In this article, two organic bases (dtb = 1,4-di(1H-1,2,4-triazol-1-yl)benzene; mimb = 1,2-bis((2-methyl-1H-imidazole-1-yl)methyl)benzen) were employed to solvethermally react with AgI in an strong acidic environment, creating two new hybrid haloargentates [pbmt](0.5)[AgI2] 1 (pbmt(2+) = 1,1'-(1,4-phenylene)bis(4-methyl-1H-1,2,4-triazol-4-ium)) and [H-2(mimb)](0.5)[Ag2I3] 2. Note that pbmt2+ in 1 originated from the in situ N-alkylation of dtb with CH3OH. X-ray single-crystal diffraction analysis reveals that (i) 1 exhibits 1-D chain structure, which can be described as an infinite extension of AgI4 tetrahedra via sharing edge; (ii) in 2, Ag+ and I- aggregate to form a 3-D iodoargentate with open-framework structure. The photoluminescence analysis reveals that at room temperature, 1 emits yellow light, while at low temperature, it just occasionally emits yellow light, and in most cases it emits yellow-green light. Whether at room temperature or low temperature, 2 always emits yellow light. It means that 1 possesses the fluorescent photo(thermo)chromic properties, whereas 2 does not have these properties. The related mechanism was also discussed.

MOFs with adequate free nitrogen sites have potential applications in dye adsorption and formic acid dehydrogenation. Here, we successfully synthesized a novel 3-D MOF 1 ([(CH3)2NH2][Cd(L)DMA]·0.5DMA·1.5H2O) with a special two-fold interpenetrating framework through a simple solvothermal reaction between CdCl2·1.5H2O and a nitrogen-rich triangular tricarboxylate-based linker (H3L, 4,4',4''-s-triazine-2,4,6-tribenzoic acid). After removing the guest molecules of dimethylacetamide (DMA) and H2O, including the coordinated DMA from 1 by vacuum activation at 423 K, a compound named 1' with a formula of [(CH3)2NH2][Cd(L)] and a similar interpenetrating framework structure was obtained. In comparison with compound 1, the total void volume of 1' is nearly doubled, and thus may provide higher potential for the adsorption of other guest molecules. Notably, the pyridine N atoms located in the middle of the triangular tricarboxylate-based linker are not involved in the coordination with Cd2+, and are all uniformly dispersed throughout the whole framework of the 3-D MOFs. Due to its unique structural features, the 3-D MOF 1' could effectively adsorb the cationic dye MB+ for recycling purposes. The rapid adsorption rate (0.7 × 10-2 g mg-1 min-1) and the relatively high capacity (900 mg g-1) for MB+ demonstrate the potential of 1' in dye adsorption. In addition, 1' may also be used as an effective support to immobilize PdAu NPs via the double-solvent method. The resultant catalyst Pd0.8Au0.2/1' exhibits decent catalytic activity for the dehydrogenation of formic acid with a TOF value of 1854 h-1 at 333 K. The existence of a large void volume and accessible pyridine N atoms provide a suitable environment for achieving a high dispersion of PdAu NPs, thereby leading to the formation of a catalytically active and stable supported noble-metal NP catalyst for H2 generation from formic acid decomposition.

Ultrafine and well-dispersed PdAu bimetallic nanoparticles (ca. 1.4 nm) are successfully immobilized on amine-containing UiO-66 frameworks (NH2-UiO-66) via a double-solvent impregnation method. By virtue of the double-solvent strategy, the incorporated PdAu nanoparticles (NPs) are mainly present in the alloy state and distributed inside the cavities of NH2-UiO-66 near the window of the cages. The resulting PdAu/UiO-66 catalysts exhibit much higher catalytic activity and stability for the dehydrogenation of formic acid than the catalyst prepared by the conventional single-solvent impregnation method. The composition-optimized Pd0.8Au0.2/UiO-66-D catalyst affords a very high turnover frequency value of 722 h(-1) at 298 K, which is among the highest one in the metal-organic framework-supported Pd-based NP catalysts ever reported under similar reaction conditions. The exceptional catalytic activity and stability of Pd0.8Au0.2/UiO-66-D could be mainly attributed to the formation of highly dispersed PdAu alloy NPs, the suitable electronic structure of Pd species adjusted by the alloy effect, and the metal-support interaction, as well as the abundant amine groups that can promote the activation of the formic acid molecule by forming HCOO- under mild conditions.

