Synthesis, crystal structures, and magnetic properties of cyanide-bridged W(V)Mn(III) anionic coordination polymers containing divalent cationic moieties: slow magnetic relaxations and spin crossover phenomenon.

Two trimetallic coordination complexes were prepared by self-assembly of [W(CN)8](3-) and the Mn(III) Schiff base followed by the addition of a Zn(II) or Fe(II) cationic unit. The octacyanotungstate connects neighboring Mn(III) centers to form a one-dimensional chain. The anionic chain requires cationic units of Zn(II) or Fe(II) to maintain charge balance in the structure. The Zn-containing complex shows ferrimagnetic behavior originating from the antiparallel alignment of W(V) and Mn(III) spins within the chain, which leads to slow magnetic relaxation at low temperatures. For the Fe(II)-containing compound, Fe(II) moieties are integrated into the ferrimagnetic chains, altering their spin states depending on the temperature. It appears that the coexistence of high- and low-spin states in the low temperature regime is responsible for the slower and faster relaxations of the magnetization.

Synthesis, structures, and magnetic properties of end-to-end azide-bridged manganese(III) chains: elucidation of direct magnetostructural correlation.

The two one-dimensional chain compounds [Mn(L1)(N3)]·H2O (1·H2O; H2L1 = 2,2'-((1E,1'E)-ethane-1,2-diylbis(azan-1-yl-1-ylidene))bis(phenylmethan-1-yl-1-ylidene)diphenol) and [Mn(L2)(N3)] (2; H2L2 = 2,2'-((1E,1'E)-2,2-dimethylpropane-1,3-diyl)bis(azan-1-yl-1-ylidene)-bis(phenylmethan-1-yl-1-ylidene)diphenol) bridged by single end-to-end azides were prepared via a self-assembly process. Each Mn(III) ion exhibits a characteristic Jahn-Teller elongation along the chain direction. For both compounds, antiferromagnetic interactions between Mn(III) spins within a chain are transmitted through the azide ligands, together with the apparent occurrence of spin canting at low temperatures. Remarkably, the coupling constants (J) for 1 and 2 exceed those reported for end-to-end azide-linked Mn(III) systems. A systematic magnetostructural relationship based on the torsion angle is established in terms of the torsion angle Mn-N(ax)···N(ax)-Mn (ax = axial) for the first time.

pH-dependent proton conducting behavior in a metal-organic framework material.

A porous metal-organic framework (MOF), [Ni2(dobdc)(H2O)2]⋅6 H2O (Ni2(dobdc) or Ni-MOF-74; dobdc(4-)=2,5-dioxido-1,4-benzenedicarboxylate) with hexagonal channels was synthesized using a microwave-assisted solvothermal reaction. Soaking Ni2(dobdc) in sulfuric acid solutions at different pH values afforded new proton-conducting frameworks, H(+)@Ni2(dobdc). At pH 1.8, the acidified MOF shows proton conductivity of 2.2×10(-2) S cm(-1) at 80 °C and 95% relative humidity (RH), approaching the highest values reported for MOFs. Proton conduction occurs via the Grotthuss mechanism with a significantly low activation energy as compared to other proton-conducting MOFs. Protonated water clusters within the pores of H(+)@Ni2(dobdc) play an important role in the conduction process.

Cyanide-bridged W(V)Mn(III) bimetallic chains composed of a blocked W hexacyanide precursor: geometry-related magnetic couplings and magnetostructural correlation.

Five one-dimensional bimetallic W(V)Mn(III) complexes 1-5, consisting of [W(CN)6(bpy)](-) anions and [Mn(Schiff base)](+) cations, were prepared. The central coordination geometry around each W atom is determined as a distorted dodecahedron (DD) for 1 and 2, and a distorted square antiprism (SAPR) for 3-5. Magnetic analyses demonstrate that compounds 1, 4, and 5 exhibit antiferromagnetic interactions between magnetic centers, which are different from the ferromagnetic couplings in 2 and 3. For the distorted DD geometry, the Mn-N(ax) (ax = axial) bond length increases when moving from 1 to 2, with the Mn-N(ax)-C(ax) angle remaining constant. The elongation of the bond length is responsible for the reduction in orbital overlap and consequent ferromagnetic coupling in 2. In comparison, for 3-5 with the distorted SAPR geometry, given that the Mn-N(ax) bond lengths are similar across all the samples, the increase in the Mn-N(ax)-C(ax) angles accounts for the enhanced magnetic strength. Notably, a correlation between structure and magnetic exchange coupling is established for the first time in W(V)Mn(III) bimetallic systems based on the [W(CN)6(bpy)](-) precursor.

