Unlocking single molecule magnetism: a supramolecular strategy for isolating neutral MnIII salen-type dimer in crystalline environments.

In [Mn(5-MeOsalen)(Cl)]2(dibenzo[24]crown-8), dibenzo[24]crown-8 formed a supramolecule via multi-point interactions with the [Mn(5-MeOsalen)(Cl)] dimer. The dimer was magnetically isolated with ST = 4 and weak interdimer magnetic interactions. The crystal exhibited single-molecule magnet behaviour with an anisotropic barrier of 26(1) K, which is the highest among the Mn-salen series reported to date.

Correction: Post-synthetic molecular modifications based on Schiff base condensation reactions for designing functional paddlewheel diruthenium(II,II) complexes.

Correction for 'Post-synthetic molecular modifications based on Schiff base condensation reactions for designing functional paddlewheel diruthenium(II,II) complexes' by Chisa Itoh et al., Dalton Trans., 2024, 53, 444-448.

Post-synthetic molecular modifications based on Schiff base condensation reactions for designing functional paddlewheel diruthenium(II,II) complexes.

A new synthetic route for constructing functional paddlewheel diruthenium(II,II) complexes ([RuII,II2]) was developed by utilizing Schiff base condensation reactions of formyl-substituted benzoate-bridged [RuII,II2] complexes with various aromatic monoamines under mild conditions. Cyclic voltammetry and DFT calculations revealed that the attached Schiff base groups significantly affected the electronic states of the resulting [RuII,II2] complexes.

CO2-Sensitive Porous Magnet: Antiferromagnet Creation from a Paramagnetic Charge-Transfer Layered Metal-Organic Framework.

Porous magnets that undergo a magnetic phase transition in response to gaseous adsorbates are desirable for the development of sustainable sensing and memory devices. Familiar gases such as O2 and CO2 are one class of target adsorbates because of their close association with life sciences and environmental issues; however, it is not easy to develop magnetic devices that respond to these ubiquitous gases. To date, only three examples of gas-responsive magnetic phase transitions have been demonstrated: (i) from a ferrimagnet to an antiferromagnet, (ii) its vice versa (i.e., change of magnetic phase), and (iii) from a ferrimagnet to a paramagnet (i.e., erasure of the magnetic phase). However, the creation of a magnet, meaning the change from a nonmagnet to a magnet by O2 or CO2 gas adsorption and magnetic switching by this phenomenon have not yet been explored. Herein, we report a CO2-induced antiferromagnet modified from a paramagnetic charge-flexible layered compound, [{Ru2(2,4-F2PhCO2)4}2TCNQ(OEt)2] (1; 2,4-F2PhCO2- = 2,4-difluorobenzoate; TCNQ(OEt)2 = 2,5-diethoxy-7,7,8,8-tetracyanoquinodimethane), where three molar equivalents of CO2 was accommodated at a CO2 pressure of 100 kPa. The magnetic change originates from charge fluctuation due to the transfer of electrons moving from the electron-donor to the electron-acceptor unit or vice versa, resulting in a change in the electron distribution induced by CO2 adsorption/desorption in the donor-acceptor-type charge transfer framework. Owing to the reversible electronic state change upon CO2 adsorption/desorption, these magnetic phases are switched, accompanied by modification of the electrical conductivity, which is boosted by the CO2 accommodation. This is the first example of the creation of a CO2-responsive magnet, which is promising for novel molecular multifunctional devices.

Densely Packed CO2 Aids Charge, Spin, and Lattice Ordering Partially Fluctuated in a Porous Metal-Organic Framework Magnet.

