Search

The reaction of MnCl2·4H2O with HL ((1-methyl-1H-imidazol-2-yl)methanol) and pdH2 (1, 3 propanediol) in a basic MeCN solution results in the formation of a mixed-valence [Mn20] cationic cluster and two [MnIICl4] counter anions. The metallic skeleton of the cluster describes two geometrically equivalent mixed-valent, linked [MnIII6MnII4] supertetrahedra in which nearest-neighbor metal ions have a different oxidation state. Magnetic susceptibility, magnetization data and heat capacity measurements support evidence of predominant ferromagnetic correlations, leading to a s = 22 spin ground state for the [MnIII6MnII4] supertetrahedra, which are pair-linked by a weak antiferromagnetic coupling. The properties are discussed in the context of the magnetocaloric effect and the potential application of this compound in cryogenic refrigeration. [ABSTRACT FROM AUTHOR]

Reaction between Mn(NO3)2 ⋅ 6H2O, Zn(NO3)2 ⋅ 6H2O, 1,3,5‐tri(2‐hydroxyethyl)‐1,3,5‐triazacyclohexane (H3L) and pyrazole in MeOH under basic conditions leads to the formation of the decanuclear complex [MnIII6MnII2ZnII2(L)2(pyr)4O4(OH)4(NO3)2 (MeOH)2(H2O)4](NO3)2 ⋅ Η2Ο (1 ⋅ Η2Ο). The metallic core of the cationic cluster consists of a central hexagonal‐bipyramidal {MnIII4MnII2ZnII2} unit connected to two peripheral trivalent Mn centers arranged in a "trans" fashion, with one MnIII center lying above and one MnIII center below the hexagonal plane. Replacing Mn(NO3)2 ⋅ 6H2O with MnBr2 ⋅ 4H2O and repeating the same reaction leads to the formation of the related, neutral decanuclear complex [MnIII6MnII2ZnII2(L)2(pyr)4O4(OH)4Br4(H2O)2] (2), displaying the same metallic core as 1. Addition of THF to the reaction mixture that produces (2) affords the neutral dodecanuclear complex [MnIII6MnII2ZnII4(L)2(pyr)6O4(OH)4Br6(H2O)4] ⋅ 8THF (3 ⋅ 8THF), whose metallic skeleton retains the central hexagonal‐bipyramidal {MnIII4MnII2ZnII2} unit found in 1 and 2 but is now connected to two peripheral {MnIIIZnII} units. Magnetic susceptibility and magnetization measurements carried out in the T=2–300 K temperature range and in fields up to B=7.0 T for all three complexes reveal dominant antiferromagnetic exchange interactions. [ABSTRACT FROM AUTHOR]

A family of Mn(II)Ln(III) dinuclear and tetranuclear complexes (Ln = Gd and Dy) has been prepared from the compartmental ligands N,N′-dimethyl-N,N′-bis(2-hydroxy-3-formyl-5-bromobenzyl)ethylenediamine (H2L1) and N,N′,N′′-trimethyl-N,N′′-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H2L2). The Mn(II)Gd(III) complexes exhibit antiferromagnetic interactions between Mn(II) and Gd(III) ions in most cases, which are supported by Density Functional Theory (DFT) calculations. Experimental magneto-structural correlations carried out for the reported complexes and other related complexes found in bibliography show that the highest ferromagnetic coupling constants are observed in di-μ-phenoxido bridged complexes, which is due to the planarity of the Mn–(μ-O)2–Gd bridging fragment and to the high Mn–O–Gd angles. The effect of these angles has been studied by DFT calculations performed on a di-μ-phenoxido doubly bridged model. The magneto-thermal properties of the Mn(II)Gd(III) based complexes have also been measured, concluding that the magnitude of the Magneto-Caloric Effect (MCE) is due to the strength rather than to the nature of the magnetic coupling. Moreover, when two Mn(II)Gd(III) dinuclear units are connected by two carbonato-bridging ligands the MCE is enhanced, obtaining a maximum magnetic entropy change of 36.4 Jkg−1 K−1 at ΔB = 7 T and T = 2.2 K. On the other hand, one of the dinuclear Mn(II)Dy(III) complexes displays Single-Molecule Magnet (SMM) behaviour with an energy barrier of 14.8 K under an applied external field of 1000 Oe. [ABSTRACT FROM AUTHOR]

