Study of gas‐phase reactions of NO2+ with aromatic compounds using proton transfer reaction time‐of‐flight mass spectrometry

The study of ion chemistry involving the NO₂⁺ is currently the focus of considerable fundamental interest and is relevant in diverse fields ranging from mechanistic organic chemistry to atmospheric chemistry. A very intense source of NO₂⁺ was generated by injecting the products from the dielectric barrier discharge of a nitrogen and oxygen mixture upstream into the drift tube of a proton transfer reaction time‐of‐flight mass spectrometry (PTR‐TOF‐MS) apparatus with H₃O⁺ as the reagent ion. The NO₂⁺ intensity is controllable and related to the dielectric barrier discharge operation conditions and ratio of oxygen to nitrogen. The purity of NO₂⁺ can reach more than 99% after optimization. Using NO₂⁺ as the chemical reagent ion, the gas‐phase reactions of NO₂⁺ with 11 aromatic compounds were studied by PTR‐TOF‐MS. The reaction rate coefficients for these reactions were measured, and the product ions and their formation mechanisms were analyzed. All the samples reacted with NO₂⁺ rapidly with reaction rate coefficients being close to the corresponding capture ones. In addition to electron transfer producing [M]⁺, oxygen ion transfer forming [MO]⁺, and 3‐body association forming [M·NO₂]⁺, a new product ion [M−C]⁺ was also formed owing to the loss of C═O from [MO]⁺.This work not only developed a new chemical reagent ion NO₂⁺ based on PTR‐MS but also provided significant interesting fundamental data on reactions involving aromatic compounds, which will probably broaden the applications of PTR‐MS to measure these compounds in the atmosphere in real time.     

Distinguishing two isomeric mephedrone substitutes with selective reagent ionisation mass spectrometry (SRI‐MS)

The isomers 4‐methylethcathinone and N‐ethylbuphedrone are substitutes for the recently banned drug mephedrone. We find that with conventional proton transfer reaction mass spectrometry (PTR‐MS), it is not possible to distinguish between these two isomers, because essentially for both substances, only the protonated molecules are observed at a mass‐to‐charge ratio of 192 (C₁₂H₁₈NO⁺). However, when utilising an advanced PTR‐MS instrument that allows us to switch the reagent ions (selective reagent ionisation) from H₃O⁺ (which is commonly used in PTR‐MS) to NO⁺, O₂⁺ and Kr⁺, characteristic product (fragment) ions are detected: C₄H₁₀N⁺ (72 Da) for 4‐methylethcathinone and C₅H₁₂N⁺ (86 Da) for N‐ethylbuphedrone; thus, selective reagent ionisation MS proves to be a powerful tool for fast detection and identification of these compounds. Copyright © 2013 John Wiley & Sons, Ltd.     

Characterization of N‐Boc/Fmoc/Z‐N′‐formyl‐gem‐diaminoalkyl derivatives using electrospray ionization multi‐stage mass spectrometry

N‐Boc/Fmoc/Z‐N′‐formyl‐gem‐diaminoalkyl derivatives, intermediates particularly useful in the synthesis of partially modified retro‐inverso peptides, have been characterized by both positive and negative ion electrospray ionization (ESI) ion‐trap multi‐stage mass spectrometry (MSⁿ). The MS² collision induced dissociation (CID) spectra of the sodium adduct of the formamides derived from the corresponding N‐Fmoc/Z‐amino acids, dipeptide and tripeptide acids show the [M + Na‐NH₂CHO]⁺ ion, arising from the loss of formamide, as the base peak. Differently, the MS² CID spectra of [M + Na]⁺ ion of all the N‐Boc derivatives yield the abundant [M + Na‐C₄H₈]⁺ and [M + Na‐Boc + H]⁺ ions because of the loss of isobutylene and CO₂ from the Boc protecting function. Useful information on the type of amino acids and their sequence in the N‐protected dipeptidyl and tripeptidyl‐N′‐formamides is provided by MS² and subsequent MSⁿ experiments on the respective precursor ions. The negative ion ESI mass spectra of these oligomers show, in addition to [M‐H]^?, [M + HCOO]^? and [M + Cl]^? ions, the presence of in‐source CID fragment ions deriving from the involvement of the N‐protecting group. Furthermore, MSⁿ spectra of [M + Cl]^? ion of N‐protected dipeptide and tripeptide derivatives show characteristic fragmentations that are useful for determining the nature of the C‐terminal gem‐diamino residue. The present paper represents an initial attempt to study the ESI‐MS behavior of these important intermediates and lays the groundwork for structural‐based studies on more complex partially modified retro‐inverso peptides. Copyright © 2013 John Wiley & Sons, Ltd.     

