Synthesis, crystal structures, and spectroscopic characterization of the neutral monomeric tetrahedral [M(Diap)2(OAc)2] · H2O complexes (M = Zn,Cd; Diap = 1,3-diazepane-2-thione; OAc = acetate) with N-H?O and O-H?O intra- and intermolecular hydrogen bonding interactions

The title complexes, [M(Diap)₂(OAc)₂] · H₂O (M = Zn,Cd; Diap = 1,3-diazepane-2-thione; OAc = acetate) with an MO₂S₂ configuration, have been characterized by X-ray crystallography as well as FT-IR, ¹H and ¹³C NMR spectroscopy. In these complexes, the metal atoms lie in a pseudo-tetrahedral environment and are coordinated by the thione sulfur atoms of two neutral 1,3-diazepane-2-thione ligands and one oxygen atom from each of two monodentate acetate anions. In both complexes, there are two intramolecular N-H?O hydrogen bonds, each being between one NH group of a Diap ligand and the uncoordinated O atom of an OAc ligand. The water molecule is also involved in hydrogen bonds, as an acceptor and as a donor twice, linking together three symmetry-related complexes. The Cd complex undergoes a structural phase transition from a monoclinic form at 150 K with Z′ = 2 to a smaller monoclinic cell at room temperature with Z′ = 1 without loss of crystallinity. The Zn complex does not exhibit an equivalent phase transition, and at 150 K is isostructural with the room-temperature form of the Cd complex. All three crystallographically independent molecules found for the Cd complex (two at low temperature and one at room temperature) have essentially the same structure except for small changes in the conformations of the ligands. Tetrahedral coordination with monodentate carboxylate ligands is common for Zn complexes of this kind, but is unusual for Cd complexes, and is the result of the bulky Diap ligands.     

Unusual packing of ET molecules caused by π-π stacking interactions with TRISPHAT molecules in two [ET][TRISPHAT] salts (ET = bis(ethylenedithio)tetrathiafulvalene, TRISPHAT = (tris(tetrachlorobenzenediolato)phosphate(V)))

The synthesis, structure and physical properties of two new radical salts formed with the organic donor bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) and a racemic mixture of the chiral anion (tris(tetrachlorobenzenediolato)phosphate(V)) (TRISPHAT) are reported. The structure of the salts (ET)₄[TRISPHAT]₄ · 3.5H₂O (1) and (ET)(TRISPHAT) · CH₂Cl₂ · CH₃CN (2) has been solved by X-ray single crystal diffraction. Unusual packings of ET molecules are obtained in the two structures. The electrical properties indicate that both compounds are insulators. This is in agreement with the isolation of the ET molecules and their complete ionization. On the other hand, the anisotropy of the ESR lines has been studied by Q-band ESR spectra.     

Succinate bridged dimeric Cu(II) system containing sandwiched non-coordinating succinate dianion: Crystal structure, spectroscopic and thermal studies of [(phen)2Cu(μ-L)Cu(phen)2]L · 12.5H2O (H2L = succinic acid; phen = 1,10-phenanthroline)

A mixed ligand and dimeric Cu^II complex [(phen)₂Cu(μ-L)Cu(phen)₂]L · 12.5H₂O (H₂L = succinic acid) containing bridging succinate moiety and also non-coordinated succinate dianion was prepared from polymeric Cu(II) succinate by nucleophilic reaction with o-phenanthroline (phen) followed by depolymerization. The dimeric product was characterized by crystallographic, spectroscopic and thermoanalytical studies. The complex crystallizes in triclinic crystal system and is composed of succinate bridged [(phen)₂Cu(μ-L)Cu(phen)₂]²⁺ complex cations, non-coordinated succinate anions and hydrogen bonded water molecules. Within the dimeric cationic unit, each of the Cu atoms is octahedrally coordinated by four N atoms of both phen ligands and both O atoms of a carboxylate moiety of the bridging succinate group in chelating form. Through intermolecular π-π stacking interactions, the complex cations form positively charged 2-D layers, between which the non-coordinating succinate anions and water molecules are sandwiched. Both the electronic and EPR studies indicate that the dimeric complex undergoes partial dissociation in solution state to exist in two structural forms. The kinetic and thermodynamic parameters involved in three stage thermal decompositions of the dimeric complex could also be evaluated using Coats-Redfern method.     

