Synthesis,Structures and Magnetic Properties of Cyano‐bridged FeIII/MnIII Heterobimetallic 1D Chain Complexes

Using the tricyanometalate building block, (nBu₄N)[(Tp*)Fe(CN)₃] [Bu₄N⁺ = tetrabutylammonium cation; Tp*^– = hydrotris(3,5‐dimethylpyrazol‐1‐yl)borate], and bidentate Schiff base ligands, HL1 or HL2 {HL1 = 2‐[[(2‐phenylethyl)imino]methyl]phenol; HL2 = 4‐methoxy‐2‐[[(2‐phenylethyl)imino]methyl]phenol}, two heterobimetallic one‐dimensional (1D) chain complexes, [Mn(L1)₂Fe(Tp*)(CN)₃]_n ( 1 ) and [Mn(L2)₂Fe(Tp*)(CN)₃]_n ( 2 ), were synthesized. Single crystal X‐ray diffraction reveal the formation of neutral cyano‐bridged zigzag single chains in 1 and 2 . Magnetic studies demonstrate that both complexes show ferromagnetic interactions between central Fe^III and Mn^III atoms.     

Multifunctionality in Bimetallic LnIII[WV(CN)8]3− (Ln=Gd,Nd) Coordination Helices: Optical Activity,Luminescence, and Magnetic Coupling

Two chiral luminescent derivatives of pyridine bis(oxazoline) (Pybox), (SS/RR)‐iPr‐Pybox (2,6‐bis[4‐isopropyl‐2‐oxazolin‐2‐yl]pyridine) and (SRSR/RSRS)‐Ind‐Pybox (2,6‐bis[8H‐indeno[1,2‐d]oxazolin‐2‐yl]pyridine), have been combined with lanthanide ions (Gd³⁺, Nd³⁺) and octacyanotungstate(V) metalloligand to afford a remarkable series of eight bimetallic CN^?‐bridged coordination chains: {[Ln^III(SS/RR‐iPr‐Pybox)(dmf)₄]₃[W^V(CN)₈]₃}_n ? dmf ? 4 H₂O (Ln=Gd, 1 ‐SS and 1 ‐RR; Ln=Nd, 2 ‐SS and 2 ‐RR) and {[Ln^III(SRSR/RSRS‐Ind‐Pybox)(dmf)₄][W^V(CN)₈]}_n ? 5 MeCN ? 4 MeOH (Ln=Gd, 3 ‐SRSR and 3 ‐RSRS; Ln=Nd, 4 ‐SRSR and 4 ‐RSRS). These materials display enantiopure structural helicity, which results in strong optical activity in the range 200–450 nm, as confirmed by natural circular dichroism (NCD) spectra and the corresponding UV/Vis absorption spectra. Under irradiation with UV light, the Gd^III‐W^V chains show dominant ligand‐based red phosphorescence, with λ_max≈660 nm for 1 ‐(SS/RR) and 680 nm for 3 ‐(SRSR/RSRS). The Nd^III‐W^V chains, 2 ‐(SS/RR) and 4 ‐(SRSR/RSRS), exhibit near‐infrared luminescence with sharp lines at 986, 1066, and 1340 nm derived from intra‐f ⁴F_3/2→⁴I_{9/2,11/2,13/2} transitions of the Nd^III centers. This emission is realized through efficient ligand‐to‐metal energy transfer from the Pybox derivative to the lanthanide ion. Due to the presence of paramagnetic lanthanide(III) and [W^V(CN)₈]^3? moieties connected by cyanide bridges, 1 ‐(SS/RR) and 3 ‐(SRSR/RSRS) are ferrimagnetic spin chains originating from antiferromagnetic coupling between Gd^III (S_Gd=7/2) and W^V (S_W=1/2) centers with J _{1 ‐(SS)}=?0.96(1) cm^?1, J _{1 ‐(RR)}=?0.95(1) cm^?1, J _{3 ‐(SRSR)}=?0.91(1) cm^?1, and J _{3 ‐(RSRS)}=?0.94(1) cm^?1. 2 ‐(SS/RR) and 4 ‐(SRSR/RSRS) display ferromagnetic coupling within their Nd^III‐NC‐W^V linkages.     

