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Using light as a local heat source to induce a temporary pyroelectric current is widely recognized as an effective way to control the polarization of crystalline materials. In contrast, harnessing light directly to modulate the polarization of a crystal via excitation of the electronic bands remains less explored. In this study, we report an Fe

Some cyanide-bridged complexes are known for exhibiting slow magnetic relaxation behavior in a light-induced metastable state. Herein, an unexpected reverse effect is observed for the first time in the S= 1 / 2 {FeII LS -CoIII LS -FeIII LS } (HS=high spin, LS=low spin) ground state of a novel V-shaped trinuclear cyanide-bridged {Fe2 Co} complex. In this complex, light-switchable iron-cobalt charge transfer with repeatable off/on switching of slow magnetic relaxation is discovered upon alternating laser irradiation at 785 and 560 nm. An important characteristic of the present compound is that the S= 1 / 2 ground state exhibits slow magnetic relaxation before irradiation, whereas this is accelerated after irradiation. This is different from the typical behavior, where the light-induced metastable state exhibits slow magnetic relaxation.

Materials demonstrating unusual large positive and negative thermal expansion are fascinating for their potential applications as high-precision microscale actuators and thermal expansion compensators for normal solids. However, manipulating molecular motion to execute huge thermal expansion of materials remains a formidable challenge. Here, we report a single-crystal Cu(II) complex exhibiting giant thermal expansion actuated by collective reorientation of imidazoliums. The circular molecular cations, which are rotationally disordered at a high temperature and statically ordered at a low temperature, demonstrate significant reorientation in the molecular planes. Such atypical molecular motion, revealed by variable-temperature single crystal X-ray diffraction and solid-state NMR analyses, drives an exceptionally large positive thermal expansion and a negative thermal expansion in a perpendicular direction of the crystal. The consequent large shape change (~10%) of bulk material, with remarkable durability, suggests that this complex is a strong candidate as a microscale thermal actuating material., Designing materials with large thermal expansion is highly desirable to fabricate microscale devices. The authors report unusually large anisotropic negative and positive thermal expansion in a simple crystalline material, through temperature-driven orientation of imidazole cations acting as molecular wheels.

Water reorientation is essential in a wide range of chemical and biological processes. However, the effects of such reorientation through rotation around the metal–oxygen bond on the chemical and physical properties of the resulting complex are usually ignored. Most studies focus on the donor property of water as a recognized σ donor-type ligand rather than a participant in the π interaction. Although a theoretical approach to study water-rotation effects on the functionality of a complex has recently been conducted, it has not been experimentally demonstrated. In this study, we determine that the magnetic anisotropy of a Co(II) complex can be effectively controlled by the slight rotation of coordinating water ligands, which is achieved by a two-step structural phase transition. When the water molecule is rotated by 21.2 ± 0.2° around the Co–O bond, the directional magnetic susceptibility of the single crystal changes by approximately 30% along the a-axis due to the rotation of the magnetic anisotropy axis through the modification of the π interaction between cobalt(II) and the water ligand. The theoretical calculations further support the hypothesis that the reorientation of water molecules is a key factor contributing to the magnetic anisotropy transition of this complex. Little is known about how the orientation of coordinated water molecules affects the magnetic properties of single molecule magnets. Here the authors combine experimental data and theoretical calculations to study how the rotation of water molecules alters the magnetic anisotropy of a pyrazine-based cobalt(II) complex.

Orbital angular momentum plays a vital role in various applications, especially magnetic and spintronic properties. Therefore, controlling orbital angular momentum is of paramount importance to both fundamental science and new technological applications. Many attempts have been made to modulate the ligand-field induced quenching effects of orbital angular momentum to manipulate magnetic properties. However, to date, reported changes in the magnitude of orbital angular momentum are small in both molecular and solid-state magnetic materials. Moreover, no effective methods currently exist to modulate orbital angular momentum. Here, we report a dynamic bond approach to realize a large change in orbital angular momentum. We have developed a Co(II) complex that exhibits coordination number switching between six and seven. This cooperative dynamic bond switching induces considerable modulation of the ligand field, thereby leading to substantial quenching and restoration of the orbital angular momentum. This switching mechanism is entirely different from those of spin-crossover and valence tautomeric compounds, which exhibit switching in spin multiplicity.

