A New Mixed‐Valence Tetranuclear Manganese [MnII2MnIII2] Cluster

A new tetranuclear manganese complex [Mn₂^IIMn₂^III(bhmcpH)₂(hmp)₄Cl₂(MeOH)₂] ( 1 ) [bhmcpH₃ = 2, 6‐bis(hydroxymethyl)‐4‐chlorophenol, hmpH = 2‐(hydroxymethyl)pyridine] was synthesized and characterized. X‐ray diffraction analyses reveal that complex 1 crystallizes in the monoclinic space group P2₁/c. It has a mixed‐valence tetranuclear dicubane unit, which comprises two Mn^II and two Mn^III ions. The temperature dependence of the magnetic susceptibilities of 1 indicates ferromagnetic interactions between the manganese ions.     

Mn4 single-molecule magnets with a planar diamond core and S=9

The syntheses and magnetic properties are reported for three Mn₄ single-molecule magnets (SMMs): [Mn₄(hmp)₆(NO₃)₂(MeCN)₂](ClO₄)₂·2MeCN (3), [Mn₄(hmp)₆(NO₃)₄]·(MeCN) (4), and [Mn₄(hmp)₄(acac)₂(MeO)₂](ClO₄)₂·2MeOH (5). In each complex there is a planar diamond core of Mn^III ₂Mn^II ₂ ions. An analysis of the variable-temperature and variable-field magnetization data indicate that all three molecules have intramolecular ferromagnetic coupling and a S=9 ground state. The presence of a frequency-dependent alternating current susceptibility signal indicates a significant energy barrier between the spin-up and spin-down states for each of these three Mn^III ₂Mn^II ₂ complexes. The fact that these complexes are SMMs has been confirmed by the observation of hysteresis in the plot of magnetization versus magnetic field measured for single crystals of complexes 3 and 4. The hysteresis loops for both of these complexes exhibit steps characteristic of quantum tunneling of magnetization. Complex 4 shows its first step at zero field, whereas the first step for complex 3 is shifted to −0.10 T. This shift is attributable to weak intermolecular antiferromagnetic exchange interactions present for complex 3.     

On the validity of the giant spin approximation and its application to single-molecule magnets

A giant spin Hamiltonian is often used to describe the low temperature magnetic behavior in single-molecule magnets (SMMs). By addressing only the ground state multiplet, the Hilbert space is reduced significantly allowing for numerical simulation of a wide body of experimental data. Analysis of the [Ni(hmp)(dmb)Cl]₄ SMM using the giant spin model is compared to a four-ion model which addresses the local anisotropy associated with each of the magnetic Ni²⁺ ions, as well as the isotropic Heisenberg coupling between these ions. Higher-order giant spin Hamiltonian parameters that are absent in the individual ion parameterization appear when exchange coupling between the Ni²⁺ ions is introduced. Thus, a parameterization under the giant spin approximation is not purely a measure of anisotropic spin–orbit coupling, but instead a combination of interactions. Furthermore, the obtained parameters do not provide adequate insights into the physical processes within a SMM.     

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^III₆Mn^II₄(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.     

Large Hexadecametallic {MnIII–LnIII} Wheels: Synthesis,Structural, Magnetic,and Theoretical Characterization

The synthesis, gas sorption studies, magnetic properties, and theoretical studies of new molecular wheels of core type {Mn^III₈Ln^III₈} (Ln=Dy, Ho, Er, Y and Yb), using the ligand mdeaH₂, in the presence of ortho‐toluic or benzoic acid are reported. From the seven wheels studied the {Mn₈Dy₈} and {Mn₈Y₈} analogues exhibit SMM behavior as determined from ac susceptibility experiments in a zero static magnetic field. From DFT calculations a S=16 ground state was determined for the {Mn₈Y₈} complex due to weak ferromagnetic Mn^III–Mn^III interactions. Ab initio CASSCF+RASSI‐SO calculations on the {Mn₈Dy₈} wheel estimated the Mn^III–Dy^III exchange interaction as ?0.1 cm^?1. This weak exchange along with unfavorable single‐ion anisotropy of Dy^III/Mn^III ions, however, led to the observation of SMM behavior with fast magnetic relaxation. The orientation of the g‐anisotropy of the Dy^III ions is found to be perpendicular to the plane of the wheel and this suggests the possibility of toroidal magnetic moments in the cluster. The {Mn₈Ln₈} clusters reported here are the largest heterometallic Mn^IIILn^III wheels and the largest {3d–4f} wheels to exhibit SMM behavior reported to date.     