Crystal structure of a cyanide-bridged heptanuclear manganese(III)–chromium(III) complex with a ground state S = 21/2

K₃[Cr(CN)₆] reacts with the mononuclear Mn^III complex Mn(salen)ClO₄ · 2H₂O [salen: N,N-ethylenebis(salicylideneiminato)dianion] to give a bimetallic heptanuclear complex cation salt [Cr{(CN)Mn(salen · H₂O)}₆][Cr(CN)₆]6H₂O. In the complex anion, [Cr{(CN)Mn(salen · H₂O)}₆]³⁺, six Mn^III ions coordinate to a Cr^III center via cyano bridges, forming a spherical species with 3 symmetry. A study of magnetic properties shows the presence of antiferromagnetic interaction through the cyanide bridge between Cr^III (S = 3/2) and Mn^III (S = 4/2) and results in a ground state S = 21/2.     

Cyano‐Bridged MnIII?MIII Single‐Chain Magnets with MIII=CoIII,FeIII, MnIII,and CrIII

A series of isostructural cyano‐bridged Mn^III(h.s.)–M^III(l.s.) alternating chains, [Mn^III(5‐TMAMsalen)M^III(CN)₆] ? 4H₂O (5‐TMAMsalen^2?=N,N′‐ethylenebis(5‐trimethylammoniomethylsalicylideneiminate), Mn^III(h.s.)=high‐spin Mn^III, M^III(l.s.)=low‐spin Co^III, Mn? Co ; Fe^III, Mn? Fe ; Mn^III, Mn? Mn ; Cr^III, Mn? Cr ) was synthesized by assembling [Mn^III(5‐TMAMsalen)]³⁺ and [M^III(CN)₆]^3?. The chains present in the four compounds, which crystallize in the monoclinic space group C2/c, are composed of an [‐Mn^III‐NC‐M^III‐CN‐] repeating motif, for which the ‐NC‐M^III‐CN‐ motif is provided by the [M^III(CN)₆]^3? moiety adopting a trans bridging mode between [Mn^III(5‐TMAMsalen)]³⁺ cations. The Mn^III and M^III ions occupy special crystallographic positions: a C₂ axis and an inversion center, respectively, forming a highly symmetrical chain with only one kind of cyano bridge. The Jahn–Teller axis of the Mn^III(h.s.) ion is perpendicular to the N₂O₂ plane formed by the 5‐TMAMsalen tetradentate ligand. These Jahn–Teller axes are all perfectly aligned along the unique chain direction without a bending angle, although the chains are corrugated with an Mn‐N_axis‐C angle of about 144°. In the crystal structures, the chains are well separated with the nearest inter‐chain M???M distance being relatively large at 9 Å due to steric hindrance of the bulky trimethylammoniomethyl groups of the 5‐TMAMsalen ligand. The magnetic properties of these compounds have been thoroughly studied. Mn? Fe and Mn? Mn display intra‐chain ferromagnetic interactions, whereas Mn? Cr is characterized by an antiferromagnetic exchange that induces a ferrimagnetic spin arrangement along the chain. Detailed analyses of both static and dynamic magnetic properties have demonstrated without ambiguity the single‐chain magnet (SCM) behavior of these three systems, whereas Mn? Co is merely paramagnetic with S_Mn=2 and D/k_B=?5.3 K (D being a zero‐field splitting parameter). At low temperatures, the Mn? M compounds with M=Fe, Mn, and Cr display remarkably large M versus H hysteresis loops for applied magnetic fields along the easy magnetic direction that corresponds to the chain direction. The temperature dependence of the associated relaxation time for this series of compounds systematically exhibits a crossover between two Arrhenius laws corresponding to infinite‐chain and finite‐chain regimes for the SCM behavior. These isostructural hetero‐spin SCMs offer a unique series of alternating [‐Mn‐NC‐M‐CN‐] chains, enabling physicists to test theoretical SCM models between the Ising and Heisenberg limits.     