Hydride transfer reactions via ion–neutral complex: fragmentation of protonated N‐benzylpiperidines and protonated N‐benzylpiperazines in mass spectrometry

An ion‐neutral complex (INC)‐mediated hydride transfer reaction was observed in the fragmentation of protonated N‐benzylpiperidines and protonated N‐benzylpiperazines in electrospray ionization mass spectrometry. Upon protonation at the nitrogen atom, these compounds initially dissociated to an INC consisting of [RC₆H₄CH₂]⁺ (R = substituent) and piperidine or piperazine. Although this INC was unstable, it did exist and was supported by both experiments and density functional theory (DFT) calculations. In the subsequent fragmentation, hydride transfer from the neutral partner to the cation species competed with the direct separation. The distribution of the two corresponding product ions was found to depend on the stabilization energy of this INC, and it was also approved by the study of substituent effects. For monosubstituted N‐benzylpiperidines, strong electron‐donating substituents favored the formation of [RC₆H₄CH₂]⁺, whereas strong electron‐withdrawing substituents favored the competing hydride transfer reaction leading to a loss of toluene. The logarithmic values of the abundance ratios of the two ions were well correlated with the nature of the substituents, or rather, the stabilization energy of this INC. Copyright © 2010 John Wiley & Sons, Ltd.     

Analysis of ToF‐SIMS spectra of poly(2‐vinylpyridine) and poly(4‐vinylpyridine) with density functional theory calculations

The time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) positive and negative ion spectra of poly(2‐vinylpyridine) (P2VP) and poly(4‐vinylpyridine) (P4VP) were analyzed using density functional theory calculations. Most of the ions from these structural isomers shared the same accurate mass, but had different relative abundance. This could be attributed to the fact that from a thermodynamics perspective, the disparity in the molecular structures can affect the ion stability if we assume that they shared the same mechanistic pathway of formation with similar reaction kinetics. The molecular structures of these ions were assigned, and their stability was evaluated based on calculations using the Kohn‐Sham density functional theory with Becke's 3‐parameter Lee‐Yang‐Parr exchange‐correlation functional and a correlation‐consistent, polarized, valence, double‐zeta basis set for cations and the same basis set with a triple‐zeta for anions. The computational results agreed with the experimental observations that the nitrogen‐containing cations such as C₅H₄N⁺ (m/z = 78), C₈H₇N^+· (m/z = 117), C₈H₈N⁺ (m/z = 118), C₉H₈N⁺ (m/z = 130), C₁₃H₁₁N₂⁺ (m/z = 195), C₁₄H₁₃N₂⁺ (m/z = 209), C₁₅H₁₅N₂⁺ (m/z = 223), and C₂₁H₂₂N₃⁺ (m/z = 316) ions were more favorably formed in P2VP than in P4VP due to higher ion stability because the calculated total energies of these cations were more negative when the nitrogen was situated at the ortho position. Nevertheless, our assumption was invalid in the formation of positive ions such as C₆H₇N⁺˙ (m/z = 93) and C₈H₁₀N⁺ (m/z = 120). Their formation did not necessarily depend on the ion stability. Instead, the transition state chemistry and the matrix effect both played a role. In the negative ion spectra, we found that nitrogen‐containing anions such as C₅H₄N^? (m/z = 78), C₆H₆N^? (m/z = 92), C₇H₆N^? (m/z = 104), C₈H₆N^? (m/z = 116), C₉H₁₀N^? (m/z = 132), C₁₃H₁₁N₂^? (m/z = 195), and C₁₄H₁₃N₂^? (m/z = 209) ions were more favorably formed in P4VP, which is in line with our computational results without exception. We speculate that whether anions would form from P2VP and P4VP is more dependent on the stability of the ions.     

