A heterometal single-molecule magnet of [MnIII2NiII2Cl2(salpa)2

The tetranuclear complex [MnIII2NiII2Cl2(salpa)2] (salpa = N-(2-hydroxybenzyl)-3-amino-1-propanol) has a spin ground state of S = 6 and was confirmed to be an SMM based on a steplike feature of the magnetization hysteresis loop at 0.55 K.     

MnIII2 (5-Rsaltmen)2NiII(pao)2(L)]2+: an S(T)=3 building block for a single-chain magnet that behaves as a single-molecule magnet

Mn(III)-Ni(II)-Mn(III) linear-type trinuclear complexes bridged by oximate groups were selectively synthesized by the assembly reaction of [Mn2(5-Rsaltmen)2(H2O)2](ClO4)2 (5-Rsaltmen2-=N,N'-(1,1,2,2-tetramethylethylene) bis(5-R-salicylideneiminate); R=Cl, Br) with [Ni(pao)2(phen)] (pao-=pyridine-2-aldoximate; phen=1,10-phenanthroline) in methanol/water: [Mn2(5-Rsaltmen)2Ni(pao)2(phen)](ClO4)2 (R=Cl, 1; R=Br, 2). Structural analysis revealed that the [Mn(III)-ON-Ni(II)-NO-Mn(III)] skeleton of these trimers is in every respect similar to the repeating unit found in the previously reported series of 1D materials [Mn2(saltmen)2Ni(pao)2(L1)2](A)(2) (L(1)=pyridine, 4-picoline, 4-tert-butylpyridine, N-methylimidazole; A=ClO4-, BF4-, PF6-, ReO4-). Recently, these 1D compounds have attracted a great deal of attention for their magnetic properties, since they exhibit slow relaxation of the magnetization (also called single-chain magnet (SCM) behavior). This unique magnetic behavior was explained in the framework of Glauber's theory, generalized for chains of ferromagnetically coupled anisotropic spins. Thus, in these 1D compounds, the [Mn(III)-ON-Ni(II)-NO-Mn(III)] unit was considered as an S(T)=3 anisotropic spin. Direct-current magnetic measurements on 1 and 2 confirm their S(T)=3 ground state and strong uniaxial anisotropy (D/k(B) approximately -2.4 K), in excellent agreement with the magnetic characteristic deduced in the study on the SCM series. The ac magnetic susceptibility of these trimers is strongly frequency-dependent and characteristic of single-molecule magnet (SMM) behavior. The relaxation time tau shows a thermally activated (Arrhenius) behavior with tau0 approximately 1x10(-7) s and Delta(eff)/k(B) approximately 18 K. The effective energy barrier for reversal of the magnetization Delta(eff) is consistent with the theoretical value (21 K) estimated from |D| S2T. The present results reinforce consistently the interpretation of the SCM behavior observed in the [Mn2(saltmen)2Ni(pao)2(L1)2](A)2 series and opens new perspectives to design single-chain magnets.     

A magnetostructural study of linear NiII MnIII NiII, NiII CrIII NiII and triangular Ni(II)3 species containing (pyridine-2-aldoximato)nickel(II) unit as a building block

Three trinuclear complexes, NiII MnIII NiII, NiII CrIII NiII and Ni(II)3 based on (pyridine-2-aldoximato)nickel(II) units are described. Two of them, and , contain metal-centers in linear arrangement, as is revealed by X-ray diffraction. Complex is a homonuclear complex in which the three nickel(II) centers are disposed in a triangular fashion. The compounds were characterized by various physical methods including cyclic voltammetric and variable-temperature (2-290 K) susceptibility measurements. Complexes and display antiferromagnetic exchange coupling of the neighbouring metal centers, while weak ferromagnetic spin exchange between the adjacent Ni II and Cr III ions in is observed. The experimental magnetic data were simulated by using appropriate models.     

In search for mixed transition metal/lanthanide single-molecule magnets: Synthetic routes to NiII/TbIII and NiII/DyIII clusters featuring a 2-pyridyl oximate ligand

Employing the mononuclear complex [Ni{(py)C(Me)NO}₂{(py)C(Me)NOH}] (1) as ‘ligand’ [(py)C(Me)NOH = methyl 2-pyridyl ketone oxime], the use of the ‘metal complexes as ligands’ approach has led to the synthesis of the mixed Ni^II/Ln^III complexes [NiTb{(py)C(Me)NO}₂(NO₃)₃{(py)C(Me)NOH}] (2), [Ni₂Ln₂{(py)C(Me)NO}₆(NO₃)₄] (Ln = Dy, 3; Ln = Tb, 4) and [Ni₂Tb{(py)C(Me)NO}₆](NO₃) (5). The structures of 2, 3, and 5, and the magnetic properties of 2 and 5 are briefly discussed.     