trans‐Bis(cyano‐κC)(1,4,8,11‐tetraazacyclotetradecane‐κ4N)manganese(III) perchlorate,a low‐spin manganese(III) complex

The crystal structure of the low‐spin (S = 1) Mn^III complex [Mn(CN)₂(C₁₀H₂₄N₄)]ClO₄, or trans‐[Mn(CN)₂(cyclam)](ClO₄) (cyclam is the tetradentate amine ligand 1,4,8,11‐tetra­aza­cyclo­tetra­decane), is reported. The structural parameters in the Mn(cyclam) moiety are found to be insensitive to both the spin and the oxidation state of the Mn ion. The difference between high‐ and low‐spin Mn^III complexes is that a pronounced tetragonal elongation of the coordination octahedron occurs in high‐spin complexes and a slight tetragonal compression is seen in low‐spin complexes, as in the title complex.     

One‐Dimensional Ferromagnetically Coupled Bimetallic Chains Constructed with trans‐[Ru(acac)2(CN)2]−: Syntheses,Structures, Magnetic Properties,and Density Functional Theoretical Study

Four cyano‐bridged 1D bimetallic polymers have been prepared by using the paramagnetic building block trans‐[Ru(acac)₂(CN)₂]^? (Hacac=acetylacetone): {[{Ni(tren)}{Ru(acac)₂(CN)₂}][ClO₄]?CH₃OH}_n ( 1 ) (tren=tris(2‐aminoethyl)amine), {[{Ni(cyclen)}{Ru(acac)₂(CN)₂}][ClO₄]? CH₃OH}_n ( 2 ) (cyclen=1,4,7,10‐tetraazacyclododecane), {[{Fe(salen)}{Ru(acac)₂(CN)₂}]}_n ( 3 ) (salen^2?=N,N′‐bis(salicylidene)‐o‐ethyldiamine dianion) and [{Mn(5,5′‐Me₂salen)}₂{Ru(acac)₂(CN)₂}][Ru(acac)₂(CN)₂]? 2 CH₃OH ( 4 ) (5,5′‐Me₂salen=N,N′‐bis(5,5′‐dimethylsalicylidene)‐o‐ethylenediimine). Compounds 1 and 2 are 1D, zigzagged NiRu chains that exhibit ferromagnetic coupling between Ni^II and Ru^III ions through cyano bridges with J=+1.92 cm^?1, z J′=?1.37 cm^?1, g=2.20 for 1 and J=+0.85 cm^?1, z J′=?0.16 cm^?1, g=2.24 for 2 . Compound 3 has a 1D linear chain structure that exhibits intrachain ferromagnetic coupling (J=+0.62 cm^?1, z J′=?0.09 cm^?1, g=2.08), but antiferromagnetic coupling occurs between FeRu chains, leading to metamagnetic behavior with T_N=2.6 K. In compound 4 , two Mn^III ions are coordinated to trans‐[Ru(acac)₂(CN)₂]^? to form trinuclear Mn₂Ru units, which are linked together by π–π stacking and weak Mn???O* interactions to form a 1D chain. Compound 4 shows slow magnetic relaxation below 3.0 K with ?=0.25, characteristic of superparamagnetic behavior. The Mn^III???Ru^III coupling constant (through cyano bridges) and the Mn^III???Mn^III coupling constant (between the trimers) are +0.87 and +0.24 cm^?1, respectively. Compound 4 is a novel single‐chain magnet built from Mn₂Ru trimers through noncovalent interactions. Density functional theory (DFT) combined with the broken symmetry state method was used to calculate the molecular magnetic orbitals and the magnetic exchange interactions between Ru^III and M (M=Ni^II, Fe^III, and Mn^III) ions. To explain the somewhat unexpected ferromagnetic coupling between low‐spin Ru^III and high‐spin Fe^III and Mn^III ions in compounds 3 and 4 , respectively, it is proposed that apart from the relative symmetries, the relative energies of the magnetic orbitals may also be important in determining the overall magnetic coupling in these bimetallic assemblies.     