两类三组份反应产物：1,3-恶嗪及嘧啶-2-酮类化合物的质谱学行为研究

电喷雾质谱被应用于分辨2-氨基-1,3-恶嗪及六氢化-4-苯基-吡喃[2,3-d]嘧啶-2-酮的杂环结构。两类化合物均为三组份反应的产物,且其杂环的结构很难用NMR判断。实验首次系统研究了两类化合物的质谱学行为（包括氘代实验和高分辨质谱研究）,发现前者在CID实验中丢失CH2N2和HCNO,而后者为直接丢失尿素。这些特征丢失为该类衍生物的结构判断,尤其是高通量的合成产物分析提供了重要的依据。     

A three‐dimensional metal–organic polymer: poly[bis(μ2‐pyrimidine‐2‐thiolato‐κ4N1,S:S,N3)lead(II)]

The title compound, [Pb(C₄H₃N₂S)₂]_n, was prepared by the reaction of [Pb(OAc)₂]·3H₂O (OAc is acetate) with pyrimidine‐2‐thione in the presence of triethylamine in methanol. In the crystal structure, the Pb^II atom has an N₄S₄ coordination environment with four ligands coordinated by N‐ and S‐donor atoms. This compound shows that the pyrimidine‐2‐thiolate anion can lead to a three‐dimensional network when the coordination number of the metal ion can be higher than 6, as is the case with the Pb^II ion. This compound presents only covalent bonds, showing that despite the possibility of the hemidirected geometries of Pb^II, the eight‐coordinated ion does not allow the formation of an isolated molecular structure with pyrimidine‐2‐thiolate as the ligand.     

Controlled Aggregation of Multiple Guanidinium Ions through a Hydrogen‐Bonded Network Assembly with Deprotonated Forms of Kemp’s Triacid

A series of five complexes that incorporate the guanidinium ion and various deprotonated forms of Kemp’s triacid (H₃KTA) have been synthesized and characterized by single‐crystal X‐ray analysis. The complex [C(NH₂)₃⁺] ? [H₂KTA^?] ( 1 ) exhibits a sinusoidal layer structure with a centrosymmetric pseudo‐rosette motif composed of two ion pairs. The fully deprotonated Kemp’s triacid moiety in 3 [C(NH₂)₃⁺] ? [KTA^3?] ( 2 ) forms a record number of eighteen acceptor hydrogen bonds, thus leading to a closely knit three‐dimensional network. The KTA^3? anion adopts an uncommon twist conformation in [(CH₃)₄N⁺] ? 2 [C(NH₂)₃⁺] ? [KTA^3?] ? 2 H₂O ( 3 ). The crystal structure of [(nC₃H₇)₄N⁺] ? 2 [C(NH₂)₃⁺] ? [KTA^3?] ( 4 ) features a tetrahedral aggregate of four guanidinium ions stabilized by an outer shell that comprises six equatorial carboxylate groups that belong to separate [KTA^3?] anions. In 3 [(C₂H₅)₄N⁺] ? 20 [C(NH₂)₃⁺] ? 11 [HKTA^2?] ? [H₂KTA^?] ? 17 H₂O ( 5 ), an even larger centrosymmetric inner core composed of eight guanidinium ions and six bridging water molecules is enclosed by a crust composed of eighteen axial carboxyl/carboxylate groups from six HKTA^2? anions.     

Three novel topologically different metal–organic frameworks built from 3‐nitro‐4‐(pyridin‐4‐yl)benzoic acid

