Chunhong Tan

Two luminescent enantiomorphic 3D metal–organic frameworks with 3D homochiral double helices

Two enantiomorphic Cd(II) coordination polymers with three-dimensional homochiral double helices have been assembled respectively from two tripodal enantiopure amino acid derivatives, which exhibit (3,4)-connected (6(3))(6(3).10(3)) topology and strong purple fluorescence.

Effect of Functionalized Groups on Gas‐Adsorption Properties: Syntheses of Functionalized Microporous Metal–Organic Frameworks and Their High Gas‐Storage Capacity

The microporous metal-organic framework (MMOF) Zn4O(L1)2⋅9 DMF⋅9 H2O (1-H) and its functionalized derivatives Zn4O(L1-CH3)2⋅9 DMF⋅9 H2O (2-CH3) and Zn4O(L1-Cl)2⋅9 DMF⋅9 H2O (3-Cl) have been synthesized and characterized (H3L1=4-[N,N-bis(4-methylbenzoic acid)amino]benzoic acid, H3L1-CH3=4-[N,N-bis(4-methylbenzoic acid)amino]-2-methylbenzoic acid, H3L1-Cl=4-[N,N-bis(4-methylbenzoic acid)amino]-2-chlorobenzoic acid). Single-crystal X-ray diffraction analyses confirmed that the two functionalized MMOFs are isostructural to their parent MMOF, and are twofold interpenetrated three-dimensional (3D) microporous frameworks. All of the samples possess enduring porosity with Langmuir surface areas over 1950 cm(2) g(-1). Their pore volumes and surface areas decrease in the order 1-H>2-CH3 >3-Cl. Gas-adsorption studies show that the H2 uptakes of these samples are among the highest of the MMOFs (2.37 wt% for 3-Cl at 77 K and 1 bar), although their structures are interpenetrating. Furthermore, this work reveals that the adsorbate-adsorbent interaction plays a more important role in the gas-adsorption properties of these samples at low pressure, whereas the effects of the pore volumes and surface areas dominate the gas-adsorption properties at high pressure.

A series of goblet-like heterometallic pentanuclear [LnIIICuII4] clusters featuring ferromagnetic coupling and single-molecule magnet behavior

A series of fascinating goblet-like clusters based on [Ln(III)Cu(II)(4)] cores have been assembled from a flexible carboxylate ligand, which exhibit a dominant ferromagnetic exchange coupling and single-molecule magnet behavior.

From antiferromagnetic to ferromagnetic interaction in cyanido-bridged Fe(III)-Ru(II)-Fe(III) complexes by change of the central diamagnetic cyanido-metal geometry.

Cis- and trans-isomeric heterotrinuclear-metallic complexes and their two-electron-oxidation products, cis-/trans-[Cp(dppe)Fe(μ-CN)Ru(bpy)2(μ-CN)Fe(dppe)Cp][PF6]2 (cis-/trans-1[PF6]2) and cis-/trans-[Cp(dppe)Fe(μ-CN)Ru(bpy)2(μ-CN)Fe(dppe)Cp][PF6]4 (cis-/trans-1[PF6]4), have been synthesized and structurally characterized. To the best of our knowledge, the complexes are the first example of a cis-/trans-isomer with multistates. Although separated by the diamagnetic cyanido-metal bridge, the two distant paramagnetic metal centers in both the oxidized complexes exhibit quite strong magnetic couplings. As a unique example, cis-1[PF6]4 is antiferromagnetic, and trans-1[PF6]4 is ferromagnetic. Density functional theory (DFT) calculations suggest that the spin-delocalization mechanism should be responsible for the magnetic interactions between the two distant paramagnetic Fe(III) centers across the diamagnetic cyanido-metal in both cis- and trans-1(4+). Most importantly, the DFT calculations revealed that the type (antiferromagnetic or ferromagnetic) and strength (J) of the magnetic interactions in such compounds can be controlled by the variation (cis or trans) of the diamagnetic central metal configurations.