Die Kristallstruktur der hydratisierten Cyanokomplexe NMe4MnII[(Mn, Cr)III(CN)6] · 3 H2O und NMe4Cd[MIII(CN)6] · 3 H2O (MIII = Fe,Co): Verwandte des Berliner Blaus

The Crystal Structure of the Hydrated Cyano Complexes NMe₄Mn^II[(Mn, Cr)^III(CN)₆] · 3 H₂O and NMe₄Cd[M^III(CN)₆] · 3 H₂O (M^III = Fe, Co): Compounds Related to Prussian Blue The crystal structures of the isotypic tetragonal compounds (space group I4, Z = 10) NMe₄Mn^II · [(Mn, Cr)^III(CN)₆] · 3 H₂O (a = 1653.2(4), c = 1728.8(6) pm), NMe₄Cd[Fe(CN)₆] · 3 H₂O (a = 1642.7(1), c = 1733.1(1) pm) and NMe₄Cd[Co(CN)₆] · 3 H₂O (a = 1632.1(2), c = 1722.4(3) pm) were determined by X‐rays. They exhibit ⊥ c cyanobridged layers of octahedra [M^III(CN)₆] and [M^IIN₄(OH₂)₂], which punctually are interconnected also || c to yield altogether a spaceous framework. The M^II atoms at the positions linking into the third dimension are only five‐coordinated and form square pyramids [M^IIN₅] with angles N–M^II–N near 104° and distances of Mn–N: 1 × 214, 4 × 219 pm; Cd–N: 1 × 220 resp. 222, 4 × 226 resp. 228 pm. Further details and structural relations within the family of Prussian Blue are reported and discussed.     

Controlled Synthesis of Heterotrimetallic Single‐Chain Magnets from Anisotropic High‐Spin 3 d–4 f Nodes and Paramagnetic Spacers

By using the node‐and‐spacer approach in suitable solvents, four new heterotrimetallic 1D chain‐like compounds (that is, containing 3d–3d′–4f metal ions), {[Ni(L)Ln(NO₃)₂(H₂O)Fe(Tp*)(CN)₃] ? 2 CH₃CN ? CH₃OH}_n (H₂L=N,N′‐bis(3‐methoxysalicylidene)‐1,3‐diaminopropane, Tp*=hydridotris(3,5‐dimethylpyrazol‐1‐yl)borate; Ln=Gd ( 1 ), Dy ( 2 ), Tb ( 3 ), Nd ( 4 )), have been synthesized and structurally characterized. All of these compounds are made up of a neutral cyanide‐ and phenolate‐bridged heterotrimetallic chain, with a {? Fe? C?N? Ni(? O? Ln)? N?C? }_n repeat unit. Within these chains, each [(Tp*)Fe(CN)₃]^? entity binds to the Ni^II ion of the [Ni(L)Ln(NO₃)₂(H₂O)]⁺ motif through two of its three cyanide groups in a cis mode, whereas each [Ni(L)Ln(NO₃)₂(H₂O)]⁺ unit is linked to two [(Tp*)Fe(CN)₃]^? ions through the Ni^II ion in a trans mode. In the [Ni(L)Ln(NO₃)₂(H₂O)]⁺ unit, the Ni^II and Ln^III ions are bridged to one other through two phenolic oxygen atoms of the ligand (L). Compounds 1 – 4 are rare examples of 1D cyanide‐ and phenolate‐bridged 3d–3d′–4f helical chain compounds. As expected, strong ferromagnetic interactions are observed between neighboring Fe^III and Ni^II ions through a cyanide bridge and between neighboring Ni^II and Ln^III (except for Nd^III) ions through two phenolate bridges. Further magnetic studies show that all of these compounds exhibit single‐chain magnetic behavior. Compound 2 exhibits the highest effective energy barrier (58.2 K) for the reversal of magnetization in 3d/4d/5d–4f heterotrimetallic single‐chain magnets.     

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.     

