Photochromism and Metal Complexation of a Macrocyclic Styryl Naphthopyran

A macrocyclic benzo‐15‐crown‐5 ether unit tethered to a photochromic naphthopyran by a styryl spacer ( MEN ) is shown to form a 1:1 complex with magnesium(II). The structure and dynamics of the specific host–metal interactions were investigated by PFG‐NMR analysis. A combination of UV/Vis and variable temperature multi‐dimensional ¹H NMR photokinetic analysis of the crown‐containing styryl naphthopyran and its metal complex was used to probe the effect of metal complexation on the photochromism.     

Metal Ion Modulated Torsion Angle in a Ditopic Oligothiophene Ligand: Toward Supramolecular Control of π Conjugation

A π‐conjugated oligomer bearing two 15‐crown‐5‐containing styryl moieties connected at the inner β positions of the terminal thiophene nuclei can adopt either a U or a Z shape depending on the structures of its complexes with magnesium and barium ions. We show that barium cations lead to the formation of a mononuclear complex in solution, which causes the system to fold into the U shape. Magnesium ions lead to the same effect at low concentration, but force the ligand to adopt the Z‐shaped geometry at high concentrations favoring formation of a binuclear complex. These geometrical reorganizations in solution are accompanied by profound changes in spectroscopic properties, which can be rationalized in terms of variations in the extent of electron delocalization along the oligothiophene backbone. The effects are analyzed by mass spectrometry and ¹H NMR, UV/Vis absorption, and fluorescence spectroscopy in the steady‐state and time‐resolved regimes. The experimental results are compared to data calculated by using MOPAC2007 with the PM6 Hamiltonian including the COSMO solvation model.     

Hydrothermal synthesis and crystal structures of two novel rare earth coordination polymers based on pyridine-2,6-dicarboxylic acid

Two novel rare earth coordination polymers, [La(pydc)₂(H₂O)][La(pydc)(H₂O)₂]·H₂O (1) and [Sm(pydc)₂(H₂O)][Sm(pydc)(H₂O)₂]·H₂O (2) (pydc=pyridine-2,6-dicarboxylate) were hydrothermally synthesized and characterized by the elemental analyses, IR spectra and TG analyses. Single crystal X-ray diffractions show that 1 and 2 are isostructural compounds. In the compounds of 1 and 2, the 1D lanthanide helical chains are connected each other by lanthanide binuclear dimer as building blocks to form a novel 3D covalent framework.     

Coordination of Alkaline Earth Metal Ions in the Inverted Cucurbit[7]uril Supramolecular Assemblies Formed in the Presence of [ZnCl4]2− and [CdCl4]2−

A convenient method to isolate inverted cucurbit[7]uril (iQ[7]) from a mixture of water‐soluble Q[n]s was established by eluting the soluble mixture of Q[n]s on a Dowex (H⁺ form) column so that iQ[7] could be selected as a ligand for coordination and supramolecular assembly with alkaline earth cations (AE²⁺) in aqueous HCl solutions in the presence of [ZnCl₄]^2? and [CdCl₄]^2? anions as structure‐directing agents. Single‐crystal X‐ray diffraction analysis revealed that both iQ[7]–AE²⁺–[ZnCl₄]^2?–HCl and iQ[7]–AE²⁺–[CdCl₄]^2?–HCl interaction systems yielded supramolecular assemblies, in which the [ZnCl₄]^2? and [CdCl₄]^2? anions presented a honeycomb effect, and this resulted in the formation of linear iQ[7]/AE²⁺ coordination polymers through outer‐surface interactions of Q[n]s.     

Hydrothermal Synthesis,Structure and Property of a Zinc Coordination Polymer Based on Aromatic Polycarboxylate and Phenanthroline Ligands

A zinc coordination polymer [Zn(μ₂‐H₂bta)_1/2(μ₄H₂bta)_1/2(phen)(H₂O)]_n ( 1 ) (H₄bta = benzene‐1,2,4,5‐tetracarboxylic acid, phen = 1, 10‐phenanthroline) has been hydrothermally synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric and single‐crystal X‐ray diffraction analyses. Compound 1 displays pucker layer structure formed from Zn²⁺ ions and μ₂‐H₂bta^2? and μ₄‐H₂bta^2? bridging ligands, and it is linked into three dimensional (3D) supramolecular frameworks through the hydrogen bonds and π‐π interactions. It exhibits strong blue fluorescence at room temperature in the solid state.     

