Weak interactions in imidazole-containing zinc(II)-based metal–organic frameworks

The self-assembly of the two zinc(II) metal–organic frameworks, [Zn₂(L)(bdc)₂]·3MeOH·4H₂O}_n ( 1 , L = 2-(pyridin-4-yl)-3H-imidazo[4,5-c]pyridine, H₂bdc = 1,4-benzenedicarboxylic acid) and [Zn₂(L)(bdc)₂]·2DMF·H₂O}_n ( 2 ), was achieved under mild reaction conditions. Both compounds 1 and 2 were structurally characterized by single-crystal X-ray diffraction analysis. Interestingly, the coordination modes of the ligand L in two structures are entirely different. Compounds 1 and 2 were made up of paddle wheel-shaped {Zn₂(O₂C)₄} secondary building unit (SBU) clusters, which adopted three-dimensional structures with a pcu topology. Rich weak interactions were observed in the structures of both 1 and 2 . The uncoordinated imidazole and pyridine moieties exhibited electron donor–acceptor interactions, π–π stacking, hydrogen bonding, and CH–π interactions. These interactions also facilitated the abilities of the framework to adsorb CO₂ molecules. Gas adsorption studies revealed that compound 1 selectively adsorbed CO₂ (131.1 cm³/g) over N₂ (23.5 cm³/g) and H₂ (36.5 cm³/g) at a pressure of 1 atm.     

Solvent‐Dependent Synthesis from Layer to Microporous Pillared‐Layer Framework for Selective Sorption of Gas Light Hydrocarbons

Three metal‐organic frameworks, [Zn₃(bdc)₃(DMA)₂] ( 1 ) (H₂bdc = terephthalic acid; DMA = N,N‐dimethylacetamide), [Zn₃(bdc)₃(DMA)(DMPU)] ( 2 ) (DMPU = 1,3‐dimethylpropyleneurea), and [Zn₃(bdc)₄(Hdma)₂] ( 3 ) [Hdma = protonated dimethylamine (Me₂NH₂)] were synthesized by using different solvents. The solvents determine the framework architectures range from layer to microporous pillared‐layer framework. The microporous framework has 8‐connected bcg topology and shows selective sorption ability for gas light hydrocarbons.     

Modular,Homochiral, Porous Coordination Polymers: Rational Design,Enantioselective Guest Exchange Sorption and Ab Initio Calculations of Host–Guest Interactions

Two new, homochiral, porous metal–organic coordination polymers [Zn₂(ndc){(R)‐man}(dmf)]?3DMF and [Zn₂(bpdc){(R)‐man}(dmf)]?2DMF (ndc=2,6‐naphthalenedicarboxylate; bpdc=4,4′‐biphenyldicarboxylate; man=mandelate; dmf=N,N′‐dimethylformamide) have been synthesized by heating Zn^II nitrate, H₂ndc or H₂bpdc and chiral (R)‐mandelic acid (H₂man) in DMF. The colorless crystals were obtained and their structures were established by single‐crystal X‐ray diffraction. These isoreticular structures share the same topological features as the previously reported zinc(II) terephthalate lactate [Zn₂(bdc){(S)‐lac}(dmf)]?DMF framework, but have larger pores and opposite absolute configuration of the chiral centers. The enhanced pores size results in differing stereoselective sorption properties: the new metal–organic frameworks effectively and stereoselectively (ee up to 62 %) accommodate bulkier guest molecules (alkyl aryl sulfoxides) than the parent [Zn₂(bdc){(S)‐lac}(dmf)]?DMF, while the latter demonstrates decent enantioselectivity toward precursor of chiral anticancer drug sulforaphane, CH₃SO(CH₂)₄OH. The new homochiral porous metal–organic coordination polymers are capable of catalyzing a highly selective oxidation of bulkier sulfides (2‐NaphSMe (2‐C₁₀H₇SMe) and PhSCH₂Ph) that could not be achieved by the smaller‐pore [Zn₂(bdc){(S)‐lac}(dmf)]?DMF. The sorption of different guest molecules (both R and S isomers) into the chiral pores of [Zn₂(bdc){(S)‐lac}(dmf)]?DMF was modeled by using ab initio calculations that provided a qualitative explanation for the observed sorption enantioselectivity. The high stereo‐preference is accounted for by the presence of coordinated inner‐pore DMF molecule that forms a weak C? H???O bond between the DMF methyl group and the (S)‐PhSOCH₃ sulfinyl group.     