Three 3‐Amino‐1, 2, 4‐Triazole‐Based Magnetic Complexes Incorporated with Different Carboxylate‐Containing Coligands: Synthesis,Structures, and Magnetic Properties

Three 3‐amino‐1, 2, 4‐triazole (atz)‐based paramagnetic complexes, [Mn(atz)(pa)]_n ( 1 ), {[Mn(atz)_1.5(hip)] · H₂O}_n ( 2 ), and [Mn(H₂O)₂(atz)₂(nb)₂] ( 3 ) (H₂pa = o‐phthalic acid, H₂hip = 5‐hydroxylisophthalic acid, and Hnb = p‐nitrobenzoic acid) were prepared by introducing different carboxylate‐containing aromatic coligands, and structurally and magnetically characterized. Helical Mn^II‐atz and bent Mn^II‐pa^2– chains are crosslinked by sharing the same metal sites to generate a honeycomb‐shaped framework of 1 . The undulated Mn^II‐atz layers constructed from 22‐member metallomacrocycles are periodically supported by ditopic hip^2– ligands to lead to a pillared‐layer structure of 2 . In contrast, complex 3 is a centrosymmetric mononuclear entity, which is assembled into a three‐dimensional supramolecular network by abundant hydrogen‐bonding interactions. The structural difference of 1 – 3 is significantly due to the combinations of the flexible coordination modes adopted by the mixed atz and carboxylate groups. Weak and comparable antiferromagnetic couplings are observed in the nearest neighbors of 1 – 3 , which are cooperatively transmitted either by short carboxylate and/or atz heterobridges or by weak non‐covalent interactions.     

A cyanide‐bridged FeIII–MnII heterobimetallic one‐dimensional coordination polymer: synthesis,crystal structure,experimental and theoretical magnetism investigation

A new cyanide‐bridged Fe^III–Mn^II heterobimetallic coordination polymer (CP), namely catena‐poly[[[N,N′‐(1,2‐phenylene)bis(pyridine‐2‐carboxamidato)‐κ⁴N,N′,N′′,N′′′]iron(III)]‐μ‐cyanido‐κ²C:N‐[bis(4,4′‐bipyridine‐κN)bis(methanol‐κO)manganese(II)]‐μ‐cyanido‐κ²N:C], {[FeMn(C₁₈H₁₂N₄O₂)(CN)₂(C₁₀H₈N₂)₂(CH₃OH)₂]ClO₄}_n, ( 1 ), was prepared by the self‐assembly of the trans‐dicyanidoiron(III)‐containing building block [Fe(bpb)(CN)₂]^? [bpb^2? = N,N′‐(1,2‐phenylene)bis(pyridine‐2‐carboxamidate)], [Mn(ClO₄)₂]·6H₂O and 4,4′‐bipyridine, and was structurally characterized by elemental analysis, IR spectroscopy, single‐crystal X‐ray crystallography and powder X‐ray diffraction (PXRD). Single‐crystal X‐ray diffraction analysis shows that CP 1 possesses a cationic linear chain structure consisting of alternating cyanide‐bridged Fe–Mn units, with free perchlorate as the charge‐balancing anion, which can be further extended into a two‐dimensional supramolecular sheet structure via inter‐chain π–π interactions between the 4,4′‐bipyridine ligands. Within the chain, each Mn^II ion is six‐coordinated by an N₆ unit and is involved in a slightly distorted octahedral coordination geometry. Investigation of the magnetic properties of 1 reveals an antiferromagnetic coupling between the cyanide‐bridged Fe^III and Mn^II ions. A best fit of the magnetic susceptibility based on the one‐dimensional alternating chain model leads to the magnetic coupling constants J₁ = ?1.35 and J₂ = ?1.05 cm^?1, and the antiferromagnetic coupling was further confirmed by spin Hamiltonian‐based density functional theoretical (DFT) calculations.     

