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 pseudo-calixarene [Co16] wheel that self-assembles as a tubular network of capsules.

Reaction of Co(OAc)2·4H2O and Hsal in a basic MeCN solution affords the hexadecanuclear wheel [Co16(sal)16(OAc)16]·16MeCN (1·16MeCN) that displays ferromagnetic nearest neighbour exchange and has pseudo-calixarene character. Symmetry equivalent wheels self-assemble to form remarkable tubular networks of capsules in the extended structure.

Constructing "Closed" and "Open" {Mn8} Clusters.

Use of the 1,3,5-tri(2-hydroxyethyl)-1,3,5-triazacyclohexane ligand, LH3, in manganese chemistry affords access to two structurally related {Mn8} clusters: a "closed" {MnIII 6MnII 2} puckered square wheel of formula [Mn8L2(LH)O3(OH)2(MeO)2Br(imH)(H2O)3](Br)3 (1; imH = imidazole) and an "open" {MnIII 8} rod of formula [MnΙΙΙ 8L2O4(aibH)2(aib)2(MeO)6(MeOH)2](NO3)2 (2, aibH = 2-amino-isobutyric acid). In each case the triaza ligands, L/LH, direct the formation of {Mn3} triangles with their N atoms preferentially bonding to the Jahn-Teller axes of the MnIII ions. Subsequent self-assembly is dependent on the anion of the Mn salt and the identity of the organic coligand employed-the terminally bonded imidazole and the chelating/bridging amino acid. The {Mn3} triangles fold up on themselves in 1, forming a wheel. However, the syn, syn-bridging carboxylates in 2 prevent this from happening, instead directing the formation of a linear rod. Magnetic susceptibility and magnetization measurements reveal competing ferro- and antiferromagnetic interactions in both complexes, the exchange being somewhat weaker in 1 due to the presence of MnII ions.

A [Mn18] wheel-of-wheels.

A [Mn18] wheel of wheels is obtained from the reaction of MnBr2·4H2O and LH3 in MeOH. The metallic skeleton reveals two asymmetric [MnIII6MnII2] square wheels connected into a larger wheel via two MnII ions. Magnetic susceptibility and magnetisation data reveal competing exchange interactions, supported by computational studies.

The first amino acid bound manganese-calcium clusters: a {[MnCa]2} methylalanine complex, and a [MnCa] trigonal prism.

An amino acid containing octanuclear heterometallic {[MnCa]2} cluster has been synthesized, alongside a structurally-related trigonal prismatic [MnCa]2+ cage.

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.

Dinuclear and Mononuclear Rhenium Coordination Compounds upon Employment of a Schiff-Base Triol Ligand: Structural, Magnetic, and Computational Studies.

The 1:1 reaction of trans-[ReIIICl3(PPh3)2(MeCN)] with 2-(ß-naphthalideneamino)-2-hydroxymethyl-1-propanol, H3L, in toluene gave the dinuclear complex [ReIII2Cl4(HL)(PPh3)]·2C7H8 (1·2C7H8), while the 1:2 reaction led to the formation of complex [ReIVCl2(HL)(PPh3)] (2). In both species, the Schiff-base ligand exists in its doubly deprotonated form, HL2-, forming chelate rings around the metallic centers. In addition, 1·2C7H8 displays a unique triple metal-to-metal bond between the two trivalent rhenium ions separated at a 2.229(1) Å bond distance, while in complex [ReIVCl2(HL)(PPh3)] (2) the two aromatic ligands, HL2- and PPh3, occupy axial positions, with the terminal Cl- ions in the trans position. Investigation of the magnetic properties revealed a Curie paramagnetic behavior ( S = 1/2) with a pronounced temperature independent paramagnetism (TIP) for 1·2C7H8 and 2. Both the geometry and the electronic structure of both compounds have been studied by means of density functional theory (DFT) calculations, confirming the triplet and doublet spin ground state of the complexes and furthermore establishing an electron-rich σ2π4δ1δ*1 bond order of 3 for 1·2C7H8. In addition, the absorption spectrum of 1·2C7H8 in CH2Cl2 was simulated by means of DFT calculations and is in excellent agreement with both the crystallographic and theoretical studies. Complex 1·2C7H8 is the first dinuclear rhenium complex with a triple metal-metal bond between trivalent rhenium centers.

A decanuclear [DyZn] cluster: a {Zn} rectangle surrounding an octahedral {Dy} single molecule magnet.