Partial charge fluctuations in the charge-ordered state of a material, often triggered by structural disorders and/or defects, can significantly alter its physical characteristics, such as magnetic long-range ordering. However, it is difficult to post-chemically fix such accidental partial fluctuations to reconstruct a uniform charge-ordered state. Herein, we report CO2 -aided charge ordering demonstrated in a CO2 -post-captured layered magnet, [{Ru2 (o-ClPhCO2 )4 }2 {TCNQ(OMe)2 }] ⋅ CO2 (1⊃CO2 ; o-ClPhCO2 - =ortho-chlorobenzoate; TNCQ(OMe)2 =2,5-dimethoxy-7,7,8,8-tetracyanoquinodimethane). Pristine porous layered magnet 1 had a partially charge-fluctuated ordered state, which provided ferrimagnetic ordering at TC =65 K. Upon loading CO2 , 1 adsorbed one mole of CO2 , forming 1⊃CO2 , and raising TC to 100 K. This was because of the vanishing charge fluctuations without significantly changing the framework structure. This research illustrates the post-accessible host-guest chemistry delicately combined with charge, spin, and lattice ordering in a spongy magnet. Furthermore, it highlights how this innovative approach opens up new possibilities for technology and nanoscale magnetism manipulation.

Guest-induced pore breathing controls the spin state in a cyanido-bridged framework.

Iron(ii) spin cross-over (SCO) compounds combine a thermally driven transition from the diamagnetic low-spin (LS) state to the paramagnetic high-spin (HS) state with a distinct change in the crystal lattice volume. Inversely, if the crystal lattice volume was modulated post-synthetically, the spin state of the compound could be tunable, resulting in the inverse effect for SCO. Herein, we demonstrate such a spin-state tuning in a breathing cyanido-bridged porous coordination polymer (PCP), where the volume change resulting from guest-induced gate-opening and -closing directly affects its spin state. We report the synthesis of a three-dimensional coordination framework {[FeII(4-CNpy)4]2[WIV(CN)8]·4H2O}n (1·4H2O; 4-CNpy = 4-cyanopyridine), which demonstrates a SCO phenomenon characterized by strong elastic frustration. This leads to a 48 K wide hysteresis loop above 140 K, but below this temperature results in a very gradual and incomplete SCO transition. 1·4H2O was activated under mild conditions, producing the nonporous {[FeII(4-CNpy)4]2[WIV(CN)8]}n (1) via a single-crystal-to-single-crystal process involving a 7.3% volume decrease, which shows complete and nonhysteretic SCO at T1/2 = 93 K. The low-temperature photoswitching behavior in 1 and 1·4H2O manifested the characteristic elasticity of the frameworks; 1 can be quantitatively converted into a metastable HS state after 638 nm light irradiation, while the photoactivation of 1·4H2O is only partial. Furthermore, nonporous 1 adsorbed CO2 molecules in a gated process, leading to {[FeII(4-CNpy)4]2[WIV(CN)8]·4CO2}n (1·4CO2), which resulted in a 15% volume increase and stabilization of the HS state in the whole temperature range down to 2 K. The demonstrated post-synthetic guest-exchange employing common gases is an efficient approach for tuning the spin state in breathing SCO-PCPs.

Unprecedented highly efficient photoluminescence in a phosphorescent Ag(I) coordination polymer.

A luminescent three-dimensional coordination polymer (CP) of [CdII(pmd){AgI(CN)2}2] (1; pmd = pyrimidine) comprising two different coordination modes of Ag+ ions was synthesised herein. 1 exhibited thermochromic luminescence, accompanied by positive thermal elongation of the Ag⋯Ag distance. Moreover, 1 showed a bright phosphorescence with the highest photoluminescence quantum yield (Φem), approximately 60% at room temperature, among previously reported phosphorescent Ag-based CPs or metal-organic frameworks.

Inter-layer magnetic tuning by gas adsorption in π-stacked pillared-layer framework magnets.