The calix[4]arene scaffold is an extremely versatile supramolecular platform that has found widespread use across many research areas due to its synthetic versatility, controllable conformation, and the presence of cavities or clefts for tailorable guest binding. The tetraphenolic lower-rim of p-tert-butylcalix[4]arene in the cone conformation is ideal for binding a variety of paramagnetic transition and lanthanide metals, and in this Perspective we review our endeavours in using such complexes as metalloligands in the synthesis of polymetallic clusters that have fascinating structural and magnetic properties. By varying reactants, stoichiometries and reaction or crystallisation conditions it is possible to access an incredible range of clusters, all of which show consistent trends in coordination preferences and assembly behaviours. p-tert-Butylcalix[4]arene has already given so much, yet it is likely that this remarkable parent calixarene will continue to surprise chemists and deliver even more in terms of novelty and function. [ABSTRACT FROM AUTHOR]

Calix[4]arenes are versatile ligands that, whilst also serving other purposes, can act as platforms for the synthesis of a wide range of 3 d, 4 f, and 3 d-4 f polymetallic clusters. The empirical metal ion binding rules established for calix[4]arene are closely mirrored by bis-calix[4]arene, a relatively new ligand in which two equivalents of the former are directly tethered at a methylene bridge position. The direct tethering within bis-calix[4]arene gives rise to some structural features that are related to calix[4]arene coordination chemistry, but the prevailing clusters have fascinating new topologies and coordination behaviors. Here, we present the synthesis of a family of new bis-calix[4]arene-supported 3 d-4 f clusters, as well as their structural characterization and magnetic properties. Comparison is drawn with calix[4]arene coordination chemistry, showing logical extension of common structural fragments and cluster capping behaviors upon moving to bis-calix[4]arene. This approach therefore holds great potential for tuning cluster formation and composition at a high level through subsequent ligand alteration. [ABSTRACT FROM AUTHOR]

The synthesis, structural, and magnetic characterization of five new members of the hexanuclear oximate [MnIII6] family are reported. All five clusters can be described with the general formula [MnIII6O2(R-sao)6(R′-CO2)2(sol)x(H2O)y] (where R-saoH2 = salicylaldoxime substituted at the oxime carbon with R = H, Me and Et; R′ = 1-naphthalene, 2-naphthalene, and 1-pyrene; sol = MeOH, EtOH, or MeCN;x = 0–4 andy = 0–4). More specifically, the reaction of Mn(ClO4)2·6H2O with salicylaldoxime-like ligands and the appropriate carboxylic acid in alcoholic or MeCN solutions in the presence of base afforded complexes1–5: [Mn6O2(Me-sao)6(1-naphth-CO2)2(H2O)(MeCN)]·4MeCN (1·4MeCN); [Mn6O2(Me-sao)6(2-naphth-CO2)2(H2O)(MeCN)]·3MeCN·0.1H2O (2·3MeCN·0.1H2O); [Mn6O2(Et-sao)6(2-naphth-CO2)2(EtOH)4(H2O)2] (3); [Mn6O2(Et-sao)6(2-naphth-CO2)2(MeOH)6] (4) and [Mn6O2(sao)6(1-pyrene-CO2)2(H2O)2(EtOH)2]·6EtOH (5·6EtOH). Clusters3,4,and5display the usual [Mn6/oximate] structural motif consisting of two [Mn3O] subunits bridged by two Ooximateatoms from two R-sao2−ligands to form the hexanuclear complex in which the two triangular [Mn3] units are parallel to each other. On the contrary, clusters1and2display a highly distorted stacking arrangement of the two [Mn3] subunits resulting in two converging planes, forming a novel motif in the [Mn6] family. Investigation of the magnetic properties for all complexes reveal dominant antiferromagnetic interactions for1,2,and5, while3and4display dominant ferromagnetic interactions with a ground state ofS = 12 for both clusters. Finally,3and4display single-molecule magnet behavior withUeff = 63 and 36 K, respectively. [ABSTRACT FROM AUTHOR]