Construction Of Two New 6‐connected Manganese(II) Metal Organic Frameworks via Isomeric Biphenyldicarboxylates Based on the Dinuclear Secondary Building Unit

Two coordination polymers, namely {[Mn(2,4′‐bpdc)(bimb)(H₂O)_0.5] · 0.5H₂O}_n ( 1 ) and [Mn(4,4′‐bpdc)(bimb)]_n · 2.5H₂O ( 2 ) [2,4′‐bpdc = biphenyl‐2,4′‐dicarboxylate, 4,4′‐bpdc = biphenyl‐4,4′‐dicarboxylate, and bimb = 1,4‐bis(1‐imidazol‐yl)‐2,5‐dimethyl benzene], were hydrothermally synthesized by reactions of manganese(II) salt with the rigid ligand 1,4‐bis(1‐imidazol‐yl)‐2,5‐dimethyl benzene and isomeric biphenyl dicarboxylate ligands. Complex 1 has an unusual 6‐connected three‐dimensional (3D) architecture with point symbol (4⁴.6¹¹). Complex 2 has also a 3D structure with two‐interpenetrated pcu topology with point symbol (4¹².6³). Structural comparisons show that the positions of the carboxylate groups in the ligand backbone play an important role in governing the structural topologies of these complexes.     

Fluorescent Cadmium Bipillared-Layer Open Frameworks: Synthesis,Structures, Sensing of Nitro Compounds,and Capture of Volatile Iodine

Fluorescent Cd metal–organic frameworks (MOFs), [Cd₂(dicarboxylate)₂(NI-bpy-44)₂] (dicarboxylate=benzene-1,4-dicarboxylate (1,4-bdc, 1 ), 2-bromobenzene-1,4-dicarboxylate (Br-1,4-bdc, 2 ), 2-nitrobenzene-1,4-dicarboxylate (NO₂-1,4-bdc, 3 ), biphenyl-4,4′-dicarboxylate (bpdc, 4 ); NI-bpy-44=N-(pyridin-4-yl)-4-(pyridin-4-yl)-1,8-naphthalimide)), featuring non- and twofold interpenetrating pcu -type bipillared-layer open structures with sufficient free voids of 58.4, 51.4, 51.5, and 41.4 %, respectively, have been hydro(solvo)thermally synthesized. MOFs 1 – 4 emitted solid-state blue or cyan fluorescence emissions at 447±7 nm, which mainly arose from NI-bpy-44 and are dependent on the incorporated solvents. After immersing the crystalline samples in different solvents, that is, H₂O and DMSO ( 1 and 2 ) as well as nitrobenzene and phenol ( 1 – 4 ), they exhibited a remarkable fluorescence quenching effect, whereas o-xylene and p-xylene ( 4 ) caused significant fluorescence enhancement. The sensing ability of MOFs 1 – 4 toward nitro compounds carried out in the vapor phase showed that nitrobenzene and 2-nitrophenol displayed detectable fluorescence quenching with 1 , 2 , and 4 whereas 4-nitrotoluene was an effective fluorescence quencher for 1 and 2 ; this is most likely attributed to their electron-deficient properties and higher vapor pressures. Moreover, MOFs 1 – 4 are highly reusable for quick capture of volatile iodine, as supported by clear crystal color change and also by immense fluorescence quenching responses owing to the donor–acceptor interaction. Low-pressure CO₂ adsorption isotherms indicate that activated materials 1′ – 4′ are inefficient at taking up CO₂.     