New approach for designing single-chain magnets: organization of chains via hydrogen bonding between nucleobases

Two one-dimensional (1D) manganese complexes, [Mn(2)(naphtmen)(2)(L)](ClO(4))·2Et(2)O·2MeOH·H(2)O (1) and [Mn(2)(naphtmen)(2)(HL)](ClO(4))(2)·MeOH (2), were synthesized by using a bridging ligand with a nucleobase moiety, 6-amino-9-β-carboxyethylpurine, and a salen-type manganese(III) dinuclear complex, [Mn(2)(naphtmen)(2)(H(2)O)(2)](ClO(4))(2) (naphtmen(2-) = N,N'-(1,1,2,2-tetramethylethylene)bis(naphthylideneiminato) dianion). In 1 and 2, the carboxylate-bridged Mn(III) dinuclear units are alternately linked by two kinds of weak Mn···O interactions into 1D chains. As a result, canted antiferromagnetic and ferromagnetic interactions are alternately present along the chains, leading to a 1D chain with non-cancellation of anisotropic spins. Since the chains connected via H-bonds between nucleobase moieties are magnetically isolated, both 1 and 2 act as single-chain magnets (SCMs). More importantly, this result shows the smaller canting angles hinder long-range ordering in favor of SCM dynamics.     

Synthesis, structure and magnetism of new single molecule magnets composed of MnII2MnIII2 alkoxo-carboxylate bridged clusters capped by triethanolamine ligands

A family of tetranuclear mixed-valent Mn(II)(2)/Mn(III)(2) complexes of type [Mn(4)(LH(2))(2)(LH)(2)(H(2)O)(x)(RCO(2))(2)](Y)2.nS has been synthesised and structurally characterised, where LH(3) = triethanolamine (N(CH(2)CH(2)OH)(3)), (R=CH(3), x=2, Y = CH(3)CO(2)-, n=2, S = H(2)O; 1), (R=C(6)H(5), x=0, Y=C(6)H(5)CO(2)-, n=1, S = CH(3)CN; 2), (R=C(2)H(5), x=0, Y=ClO(4)(-), n=0; 3). A common structural core was deduced from X-ray crystallography and consists of a rhomboidal (planar-diamond) array with two 7-coordinate Mn(II) "wingtip (w)" centres and two 6-coordinate Mn(III) "body (b)" centres. The Mn(III) ions are bridged to the Mn(II) ions by mu3-oxygen atoms from a deprotonated alcohol "arm" of each tridentate LH(2-) ligand and by mu2-oxygen atoms from each tetradentate LH(2)(-) ligand. The four nitrogen atoms from LH(2-) and LH(2)(-) groups, together with bridging and terminal carboxylates oxygens complete the outer coordination sites around the Mn atoms. A feature of these clusters is that they are linked together in the crystal lattice by hydrogen-bonding interactions involving a non-coordinated hydroxyl arm on each LH(2-) group. Detailed DC and AC magnetic susceptibility measurements and magnetisation isotherms have been made on the three complexes and show that intra-cluster ferromagnetic coupling is occurring between the S = 2 Mn(III) and S = 5/2 Mn(II) ions to yield S = 9 ground states. The g, J(bb) and J(wb) parameters have been deduced. Inter-cluster antiferromagnetic coupling was noted in and this influences the magnetisation versus field behaviour and the temperature and magnitude of the out-of-phase AC chi"M maxima in comparison to those observed for and. An Arrhenius plot of the reciprocal temperature of the maxima in chi"M obtained at different frequencies (10 to 1500 Hz), in the range 1.75 K to 4 K, against the natural logarithm of the magnetization relaxation rate (1/tau) yielded values of the activation energies and pre-exponential factors for two of these new tetranuclear single-molecule magnets (SMMs), and. The activation energies were compared with the potential energy barrier height, U, for magnetisation direction reversal (U = DS(2)) using the axial zero-field splitting parameter, D, deduced from the DC M/H isotherm analysis for these S = 9 species. The very small separation of S = 9 and 8 levels for these clusters highlights the limitations in the determination of D values from M/H data at low temperatures.     