Porous coordination polymers with organic aminium as one of the guest species possess a potential application in dye adsorption and white-light material manufacture. Polycarboxylic acid with multiple-COOH substituents tends to form this type of porous material (with metal ion). Here the solvothermal self-assembly between Cd2+ and a hexacarboxylic acid creates such a porous material [(CH3)(2)NH2](6)[Cd-3(L)(2)]center dot 5DMF center dot 3H(2)O (H6L = 3,4-di(3,5-dicarboxyphenyl)phthalic acid) 1. Total potential guest accessible void volume in 3-D 1 is found to be 4327 angstrom(3). Based on its better porous structure and stability, the ability of 1 to adsorb organic dyes is investigated. It has been proved that (i) 1 can selectively adsorb cationic dyes as Azure A (AA(+)) and/or Methylene Blue (MB+), rather than neutral and anionic ones; (ii) the maximum adsorption capacity is 698.2 mg.g(-1) for AA(+) and 573.2 mg.g(-1) for MB+, respectively; and (iii) to the adsorption of AA(+), it can be recycled for at least five rounds. Also, it is utilized to fabricate the while-light emitting material. Based on the blue-light emission of 1, the trace Eu3+ and Tb3+ ions are introduced into the pores of 1 successfully, obtaining a white-light emitting material Eu3+/Tb3+@1 (CIE chromaticity coordinates: (0.33, 0.32)). Meanwhile, Eu3+/Tb3+@1 is found to be a potential fluorescence photochromic material, showing a yellow-white-blue light emission. According to these investigations, the relationship between material structure and its adsorption property for dyes, the points that should be paid attention to in the construction of white-light emitting materials as well as the potential adsorption mechanism for dyes and rare earth ions are deeply discussed. (C) 2021 Elsevier B.V. All rights reserved.

Diamine-containing UiO-66 (UiO-66-(NH2)(2)) was utilized as a support to load PdAu nanoparticles (NPs) through a double-solvent strategy for the catalytic application in the dehydrogenation of formic acid. A variety of characterization results demonstrate that tiny PdAu NPs (below 1.1 nm) are successfully encapsulated inside the cavities of the Zr-based metal-organic frameworks (Zr-MOFs). The resultant Pd0.8Au0.2/UiO-66-(NH2)(2) catalyst affords a turnover frequency (TOF) value of 3660 h(-1) for hydrogen generation from formic acid at 323 K and could also work well at room temperature with a TOF of 980 h(-1), much higher than that of the reference catalyst derived from the monoamine-containing UiO-66 support and other MOF-supported Pd-based catalysts reported in the literature. In addition, Pd0.8Au0.2/UiO-66-(NH2)(2) exhibits very high stability against aggregation and can be easily recycled seven times without obvious loss in catalytic activity. The excellent catalytic activity and stability of Pd0.8Au0.2/UiO-66-(NH2)(2) should be mainly attributed to the presence of a higher concentration of amino groups throughout the whole frameworks of the Zr-MOFs, which can coordinate with the precursors of Pd/Au species during the process of catalyst preparation and can also efficiently inhibit the aggregation of the subsequently formed nanoparticles confined inside the cavities of UiO-66-(NH2)(2). This work demonstrates that the choice of suitable supports and preparation strategies plays a critical role in fabricating highly efficient and stable supported Pd-based NP catalysts for formic acid dehydrogenation.