The C-F…F-C short contacts in the metal complexes of fluoro-phenyl-acrylic acids

Four new complexes of fluoro-phenyl-acrylic acids (E)-3-(3-fluoro-phenyl)-acrylic acid (L1) [Mn₃(L1)₆(L2)₂]·H₂O·CH₃CN (1), [Zn₂(L1)₄(L3)]_n (2), [Mn(L1)₂(H₂O)₂]_n (3) and [Co(L1)₂(H₂O)₂]_n (4) (L2=1,10-phenanthroline, L3=4,4′-bipy) have been synthesized based on the molecular design and research of halogen-halogen interactions (especially fluoro-fluoro contact). The structure analyses reveal that complex 1 is a trinuclear complex, which is blocked by L2. Complex 2 is a 1D chain bridged through L3. Complexes 3 and 4 exhibit 2D grid like metal-organic framework structures through carboxylato bridge ligand. Variable-temperature magnetic measurements showed an antiferromagnetic interaction between Mn(II) ions and between Co(II) ions in complexes 3 and 4, respectively. A short C−F…F−C contact with a distance of 2.953 Å was found between the trinuclear coordination compound 1.     

Surface organobarium and organomagnesium chemistry on periodic mesoporous silica MCM-41: convergent and sequential approaches traced by molecular models

The alkaline earth metal alkyl complexes [Ba(AlEt(4))(2)](n) and Mg(AlMe(4))(2) were directly grafted onto periodic mesoporous silica MCM-41, which had been dehydroxylated at 270 °C (specific surface area a(s): 1023 m(2) g(-1); pore volume V(p): 1.08 cm(3) g(-1); main pore diameter 3.4 nm). Alternatively, barium alkyl surface species were generated by sequential grafting of MCM-41 with Ba[N(SiHMe(2))(2)](2)(thf)(4) and AlEt(3) to yield the hybrid material AlEt(3)@Ba[N(SiHMe(2))(2)](2)(thf)(4)@MCM-41. For a better understanding of the surface chemistry, AlEt(3)@MCM-41 was also accessed. All hybrid materials were analyzed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, elemental analysis, nitrogen physisorption, and solid-state NMR spectroscopy; this clearly revealed distinct surface chemistry for the alkylaluminate-treated materials [Ba(AlEt(4))(2)]@MCM-41 and Mg(AlMe(4))(2)@MCM-41. In an attempt to mimic the surface chemistry, the organometallic precursors were treated with HOSi(OtBu)(3). The reaction of equimolar amounts of {Ba[N(SiHMe(2))(2)](2)}(n) and HOSi(OtBu)(3) produced a mixed silylamido/siloxide cluster of Ba(3)[OSi(OtBu)(3)](3)[N(SiHMe(2))(2)](3) with bridging-only siloxide ligands as well as one bridging and two terminal silylamido ligands. The Schlenk equilibrium was found to govern the [Ba(AlEt(4))(2)](n)-HOSi(OtBu)(3) and Mg(AlMe(4))(2)-HOSi(OtBu)(3) reactions, leading to the isolation of complexes of [Ba(AlEt(4))(2) (toluene)](2) and Mg[OSi(OtBu)(3))](2)(AlMe(3))(2), respectively. Allowing for a donor-induced cleavage of Mg(AlMe(4))(2), the reaction of [MgMe(2)] with one or two equivalents of HOSi(OtBu)(3) was studied. While putative Mg[OSi(OtBu)(3)](Me) and Mg[OSi(OtBu)(3)](2) could not be crystallized from the reaction mixtures, cluster complexes Mg(5)(O)[OSi(OtBu)(3)](5)Me(3) and Mg(4)(OH)(2)[OSi(OtBu)(3)](6) could be unambiguously identified by X-ray crystallography.     

Effect of group II metal cations on catecholate oxidation.

The unexpected effects of Ca(2+) on the free-radical chain reactions of dopamine, norepinephrine, isoproterenol, and pyrocatechol oxidation are studied using oxygen consumption measurements, EPR-spectroscopy, UV/VIS spectrophotometry, and by potentiometric titration. It is found that the formation of Ca(2+)-catecholate complexes is accompanied by an increase in the dissociation constants (K(ai) ) of their phenolic hydroxyls. At pH>pK(ai) and in the presence of alkaline-earth metal cations, the rate of catecholate oxidation increases (Ca(2+), Mg(2+)> Sr(2+), Ba(2+)), whereas on addition of Zn ions the rate decreases. The effects of Group II metal cations on catecholate autoxidation are concomitant with a transient increase of the EPR signal for metal-semiquinonate complexes. Therefore, the effects of Ca(2+) and other alkaline-earth metal cations on catecholate autoxidation can be defined as 1) additional deprotonation of catechol OH-groups involved in the formation of M(2+)-catecholate complexes, the latter exceeding catechols in the susceptibility to dioxygen-induced oxidation and 2) formation of relatively stable free-radical intermediates responsible for chain propagation.     

