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Two Ni(II) carboxyphosphonates, namely [Ni(H4L)2] (1) and [Ni(H3L)(H2O)]·2H2O (2) (H5L=HOOCC6H4CH2N(CH2PO3H2)2), have been hydrothermally synthesized. Structural analyses reveal that 1 shows a two-dimensional (2D) inorganic layer structure, and the layers are further packed into a three-dimensional (3D) supramolecular structure through the interlayer hydrogen-bonding interactions. In 2, two adjacent {NiO5N} polyhedra are connected to form a {Ni2O8N2} dimer, and these dimers are further linked by {CPO3} tetrahedra to form a one-dimensional (1D) chain. Consecutive chains are further connected by the intermolecular hydrogen-bonding interactions, resulting in a 2D supramolecular layer structure. Magnetic analyses exhibited that 1 shows major antiferromagnetic behavior, whereas 2 displays ferromagnetic interactions at low temperatures. Meanwhile, the magnetic properties of 1 and 2 have also been quantified using the Curie–Weiss law and the PHI program package, respectively. Two nickel(II) carboxyphosphonates with different structures showed different magnetic behaviors. Meanwhile, the magnetic properties of 1 and 2 have also been quantified using the Curie–Weiss law and the PHI program package.

Construction and investigation of dual-functional metal-organic frameworks (MOFs) with luminescent sensing and proton conduction provide widespread applications in clean energy and environmental monitoring fields. By selecting a phosphonic acid ligand 4-pyridyl-CH

Construction of metal–organic polyhedral clusters is promising and challenging in science due to their highly symmetric structures and potential application to molecular devices. In this work, three neutral nanocages of {[Fe(Tp)(CN)3]24[M(H2O)2]6[M(L)(H2O)]12}·xH2O (1-Fe, 2-Ni, and 3-Mn for M = Fe, Ni, Mn and x = 6, 2, 4, respectively; Tp = hydrotris(pyrazolyl)borate and L = pyridine-4-carboxylate) were prepared through the assembly of [Fe(Tp)(CN)3]− with FeII, NiII, or MnII ions and pyridine-4-carboxaldehyde, which was oxidized to pyridine-4-carboxylic acid during the reactions. Single crystal structure analyses revealed that each cage has the same core structure of an Archimedean polyhedra, the pseudo-rhombicuboctahedron. Elemental analyses and magnetic and spectroscopic measurements were performed to determine the oxidation and spin states of the composite metal ions, demonstrating that their electron configurations can be altered by changing the metal ions and deprotonating the auxiliary ligands. In addition, magnetic studies indicated that the metal ions were ferromagnetically coupled within the cage structure. These clusters exhibited magnetocaloric effects (MCEs) with the entropy changes of 11.55 J kg−1 K−1 for 1-Fe, 5.84 J kg−1 K−1 for 2-Ni, and 19.84 J kg−1 K−1 for 3-Mn at 3 K and 8.5 T, and 3-Mn is among the family of high-performance 3d-metal-based magnetic coolants.

Two tetra-nuclear YbIII-incorporated selenotungstate clusters, Keggin (C2H8N)6Na14[Yb4Se6W44O160(H2O)12]·40H2O (1) and Wells–Dawson (C2H8N)4Na14[Yb4Se6W45O159(OH)6(H2O)11]·38H2O (2), have been isolated through a pH-controlled assembly, which exhibit the first YbIII-containing polyoxotungstates with selenium heteroatoms. Their assemblies rely on the structure-directing effects of SeO32− anion templates to give rise to available Se-containing Keggin-/Wells–Dawson-type motifs. Both compounds were characterized by single-crystal X-ray diffraction, IR spectroscopy, power X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) as well as electrospray ionization mass spectrometry (ESI-MS). Furthermore, systematic magnetic studies revealed that 1 exhibits field-induced single-molecule magnetic behavior with a pre-exponential factor of τ0 = 6.60(7) × 10−8 s and a relaxation energy barrier of ΔE/kB = 39.44(2) K, while 2 only displays antiferromagnetic interactions between the ytterbium centers.

It remains a challenge to exploit dual-functional metal-organic frameworks (MOFs) for applications, including luminescence detection and proton conduction. With the deliberate selection of the bifunctional organic ligand 5-sulfoisophthalic acid monosodium salt (NaH2bts), and the phosphonic acid ligand N,N'-piperazine (bismethylenephosphonic acid; H4L), a robust three-dimensional (3D) noninterpenetrating dual-functional MOF, [Tb(H2L)(H2bts)(H2O)]·H2O (1), has been synthesized hydrothermally. On the basis of the excellent thermal and chemical as well as superior luminescence stabilities in water and solutions with different pHs, 1 can serve as the simple, rapid, and highly selective and sensitive luminescence detection of the carcinoid biomarkers 5-hydroxytryptamine (HT) and its metabolite 5-hydroxyindole-3-acetic acid (HIAA) with detection limits of nanomolar magnitude in water and in simulated blood plasma and urine systems. Due to the change in the signals that could be readily differentiated by the naked eye under a UV lamp, a portable test paper has been developed. The probable quenching mechanisms are discussed in detail. In addition, a great number of hydrogen-bonding networks are formed among the uncoordinated carboxylic oxygen atoms, sulfonate oxygen atoms, protonated nitrogen atoms, and water molecules, which provide potential proton-hopping sites for proton conduction, leading to a maximum proton conductivity of 2.3 × 10-4 S cm-1 at 368 K and 95% relative humidity. The above results suggest that rationally designed dual-functional MOFs can open an avenue for the development of occupational diagnostic tools and alternative energy technology.