Modulating Magnetic and Photoluminescence Properties in 2-Aminonicotinate-Based Bifunctional Coordination Polymers by Merging 3d Metal Ions

Herein, the synthesis and study of bifunctional coordination polymers (CPs) with both magnetic and photoluminescence properties, derived from a heterometallic environment, are reported. As a starting point, three isostructural monometallic CPs with the formula [M(μ-2ani)₂]_n (M^II=Mn ( 1_Mn ), Co ( 3_Co ) and Ni ( 4_Ni ); 2ani=2-aminonicotinate), crystallise as chiral 2D-layered structures stacked by means of supramolecular interactions. These compounds show high thermal stability in the solid state (above 350 °C), despite which, in aqueous solution, compound 1_Mn is shown to partially transform into a novel 1D chain CP with the formula [Mn(2ani)₂(μ-H₂O)₂]_n ( 2_Mn ). A study of the direct current (dc) magnetic properties of 1_Mn , 3_Co and 4_Ni reveals a spin-canted structure derived from antisymmetric antiferromagnetic weak exchanges along the chiral network (as confirmed by DFT calculations) and magnetic anisotropy of the ions, in such a way that long-range ordering is observed with variable magnitude for the spin carriers. Moreover, compounds 3_Co and 4_Ni show no frequency-dependent alternating current (ac) susceptibility curves under zero dc field; this is characteristic behaviour of a glassy state that may be partially supressed for 3_Co by applying an external dc field. To overcome long-range magnetic ordering, Co^II ions are diluted in a diamagnetic Zn^II-based matrix, which enables single-molecule magnet behaviour. Interestingly, this strategy allows a bifunctional Co_xZn_1−x2ani material, which is imbued with a strong photoluminescent emitting capacity, as characterised by an intense blue light followed by a green afterglow, to be obtained.     

A unique 2-D hollow sheet structure and magnetic behavior of a cyanide- and triamine-bridged MnIICrIII ferrimagnet

A 2-D cyanide- and triamine-bridged Mn^IICr^III ferrimagnet, [Mn₃(dien)₂(H₂O)₂][Cr(CN)₆]₂ · 4H₂O (1), has been prepared by the combination of Mn²⁺, diethylenetriamine (dien) co-ligand and [Cr(CN)₆]³⁻. This compound forms a unique 2-D hollow sheet structure constructed by 1-D ribbon networks on the basis of triamine (dien)-bridged trinuclear Mn^II units. Compound 1 readily looses all lattice water molecules and irreversibly changes to a dehydrated form, [Mn₃(dien)₂(H₂O)₂][Cr(CN)₆]₂ (1a), in the air. Cryomagnetic studies of 1 and 1a reveal an antiferromagnetic interaction between Cr^III and Mn^II ions, and an unusual long-range ferrimagnetic ordering below 30 K (1) and 40 K (1a) with multiple magnetic phase changes below T_C. MCD spectra of 1a show a strong Faraday ellipticity associated with the LMCT band of the Cr–CN below 300 nm. Faraday ellipticity is remarkably enhanced below T_C in line with the characteristics long-range ferrimagnetic ordering.     