The design and synthesis of metal–organic frameworks (MOFs) have attracted much interest due to the intriguing diversity of their architectures and topologies. However, building MOFs with different topological structures from the same ligand is still a challenge. Using 3‐nitro‐4‐(pyridin‐4‐yl)benzoic acid (HL) as a new ligand, three novel MOFs, namely poly[[(N,N‐dimethylformamide‐κO)bis[μ₂‐3‐nitro‐4‐(pyridin‐4‐yl)benzoato‐κ³O,O′:N]cadmium(II)] N,N‐dimethylformamide monosolvate methanol monosolvate], {[Cd(C₁₂H₇N₂O₄)₂(C₃H₇NO)]·C₃H₇NO·CH₃OH}_n, ( 1 ), poly[[(μ₂‐acetato‐κ²O:O′)[μ₃‐3‐nitro‐4‐(pyridin‐4‐yl)benzoato‐κ³O:O′:N]bis[μ₃‐3‐nitro‐4‐(pyridin‐4‐yl)benzoato‐κ⁴O,O′:O′:N]dicadmium(II)] N,N‐dimethylacetamide disolvate monohydrate], {[Cd₂(C₁₂H₇N₂O₄)₃(CH₃CO₂)]·2C₄H₉NO·H₂O}_n, ( 2 ), and catena‐poly[[[diaquanickel(II)]‐bis[μ₂‐3‐nitro‐4‐(pyridin‐4‐yl)benzoato‐κ²O:N]] N,N‐dimethylacetamide disolvate], {[Ni(C₁₂H₇N₂O₄)₂(H₂O)₂]·2C₄H₉NO}_n, ( 3 ), have been prepared. Single‐crystal structure analysis shows that the Cd^II atom in MOF ( 1 ) has a distorted pentagonal bipyramidal [CdN₂O₅] coordination geometry. The [CdN₂O₅] units as 4‐connected nodes are interconnected by L^? ligands to form a fourfold interpenetrating three‐dimensional (3D) framework with a dia topology. In MOF ( 2 ), there are two crystallographically different Cd^II ions showing a distorted pentagonal bipyramidal [CdNO₆] and a distorted octahedral [CdN₂O₄] coordination geometry, respectively. Two Cd^II ions are connected by three carboxylate groups to form a binuclear [Cd₂(COO)₃] cluster. Each binuclear cluster as a 6‐connected node is further linked by acetate groups and L^? ligands to produce a non‐interpenetrating 3D framework with a pcu topology. MOF ( 3 ) contains two crystallographically distinct Ni^II ions on special positions. Each Ni^II ion adopts an elongated octahedral [NiN₂O₄] geometry. Each Ni^II ion as a 4‐connected node is linked by L^? ligands to generate a two‐dimensional network with an sql topology, which is further stabilized by two types of intermolecular OW—HW…O hydrogen bonds to form a 3D supramolecular framework. MOFs ( 1 )–( 3 ) were also characterized by powder X‐ray diffraction, IR spectroscopy and thermogravimetic analysis. Furthermore, the solid‐state photoluminescence of HL and MOFs ( 1 ) and ( 2 ) have been investigated. The photoluminescence of MOFs ( 1 ) and ( 2 ) are enhanced and red‐shifted with respect to free HL. The gas adsorption investigation of MOF ( 2 ) indicates a good separation selectivity (71) of CO₂/N₂ at 273 K (i.e. the amount of CO₂ adsorption is 71 times higher than N₂ at the same pressure).     

Two New Silver(I) Ammine Complexes by Displacement Reaction Between [Ag(NH3)2]+ Ions and Different Pyridine‐4,5‐Imidazoledicarboxylic Acids

[Ag(NH₃)₂]⁺ ions are chosen as an initial reaction precursor because of its simple displacement reaction and intrinsic arrangement as well as specific coordination directionality. Two new silver(I) ammine complexes, Ag₂(NH₃)HL² ( 2 ) and Ag₂(NH₃)₂HL³ ( 3 ), were obtained by a simple substitution reaction between [Ag(NH₃)₂]⁺ ions and pyridine‐4,5‐imidazoledicarboxylic acid [H₃L² = 2‐(3′‐pyridyl) 4,5‐imidazoledicarboxylic acid and H₃L³ = 2‐(4′‐pyridyl) 4,5‐imidazoledicarboxylic acid]. Silver dimers are connected into a 2D layer and 1D chain in complexes 2 and 3 , respectively. In complex 2 two kinds of displacement reactions (mono‐substituting and bis‐substituting) occurred between the ammine molecules in [Ag(NH₃)₂]⁺ ions and H₃L², however, only the mono‐substituting reaction occurs in complex 3 .     

Synthesis and crystal structure of a two‐dimensional sodium coordination polymer of 4,4′‐(diazenediyl)bis(1H‐1,2,4‐triazol‐5‐one)

The crystal engineering of coordination polymers has aroused interest due to their structural versatility, unique properties and applications in different areas of science. The selection of appropriate ligands as building blocks is critical in order to afford a range of topologies. Alkali metal cations are known for their mainly ionic chemistry in aqueous media. Their coordination number varies depending on the size of the binding partners, and on the electrostatic interaction between the ligands and the metal ions. The two‐dimensional coordination polymer poly[tetra‐μ‐aqua‐[μ₄‐4,4′‐(diazenediyl)bis(5‐oxo‐1H‐1,2,4‐triazolido)]disodium(I)], [Na₂(C₄H₂N₈O₂)(H₂O)₄]_n, (I), was synthesized from 4‐amino‐1H‐1,2,4‐triazol‐5(4H)‐one (ATO) and its single‐crystal structure determined. The mid‐point of the imino N=N bond of the 4,4′‐(diazenediyl)bis(5‐oxo‐1H‐1,2,4‐triazolide) (ZTO²⁻) ligand is located on an inversion centre. The asymmetric unit consists of one Na⁺ cation, half a bridging ZTO²⁻ ligand and two bridging water ligands. Each Na⁺ cation is coordinated in a trigonal antiprismatic fashion by six O atoms, i.e. two from two ZTO²⁻ ligands and the remaining four from bridging water ligands. The Na⁺ cation is located near a glide plane, thus the two bridging O atoms from the two coordinating ZTO²⁻ ligands are on adjacent apices of the trigonal antiprism, rather than being in an anti configuration. All water and ZTO²⁻ ligands act as bridging ligands between metal centres. Each Na⁺ metal centre is bridged to a neigbouring Na⁺ cation by two water molecules to give a one‐dimensional [Na(H₂O)₂]_n chain. The organic ZTO²⁻ ligand, an O atom of which also bridges the same pair of Na⁺ cations, then crosslinks these [Na(H₂O)₂]_n chains to form two‐dimensional sheets. The two‐dimensional sheets are further connected by intermolecular hydrogen bonds, giving rise to a stabile hydrogen‐bonded network.     