Concurrent two one‐electron transfer in the oxidation of chromium(III) complexes with trans‐1,2‐diaminocyclohexane‐N,N,N′,N′‐tetraacetate and diethylenetriaminepentaacetate ligands by periodate ion

The kinetics of oxidation of [Cr^IIIcdta(H₂O)]^? and [Cr^IIIdtpa(H₂O)]^2? (where cdta = trans‐1,2‐diaminocyclohexane‐N,N,N′,N′‐tetraacetate and dtpa = diethylenetriaminepentaacetate) by periodate ion has been studied in aqueous solutions. The oxidation of these complexes was carried out in the pH range 5.52–7.44 for the [Cr^IIIcdta(H₂O)]^? complex and the pH range 5.56–8.56 for the [Cr^IIIdtpa(H₂O)]^2? complex. The reaction exhibited an uncommon second‐order dependence on [Cr^IIIL(H₂O)]ⁿ (L = cdta or dtpa and n=?1 or ?2, respectively) and a first‐order dependence on [IO^?₄]. At fixed reaction conditions, the reaction rate is described by Eq. (i). The third‐order rate constant, k₃, varied with [H⁺] according to Eq. (ii). (i) (ii) A mechanism in which simultaneous one‐electron transfer from two [Cr^IIIL(OH)]^n?1 ions to I(VII) is proposed. The two [Cr^IIIL(OH)]^n?1 ions are bridged to I(VII) via the hydroxo group. Periodate ion is known to undergo rapid substitution or expansion of its coordination number from four to six. The activation parameters ΔH* and ΔS* were calculated using the Eyring equation. The relatively high negative values of ΔS* are consistent with an associative process preceding electron transfer. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 729–735, 2012     

A 1,2,4‐Triazole‐based Polynuclear Mixed‐valence MnIIMnIII Complex: Synthesis,Characterization, and Magnetic Property

A mixed‐valence Mn complex {[Mn^IIMn^III(HL)₂(4,4′‐bpy)(H₂O)₂] · (ClO₄)(DMF)₃(4,4′‐bpy)_0.5}_n ( 1 ) [H₂L = 3‐(2‐phenol)‐5‐(pyridin‐2‐yl)‐1,2,4‐triazole] was synthesized and characterized by X‐ray single‐crystal structure analysis and magnetic susceptibility. Single‐crystal X‐ray analysis revealed that complex 1 has a dinuclear core, in which adjacent central Mn^III atoms are linked by 4,4′‐bipyridine to form an infinite one‐dimensional (1D) molecular configuration. According to the Mn surrounding bond lengths and bond valence sum (BVS) calculations, we demonstrated that the Mn atom coordinated to the pyridine N atoms is in the +2 oxidation state, while another Mn atom coordinated to the phenolic oxygen atoms is in the +3 oxidation state. Magnetic susceptibility data of the complex 1 indicate that the ferromagnetic interaction dominates in this complex.     

A Three‐Dimensional MnII‐[MoIII(CN)7]4– Ferrimagnet Containing Formate as a Second Bridging Ligand

Self‐assembly of the [Mo(CN)₇]^4– anion and the Mn²⁺ ion in the aqueous solution containing ammonium formate results in a new coordination polymer, {(NH₄)₃[(H₂O)Mn₃(HCOO)][Mo(CN)₇]₂·4H₂O}_n. Single crystal X‐ray analysis revealed a very complicated three‐dimensional (3D) framework, where both the [Mo(CN)₇]^4– and the formate anions act as bridges between the Mn^II centers. Magnetic measurements revealed that this compound displays ferrimagnetic ordering below 70 K. Competing antiferromagnetic interactions between the spin carriers might lead to spin frustration and non‐linear alignment of the magnetic moments. Specifically, this compound is the first mixed [Mo(CN)₇]^4–/HCOO^– bridged molecule magnet.     