An octacoordinated Fe(II) complex, [FeII(dpphen)2](BF4)2·1.3H2O (1; dpphen = 2,9-bis(pyrazol-1-yl)-1,10-phenanthroline), with a pseudo-D2d-symmetric metal center has been synthesized. Magnetic, high-frequency/-field electron paramagnetic resonance (HF-EPR), and theoretical investigations reveal that 1 is characterized by uniaxial magnetic anisotropy with a negative axial zero-field splitting (ZFS) (D ≈ -6.0 cm-1) and a very small rhombic ZFS (E ≈ 0.04 cm-1). Under applied dc magnetic fields, complex 1 exhibits slow magnetic relaxation at low temperature. Fitting the relaxation time with the Arrhenius mode combining Orbach and tunneling terms affords a good fit to all the data and yields an effective energy barrier (17.0 cm-1) close to the energy gap between the ground state and the first excited state. The origin of the strong uniaxial magnetic anisotropy for 1 has been clearly understood from theoretical calculations. Our study suggests that high-coordinated compounds featuring a D2d-symmetric metal center are promising candidates for mononuclear single-molecule magnets.

Flexible porous materials generally switch their structures in response to guest removal or incorporation. However, the design of porous materials with empty shape-switchable pores remains a formidable challenge. Here, we demonstrate that the structural transition between an empty orthorhombic phase and an empty tetragonal phase in a flexible porous dodecatuple intercatenated supramolecular organic framework can be controlled cooperatively through guest incorporation and thermal treatment, thus inducing empty shape-memory nanopores. Moreover, the empty orthorhombic phase was observed to exhibit superior thermoelasticity, and the molecular-scale structural mobility could be transmitted to a macroscopic crystal shape change. The driving force of the shape-memory behaviour was elucidated in terms of potential energy. These two interconvertible empty phases with different pore shapes, that is, the orthorhombic phase with rectangular pores and the tetragonal phase with square pores, completely reject or weakly adsorb N2 at 77 K, respectively., Designing porous materials with empty shape-switchable pores remains a formidable challenge. Here, the authors fabricate a supramolecular organic framework possessing empty shape-memory nanopores which operates via a ferroelastic transition, endowing it with switchable sorption properties.

Network structures based on Star-of-David catenanes with multiple superior functionalities have been so far elusive, although numerous topologically interesting networks are synthesized. Here, a metal-organic framework featuring fused Star-of-David catenanes is reported. Two triangular metallacycles with opposite handedness are triply intertwined forming a Star-of-David catenane. Each catenane fuses with its six neighbors to generate a porous twofold intercatenated gyroid framework. The compound possesses exceptional stability and exhibits multiple functionalities including highly selective CO

The development of magnetic molecules with long spin reversal/decoherence times highly depends on the understanding of relaxation behavior under different external conditions. Herein, a magnetic study on a RuIII complex (1) is presented. Detailed analysis of the relaxation time and the magneto-heat capacity data suggests that the resonant phonon trapping process dominates the magnetic relaxation in the crystalline sample of 1, slowing down the spin relaxation rate, as further confirmed by the measurements on a ground sample and frozen solution. Thus, it provides a rare example showing that 4d metal-centered mononuclear compounds without second-order anisotropy can display slow magnetic relaxation.