Charge and substituent effects on the stability of porphyrin/G‐quadruplex adducts

The adduct ions of two tetramolecular G‐quadruplexes formed from the d(TGGGGT) and d(TTGGGGGT) single strands with a group of cationic porphyrins, with different charges and substituents, and one neutral porphyrin, were investigated by ESI‐MS and ESI‐MS/MS in the negative ion mode. Formation of [Q + nNH₄⁺+P^p+‐(z + n + p)H⁺]^z‐ adduct ions (where Q = quadruplex, n = number of quartets minus 1, P = porphyrin and p⁺ =0,1,2,3,4) indicates that the porphyrins are bound outside the quadruplexes providing an additional stabilization to those structures. The fragmentation pathways of the [Q + nNH₄⁺+P^p+‐(z + n + p)H⁺]^z‐ adduct ions depend on the number of positive charges (p⁺) of the porphyrins and on the overall complex charge (z^‐), but do not show a significant dependence on the type of the substituent groups in the porphyrins. Formation of the ‘unfilled’ ions [Q + P^p+‐(z + p)H⁺]^z‐ predominates for porphyrins with a higher number of positive charges. Strand separation with the formation of [T + P^p+‐(z‐2 + p)H⁺]^(z‐2)‐ and (SS‐2H⁺)^2‐ ions, where T = [d(TG₄T)]₃ and [d(T₂G₅T)]₃ and SS = d(TG₄T) and d(T₂G₅T) is only observed for the complexes with a higher overall negative charge. Porphyrin loss with the formation of [Q + nNH₄⁺‐(z + n)H⁺]^z‐ ions occurs predominantly for the neutral and monocharged porphyrins. The predominant formation of the ‘unfilled’ ions, [Q + P^p+‐(z + n)H⁺]^z‐, for porphyrins with a higher number of charges shows that these porphyrins can prevent strand separation and preserve, at least partially, the quadruplex structure. Copyright © 2012 John Wiley & Sons, Ltd.     

Gas‐phase fragmentation of metal adducts of alkali‐metal oxalate salts

Upon collisional activation, gaseous metal adducts of lithium, sodium and potassium oxalate salts undergo an expulsion of CO₂, followed by an ejection of CO to generate a product ion that retains all three metals atoms of the precursor. Spectra recorded even at very low collision energies (2 eV) showed peaks for a 44‐Da neutral fragment loss. Density functional theory calculations predicted that the ejection of CO₂ requires less energy than an expulsion of a Na⁺ and that the [Na₃CO₂]⁺ product ion formed in this way bears a planar geometry. Furthermore, spectra of [Na₃C₂O₄]⁺ and [³⁹K₃C₂O₄]⁺ recorded at higher collision energies showed additional peaks at m/z 90 and m/z 122 for the radical cations [Na₂CO₂]^+? and [K₂CO₂]^+?, respectively, which represented a loss of an M^? from the precursor ions. Moreover, [Na₃CO₂]⁺, [³⁹K₃CO₂]⁺ and [Li₃CO₂]⁺ ions also undergo a CO loss to form [M₃O]⁺. Furthermore, product‐ion spectra for [Na₃C₂O₄]⁺ and [³⁹K₃C₂O₄]⁺ recorded at low collision energies showed an unexpected peak at m/z 63 for [Na₂OH]⁺ and m/z 95 for [³⁹K₂OH]⁺, respectively. An additional peak observed at m/z 65 for [Na₂¹⁸OH] ⁺ in the spectrum recorded for [Na₃C₂O₄]⁺, after the addition of some H₂¹⁸O to the collision gas, confirmed that the [Na₂OH] ⁺ ion is formed by an ion–molecule reaction with residual water in the collision cell. Copyright © 2014 John Wiley & Sons, Ltd.     