Two tetra-nuclear Yb

It is promising and challenging to manipulate the electronic structures and functions of materials utilizing both metal-to-metal charge transfer (MMCT) and spin-crossover (SCO) to tune the valence and spin states of metal ions. Herein, a metallocyanate building block is used to link with a FeII -triazole moiety and generates a mixed-valence complex {[(Tp4-Me )FeIII (CN)3 ]9 [FeII 4 (trz-ph)6 ]}⋅[Ph3 PMe]2 ⋅[(Tp4-Me )FeIII (CN)3 ] (1; trz-ph=4-phenyl-4H-1,2,4-triazole). Moreover, MMCT occurs between FeIII and one of the FeII sites after heat treatment, resulting in the generation of a new phase, {[(Tp4-Me )FeII (CN)3 ][(Tp4-Me )FeIII (CN)3 ]8 [FeIII FeII 3 (trz-ph)6 ]}⋅ [Ph3 PMe]2 ⋅[(Tp4-Me )FeIII (CN)3 ] (1 a). Structural and magnetic studies reveal that MMCT can tune the two-step SCO behavior of 1 into one-step SCO behavior of 1 a. Our work demonstrates that the integration of MMCT and SCO can provide a new alternative for manipulating functional spin-transition materials with accessible multi-electronic states.

Three one-dimensional (1D) cyanide-bridged heterobimetallic chains {[FeIII(Tp)(CN)3]2CoII(mep)2}·2CH3OH (1; Tp = hydrotris(pyrazolyl)borate, mep = 4‑[(1E)‑2‑(4‑Methylphenyl)ethenyl]pyridine), {[FeIII(Tp)(CN)3]2CoII(eep)2}·2CH3OH (2; eep = 4‑[(1E)‑2‑(4‑Ethylphenyl)ethenyl]pyridine) and {[FeIII(Tp)(CN)3]4CoII2(nep)4}·3H2O·CH3OH (3; nep = 4‑[(1E)‑2‑(2‑Naphthalenyl)ethenyl]pyridine) have been synthesized via self-assembly of the same [FeIII(Tp)(CN)3]− unit and CoII ion in the presence of different N-substituted pyridine ligands. Magnetic measurements reveal that complex 1 exhibits ferromagnetic interactions and a long-range magnetic ordering below 3.5 K. Complex 2 shows antiferromagnetic long-range ordering below 3.3 K, while complex 3 shows a typical ferrimagnetic coupling at low temperatures. These results highlight the significant influence of the coligands on their magnetic properties.

Utilizing the building block [(TpR)FeIII(CN)3]− featuring different steric hindrance, a trinuclear [NiII(4-Clbpy)2][(pzTp)FeIII(CN)3]2·4H2O (1) (pzTp = tetrakis(pyrazolyl)borate; 4‑Clbpy = 4‑chlorine‑2,2′‑dibipyridine) and a tetranuclear {[NiII(4-Clbpy)2][(Tp*)FeIII(CN)3]}2·4CH3OH·2H2O (2) (Tp* = hydrotris(3,5‑dimethylpyrazolyl)borate) were successfully synthesized. Magnetic studies revealed that both compound 1 and 2 exhibited intramolecular ferromagnetic interaction. Dynamic susceptibility study indicated that compound 2 exhibited slow magnetic relaxation. The relaxation energy barrier was Δ/kB = 62.31 K with the pre-exponential factor of τ0 = 2.87 × 10−10 s. In addition, compound 2 can exhibit hysteresis at 1.8 K.

Three novel cyano-bridged one-dimensional chains {[(pzTp)Fe(CN)3]2M(BYI)2(CH3OH)2·2CH3OH}n (M = Mn (1), Co (2) and Ni (3), BYI = 1, 1′-(1, 4-Butanediyl)bis(imidazole)) composed of cyano-bridged trinuclear FeIII2MII units were successfully synthesized based on [(pzTp)Fe(CN)3]− (pzTp = tetrakis(pyrazolyl)borate) unit and bidentate bridging ligand. Structural characterization showed that the three compounds were isostructural. The magnetic interactions could be adjusted by replacing the metal ions with different magnetic anisotropy. Magnetic studies revealed that compound 1 showed antiferromagnetic interaction, while compounds 2 and 3 exhibited ferromagnetic interaction. Interestingly, compound 3 showed the spin glass behavior with the typical slow magnetic relaxation due to the large anisotropy for NiII ions and the non-negligible interchain interaction.

Electron transfer in solid is crucial to switchable magnetic, electrical, optical and mechanical properties. However, it is a formidable challenge to control electron-transfer behaviors via manipulation of crystalline phases, especially through dynamic crystalline transformation. Herein, three crystalline phases of an {Fe2Co2} compound were obtained via enhancement of intermolecular π···π interactions inducing successive single-crystal-to-single-crystal transformations, from solvated 1·2CH3OH·4H2O, to desolvated 1 and its polymorph 1a accompanying electron transfer. 1·2CH3OH·4H2O showed thermally induced reversible intermetallic electron transfer in mother liquor. No electron-transfer behavior was observed in 1. 1a showed reversible intermetallic electron transfer upon thermal treatment or alternative irradiation with 808- and 532-nm lasers at cryogenic temperatures. The electron-transfer behaviors significantly change the magnetic and optical properties, providing a strategy to realize different electron-transfer behaviors and switchable functions via π···π interactions manipulated dynamic crystalline transformation.