Organic carboxylate anions effect on the structures of a series of Mn(II) complexes based on 2-phenylimidazo[4,5-f]1,10-phenanthroline ligand

In our efforts to tune the structures of Mn(II) complexes by selection of organic carboxylic acid ligands, six new complexes [Mn(PIP)₂Cl₂] (1), [Mn(PIP)₂(4,4′-bpdc)(H₂O)]·2H₂O (2), [Mn(PIP)₂(1,4-bdc)] (3), [Mn(PIP)(1,3-bdc)] (4), [Mn(PIP)₂(2,6-napdc)]·H₂O (5), and [Mn(PIP)(1,4-napdc)]·H₂O (6) were obtained, where PIP=2-phenylimidazo[4,5-f]1,10-phenanthroline, 4,4′-H₂bpdc=biphenyl-4,4′-dicarboxylic acid, 1,4-H₂bdc=benzene-1,4-dicarboxylic acid, 1,3-H₂bdc=benzene-1,3-dicarboxylic acid, 2,6-H₂napdc=2,6-naphthalenedicarboxylic acid, 1,4-H₂napdc=1,4-naphthalenedicarboxylic acid. All complexes have been structurally characterized by IR, elemental analyses, and single crystal X-ray diffraction. Structural analyses show that complexes 1 and 2 possess mononuclear structures, complexes 3, 4, and 5 feature chain structures, and complex 6 exhibits a 2D (4,4) network. The structural difference of 1–6 indicates that organic carboxylate anions play important roles in the formation of such coordination architectures. Furthermore, the thermal properties of complexes 1–6 and the magnetic property of 4 have been investigated.     

Poly[bis(μ‐benzene‐1,4‐dicarboxylato)bis[μ‐6‐(4‐pyridyl)‐5H‐imidazolo[4,5‐f][1,10]phenanthroline]dilead(II)]: an interpenetrating α‐Po net

The asymmetric unit of the title compound, [Pb₂(C₈H₄O₄)₂(C₁₈H₁₁N₅)₂]_n, contains two Pb^II atoms, two benzene‐1,4‐dicarboxylate (1,4‐bdc) dianions and two 6‐(4‐pyridyl)‐5H‐imidazolo[4,5‐f][1,10]phenanthroline (L) ligands. Each Pb^II atom is eight‐coordinated by three N atoms from two different L ligands and five carboxylate O atoms from three different 1,4‐bdc dianions. The two 1,4‐bdc dianions (1,4‐bdc₁ and 1,4‐bdc₂) show different coordination modes. Each 1,4‐bdc₁ coordinates to two Pb^II atoms in a chelating bis‐bidentate mode. Each carboxylate group of the 1,4‐bdc₂ anion connects two Pb^II atoms in a chelating–bridging tridentate mode to form a dinuclear unit. Neighbouring dinuclear units are connected together by the aromatic backbone of the 1,4‐bdc dianions and the L ligands into a three‐dimensional six‐connected α‐polonium framework. The most striking feature is that two identical three‐dimensional single α‐polonium nets are interlocked with each other, thus leading directly to the formation of a twofold interpenetrated three‐dimensional α‐polonium architecture. The framework is held together in part by strong N—H...O hydrogen bonds between the imidazole NH groups of the L ligands and the carboxylate O atoms of 1,4‐bdc dianions within different α‐polonium nets.     