Mixed-valent and radical states of complexes [(bpy)2M(μ-abpy)M′(bpy)2], M,M′ = Ru or Os, abpy = 2,2′-azobispyridine: Electron transfer vs. hole transfer mechanism in azo ligand-bridged complexes

The title complexes were obtained as M^IIM′^II species [(bpy)₂M(μ-abpy)M′(bpy)₂](PF₆)₄, M,M′ = Ru or Os, using the new mononuclear precursor [(bpy)₂Os(abpy)](PF₆)₂ for the osmium-containing dinuclear complexes. One-electron reduction produces radical complexes [(bpy)₂M(μ-abpy)M′(bpy)₂]³⁺ and [(bpy)₂M(abpy)]⁺ with significant contributions from the metals, as evident from the EPR effects on successive replacement of ruthenium by osmium with its much higher spin-orbit coupling constant. The diruthenium and diosmium radical complexes were also studied by EPR at high-frequency (285 GHz), the latter shows an unusually large g anisotropy g₁ − g₃ = 0.25 in frozen solution. Further reduction was monitored by UV/Vis spectroelectrochemistry. Oxidation produced Os^III EPR signals for [(bpy)₂Os(abpy)]³⁺ and [(bpy)₂Os(μ-abpy)Ru(bpy)₂]⁵⁺, indicating a Ru^IIOs^III species for the latter. The diosmium(III,II) and diruthenium(III,II) mixed-valent species remained EPR silent at 4 K, however, they exhibit weak inter-valence charge transfer (IVCT) bands at about 1460 nm. Whereas the cyclic voltammetric response towards reduction is only marginally different for the three dinuclear complexes, successive replacement of ruthenium by osmium causes the first oxidation potential to decrease. The much higher comproportionation constant K_c for the mixed valent diosmium(III,II) state (K_c > 10¹⁵) in comparison to the diruthenium(III,II) analogue with K_c = 10¹⁰ confirms the electron transfer alternative for the valence exchange mechanism, in contrast to the hole transfer established for analogous dinuclear complexes with the formally related diacylhydrazido(2−) bridging ligands.     

Variation of the electron population by four units in the cluster series [(η-Cp′)3Mo3S4Co(L)] (L = I, CO, PPh3, NO; n = 0, 1)

The versatility of cuboidal Mo₃S₄Co clusters for the preparation of complexes with different numbers of valence shell electrons (VSE) in the cluster is described. The reaction of the geometrically incomplete cuboidal cluster salt [(η⁵-Cp′)₃Mo₃S₄][pts] (pts = p-toluenesulfonate) with one molar equivalent of [Co₂(CO)₈] afforded almost quantitatively the electroneutral 60 VSE cluster [(η⁵-Cp′)₃Mo₃S₄Co(CO)] (1), which previously has been prepared in low yield by Curtis et al. in autoclave syntheses [M.D. Curtis, U. Riaz, O.J. Curnow, J.W. Kampf, Organometallics 14 (1995) 5337]. Cluster 1 was also obtained in high yield by reaction of [(η⁵-Cp′)₃Mo₃S₄][pts] with [(η⁵-Cp^∗)Co(CO)₂]. Reaction of [(η⁵-Cp′)₃Mo₃S₄][pts] with two molar equivalents of [Co(I)(CO)₃(PPh₃)] led to a complex mixture of products, of which the electron deficient 58 VSE cluster salt [(η⁵-Cp′)₃Mo₃S₄Co(I)][Co(I)₃(thf)] ([2][Co(I)₃(thf)]) was isolated as single crystals. In the crystal structures of 1 and [2][Co(I)₃(thf)], the Co-Mo bond lengths are almost identical, indicating a delocalization of the electron deficiency in [2]⁺. The reduced form of [2]⁺, [(η⁵-Cp′)₃Mo₃S₄Co(I)] (2), was prepared by oxidative substitution of the carbonyl ligand in 1 by I₂. Further reactions of 1 with PPh₃ and NO leading to the 60 and 61 VSE cluster complexes [(η⁵-Cp′)₃Mo₃S₄Co(PPh₃)] (3) and [(η⁵-Cp′)₃Mo₃S₄Co(NO)] (4), respectively, enabled the preparation of Mo₃S₄Co clusters in altogether four different oxidation states.     