Acid-base and metal-ion-binding properties of xanthosine 5'-monophosphate (XMP) in aqueous solution: complex stabilities, isomeric equilibria, and extent of macrochelation

The four acidity constants of threefold protonated xanthosine 5'-monophosphate, H3(XMP)+, reveal that at the physiological pH of 7.5 (XMP-H)(3-) strongly dominates (and not XMP(2-) as given in textbooks); this is in contrast to the related inosine (IMP(2-)) and guanosine 5'-monophosphate (GMP(2-)) and it means that XMP should better be named as xanthosinate 5'-monophosphate. In addition, evidence is provided for a tautomeric (XMP-HN1)(3-)/(XMP-HN3)(3-) equilibrium. The stability constants of the M(H;XMP)+ species were estimated and those of the M(XMP) and M(XMP-H)- complexes (M2+=Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+) measured potentiometrically in aqueous solution. The primary M2+ binding site in M(XMP) is (mostly) N7 of the monodeprotonated xanthine residue, the proton being at the phosphate group. The corresponding macrochelates involving P(O)2(OH)- (most likely outer-sphere) are formed to approximately 65% for nearly all M2+. In M(XMP-H)- the primary M2+ binding site is (mostly) the phosphate group; here the formation degree of the N7 macrochelates varies widely from close to zero for the alkaline earth ions, to approximately 50% for Mn2+, and approximately 90% or more for Co2+, Ni2+, Cu2+, Zn2+, and Cd2+. Because for (XMP-H)(3-) the micro stability constants quantifying the M2+ affinity of the xanthosinate and PO3(2-) residues are known, one may apply a recently developed quantification method for the chelate effect to the corresponding macrochelates; this chelate effect is close to zero for the alkaline earth ions and it amounts to about one log unit for Co2+, Ni2+, Cu2+. This method also allows calculation of the formation degrees of the monodentatally coordinated isomers; this information is of relevance for biological systems because it demonstrates how metal ions can switch from one site to another through macrochelate formation. These insights are meaningful for metal-ion-dependent reactions of XMP in metabolic pathways; previous mechanistic proposals based on XMP(2-) need revision.     

Synthesis and Crystal Structures of Alkali and Alkaline Earth Metal Complexes of 3,5-Dinitropyrazolyl-4-carboxylate

The synthesis and crystal structures of 3,5-dinitro-1H-pyrazolyl-4-carboxylic acid (H₂dnpzc) and its four complexes with Ca²⁺, Ba²⁺, Na⁺ and K⁺ are reported in this paper. Ca(dnpzc) · 5H₂O exhibits a 1D polymeric structure, whereas Ba(dnpzc) · 4H₂O possesses a 2D structure. The structure of Na₂(dnpzc) · 4H₂O consists of 2D layers of [Na(dnpzc)]^–_n and 1D chains of [Na(H₂O)₃]⁺_n. K₂(dnpzc) · H₂O has a true 3D structure. It was observed that the doubly deprotonated ligand (dnpzc^2–) can act as a versatile bridge to form polymeric structures by varying combinations of its 8 potential donor atoms (two carboxy O atoms, two pyrazolyl N atoms and four nitro O atoms). Particularly in the structure of K₂(dnpzc) · H₂O, all the 8 donor atoms of dnpzc^2– take part in the coordination and as many as 10 potassium atoms are connected by one ligand.     

Electrochemical behavior of benzenepolycarboxylic acids on solid electrodes in aqueous and mixed solutions

Electrochemical behavior of biologically active benzenepolycarboxylic (trimellitic, trimesic, pyromellitic, mellitic) acids is studied by a voltammetry method on Pt, Cu, Ta, and Cu-Hg in aqueous media and water mixtures with ethanol and pyridine. In all cases, voltammograms for the acids display waves corresponding to the discharge of hydrogen ions. In the case of Cu-Hg, voltammograms for trimellitic, trimesic, and pyromellitic acids additionally exhibit poorly pronounced prewaves. Concentrations of ionized and non-ionized forms in dilute solutions of the acids are calculated. Apparent dissociation constants K _a ^II and K _a ^III for mellitic acid are calculated from the voltammetry data.     