Magnetic properties of two double‐layer structures built from hydroxy­naphthoic acids and manganese

Double‐layer structures consisting of alternating polar and non‐polar layers have been prepared using Mn²⁺ ions and o‐hydroxy­naphthoic acids. The polar layers contain the Mn²⁺ ions, carboxylate groups, hydr­oxy groups and water mol­ecules. The non‐polar layers are built up from the naphthalene moieties. In catena‐poly[[diaqua­manganese(II)]bis­(μ‐3‐hy­droxy‐2‐naphthoato‐κ²O:O′)] (also called manganese 3‐hy­droxy‐2‐naphthoate dihydrate), [Mn(C₁₁H₇O₃)₂(H₂O)₂]_n, (I), the Mn²⁺ ions are connected by carboxylate groups to form two‐dimensional networks. This compound shows distinct antiferromagnetic inter­actions and long‐range ordering at low temperature. In contrast, tetra­aqua­bis(1‐hydr­oxy‐2‐naph­thoato‐κO)manganese(II), [Mn(C₁₁H₇O₃)₂(H₂O)₄], (II), which lacks a close linkage between the Mn²⁺ ions, reveals purely paramagnetic behaviour. In (II), the Mn²⁺ ion lies on an inversion centre.     

A Single‐Chain Magnet Tape Based on Hexacyanomanganate(III)

The tape‐like chain {[(tptz)Mn^II(H₂O)Mn^III(CN)₆]₂Mn^II(H₂O)₂}_n?4n MeOH?2n H₂O based on the anisotropic building block hexacyanomanganate(III) exhibits long‐range magnetic ordering below 5.1 K as well as single‐chain magnetic behavior at lower temperatures with an effective energy barrier of 40.5(7) K.     

Anomalous Stoichiometry and Antiferromagnetic Ordering for the Extended Hydroxymanganese(II) Cubes/Hexacyanometalate-Based 3D-Structured [MnII4(OH)4][MnII(CN)6](OH2)6⋅H2O

The reaction of Mn^II(O₂CMe)₂ and NaCN or LiCN in water forms a light green insoluble material. Structural solution and Rietveld refinement of high-resolution synchrotron powder diffraction data for this unprecedented, complicated compound of previously unknown composition revealed a new alkali-free ordered structural motif with [Mn^II₄(μ₃-OH)₄]⁴⁺ cubes and octahedral [Mn^II(CN)₆]⁴⁻ ions interconnected in 3D by Mn^II-N≡C-Mn^II linkages. The composition is {[Mn^II(OH₂)₃][Mn^II(OH₂)]₃}(μ₃-OH)₄][Mn^II(μ-CN)₂(CN)₄] ⋅ H₂O=[Mn^II₄(μ₃-OH)₄(OH₂)₆][Mn^II(μ-CN)₂(CN)₄] ⋅ H₂O, which is further simplified to [Mn₄(OH)₄][Mn(CN)₆](OH₂)₇ ( 1 ). 1 has four high-spin (S=5/2) Mn^II sites that are antiferromagnetically coupled within the cube and are antiferromagnetically coupled to six low-spin (S=1/2) octahedral [Mn^II(CN)₆]⁴⁻ ions. Above 40 K the magnetic susceptibility, χ(T), can be fitted to the Curie–Weiss expression, χ ∝(T−θ)⁻¹, with θ=−13.4 K, indicative of significant antiferromagnetic coupling and 1 orders as an antiferromagnet at T_c=7.8 K.     

Magnetic Relaxation Probing of the State of Diheptyl Dithiophosphate Ions in Water and Aqueous Triton X-100 Solutions

The nuclear magnetic relaxation was used to study the state of diheptyl dithiophosphoric acid (D7DTP, L₇) anions in water and aqueous solutions of the nonionic surfactant, Ttiton X-100, at 298 K in the presence of paramagnetic probes, Mn²⁺ions. It was found that increase in the spin-lattice relaxation rate of water protons is caused by formation of simple and mixed (with surfactant) aggregates of D7DTP. Unlike the Mn²⁺–sodium dodecyl sulfate –Triton X-100 system, studied previously an influence of a probe concentration was found at surfactant concentration close to the CMC. It was suggested that two types of mixed species containing diheptyl dithiophosphate ions, Mn(II), and nonionic surfactant can be formed: micellar aggregates, {Mn(L₇)₂(TX)}, and polynuclear associates, [Mn _x (L₇) _y (tx) _z ]. The associates likely contain surfactant in the form of monomers (tx).     

