnetization by ac susceptibility, and single-ion magnetic anisotropy using high-field EPR. By heat capacity and magnetization vs. field at various temperatures we determine the magnetic entropy change of compound 1. We then grow 1 on functionalized silicon, and show that the surface-deposited 2D MOF 1Si can be used as an on-surface magnetic cryogenic coolant. [ABSTRACT FROM AUTHOR]

Heterometallic 3d–4f SMM [Co4Dy(OH)2(SALOH)5(chp)4(MeCN)(H2O)2] (1) has been deposited onto iron oxide nanoparticles (NPs) with an oleate self-assembled monolayer (SAM) as a surfactant. The obtained hybrid molecular-inorganic system 1-NP has been thoroughly characterized. The oleate SAM separates SMM 1 from the magnetic substrate to avoid the strong-coupling between the surface and molecule to ensure that 1 retains its magnetic properties in 1-NP. The magnetic properties of the hybrid system 1-NP have been characterized by element specific XMCD: the heterometallic SMM retains its magnetic properties on the surface of the iron oxide NPs while there is an enhancement of the magnetic properties of the NPs. [ABSTRACT FROM AUTHOR]

The heterometallic bridging potential of the anion of 1-(2-hydroxy-3-methoxybenzylidene)semicarbazide (HL) to CoII and four 4f ions was examined during a 4f ion coordination-driven cleavage of [Co2(μ-OH2)(O2CCMe3)4(HO2CCMe3)4] (Co2-Piv) and scrambling of pivalate anions from the starting material. Room-temperature reactions with four different lanthanide nitrate salts yielded [CoLnL(μ2-OOCCMe3)4(CH3OH)]·3CH3OH [Ln = Gd (1), Tb (2), Dy (3) and Ho (4)]. The formation in solution and the crystallization in the solid state indicated that the reactions inhibit any further aggregation of Co-Ln cores to higher order aggregates. After scrambling, the pivalate ions in [Co-Ln] show three types of coordination modes to sustain the dinuclear aggregates with varying degrees of distortion in the dinuclear entities bound to a single L− ion. Atom economy was maintained with respect to the pivalate ions as no external addition of these anions was made. The dc magnetic measurements revealed the presence of weak ferromagnetic interactions in complexes 1 and 2 and weak antiferromagnetic interactions in complexes 3 and 4. [ABSTRACT FROM AUTHOR]

A family of tetranuclear Ni-4f coordination aggregates (CAs) from the support of a carbazido ligand is described. The option of altering the 4f ions during synthesis within the family, without altering the core topology, gave the four members of the family. Tetranuclear (2:2) heterometallic compounds [NiII2LnIII2(μ3-L)2(μ3-OH)2(μ-OAc)3(AcO)(H2O)3]Cl2·4H2O (Ln = Gd, 1; Tb, 2; Dy, 3; Ho, 4) have been assembled through the utilization of all the coordination sites of the anionic form of 1-(2-hydroxy-3-methoxybenzylidene)semicarbazide (HL) and bridging supports from HO- and AcO- ions. The four metal ion centers of two different types, are held together by two μ-L-, two μ3-HO- and three μ1,3-AcO- bridges to self-assemble into Ni2Ln2O4 hetero-cubane structures. In each cube, LnIII ions are linked by two hydroxido and one phenoxido bridge and each NiII ion is linked by two phenoxido and one hydroxido bridge, so that each hydroxido group in μ3-mode is linked to two LnIII and one NiII and each phenoxido ion in μ3-mode is linked to two NiII and one LnIII. Variable temperature magnetic properties have been examined to find the role of magnetic anisotropy for the single molecule magnet (SMM) behavior. All of them show large ground state magnetic moment values and absence of out-of-phase ac susceptibility signals. The absence of SMM behavior is ascribed to the lack of axial magnetic anisotropy. [ABSTRACT FROM AUTHOR]