Tuning CO2 Uptake and Reversible Iodine Adsorption in Two Isoreticular MOFs through Ligand Functionalization

The synthesis and characterization of two isoreticular metal–organic frameworks (MOFs), {[Cd(bdc)(4‐bpmh)]}_n?2 n(H₂O) ( 1 ) and {[Cd(2‐NH₂bdc)(4‐bpmh)]}_n?2 n(H₂O) ( 2 ) [bdc=benzene dicarboxylic acid; 2‐NH₂bdc=2‐amino benzene dicarboxylic acid; 4‐bpmh=N,N‐bis‐pyridin‐4‐ylmethylene‐hydrazine], are reported. Both compounds possess similar two‐fold interpenetrated 3D frameworks bridged by dicarboxylates and a 4‐bpmh linker. The 2D Cd‐dicarboxylate layers are extended along the a‐axis to form distorted square grids which are further pillared by 4‐bpmh linkers to result in a 3D pillared‐bilayer interpenetrated framework. Gas adsorption studies demonstrate that the amino‐functionalized MOF 2 shows high selectivity for CO₂ (8.4 wt % 273 K and 7.0 wt % 298 K) over CH₄, and the uptake amounts are almost double that of non‐functional MOF 1 . Iodine (I₂) adsorption studies reveal that amino‐functionalized MOF 2 exhibits a faster I₂ adsorption rate and controlled delivery of I₂ over the non‐functionalized homolog 1 .     

1-D wave-like chain,twofold 2-D layer,and chiral 3-D open framework based on multidentate ligand: structural diversities,thermal properties,and photoluminescence

From 1-D to 3-D zinc coordination polymers based on multifunctional flexible 4-(1,2,4-triazole-methylene)-benzonitrile (tzbt), {[Zn(tzbt)₂(bdc)]·2H₂O}_n (1), [Zn(tzbc)₂]_n (2), and [Zn(bpdc)(H₂O)]_n (3) (bdc = 1,4-benzenedicarboxylic acid, tzbc = 4-(1,2,4-triazole-methylene)-benzoic acid, bpdc = 4,4′-biphenyldicarboxylic acid), were synthesized under hydrothermal conditions. The tzbt was synthesized by N-alkylation and hydrolyzed in situ to produce tzbc (in 2). Single-crystal X-ray diffraction analysis reveals that 1 displays 1-D wave-like chains based on [Zn(bdc)]_n. 2 is a chiral twofold interpenetrating 2-D architecture constructed with “V”-shaped tzbc. 3 is a 3-D chiral compound constructed from achiral H₂bpdc with right-handed helical chains. 1–3 display stable blue-emitting luminescence with emission maxima ranging from 383 to 410 nm, depending on ligand-centered π*→π transitions. The effects of different polarity solvents and temperature on luminescence are discussed. TGA and VT-XPRD reveal that 2 has thermal stability to 360 °C.     

Controlling the BET Surface Area of Porous Carbon by Using the Cd/C Ratio of a Cd–MOF Precursor and Enhancing the Capacitance by Activation with KOH

Herein, four new cadmium metal–organic frameworks (Cd–MOFs), [Cd(bib)(bdc)]_∞ ( 1 ), [Cd(bbib)(bdc)(H₂O)]_∞ ( 2 ), [Cd(bibp)(bdc)]_∞ ( 3 ), and [Cd₂(bbibp)₂(bdc)₂(H₂O)]_∞ ( 4 ), have been constructed from the reaction of Cd(NO₃)₂ ? 4 H₂O with 1,4‐benzenedicarboxylate (H₂bdc) and structure‐related bis(imidazole) ligands (1,4‐bis(imidazol‐1‐yl)benzene (bib), 1,4‐bis(benzoimidazol‐1‐yl)benzene (bbib), 4,4′‐bis(imidazol‐1‐yl)biphenyl (bibp), and 4,4′‐bis(benzoimidazol‐1‐yl)biphenyl (bbibp)) under solvothermal conditions. Cd–MOF 1 shows a 2D (4,4) lattice with parallel interpenetration, whereas 2 displays an interesting 3D interpenetrating dia network, 3 exhibits an unusual 3D interpenetrating dmp network, and 4 presents a 3D self‐catenated pillar‐layered framework with a Schäfli symbol of [4³ ? 6³]₂ ? [4⁶ ? 6¹⁶ ? 8⁶]. The structural diversity indicates that the backbone of the bis(imidazole) ligand (including the terminal group and spacer) plays a crucial role in the assembly of mixed‐ligand frameworks. By using the pore‐forming effect of cadmium vapor, for the first time we have utilized these Cd–MOFs as precursors to further prepare porous carbon materials (PCs) in a calcination–thermolysis procedure. These PCs show different porous features that correspond to the topological structures of Cd–MOFs. Significantly, it was found that the specific surface area and capacitance of PCs are tuned by the Cd/C ratio of the MOF. Furthermore, the as‐synthesized PCs were processed with KOH to obtain activated porous carbon materials (APCs) with higher specific surface area and porosity, which greatly promoted the energy‐storage capacity. After full characterization, we found that APC‐bib displays the largest specific surface area (1290 m² g^?1) and total pore volume (1.37 cm³ g^?1) of this series of carbon materials. Consequently, APC‐bib demonstrates the highest specific capacitance of 164 F g^?1 at a current density of 0.5 A g^?1, and also excellent retention of capacitance (≈89.4 % after 5000 cycles at 1 A g^?1). Therefore, APC‐bib has great potential as the electrode material in a supercapacitor.     

