Chong-Bin Tian

Highly chemical and thermally stable luminescent EuxTb1−x MOF materials for broad-range pH and temperature sensors

New luminescent Ln-MOFs, [Ln2(D-cam)(Himdc)2(H2O)2] (Ln = Eu 1, Tb 2, D-H2cam = D-camphoric acid, H3imdc = 4,5-imidazole dicarboxylic acid) have been synthesized via hydro(solvo)thermal reactions. X-ray single crystal structure analysis reveals that they are isomorphic and both crystallize in the orthorhombic space group Pna21. Compound 1 shows good chemical resistance to both acidity and alkalinity solutions with pH ranging from 2 to 13 and is highly stable in several boiling solvents, which make it potentially useful for wide-range pH sensors, especially in the physiological environment with pH = 6.8–8.0. Careful adjusting of the codoping ratio of Eu3+/Tb3+ into the same framework of 1 affords a mixed Ln-MOF, formulated as [Eu0.7Tb0.3(D-cam)(Himdc)2(H2O)2]3, which has demonstrated to be a viable probe for sensing temperature in a wide temperature range from 100 to 450 K.

Two new ferrimagnetic MnII-carboxylate coordination polymers constructed from 5-tert-butyl isophthalic acid with (5/2, 15/2) and (5/2, 10/2) spin topologies

Two new MnII coordination polymers, {[Mn4(TBIP)4(CH3OH)2]·(H2O)2}n (1) and {[Mn3(TBIP)2(HTBIP)2((CH3)2CHOH)2]}n (2) (H2TBIP = 5-tert-butyl isophthalic acid), have been synthesized by a solvothermal reaction and characterized magnetically. Single-crystal X-ray diffraction studies reveal that 1 is a three-dimensional framework, which is based on a helical chain with a new periodic –J1J1J2J2– sequence. Compound 2 has a two dimensional layer structure constructed by trinuclear Mn(II) subunits that are extended into a 3D architecture by hydrogen bonds. Magnetic measurements indicate that both of the compounds show ferrimagnetic behaviour with different spin topologies. Compound 1 is a rare even-spin centre homometallic ferrimagnetic compound, in which the ferrimagnetism arises from the nature of carboxylate bridging modes. It is also the first example of a 3D homometallic ferrimagnetic compound, featuring a ferrimagnetic helical chain with a (5/2, 15/2) spin topology and a 1/2 magnetization plateau. Compound 2 is a three-spin centre homometallic ferrimagnetic complex with a (5/2, 10/2) spin topology and a 1/3 magnetization plateau.

A dual-walled cage MOF as an efficient heterogeneous catalyst for the conversion of CO2 under mild and co-catalyst free conditions

A novel 3D → 3D interpenetrated Zn-polyhedral MOF [Zn6(TATAB)4(DABCO)3(H2O)3]·12DMF·9H2O (1) (H3TATAB = 4,4′,4′′-s-triazine-1,3,5-triyl-tri-p-aminobenzoic acid, DABCO = 1,4-diazabicyclo[2.2.2]octane) based on a dual-walled icosahedral cage has been assembled by incorporating zinc paddlewheel units with nitrogen-rich tritopic carboxylate ligands. Owing to the high density of Lewis acid active sites and affinity to CO2 of the cage, this material exhibits an excellent catalytic efficiency in the cycloaddition of propylene oxide with CO2 into propylene carbonate under mild conditions (100 °C and ambient CO2 pressure) with a high yield of 99% over 16 h. Moreover, the catalytic reaction is environmentally friendly without any need for co-catalysts and solvents.

An alternative strategy to construct Fe(II)-based MOFs with multifarious structures and magnetic behaviors

An alternative strategy using cyclopentadienyliron dicarbonyl dimer as a starting material has been applied to construct six new Fe(II)-based MOFs, formulated as [Fe2(Nic)4(μ-H2O)]·CH3CN (1), [Fe(PIP)(H2O)]·H2O (2), [Fe(Hbidc)(H2O)] (3), [Fe(Hbidc)] (4), [Fe(Py-3,4-BDC)(H2O)2]·H2O (5) and [Fe(Py-3,4-BDC)(H2O)2] (6) (HNic = nicotinic acid, H2PIP = 5-(pyridin-4-yl) isophthalic acid, H3bidc = benzimidazole-5,6-dicarboxylic acid and Py-3,4-H2BDC = 3,4-pyridinedicarboxylic acid). X-ray structural analysis reveals that 1 possesses a 3D framework, while the rest of the compounds are 2D layer structures which are further connected by hydrogen bonding into 3D supramolecular architectures. Magnetic analyses have been performed with the classical spin approximation, revealing that 2, 5 and 6 exhibit ferromagnetic interactions between Fe(II) ions, while 3 and 4 show antiferromagnetic interactions between Fe(II) centres. The successful preparation of compounds 1–6 may provide an alternative and useful approach for the synthesis of Fe(II)-based MOFs in the future.

Two enantiomorphic 3D Zn(II)–carboxylate MOFs with double helical structures serving as a chiral source induced by hydrogen bonding

Two enantiomorphic 3D Zn(II)–carboxylate metal–organic frameworks [Zn(bpydc)(H2O)2] (1M and 1P) (H2bpydc = 2,2′-bipyridyl-5,5′-dicarboxylic acid) have been synthesized. They both contain an elegant double helix, self-organized through hydrogen bonds between the coordinated water molecules and uncoordinated carboxylate oxygen atoms. This double helical structure serves as a chiral source which transmits chiral information over the whole 3D framework.