From discrete [Mn4] cluster to 1D complex: Two new mixed-valence manganese complexes with slow magnetization relaxation

A tetranuclear manganese complex [Mn₄(HL)₄(MeOH)₄(SCN)₂]·3MeOH (1) and a one-dimensional assembly of [Mn₄] units, [Mn₄(HL)₄(MeOH)₄(N(CN)₂)₂]·2.5MeOH (2) (H₃L = 2,6-bis(hydroxymethyl)-4-methylphenol), have been synthesized and studied. Complexes 1 and 2 crystallize in the triclinic space group P $ \bar 1 $ \bar 1 and monoclinic space group P21/n, respectively. Complex 1 possesses a mixed-valence tetranuclear dicubane unit, which comprises two Mn^II and two Mn^III ions. Complex 2 is built from the similar tetranuclear [Mn₄] units connected through two N(CN)₂⁻ anions into a 1-D chain. The temperature dependence of the magnetic susceptibilities of 1 and 2 indicates ferromagnetic interactions between the manganese ions. Frequency-dependent out-of-phase signals of alternating current magnetic susceptibilities are observed in the low temperature range for both complexes, indicating a slow magnetic relaxation.     

单分子磁体

单分子磁体是涉及合成化学、材料科学和凝聚态物理等边缘学科的一个新颖课题。本文对单分子磁体的主要性质、功能、研究方法和最新进展做了评述。重点介绍了含Mn和Fe这两类重要的单分子磁体。     

Insertion of a Single‐Molecule Magnet inside a Ferromagnetic Lattice Based on a 3D Bimetallic Oxalate Network: Towards Molecular Analogues of Permanent Magnets

The insertion of the single‐molecule magnet (SMM) [Mn^III(salen)(H₂O)]₂²⁺ (salen^2?=N,N′‐ethylenebis‐(salicylideneiminate)) into a ferromagnetic bimetallic oxalate network affords the hybrid compound [Mn^III(salen)(H₂O)]₂[Mn^IICr^III(ox)₃]₂ ? (CH₃OH) ? (CH₃CN)₂ ( 1 ). This cationic Mn₂ cluster templates the growth of crystals formed by an unusual achiral 3D oxalate network. The magnetic properties of this hybrid magnet are compared with those of the analogous compounds [Mn^III(salen)(H₂O)]₂[Zn^IICr^III(ox)₃]₂ ? (CH₃OH) ? (CH₃CN)₂ ( 2 ) and [In^III(sal₂‐trien)][Mn^IICr^III(ox)₃] ? (H₂O)_0.25 ? (CH₃OH)_0.25 ? (CH₃CN)_0.25 ( 3 ), which are used as reference compounds. In 2 it has been shown that the magnetic isolation of the Mn₂ clusters provided by their insertion into a paramagnetic oxalate network of Cr^III affords a SMM behavior, albeit with blocking temperatures well below 500 mK even for frequencies as high as 160 kHz. In 3 the onset of ferromagnetism in the bimetallic Mn^IICr^III network is observed at T_c=5 K. Finally, in the hybrid compound 1 the interaction between the two magnetic networks leads to the antiparallel arrangement of their respective magnetizations, that is, to a ferrimagnetic phase. This coupling induces also important changes on the magnetic properties of 1 with respect to those of the reference compounds 2 and 3 . In particular, compound 1 shows a large magnetization hysteresis below 1 K, which is in sharp contrast with the near‐reversible magnetizations that the SMMs and the oxalate ferromagnetic lattice show under the same conditions.     

Magnetothermal studies of a series of coordination clusters built from ferromagnetically coupled {Mn(II) (4)Mn(III) (6)} supertetrahedral units