Under hydro(solvo)thermal conditions, four organic bidentate bridging N,N′-donor ligands 1,3-bis(2-methylimidazol-1-yl)propane (L1), 4,4′-di(1 H -imidazol-1-yl)-1,1′-biphenyl (L2), 1,2-bis(2-methyl-1 H -imidazol-1-ylmethyl)benzene (L3) and 5,6,7,8-tetrahydroquinoxaline (L4) were employed to react with CuBr/CuI, generating four 2-D layered copper(I)–polymer coordination polymer materials [Cu_2Br_2(L1)] 1 , [CuI(L2)] 2 , [CuI(L3)] 3 and [CuI(L4)_0.5] 4 . In 1–4 , different Cu–X motifs are found: a cubic Cu_4Br_4 core in 1 ; a castellated Cu–I single chain in 2 ; a rhombic Cu_2I_2 core in 3 ; and a staircase-like Cu–I double chain in 4 . The 2-D layer networks of 1–3 can all be simplified into a simple 4^4 topology (planar for 1 and 3 ; wave-like for 2 ), while the 2-D layer network of 4 has a 6^3 topology. The photoluminescence behaviors of 1–4 under a UV lamp suggest that 1 and 2 possess fluorescence thermochromism properties. Under the UV lamp, with the decrease in temperature, (i) 1 exhibits a yellow-to-red emission; (ii) 2 exhibits a yellow-to-green emission; (iii) 3 always emits green light; and (iv) 4 never emits light. These are further confirmed by their emission spectra. From 297 K to 77 K, the emission of 1 exhibits a large red shift from 561 nm to 623 nm; the emission of 2 exhibits a large blue shift from 571 nm to 515 nm; only a minor red shift is observed for the emission of 3 ; and no peaks appear in the emission spectra of 4 . The crystal data of 1 and 2 at different temperatures have been collected for revealing the origination of their fluorescence thermochromism properties. Based on the above investigations, the effect of the rigidity/flexibility of the organic ligand on the fluorescence thermochromism properties of copper(I)–polymer coordination polymer materials is discussed. The quantum yields at 297 K and the photoluminescence lifetimes at 297 K and 77 K for 1–3 were also measured for better understanding their photoluminescence properties.

The simple solvothermal self-assemble of CuI, 1,4-bis(2-methyl-1H-imidazol-1-yl)butane (L1) and HI in a C2H5OH solvent at pH = 2 created a new H2(L1)2+-templated 1-D chained iodocuprate(I) [H2(L1)][Cu3I5] 1. The crystal data reveal that the Cu-I chain mode in 1 is rare. Two folded Cu2I2 cores first aggregate into a trinuclear cluster by sharing an edge. Then the extra I− ions doublely bridge these trinuclear clusters into the title 1-D chain of 1. Synchronously, a non-folded Cu2I2 cluster is formed. In 1, all of the Cu···Cu distances are smaller than 2.8 Å. The investigation on photoluminescence property indicates that with the decrease of the temperature, the photoluminescence emission for 1 exhibits a minor change from the green-yellow light (298 K) to yellow light (77 K). This means that 1 might possess the fluorescent thermochromic property.

2,4,6-Trinitrophenol (TNP), compared with the other nitro compounds, not only has a strong electron-withdrawing ability, but also has a strong light absorption capacity a a large excitation wavelength. Therefore, the fluorescence material with a large excitation wavelength might be a potential probe for the detection of TNP. Here, by employing the in situ acylation of organic acid with N2H4, two acylhydrazinotetracarboxylate-based coordination polymers [Cd-2(HL1)(phen)(2)(H2O)1-4.5H(2)O (H(5)L1 = 5,5'-(1,4-dioxo-1,2,3,4-tetrahydrophthalazine-6,7-diyebis(oxy)diisophthalic acid; phen = 1,10-phenanthroline) 1 and [Mn-2(HL1)(phen)(2)]-7H(2)O(2) were obtained. Phen is used to prevent the formation of a dense network and many hydrogen bonds, which might quench any emission of material. As predicted, 1 only possesses a 1-D broad-ribbon structure, whereas 2 just has a 1-D tube-like structure. And both are found to emit the yellow light, corresponding to the charge transfer from benzene ring moiety to acylhydrazine ring moiety. It means that the acylation changes thoroughly the photoluminescence behavior of organic ligand. Based on their good photoluminescence properties, the sensing ability of both towards TNP was investigated. It is turned out that 1 is not an ideal sensor, even though it can also sense TNP. However, 2 can be considered as an excellent sensor for the detection of TNP. The emission of 2 is almost completely quenched by TNP, while only 20% quenching is observed for the potential interfering analyze 4-nitroaniline (4-NA). The related sensing mechanism is discussed in details.