Six novel complexes, namely, {[Zn1.5(L)(bix)1.5(H2O)]·H2O}n (1), {[Co1.5(L)(bix)1.5(H2O)]·H2O}n (2), {[Co3(L)2(4,4′-bpy)3]·5H2O}n (3), {[Cd3(L)2(4,4′-bpy)3]·4.5H2O}n (4), {[Cu3(L)2(4,4′-bpy)3]·3H2O}n (5), and {[Ni1.5(L)(4,4′-bpy)1.5(H2O)3]·2H2O}n (6) have been synthesized by the hydrothermal reaction of 5-(4-carboxy-2-nitrophenoxy)isophthalic acid (H3L) with different transition metal ions in the presence of ancillary ligands, 1,4-bis(imidazol-1-ylmethyl)benzene (bix) and 4,4′-bipyridine (4,4′-bpy). Complexes 1 and 2 are isostructural, possessing a (3,8)-connected tfz-d type topology with the Schlafli symbol of {43}2{46·618·84}. The 3D structures of complexes 3–5 are very similar to complex 1 with only a little difference of the H3L coordination motif in complexes 4 and 5. Meanwhile, we use 4,4′-bpy instead of bix as the ancillary ligand in all three complexes. Complex 6 is a mixed one-dimensional chain and two-dimensional sheet structure, which are further linked to each other in a three-dimensional fram...

Proton transport via dynamic molecules is ubiquitous in chemistry and biology. However, its use as a switching mechanism for properties in functional molecular assemblies is far less common. In this study, we demonstrate how an intra-carboxyl proton shuttle can be generated in a molecular assembly akin to a rack-and-pinion cascade via a thermally induced single-crystal-to-single-crystal phase transition. In a triply interpenetrated supramolecular organic framework (SOF), a 4,4′-azopyridine (azpy) molecule connects to two biphenyl-3,3′,5,5′-tetracarboxylic acid (H4BPTC) molecules to form a functional molecular system with switchable mechanical properties. A temperature change reversibly triggers a molecular movement akin to a rack-and-pinion cascade, which mainly involves 1) an intra-carboxyl proton shuttle coupled with tilting of the azo molecules and azo pedal motion and 2) H4BPTC translation. Moreover, both the molecular motions are collective, and being propagated across the entire framework, leading to a macroscopic crystal expansion and contraction.

Two polymorphic structures have been well determined in a valence tautomeric (VT) dinuclear cobalt complex. These polymorphs showdistinct thermal and photo magnetic behaviors, and are thus, ideal for studyingthe "pure" intermolecular factors to VT transitions. In polymorph 1A, the VT cations are arranged head-to-waist with their neighbors and exhibit weak pai-pai interactions, resulting in a gradual and incomplete thermal VT transition. In contrast, the cations in polymorph 1B are arranged head-to-tail and exhibit relatively strong pai-pai interactions, leading to an abrupt and complete thermal VT transition with adjustable hysteresis loop at around room temperature. The VT process for both polymorphs can be induced by light, but the light-excited state of 1B*2H2O has a higher thermal relaxation temperature than that of 1A*3H2O.

Atypically anisotropic and large changes in magnetic susceptibility, along with a change in crystalline shape, were observed in a CoII complex at near room temperature. This was achieved by combining oxalate molecules, acting as rotor, and a CoII ion with unquenched orbital angular momentum. A thermally controlled 90° rotation of the oxalate counter anion triggered a symmetry-breaking ferroelastic phase transition, accompanied by contraction-expansion behavior (ca. 4.5 %) along the long axis of a rod-like single crystal. The molecular rotation induced a minute variation in the coordination geometry around the CoII ion, resulting in an abrupt decrease and a remarkable increase in magnetic susceptibility along the direction perpendicular and parallel to the long axis of the crystal, respectively. Theoretical calculations suggested that such an unusual anisotropic change in magnetic susceptibility was due to a substantial reorientation of magnetic anisotropy induced by slight disruption in the ideal D3 coordination environment of the complex cation.