Characterization of N‐methylated amino acids by GC‐MS after ethyl chloroformate derivatization

Methylation is an essential metabolic process in the biological systems, and it is significant for several biological reactions in living organisms. Methylated compounds are known to be involved in most of the bodily functions, and some of them serve as biomarkers. Theoretically, all α‐amino acids can be methylated, and it is possible to encounter them in most animal/plant samples. But the analytical data, especially the mass spectral data, are available only for a few of the methylated amino acids. Thus, it is essential to generate mass spectral data and to develop mass spectrometry methods for the identification of all possible methylated amino acids for future metabolomic studies. In this study, all N‐methyl and N,N‐dimethyl amino acids were synthesized by the methylation of α‐amino acids and characterized by a GC‐MS method. The methylated amino acids were derivatized with ethyl chloroformate and analyzed by GC‐MS under EI and methane/CI conditions. The EI mass spectra of ethyl chloroformate derivatives of N‐methyl ( 1–18 ) and N,N‐dimethyl amino acids ( 19–35 ) showed abundant [M‐COOC₂H₅]⁺ ions. The fragment ions due to loss of C₂H₄, CO₂, (CO₂ + C₂H₄) from [M‐COOC₂H₅]⁺ were of structure indicative for 1–18 . The EI spectra of 19–35 showed less number of fragment ions when compared with those of 1–18 . The side chain group (R) caused specific fragment ions characteristic to its structure. The methane/CI spectra of the studied compounds showed [M + H]⁺ ions to substantiate their molecular weights. The detected EI fragment ions were characteristic of the structure that made easy identification of the studied compounds, including isomeric/isobaric compounds. Fragmentation patterns of the studied compounds ( 1–35 ) were confirmed by high‐resolution mass spectra data and further substantiated by the data obtained from ¹³C₂‐labeled glycines and N‐ethoxycarbonyl methoxy esters. The method was applied to human plasma samples for the identification of amino acids and methylated amino acids. Copyright © 2016 John Wiley & Sons, Ltd.     

Cyano‐Bridged ‘Oximato’ Complexes: Synthesis,Structure, and Catalase‐Like Activities

The reaction of the ‘oximato’‐ligand precursor A (Fig. 1) and metal salts with KCN gave two mononuclear complexes [ML(CN)(H₂O)_n](ClO₄) ( 1 and 2 ; L={N‐(hydroxy‐κO)‐α‐oxo‐N′‐[(pyridin‐2‐yl‐κN)methyl[1,1′‐biphenyl]‐4‐ethanimidamidato‐κN′}; M=Co^II ( 1 ), Cu^II ( 2 ); n=2 for Co^II, n=0 for Cu^II; Figs. 2 and 3). The new cyano‐bridged pentanuclear ‘oximato’ complexes [{ML(H₂O)_n(NC)}₄M¹(H₂O)_x](ClO₄)₂ ( 3 – 6 ) and trinuclear complexes [{ML(H₂O)_n(NC)}₂M¹L](ClO₄) ( 7 – 10 ) ([M¹=Mn^II, Cu^II; x=2 for Mn^II, x=0 for Cu^II] were synthesized from mononuclear complexes and characterized by elemental analyses, magnetic susceptibility, molar conductance, and IR and thermal analysis. The four [ML(CN)(H₂O)_n]⁺ moieties are connected by a metal(II) ion in the pentanuclear complexe 3 – 6 , each one involving four cyano bridging ligands (Fig. 4). The central metal ion displays a square‐planar or octahedral geometry, with the cyano bridging ligands forming the equatorial plane. The axial positions are occupied by two aqua ligands in the case of the central Mn‐atom. The two [ML(CN)(H₂O)_n]⁺ moieties and an ‘oximato’ ligand are connected by a metal(II) ion in the trinuclear complexes 7 – 10 , each one involving two cyano bridging ligands (Fig. 5). The central metal ions display a distorted square‐pyramidal geometry, with two cyano bridging ligands and the donor atoms of the tridentate ‘oximato’ ligand. Moreover catalytic activities of the complexes for the disproportionation of hydrogen peroxide (H₂O₂) were also investigated in the presence of 1H‐imidazole. The synthesized homopolynuclear Cu^II complexes 6 and 10 displayed eficiency in disproportion reactions of H₂O₂ producing H₂O and dioxygen thus showing catalase‐like activity.     