A novel threefold‐interpenetrating primitive cubic network based on a dinuclear Zn2 node

In the mixed‐ligand metal–organic polymeric compound poly[[μ₂‐1,4‐bis(imidazol‐1‐yl)benzene](μ₂‐terephthalato)dizinc(II)], [Zn₂(C₈H₄O₄)₂(C₁₂H₁₀N₄)]_n or [Zn₂(bdc)₂(bib)]_n [H₂bdc is terephthalic acid and bib is 1,4‐bis(imidazol‐1‐yl)benzene], the asymmetric unit contains one Zn^II ion, with two half bdc anions and one half bib molecule lying around inversion centers. The Zn^II ion is in a slightly distorted tetrahedral environment, coordinated by three carboxylate O atoms from three different bdc anions and by one bib N atom. The crystal structure is constructed from the secondary building unit (SBU) [Zn₂(CO₂)₂N₂O₂], in which the two metal centers are held together by two bdc linkers with bis(syn,syn‐bridging bidentate) bonding modes. The SBU is connected by bdc bridges to form a two‐dimensional grid‐like (4,4)‐layer, which is further pillared by the bib ligand. Topologically, the dinuclear SBU can be considered to be a six‐connected node, and the extended structure exhibits an elongated primitive approximately cubic framework. The three‐dimensional framework possesses a large cavity with dimensions of approximately 10 × 13 × 17 Å in cross‐section. The potential porosity is filled with mutual interpenetration of two identical equivalent frameworks, generating a novel threefold interpenetrating network with an α‐polonium topology [Abrahams, Hoskins, Robson & Slizys (2002). CrystEngComm, 4 , 478–482].     

Metal-ion-dependent,Solvent-mediated Structural Transformation and Simultaneous Partial Transmetalation of an srs Framework into Desulfurization-efficient Co-Cu-HKUST-1

[Co₂(BTC)(Cl)(DMA)₃] ( 1 ) (BTC^3– = benzene-1,3,5-tricarboxylate, DMA = N,N-dimethylacetamide) obtained from the reaction between Co²⁺ and H₃BTC in DMA features a three-dimensional srs framework built of 3-connected {Co₂(COO)₃} as secondary building units and BTC^3– as spacers. When exposed to DMA solution of Cu(NO₃)₂, 1 was progressively transformed into the first heterometallic Co-Cu-HKUST-1 ([Co_0.14Cu_2.86(BTC)₂]) ( 2 ) of such kind via unusually solvent-mediated structural transformation and simultaneous partial transmetalation. While the mechanism for such conversion is proposed based on systematic studies, 2 was revealed to be an equally efficient desulfurization adsorbent as the homometallic Cu-HKUST-1 in removing thiophene (0.142 mmol S per gram of adsorbent). However, when exposed to Zn(NO₃)₂ solution in DMA for longer time, 1 retained its framework with limited metal-ion exchange, resulting in the formation of [Co_1.93Zn_0.07(BTC)(Cl)(DMA)₃] ( 3 ). Possible reasons responsible for the formation of 2 and 3 through different routes could be due to the less solubility and more thermodynamic stability of 2 in comparison with those of 1 , and the different coordination geometries which Co²⁺, Zn²⁺ and Cu²⁺ prefer.     