An octahedral {DyIII6} cage within a diamagnetic {ZnII4} rectangle is reported, with magnetic relaxation studies revealing single-molecule magnet behaviour for the complex under zero external dc field with Ueff = 43 K and τo = 1 × 10-5 s.

Heterometallic lanthanide-centred [NiLnIII] rings.

A [NiII6DyIII] heptanuclear complex featuring a rare six-membered {NiII6} metal ring surrounding the central Dy(iii) ion is reported. Magnetic studies reveal single-molecule magnet behaviour for the complex under zero external dc field, while replacing the DyIII ion with [capital Upsilon]III or GdIII ions allows for a comprehensive understanding of the magnetic behaviour.

A [Cr2Ni] coordination polymer: slow relaxation of magnetization in quasi-one-dimensional ferromagnetic chains.

The reaction of [Cr3IIIO(OAc)6(H2O)3]NO3·AcOH with 2-hydroxynaphthaldehyde, 2-amino-isobutyric acid and NiCl2·6H2O in MeOH, under basic and solvothermal conditions, led to the formation of the quasi-1D coordination polymer {[CrIII2NiII(L)4(MeOH)2]}n (where L = the dianion of the Schiff base between 2-hydroxynaphthaldehyde and 2-amino-isobutyric acid), which behaves as a ferromagnetic chain, displaying slow relaxation of magnetization.

Constructing CrIII-centered heterometallic complexes: [NiCrIII] and [CoCrIII] wheels.

The solvothermal reaction between Cr(acac)3, MCl2·6H2O (M = Ni, Co) and 2-hydroxy-4-methyl-6-phenyl-pyridine-3-amidoxime (H2L), under basic conditions, led to the synthesis of the heterometallic heptanuclear clusters [MCr(HLzw)6(HL)6]·3Cl (M = Ni, 1; Co, 2), with the nickel analogue displaying an S = 9/2 spin ground-state.

A [Ce21] keplerate.

The solvothermal reaction between Ce(NO3)3·6H2O, 2-amino-isobutyric acid, 2-hydroxy-1-naphthaldehyde and 2-amino-2-methyl-1,3-propanediol in MeOH, in the presence of base, leads to the formation of a unique [CeCe ] keplerate cage.

Tetradecanuclearity in 3d-4f chemistry: relaxation and magnetocaloric effects in [NiLn] species.

The employment of 2-amino-isobutyric acid, Haib, and 2-hydroxy-1-naphthaldehyde, Hnaphth, in NiII/LnIII chemistry has led to the isolation and characterization of two new isostructural 3d-4f tetradecanuclear [NiLn] clusters (Ln = GdIII, DyIII), with the Dy analogue displaying temperature and frequency dependent out-of-phase signals, and the Gd analogue showing interesting magnetocaloric properties.

Building 1D lanthanide chains and non-symmetrical [Ln2] "triple-decker" clusters using salen-type ligands: magnetic cooling and relaxation phenomena.

A solvothermal reaction between Ln(NO3)3·6H2O (Ln: Gd, Tb and Dy), 2-hydroxy-1-naphthaldehyde, 2-OH-naphth, and ethylenediamine, en, in MeOH in the presence of a base, NEt3, led to the formation of the 1D coordination polymers [Ln(L)(MeO)(MeOH)0.5]n·MeOH (Ln = Gd (1·MeOH), Tb(2), Dy (3·MeOH); H2L = 1,1'-((1E,1'E)-(ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(naphthalen-2-ol), the Schiff-base ligand derived from the condensation of 2-OH-naphth and en), while a similar reaction in an excess of NaN3 yielded 1D coordination polymers [Ln(L)(N3)0.75(MeO)0.25(MeOH)]n (Ln = Gd (4), Tb (5), Dy (6)). Finally, upon replacing ethylenediamine with o-phenylenediamine, o-phen, we managed to isolate the discrete dimers [Dy2(L')3(MeOH)]·2MeOH (7·2MeOH) and [Gd2(L')3(MeOH)]·2MeOH (8·2MeOH) (H2L' = 1,1'-((1E,1'E)-(1,2-phenylenebis(azanylylidene))bis(methanylylidene))bis (naphthalen-2-ol), the Schiff-base ligand from the condensation of 2-OH-naphth and o-phen). Polymers 1-3 describe one-dimensional chains, containing alternating seven- and eight-coordinate LnIII metal centers, polymers 4-6 contain eight-coordinate lanthanide ions, while in both 7 and 8 the two LnIII centers are eight- and seven-coordinate, adopting square antiprismatic and "piano-stool" geometry, respectively. The magnetocaloric properties of the three GdIII analogues were determined from magnetic measurements, yielding the magnetic entropy change -ΔSm = 21.8, 23.0 and 16.0 J kg-1 K-1 at T = 3.0 K on demagnetization of 7 T to 0, for 1, 4 and 8, respectively. The study of the magnetic properties also revealed that all three DyIII analogues (3, 6 and 7) display out-of-phase signals, therefore suggesting slow magnetic relaxation, while such behaviour was not established in the TbIII analogues.