The preparation of single-chain magnets (SCMs) with photo-switchable bistable states is essential for the development of high-density photo-recording devices. However, the reversible switching of the SCM behavior upon light irradiation is a formidable challenge. Here we report a well-isolated double zigzag chain {[Fe(bpy)(CN)4]2[Co(phpy)2]}·2H2O (bpy = 2,2'-bipyridine, phpy = 4-phenylpyridine), which exhibits reversible redox reactions with interconversion between FeIIILS(μ-CN)CoIIHS(μ-NC)FeIIILS (LS = low-spin, HS = high-spin) and FeIIILS(μ-CN)CoIIILS(μ-NC)FeIILS linkages under alternating irradiation with 808 and 532 nm lasers. The bidirectional photo-induced metal-to-metal charge transfer results in significant changes of anisotropy and intrachain magnetic interactions, reversibly switching the SCM behavior. The on-switching SCM behavior driven by light irradiation at 808 nm could be reversibly switched off by irradiation at 532 nm. The results provide an additional and independent way to control the bistable states of SCMs by switching in the 0 → 1 → 0 sequence, with potential applications in high density storage and molecular switches.

Two types of lanthanide(III) oxalatophosphonates, namely, [Ln(H2L)(C2O4)]·H2O [Ln = La (1), Ce (2), Pr (3)] and [Ln2(H3L)(C2O4)3(H2O)4]·2H2O [Ln = Eu (4) and Dy (5)] have been hydrothermally obtained by using (4-carboxypiperidyl)-N-methylenephosphonic acid (H3L) as the phosphonate ligand and oxalate as the second ligand. These five compounds have the same precursor, but they exhibit two different 2D layered structures. Compounds 1–3 are isostructural and exhibit a 2D layered structure in which {Ln(1)O9}, {Ln(2)O9} and {CPO3} polyhedra via corner-sharing and edge-sharing are interconnected into a 1D chain. These chains are further cross-linked by oxalate anions into a 2D layered structure, and the uncoordinated carboxylate groups are oriented toward the interlayer space. Compounds 4 and 5 are isostructural and also show a 2D layered structure. Lanthanide ions are interconnected by oxalate anions forming a 2D layered structure, and the carboxyl groups of H3L are grafted on the two sides of the layer. The structure variations are attributed to the effect of lanthanide contraction. In addition, the luminescence properties of compounds 4 and 5, and the magnetic properties of compound 5 have been studied.

Using different cyanometallate building blocks ([(TpR)Fe(CN)3]–) and pyrazino[2, 3-f][1,10]phenanthroline (dpq) ligand, three cyanide–bridged {Fe2Co2} tetranuclear complexes {[(Tp*)Fe(CN)3]2[Co(dpq)2]2[ClO4]2}·4H2O (1), {[(Tp4-Me)Fe(CN)3]2[Co(dpq)2]2[ClO4]2}·4H2O (2) and {[(Tp)Fe(CN)3]2[Co(dpq)2]2 [(Tp)Fe(CN)3][ClO4]}·2CH3OH·5H2O (3) were synthesized. Single crystal X-ray diffraction study showed that all compounds shared the similar square tetranuclear structures. Magnetic study indicated that 1 maintained the high-spin state for the CoII ion in the whole temperature range, and showed the ferromagnetic interaction between low-spin FeIII and high-spin CoII ions. In contrast, 2 and 3 showed thermally and photoinduced intramolecular metal-to-metal charge transfer (MMCT) between the FeII/III and CoII/III redox pairs. The comparison study suggested that the electronic and steric effects of the substituents in cyanometallate building blocks as well as the intermolecular interactions can affect the redox potential of metal ions, thereby resulting in different MMCT properties.

Two metal phosphonates with or without the free Lewis basic pyridyl sites, namely, [Zn1.5(HL)]·2H2O (1) and [Cd0.5(H3L1)]·H2O (2) have been hydrothermally obtained from 4–pyridyl–CH2N(CH2PO3H2)2 (H4L) and 3–pyridyl–CH2N(CH2PO3H2)2 (H4L1). The pyridyl N atom of 1 is uncoordinated with Zn(II) ion, whereas the pyridyl N atom of 2 is coordinated with Cd(II) ion, which leads to the different luminescent sensing abilities for Cu2+ ion. Compound 1 shows a highly selective and sensitive luminescent sensor for sensing Cu2+ with a low detection limit of 2.7 nM in aqueous solution. However, 2 can not be used as a luminescent sensor for metal ions. The result indicates that the presence of the free Lewis basic pyridyl sites in the framework plays an important role in the recognition of metal cations. Meanwhile, the quenching mechanism for 1 is also investigated, which can be attributed to the weak interaction between the free Lewis basic sites from the HL3– ligands and Cu2+ ions.

Tuning the spin crossover (SCO) behavior through paramagnetic building blocks with different steric hindrance is of great interest for the synergy between SCO and magnetic interactions. Here we modified the steric effect of specified FeIII building blocks from large steric hindrance Tp* (hydridotris(3,5-dimethylpyrazol-1-yl)borate) analogue to small steric hindrance Tp (hydrotris(pyrazolyl)borate) derivative, the FeII SCO unit and FeIII paramagnetic ions were incorporated into three well-isolated trinuclear complexes featuring thermally- and light-induced SCO properties. Reanalyzing the structures uncovered that π-π-stacking interactions played a key role in the thermal hysteresis and anomalous octahedral distortion parameter Σ around FeII ion; the Tp* ligand showing the largest steric hindrance induced the elongated FeII-N bond lengths and bending of C≡N-FeII angle in 1, as well as its relatively large electron donor effect, leading to the lowest thermal transition temperature among three compounds.