Distinct anion sensing by a 2D self-assembled Cu(ι)-based metal–organic polymer with versatile visual colorimetric responses and efficient selective separations via anion exchange

A novel 2D Cu(ι) metal–organic polymer could display extensive visual colorimetric changing ranges toward 11 anionic species in aqueous solutions. Additionally, among a series of anion combinations, it still exhibits high selective separation with corresponding colorimetric responses.

Lanthanide coordination polymers assembled from triazine-based flexible polycarboxylate ligands and their luminescent properties

Two flexible triazine-based polycarboxylate ligands, 1,3,5-triazine-2-iminodiacetic acid-4,6-bis(L-alanine) (H4L1) and 1,3,5-triazine-2-iminodiacetic acid-4,6-biglycine (H4L2), have been designed and used to construct a series of luminescent lanthanide coordination polymers {[Ln(HL1)](H2O)5}n (Ln = 1, Tb; 2, Eu; 3, Gd) and {[Ln(HL2)(H2O)](H2O)2}n (Ln = 4, Tb; 5, Eu; 6, Gd). The complexes were structurally authenticated by single-crystal X-ray diffraction, revealing that isostructural complexes 1–3, derived from H4L1, possess a 2-D framework with the monoclinic space group C2/c, whereas isostructural complexes 4–6, based on H4L2, exhibit a 2-D layer structure with the monoclinic space group P2(1)/c. Solid-state photoluminescence properties of the complexes were investigated. Complexes 1 and 2 exhibit remarkable green and red luminescence emissions with high quantum yields up to 67% and 68%, respectively, and millisecond-level lifetimes. Nevertheless, complexes 4 and 5 feature weak quantum yields (9.9% for 4; and 30% for 5).

Two cationic metal–organic frameworks featuring different cage-to-cage connections: syntheses, crystal structures, photoluminescence and gas sorption properties

Solvothermal reactions of a neutral rigid tripodal ligand, 1,3,5-tris(1-imidazolyl)benzene (tib), with Zn(NO3)2·6H2O and Zn(ClO4)2·6H2O produced two metal–organic frameworks, [Zn3(tib)4·6NO3·6H2O·3DMA]n (1) and [Zn2(tib)3·4ClO4·6H2O·6DMA]n (2) (DMA = N,N-dimethylacetamide), respectively, which feature different cage-to-cage connections. Both compounds 1 and 2 exhibit 3D cationic frameworks with charge-balancing extraframework anions. Interestingly, the counterions NO3− and ClO4− play an important role in the fabrication of structures of 1 and 2. Compound 1 shows 2-fold interpenetration while 2 gives a non-interpenetrated 3D porous framework. Adjacent M6L4 octahedral cages in compound 1 are further linked via vertex sharing to construct a 3D framework. For compound 2, neighboring octahedral cages connect with each other through sharing four metal ions which are in the equatorial plane to generate a 2D layer. Furthermore, the 2D layers are linked by other layers via sharing the other two metal ions which are in the axial position, finally forming a 3D supramolecular framework. The photoluminescence of compounds 1 and 2 has been investigated in the solid state. Gas sorption measurements were conducted on the activated 1, showing a H2 uptake of 1.2 wt% at 77 K and 1 bar with high initial adsorption enthalpy of 8.4 kJ mol−1.

Effect of anions on the self-assembly of Zn(II) with a hydrogenated Schiff base ligand: structural diversity and photoluminescent properties

A flexible tetradentate ligand, 1,2-bis(4′-pyridylmethylamino)ethane (L), has been used for assembly with different Zn(II) salts. Six complexes with diverse structures from zero- to two-dimensional array have been prepared under mild conditions. Complexes (Zn2LCl4·2H2O)2 (1) and (Zn2LBr4·H2O)2 (2) form novel discrete M4L2 square metallacycles, which are further linked by Cl (or Br)⋯H hydrogen bonds and weak intermolecular interactions to result in 3D frameworks. Complex [ZnL(SCN)2·2H2O]n (3) is a one-dimensional hinged chain. Different chains are stacked in a staggered pattern by the π–π interactions. Complex (ZnLCl2·2H2O)n (4) displays an infinite one-dimensional hinged chain too, but its 3D supramolecular structure is formed by the intrachain and interchain hydrogen bonds. Both complexes [ZnL(H2O)2·2ClO4·4H2O]n (5) and [ZnLAc(H2O)·Ac·2H2O]n (6) exhibit 2D networks. Structural analyses of complexes 1–6 suggest that anions Cl−, Br−, SCN−, ClO4−, and Ac− play an important role in the formation of those complexes with hydrogenated Schiff base L. Furthermore, the photoluminescence of complexes 1–6 have also been investigated in the solid state.