Nine coordination polymers, formulated as {[Zn(p-bdc)(bix)](DMF)2}n (1), {[Co(p-bdc)(bix)](DMF)2}n (2), {[Cd(p-bdc)(bix)](DMF)2}n (3), {[Zn(bpdc)(bix)](DMF)3}n (4), {[Co(bpdc)(bix)](DMF)3}n (5), {[Cd(m-bdc)(bix)(H2O)](DMF)}n (6), {[Zn(m-bdc)(bix)](solv)x}n (7), {[Zn2(m-bdc)2(bix)2](solv)x}n (8), and {[Zn(m-bdc)(bix)](solv)x}n (9) (p-H2bdc = 1,4-benzenedicarboxylic acid, H2bpdc = biphenyl-4,4′-dicarboxylic acid, m-H2bdc = 1,3-benzenedicarboxylic acid), have been prepared by solvothermal reactions of the semirigid neutral ligand 1,4-bis(imidazol-l-yl-methyl)benzene (bix) with metal ions in the presence of various aromatic dicarboxylic acids. These complexes were characterized by Fourier transform infrared (FT-IR) spectroscopy, elemental analysis, thermogravimetric analysis (TGA), and single-crystal X-ray diffraction analysis. Isostructural complexes 1 and 2 reveal a 3-fold interpenetrating three-dimensional (3D) framework with dia topological type. Compound 3 exhibits a non-interpenetrating, highly undulati...

Harnessing molecular motion to reversibly control macroscopic properties, such as shape and size, is a fascinating and challenging subject in materials science. Here we design a crystalline cobalt(II) complex with an n-butyl group on its ligands, which exhibits a reversible crystal deformation at a structural phase transition temperature. In the low-temperature phase, the molecular motion of the n-butyl group freezes. On heating, the n-butyl group rotates ca. 100° around the C–C bond resulting in 6–7% expansion of the crystal size along the molecular packing direction. Importantly, crystal deformation is repeatedly observed without breaking the single-crystal state even though the shape change is considerable. Detailed structural analysis allows us to elucidate the underlying mechanism of this deformation. This work may mark a step towards converting the alkyl rotation to the macroscopic deformation in crystalline solids., Molecular motion can potentially be harnessed to control macroscopic properties such as size and shape. Here, the authors show that the phase transition of a cobalt(II) complex with an n-butyl group on its ligands, results in a reversible crystal deformation at the structural phase transition temperature.

A unique 3D Cu(II) complex based on a molybdate oxide cluster and 5-triazole isophthalic acid was synthesized under hydrothermal condition: {Cu(2)(HL)(2)[Mo(4)O(13)]}·2H(2)O (H(2)L = 5-triazole isophthalic acid) (1). Compound 1 shows a spin canting magnetization behavior, and a definite hysteresis loop with a large coercive field of 6.85 kOe.

A family of polyoxometalate compounds based on Preyssler anions and lanthanide cations, K(5)Na(5)[{Pr(4)(H(2)O)(12)(pydc)(4)}{Na(H(2)O)P(5)W(30)O(110)}]·46H(2)O (1, H(2)pydc = pyridine-2,6-dicarboxylic acid), Na(7)[{Pr(4)(H(2)O)(20)(pydc)(2)(Ac)}{Na(H(2)O)P(5)W(30)O(110)}]·23H(2)O (2), and Na(10)H(2) [{Ln(2)(H(2)O)(10)(pydc)(2)}{Na(H(2)O)P(5)W(30)O(110)}]·XH(2)O (Ln = Sm 3, Eu 4, Gd 5; X = 11 for 3 and 5, 13 for 4), have been synthesized and characterized by elemental analysis and single crystal X-ray diffraction. Compound 1 exhibits a two-dimensional honeycomb layer which is built up from unique {Pr(4)} metallacycles and Preyssler anions. Remarkably, the strong involvement of the sodium countercations leads to the formation of a unique three-dimensional open architecture with one-dimensional channels. The 2D grid layer of compound 2 is constructed by the longest currently known rare-earth metal clusters {Pr(8)} and Preyssler anions. Isostructural compounds 3, 4, and 5, obtained by introduction of the intermediate lanthanide ions into the above reaction system, exhibit bisupporting [{Ln(2)(H(2)O)(10)(pydc)(2)}{Na(H(2)O)P(5)W(30)O(110)}](12-) polyoxometalate cluster structures. The magnetic properties of compounds 1 and 2 and the luminescent properties of compounds 3 and 4 are discussed in this paper.