The crystal structure and magnetic properties of the compound Na5[Mn(l-tart)2]·12H2O (1, l-tart = l-tartrate) have been investigated over the pressure range 0.34–3.49 GPa. The bulk modulus of 1 has been determined as 23.9(6) GPa, with a compression of the coordination spheres around the Na+ ions observed. 1 is therefore relatively incompressible, helping it to retain its magnetic anisotropy under pressure. [ABSTRACT FROM AUTHOR]

The central MnII ions in a series of calix[4]arenestabilised butterflies can be sequentially replaced with LnIII ions, maintaining the structural integrity of the molecule but transforming its magnetic properties. The replacement of MnII for GdIII allows for the examination of the transferability of spin-Hamiltonian parameters within the family as well as permitting their reliable determination. The introduction of the 4f ions results in weaker intramolecular magnetic exchange, an increase in the number of low-lying excited states, and an increase in magnetisation relaxation, highlighting the importance of exchange over single-ion anisotropy for the observation of SMM behaviour in this family of complexes. The presence of the [TMII/III(TBC[4])(OH)(solvent)] metalloligand (TM=transition metal, TBC=p-tBu-calix[4]arene) suggests that magnetic calix[n]arene building blocks can be employed to encapsulate a range of different "guests" within structurally robust "hosts". [ABSTRACT FROM AUTHOR]

The reaction of the pro-ligand H4L, which combines the complementary phenolic oxime and diethanolamine moieties within the same organic framework, with Zn(NO3)2·6H2O and Ln(NO3)3·6H2O in a basic methanolic solution generates a family of isostructural heterometallic coordination compounds of general formula [Ln6Zn2(CO3)5(OH)(H2L)4(H3L)2(H4L)]NO3·xMeOH [Ln = Gd, x = 30 (1), Ln = Dy, x = 32 (2), Ln = Sm, x = 31 (3), Ln = Eu, x = 29 (4), Ln = Tb, x = 30 (5)]. The octametallic skeleton of the cage describes a heavily distorted [GdSTACKABOVEIII/ABOVEBELOW6/BELOW/STACK] octahedron capped on two faces by ZnII ions. The metal core is stabilised by a series of μ3- and μ4-CO32− ions, originating from the serendipitous fixation of atmospheric CO2. The magnetic properties of all family members were examined via SQUID magnetometry, with the χMT product and VTVB data of the Gd analogue (1) being independently fitted by numerical diagonalisation to afford the same best-fit parameter JGd–Gd = −0.004 cm−1. The MCE of complex 1 was elucidated from specific heat data, with the magnetic entropy change reaching a value of 22.6 J kg−1 K−1 at T = 1.7 K, close to the maximum entropy value per mole expected from six GdIII spins (SGd = 7/2), 23.7 J kg−1 K−1. [ABSTRACT FROM AUTHOR]

In an attempt to employ salicylic acid (HOsalH), 2,6-dihydroxy benzoic acid {(HO)2PhCO2H}, and naphthalene-1,8-dicarboxylic acid {1,8-naph(CO2H)2} in Mn(III) salicylaldoximate chemistry as a means to alter the structural identity of the hexanucluear clusters usually obtained from this reaction system, we have isolated a family of hexanuclear Mn(III) complexes based on salicyladloxime (saoH2) and 2-hydroxy-1-naphthaldehyde oxime (naphthsaoH2). Five hexanuclear clusters, [Mn6O2(sao)6(HOsal)2(EtOH)4]·EtOH (1·EtOH), [Mn6O2(sao)6{1,8-naph(CO2Me)(CO2)}2(MeOH)6]·3MeOH (2·3MeOH), [Mn6O2(naphthsao)6{1,8-naph(CO2Et)(CO2)}2(EtOH)6] (3·2MeOH), [Mn6O2(naphthsao)6(MeCO2)2(EtOH)4]·2H2O (4·2H2O), and [Mn6O2(naphthsao)6{(HO)2PhCO2}2(EtOH)4]·4EtOH (5·4EtOH), have been synthesized and characterized by single-crystal X-ray crystallography. The magnetic properties of3,4, and5are discussed. [ABSTRACT FROM PUBLISHER]