Magnetism of layered magnets depends on the inter-layer through-space magnetic interactions (J NNNI). Using guest sorption to address inter-layer pores in bulk-layered magnets is an efficient approach to magnetism control because the guest-delicate inter-layer distance (l trans) is a variable parameter for modulating J NNNI. Herein, we demonstrated magnetic changes induced by the adsorption of CO2, N2, and O2 gases in various isostructural layered magnets with a π-stacked pillared-layer framework, , (M = Co, 1, Fe, 2, Cr, 3; Cp* = η5-C5Me5; 2,3,5,6-F4PhCO2 - = 2,3,5,6-tetrafluorobenzoate; TCNQ = 7,7,8,8-tetracyano-p-quinodimethane). Each compound had almost identical adsorption capability for the three types of gases; only CO2 adsorption was found to have a gated profile. A breathing-like structural modulation involving the extension of l trans occurred after the insertion of gases into the isolated pores between the [Ru2]2-TCNQ ferrimagnetic layers, which is more significant for CO2 than for O2 and N2, due to the CO2-gated transition. While adsorbent 1 with M = Co (S = 0) was an antiferromagnet with T N = 75 K, 1⊃CO2 was a ferrimagnet with T C = 76 K, whereas 1⊃N2 and 1⊃O2 were antiferromagnets with T N = 68 K. The guest-insertion effect was similarly confirmed in 2 and 3, and was characteristically dependent on the type of sandwiched spin in as M = Fe (S = 1/2) and Cr (S = 3/2), respectively. This study reveals that common gases such as CO2, O2, and N2 can serve as crucial triggers for the change in magnetism as a function of variable parameter l trans.

Considerations on Gated CO2 Adsorption Behavior in One-Dimensional Porous Coordination Polymers Based on Paddlewheel-Type Dimetal Complexes: What Determines Gate-Opening Temperatures?

Low-dimensional coordination polymers such as one-dimensional chains often exhibit gated guest sorption accompanying structural transition at a temperature (TG), which is associated with an external pressure of the guest (PG) characteristic to the material and guest used. This phenomenon can be evaluated using the Clausius-Clapeyron relationship with the equation d(ln PG)/d(1/TG) = ΔHG/R, where ΔHG and R are the transition enthalpy and gas constant, respectively. In this study, gated CO2 adsorption behavior was investigated in a one-dimensional chain based on a benzoate-bridged paddlewheel diruthenium(II,II) complex with a phenazine (phz) linker, [Ru2(p-MeOPhCO2)4(phz)] (1; p-MeOPhCO2- = p-anisate). Surprisingly, 1 underwent gate opening (GO)/closing (GC) at a much higher TG, e.g., 385 K for GC, under PCO2 = 100 kPa than those previously reported for such chain compounds, which usually appeared in the temperature range of 200-270 K. The transition entropy ΔSG in each system plays a key role in shifting TG; 1 results in a much smaller |ΔSG| in the series. Only 1 produced a CO2-accessible two-dimensional topological pore in its CO2-adsorbed phase 1⊃CO2, whereas the others reported previously produced one-dimensional or discrete topological pores for CO2 accommodation, strongly reflecting the degree of freedom of CO2 molecules in pores, which is related to ΔSG.

Syntheses, Structures, and Properties of Coordination Polymers with 2,5-Dihydroxy-1,4-Benzoquinone and 4,4'-Bipyridyl Synthesized by In Situ Hydrolysis Method.

The coordination polymers (CPs) with binary ligands, including 2,5-dihydroxy-1,4-benzoquinone (H2DHBQ) and 4,4'-bipyridyl (bpy), were synthesized using in situ hydrolysis of 2,5-dimethoxy-1,4-benzoquinone (DMBQ). Three kinds of CPs were obtained depending on the metal ions. For M = Mn and Zn, a 1D zigzag chain structure with cis conformation ( cis-1D-M) was obtained, whereas Co, Ni, and Cu compounds afforded a 2D net structure with trans conformation (trans -2D-M) with a 1D pore. A linear chain structure was also obtained for M = Cu. Magnetic susceptibility (χM T) at 300 K in cis -1D-Mn and trans -2D-Co was evaluated to be 4.421 and 2.950 cm3 K mol-1, respectively, indicating that both compounds are in the high-spin state. According to the N2 adsorption isotherms at 77 K, trans -2D-Ni showed microporosity with the BET surface area of 177 m2 g-1, whereas the isomorphic trans -2D-Co rarely adsorbed N2 at 77 K. This phenomenon was explained by the difference of diffusion kinetics of the adsorbent molecules, which was supported by the CO2 adsorption isotherms at 195 K. The optical band gaps of cis -1D-Mn, cis -1D-Zn, trans -2D-Co, and trans -2D-Ni were estimated to be 1.6, 1.8, 1.0, and 1.1 eV, respectively, by using UV-vis-NIR spectroscopy.