Synthese und Strukturen der ersten mehrkernigen Mangan‐Guanidin‐Komplexe und der ersten Mangan‐Komplexe mit mono‐protonierten Bis‐Guanidinliganden

Syntheses and Structures of the First Polynuclear Manganese Guanidine Complexes and of the First Manganese Complexes Containing Mono‐Protonated Bis‐Guanidine Ligands Metallation of two differently alkylated bis‐guanidine ligands containing a central pyridine functionality, namely N²,N⁶‐bis(1,3‐dimethylimidazolidin‐2‐ylidene)pyridine‐2,6‐diamine (DMEG₂py {N₇C₁₅H₂₃}, L¹ ) and N²,N⁶‐bis(1,1,3,3‐tetramethyl‐guanidine)pyridine‐2,6‐diamine (TMG₂py {N₇C₁₅H₂₇}, L² ), with manganese(II) bromide and chloride leads to the formation of the novel complexes [MnBr₃(TMG₂pyH)] ([MnBr₃(N₇C₁₅H₂₈)], ( 1 )), [MnBr₂(DMEG₂pyH)₂]²⁺ ([MnBr₂(N₇C₁₅H₂₄)₂]²⁺, ( 2 )), and [Mn₂X₃(DMEG₂py)₂]⁺ ([Mn₂X₃(N₇C₁₅H₂₃)₂]⁺; ( 3a ): X = Cl; ( 3b ): X = Br). 2 and 3 have been isolated as tetrahalomanganate salts. Single crystal X‐ray analyses show that all of them contain the manganese atoms in unusual pseudo‐tetrahedral coordination environments. 3a· 1/2[MnCl₄] and 3b· 1/2[MnBr₄] are isostructural and crystallize in the monoclinic space group C2c. The complex cations 3 exhibit a binuclear structure with two terminal and one bridging halide ion, respectively. The compounds 1 and 2 are mononuclear species crystallizing in the orthorhombic space group P2₁2₁2₁ in the case of 1 and in the triclinic space group in the case of 2· [MnBr₄]. The ability of L¹ and L² to bind either two manganese ions naked or only one of them in the mono‐protonated stage is the most remarkable property of these ligands. Further striking features are the spatial arrangements of the pyridine‐to‐manganese bonds which deviate significantly from the situation expected for nitrogen donor functions in sp² hybridized stages. Moreover, regarding each chelating ligand portion as a component which occupies one coordination site of the metal atom, a pseudo‐tetrahedral metal coordination is identified. To our knowledge, 1 and 2 are the first manganese complexes containing mono‐protonated bis‐guanidine ligands, whereas 3a and 3b are the first polynuclear manganese‐guanidine compounds known so far.     

Hexa­aqua­magnesium(II) bis­[N‐(6‐amino‐3,4‐di­hydro‐3‐methyl‐5‐nitro­so‐4‐oxopyrimidin‐2‐yl)­glycinate] dihydrate

The analysis of the title compound, [Mg(H₂O)₆](C₇H₈N₅O₄)₂·2H₂O, continues our study of the reactivity of metal ions with N‐protected amino acids. The Mg ion lies on an inversion centre with Mg—O 2.0437 (10)‐2.0952 (10) Å. The [Mg(H₂O)₆]²⁺cations, anions and water mol­ecules are linked by an extensive hydrogen‐bond network.     

Unusual Coordination Modes of Tris(pyrazol‐1‐yl)borates: Synthesis and Solid State Structures of Sodium[(dimethylamino)tris(pyrazol‐1‐yl)borate], Potassium[(dimethylamino)tris(pyrazol‐1‐yl)borate], and Potassium[phenyltris(pyrazol‐1‐yl)borate]

We report the optimized syntheses and the solid state structures of the alkali metal tris(pyrazol‐1‐yl)borates M[Me₂NBpz₃] (M = Na⁺ ( 1 ), K⁺ ( 2 ); pz = pyrazol‐1‐yl) and K[PhBpz₃] ( 3 ). Even though 1 and 2 consist of polymeric chains in the solid state, it is possible to identify subunits where the [Me₂NBpz₃]^? ion acts as tridentate ligand towards Na⁺ and K⁺ and binds via two of its pyrazolyl rings and its dimethylamino nitrogen atom (κ³N_pz,N_pz,N_NMe). In 3 , the ligand [PhBpz₃]^? employs two pyrazolyl donors and the π‐face of its phenyl substituent for potassium coordination (κ³N,N,C).     