Two supramolecular isomers, [H2tpim·H4betc]·I (1) and [H2tpim·H4betc]·I3·2H2O (2), have been synthesized by one-pot reactions. Single-crystal to single-crystal transformations are observed between the two supramolecular isomers which are induced by release of in situ generated I2.

Five POM/Ag-based hybrids were obtained under hydrothermal conditions: (AgLa)2[Ag2La2(SiW12O40)] (1), [(AgLb)2-Ag2Lb2][(SiW12O40)] (2) Na2[AgLa(HLa)]2[Ag5La4(H2O)2][H(P2W18O62)2] ·21.6H2O (3), [Ag5Lb5][K2(OH)P2W18O62]·H2O (4) and [Ag2La2][HPW12O40]·7.5H2O (5) (La = 1,2-bis(imidazol-1-ylmethyl)benzene; Lb = 1,3-bis(imidazol-1-ylmethyl)benzene). It is likely that the forms and assembly of [AgxLy] complexes are crucial to the eventual structures, which are quite dependent on the POM and isomeric ligands in combination. Compound 1 shows a “S”-like chain structure with [(AgLa)2]n2n+ templates, while compound 2 features a unique 2D layer constructed by polypseudo-rotoxane motifs and infinite Ag chains. Compound 3 exhibits a 2D layer consisting of {Dawson-Ag5} double chain and [AgLa2] complexes. Compound 4 possesses a 3D poly-threading framework containing {POM-K} chains and interdigitated metal–organic layers. Compound 5 is a 1D chain, formed by Keggin anions and [Ag2La2] circles. Further, the luminescent and electrochemical properties of 1–5 are also investigated.

Six novel metal-organic frameworks (MOFs), {Mn(bpydb)(bpyHdbH)}(n) (1) {[Co(2)(bpydb)(2)](H(2)O)(0.5)}(n) (2), {[Ni(0.5)(bpydbH)(H(2)O)](DMF)(2)}(n) (3), {[Cu(2)(bpydb)(2)](H(2)O)(0.5)}(n) (4), {Zn(bpyHdb)(2)}(n) (5) and {[Cd(0.5)(bpydb)(0.5)(DMF)](H(2)O)}(n) (6), were successfully synthesized by assembling transition metal salts with trigonal heterofunctional ligand 4,4'-(4,4'-bipyridine-2,6-diyl) dibenzoic acid (bpydbH(2)) under hydrothermal and/or solvothermal conditions. Compound 1 features a rare 4-fold interpenetrating (3,5)-connected framework with hms-type topology. Isostructural compounds 2 and 4, constructed by M(2)(COO)(4) secondary building units, exhibit a robust 3D framework with alb topological type in 2-fold interpenetrating mode. Compound 3 consists of 2D (4,4) networks, which are further assembled into the new topological framework with the symbol (5(3)·6(2)·8)(5(3)·6(3))(2) through O-HO interactions. Compound 5 manifests a novel 4-connected interpenetrating framework, constructed by 2D (4,4) layers and interbedded N-HO interactions. Non-interpenetrating honeycomb networks are observed in compound 6, and further packed into a 3D framework featuring 1D channels. The magnetic susceptibility of compound 2 indicates antiferromagnetic interactions between cobalt ions. The photoluminescent properties of 5 and 6 were investigated in the solid state at room temperature.