Adsorptive separation is very important in industry. Generally, the process uses porous solid materials such as zeolites, activated carbons, or silica gels as adsorbents. With an ever increasing need for a more efficient, energy-saving, and environmentally benign procedure for gas separation, adsorbents with tailored structures and tunable surface properties must be found. Metal–organic frameworks (MOFs), constructed by metal-containing nodes connected by organic bridges, are such a new type of porous materials. They are promising candidates as adsorbents for gas separations due to their large surface areas, adjustable pore sizes and controllable properties, as well as acceptable thermal stability. This critical review starts with a brief introduction to gas separation and purification based on selective adsorption, followed by a review of gas selective adsorption in rigid and flexible MOFs. Based on possible mechanisms, selective adsorptions observed in MOFs are classified, and primary relationships between adsorption properties and framework features are analyzed. As a specific example of tailor-made MOFs, mesh-adjustable molecular sieves are emphasized and the underlying working mechanism elucidated. In addition to the experimental aspect, theoretical investigations from adsorption equilibrium to diffusion dynamics via molecular simulations are also briefly reviewed. Furthermore, gas separations in MOFs, including the molecular sieving effect, kinetic separation, the quantum sieving effect for H2/D2 separation, and MOF-based membranes are also summarized (227 references).

Selective gas adsorption and separation in metal–organic frameworks

Luminescent Functional Metal–Organic Frameworks

Metal–organic frameworks (MOFs) display a wide range of luminescent behaviors resulting from the multifaceted nature of their structure. In this critical review we discuss the origins of MOF luminosity, which include the linker, the coordinated metal ions, antenna effects, excimer and exciplex formation, and guest molecules. The literature describing these effects is comprehensively surveyed, including a categorization of each report according to the type of luminescence observed. Finally, we discuss potential applications of luminescent MOFs. This review will be of interest to researchers and synthetic chemists attempting to design luminescent MOFs, and those engaged in the extension of MOFs to applications such as chemical, biological, and radiation detection, medical imaging, and electro-optical devices (141 references).

Luminescent Metal–Organic Frameworks

Lanthanide-based luminescent hybrid materials.

Metal–organic frameworks based on trivalent lanthanides (LnMOFs) are a very promising class of materials for addressing the challenges in engineering of luminescent centres. Lanthanide-bearing phosphors find numerous applications in lighting, optical communications, photonics and biomedical devices. In this critical review we discuss the potential of LnMOFs as multifunctional systems, which combine light emission with properties such as microporosity, magnetism, chirality, molecule and ion sensing, catalysis and activity as multimodal imaging contrast agents. We argue that these materials present a unique chance of observing synergy between several of these properties, such as the coupling between photoluminescence and magnetism. Moreover, an integrated approach towards the design of efficient, stable, cheap, environmentally-friendly and multifunctional luminescent LnMOFs is still missing. Although research into LnMOFs is at its early stage and much basic knowledge is still needed, the field is ripe for new ideas, which will enable sensor devices and photonic prototypes to become a commercial reality (81 references).

Luminescent multifunctional lanthanides-based metal–organic frameworks

Two 3d-4f heterometallic coordination polymers {[Ln(PDA)3Mn1.5(H2O)3].3.25H2O}infinity with 1D channels were synthesized under hydrothermal conditions (PDA = pyridine-2,6-dicarboxylic acid; Ln = Eu (1); Ln = Tb (2)). The emission intensities of 1 and 2 increased significantly upon addition of Zn2+, while the introduction of other metal ions caused the intensity to be either unchanged or weakened. The case implies that 1 and 2 may be used as luminescent probes of Zn2+.

Coordination Polymers Containing 1D Channels as Selective Luminescent Probes

A nanotubular 3D heterometallic zeolitic polymer, {[Yb(PDA)3Mn1.5(H2O)3]·1.5H2O}n (2), was designed and synthesized by simply tuning the amount of coordinated water on the Mn ion in the molecular ladder polymer {[Yb(PDA)3Mn1.5(H2O)6]·6H2O}n (1). 1 and 2 were structurally and magnetically characterized. The water molecules capsulated within the nanotube were arrayed into an unprecedented “water” pipe. The robust 2 retained intact networks after the removal of guest water trapped in the nanotubes and even after methanol replaced guest water.

Design and synthesis of 3d-4f metal-based zeolite-type materials with a 3D nanotubular structure encapsulated "water" pipe.

Two Dy-Mn polymers, {[Dy(L1)3Mn(1.5)(H2O)3]3.125H2O}n (1, L1 = pyridine-2,6-dicarboxylic acid) and {[Dy(L2)3Mn(1.5)(H2O)6]8.25H2O}n (2, L2 = 4-hydroxylpyridine-2,6-dicarboxylic acid), with high symmetry (S6) have been prepared. Polymer 1 has a nanoporous 3D framework with channel of about 17.6 A diameter, while 2 has a honeycomb-type 2D structure with the cavity of approximately 14.4 A diameter. In the construction of multidimensional porous polymers with 3d-4f mixed metals, it is the first observation that a ligand substituent effect leads to dramatic differences in the structures formed. Luminescent studies reveal that the emission intensities of 1 and 2 increase significantly upon the addition of Mg2+, whereas the introduction of other metal ions leaves the intensity unchanged or even weakens it; hence, both of them may serve as good candidates of Mg2+ luminescent probes. To our knowledge, complex 1 is also the first example of a 3d-4f metal-based nanoporous polymer to exhibit luminescent selectivity for Mg2+. Magnetic susceptibility measurements reveal a rather rare ferromagnetic interaction in 2. Thermal gravimetric analyses and powder X-ray diffraction investigations have also been performed, suggestive of high thermal stability of 1.

A Promising MgII‐Ion‐Selective Luminescent Probe: Structures and Properties of Dy–Mn Polymers with High Symmetry

A series of novel two-dimensional (2D) and three-dimensional (3D) praseodymium coordination polymers, namely, {[Pr3(PDA)4(HPDA)(H2O)8]·8H2O}n (2), {[Pr2(PDA)3(H2O)3]·H2O}n (3), {[Pr(PDA)(H2O)4]·ClO4}n (4), and {[Pr2(PDA)2(H2O)5SO4]·2H2O}n (5) (PDA = pyridine-2,6-dicarboxylic anion), was designed and synthesized under hydrothermal conditions. Complexes 1−3 (chainlike polymer, {[Pr(PDA)(HPDA)(H2O)2]·4H2O}n (1) was also obtained independently by us, although it has been reported recently by Ghosh et al.) were fabricated successfully by simply tuning the Pr/PDA ratio and exhibited various and intriguing topological structures from a 1D chain to a 3D network. While the synthetic strategy of 5 was triggered and further performed only after 1 was structurally characterized. The complexes were characterized by X-ray single-crystal determination, spectroscopic, and variable-temperature magnetic susceptibility analyses. In complex 2 an unusual nanosized square motif as a building block constructed by eight Pr ions ...

Xiao-Yan Chen

Papers

Coordination Polymers Containing 1D Channels as Selective Luminescent Probes

Design and synthesis of 3d-4f metal-based zeolite-type materials with a 3D nanotubular structure encapsulated "water" pipe.

A Promising MgII‐Ion‐Selective Luminescent Probe: Structures and Properties of Dy–Mn Polymers with High Symmetry

Systematic investigation of the hydrothermal syntheses of Pr(III)-PDA (PDA = pyridine-2,6-dicarboxylate anion) metal-organic frameworks.

A porous 3D heterometal-organic framework containing both lanthanide and high-spin Fe(II) ions