A new calix[4]arene-supported MnIIIMnII cluster, formed by the introduction of 3,5-dichlorobenzoate to a system known to afford Mn2IIIMn2II Single-Molecule Magnets (SMMs), assembles in a layered manner through halogen interactions; structural and magnetic properties of this new cluster are presented. [ABSTRACT FROM AUTHOR]

The first 3d-4fclusters built using derivatised salicylaldoximes (R-saoH2) describe unusual hexagonal prisms. Replacement of the paramagnetic Gd(iii) ions with diamagnetic Ln(iii) ions allows for a more thorough understanding of the magnetic properties, whilst replacement with Tb(iii) doubles Ueff. [ABSTRACT FROM AUTHOR]

Two novel Fe II –Re IV compounds of general formula [Fe II (DEA) 6 ][Re IV X 6 ] where DEA = diethylacetamide and X = Cl ( 1 ) and Br ( 2 ) have been prepared and magnetostructurally characterised. Complexes 1 and 2 are isomorphic ionic salts that crystallise in the trigonal crystal system with space group R (−3). The rhenium(IV) ion in 1 and 2 is six-coordinate with six chloro ( 1 ) or bromo ( 2 ) ligands building a regular octahedral chromophore. The Fe II ion is also six-coordinate, and bonded to six oxygen atoms from six DEA molecules. [Fe II (DEA) 6 ] 2+ cations and [Re IV X 6 ] 2− anions alternate in the crystal lattice of 1 and 2 generating supramolecular structures whose magnetic properties are dominated by the high anisotropy of the six-coordinate iron(II) and rhenium(IV) ions. Variable-temperature magnetic susceptibility data of 1 and 2 are well reproduced by a model of isolated S = 2 (Fe II ) and S = 3/2 (Re IV ) centres with high values of the local zero-field splitting. 1 and 2 are the first examples of hexahalorhenate(IV) salts incorporating Fe II complex cations to have been magnetostructurally investigated. [ABSTRACT FROM AUTHOR]

New double stranded metallacyclophanes Ln–M–M–Ln (Ln = GdIII, DyIII, YIII; M = NiII, CoII) with linear topology have been reported to exhibit weak ferromagnetic MII–LnIII and weak antiferromagnetic MII–MII couplings. Ni 2 Dy 2 counterparts show slow relaxation of the magnetization with U eff values that increase in the order of the NiDy magnetic coupling. The coordination-driven self-assembly of two polydentate linear Schiff base ligands (either N,N-bis(2-hydroxy-3-methoxy-benzyliden)-1,4-diaminobenzene, L2, or N,N-bis(2-hydroxy-3-methoxy-benzyliden)-1,5-diaminonaphthalene, L3) with two transition metal ions (MII = NiII or CoII) and two lanthanide ions (LnIII = GdIII or DyIII) afforded seven linear M 2 Ln 2 complexes of formula [Ni 2 Ln 2 (L2) 2 (CH 3 CN) 3 (H 2 O)(NO 3) 6 ](CH 3 CN) 2 (H 2 O) (LnIII = Gd 1 and Dy 2) and [M 2 Ln 2 (L3) 2 (CH 3 CN) 4 (NO 3) 6 ](CH 3 CN) x (M = NiII, CoII; Ln = DyIII, GdIII,YIII; x = 0–4) (3 – 7). Within the tetranuclear units of these complexes, two ligands coordinate through the N,O phenoxide donor sets to two M(II) ions, giving rise to M 2 metallacycles. In the case of complexes 1 – 2 , the Ni 2 -metallacycle contains 14-members, where the NiII ions are bridged by para-phenylenediimine groups. In complexes 3 – 7 , the M 2 -metallacycle consists of 18-members, where the transition metal ions are linked by naphthalenediimine bridging groups. At both sides of these metallacycles, the MII ions are connected to LnIII ions through phenoxido bridging groups. The analysis of the dc and ac magnetic properties of these complexes reveals that: (i) all the compounds exhibit weak ferromagnetic exchange interactions between the MII and LnIII ions through the bis(phenoxido) bridging groups and weak antiferromagnetic MII–MII interactions transmitted by the acenediimine bridging groups; (ii) DFT calculations not only support the nature and magnitude of the magnetic exchange interactions, but also the polarization mechanism for the MII–MII interactions through the acene bridging legends; (iii) the antiferromagnetic interaction for 1 is stronger than for 3 , which can be justified by the longer intermetallic Ni⋯Ni distance and α,α′-substitution for the latter; (iv) complexes 2 and 4 show slow relaxation of the magnetization below 5 K at zero static magnetic field with U eff / k B values of 19 K and 15.9 K respectively, the higher U eff / k B value corresponding to the stronger J DyGd coupling constant; (v) the change of −Δ S m for the M 2 Gd 2 complexes 1 , 3 and 6 has been analyzed by taking into account the values of their J and J 1 magnetic exchange interactions and single-ion anisotropies. [ABSTRACT FROM AUTHOR]