Highly symmetric enneanuclear copper(II) phosphates [Cu9(Pz)6(μ-OH)3(μ3-OH)(ArOPO3)4(DMF)3] (PzH = pyrazole, Ar = 2,6-(CHPh2)2-4-R-C6H2; R = Me, 2MeAr; Et, 2EtAr; iPr, 2iPrAr; and Ar = 2,6-iPr2C6H3, 2Dip) comprising nine copper(II) centers and pyrazole, hydroxide and DMF as ancillary ligands were synthesized by a reaction involving the arylphosphate monoester, 1, copper(I)chloride, pyrazole, and triethylamine in a 4 : 9 : 6 : 14 ratio. All four complexes were characterized by single crystal structural analysis. The complexes contain two distinct structural motifs within the multinuclear copper scaffold: a hexanuclear unit and a trinuclear unit. In the latter, the three Cu(II) centres are bridged by a μ3-OH. Each pair of Cu(II) centers in the trinuclear unit are bridged by a pyrazole ligand. The hexanuclear unit is made up of three dinuclear Cu(II) motifs where the two Cu(II) centres are bridged by an –OH and a pyrazole ligand. The three dinuclear units are connected to each other by phosphate ligands. The latter also aid the fusion of the trinuclear and the hexanuclear motifs. Magnetic studies reveal a strong antiferromagnetic exchange between the Cu(II) centres of the dinuclear units in the hexanuclear part and a strong spin frustration in the trinuclear part leading to a degenerate ground state. [ABSTRACT FROM AUTHOR]

Compounds [Co(L-N4R2)(dbdiox)](BPh4) (L-N4R2 = N,N′-di-alkyl-2,11-diaza[3.3]-(2,6)pyridinophane, R = iPr (1a), Et (2a); dbdiox = 3,5-di-tert-butyldioxolene) and [M(L-N4iPr2)(dbdiox)](BPh4) (M = Mn (3a), Fe (4a)) have been synthesized and investigated with a view to possible valence tautomeric (VT) or spin crossover (SCO) interconversions. Single crystal X-ray diffraction data for all compounds at 100 or 130 K indicate trivalent metal cations and di-tert-butylcatecholate (dbcat2−) dioxolene ligands. Variable temperature magnetic susceptibility data for all species between 2 and 340 K are consistent with these redox states, with low spin configurations for the cobalt(iii) ions and high spin for the manganese(iii) and iron(iii) ions. Above 340 K, compound 1a exhibits an increase in magnetic susceptibility, suggesting the onset of a VT interconversion from low spin Co(iii)-dbcat to high spin Co(ii)-dbsq (dbsq− = di-tert-butylsemiquinonate) that is incomplete up to 400 K. In solution, variable temperature electronic absorption spectra and Evans NMR method magnetic susceptibility data indicate reversible VT interconversions for 1a in several solvents, with the transition temperature varying with solvent. Variable temperature electronic absorption spectra are temperature-invariant for 3a and 4a, while spectra for 2a in 1,2-dichloroethane suggest the onset of a VT transition at the highest temperatures measured. Density functional theory calculations on all four compounds and literature analogues provide key insights into the relative energies of the different electromeric forms and the possibilities for VT versus SCO interconversions in this family of compounds. [ABSTRACT FROM AUTHOR]

A series of three isostructural tetranuclear complexes with the general molecular formula [Ln4(μ3-OH)4(L)4(μ2-piv)4(MeOH)4] (Ln = Gd 1, Dy 2 and Ho 3; LH = [1,3-bis(o-methoxyphenyl)-propane-1,3-dione]) were isolated and unambiguously characterized by single crystal XRD. Under similar reaction conditions, simply changing the co-ligand from pivalate to 2,6-bis(hydroxymethyl)-p-cresol (LH′3) led to the isolation of dinuclear Ln(iii) complexes with the general molecular formula [Ln2(L)4(μ2-LH′2)2]·4DMF (Ln = Gd 4, Dy 5 and Ho 6). Direct current magnetic susceptibility data studies on the polycrystalline sample of 1–6 and the results reveal the existence of weak antiferromagnetic exchange interactions between the lanthanide ions in 1 which is evident from the spin Hamiltonian (SH) parameters (J1 = −0.055 cm−1 and g = 2.01) extracted by fitting χMT(T). On the other hand, though complex 4 exhibits weak antiferromagnetic coupling (J1 = −0.048 cm−1 and g = 1.99) between the Gd(iii) ions, the χMT(T) data of complexes 5 and 6 unambiguously disclose the presence of ferromagnetic interactions between Dy(iii) and Tb(iii) ions at lower temperature. Magnetization relaxation dynamics studies performed on 2 show frequency dependent out-of-phase susceptibility signals in the presence of an optimum external magnetic field of 0.5 kOe. In contrast, complex 5 shows slow magnetization relaxation with an effective energy barrier (Ueff) of 38.17 cm−1 with a pre-exponential factor (τ0) of 1.85 × 10−6 s. The magnetocaloric effect (MCE) of complexes 1 and 4 was extracted from the detailed magnetization measurement and the change in the magnetic entropy (−ΔSm) of 1 and 4 was found to be 25.57 J kg−1 K−1 and 12.93 J kg−1 K−1, respectively, at 3.0 K for ΔH = 70 kOe. [ABSTRACT FROM AUTHOR]