Three high‐nuclearity mixed valence manganese^II/III coordination clusters, have been synthesised, that is, [Mn ^III ₆Mn ^II ₄(μ₃‐O)₄(HL¹)₆(μ₃‐N₃)₃(μ₃‐Br)(Br)](N₃)_0.7/(Br)_0.3 ? 3 MeCN ? 2 MeOH ( 1 ) (H₃L¹=3‐methylpentan‐1,3,5‐triol), [Mn^III₁₁Mn^II₆(μ₄‐O)₈(μ₃‐Cl)₄(μ,μ₃‐O₂CMe)₂(μ,μ‐L²)₁₀Cl_2.34(O₂CMe)_0.66(py)₃(MeCN)₂] ? 7 MeCN ( 2 ) (H₂L²=2,2‐dimethyl‐1,3‐propanediol and py is pyridine), and [Mn^III₁₂Mn^II₇(μ₄‐O)₈(μ₃‐η¹N₃)₈(HL³)₁₂(MeCN)₆]Cl₂ ? 10 MeOH ? MeCN ( 3 ) (H₃L³=2,6‐bis(hydroxymethyl)‐4‐methylphenol) with high ground‐spin states, S=22, 28±1, and 83/2, respectively; their magnetothermal properties have been studied. The three compounds are based on a common supertetrahedral building block as seen in the Mn₁₀ cluster. This fundamental magnetic unit is made up of a tetrahedron of Mn^II ions with six Mn^III ions placed midway along each edge giving an inscribed octahedron. Thus, the fundamental building unit as represented by compound 1 can be described as a Mn₁₀ supertetrahedron. Compounds 2 and 3 correspond to two such units joined by a common edge or vertex, respectively, resulting in Mn₁₇ and Mn₁₉ coordination clusters. Magnetothermal studies reveal that all three compounds show interesting long‐range magnetic ordering at low temperature, originating from negligible magnetic anisotropy of the compounds; compound 2 shows the largest magnetocaloric effect among the three compounds. This is as expected and can be attributed to the presence of a small magnetic anisotropy, and low‐lying excited states in compound 2 .     

Hexanuclear and Tetranuclear Mn/Ln clusters using 2‐(hydroxymethyl)pyridine: Synthesis,structures and magnetic properties

Reactions of manganese benzoate dihydrate and lanthanide nitrate hexahydrate with 2‐(hydroxymethyl)pyridine (hmpH) as ligand in the mixture solutions of acetonitrile and ethanol according to different molar ratios of NEt₃ generated two kinds of Mn‐Ln compounds [Mn^III₄La^III₂(O)₂(hmp)₇(PhCO₂)₂(NO₃)₅] ·5H₂O ( 1 ) and [Mn^III₂Gd^III₂(hmp)₆(PhCO₂)₄(NO₃)₂] ·3CH₃CN·3C₂H₅OH·2H₂O ( 2 ). By comparison of the two compounds, there exist considerable effects of reaction alkalinity on the structures and magnetic properties of products. Compound 1 possesses a core of [Mn^III₄La^III₂(μ ₄‐O)(μ ₃‐O)(μ ₃‐OR)(μ ₂‐O)₇]²⁻, which comprises three face‐sharing defected cubane units. The core topology represents a new core type of Mn‐Ln clusters. Compound 2 has a planar‐butterfly structure. The solid‐state dc magnetic susceptibility analyses indicate the antiferromagnetic interactions within compound 1 and ferromagnetic interactions within compound 2 . Compound 1 has an S  = 0 ground state, while compound 2 possesses an S  = 11 ground state, fitting of the dc data for the tetranuclear Mn₂Gd₂ with the Magpack program gives parameters of J _Mn‐Mn  = 3.11 cm⁻¹, J _Mn‐Gd  = 0.02 cm^—1 and g  = 1.96.     

A mixed‐valence manganese(III)–manganese(IV) di‐μ‐oxo complex, [(cyclam)MnO]2(ClO4)2(NO3)

The title dinuclear di‐μ‐oxo‐bis­[(1,4,8,11‐tetra­aza­cyclo­tetra­decane‐κ⁴N)­manganese(III,IV)] diperchlorate nitrate complex, [Mn₂O₂(C₁₀H₂₄N₄)₂](ClO₄)₂(NO₃) or [(cyclam)Mn­O]₂(ClO₄)₂(NO₃), was self‐assembled by the reaction of Mn²⁺ with 1,4,8,11‐tetra­aza­cyclo­tetra­decane in aqueous media. The structure of this compound consists of a centrosymmetric binuclear [(cyclam)MnO]³⁺ unit, two perchlorate anions and one nitrate anion. While the low‐temperature electron paramagnetic resonance spectra show a typical 16‐line signal for a di‐μ‐oxo Mn^III/Mn^IV dimer, the magnetic susceptibility studies also confirm a characteristic antiferromagnetic coupling between the electronic spins of the Mn^IV and Mn^III ions.     