A Host-Guest Electron Transfer Mechanism for Magnetic and Electronic Modifications in a Redox-Active Metal-Organic Framework.

Host-guest electron transfer (HGET) in molecular framework systems is a critical trigger for drastic functional changes in both host framework and guest. A reversible magnetic phase transition was achieved via HGET in a layered framework, [{Ru2 (2,6-F2 PhCO2 )4 }2 (BTDA-TCNQ)] (1), where 2,6-F2 PhCO2 - and BTDA-TCNQ represent 2,6-difluorobenzoate and bis[1,2,5]dithiazolotetracyanoquinodimethane, respectively. The guest-free 1 with an antiferromagnetic ground state transformed into a paramagnet, [{Ru2 (2,6-F2 PhCO2 )4 }2 (BTDA-TCNQ)]I3 (1-I3 ), by adsorbing iodine (I2 ). The local charge distribution of [{Ru2 II,III }+ -(BTDA-TCNQ).- -{Ru2 II,II }] in 1 was reversibly modified to [{Ru2 II,III }+ -(BTDA-TCNQ)0 -{Ru2 II,II }](I3 - ) in 1-I3 through HGET. Theoretical calculations of 1-I3 indicated a partial charge delocalization as [{Ru2 }(1-δ)+ -(BTDA-TCNQ)0 -{Ru2 }δ+ ](I3 - ) with δ≈0.2, aided by weak ferromagnetic coupling. 1-I3 exhibited a hundred-fold enhancement in electrical conductivity compared to that of 1.

Role of intramolecular hydrogen bonding in the redox chemistry of hydroxybenzoate-bridged paddlewheel diruthenium(II,II) complexes.

The synthesis of a series of trans-heteroleptic paddlewheel diruthenium(II,II) complexes with various hydroxy-substituted benzoate ligands, [Ru2((OH)xPhCO2)2(2,6-(CF3)2PhCO2)2(THF)2] ([RuII,II2]) as tetrahydrofuran (THF) adducts is reported, where (OH)xPhCO2- stands for o-hydroxybenzoate (o-OH), m-hydroxybenzoate (m-OH), p-hydroxybenzoate (p-OH), 2,3-dihydroxybenzoate (2,3-(OH)2), 2,4-dihydroxybenzoate (2,4-(OH)2), 2,5-dihydroxybenzoate (2,5-(OH)2), 2,6-dihydroxybenzoate (2,6-(OH)2), or 3,4-dihydroxybenzoate (3,4-(OH)2), and 2,6-(CF3)2PhCO2- represents 2,6-bis(trifluoromethyl)benzoate. In this heteroleptic series, the redox potential (E1/2) of the [RuII,II2]/[RuII,III2]+ couple in THF varies over a wide range, from -18 mV (vs. Ag/Ag+) for p-OH to 432 mV for 2,6-(OH)2. The redox properties are linearly dependent on the acidity (pKa) of the OH-substituted benzoic acids, but do not depend on the number of ortho-substituted hydroxy (o-OH) groups. This indicates that the steric effect of o-substituents is irrelevant in the case of hydroxyl groups, owing to the formation of intramolecular hydrogen bonds between the o-OH group and carboxylate oxygens. The value of the Hammett constant σo for the o-OH substituent was determined to be 0.667, indicating a strongly electron-withdrawing character, contrary to the expectation of electron-donating character for an OH group. The redox properties of the compounds were well explained in a framework of Hammett analyses and were also consistent with their HOMO energy levels evaluated by DFT calculations based on the atomic coordinates. The unexpected electron-withdrawing character of the o-OH groups could be attributed to the direct effect of intramolecular hydrogen bonding on the charge density on the carboxylate oxygen.

Tunable Synchronicity of Molecular Valence Tautomerism with Macroscopic Solid-Liquid Transition by Molecular Lattice Engineering.