Acentric and chiral heterometallic inorganic–organic hybrid frameworks mediated by alkali or alkaline earth ions: synthesis and NLO properties

The rapid development in inorganic–organic hybrid frameworks has enabled the discovery of many structurally fascinating and technologically useful materials. The design of such hybrid crystals with noncentrosymmetric frameworks is particularly important because of their interesting electronic and optical properties. Several synthetic approaches, including the use of chiral and unsymmetric ligands, or spontaneous resolution via using achiral building blocks, have been applied to facilitate the formation of acentric and chiral hybrid materials. In this highlight, we will review another way to increase the chance of obtaining acentric and chiral frameworks by adding alkali or alkaline earth metals into heterometallic systems. The synthesis of these frameworks is discussed along with their potential NLO properties.

Synthesis, structures, and magnetic properties of a series of new heterometallic hexanuclear Co2Ln4 (Ln = Eu, Gd, Tb and Dy) clusters

A series of new Co–Ln heterometallic clusters formulated as [Co2Ln4(μ3-OH)2(piv)4(hmmp)4(ae)2]·(NO3)2·2H2O (Ln = Eu (1), Gd (2), Tb (3), Dy (4), H2hmmp = 2-[(2-hydroxyethylimino)methyl]-6-methoxyphenol, Hae = 2-aminoethanol, Hpiv = pivalic acid) were synthesized and characterized. X-ray crystallography reveals that each of them contains a heterometallic {Ln4Co2} core, which is supported by two μ3-hydroxide, four piv−, four hmmp2− and two ae− ligands. The magnetic investigation indicates that 2 exhibits weak antiferromagnetic interactions between GdIII ions, and a large MCE value of 24.9 J kg−1 K−1, while 4 shows a fast relaxation of magnetization. The TGA and VT-PXRD measurements suggest that all the compounds show good thermal stability and can be stable up to about 220 °C. In addition, to address the influence of the Gd–O–Gd angles on the magnetic properties, compound 2 was compared with a series of compounds involving different bridges between GdIII ions. The comparison reveals that the tiny difference in the Gd–O–Gd angles favors different magnetic coupling.

Interweaving of two enantiomorphic 3D Cd(II)/K(I) coordination polymers with homochiral unequal triple concentric helical chains

The solvothermal reaction of Cd(NO3)2·4H2O and KNO3 with 1,3-benzenedicarboxylic acid (m-H2BDC) in the presence of D- or L-2-amino-1-propanol (D- or L-APA) in ethanol led to two enantiomorphic Cd(II)/K(I) coordination polymers, namely [Cd3K3(D-HAPA)3(m-BDC)6(EtOH)3]n (1D) and [Cd3K3(L-HAPA)3(m-BDC)6(EtOH)3]n (1L). They are 3D coordination polymers with multi-walled tubular channels constructed from a novel homochiral triple concentric helical structure in which a single helix {CdK–BDC}n is wrapped by unequal double-helical chains {Cd–BDC}n. Both complexes are NLO-active with weak SHG efficiencies.

Synthesis, structure and magnetic study of a novel mixed-valent CoII10CoIII4 shield constructed by mixed pyridine–alcoholate ligands

A novel tetradecanuclear mixed-valent cobalt cluster, formulated as [Co(II)(10)Co(III)(4)(OH)(2)O(6)(hmp)(10)(pdm)(4)(CH(3)OH)(2)]·5H(2)O (1), was obtained using mixed ligands of 2-(hydroxymethyl)pyridine (hmpH) and 2,6-pyridinedimethanol (pdmH(2)). The cobalt ions in 1 are connected by ten chelating hmp(-) ligands, four tris-chelating pdm(2-) ligands and six μ(3)-oxide/hydroxide anions, forming a unique shield-like planar structure that is rarely observed for Co-based clusters. Compound 1 displays slight frequency dependence at static zero field below 4.5 K, suggesting that it might be a single molecule magnet (SMM).

An unprecedented anionic Ln-MOF with a cage-within-cage motif: spontaneous reduction and immobilization of ion-exchanged Pd(II) to Pd-NPs in the framework

An unprecedented microporous anionic Ln-MOF, [Me2NH2]24[Tb12(TATB)16(HCOO)12]·12DMF·48H2O (1) (H3TATB = 4,4′,4′′-s-triazine-2,4,6-tribenzoic acid), which is a rare cage-within-cage structure through interpenetration rather than covalent bonding, has been synthesized. Compound 1 contains a 3D net which is constructed using a large and a small Ln-carboxylate cage alternately arranged by sharing faces with each other. Interpenetration of two identical 3D nets occurs in such a way that each small cage of one net is encapsulated within the large cage of the other and vice versa, generating an overall 3D double-walled cage framework. Such interpenetration creates a unique structure of double-shelled hollow space to accommodate Pd nanoparticles (Pd-NPs), which could effectively prevent Pd-NPs from aggregation and leaching. Moreover, the ion-exchanged Pd(II) embedded in the framework can be readily reduced at room temperature with no requirement of any chemical or thermal treatments, affording Pd-NPs with uniform size and even distribution. As a result, the as-prepared Pd-NPs@1 exhibits excellent activity and cycling stability for the hydrogenation of styrene and its derivatives.