Multifunctional molecules that respond both to magnetic fields and light are subject of study due to possible applications in fields as diverse as imaging or information processing and storage. In this paper we report visible and NIR emitting single-molecule magnets (SMMs) of Yb(iii) and Er(iii) with symmetric (SYML) and asymmetric (AZOL) Schiff base ligands. The prepared complexes SYML–Ln2 and AZOL–Ln3 (Ln = Er, Yb) are SMMs, with the exception of AZOL–Yb3, with a relaxation behavior dominated by quantum tunneling of magnetization. The multi-level double-decker structure of the complexes is ideal for surface deposition in carbon-based materials. [ABSTRACT FROM AUTHOR]

The promising potential applications, such as information processing and storage or molecular spintronics, of single-molecule magnets (SMMs) have spurred on the research of new, better SMMs. In this context, lanthanide ions have been seen as ideal candidates for new heterometallic transition metal–lanthanide SMMs. This perspective reviews 3d–4f SMMs up to 2014 and highlights the most significant advances and challenges of the field. [ABSTRACT FROM AUTHOR]

A linear trimeric cluster of molecular formula [Ni2Gd(L-)6](NO3) (1) (L- = (C14H12NO2) has been isolated with its structure determined via single crystal X-ray diffraction. Magnetic susceptibility measurements of 1 show that the nickel and gadolinium ions are coupled ferromagnetically, with a ground total spin state (S) of 11/2. Best fit spin Hamiltonian parameters obtained for 1 are J1(Ni-Gd) = +0.54 cm-1, g = 2.01. EPR measurements confirm a low magnetic anisotropy (D = -0.135 cm-1) for 1. Heat capacity determination of the magnetocaloric effect (MCE) parameters for 1 shows that the change in magnetic entropy (-ΔSm) achieves a maximum of 13.74 J kg-1 K-1 at 4.0 K, with the ferromagnetic coupling giving a rapid change in low applied fields, confirming the potential of Gd molecular derivatives as coolants at liquid helium temperature. [ABSTRACT FROM AUTHOR]

A ferrocene-based compartmental ligand, H2L, was synthesized by the reaction of diacetyl ferrocene with hydrazine hydrate followed by a condensation reaction with o-vanillin. [L]2− possesses a dual coordination pocket, an inner pocket of 2 imino nitrogens and two phenolate oxygens and an outer pocket of two phenolate and two methoxy oxygen atoms. Utilizing this ligand, several ZnII/LnIII heterobimetallic complexes were assembled: [LZn(μ-OAc)Dy(NO3)2] (2), [LZn(μ-OAc)Tb(NO3)2] (3), [LZn(μ-OAc)Gd(NO3)2·2CHCl3] (4), [LZn(μ-OAc)Er(NO3)2] (5), [LZn(μ-OAc)Ho(NO3)2] (6), [LZn(μ-OAc)Eu(NO3)2] (7). All of these metal complexes are neutral and isostructural: the ZnII ion occupies the inner coordination pocket while the LnIII ion occupies the outer coordination pocket of the doubly deprotonated ligand [L]2−. Zn(ii) has a coordination number of 5 (2N, 3O) in a square pyramidal coordination geometry while Ln(iii) has a coordination number of 9 (9O) in a distorted tricapped trigonal prismatic geometry. Zn(ii) and the 4f metal ion are bridged to each other by two phenolate oxygen atoms and an acetate ligand. ESI-MS reveals that 2–7 retain their structural integrity in solution. Cyclic voltammetry of 1–7 revealed a quasi-reversible oxidation (involving the ferrocene motif) and an irreversible reduction of the hydrazone unit. Magnetic studies of 2, 3 and 6 were carried out. Ac susceptibility studies did not reveal slow relaxation of magnetization. [ABSTRACT FROM AUTHOR]