X-ray diffraction study of Al-Si melts

New layered metal-organic coordination polymers [Zn₃(bpdc)₃(DMA)₂]·3DMA (1) (H₂bpdc = 4,4′-biphenyldicaboxylic acid, DMA = N,N′-dimethylacetamide) and [Zn₃(bdc)₃(im)₂]·1.5H₂O (2) (H₂bdc = terephtalic acid, im = imidazole) are synthesized and characterized by X-ray crystallography.     

A Co‐MOF with a (4,4)‐connected binodal two‐dimensional topology: synthesis,structure and photocatalytic properties

The Co‐MOF poly[[diaqua{μ₄‐1,1,2,2‐tetrakis[4‐(1H‐1,2,4‐triazol‐1‐yl)phenyl]ethylene‐κ⁴N:N′:N′′:N′′′}cobalt(II)] benzene‐1,4‐dicarboxylic acid benzene‐1,4‐dicarboxylate], {[Co(C₃₄H₂₄N₁₂)(H₂O)₂](C₈H₄O₄)·C₈H₆O₄}_n or {[Co(ttpe)(H₂O)₂](bdc)·(1,4‐H₂bdc)}_n, (I), was synthesized by the hydrothermal method using 1,1,2,2‐tetrakis[4‐(1H‐1,2,4‐triazol‐1‐yl)phenyl]ethylene (ttpe), benzene‐1,4‐dicarboxylic acid (1,4‐H₂bdc) and Co(NO₃)₂·6H₂O, and characterized by single‐crystal X‐ray diffraction, IR spectroscopy, powder X‐ray diffraction (PXRD), luminescence, optical band gap and valence band X‐ray photoelectron spectroscopy (VB XPS). Co‐MOF (I) shows a (4,4)‐connected binodal two‐dimensional topology with a point symbol of {4⁴·6²}{4⁴·6²}. The two‐dimensional networks capture free neutral 1,4‐H₂bdc molecules and bdc^2? anions, and construct a three‐dimensional supramolecular architecture via hydrogen‐bond interactions. MOF (I) is a good photocatalyst for the degradation of methylene blue and rhodamine B under visible‐light irradiation and can be reused at least five times.     

Three Functionalized Zinc(II)/Cobalt(II) Coordination Complexes Demonstrating Fluorescent Sensing Activities towards Fe3+ Ions and Photocatalytic Selectivity for Organic Dyes

Three new zinc(II)/cobalt(II) coordination complexes [Zn(HBTB)(L)_0.5] ( 1 ), [Zn(HCPPA)(L)] ( 2 ), and [Co(HCPPA)(L)] · 2H₂O ( 3 ) [H₃BTB = 1,3,5-tri(4-carboxylphenyl)benzene, H₃CPPA = 5-(4-carboxyl-phenoxy)-isophthalic acid, L = N¹,N⁴-bis(3-pyridyl)naphthaldiamide] were solvothermally synthesized. The structural characterization reveals that complex 1 represents a 3D coordination framework with a binodal 3,4-connected {4.10²}₂{4.10⁵}₂ topology constructed from the 2D [Zn(HBTB)]_n polymeric double-layers and the bidentate L ligands. Complex 2 is a 1D metal-organic chain derived from the dinuclear [Zn₂(HCPPA)₂] loops and [Zn₂(L)₂] loops. Complex 3 possesses a binodal 3,5-connected {4².6}{4³.6.8⁴.10²} topological 2D layered architecture based on the [Co₂(HCPPA)₂] ribbon chains and the bidentate L ligands. For 2 and 3 , their adjacent chains or layers are respectively stacked into 3D supramolecular architectures via the hydrogen bonds. Moreover, the fluorescent and fluorescent sensing activities towards small solvent molecules of coordination complexes 1 and 2 , the photocatalyitc properties of 1 – 3 towards organic dyes were studied.     