A new one‐dimensional ZnII coordination polymer based on 2‐[(1H‐imidazol‐1‐yl)methyl]‐1H‐benzimidazole and benzene‐1,2‐dicarboxylate

Multidentate N‐heterocyclic compounds form a variety of metal complexes with many intriguing structures and interesting properties. The title coordination polymer, catena‐poly[zinc(II)‐bis{μ‐2‐[(1H‐imidazol‐1‐yl)methyl]‐1H‐benzimidazole}‐κ²N³:N^3′;N^3′:N³‐zinc(II)‐bis(μ‐benzene‐1,2‐dicarboxylato)‐κ²O¹:O²;κ³O¹,O^1′:O²], [Zn₂(C₈H₄O₄)₂(C₁₁H₁₀N₄)₂]_n, has been synthesized by the reaction of Zn(NO₃)₂ with 2‐[(1H‐imidazol‐1‐yl)methyl]‐1H‐benzimidazole (imb) and benzene‐1,2‐dicarboxylic acid (H₂bdic) under hydrothermal conditions. There are two crystallographically distinct imb ligands [imb(A) and imb(B)] in the structure which adopt very similar coordination geometries. The imb(A) ligand bridges two symmetry‐related Zn1 ions, yielding a binuclear [(Zn1)₂{imb(A)}₂] unit, and the imb(B) ligand bridges two symmetry‐related Zn2 ions resulting in a binuclear [(Zn2)₂{imb(B)}₂] unit. The above‐mentioned binuclear units are further connected alternately by pairs of bridging bdic²⁻ ligands, forming an infinite one‐dimensional chain. These one‐dimensional chains are further connected through N—H...O hydrogen bonds, leading to a two‐dimensional layered structure. In addition, the title polymer exhibits good fluorescence properties in the solid state at room temperature.     

Crystal structure,shape analysis and bioactivity of new LiI,NaI and MgII complexes with 1,10‐phenanthroline and 2‐(3,4‐dichlorophenyl)acetic acid

Reactions of 1,10‐phenanthroline (phen) and 2‐(3,4‐dichlorophenyl)acetic acid (dcaH) with M_n(CO₃) (M = Li^I, Na^I and Mg^II; n = 1 and 2) in MeOH yield the mononuclear lithium complex aqua[2‐(3,4‐dichlorophenyl)acetato‐κO](1,10‐phenanthroline‐κ²N,N′)lithium(I), [Li(C₈H₅Cl₂O₂)(C₁₂H₈N₂)(H₂O)] or [Li(dca)(phen)(H₂O)] ( 1 ), the dinuclear sodium complex di‐μ‐aqua‐bis{[2‐(3,4‐dichlorophenyl)acetato‐κO](1,10‐phenanthroline‐κ²N,N′)sodium(I)}, [Na₂(C₈H₅Cl₂O₂)₂(C₁₂H₈N₂)₂(H₂O)₂] or [Na₂(dca)₂(phen)₂(H₂O)₂] ( 2 ), and the one‐dimensional chain magnesium complex catena‐poly[[[diaqua(1,10‐phenanthroline‐κ²N,N′)magnesium]‐μ‐2‐(3,4‐dichlorophenyl)acetato‐κ²O:O′] 2‐(3,4‐dichlorophenyl)acetate monohydrate], {[Mg(C₈H₅Cl₂O₂)(C₁₂H₈N₂)(H₂O)₂](C₈H₅Cl₂O₂)·H₂O}_n or {[Mg(dca)(phen)(H₂O)₂](dca)·H₂O}_n ( 3 ). In these complexes, phen binds via an N,N′‐chelate pocket, while the deprotonated dca^? ligands coordinate either in a monodentate (in 1 and 2 ) or bidentate (in 3 ) fashion. The remaining coordination sites around the metal ions are occupied by water molecules in all three complexes. Complex 1 crystallizes in the triclinic space group P with one molecule in the asymmetric unit. The Li⁺ ion adopts a four‐coordinated distorted seesaw geometry comprising an [N₂O₂] donor set. Complex 2 crystallizes in the triclinic space group P with half a molecule in the asymmetric unit, in which the Na⁺ ion adopts a five‐coordinated distorted spherical square‐pyramidal geometry, with an [N₂O₃] donor set. Complex 3 crystallizes in the orthorhombic space group P2₁2₁2₁, with one Mg²⁺ ion, one phen ligand, two dca^? ligands and three water molecules in the asymmetric unit. Both dcaH ligands are deprotonated, however, one dca^? anion is not coordinated, whereas the second dca^? anion coordinates in a bidentate fashion bridging two Mg²⁺ ions, resulting in a one‐dimensional chain structure for 3 . The Mg²⁺ ion adopts a distorted octahedral geometry, with an [N₂O₄] donor set. Complexes 1 – 3 were evaluated against urease and α‐glucosidase enzymes for their inhibition potential and were found to be inactive.