Single-molecule magnets: a family of MnIII/CeIV complexes with a [Mn8CeO8]12+ core

Four heterometallic, enneanuclear Mn8Ce clusters [Mn8CeO8(O2CMe)12(H2O)4] (4), [Mn8CeO8(O2CMe)12(py)4] (5), [Mn8CeO8(O2CPh)12(MeCN)4] [Mn8CeO8(O2CPh)12(dioxane)4] (6), and [Mn8CeO8(O2CCHPh2)12(H2O)4] (7) have been prepared by various methods. Their cores are essentially isostructural and comprise a nonplanar, saddlelike [MnIII8O8]8+ loop containing a central CeIV ion attached to the eight micro3-O2- ions. Peripheral ligation around the [Mn8CeO8]12+ core is provided by eight micro- and four micro3-O2CR- groups. Terminal ligation on four MnIII atoms is provided by H2O in 4 and 7, pyridine in 5, and MeCN/dioxane in 6. Solid-state magnetic susceptibility studies, fits of dc magnetization vs field and temperature data, and in-phase ac susceptibility studies in a zero dc field have established that complexes 4, 5, and 7 possess S=16, S=4 or 5, and S=6+/-1 spin ground states, respectively, but in all cases there are very low-lying excited states. The large variation in the ground-state spins for this isostructural family is rationalized as due to a combination of weak exchange interactions between the constituent MnIII atoms, and the presence of both nearest-neighbor and next-nearest-interactions of comparable magnitudes. Magnetization vs applied dc field sweeps on single crystals of 4.4H2O and 7.4H2O.3MeCN.2CH2Cl2 down to 0.04 K have established that these two complexes are new single-molecule magnets (SMMs). The former also shows an exchange-bias, a perturbation of its single-molecule properties from very weak intermolecular interactions mediated by hydrogen-bonding interactions with lattice-water molecules of crystallization.     

A canted antiferromagnetic ordered phase of cyanido-bridged Mn(III)(2)Re(IV) single-chain magnets

A new cyanido-bridged Re(IV)-Mn(III) heterometallic 1D system, [Mn(III)(5-Me-saltmen)](2)[Re(IV)Cl(4)(CN)(2)]·3CH(3)CN (), was designed and structurally characterized. Interchain interactions stabilize a canted antiferromagnetic ordered state below 6.2 K that does not prevent slow relaxation of the magnetization reminiscent of the single-chain magnet properties of the individual chains.     

The DFT rationalization of exchange and anisotropy in one-dimensional d-p magnets: The [MnIII(porphyrin)][TCNE] case study

We report here numerical experiments, modeling and interpretations dealing with the magnetic interactions necessary for building nano-scale magnets in quasi-one-dimensional systems based on the assembling of [Mn(porphyrin)]⁺ magnetically anisotropic d units and TCNE-p-type spin carriers. The magnetic ordering and its coupling parameter are studied by Broken Symmetry DFT calculations for various model structures, allowing for the rationalization of geometry dependence of the effective exchange. The roles of the phenyl substituent, as well as of the basis set and the DFT functional used in the computation are discussed. The intrinsic anisotropy of these systems is studied in an original manner, extracting Ligand Field and Spin Orbit parameters by combined fits to non-relativistic and relativistic DFT calculations, allowing the explicit estimation of the Zero Field Splitting parameters.     

Linear ion trap with added octopole field component: the property and method

It is well known that superimposition of some positive octopole field will benefit the performance of ion trap mass analyzer. In the radial‐ejection linear ion trap (LIT), adding some octopole field component to the main quadrupole field is usually accomplished by stretching the ejection rod pair. In this study, the effect of octopole potential and some other higher order potential on the performance of LIT mass analyzer is investigated. A simple and effective method, which is to add some octopole component by building a LIT with a pair of rectangular electrodes and a pair of semi‐circular electrodes, is reported. Its properties were studied by numerical simulations and experiments. The results showed that a certain amount of positive octopole component could be produced by simply adjusting the position and width of the rectangular electrodes. A resolution of over 1200 at m/z 609 (~1600 Da/s) was observed in this type of LIT. They also performed tandem mass spectrometry well. The device with optimum geometry for ion ejection from rectangular electrodes provided comparable performance to that for ion ejection from semi‐circular electrodes. This type of LIT design is easy for fabrication and assembly. Copyright © 2015 John Wiley & Sons, Ltd.     