The combination of a cobalt-dioxolene core that exhibits valence tautomerism (VT) with pyridine-3,5-dicarboxylic acid functionalized with chains bearing two, four, or six oxyethylene units led to new complexes ConEGEspy (n = 2, 4, and 6). These complexes commonly form violet crystals of the low-spin (ls)-[CoIII (nEGEspy)2 (3,6-DTBSQ)(3,6-DTBCat)] (ls-[CoIII ], 3,6-DTBSQ = 3,6-di-tert-butyl semiquinonato, 3,6-DTBCat = 3,6-di-tert-butyl catecholato). Interestingly, violet crystals of Co2EGEspy in the ls-[CoIII ] transitioned into a green liquid, accompanied by an almost complete VT shift (94 %) to the high-spin (hs)-[CoII (nEGEspy)2 (3,6-DTBSQ)2 ] (hs-[CoII ]) upon melting. In contrast, violet crystals of Co4EGEspy and Co6EGEspy in the ls-[CoIII ] exhibited partial VT (33 %) and only a 9.3 % VT shift after melting, respectively. These data demonstrate the tunability of the synchronicity of the molecular VT and macroscopic solid-liquid transitions by optimizing the tethered chains, thus establishing a new strategy for coupling bistable molecules with the macroscopic world.

Guest-selective and reversible magnetic phase switching in a pseudo-pillared-layer porous magnet.

A novel porous magnet consisting of cationic two-dimensional (2-D) layers extended by FeIII-CN-NiII linkages and pseudo-pillar dianions was synthesized. The size-selective guest adsorption behaviour of water and methanol molecules originates from the narrow bottle-neck-type pores in the flexible pseudo-pillared-layer structure, which results in the switching of the magnetic phases from antiferromagnetic to ferromagnetic, involving significant changes in the interlayer distance.

Magnet Creation by Guest Insertion into a Paramagnetic Charge-Flexible Layered Metal-Organic Framework.

Changing nonmagnetic materials to spontaneous magnets is an alchemy-inspiring concept in materials science; however, it is not impossible. Here, we demonstrate chemical modification from a nonmagnet to a bulk magnet of either a ferrimagnet or antiferromagnet, depending on the adsorbed guest molecule, in an electronic-state-flexible layered metal-organic framework, [{Ru2(2,4-F2PhCO2)4}2TCNQ(EtO)2] (1; 2,4-F2PhCO2- = 2,4-difluorobenzoate; TCNQ(EtO)2 = 2,5-diethoxy-7,7,8,8-tetracyanoquinodimethane). The guest-free paramagnet 1 undergoes a thermally driven intralattice electron transfer involving a structural transition at 380 K. This charge modification can also be implemented by guest accommodations at room temperature; 1 adsorbs several organic molecules, such as benzene (PhH), p-xylene (PX), 1,2-dichloroethane (DCE), dichloromethane (DCM), and carbon disulfide (CS2), forming 1-solv with intact crystallinity. This induces an intralattice electron transfer to produce a ferrimagnetically ordered magnetic layer. According to the interlayer environment tuned by the corresponding guest molecule, the magnetic phase is consequently altered to a ferrimagnet for the guests PhH, PX, DCE, and DCM or an antiferromagnet for CS2. This is the first demonstration of the postsynthesis of bulk magnets using guest-molecule accommodations.

Ionicity Diagrams for Electron-Donor and -Acceptor Metal-Organic Frameworks: DA Chains and D2A Layers Obtained from Paddlewheel-Type Diruthenium(II,II) Complexes and Polycyano-Organic Acceptors.

Recent developments in research concerning metal-organic frameworks and coordination polymers have provided the successful design of charge-variable molecular frameworks. However, few comprehensive studies exist that investigate the control of charge states in series of molecular frameworks such as these. Herein, we discuss the ionicity diagrams of two series containing electron-donor (D) and -acceptor (A) units: one-dimensional DA chains and two-dimensional D2A layers. The series were obtained by reacting paddlewheel-type diruthenium(II,II) complexes ([Ru2II,II]), which served as D units, with the polycyano-organic acceptors N,N'-dicyanoquinodiimine (DCNQI) and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ), which served as A units. Fifteen novel members of neutral charged DA chains were fabricated in this study to characterize the ionicity diagrams for DA and D2A systems.