A {Tb2Fe3} Pyramid Single‐Molecule Magnet with Ferromagnetic Tb‐Fe Interaction

The influence of magnetic interactions to the magnetization dynamics was well experimentally studied in a 3d‐4f single‐molecule magnet (SMM) [Tb^III₂Fe^III₃(μ₅‐O)L₂(NO₃)₄Cl] ( 1 , H₄L = N,N,N’,N’‐tetrakis(2‐hydroxyethyl)ethylene diamine) and its diamagnetic‐ ion‐diluted samples. Significant ferromagnetic coupling between Tb^III and Fe^III ions and SMM behavior of 1 were observable, which proved clearly that the magnetic interaction between 3d‐4f spin carriers has also an excessive impact on fine‐tuning the magnetization dynamic behaviors of 3d‐4f complexes.     

Octanuclear Ni4Ln4 Coordination Aggregates from Schiff Base Anion Supports and Connecting of Two Ni2Ln2 Cubes: Syntheses,Structures, and Magnetic Properties

A family of 3d–4f aggregates have been reported through guiding the dual coordination modes of ligand anion (HL^?) and in situ generated ancillary bridge driven self‐assembly coordination responses toward two different types of metal ions. Reactions of lanthanide(III) nitrate (Ln=Gd, Tb, Dy, Ho and Yb), nickel(II) acetate and phenol‐based ditopic ligand anion of 2‐[{(2‐hydroxypropyl)imino}methyl]‐6‐methoxyphenol (H₂L) in MeCN‐MeOH (3 : 1) mixture and LiOH provided five new octanuclear Ni‐4f coordination aggregates from two Ni₂Ln₂ cubanes. Single‐crystal X‐ray diffraction analysis reveals that all the members of the family are isostructural, with the central core formed from the coupling of two distorted [Ni₂Ln₂O₄] heterometallic cubanes [Ni₂Ln₂(HL)₂(μ₃‐OH)₂(OH)(OAc)₄]⁺ (Ln=Gd ( 1 ), Tb ( 2 ), Dy ( 3 ), Ho ( 4 ) and Yb ( 5 )). Higher coordination demand of 4f ions induced the coupling of the two cubes by (OH)(OAc)₂ bridges. Variable temperature magnetic study reveals weak coupling between the Ni²⁺ and Ln³⁺ ions. For the Tb ( 2 ) and Dy ( 3 ) analogs, the compounds are SMMs without an applied dc field, whereas the Gd ( 1 ) analogue is not an SMM. The observation revealed thus that the anisotropy of the Ln³⁺ ions is central to display the SMM behavior within this structurally intriguing family of compounds.     

Structural study by X-ray diffraction, magnetic susceptibility and Mössbauer spectroscopy of the Na2Mn2(1 − x)Cd2xFe(PO4)3 (0 ≤ x ≤ 1) solid solution

Na₂Mn_{2(1 − x)}Cd_2xFe(PO₄)₃ (0 ≤ x ≤ 1) phosphates were prepared by solid state reaction and characterized by powder X-ray diffraction, magnetic susceptibility and Mössbauer spectroscopy. The X-ray diffraction patterns indicated the formation of a continuous solid solution which crystallizes in the alluaudite structural type characterized by the general formula X(2)X(1)M(1)M(2)₂(PO₄)₃. The cation distribution, deduced from a structure refinement of the x = 0, 0.5 and 1 compositions, is ordered in the X(2) sites and disordered in the remaining X(1), M(1) and M(2) sites. The magnetic susceptibility study revealed an antiferromagnetic behaviour of the studied compounds. The ⁵⁷Fe Mössbauer spectroscopy confirmed the structural results and proved the exclusive presence of Fe³⁺ ions.