A tetranuclear cyanide-bridged FeIII2NiII2 cluster [FeIII(Tp)(CN)3]2NiII2(4, 4′-dibromo-2, 2′-bpy)4·2ClO4 (1) (Tp = hydrotris(pyrazolyl)borate) was synthesized. Magnetic measurements indicated that this compound displayed single-molecule magnet behavior with the pre-exponential factor of τ0 = 1.79(8) × 10− 10 s and the relaxation energy barrier of Δ/kB = 65.1(9) K.

The reaction of mid-lanthanide (Ln) ions with the preformed {Se6W39} precursor under reasonably acidic aqueous conditions in the presence of organic amine cations results in an unprecedented nanoscale lanthanide-functionalized polyoxotungstate family, which are rare examples of mid-lanthanide-containing selenotungstates. (C4H10NO)9Na3[Dy3Se3.5W30O107.5(H2O)10]·22H2O (1) and (NH4)3(C2H8N)Na2[Dy4Se6W38O132(H2O)26(OH)6]·18H2O (2) reveal a trimeric Keggin assembly and a cyclic {Se6W38}-based chain, respectively, whereas (NH4)4Na8[Gd4Se6W48O166(H2O)20(OH)4]·21H2O (3) and (NH4)9(C2H8N)4Na5[Ln6Se6W58O202(H2O)20(OH)4]·58H2O (4; Ln = Gd, Tb, or Dy) are a few examples of polyoxometalates consisting of both classical Keggin and Wells-Dawson building blocks, and (NH4)4(C2H8N)5Na13[Ln4Se8W56O196(H2O)x(OH)10]·40H2O (5; Ln = Gd, Tb, or Dy; x = 12 for Gd and Tb and 10 for Dy) features the largest "pure" Wells-Dawson selenotungstate {Se8W56} bearing a length of 3.73 nm. A library of Se-templated species involving the first reported Keggin {α-SeW8} and Wells-Dawson {α-Se2W16} building blocks as well as some decisive assembly factors during the synthesis is responsible for these architectures. All of the compounds were structurally characterized in the solid and solution by single-crystal X-ray diffraction, IR, thermogravimetric-differential thermal analysis, and electrospray ionization mass spectrometry. Magnetic properties indicate that 1 and 4-Dy show probable single-molecule-magnet behavior with obvious frequency dependence, whereas 3 and 4-Gd present the antiferromagnetic interactions between the GdIII centers.

Understanding the effects of intermolecular interactions on metal-to-metal charge transfer (MMCT) is crucial to develop molecular devices by grafting MMCT-based molecular arrays. Herein, we report a series of solvent-free {Fe2 Co2 } compounds sharing the same cationic tetranuclear {[Fe(PzTp)(CN)3 ]2 [Co(dpq)2 ]2 }2+ (PzTp- =tetrakis(pyrazolyl)borate, dpq=dipyrido[3,2-d:2',3'-f]quinoxaline) square units but having anions with different size, including BF4- , PF6- , OTf- , and [Fe(PzTp)(CN)3 ]- . Intermolecular π⋅⋅⋅π interactions between dpq ligands, which coordinate to cobalt ions in the {[Fe(PzTp)(CN)3 ]2 [Co(dpq)2 ]2 }2+ units, can be modulated by introducing different counterions, regulating the distortion of the CoN6 octahedron and ligand field around the cobalt ions. This change results in different MMCT behavior. Computational analyzes reveal the substantial role of the intermolecular interactions tuned by the presence of different counteranions on the MMCT behavior.

Two novel zinc(II) phosphonates, [Zn(H4L)]·2H2O (1) and [Zn(H4L)(2,2′-biim)] (2) (2,2′-biim = 2,2′-biimidazole), were synthesized based on (2,4,6-trimethylbenzene-1,3,5-triyl) tris(methylene) triphosphonic acid (H6L), via hydrothermal techniques. Structural characterization was conducted using single-crystal X-ray diffraction analyses, X-ray powder diffraction analyses (PXRD), FT–IR spectroscopy, thermogravimetric analyses (TGA) and elemental analyses (EA). Compound 1 was a 2D layered structure that exhibited high selectivity and sensitivity as a luminescent probe for the detection of polychlorinated benzene, with a very low detection limit of 8.20 × 10−7 M. Compound 2 possessed a one-dimensional chain structure that transformed into a 2D supramolecular structure through hydrogen bonding interactions. The excellent Lewis base recognition sites in 2 facilitated high sensitivity toward Hg2+ ions, with a low detection limit of 5.30 × 10−7 M. The test paper experiment showed that 2 could be made into the test paper to quickly detect Hg2+ by naked eye. Meanwhile, the probable sensing mechanisms were also discussed in this paper.