Syntheses,Structures, and Catalytic Properties of Two 2D Manganese(II) Coordination Polymers Containing Flexible Bis(benzimidazole) Ligands

Two Mn^II coordination polymers based on the flexible bis(benzimidazole) and dicarboxylic acids, namely, [Mn(L1)(bpdc)(H₂O)_0.5]_n ( 1 ) and [Mn(L2)(Htbi)₂]_n ( 2 ) [L1 = 1,4‐bis(5,6‐dimethylbenzimidazol‐1‐ylmethyl)benzene, H₂bpdc = 4,4′‐biphenyldicarboxylic acid, L2 = 1,4‐bis(5,6‐dimethylbenzimidazole)butane, H₂tbi = 5‐tert‐butyl isophthalic acid] were hydrothermally synthesized and characterized by elemental analysis, IR spectroscopy, as well as single‐crystal X‐ray diffraction. Both of the complexes crystallize in the triclinic P$\bar{1}$ space group and present distorted octahedral configurations. Complex 1 possesses a 2D binodal (3,5)‐connected 3,5L2 network with the point symbol of (4².6⁷.8)(4².6), whereas 2 features a 2D uninodal 3‐connected hcb topology and the Schläfli symbol is (6³). Complexes 1 and 2 ultimately are extended into 3D supramolecular framework via π–π stacking and O–H ··· O hydrogen bonding interaction, respectively. Moreover, both of the complexes manifest excellent catalytic activities for the degradation of Congo red.     

NO Reactions Inside Crystals

Reactions of chemisorbed reagents inside the crystalline molecular solid state are rare but offer unexploited methods for selective solvent-free chemical synthesis. Here we show that the greenhouse gas precursor, nitric oxide (NO) is chemisorbed by crystals of the hexafluorophosphate salts of complexes containing dicobalt sites. On NO sorption a cascade of reactions results in the in-crystal synthesis of nitrite and other gaseous NO_x. Recrystallization enabled structural elucidation of the mixed valent {[(bpbp)Co₂(μ-(η¹-O : η¹-N)-ONO)]₂(bdc)}⁴⁺ (bpbp=2,6-bis(N,N-bis(2-pyridylmethyl)aminomethyl)-4-tert-butylphenolato, bdc=1,4-benzenedicarboxylato) cation. Overlapping signals in the solid-state EPR spectra confirm the Co^IICo^III oxidation state and the presence of NO₂ trapped inside the unrecrystallised solid products (br. g=4, triplet g=2 (340 mT), A(N)=73 MHz), despite three cycles of vacuum and N₂ flushing. Consistently, ν_N−O bands appear in the Raman and IR spectra that are due to the coordinated nitrate and the trapped NO₂ that were synthesized in-crystal. The latter is expelled by heating the solid to 160 °C or by recrystallization. Dimetallic cooperativity is proposed for the NO transformations in these rare examples of selective, chemisorptive substrate reactions in the solid-state.     