A luminescent trinuclear DyIIIcomplex, in which the three DyIIIcenters with different geometries take a nearly linear disposition, shows the slow magnetic relaxation processes of single ion origin. [ABSTRACT FROM AUTHOR]

Ten coordination polymers {[Cd(L1)2]}n(1), {[Cu(L1)2]}n(2), {[Cd2(L1)2(HCOO)2(H2O)]}n(3), {[Cd2(L1)4]·3H2O}n(4), {[Cd(L1)(CH3COO)]}n(5), {[Cd(L1)2(C5H5N)]·2.5H2O}n(6), {[Zn(L2)2]}n(7), {[Cd2(L2)4]·H2O}n(8), {[Cd3(L2)6(H2O)]·2EtOH·H2O}n(9) and {[Cd(L3)2]·2DMF·4H2O}n(10), where HL1= 4-imidazole-1-yl-benzoic acid, HL2= 3-imidazole-1-yl-benzoic acid and HL3= 4-benzmidazole-1-yl-benzoic acid, have been synthesized under different experimental conditions. Their structures are determined by single-crystal X-ray diffraction analyses and further characterized by IR spectra, thermogravimetric (TG) and elemental analyses. The structure of 1is a 2D → 2D (2D = two dimensional) interpenetrating network with (4,4) grid topology while 2has an interesting Kagome structure. Compounds 4and 6crystallize in 4- and 3-fold interpenetrating diamondoid frameworks respectively. Compound 7is a layered non-interpenetrating (4,4) grid network whereas 8has an unprecedented self-penetrating structure with 2D framework. Compound 9is a self-penetrating 3D structure while 10crystallizes in a non-interpenetrating (4,4) square-grid with one-dimensional (1D) channels. From these results, it is demonstrated that the structures of the coordination polymers are strongly dependent on the geometry of L1, L2and reaction conditions. Variable temperature magnetic susceptibility study of 2has also been performed. [ABSTRACT FROM AUTHOR]

The employment of the 1,3-bis(dimethylamino)-2-propanolate (bdmap) ligand as a chelating/bridging ligand in manganese chemistry is described. The reaction of Mn(R-BzO)2and bdmap affords [Mn8(O)4(R-BzO)12(bdmap)2(H2O)2], R = H (1), R = 3-Cl (2) and R = 4-Cl (3), which are mixed-valence MnII2MnIII6clusters. Structural characterization was achieved for 1and 2, which can be described as a central double defective dicubane MnIII4subunit, capped by two oxo-bridged MnII-μ(bdmap)-MnIIIdinuclear units. DC variable-temperature magnetic susceptibility studies were carried out in the 2–300 K range, revealing an overall antiferromagnetic behaviour for 1–3. This work demonstrates for the first time the ability of this kind of polytopic ligands in high nuclearity manganese chemistry. [ABSTRACT FROM AUTHOR]

The synthesis, structure, magnetic and electronic properties of soluble transition metal phosphonate cages utilizing tritylphosphonic acid (TPA) as ligand are reported. [ABSTRACT FROM AUTHOR]