Five chiral and achiral copper(II) carboxyphosphonates, namely, [Cu(4-cppH)(2,2′-bipy)(H2O)] (1: R-1 and S-1), [Cu9(4-cpp)6(2,2′-bipy)6] (2), [Cu3(4-cpp)2(2,2′-bipy)2] (3), [Cu3(4-cpp)2(1,10-phen)2]·4H2O (4), and [Cu(4-cppH)(1,10-phen)]·H2O (5), had been hydrothermally synthesized. Among them, 1 showed an unexpected 1D chiral helical chain from achiral carboxyphosphonate ligand by spontaneous resolution. In 2, the interconnection of {CuN2O3}, {CuO4}, and {CPO3} polyhedra formed a 1D chain. Such chains were further connected to a 2D layer through the carboxyphosphonates ligands. Compounds 3 and 4 were isostructural and exhibited a 2D layer, which was constructed from {CuO3N2}/{CuO4} polyhedra and the carboxyphosphonate ligands. In 5, the interconnection of neighboring {CuN2O3} polyhedra formed a dimer. These dimers were connected with the carboxyphosphonate ligands to form a chain. Interestingly, the homochiral copper(II) phosphonate (R-1 or S-1) could be obtained by utilizing the (+)-cinchonine or (−)-cin...

A cyano-bridged ferromagnetic {FeIII2FeII} alternating chain {[FeIII(pzTp)(CN)3]2[FeII(imidazole)(H2O)]}·3H2O (1) (pzTp = tetrakis(pyrazolyl)borate) was synthesized via rational design. Crystal structure analysis studies demonstrated that complex 1 had a one-dimensional double zigzagging chain-like structure. Magnetic measurements showed that ferromagnetic interactions dominate in 1 and the AC magnetic susceptibility revealed two limit regimes in accordance with the single chain magnet and spin-glass behavior.

A cyanide-bridged FeIII 2CoII double zigzag chain, {[FeIII(bipy)(CN)4]2CoII(btab)2} n [bipy=2,2′-bipyridine, btab=4,4′-(1,3-phenylene)-bis-4H-1,2,4-triazole] (1), was obtained with tetracyanometalate precursors and CoII ions. The chains were further linked by the ditopic btab ligands to a layer. Magnetic property studies demonstrate that 1 shows both metamagnetism with a critical field H c=400 Oe and single-chain magnet behavior.

With the use of the tailored cyanometalate precursor, Bu4N[Fe(Tp*)(CN)3] (Tp* = hydridotris(3,5-dimethylpyrazol-1yl)borate), as the building block to react with fully solvated MII cations, three new one-dimensional (1D) heterobimetallic cyano-bridged chain complexes of squares, {[Fe(Tp*)(CN)3]2M (CH3CH2OH)2}·4H2O (M = Mn(1), Fe(2), Co(3)), have been prepared. In these compounds, the MII ions have slightly distorted octahedral coordination geometries, and they were bridged by [Fe(Tp*)(CN)3]− to form similar 1D chains of squares. The magnetic studies demonstrated that compound 1 exhibited weak ferromagnetism due to spin canting, compound 2 showed ferrimagnetic behavior in a low temperature region, whereas compound 3 indicated the presence of typical antiferromagnetic coupling.

Four new transition metal phosphonates with 2D and 3D supramolecular structures, namely [Cu2(1,10-phen)2(HL)2(L)]·H2L (1), [Zn(1,10-phen)(HL)2] (2), [M(1,10-phen)(HL)2(H2L)] (M = Mn (3), and Cd (4)) (H2L = phenylphosphonic acid, 1,10-phen = 1,10-phenanthroline), have been synthesized under hydrothermal conditions. In compound 1, two {CuN2O3} square pyramids and three {CPO3} tetrahedra are interconnected through phosphonate oxygen atoms to form a cluster unit via edge- and corner-sharing. Neighboring units are further assembled into a 3D supramolecular structure through π–π stacking and hydrogen bonding interactions. For compound 2, two {ZnO3N2} square pyramids and four {CPO3} tetrahedra are interconnected by phosphonate oxygen atoms to a cluster unit via corner-sharing. Then the adjacent clusters are further assembled into a 3D supramolecular structure through π–π stacking interactions. Compounds 3 and 4 are isomorphous and adopt a 2D supramolecular structure. The interconnection of {MO4N2} and {CPO3} polyhedra leads to a cluster unit through corner-sharing, and such units are further assembled into a 2D supramolecular structure by π–π stacking and hydrogen bonding interactions. The surface photovoltage properties of compounds 1 and 3 and luminescence properties of compounds 2 and 4 have been studied. The surface photovoltage spectra (SPS) and field-induced surface photovoltage spectra (FISPS) of compounds 1 and 3 indicate that they all possess certain photo-electric conversion properties and show p-type semiconductor characteristics. Luminescence properties of compounds 2 and 4 indicate that they may be candidates for potential luminescent materials.

A cyanide-bridged Fe2Co 4,2-ribbon single-chain magnet, {[Fe(bipy)(CN)4]2[Co(phpy)2]} (1, bipy = 2,2-bipyridine; phpy = 4-phenylpyridine) was obtained by the dehydration of {[Fe(bipy)(CN)4]2[Co(phpy)2]}·2H2O (1·2H2O). The electron-transfer-coupled spin transition (ETCST) was achieved during the dehydration process from 1·2H2O to 1, with the electronic configurations transforming from {FeIILS(µ-CN)CoIIILS(µ-NC)FeIIILS} to {FeIIILS(µ-CN)CoIIHS(µ-NC)FeIIILS} (LS = low spin, HS = high spin). The magnetic characterization indicates that the dehydrated 1 exhibits the dehydration-actuated single-chain magnetic (SCM) behaviour.