A Systematic Study of Fluorescence‐Based Detection of Nitroexplosives and Other Aromatics in the Vapor Phase by Microporous Metal–Organic Frameworks

A systematic study is conducted on four microporous metal–organic framework compounds built on similar ligands but different structures, namely [Zn₃(bpdc)₃(bpy)] ? 4 DMF ? H₂O ( 1 ), [Zn₃(bpdc)₃(2,2′dmbpy)] ? 4 DMF ? H₂O ( 2 ), [Zn₂(bpdc)₂(bpe)] ? 2 DMF ( 3 ), and [Zn(bpdc)(bpe)] ? DMF ( 4 ) (bpdc=4,4′‐biphenyldicarboxylate; bpy=4,4′‐bipyridine; 2,2′dmbpy=2,2′‐dimethyl‐4,4′bipyridine; bpe=1,2‐bis(4‐pyridyl)ethane; DMF=N,N′‐dimethylformamide) to investigate their photoluminescence properties and sensing/detection behavior upon exposure to vapors of various aromatic molecules (analytes) including nitroaromatic explosives. The results show that all four compounds are capable of detecting these molecules in the vapor phase through fluorescence quenching or enhancement. Both electrochemical measurements and theoretical calculations are performed to analyze the analyte–MOF interactions, to explain the difference in signal response by different analytes, and to understand the mechanism of fluorescence quenching or enhancement observed in these systems. Interestingly, compound 3 also shows an emission frequency shift when exposed to benzene (BZ), chlorobenzene (ClBZ), and toluene (TO), which provides an additional variable for the identification of different analytes in the same category.     

A series of coordination polymers constructed from flexible bis(benzimidazole)ether ligands and different carboxylates

Six new coordination polymers constructed from two structurally related ligands, 2,2′-bis(2-methylbenzimidazole) ether (L1) and 2,2′-bis(2-ethylbenzimidazole)ether (L2), have been synthesized. They are [Cu(L1)(bz)₂] (1), [Cu(L2)(bz)₂] (2), [Zn₂(L1)(m-bdc)₂] (3), [Cd₂(L2)(m-bdc)₂(H₂O)]₂·H₂O (4), [Zn(L1)(OH-bdc)-(H₂O)] (5) and [Zn₂(L₂)(btca)] (6), where Hbz = benzoic acid, m-H₂bdc = 1,3-benzenedicarboxylic acid, OH-H₂bdc = 5-hydroxyisophthalic acid, and H₄btca = 1,2,4,5-benzenetetracarboxylic acid. In 1 and 2, the bidentate N-donor ligands (L1 and L2) bridge neighboring metal centers to form 1D single chains. The bz anions are attached on both sides of the chains. In 3 and 4, the N-donor ligands (L1 and L2) in cis conformations bridge two metal centers to generate a [M₂(L1)]⁴⁺ unit (M = Zn(II) and Cd(II)). The adjacent [M₂(L1)]⁴⁺ units are further linked via the dicarboxylate anions to form 1D double chain structures. In 5, the Zn(II) cations are bridged by OH-m-bdc anions to form an infinite polymeric chain. The L1 ligands are attached on one side of the chain in a monodentate mode. In 6, two Zn(II) cations are bridged by two L2 ligands to form a [ZnL2]₂ ⁴⁺ ring, which is further linked by btca anions to generate a 2D layer. The luminescent properties of the ligands and 3–6 in the solid state at room temperature were also studied.     

Urothermal Syntheses of two New Luminescent Zinc(II) Compounds via Dual-ligand Strategy

Urothermal reaction of Zn(NO₃)₂ · 6H₂O, Htrz and NH₂H₂pdc or H₂pdc affords two new compounds, namely [Zn₂(NH₂bdc)(trz)₂]_n · 2n(e-urea) ( 1 ) and [Zn₄(bdc)₂(trz)₄(H₂O)(e-urea)]_n · n(e-urea) ( 2 ) (Htrz = 1,2,4-triazole, NH₂H₂bdc = 2-aminoterephthalic acid, H₂bdc = terephthalic acid, e-urea = 1,3-ethyleneurea). X-ray structural analyses revealed that both compounds 1 and 2 feature e-urea-templated 3D pillar-layer framework with 2D Zn^II-triazole layer and 6-connected pcu topological network. These two compounds not only have high thermal stabilities but also show intense luminescence at room temperature.