Influence of Central Metalloligand Geometry on Electronic Communication between Metals: Syntheses, Crystal Structures, MMCT Properties of Isomeric Cyanido-Bridged Fe2Ru Complexes, and TDDFT Calculations

To investigate how the central metalloligand geometry influences distant or vicinal metal-to-metal charge-transfer (MMCT) properties of polynuclear complexes, cis- and trans-isomeric heterotrimetallic complexes, and their one- and two-electron oxidation products, cis/trans-[Cp(dppe)Fe(II)NCRu(II)(phen)2CN-Fe(II)(dppe)Cp][PF6]2 (cis/trans-1[PF6]2), cis/trans-[Cp(dppe)Fe(II)NCRu(II)(phen)2CNFe(III)-(dppe)Cp][PF6]3 (cis/trans-1[PF6]3) and cis/trans-[Cp(dppe)Fe(III)NCRu(II)(phen)2CN-Fe(III)(dppe)Cp][PF6]4 (cis/trans-1[PF6]4) have been synthesized and characterized. Electrochemical measurements show the presence of electronic interactions between the two external Fe(II) atoms of the cis- and trans-isomeric complexes cis/trans-1[PF6]2. The electronic properties of all these complexes were studied and compared by spectroscopic techniques and TDDFT//DFT calculations. As expected, both mixed valence complexes cis/trans-1[PF6]3 exhibited different strong absorption signals in the NIR region, which should mainly be attributed to a transition from an MO that is delocalized over the Ru(II)-CN-Fe(II) subunit to a Fe(III) d orbital with some contributions from the co-ligands. Moreover, the NIR transition energy in trans-1[PF6]3 is lower than that in cis-1[PF6]3, which is related to the symmetry of their molecular orbitals on the basis of the molecular orbital analysis. Also, the electronic spectra of the two-electron oxidized complexes show that trans-1[PF6]4 possesses lower vicinal Ru(II) → Fe(III) MMCT transition energy than cis-1[PF6]4. Moreover, the assignment of MMCT transition of the oxidized products and the differences of the electronic properties between the cis and trans complexes can be well rationalized using TDDFT//DFT calculations.

Self assembly of a tren-derivative hydrogenated Schiff base with transition metal ions: syntheses, crystal structures and photoluminescent properties

A new flexible multidentate hydrogenated Schiff base tris{2-[(4′-pyridylmethyl)amino]ethyl}amine (L), derived from tren (tris(2-aminoethyl)amine) and 4-pyridinecarboxaldehyde, has been used to prepare four novel complexes 1–4. Complex {[Zn1.5L(H2O)3](NO3)3·2.5H2O}2 (1) exhibits a mononuclear zero-dimensional structure. Complex {[Cd2LCl4(H2O)]·H2O}n (2) shows a one-dimensional meso-helical structure which consists of two adjacent hydrogen-bonded three-stranded single-helical (P and M) chains. Intermolecular CH (or NH)⋯Cl hydrogen bonds play important roles in the formation of the triple helices and meso-helical structure. Complexes {[Cd1.5L(NO3)2(H2O)]NO3·2H2O}n (3) and {[Mn1.5LCl2(H2O)]Cl·6H2O}n (4) display similar 2D layer networks, which are composed of alternate right-handed and left-handed helical chains by sharing Cd or Mn ions. Moreover, the photoluminescence of complexes 1–3 have also been investigated in the solid state.