The preparation, single-crystal X-ray crystallography and magnetic properties are reported for two single-zigzag chain complexes {[W(CN)8][Ni(imi)4]}·Bu4N·CH3OH·2H2O (1) and {[Mo(CN)8][Ni(imi)4]}·Bu4N·2H2O (2) (imi = imidazole, Bu = normal-butyl). The structure studies reveal that both complexes feature one-dimension anion chains linked by [W(CN)8]3 − units in 1 or [Mo(CN)8]3 − units in 2. Magnetic studies show that strong ferromagnetic exchange is operative within the WV(μ-CN)NiII units for (1) and MoV(μ-CN)NiII units for (2).

One trinuclear and two tetranuclear cyanide-bridged Fe(III)-Ni(II) complexes were synthesized via treatment of a tricyanometallate with divalent Ni salts in the presence of 1-butylimidazole, 2,2-bipyrimidyl and 1,10-phenanthroline, respectively. Magnetic property studies demonstrated that the three complexes exhibit single-molecule magnet behavior as a result of strong intracluster ferromagnetic coupling and weak intercluster magnetic interactions.

Three new transition metal(II) phosphonates with 3D framework and supramolecular structures, namely, [M1.5(L)(H2O)]·NH2(CH3)2·H2O (M = Ni (1), Co (2)) and [Zn2(H2L)(HL)]·NH2(CH3)2·3H2O (3) (H4L = C5H4NCH2C(OH)(PO3H2)2), have been synthesized under mixed-solvothermal conditions and structurally characterized. Compounds 1 and 2 are isostructural and adopt a 3D framework structure. The {M(1)O5N} octahedra and {CPO3} tetrahedra are interconnected into a 1D chain via corner-sharing, which is further linked to adjacent chains through pyridyl rings to form a 2D layer structure. Neighboring layers are bridged through {M(2)O6}, leading to a 3D framework structure with a 1D channel system along the b-axis. For compound 3, the {Zn(1)O4} and {Zn(2)O4} polyhedra are interconnected by phosphonate groups into a 1D double chain, and the double chain is further connected to adjacent chains through hydrogen bonds to form a 2D supramolecular network. Then these neighboring layers are further connected through hydrogen bonding interactions to give rise to a 3D supramolecular structure. Surface photovoltage spectroscopy (SPS) and field-induced surface photovoltage spectroscopy (FISPS) of compounds 1 and 2 indicate that they possess a positive SPV response in the range of 300–800 nm and show p-type semiconductor characteristics. Compound 3 has been realized for the sensitive sensing of N,N-dimethylformamide (DMF) by a luminescent method.

Three new alkaline earth metal carboxyphosphonates with a 3D supramolecular structure, namely, Ca[(H3L)(H2O)] (1), Sr[(H3L)(H2O)2] (2) and Ba[(H3L)(H2O)] (3) (H5L = 4-{[bis(phosphonomethyl)amino]methyl}benzoic acid), have been synthesized under hydrothermal conditions. For compound 1, {CaO6} and {CPO3} polyhedra are interconnected into a 1D double-chain via corner-sharing. Adjacent chains are further cross-linked via the organic backbone {–C6H4CH2N(CH2)2–} of the carboxyphosphonate ligands, generating a 2D layer. These neighboring 2D metal phosphonate layers are connected through hydrogen bonding interactions to form a 3D supramolecular structure. In compound 2, two edge-sharing {SrO7} polyhedra form centrosymmetric {Sr2O12} units. Then, these {Sr2O12} units are connected by phosphonate groups to form a 1D chain, which is further cross-linked by N atoms from carboxyphosphonate ligands to form a 2D inorganic layer. These 2D inorganic layers interdigitate through hydrogen bonding interactions to generate a 3D supramolecular structure. In compound 3, the connections of {BaO10} and {CPO3} polyhedra form a 2D layer via corner-sharing and edge-sharing. Then adjacent layers are further assembled into a 3D supramolecular structure through hydrogen bonding interactions. The thermal stabilities and luminescence properties of compounds 1–3 were investigated. Interestingly, compounds 1–3 are selective and reversible for sensing of 1-butanol, 1-propanol and ethanol, respectively.

It remains a challenge to control the magnetic properties of molecule-based magnetic materials through chemical modification. Utilizing two tricyanometalate precursors with different steric hindrance, the cis–trans arrangement can be tuned in cyano-bridged {Fe2Cu} trinuclear complexes. The cis trinuclear [FeIII(Tp)(CN)3]2CuII(dpa)2·2H2O (1) (Tp = hydrotris(pyrazolyl)borate, dpa = 2,2-dipyridylamine) was obtained with tricyanometalate possessing smaller steric hindrance, whereas the trans trinuclear [FeIII(pzTp)(CN)3]2CuII(dpa)2 (2) (pzTp = tetrakis(pyrazolyl)borate) was obtained using tricyanometalate with larger steric hindrance. The cis and trans arrangement leads to ferromagnetic and antiferromagnetic behaviors, respectively. Density functional theory (DFT) calculations were carried out to further substantiate the magnetic behaviors of both complexes. DFT computations show that the calculated magnetic coupling constant J was in agreement with the experimental results.