The use of methylene-bridged calix[4]arenes in 3d/4f chemistry produces a family of clusters of general formula [MnIII4LnIII4(OH)4(C4)4(NO3)2(DMF)6(H2O)6](OH)2 (where C4 = calix[4]arene; Ln = Gd (1), Tb (2), Dy (3)). The molecular structure describes a square of LnIII ions housed within a square of MnIII ions. Magnetic studies reveal that 1 has a large number of molecular spin states that are populated even at the lowest investigated temperatures, while the ferromagnetic limit S = 22 is being approached only at the highest applied fields. This, combined with the high magnetic isotropy, makes the complex an excellent magnetic refrigerant for low-temperature applications. Replacement of the isotropic GdIII ions with the anisotropic TbIII and DyIII ions "switches" the magnetic properties of the cluster so that 2 and 3 behave as low-temperature molecular magnets, displaying slow relaxation of the magnetization. [ABSTRACT FROM AUTHOR]

Magnetic properties of the family of Mn6 complexes with oximato bridging ligands, some of them showing the highest anisotropy energy barriers known to date, have been studied using theoretical methods based on density functional theory. The different magnetic behaviors, total spin values from 4 to 12, are well reproduced by the calculated exchange coupling constants. The analysis of the magnetostructural correlations indicates that the Mn — N — O — Mn torsion angels play a crucial role, with the out-of-plane shift of the central oxo bridging ligand involved to a lesser degree. The Mn — N — O — Mn torsion angles are mainly controlled by the existence of an intramolecular hydrogen bond between the NO group of the bridging ligand and the substituents of the equatorial oximato bridging ligand and the presence of bulky substituents in the axial carboxylato ligands. [ABSTRACT FROM AUTHOR]

Abstract: The use of di-2-pyridyl ketone, (py)2CO, in manganese(II) benzoate chemistry has yielded two linkage isomers containing the ketone form of the ligand and a neutral cubane cluster containing the gem-diolate(-1) form of the ligand. The 3:2 Mn(O2CPh)2 ·2H2O/(py)2CO reaction system in MeCN gives a mixture of the orange complex [Mn3(O2CPh)6{(py)2CO-κ2 N,N′}2] (1) and the yellow compound [Mn3(O2CPh)6{(py)2CO-κ2 N,O}2]·2MeCN (2 ·2MeCN). The known compound [Mn6O2(O2CPh)10(MeCN)4] (3) appears as a by-product when the initial reaction solution, that leads to 1 and 2 ·2MeCN, is allowed to slowly evaporate in the air. The trinuclear molecules adopt a linear structure in both complexes, with one monoatomically bridging η1:η1:μ2 and two syn,syn-η1:η1:μ2 carboxylate groups spanning each pair of MnII ions. The terminal MnII ions are each capped by one chelating-N,N′ (py)2CO ligand in 1 and by one chelating-N,O (py)2CO molecule in 2. The 1:1 reaction of Mn(O2CPh)2 ·2H2O and (py)2CO in CH2Cl2 results in the isolation of[Mn4(O2CPh)4{(py)2C(OH)O}4] (4). The tetranuclear molecule has a cubane topology with the MnII ions and the deprotonated oxygen atoms from the (py)2C(OH)O− ligands occupying alternate vertices. The IR data are discussed in terms of the nature of the bonding. The magnetic properties of 4 in the 300–5K range have been modeled with two J values and reveal weak intramolecular antiferromagnetic interactions. The low temperature X-band EPR spectra of 1, 2 and 4 are also discussed. [Copyright &y& Elsevier]