A metal-organic framework that exhibits CO2-induced transitions between paramagnetism and ferrimagnetism.

With adequate building blocks, metal-organic frameworks (MOFs) can combine magnetic ordering and porosity. This makes MOFs a promising platform for the development of stimuli-responsive materials that show drastically different magnetic properties depending on the presence or absence of guest molecules within their pores. Here we report a CO2-responsive magnetic MOF that converts from ferrimagnetic to paramagnetic on CO2 adsorption, and returns to the ferrimagnetic state on CO2 desorption. The ferrimagnetic material is a layered MOF with a [D+-A--D] formula, produced from the reaction of trifluorobenzoate-bridged paddlewheel-type diruthenium(II) clusters as the electron donor (D) with diethoxytetracyanoquinodimethane as the electron acceptor (A). On CO2 uptake, it undergoes an in-plane electron transfer and a structural transition to adopt a [D-A-D] paramagnetic form. This magnetic phase change, and the accompanying modifications to the electronic conductivity and permittivity of the MOF, are electronically stabilized by the guest CO2 molecules accommodated in the framework.

Molecular motion in the nanospace of MOFs upon gas adsorption investigated by in situ Raman spectroscopy.

Molecular motions taking place in the nanospace of metal-organic frameworks (MOFs) are an interesting research subject, although not yet fully investigated. In this work, we utilized in situ Raman spectroscopy in the ultralow-frequency region to investigate the libration motion (including the rotational motion of phenylene rings) of MOFs, in particular [Cu2(bdc)2(dabco)] (Cu-JAST-1), where bdc = 1,4-benzenedicarboxylate and dabco = 1,4-diazabicyclo[2.2.2]octane. The libration mode of Cu-JAST-1 was found to be significantly suppressed by the adsorption of various guest molecules, such as CO2, Ar, and N2. In addition, an appreciable correlation between the libration mode and adsorption equilibrium time was identified, which provides useful novel tools in the design of MOFs acting as molecular adsorption and separation materials.

Coordination distortion induced water adsorption in hydrophobic flexible metal-organic frameworks.

Herein, we synthesized four isostructural flexible interdigitated hydrophobic metal-organic frameworks that differ only in their central metal ion. The water-adsorption properties are dependent on the metal species, which was revealed to be caused by coordination distortion around the metal ions.

Magnetic Correlation Engineering in Spin-Sandwiched Layered Magnetic Frameworks.

The insertion of "sandwiched spins" between magnetic layers could efficiently affect the interlayer magnetic correlations, but doing so increases the complexity in the interlayer spin alignment because of competition between the inserted spin-layer interaction JNNI and the interlayer through-space interaction JNNNI if the magnitude of JNNI is of the same order as JNNNI with reciprocal signs of the respective interactions. Herein, systematic tuning of the magnetic phase variations by JNNI and JNNNI in two kinds of metal-variable isostructural series of supramolecular pillared layer magnets [MCp*2 ][{Ru2 II,II (2,3,5,6-F4 CO2 )4 }2 (TCNQ)]⋅2 DCE (M=Co, Fe, Cr; 2,3,5,6-F4 PhCO2 - =2,3,5,6-tetrafluorobenzoate; TCNQ=7,7,8,8-tetracyano-p-quinodimethane; DCE=1,2-dichloroethane) and their DCE-free series, in which [MCp*2 ]+ (Cp*=η5 -C5 Me5 ) species with S=0, 1/2, and 3/2 for M=Co, Fe, Cr, respectively, are sandwiched between ferrimagnetic layers of [{Ru2 }2 (TCNQ)]- , is demonstrated. The results showed that the flexible magnetic natures of these magnets are changeable in dependence on JNNI and JNNNI , as well as on interlayer inserted spins M.