A tetranuclear cluster and an alternating zigzag chain were synthesized via rational assembly of the same cyanometalate building blocks with different Mn(III) Schiff bases possessing varying proportions of sterically hindered groups causing steric hindrances. The tetranuclear cluster [(Tp*)Fe(CN)3]2[Mn(salen)]2·H2O [1; [(Tp*)Fe(CN)3]− [Tp* = hydrotris(3,5-dimethylpyrazol-1-yl) borate], salen = N,N′-ethylenebis(salicylideneiminato) dianion] was formed with Schiff bases possessing smaller steric hindrances, whereas the one-dimensional alternating zigzag chain {[(Tp*)Fe(CN)3Mn(salcyen)]·2CH3OH·H2O}n [2; salcyen = N,N′-(1,2-cyclohexanediylethylene)bis(salicylideneiminato) dianion] was formed with Schiff bases possessing larger steric hindrances. Magnetic measurements revealed that 1 exhibits single-molecule-magnet behavior with dominant ferromagnetic interactions, whereas 2 exhibits spin-canting behavior with dominant antiferromagnetic interactions.

Two new metal carboxyphosphonates with 3D framework structures, [Sn2(HL)·2H2O] (1) and [Pb2Cl(H2L)] (2) (H5L = 4-HOOCC6H4CH2N(CH2PO3H2)2), have been synthesized under hydrothermal conditions. For compound 1, every two Sn(1)O3 and Sn(2)O3 polyhedra are linked by CPO3 tetrahedra to form a 2D inorganic layer via corner-sharing in the bc-plane. Then the adjacent layers are further assembled into a 3D supramolecular structure through π–π stacking interactions. Compound 2 features a 3D open-framework structure. The Pb(1)O5Cl, Pb(2)O5 polyhedra and CPO3 tetrahedra are interconnected into a 2D inorganic layer via corner-sharing in the ac-plane. Such layers are further connected through carboxyphosphonate ligands to form a 3D open-framework structure. The luminescent properties of compounds 1 and 2 have also been studied.

Two new cobalt phosphonates, [enH 2 ] 0.5 [Co(HL)(H 2 O)] · H 2 O (1) and [Co 2 (HL)(H 2 L) 2 ] · 2NH(CH 3 ) 2 · 3H 2 O (2) (H 3 L = 2-hydroxyphosphonoacetic acid; en = ethylenediamine), have been synthesized under hydrothermal conditions and structurally characterized by X-ray single-crystal diffraction, X-ray powder diffraction, infrared spectroscopy, elemental analysis and thermogravimetric analysis. For compound 1 , Co(II) atoms are octahedrally coordinated. The CoO 6 octahedra and CPO 3 tetrahedra are linked by HL 2 − into a 2D layered structure in the bc -plane. The ethylenediamine molecules and solvate water molecules are located between two adjacent layers. The structure of compound 2 composed of Co1O 6 and Co2O 6 octahedra via bridging phosphonate ligands leads to a 2D layered structure with one-dimensional channel system along c -axis direction. The dimethylamine molecules and solvate water molecules are located between two adjacent layers. The surface photovoltage properties of compounds 1 and 2 have also been studied.

By the introduction of oxalate as the second ligand, five new lanthanide oxalatophosphonate hybrids with a 2D layered structure, namely, [Ln(H2L)(C2O4)(H2O)]·2H2O [Ln = Nd (1), Sm (2), Eu (3), Tb (4), Dy (5), H3L = H2O3PCH2NCH2(CH2CH2OPO2H)], have been hydrothermally synthesized and structurally characterized by X-ray single-crystal diffraction, X-ray powder diffraction, infrared spectroscopy, elemental analysis and thermogravimetric analysis. Compounds 1-5 are isostructural and exhibit a 2D layer formed by the interconnection of a 1D zigzag chain of {Ln(C2O4)}(+) with the phosphonate ligands. The effect of lanthanide contraction induces the decrease of the lattice parameters and crystal size from Nd to Dy. The luminescence properties of compounds 2-5 have been studied.

By introduction of 4,4′-bipyridine (4,4′-bipy) as a second organic ligand, two new nickel(II) carboxyphosphonates with a 3D framework structure, namely, [Ni3(H2L)2(4,4′-bipy)(H2O)4] (1) and [Ni3(H2L′)2(4,4′-bipy)2(H2O)2]·4H2O (2) (H5L = 4-{[bis(phosphonomethyl)amino]methyl}benzoic acid; H5L′ = N,N-bis(phosphonomethyl)aminoacetic acid) have been synthesized under hydrothermal conditions. Compounds 1 and 2 both feature three-dimensional (3D) framework structures with two-dimensional (2D) layers pillared by 4,4′-bipy. For compound 1, {Ni(1)O4N2}, {Ni(2)O6} and {CPO3} polyhedra form a 2D inorganic layer in the bc-plane via corner-sharing. Then adjacent layers are further pillared by 4,4′-bipy ligands into a 3D pillar-layered structure. In compound 2, {Ni(1)O4N2}, {Ni(2)O4N2} and {CPO3} polyhedra are interconnected by carboxyphosphonate ligands to a 2D layer in the ab-plane. Neighboring layers are further cross-linked via 4,4′-bipy ligands, generating a 3D framework structure. Whereas the carboxylate oxygen atoms of carboxyphosphonate ligands are coordinated to Ni(II) atoms in compound 2 but not in compound 1. The surface photovoltage and luminescence properties of compounds 1 and 2 have been investigated at the same time.