An investigation of the electron density of a Jahn–Teller‐distorted CrII cation: the crystal structure and charge density of hexakis(acetonitrile‐κN)chromium(II) bis(tetraphenylborate) acetonitrile disolvate

In the crystal structure of the title homoleptic Cr^II complex, [Cr(CH₃CN)₆](C₂₄H₂₀B)₂·CH₃CN, the [Cr(CH₃CN)₆]²⁺ cation is a high‐spin d⁴ complex with strong static, rather than dynamic, Jahn–Teller distortion. The electron density of the cation was determined by single‐crystal X‐ray refinements using aspherical structure factors from wavefunction calculations. The detailed picture of the electronic density allowed us to assess the extent and directionality of the Jahn–Teller distortion of the Cr^II cation away from idealized octahedral symmetry. The topological analysis of the aspherical d‐electron density about the Cr^II cation showed that there are significant valence charge concentrations along the axial Cr—N axes. Likewise, there were significant valence charge depletions about the Cr^II cation along the equatorial Cr—N bonds. These charge concentrations are in accordance with a Jahn–Teller‐distorted six‐coordinate complex.     

A new heteroleptic oxalate‐based compound: poly[[2‐(aminomethyl)pyridine]di‐μ6‐oxalato‐chromium(III)potassium(I)]

The title compound, [KCr(C₂O₂)₂(C₆H₈N₂)]_n, was obtained from aqueous solution and analyzed with single‐crystal X‐ray diffraction at 100 K. It crystallizes in the monoclinic space group C2/c and displays a three‐dimensional polymeric architecture built up by bimetallic oxalate‐bridged Cr^III–K helical chains linked through centrosymmetric K₂O₂ units to yield a sheet‐like alternating P/M arrangement which looks like that of the previously described two‐dimensional [NaCr(ox)₂(pyim)(H₂O)]·2H₂O [pyim is 2‐(pyridin‐2‐yl)imidazole; Lei et al. (2006). Inorg. Chem. Commun. 9 , 486–488]. The Cr^III ions in each helix have the same chirality. The infinite neutral sheets are eclipsed with respect to each other and are held together by a hydrogen‐bonding network involving 2‐(aminomethyl)pyridine H atoms and oxalate O atoms. Each sheet gives rise to channels of Cr₄K₄ octanuclear rings and each resultant hole is occupied by a pair of 2‐(aminomethyl)pyridine ligands with partial overlap. The shortest Cr...Cr distance [5.593 (4) Å] is shorter than usually observed in the K–M^III–oxalate family.     

Cyanide-bridged FeIII–MnIII bimetallic chain derived from [Fe(bipy)(CN)4]−: synthesis,structure and magnetic characteristics

A chain-like compound of [Mn(salpn)][Fe(bipy)(CN)₄] (1) (salpn = N,N′-propylenebis(salicylideneiminato)dianion; bipy = 2,2′-bipyridine), assembled from building blocks of [Fe(bipy)(CN)₄]^? and [Mn(salpn)]⁺, has been characterized by elemental analyses, ICP, IR, thermoanalysis, single crystal X-ray structure analysis and magnetic measurements. In 1, each [Fe(bipy)(CN)₄]^? anion coordinates with two [Mn^III(salpn)]⁺ cations via two trans-CN^? groups, and each [Mn^III(salpn)]⁺ cation is axially coordinated by two [Fe(bipy)(CN)₄]^? ions, resulting in a straight 1-D chain. The chains stack via aromatic π–π-type interactions. Magnetic studies reveal the presence of weak antiferromagnetic interactions between adjacent Fe^III and Mn^III ions through cyanide-bridges.     

Role of Dicarboxylate Linkers in MnIII‐Salicylaldoximate Based Extended Structures: Synthesis,Structures, and Magnetic Behavior