Reversible crystal-to-amorphous structural conversion in the single end-on azide-bridged Co(II) complex: concomitant color and magnetic modulations.

Crystal clear: An end-on (EO) azide-bridged Co(II) layer (see scheme; 1) with coordinated water molecules, long spacer p-XBP4 ligands, and unbound azide anions was evacuated to generate a dehydrated sample of 2. A reversible crystal-to-amorphous structural transformation accompanied by color and magnetic changes takes place between 1 and 2 by using a desolvation-solvation protocol.

One-dimensional end-to-end azide-bridged Mn(III) complexes incorporating alkali metal ions: slow magnetic relaxations and metamagnetism.

Three azide-bridged Mn(III) chains [Mn(3-MeOsalpn)(N(3))]⋅0.5 AClO(4) (A = Na (1), K (2), Rb (3); 3-MeOsalpn = N,N'-propylenebis(3-methoxysalicylideneiminato) dianion) incorporating alkali metal ions and perchlorate anions were systematically synthesized. The overall structure can be described as a one-dimensional chain bridged by end-to-end azide ligands, although spatial arrangements of Jahn-Teller axes of Mn in 1 and 2 are different from that in 3. Relying on the alkali metal ions, magnetic properties are varied from a two-step phase transition (1) to metamagnetic transitions (2 and 3). In this system, spin canting definitely plays a central role in giving rise to the apparent slow magnetic relaxations in 1 and 2 because application of a high external magnetic field tends to destroy single-chain magnet (SCM) properties. Despite the existence of a long-range antiferromagnetic order at T(N) , slow magnetic relaxation is notably observed in 2, which likely emanates from the operative spin canting below T(N) .

Cyano-bridged pentanuclear and honeycomblike M(III)Cu(II) (M = Fe, Cr) bimetallic assemblies: structural variations modulated by side groups of macrocyclic ligands and magnetic properties.

Three two-dimensional (2D) layered M(III)-Cu(II) (M = Fe, Cr) bimetallic complexes and a discrete cluster were prepared using [M(CN)(6)](3-) and respective Cu macrocycles with methyl (1, 3) or ethyl (2, 4) side groups. The crystal structures can be described as aesthetic honeycomb-like M(2)Cu(3) neutral sheets (1, 3, 4) and a pentanuclear Fe(2)Cu(3) entity (2) with an isolated Cu(L2)(2+) moiety. The steric hindrance induced by the pendant groups renders the internal parameters of the Cu-N(ax) (where the "ax" subscript denotes axial) length and Cu-N(ax)-C(ax) angle to become elongated and acute. The magnetic data disclose that ferromagnetic couplings are transmitted between M(III) and Cu(II) ions through the CN links. For 4, particularly, there is a magnetically defined chain (J(c)) composed of dimers (J(d)) and trimers (J(t)), based on the structural considerations. The intramolecular magnetic coupling constants are J(d) = 3.73 cm(-1) and J(t) = 4.08 cm(-1), while the J(c) value corresponds to 0.17 cm(-1). From a magnetostructural point of view, it is reasoned that the Cu-N(ax) bond length is probably a determining factor of the strength of magnetic couplings in 4.

End-to-end azide-bridged manganese(III) chain compounds: field-induced magnetic phase transitions and variation of T(C) to 38 K depending on the side groups of the Schiff bases.