Heavy Grignard reagents: challenges and possibilities of aryl alkaline earth metal compounds

Compounds of the type aryl--M--X, with M=Ca, Sr, Ba and X as any kind of ligand (such as halide, phosphanide, amide, aryl), are presented. The low reactivity of the heavy alkaline earth metals calcium, strontium, and barium enforces an activation prior to use for the direct synthesis. The insertion of these metals into C--I bonds of aryl iodides (direct synthesis) yields aryl metal iodides and has to be performed at low temperatures and in THF. Aryl alkaline-earth-metal compounds show some characteristics: 1) the ease of ether cleavage enforces low reaction temperatures, 2) for Sr and Ba the Schlenk equilibrium is shifted towards homoleptic MI2 and MPh2, 3) high solubility of diaryl alkaline-earth-metal derivatives in THF even at low temperatures initiated quantum chemical investigations on the aggregation behavior, and 4) a strong low field shift of the 13C resonances of the ipso carbon atoms in NMR spectra was observed. First results from quantum chemical calculations on diaryl dicalcium(I) suggest a long Ca--Ca bond with a considerable Ca--Ca bond dissociation energy. Initial results on a selection of applications such as metallation, metathesis, and addition reactions of aryl calcium compounds are presented as well.     

Luminescent Nitridophosphates CaP2N4:Eu2+, SrP2N4:Eu2+, BaP2N4:Eu2+, and BaSr2P6N12:Eu2+

Nitridophosphates MP₂N₄:Eu²⁺ (M=Ca, Sr, Ba) and BaSr₂P₆N₁₂:Eu²⁺ have been synthesized at elevated pressures and 1100–1300 °C starting from the corresponding azides and P₃N₅ with EuCl₂ as dopant. Addition of NH₄Cl as mineralizer allowed for the growth of single crystals. This led to the successful structure elucidation of a highly condensed nitridophosphate from single‐crystal X‐ray diffraction data (CaP₂N₄:Eu²⁺ (P6₃, no. 173), a=16.847(2), c=7.8592(16) Å, V=1931.7(6) ų, Z=24, 2033 observed reflections, 176 refined parameters, wR₂=0.096). Upon excitation by UV light, luminescence due to parity‐allowed 4f⁶(⁷F)5d¹→4f⁷(⁸S_7/2) transition was observed in the orange (CaP₂N₄:Eu²⁺, λ_max=575 nm), green (SrP₂N₄:Eu²⁺, λ_max=529 nm), and blue regions of the visible spectrum (BaSr₂P₆N₁₂:Eu²⁺ and BaP₂N₄:Eu²⁺, λ_max=450 and 460 nm, respectively). Thus, the emission wavelength decreases with increasing ionic radius of the alkaline‐earth ions. The corresponding full width at half maximum values (2240–2460 cm^?1) are comparable to those of other known Eu²⁺‐doped (oxo)nitrides emitting in the same region of the visible spectrum. Following recently described quaternary Ba₃P₅N₁₀Br:Eu²⁺, this investigation represents the first report on the luminescence of Eu²⁺‐doped ternary nitridophosphates. Similarly to nitridosilicates and related oxonitrides, Eu²⁺‐doped nitridophosphates may have the potential to be further developed into efficient light‐emitting diode phosphors.     

燃烧过程中碱/碱土金属对重金属迁移转化影响的研究进展

碱/碱土金属广泛存在于各种固体燃料中，在燃烧过程中碱/碱土金属与燃料中重金属及其他矿物发生复杂的物理化学反应，从而影响重金属的迁移和转化。本研究主要介绍了碱/碱土金属对As、Se、Pb和Cr四种重金属迁移转化的影响规律，包括碱金属和碱土金属对重金属迁移转化的影响，颗粒物团聚与黏结对重金属排放的影响三个方面。碱/碱土金属能够抑制重金属的挥发：碱金属与Cl元素的结合，降低了PbCl₂的生成；碱金属的存在有利于提升高岭土对Pb的吸附效率；碱/碱土金属可以与As和Se形成稳定的化合物。但同时需要注意碱/碱土金属与Cr的部分结合产物中，Cr以六价态存在，具有较高的毒性。碱/碱土金属对于团聚现象发生，分别起到了促进和抑制作用，适当含量的碱金属有利于减少重金属的释放。通过总结碱/碱土金属对重金属迁移转化的影响规律，以期为降低重金属的危害提供思路。     