Four new cadmium carboxyphosphonates with 2D layered and 3D supramolecular structures, namely, Cd3[(4-cppH)2(4-cppH2)2] (1), Cd[(2,2′-bipy)(4-cppH)] (2), [Cd3(1,10-phen)3(4-cpp)2]·6H2O (3) and [Cd(4,4′-bipy)(4-cppH)(H2O)2]·2H2O (4) (4-cppH3 = 4-carboxyphenylphosphonic acid, 2,2′-bipy = 2,2′-bipyridine, 1,10-phen = 1,10-phenanthroline and 4,4′-bipy = 4,4′-bipyridine), were synthesized under hydrothermal conditions. In compound 1, {Cd(1)O6}, {Cd(2)O6}, {Cd(3)O6} and {CPO3} polyhedra form a layer in the ab plane via edge- and corner-sharing. Neighboring layers assemble into a 3D supramolecular network by hydrogen bonding interactions. The structure of compound 2 shows a new layered structure, in which the interconnection of two {Cd(1)O4N2} and two {CPO3} polyhedra via corner-sharing forms a tetranuclear cluster, and the so-built tetranuclear clusters are bridged by phosphonate ligands into a 2D layer. For compound 3, {Cd(1)O4N2}, {Cd(2)O4N2}, {Cd(3)O3N2} and {CPO3} polyhedra are interconnected by carboxyphosphonate ligands to a 2D layer in the ac plane. Then the adjacent layers are further assembled into a 3D supramolecular structure through π–π stacking interactions. Cd(II) ions in compound 4 are bridged by 4,4′-bipy molecules into layers in the ab plane. These layers are held together by hydrogen bonds into a 3D supramolecular structure. The thermal stabilities and luminescence properties of compounds 1–4 were investigated. Interestingly, compound 1 is selective and reversible for sensing of DMF and acetone.

A major challenge is the development of multifunctional metal-organic frameworks (MOFs), wherein magnetic and electronic functionality can be controlled simultaneously. Herein, we rationally construct two 3D MOFs by introducing the redox active ligand tetra(4-pyridyl)tetrathiafulvalene (TTF(py)4 ) and spin-crossover FeII centers. The materials exhibit redox activity, in addition to thermally and photo-induced spin crossover (SCO). A crystal-to-crystal transformation induced by I2 doping has also been observed and the resulting intercalated structure determined. The conductivity could be significantly enhanced (up to 3 orders of magnitude) by modulating the electronic state of the framework via oxidative doping; SCO behavior was also modified and the photo-magnetic behavior was switched off. This work provides a new strategy to tune the spin state and conductivity of framework materials through guest-induced redox-state switching.

Two hexanuclear complexes of formula [FeIII(Tp*)(CN)3]4[FeII(tptz)]2 (1), [FeIII(Tp*)(CN)3]4[CoII(tptz)]2 (2) [Tp* = hydridotris(3,5-dimethylpyrazolyl)borate, tptz = (2,4,6-tris-(2-pyridyl)1,3,5-triazine] have been synthesized via directional assembly of metallocyanate precursor and metal cationic ions. The magnetic properties characterization indicate that ferromagnetic interactions dominate in the two complexes, resulting in a spin ground state of S = 5 and S = 6, respectively.

Two novel divalent metal carboxyphosphonates with a 3D pillared-layered structure, [Zn(HL)] (1) and [CdCl(H2L)] (2) (H3L = 4-HOOCC6H4CH2NHCH2PO3H2), have been synthesized under hydrothermal conditions. Compounds 1 and 2 both feature three-dimensional (3D) framework structures with two-dimensional (2D) inorganic layers pillared by H3L. In compound 1, each {ZnO4} tetrahedron is linked via corner-sharing by three {CPO3} tetrahedra to form a two-dimensional (2D) inorganic layer in the ac-plane. The adjacent layers are further pillared by the organic backbone {–C6H4CH2NHCH2–} of the carboxyphosphonate ligand, generating a 3D pillared-layered structure. For compound 2, each Cd(II) cation is six-coordinated, and the interconnection of two {CdCl2O4} octahedra forms a dimer via edge-sharing. The dimers are interconnected by {CPO3} tetrahedra via corner-sharing to form a 2D inorganic layer in the ab-plane. Such neighboring 2D inorganic layers are further cross-linked through the organic pillars of the carboxyphosphonate ligand, thus resulting in a 3D pillared-layered structure. An interesting feature of compounds 1 and 2 is the presence of alternate left- and right-handed helical chains in their structures. It is of note that two title compounds are both stable up to high temperature. The luminescent properties of compounds 1 and 2 have also been studied.

Four novel organic–inorganic hybrid materials of the copper(II)–molybdophosphonate family, [Cu(1,10-phen)Mo2O5(H2O)(hedp)] (1), [{Cu(1,10-phen)}{Cu(1,10-phen)(H2O)}MoO2(hedpH)2]·H2O (2), [Cu(1,10-phen)Mo0.5O(hedpH)] (3), and [{Cu(2,2′-bipy)(H2O)}MoO2(hedp)]·2H2O (4) (hedpH4 = 1-hydroxyethylidenediphosphonate, 2,2′-bipy = 2,2′-bipyridine, 1,10-phen = 1,10-phenanthroline), have been synthesized under hydrothermal conditions. In compound 1, the interconnection of {MoO6}, {CuN2O2}, and {CPO3} polyhedra leads to a 2D layer through edge-sharing and corner-sharing, and such layers are further assembled into a 3D supramolecular structure by π–π stacking interactions. Compound 2 contains a 1D chain built up from {MoO6}, {CuN2O3}, and {CPO3} polyhedra, and then these 1D chains are further extended into 2D supramolecular layer by hydrogen bonding interactions. Such neighboring layers are further assembled into a 3D supramolecular structure via the π–π stacking interactions. For compound 3, the [{Cu(1,10-phen)}2MoO2(...