This work introduces a novel family of Co II species having a curcuminoid (CCMoid) ligand, 9Accm, attached, namely [Co(9Accm) 2 (py) 2 ] ( 1 ) and [Co(9Accm) 2 (2,2'-bpy)] ( 2 ), achieved in high yields by the use of a microwave reactor, and exhibiting two different arrangements for the 9Accm ligands, described as " cis "( 2 ) and " trans "( 1 ). The study of the similarities/differences of the magnetic, luminescent and surface behaviors of the two new species, 1 and 2 , is the main objective of the present work. The determined single-crystal structures of both compounds are the only Co II -CCMoid structures described in the literature so far. Both compounds exhibit large positive D values, that of 1 ( D = +74 cm -1 ) being three times larger than that of 2 ( D = +24 cm -1 ), and behave as mononuclear Single-Molecule Magnets (SMMs) in the presence of an external magnetic field. Their similar structures but different anisotropy and SMM characteristics provide, for the first time, deep insight on the spin-orbital effects thanks to the use of CASSCF/NEVPT2 calculations implementing such contributions. Further magnetic studies were performed in solution by means of paramagnetic 1 H NMR, where both compounds ( 1 and 2 ) are stable in CDCl 3 and display high symmetry. Paramagnetic NMR appears to be a useful diagnostic tool for the identification of such molecules in solution, where the resonance values found for the methine group (-CH-) of 9Accm vary significantly depending on the cis or trans disposition of the ligands. Fluorescence studies show that both systems display chelation enhancement of quenching (CHEQ) with regard to the free ligand, while 1 and 2 display similar quantum yields. Deposition of 1-2 on HOPG and Si(100) surfaces using spin-coating was studied using AFM; UV photoemission experiments under the same conditions display 2 as the most robust system. The measured occupied density of states of 2 with UV photoemission is in excellent agreement with theoretical DFT calculations.

Two new coordination polymers have been synthesized with Mn(2+) and Dy(3+) ions using a new bent ether-bridged tricarboxylic acid ligand, o-cpiaH(3) (5-(2-carboxy-phenoxy)-isophthalic acid). The ligand readily reacts with a Mn(2+) salt in presence of pyridine (py) under hydrothermal condition to afford a 3D coordination polymer {[Mn(9)(o-cpia)(6)(py)(3)(3H(2)O)]·H(2)O}(n) (1), that contains two types of polymeric chains. One of them is merely carboxylate bridged Mn(2+) where each metal ion shows both penta- and hexa-coordination. The other chain consists of carboxylate-bridging along with terminally bound pyridines providing both penta- and hexa-coordination to each metal ion. When o-cpiaH(3) is treated with Dy(NO(3))(3).xH(2)O under solvothermal condition, it gives rise to an unusual double layer (6,6) connected 2D coordination polymer {[Dy(o-cpia)]}(n)(2), where each metal ion is hexacoordinated. The double layer 2D sheets are stacked to each other in AA··· fashion through strong C-H···π interactions to generate an overall 3D supramolecular architecture. Both the complexes have been characterized by single crystal X-ray diffraction, IR spectroscopy, thermogravimetry and elemental analysis. Variable temperature magnetic susceptibility measurements indicate that 1 exhibits metamagnetic behavior while 2 shows weak antiferromagnetic behavior.

The reaction of VCl(3) with 3,5-dimethylpyrazole (3,5-Me(2)PzH) and trichloromethylphosphonic/tert-butylphosphonic acid in the presence of triethylamine as a hydrogen chloride scavenger afforded the tetranuclear V(IV) assemblies, [(VO)(4)(3,5-Me(2)PzH)(8)(CCl(3)PO(3))(4)] (1) and [(VO)(4)(3,5-Me(2)PzH)(4)(t-BuPO(3))(4)] (2). Both of these compounds possess a distorted cubic framework structures containing V(IV) ions and phosphorus atoms in the alternate corners of the cube. The edges of the cube contain oxygen atoms derived from the phosphonate ligand. The phosphonate ligand in both of these compounds is dianionic and helps to bind to three V(IV) centers. The faces of the cubic ensembles contain puckered V(2)P(2)O(4) eight-membered rings. The V(IV) center in 1 is six-coordinate in a distorted octahedral geometry while in 2 it is five-coordinate in a distorted square-pyramidal geometry. Magnetic studies carried out on 1 and 2 reveal that the V(IV) centers are anti-ferromagnetically coupled to each other, albeit weakly, through the mediation of the phosphonate ligands.