A triacontanuclear [Zn12Dy18] cluster: a ring of [Dy4] cubes.

The reaction between Dy(NO3)3·6H2O, Zn(OAc)2·4H2O, salicylaldehyde and 2-amino-isobutyric acid, in MeOH in the presence of NEt3 under solvothermal conditions, led to the isolation of the triacontanuclear mixed-metal cluster [Zn(II)12Dy(III)18(OH)30(L)12(sal)6(OAc)6(NO3)3(H2O)6](NO3)3·12MeOH·5H2O (1·12MeOH·5H2O), which displays frequency- and temperature-dependent out-of-phase magnetic susceptibility signals.

Solvothermal synthesis of enneanuclear [Cu7(II)Ln2(III)] clusters.

Employment of H3L (= 2-(ß-naphthalideneamino)-2-hydroxymethyl-1-propanol) in mixed-metal copper-lanthanide cluster chemistry has led to the isolation of four new enneanuclear heteronuclear isostructural [Cu7(II)Ln2(III)] complexes. More specifically, the solvothermal reaction of Cu2(OAc)4·2H2O with H3L and the corresponding lanthanide nitrate salt in MeCN in the presence of a base, NEt3, yielded three complexes with the general formula [Cu7(II)Ln2(III)(L)4(HL)2(OAc)4]·2MeCN (Ln: Gd, 1·2MeCN; Tb, 2·2MeCN; Dy, 3·2MeCN), while in addition the Y(III) analogue, [Cu7(II)Y2(III)(L)4(HL)2(OAc)4]·2MeCN (4·2MeCN), was also synthesized in the same manner. The structure of the cluster describes two corner-sharing [Cu3Ln] cubane metallic units, each one further connected to one Cu(II) ion. Dc magnetic susceptibility studies in the 5-300 K range for complexes 1-4 reveal the presence of both ferromagnetic and antiferromagnetic exchange interactions within the metallic clusters.

Enneanuclear [Ni6Ln3] Cages: [Ln(III)3] Triangles Capping [Ni(II)6] Trigonal Prisms Including a [Ni6Dy3] Single-Molecule Magnet.

The use of (2-(ß-naphthalideneamino)-2-hydroxymethyl-1-propanol) ligand, H3L, in Ni/Ln chemistry has led to the isolation of three new isostructural [Ni(II)6Ln(III)3] metallic cages. More specifically, the reaction of Ni(ClO4)2·6H2O, the corresponding lanthanide nitrate salt, and H3L in MeCN, under solvothermal conditions in the presence of NEt3, led to the isolation of three complexes with the formulas [Ni6Gd3(OH)6(HL)6(NO3)3]·5.75MeCN·2Et2O·1.5H2O (1·5.75MeCN·2Et2O·1.5H2O), [Ni6Dy3(OH)6(HL)6(NO3)3]·2MeCN·2.7Et2O·2.4H2O (2·2MeCN·2.7Et2O·2.4H2O), and [Ni6Er3(OH)6(HL)6(NO3)3]·5.75MeCN·2Et2O·1.5H2O (3·5.75MeCN·2Et2O·1.5H2O). The structure of all three clusters describes a [Ln(III)3] triangle capping a [Ni(II)6] trigonal prism. Direct current magnetic susceptibility studies in the 5-300 K range for complexes 1-3 reveal the different nature of the magnetic interactions within the clusters: dominant antiferromagnetic exchange interactions for the Dy(III) and Er(III) analogues and dominant ferromagnetic interactions for the Gd(III) example. Alternating current magnetic susceptibility measurements under zero external dc field displayed fully formed temperature- and frequency-dependent out-of-phase peaks for the [Ni(II)6Dy(III)3] analogue, establishing its single molecule magnetism behavior with Ueff = 24 K.

Dodecanuclear [Mn6(III)Ln6(III)] species: synthesis, structures and characterization of magnetic relaxation phenomena.