Construction of open metal-organic frameworks based on predesigned carboxylate isomers: from achiral to chiral nets

The four-connected carboxylate ligand N,N,N',N'-tetrakis(4-carboxyphenyl)-1,4-phenylenediamine (TCPPDA) exists as three stereoisomers: a pair of enantiomers (deltaD2- and lambdaD2-TCPPDA) and a diastereomer (C2h-TCPPDA). TCPPDA was predesigned for the construction of isomeric coordination networks. Reactions of M(NO3)2 (M=Cu, Zn, Co) or Nd(NO)3 with TCPPDA under solvothermal conditions gave rise to five novel porous metal-organic frameworks: [Cu2(D2-tcppda)(H2O)2].2 DMSO.6H2O (1), [Cu2(C2h-tcppda)(H2O)2].2DMSO.6H2O (2), [Co3(D2-Htcppda)2].4DEF.5H2O (3), [Nd2(D2-tcppda)(C2h-tcppda)0.5(DMSO)3]3 DMSO5 H2O (4), and [Zn4O(D2-tcppda)1.5].DMF.H2O (5) (DMSO=dimethyl sulfoxide, DEF=diethylformamide, DMF=dimethylformamide). Complexes 1 and 2 are supramolecular isomers, in which all the ligands adopt pseudotetrahedral (both deltaD2- and lambdaD2-TCPPDA) and rectangular (C2h-TCPPDA) geometries, respectively. Both compounds connect paddlewheel secondary building units (SBUs) to form three-dimensional porous networks possessing PtS and NbO nets, respectively. In 3, all ligands possess pseudotetrahedral (both deltaD2- and lambdaD2-TCPPDA) geometry and link hourglass SBUs to form a three-dimensional porous framework. Compound 4 contains all three stereoisomers (C2-, deltaD2-, and lambdaD2-TCPPDA), thus, has both pseudotetrahedral and rectangular geometries. D2-TCPPDA connects the binuclear neodymium units to generate a two-dimensional layer, further linked by C2h-TCPPDA to create a three-dimensional open framework. In 5, all the ligands possess pseudotetrahedral geometry (D2-TCPPDA), as found in 1 and 3. However, all the TCPPDA ligands in 5 appear as either the deltaD2 or the lambdaD2 form, thus, the whole structure is homochiral. Complex 5 crystallizes in the I4(1)32 space group and the octahedral SBU in 5 is connected by the enantiopure TCPPDA to generate a three-dimensional porous network possessing the corundum Al2O3 net. Complexes 1, 2, and 5 possess permanent porosity, and 4 and 5 exhibit strong luminescence at lambdamax=423 and 424 nm, respectively, upon excitation at 268.5 nm.     

Four silver-containing coordination polymers based on bis(imidazole) ligands

Four coordination polymers, [Ag(L¹)](m-Hbdc) (1), [Ag(L¹)]₂(p-bdc)?·?8H₂O (2), [Ag(Hbtc)(L¹)][Ag(L¹)]?·?2H₂O (3) and [Ag₂(L²)₂](OH-bdc)₂?·?4H₂O (4), where L¹?=?1,1′-(1,4-butanediyl)bis(imidazole), L²?=?1,2-bis(imidazol-1-ylmethyl)benzene, m-H₂bdc?=?1,3-benzenedicarboxylic acid, p-H₂bdc?=?1,4-benzenedicarboxylic acid, H₃btc?=?1,3,5-benzenetricarboxylic acid, and OH–H₂bdc?=?5-hydroxisophthalic acid, were synthesized under hydrothermal conditions. Compound 1 contains a–Ag-L¹–Ag-L¹–chain and a hydrogen-bonding interaction induced–(m-Hbdc)-(m-Hbdc)–chain. Compound 2 consists of two independent–Ag-L¹–Ag-L¹–chains. P-bdc anions are not coordinated. Hydrogen bonds form a 3D supramolecular structure. A novel (H₂O)₁₆ cluster is formed by lattice water molecules in 2. Compound 3 contains a–Ag-L¹–Ag-L¹–and a–Ag(Hbtc)-L¹–Ag(Hbtc)-L¹–chain. The packing diagram shows a 2D criss-cross supramolecular structure, with?π?···?π?and C–H ···?π?interactions stabilizing the framework. Compound 4 contains a [Ag₂(L²)₂]²⁺ dimer with hydrogen-bonding,?π?··· π, and Ag ··· O interactions forming a 3D supramolecular framework. The luminescent properties for these compounds in the solid state are discussed.