A metal-organic framework (MOF) with helical channels has been constructed by bridging helical chain secondary building units with 2,6-di-p-carboxyphenyl-4,4'-bipyridine ligands. The activated MOF shows permanent porosity and gas adsorption selectivity. Remarkably, the MOF exhibits a facile transition from micro- to meso-porosity., (This journal is © The Royal Society of Chemistry 2012)

Octanuclear and enneanuclear Ni(II) complexes have been synthesized using a microwave reactor. The octanuclear complex Ni(8) presents a new triply bridging coordination mode for the NO(2)(-) ligand.

Pyridine-2,4,6-tricarboxylic acid (ptcH(3)) reacts with Cd(II), Mn(II), Ni(II), Mg(II), Ca(II), Sr(II), Ba(II), Dy(III) salts forming different products depending on the reaction conditions. In the presence of pyridine at room temperature the acetate, chloride or nitrate salt of Cd(II) breaks the ligand to form an open framework structure with the empirical formula, {[Cd(Ox)(H(2)O)(2)]H(2)O}(n) (Ox = oxalate), 1. In the absence of pyridine, no crystalline compound could be isolated at room temperature (RT). However, under hydrothermal conditions and in the absence of pyridine, a discrete tetrameric complex with the formula, {[Cd(2)(cda)(2)(H(2)O)(4)](H(2)O)(3)}(2) (cdaH(2) = 4-hydroxypyridine-2,6-dicarboxylic acid), 2, is formed where the carboxylate group at the 4-position of the ligand is reduced to a hydroxyl group. When Ni(II), Mn(II), Mg(II), Ca(II), Sr(II), Ba(II), Dy(III) salts are used in place of Cd(II), no crystalline product could be isolated at RT. But under hydrothermal conditions, coordination polymers ({[Ni(1.5)(ptc)(pip)(0.5)(H(2)O)(4)].H(2)O}(n), (pip = piperazine), 3; {Mn(1.5)(ptc).2H(2)O}(n), 4; {Mg(3)(ptc)(2).8H(2)O}(n), 5; {[Mg(ptc)(H(2)O)(2)].1/2[Mg(H(2)O)(6)].H(2)O}(n), 6; {Ca(1.5)(ptc).2H(2)O}(n), 7; {Sr(1.5)(ptc).5H(2)O}(n), 8; {[Ba(ptc)(H(2)O)][Ba(ptcH(2))H(2)O]}(n), 9; {[Dy(ptc).3H(2)O].H(2)O}(n), 10) are formed. The structures exhibit different dimensionality depending on the nature of the metal ions. In 1 a discrete acyclic water hexamer is also identified. All the compounds are characterized in the solid state by X-ray crystallography, IR and elemental analysis.

An azido-metal-1,2,4-triazolate coordination polymer, [Cu(trz)(N(3))](n) (trz = 1,2,4-triazolate) was synthesized using hydrothermal methods; the complex has a rare three-dimensional non-interpenetrated utp or (10,3)-d topological network structure and exhibits spin-canted antiferromagnetism at low temperature.

Cyclic octanuclear complexes, each containing seven group 13 metals and one d-block metal are reported and preliminary physical characterisation of the compounds discussed.

The solvothermal synthesis, crystal structure and preliminary magnetic studies are reported of the first high nuclearity V(III)-based polyoxo(alkoxo)vanadium cage, a V(III)16V(IV)2 complex.

Solid-state decomposition of [V3O(O2CPh)6(H2O)3]Cl at 300 degrees C followed by alcoholysis of the product gives the new vanadium complexes [V6O6(PhCO2)6(CH3O)6(CH3OH)3] (1), [V6O6(PhCO2)6(C2H5O)6(C2H5OH)3] (2), [V6O6(PhCO2)6(C3H7O)6(C3H7OH)3] (3), [V6O6(PhCO2)6(C4H9O)6(C4H9OH)3] (4) and [V4O4(OCH3)6(O2CPh)2(HOCH3)2] (5). Complexes 2, 3 and 5 have been crystallographically characterised. DC magnetic susceptibility studies on complex shows antiferromagnetic coupling leading to a S = 0 spin ground state.