The use of H3L (= 2-(ß-naphthalideneamino)-2-hydroxymethyl-1-propanol) in mixed-metal manganese-lanthanide carboxylate cluster chemistry has led to the isolation of two new dodecametallic heteronuclear isostructural [Mn6(III)Ln6(III)] complexes (Ln = Gd, Dy), with the Dy analogue displaying temperature and frequency dependent out-of-phase signals suggesting possible single molecule magnetism behaviour.

A family of dinuclear lanthanide(III) complexes from the use of a tridentate Schiff base.

The use of N-salicylidene-o-aminophenol (H2saph) in 4f-metal chemistry has led to the isolation of seven new isostructural lanthanide(iii) [Ln(III)] complexes. More specifically the Ln(NO3)3·xH2O/H2saph/Et3N (1 : 1 : 1) reaction mixtures in DMF/MeCN gave complexes [Ln2(NO3)2(saph)2(DMF)4] (Ln = Sm (); Eu (); Gd (); Tb (); Dy (); Ho (); Er ()) in good yields (∼65%). The structures of the isomorphous complexes and were solved by single-crystal X-ray crystallography; the other complexes are proposed to be isostructural with and based on elemental analyses, IR spectra and powder XRD patterns. The two Ln(III) atoms in the centrosymmetric molecules of and are doubly bridged by the deprotonated iminophenolato oxygen atoms of two nearly planar η(1):η(1):η(2):µ saph(2-) ligands. The imino nitrogen and five terminal oxygen atoms (the salicylaldiminate, two from one bidentate chelating nitrato group and two from two DMF ligands) complete square antiprismatic coordination at each metal centre. The IR spectra of the complexes are discussed in terms of the coordination modes of the ligands present in the complexes. Solid-state emission studies for all display identical ligand-based photoluminescence. Dc magnetic susceptibility studies in the 2-300 K range reveal the presence of a weak, intramolecular antiferromagnetic exchange interaction (J = -0.19(1) cm(-1) based on the spin Hamiltonian H = -J(SGd·SGd')) for and probably ferromagnetic exchange interaction within the molecules of and . Ac magnetic susceptibility measurements in zero dc field show temperature- and frequency-dependent out-of-phase signals with two well defined, thermally-activated processes for , suggesting potential single-molecule magnetism character. The Ueff value is 17.4 cm(-1) for the higher temperature process and 16.2 cm(-1) for the lower temperature one. The combination of photoluminescence and single-molecule behaviour in the Dy complex is critically discussed.

A family of [Mn(III)6Ln(III)2] rod-like clusters.

Employment of H3L (= 2-(ß-naphthalideneamino)-2-hydroxymethyl-1-propanol) in mixed-metal manganese-lanthanide cluster chemistry has led to the isolation of five new octametallic heteronuclear isostructural [Mn(III)6Ln(III)2] complexes. More specifically, the reaction of Mn(ClO4)2·6H2O with H3L and the corresponding lanthanide nitrate in MeCN in the presence of a base, NEt3, yielded four complexes with the general formula [Mn(III)6Ln(III)2O2(OH)2(H2O)2(HL)6(NO3)6]·6MeCN·0.5H2O (Ln: Gd, 1·6MeCN·0.5H2O; Tb, 2·6MeCN·0.5H2O; Dy, 3·6MeCN·0.5H2O; Er, 4·6MeCN·0.5H2O). Furthermore, the Y(III) analogue, [Mn(III)6Y(III)2O2(OH)2(H2O)2(HL)6(NO3)6]·6MeCN·0.5H2O (5·6MeCN·0.5H2O), was also synthesized in the same manner. All five clusters describe a central rod-like topology consisting of four face-sharing defective cubane metallic units, forming a planar hexametallic [Mn(III)4Ln(III)2] core, which is further capped by two Mn(III) ions. Dc magnetic susceptibility studies in the 5-300 K range for complexes 1-5 reveal the presence of dominant antiferromagnetic exchange interactions within the metallic clusters, while ac magnetic susceptibility measurements show temperature and frequency dependent out-of-phase signals for the Dy(III) analogue (3·6MeCN·0.5H2O), suggesting potential single molecule magnetism character. Furthermore, the Y(III) analogue yielded a diamagnetic ground-state for the [Mn(III)6] core, thus proving that the SMM character displayed by 3·6MeCN·0.5H2O is due to the presence of the Dy(III) centres.