Three one-dimensional coordination polymers [Mn(L)(N(3))](n) [L = L1 (1), L2 (2), L3 (3); L1H(2) = N,N'-bis(5-chlorosalicylideneiminato)-1,3-diaminopentane, L2H(2) = N,N'-bis(5-bromosalicylideneiminato)-1,3-diaminopentane, L3H(2) = N,N'-bis(5-bromosalicylideneiminato)-1,3-diamino-2-dimethylpropane] bridged by end-to-end azides were prepared. The crystal systems differ according to the Schiff bases used. Each Mn atom adopts a typical Jahn-Teller distortion. The helicity of the chains occurs in a racemic manner only for 2. No noncovalent forces are relevant in 2, while π-π contacts are visible in 1 and 3. Magnetic measurements show the presence of apparent spin canting. Complexes 1 and 3 exhibit a field-induced metamagnetic transition from an antiferromagnetic state to a weak ferromagnetic phase, whereas 2 embraces a field-induced two-step magnetic phase transition. The critical temperature is observed at 38 K for 2, which is relatively higher than those for 1 (11 K) and 3 (10 K). The pronounced long-range order may contribute from intrachain exchange couplings and through-space dipolar interactions between adjacent chains.

Cyanide-bridged W(V)Mn(III) single-chain magnet with isolated Mn(III) moieties exhibiting two types of relaxation dynamics.

A 5d-3d bimetallic compound was prepared by self-assembling [W(CN)(8)](3-) and the Mn(III) Schiff bases. This neutral complex consists of cyanide-linked W(V)Mn(III) anionic chains and isolated Mn(III) Schiff base cations. We demonstrate that two types of relaxation processes are involved in the system; the low-T dynamics may come from magnetic domain dynamics and the high-T relaxation stems from the anionic chain, revealing single-chain magnet character.

Microporous lanthanide-organic frameworks with open metal sites: unexpected sorption propensity and multifunctional properties.

Isostructural lanthanide-organic frameworks were prepared by a solvothermal reaction of the corresponding metal ions and the phosphine-oxide-based tricarboxylate ligand. The gravimetric gas uptake was unexpectedly increased when going from Nd(3+) to Gd(3+), which is associated with the enhanced surface areas and electrostatic interactions between exposed metal ions and gas molecules with quadrupole moments.

Cyanide-bridged Fe(III)-Mn(III) bimetallic systems assembled from the fac-Fe tricyanide and Mn Schiff bases: structures, magnetic properties, and density functional theory calculations.

Reaction of [(Tp)Fe(CN)(3)](-) [Tp = hydrotris(pyrazolyl)borate] with respective Mn(III) Schiff bases led to the formation of four dimeric molecules, [(Tp)Fe(CN)(3)][Mn(1-napen)(H(2)O)].MeCN.4H(2)O [1; 1-napen = N,N'-ethylenebis(2-hydroxy-1-naphthylideneiminato) dianion], [(Tp)Fe(CN)(3)][Mn(5-Clsalen)(H(2)O)] [2; 5-Clsalcy = N,N'-(trans-1,2-cyclohexanediylethylene)bis(5-chlorosalicylideneiminato) dianion], [(Tp)Fe(CN)(3)][Mn(2-acnapen)(MeOH)].MeOH [3; 2-acnapen = N,N'-ethylenebis(1-hydroxy-2-acetonaphthylideneiminato) dianion], [(Tp)Fe(CN)(3)][Mn(3-MeOsalen)(H(2)O)] [4; 3-MeOsalen = N,N'-ethylenebis(3-methoxysalicylideneiminato) dianion], and a one-dimensional (1D) zigzag chain [(Tp)Fe(CN)(3)][Mn(2-acnapen)].H(2)O (5). The dimers contain multiple intermolecular interactions such as hydrogen bonds, face-to-face pi-pi contacts, and edge-to-face CH-pi forces, raising molecular dimensions from one-dimensional (1D) up to three-dimensional (3D) arrays, whereas there are no pi-pi stacking interactions in the 1D chain compound. Magnetic measurements reveal that ferromagnetic couplings are obviously operative between Mn(III) and Fe(III) spin centers transmitted by CN bridges for 1-3 and 5, and antiferromagnetic interactions are however unexpectedly present in 4. On the basis of the proper spin Hamiltonians, magnetic exchange couplings are estimated to be in the span from 1.79 to 7.48 cm(-1) for the ferromagnetically coupled systems and -1.40 cm (-1) for the antiferromagnetic dimer. A slow magnetic relaxation is tangible in 5, which is in connection with isolated chains devoid of any intermolecular noncovalent interactions. Density Functional Theory (DFT) calculations and comparison of structural parameters suggest that the observed magnetic behaviors are mainly associated with the bending of the Mn-N[triple bond]C angle in the bridging pathway.