Dental caries have become a major global public health problem. Plaque control and remineralization of initial enamel lesions are paramount for the prevention and control of caries. Polyhexamethylene biguanide (PHMB) is a type of cationic amphipathic antibacterial agent with broad-spectrum antibacterial properties and good biological safety. Fluoride delays demineralization and promotes the remineralization of hard dental tissues. However, a high concentration is needed for it to function as an antibacterial agent. In order to create a PHMB with the benefits associated with fluoride, we synthesized a fluorine-containing cationic polymer, PHMB-F. Fourier transform-infrared spectroscopy and solid state nuclear magnetic resonance characterization confirmed the successful synthesis of PHMB-F. Antibacterial tests showed that PHMB-F had better antiseptic efficacy for Streptococcus mutans compared with just PHMB. Moreover, positively-charged PHMB-F allows fluoride ions to exist closer to the enamel surface with negative potential, which markedly lowers the ion concentrations in the microenvironment adjacent to hard dental tissues needed to maintain equilibrium. Thus, only low concentrations of PHMB-F are required for enamel remineralization.

The structures of six new diacylhydrazidate-based coordination polymers were reported. Based on their better photoluminescence properties, their sensing abilities towards Cr2O72− were investigated.

The simple hydrothermal self‐assembly of metal ions, 5,5′‐(4,5‐dicarboxy‐1,2‐phenylene)bis(oxy)diisophthalic acid (L1'), and N2H4·H2O at pH = 8 (adjusted by oxalic acid) created two new acylhydrazinetetracarboxylate‐extended 3‐D Sr2+ and Ba2+ coordination polymers [Sr2(HL1)(H2O)] (H5L1 = 5,5′‐(1,4‐dioxo‐1,2,3,4‐tetrahydrophthalazine‐6,7‐diyl)bis(oxy)diisophthalic acid) 1 and [Ba5(HL1)2(ox)(H2O)2]·6H2O·N2H4 (ox = oxalate) 2. H5L1 originated from the in situ acylation of L1′ with N2H4. X‐ray single‐crystal diffraction analysis reveals that (i) the 3‐D network of 1 is based on a rod‐like secondary building unit (SBU), which can be described as an alternate arrangement of two types of dinuclear Sr‐O clusters; (ii) the 3‐D network of 2 is also based on a rod‐like SBU. The different is that the SBU for 2 can be described as an alternate arrangement of a kind of trinuclear cluster and a kind of tetranuclear cluster. Both 1 and 2 emit blue light. With regard to their good photoluminescence properties, their trinitrophenol (TNP) sensing ability was investigated. The results indicate that both can selectively detect TNP. The quenching constants Ksv are calculated to be 3.21 × 104 m–1 for 1 and 2.98 × 104 m–1 for 2, respectively.

Simple room-temperature self-assemblies between Cd2+ salts, SCN- and bisimidazole molecules at pH = 2 created three new organically templated thiocyanatocadmates [H2(L1)][Cd(SCN)4]·H2O (L1 = 1,4-bis(1H-imidazol-1-yl)benzene) 1, [H2(L2)][Cd(SCN)4] (L2 = 1,3-bis(2-methylimidazol-1-yl)propane) 2, and [H2(L3)][Cd2(SCN)6] (L3 = 1,4-bis(2-methyl-1H-imidazol-1-yl)butane) 3. X-ray single-crystal diffraction analysis reveals that (i) in 1-3, the SCN- groups doubly bridge the Cd2+ centers to form different thiocyanatocadmates: a linear chain in 1; a zigzag chain in 2; and a 2-D layer network (63 net) in 3; and (ii) in 1, via Nbase-HNSCN interactions, the L1 molecules extend the thiocyanatocadmate chains into a 2-D supramolecular layer, whereas in 2, the zigzag thiocyanatocadmate chains self-assemble into a 3-D supramolecular network via weak SS interactions. Photoluminescence analysis indicates that the three title compounds all emit light: blue light for 1 and 2 and green light for 3. At low temperatures, the emission positions of the three compounds hardly change, but the emission intensities are largely enhanced. Interestingly, after turning off the UV lamp, 1 and 2 still briefly emit light (ca. 2 s), which means that 1 and 2 possess phosphorescence properties. Phosphorescence lifetimes at 77 K are 1619 ms for 1 and 247 ms for 2.