Magnetic Properties of Mixed Ligand NiII2 and NiII4 Complexes Composed of Macrocyclic Hexaamine‐Dithiophenolato and Bridging Tetrazolato Ligands

The magnetic properties of the dinuclear and tetranuclear nickel(II) tetrazolato complexes [Ni₂L(RCN₄)][BPh₄] (R = H ( 4 ), Me ( 5 ), Ph ( 6 )) and [(Ni₂L)₂(1,4‐(CN₄)₂‐C₆H₄)][BPh₄]₂ ( 7 ), where (L)^2– represents a 24‐membered macrocyclic N₆S₂ supporting ligand, are reported. Analysis of temperature‐dependent magnetic susceptibility measurements over the temperature range from 2 to 300 K revealed the presence of weak ferromagnetic exchange interactions between the Ni^II ions in the binuclear [Ni₂L(μ‐L′)]⁺ subunits with magnetic exchange coupling constant values of J₁ = 13.5 cm^–1 for 4 , J₁ = 20.0 cm^–1 for 5 , J₁ = 19.2 cm^–1 for 6 , and J₁ = 15.2 cm^–1 for 7 ( H = –2JS₁S₂). The exchange coupling J₂ across the bistetrazolato bridge in 7 is less than 0.1 cm^–1, which suggests that no significant interdimer coupling occurs in this compound. The synthesis and crystal structure of the new complex 7 ·2MeCN is also reported.     

New mixed-valence MnII2MnIII2 clusters exhibiting an unprecedented MnII/III oxidation state distribution in their magnetically coupled cores

The synthesis and magnetic properties of the high-spin tetranuclear cluster [Mn(III)(2)Mn(II)(2)(O(2)CC(CH(3))(3))(2)(teaH(2))(2)(teaH)(2)](O(2)CC(CH(3))(3))(2) (1) (where teaH(3) = triethanolamine) is described. Complex 1 is the pivalate analogue of our previously reported family of tetranuclear mixed-valence carboxylate clusters. The teaH(2)(-) and teaH(2-) anions in complex 1 act as oxygen donors in the {Mn(III)(2)Mn(II)(2)O(2)} "butterfly" core. Detailed dc and ac magnetic susceptibility measurements and magnetisation isotherms have been made and show that intra-cluster ferromagnetic coupling is occurring between the S = 2 Mn(III) and S = 5/2 Mn(II) ions to yield a S = 9 ground state and the g, J(bb) and J(wb) parameters have been deduced (b = body, w = wingtip). Incorporation of the acetylacetonate (acac(-)) ligand has led to three new clusters: [Mn(III)(2)Mn(II)(2)(O(2)CPh)(4)(teaH)(2)(acac)(2)].MeCN (2), [Mn(III)(2)Mn(II)(2)(teaH)(2)(acac)(4)(MeOH)(2)](ClO(4))(2) (3) and [Mn(III)(2)Mn(II)(2)(bheapH)(2)(acac)(4)(MeOH)(2)](ClO(4))(2) (4) (where bheapH(3) = 1-[N,N-bis(2-hydroxyethyl)amino]-2-propanol). Unlike any previously reported tetranuclear clusters containing the Mn(II)(2)Mn(III)(2) core, 2, 3, and 4 exhibit a reversal in their Mn(II)(2)Mn(III)(2) oxidation state distribution. In these clusters, the "wing-tip" Mn atoms exhibit Mn(III) (S = 2) oxidation states while the Mn(II) ions occupy the central "body" positions. Furthermore, the cores in 2, 3, and 4 contain at least one mu(2)-oxygen based bridging ion as opposed to the standard two mu(3)-oxygen bridges previously reported. More precisely, cluster 2 exhibits one mu(3)-O bridge and two mu(2)-bridges in a {Mn(II)(2)Mn(III)(2)O(3)} core while clusters 3 and 4 exhibit two mu(2)-O linkers within the {Mn(II)(2)Mn(III)(2)O(2)} core. All display trigonal prismatic coordination around the Mn(II) centres. These structural and oxidation state differences lead to very different magnetic coupling interactions between the four Mn(II/III) centres compared to 1. Direct current magnetic susceptibility measurements and magnetisation isotherms show that clusters 3 and 4 have ground states of S = 1. The g, J(bb) and J(wb) parameters have been deduced.     

Three-coordinate NiII: tracing the origin of an unusual, facile Si-C(sp3) bond cleavage in [(tBu2PCH2SiMe2)2N]Ni+