An end-on azide-bridged antiferromagnetic single-chain magnet involving spin canting and field-induced two-step magnetic transitions.

Two-step magnetic transitions: An azide-bridged 1D Mn(III) coordination polymer with a unique single end-on mode was prepared; it displayed atypical antiferromagnetic couplings and field-induced two-step magnetic transitions (see figure). The spin-canted phenomenon in the antiferromagnetic chain complex plays a pivotal role in establishing the slow magnetic relaxation.

One-dimensional cyanide-bridged Mn(III)W(V) bimetallic complexes: metamagnetism, spontaneous resolution, and slow magnetic relaxation.

The reaction of [W(CN)(6)(bpy)](-) with the corresponding Mn Schiff bases led to the formation of two antiferromagnetic (1) and ferromagnetic (2) chains. The formation of the conglomerate (2) is associated with chiral induction by the enantiomeric chelate-ring conformation of the Mn Schiff base. Modulation of the linking groups in the Mn Schiff bases affects the interchain contacts, causing alteration of the magnetic behaviors from metamagnetism (1) to slow magnetic relaxation (2).

Octacyanometalate-based ferrimagnetic M(V)Mn(III) (M = Mo, W) bimetallic chain racemates with slow magnetic relaxations.

Cyanide-bridged M(V)-Mn(III) (M = Mo, W) bimetallic chain complexes with racemic spatial dispositions were constructed by self-assembling [M(CN)(8)](3-) precursors and Mn(III) Schiff bases. Antiferromagnetic couplings between spin centers within a chain result in a ferrimagnetic nature, and slow magnetic relaxations are observed as well.

Cyanide-bridged Fe(III)-Mn(III) bimetallic complexes with dimeric and chain structures constructed from a newly made mer-Fe tricyanide: structures and magnetic properties.

Four cyanide-linked Fe(III)-Mn(III) complexes were prepared by reacting Mn Schiff bases with a new molecular precursor (PPh(4))[Fe(qcq)(CN)(3)] [1; qcq = 8-(2-quinolinecarboxamido)quinoline anion]. They include a dimeric molecule, [Fe(qcq)(CN)(3)][Mn(3-MeOsalen)(H(2)O)] x 2 H(2)O [2 x 2 H(2)O; 3-MeOsalen = N,N'-ethylenebis(3-methoxysalicylideneiminato) dianion], and three 1D zigzag chains, [Fe(qcq)(CN)(3)][Mn(5-Clsalen)] x 3 H(2)O [3 x 2 MeOH; 5-Clsalen = N,N'-ethylenebis(5-chlorosalicylideneiminato) dianion], [Fe(qcq)(CN)(3)][Mn(5-Brsalen)] x 2 MeOH [4 x 2 MeOH; 5-Brsalen = N,N'-ethylenebis(5-bromosalicylideneiminato) dianion], and Fe(qcq)(CN)(3)][Mn(salen)].MeCN x H(2)O [5 x MeCN; salen = N,N'-ethylenebis(salicylideneiminato) dianion]. The complexes consist of extensive hydrogen bonding and pi-pi stacking interactions, generating multidimensional structures. Magnetic studies demonstrate that antiferromagnetic couplings are operative between Fe(III) and Mn(III) centers bridged by cyanide ligands. On the basis of an infinite chain model, magnetic coupling parameters of 2-5 range from -9.3 to -14.1 cm(-1). A long-range order is observed at 2.3 K for 3 and 2.2 K for 4, while compound 5 shows spin glass behavior possibly coupled with magnetic ordering.

Exceptional CO2 working capacity in a heterodiamine-grafted metal-organic framework.