Four new oxo‐centered Mn^III‐salicylaldoximate triangle‐based extended complexes [Mn^III₆O₂(salox)₆(EtOH)₄(phda)]_n?(saloxH₂)_n?(2H₂O)_n ( 1 ), [Mn^III₆O₂(salox)₆(MeOH)₅(5‐I‐isoph)]_n?(3 MeOH)_n ( 2 ), [Mn^III₆O₂(salox)₆(MeOH)₄(H₂O) (5‐N₃‐isoph)]_n?(4 MeOH)_n ( 3 ) and [Mn^III₃NaO(salox)₃(MeOH)₄(5‐NO₂‐isoph)]_n?(MeOH)_n (H₂O)_n ( 4 ) [salox=salicylaldoximate, phda=1,3‐phenylenediacetate, isoph=isophthalate] have been synthesized under similar reaction conditions. Single crystal X‐ray structures show that in 1 , only one type of Mn₆ cluster is arranged in 1 D, whereas in 2 and 3 there are two types of clusters, differing in the way the triangle units are joined and assembled. In complex 4 , however, the basic building structure is heteronuclear and based on Mn₃ units extended in 2 D. Susceptibility measurements (dc and ac) over a wide range of temperatures and fields show that the complexes 1 , 2 , and 3 behave as single molecule magnets (SMMs) with S=4 ground state, while 4 is dominantly antiferromagnetic with a ground spin state S=2. Density functional theory calculations have been performed on model complexes to provide a qualitative theoretical interpretation for their overall magnetic behavior.     

Trinuclear Cyanido-Bridged [Cr2Fe] Complexes: To Be or not to Be a Single-Molecule Magnet,a Matter of Straightness

Trinuclear systems of formula [{Cr(L^N3O2Ph)(CN)₂}₂M(H₂L^N3O2R)] (M=Mn^II and Fe^II, L^N3O2R stands for pentadentate ligands) were prepared in order to assess the influence of the bending of the apical M−N≡C linkages on the magnetic anisotropy of the Fe^II derivatives and in turn on their Single-Molecule Magnet (SMM) behaviors. The cyanido-bridged [Cr₂M] derivatives were obtained by assembling trans-dicyanido Cr^III complex [Cr(L^N3O2Ph)(CN)₂]⁻ and divalent pentagonal bipyramid complexes [M^II(H₂L^N3O2R)]²⁺ with various R substituents (R=NH₂, cyclohexyl, S,S-mandelic) imparting different steric demand to the central moiety of the complexes. A comparative examination of the structural and magnetic properties showed an obvious effect of the deviation from straightness of the M−N≡C alignment on the slow relaxation of the magnetization exhibited by the [Cr₂Fe] complexes. Theoretical calculations have highlighted important effects of the bending of the apical C−N−Fe linkages on both the magnetic anisotropy of the Fe^II center and the exchange interactions with the Cr^III units.     

Cyano‐Bridged Aqua(N,N‐Dimethylacetamide)(cyanoiron)lanthanides from Samarium,Gadolinium, or Holmium Nitrate and Potassium Hexacyanoferrate: Crystal Structures and Magnetochemistry

Three cyano‐bridged aqua(N,N‐dimethylacetamide)(cyanoiron)lanthanide complexes were synthesized by the reaction of K₃Fe(CN)₆, Ln(NO₃)₃⋅6 H₂O (Ln=Sm, Gd, Ho), and N,N‐dimethylacetamide (DMA). The obtained complexes 1 – 3 exhibit different coordination geometries and crystal structures. The polymeric {[Sm(DMA)₂(H₂O)₄Fe(CN)₆⋅5 H₂O}_n ([SmFe]_n; 1 ) has a one‐dimensional chain structure with approximately parallel trans‐positioned bridging CN ligands between the Sm‐ and Fe‐atoms. [(Gd(DMA)₃(H₂O)₄)₂Fe(CN)₆]⋅[Fe(CN)₆]⋅3 H₂O (Gd₂Fe; 2 ) is an isolated trinuclear Gd(1)−Fe−Gd(2) complex with two approximately perpendicular cis‐positioned bridging CN ligands between the two Gd‐atoms and the Fe‐atom. [Ho(DMA)₃(H₂O)₃Fe(CN)₆]⋅3 H₂O (HoFe; 3 ) adopts a single dinuclear crystal structure with only one bridging CN between the Ho‐ and Fe‐atom. Magnetochemistry experiments establish weak antiferromagnetic interactions between Gd^III (and Ho^III) and Fe^III atoms. Especially the [SmFe]_n complex 1 exhibits long‐range magnetic ordering, T_c=3.5 K, and a stronger coercive force, H_c=1400 Oe.