By employing the solvothermal in situ N-alkylation of organic bases with alcohol molecules, four new organically templated iodometallates as [L1][Ag2I4] (L1(2+) = 1,1,4,4-tetramethyl-1 lambda(4),4 lambda(4)-piperazinium) 1, [L2](1.5)[AgI4] (L2(2+) = 1,4-dibenzyl-1 lambda(4),4 lambda(4)-diazabicyclo[2.2.2]octanium) 2, [L2]1.5[CuI4] 3 and [L3][CuI3] (L3(2+) = 4,4'-bis(3-methyl-1H-3 lambda(4)-imidazol-1-yl)-1,1'-biphenylium) 4 were obtained. In 1, the in situ substitution and N-alkylation of 1,4-bis(pyridin-4-ylmethyl)piperazine (L1') with CH3OH has occurred, producing L1(2+). Templated by L1(2+), Ag+ and I- aggregate into a chained iodoargentate, which can be described as a linear arrangement of AgI4 tedrahedra by sharing the edges. 2 and 3 are isostructural. In 2 and 3, the in situ N-alkylation of 1,4-diazabicyclo[2,2,2]octane (L2') with phenylmethanol has occurred, generating L2(2+). Templated by L2(2+), Ag+ (or Cu+) and I- aggregate into a mononuclear iodometallate with a tetrahedral structure. In 4, the in situ N-alkylation of 4,4'-di(1H-imidazol-1-yl)-1,1'-biphenyl (L3') with CH3OH has occurred, creating L3(2+). Templating by L3(2+), Cu+ and aggregate into a mononuclear iodocuprate(I) with a planar trigonal structure. The photoluminescence analysis reveals that (i) at the room temperature, only 1 emits light (lambda(em) = 550 nm); (ii) at the low temperature, 4 is found to possess the photoluminescence property (lambda(ern) = 546 nm at 77 K) with a ms-grade lifetime (tau = 4.915 ms).

Three bisimidazole-based chained iodoargentates were solvothermally synthesized, and their photoluminescent behaviors at different temperatures were investigated. Of those, 3 has been found to possess photochromic luminescence properties.

At pH 2, the simple room-temperature self-assemblies between Cd2+ salts, SCN− and organic bases created one new thiocyanatocadmate as [H2(L1)][Cd2(SCN)6] (L1 = 1,4-bis(2-methyl-1H-imidazol-1-ylmethyl)benzene) 1, and two new halo-thiocyanatocadmates as [H2(L2)][CdI2(SCN)2]·H2O (L2 = 3,5-bis (4-pyridyl)-1,2,4-triazole) 2, and [CdCl(SCN)(L3)] (L3 = 3-pyrazinyl-1,2,4-triazole) 3. X-ray single-crystal diffraction analysis reveals that (a) in 1, with H2(L1)2+ as the countercation, the SCN− groups tri-bridge the Cd2+ centers into a 1-D chained thiocyanatocadmate; (b) 2 is only a mononuclear iodo-thiocyanatocadmate, and H2(L2)2+ acts as the countercation. But via the π···π and Npyridyl–H···NSCN interactions, H2(L2)2+ and CdI2(SCN) 2 2− aggregate together to form a 1-D supramolecular tube. Amongst the tubes, a chained water cluster with a zig-zag shape is observed; (c) 3 is an organically extended chloro-thiocyanatocadmate. Note that the report on this type of material is rather rare. It possesses a 3-D network structure with a dia topology, in which a castellated CdCl+ single chain is observed. L3 and Cl− act as a mixed bridge, whereas SCN− just serves as a terminal ligand in 3. The photoluminescence analysis indicates that the title compounds 1–3 all emit light (green light for 1, blue light for 2 and 3), which should be attributed to the ligand-centered electronic excitations.

Under the hydrothermal conditions, the simple self-assembly between Cd2+, 2,3,5,6-pyridinetetracarboxylic acid (L1′), and N2H4 created a L12−-based Cd2+ coordination polymer [Cd(L1)(N2H4)] · 2H2O (L12− = 2,3,5,6-pyridinetetracarboxylhydrazidate) 1. H2L1 derived from the in situ acylation of L1′ with N2H4. X-ray single-crystal diffraction analysis reveals that 1 possesses a 1-D chained structure co-bridged by L12− and N2H4, where a castellated CdO single-chain is observed. It is noteworthy that between the L12− molecules, two types of cyclic hydrogen-bonded synthons are found. Via these weak intermolecular interactions, 1 self-assembles into a 3-D porous supramolecular network (window size: 8 × 7 Å2). The tetrahenuclear water clusters with a tetrahedral structure are observed in the pores.