All attempts to synthesize (PNP)Ni(OTf) form instead ((t)Bu(2)PCH(2)SiMe(2)NSiMe(2)OTf)Ni(CH(2)P(t)Bu(2)). Abstraction of F(-) from (PNP)NiF by even a catalytic amount of BF(3) causes rearrangement of the (transient) (PNP)Ni(+) to analogous ring-opened [((t)Bu(2)PCH(2)SiMe(2)NSiMe(2)F)]Ni(CH(2)P(t)Bu(2)). Abstraction of Cl(-) from (PNP)NiCl with NaB(C(6)H(3)(CF(3))(2))(4) in CH(2)Cl(2) or C(6)H(5)F gives (PNP)NiB(C(6)H(3)(CF(3))(2))(4), the key intermediate in these reactions is (PNP)Ni(+), [(PNP)Ni](+), in which one Si-C bond (together with N and two P) donates to Ni. This makes this Si-C bond subject to nucleophilic attack by F(-), triflate, and alkoxide/ether (from THF). This σ(Si-C) complex binds CO in the time of mixing and also binds chloride, both at nickel. Evidence is offered of a "self-healing" process, where the broken Si-C bond can be reformed in an equilibrium process. (PNP)Ni(+) reacts rapidly with H(2) to give (PN(H)P)NiH(+), which can be deprotonated to form (PNP)NiH. A variety of nucleophilic attacks (and THF polymerization) on the coordinated Si-C bond are envisioned to occur perpendicular to the Si-C bond, based on the character of the LUMO of (PNP)Ni(+).     

Synthesis of oligomeric chlorophosphazenes in the presence of ZnCl2

With the use of ³¹P NMR spectroscopy and gas chromatography-mass spectrometry, the partial ammonolysis of PCl₅ by ammonium chloride in chlorobenzene in the presence of zinc chloride is investigated. The use of zinc chloride reduces the reaction time to 1.5 h and increases the yield of oligomeric chlorophosphazenes up to 95%. Some assumptions are made about the role of ZnCl₂ in the process and about the feasibility of the mechanism of formation of higher cyclic chlorophosphazenes, the hexamer and the octamer.     

Probing single-chain magnets in a family of linear chain compounds constructed by magnetically anisotropic metal-ions and cyclohexane-1,2-dicarboxylate analogues

Five new metal-carboxylate chain-based laminated compounds, namely, infinity2[FeII(e,e-trans-1,2-chdc)] (3) (1,2-chdc = cyclohexane-1,2-dicarboxylate), infinity2[NiII(mu-OH2)(e,a-cis-1,2-chdc)] (4), infinity2[CoII(mu-OH2)(1,2-chedc)] (5) (1,2-chedc = cyclohex-1-ene-1,2-dicarboxylate), infinity2[Co5II(mu3-OH)2(OH2)2(1,2-chedc)4] (6), and infinity2[CoII(4-Me-1,2-chdc)] (7) (4-Me-1,2-chdc = trans-4-methylcyclohexane-1,2-dicarboxylate) have been hydrothermally synthesized. In these series of magnetic chain-based compounds, 3 and 7 have the same dimeric paddle-wheel M(II)-carboxylate chain as the previously reported compound, infinity2[CoII(trans-1,2-chdc)] (2). However, compound 3 does not behave as a single-chain magnet (SCM) but simply an alternating ferro-antiferro magnetic chain. Compound 4 has the cis conformation of 1,2-chdc ligand, which leads to a uniform aqua-carboxylate-bridged Ni(II) chain. Such a Ni-O chain exhibits strong antiferromagnetic interactions, leading to a diamagnetic ground state. Compound 5 features a corner-sharing triangular chain, or delta-chain, which is part of a Kagom lattice. However, 5 does not exhibit a spin-frustrated effect but simply spin competition. Compound 6 has a unique pentanuclear CoII cluster, which is further connected by the syn-anti carboxylate into a chain structure. Compound 6 exhibits antiferromagnetic interactions among the Co(II) ions, and no SCM behavior is observed. These results might indicate that the dimeric paddle-wheel Co(II)-carboxylate chain is essential in obtaining SCM behavior in this family of compounds. Although 2 and 7 have very similar SCM behavior, alternating current magnetic studies show that 7 has a higher energy barrier than that of 2. Such behavior is probably caused by the larger anisotropic energy barrier in 7.     

Spectroscopic properties of gallium arsenide tetramers: Ga2As2, Ga2As2+ and Ga2As2-

Spectroscopic properties of the low-lying electronic states of Ga2As2 and its ions are studied using the complete active-space self-consistent field (CASSCF) and density function theory (DFT) followed by the coupled-cluster single and double substitutions (including triple excitations) (CCSD(T)) calculations. The stability of low-lying electronic states is examined by computing vibrational frequency. The energies of the ground states and a number of excited electronic states have been computed to predict the spectra of Ga2As2 and its ions. The ionization energy, electronic affinity, and atomization energy are estimated at the CCSD(T)/6-311+G(d) level and compared with the available experimental results.     

Self-assembly of ordered water tetramers in an encapsulated [Br(H2O)12]- complex

An unanticipated anion-water cluster is assembled by one bromide and three highly-ordered "water tetramers" within the cavity of a receptor, providing a perfect C(3) symmetric propeller-shaped bromide-water cluster of [Br(H(2)O)(12)](-).