An amine-functionalized metal-organic framework (MOF), dmen-Mg2(dobpdc) (dmen = N,N-dimethylethylenediamine), which contains a heterodiamine with both primary and tertiary amines, was prepared via a post-synthetic method. This material exhibits a significant selectivity factor for CO2 over N2 that is commensurate with top-performing MOFs. It is remarkable that the solid is fully regenerated under vacuum or flowing Ar at low desorption temperatures, and following this can take up CO2 at more than 13 wt%. An exceptionally high working capacity is achieved at low regeneration temperatures and after exposure to humid conditions, which are important parameters for a real post-combustion CO2 capture process.

Dehydration-triggered magnetic phase conversion in the porous Cu(II)Mn(III) metal-organic framework.

Dehydration of the three-dimensional Cu(II)-Mn(III) coordination network undergoes a dramatic magnetic phase transformation from a paramagnetic state to a long-range magnetic ordered phase with glassy behavior. The gas adsorption behavior and re-entrant spin glass character are uniquely apparent in the dehydrated sample.

Reversible structural transformation and selective gas adsorption in a unique aqua-bridged Mn(II) metal-organic framework.

An aqua-bridged Mn metal-organic framework was prepared, and a dramatic structural transformation occurs upon solvent exchange-resolvation and desolvation-resolvation processes. The desolvated phase, formed by removing the aqua bridges, exhibits selective CO(2) uptake over N(2), H(2), and CH(4). Further, antiferromagnetic couplings are also found between Mn spins in the secondary building units.

Synthesis, structures and magnetic characterizations of isostructural tetranuclear Ln4 clusters (Ln = Dy, Ho, and Eu).

Isostructural tetranuclear clusters [Ln4(salen)6]·xH2O [Ln = Dy, 1·5.5H2O; Ho, 2·4.6H2O; Eu, 3·5.2H2O; salen = N,N'-ethylenebis(salicylideneiminato)dianion] were prepared by self-assembling the corresponding lanthanide ions and a quadridentate Schiff base. Interestingly, the Ln ions are surrounded by the N- and O-donors of the Schiff bases, leading to seven- and eight-coordinate environments. The heptacoordinated Ln centers adopt a distorted capped trigonal prism, while the octacoordinated Ln atoms are in a dodecahedral disposition. The Dy complex exhibits slow magnetic relaxation, characteristic of a single-molecule magnet. Two relaxation modes in the Dy system are evident when H(dc) = 1.4 kG is applied, which is attributable to the existence of the dissimilar coordination geometries around Dy. In comparison, the Ho and Eu analogues were magnetically inspected, displaying no typical slow magnetic relaxation. These findings elucidate that the metal component in the system plays a central role in the occurrence of the magnetization relaxation process. The pronounced long-range order may contribute to intrachain exchange couplings and through-space dipolar interactions between adjacent chains.

Syntheses, structures, and magnetic properties of cyano- and phenoxide-bridged Fe(III)-Mn(III) tetrameric assemblies formed by blocked fac-Fe tricyanide with aliphatic rings.

Three tetranuclear clusters [(Tp(Me,mt3))Fe(CN)3Mn(L)]2 (1, L = 5-Clacphmen; 2, L = 5-Clsalen; 3, L = 5-MeOsalen; Tp(Me,mt3) = hydrotris(3-methyl-4,5-propylene-5-methylpyrazol-1-yl)borate) were prepared by assembling the fac-Fe tricyanide with the corresponding Mn Schiff bases. The assembled molecules are linked by cyanide and phenoxide bridges. Weak π-π contacts between molecules are evident in these clusters. Compounds 1-3 exhibit slow relaxation of the magnetization. The phenoxide linkers mediate ferromagnetic coupling between the Mn centers, which is ascribed to the long axial Mn-O* length. The overall magnetic exchange coupling nature of the Fe-C≡N-Mn route is accounted for by the important structural parameters of bridging pathways such as Mn-N(cyano) length, Mn-N(cyano)-C(cyano) angle, and C(eq)-Fe···Mn-N(eq) (eq = equatorial) torsion angle.