By employing the hydrothermal in situ acylation of organic acid with N2H4, we constructed a new acylhydrazidate-based Zn2+ coordination polymer [Zn-2(apo)(2)]center dot H2O (H-2(apo) = 4,5-diamino-1,2-dihydropyridazine-3,6-diol) 1. Interestingly, besides the acylation of 2,3-pyrazinedicarboxylic acid (pca) with N2H4, the breaking of partial C-(=)N bonds in the pyrazine ring also occurred, creating a new bridging-type acylhydrazide molecule H-2(apo). In 1, the apo(2-) molecules exhibit a mu(4) coordination mode, linking the tetrahedral Zn2+ centers into a 2-D layer network with a 4(4) topology. The photoluminescence analysis indicates that the title compound 1 emit the green light with the maximum at 490 nm upon excitation (lambda(ex) = 380 nm, tau = 12.6 mu s). Based on the better photoluminescence behavior of 1, the sensing ability of 1 on nitroaromatic explosives and inorganic anions were investigated. The results suggest that 1 can selectively detect 2,4,6-trinitrophenol (TNP) and Cr2O72-. This should be associated with the larger light adsorption at 380 nm for TNP and Cr2O72-. The light adsorption at 380 nm for the other nitroaromatic explosives and inorganic anions is weak.

We employed a rigid bridging-type tetracarboxylic acid molecule, namely, 5,5'-(pyridine-3,5-diyl)diisophthalic acid (H4L; containing two isophthalic acid moieties and one pyridine spacer), to construct three new isomorphic Ln-metal-organic framework (Ln-MOF) materials [(CH3)(2)NH2](2)[Ln(2)(L)(2)(H2O)]center dot 2DMF center dot 2H(2)O (Ln(3+) = Tb3+ 1, Eu3+ 2, Gd3+ 3; DMF = N,N-dimethylformamide). Since the pyridyl N atom does not coordinate to Ln 3 +, the larger pores are observed in the three-dimensional networks of 1-3. On the basis of their photoluminescence properties, the white-light-emitting materials 4-7 with longer fluorescence lifetime (millisecond grade) and higher quantum yield (e.g., 48.29% for 5) are fabricated. We also find that the title Ln-MOF materials not only can selectively sense polychlorinated benzenes, but also can highly sensitively detect the Fe3+ ion (K-sv = 7.58 X 10(4) M-1). This should be associated with these three structural factors in 1-3: the larger it-conjugated structure of L4-; the larger porous structures in 1-3; and the existence of uncoordinated N atom on L4-. The test paper experiments reveal that 1 can be made into the test paper (a naked eye probe) to quickly detect the analytes.

Seven compounds based on [P2W18O62]6- ({P2W18}) were successfully prepared and carefully characterized. [HC5H5N][Cu(2,2'-bpy)2]2[HP2W18O62]·2H2O (bpy = bipyridine) (1) is constructed from {P2W18} bridged by [Cu(2,2'-bpy)2]2+. [HC5H5N][Zn(2,2'-bpy)2]2[HP2W18O62]·4H2O (1a) is isostructural and isomorphous with compound 1. [Cu4(2,2'-bpy)3(nic)3(OH)2(H2O)][H3P2W18O62]·0.5H2O (nic = nicotinic acid) (2) is formed by {P2W18} and tetracopper transition metal mixed organic ligand complexes (TMMCs). [Cu2(2,2'-bpy)2(C2O4)]3[P2W18O62]·3H2O (3) is made up of {P2W18} and bicopper TMMCs, [Cu6(2,2'-bpy)6(OH)6][P2W18O62]·2H2O (4) is built up from {P2W18}, and hexacopper complexes of 2,2'-bpy and hydroxyls. [Cu(2,2'-bpy)(hnic)0.5][Cu3(2,2'-bpy)3(hnic)2(H2O)2][H3P2W18O62] (hnic = hydroxyl nicotinic acid) (5a) contains two different TMMCs. In addition, compound 5a is the first example of a compound that contains Cu-π interactions. [Cu2(2,2'-bpy)2(hnic)][H4P2W18O62]· xH2O ( x ≈ 50) (5b) is based on {P2W18} and [Cu2(2,2'-bpy)2(hnic)]2+. We discuss the mechanisms for the formations of these compounds. All the catalytic performances of the compounds for styrene epoxidation to styrene oxide are high.