The deliberate ‘stepwise’ structural distortion of the [MnIII6O2(sao)6(O2CR)2L4] (S = 4, Ueff = 28 K) family of SMMs (where sao2- is the dianion of salicylaldoxime or 2-hydroxybenzaldeyhyde oxime and L = MeOH, EtOH) via the use of derivatized oxime ligands and bulky carboxylates leads to a family of single-molecule magnets with larger spin ground states and enhanced blocking temperatures. Replacing sao2- and HCO2- in the molecule [MnIII6O2(sao)6(O2CH)2(MeOH)4] (1), with Et-sao2- (Et-saoH2 = 2-hydroxypropiophenone oxime) and Me3CCO2- (pivalate), produces the complex [MnIII6O2(Et-sao)6(O2-CCMe3)2(EtOH)5] (2) that displays an S = 7 ground state with Ueff = 30 K. Replacing Me3CCO2- with PhCO2- produces the complex [MnIII6O2(Et-sao)6(O2CPh)2(EtOH)4(H2O)2] (3) that displays an S = 12 ground state with Ueff = 53 K. The ligand substitution invokes a subtle structural distortion to the core of the molecule evidenced by an increased ‘twisting’ of the oxime moiety (Mn-N-O-Mn) and a change in carboxylate ligation, which, in turn, invokes a dramatic change in the observed magnetic properties by switching weak antiferromagnetic exchange to weak ferromagnetic exchange. [ABSTRACT FROM AUTHOR]

The synthesis and magnetic properties of four new Mn complexes containing tripodal alcohol ligands are reported: [Mn6(OAc)6(H2tea)2(tmp)2]·2MeCN (1·2MeCN), [Mn6(acac)4(OAc)2(Htmp)2(H2N-ep)2] (2), [Mn6(OAc)8(tmp)2(py)4]·2py (3·2py), and [Mn6(OAc)8(thme)2(py)4]·2py (4·2py) [H3tea, triethanolamine; H3tmp, 1,1,1-tris(hydroxymethyl)propane; H2N-H2ep, 2-amino-2-ethyl-1,3-propanediol; H3thme, 1,1,1-tris(hydroxymethyl)ethane]. All complexes are mixed-valent with a [MnIII2MnII4] oxidation assignment and are constructed from four edge-sharing triangles but differ slightly in that complexes 1 and 2 display a [MnIII2MnII4(μ2-OR)6(μ3-OR)4]4+ core, while complexes 3 and 4 feature [MnIII2MnII4(μ2-OR)2(μ3-OR)4]8+ and [MnIII2MnII4(μ2-OR)4(μ3-OR)4]4+ cores, respectively. dc and ac magnetic susceptibility studies in the 2-300 K range for complexes 1-4 reveal the presence of dominant antiferromagnetic exchange interactions, leading to ground states of S = 0 for 1 and 2, while complexes 3 and 4 display S = 4 ground states with D = -0.44 and -0.58 cm-1, respectively. Single-molecule magnetism behavior was confirmed for 3 and 4 by the presence of sweep-rate and temperature-dependent hysteresis loops in single-crystal M vs H studies at temperatures down to 40 mK. Theoretical density functional calculations were used to evaluate the individual pairwise exchange interactions present, confirming the diamagnetic ground states for 1 and 2 and the S = 4 ground states for 3 and 4. [ABSTRACT FROM AUTHOR]

Abstract: We report on the magnetic properties of the enneanuclear mixed-valent single-molecule magnet [Mn9O7(OAc)11(thme)(py)3(H2O)2] (1). Using inelastic neutron scattering (INS) spectroscopy, we have confirmed the S =17/2 cluster ground state of 1. Furthermore, we have determined accurately the anisotropy parameters of the zero field split ground state. The cluster 1 exhibits a strong negative axial anisotropy where D =−0.249(5)cm−1. It is necessary to include an axial higher order term in the effective spin Hamiltonian to account for the experimental data. [Copyright &y& Elsevier]