Theoretical studies of the spectroscopic properties of (L)Pt [(1,2-η)-Ph-(CC)n-Ph] (L = dppp or (PPh3)2, n = 1 or 2)

Electronic structures and spectroscopic properties of (L)Pt[(1,2-η²)-Ph-(CC)_n-Ph] (n = 1, L = (PPh₃)₂ (1), n = 1, L = dppp (2), and n = 2, L = (PPh₃)₂ (3)) are studied by the ab initio and DFT methods, respectively. The ground- and excited-state structures are optimized by the B3LYP and CIS methods, respectively. The calculated bond lengths and bond angles in the ground-state agree well with the corresponding experimental values and the structures in the ground and excited-states have only slightly change. At the TD-DFT level with the PCM model, the absorption and emission spectra in solution are obtained. The lowest-energy absorptions of 1-3 are attributed to the mixing MLCT/ILCT transitions and phosphorescent emissions are attributed to coming from the combination of ³MLCT/³ILCT transitions. Furthermore, the lowest-energy absorptions and emissions of 1-3 are red-shifted in the order 1 < 2 < 3. It is shown that with the increase of the π-conjugated effect of alkyne or electron-donating ability of the phosphane atom, lowest-energy emission energy for 1-3 is correspondingly decreased.     

Bidimensional self-assembling of [Hg(RPhNNNPhR′)2] (R = acetyl, R′ = F) through metal-η-arene π-interactions and non classical C-H?O bonding: Synthesis and X-ray characterization of a bis diaryl asymmetric-substituted triazenide complex polymer of Hg(II)

Deprotonated 3-(2-fluorophenyl)-1-(4-acetylphenyl)triazene reacts with Hg(CH₃COO)₂ in tetrahydrofuran to give light yellow crystals of [Hg^II(RPhNNNPhR′)₂]_n (R = acetyl, R′ = F). The new polymeric triazenide complex of Hg(II) belongs to the monoclinic space group C2/c. The lattice of [Hg^II(RPhNNNPhR′)₂]_n can be viewed as a bidimensional assembly of planar tectons [Hg^II(RPhNNNPhR′)₂], occurring through metallocene alike Hg(II)-η²,η²-arene π-interactions along the crystallographic axis b and non classical C-H?O bonding along the axis a.     

Spin crossover behavior of a one-dimensional polymeric-chain compound {[Fe(abpt)2(μ-Ni(CN)4)]·xH2O}n (x = 0.5 → 0): Synthesis, spectral, thermal and magnetic properties

A one-dimensional polymeric-chain iron(II)-nickel(II) cyanido-bridged complex of the composition {[Fe(abpt)₂(μ-Ni(CN)₄)]·0.5H₂O}_n (1·0.5H₂O), where abpt = 4-amino-3,5-di-2-pyridyl-4H-1,2,4-triazole, was prepared and characterized by elemental and thermal analyses, FTIR and ⁵⁷Fe Mössbauer spectroscopies, and magnetic measurements. The incomplete spin crossover phenomenon was observed with approximately 12% of the frozen high-spin fraction at low temperatures and with the spin transition critical temperature above room temperature.     

Isovalent and mixed-valent molybdenum complexes containing Mo(μ-E)(μ-S2)Mo (E = O, S) core units

The reactions of Tp^iPrMoO(SR)(NCMe) (Tp^iPr = hydrotris(3-isopropylpyrazolyl)borate) with propylene sulfide in toluene result in the formation of the diamagnetic, isovalent Mo(V) complex, [Tp^iPrMo^VO]₂(μ-S)(μ-S₂). This complex and its previously reported μ-oxo analog, [Tp^iPrMo^VO]₂(μ-O)(μ-S₂), react with cobaltocene to produce one-electron-reduced, mixed-valent complexes, [CoCp₂][{Tp^iPrMo^IV,VO}₂(μ-E)(μ-S₂)] (E = S or O, respectively). All complexes have been isolated and characterized by microanalysis, mass spectrometry, IR and ¹H NMR or EPR spectroscopies, and X-ray crystallography. Neutral [Tp^iPrMo^VO]₂(μ-S)(μ-S₂) exhibits a pseudo-C₂ symmetric structure, with distorted octahedral anti oxo-Mo(IV) centers coordinated by Tp^iPr and linked by μ-sulfido and μ-disulfido ligands. A similar structure is adopted by the anion in mixed-valent [CoCp₂][{Tp^iPrMo^IV,VO}₂(μ-S)(μ-S₂)]; this compound adopts a hexagonal, supramolecular structure with columns of tight ion-pairs with interactions, interconnected through weaker contacts to three neighboring columns. The structure contains large interstitial voids filled with lattice solvent molecules. EPR investigation of the mixed-valent complexes gave rise to unusually broad signals with no evident hyperfine splitting. The synthesis and characterization of a number of cis-dioxo-Mo(VI) precursors are also reported.     

A family of lanthanide-containing molecular open frameworks with high porosity: [Ln(abdc)(Habdc), nH2O]∞ with Ln = La-Eu and 8 ? n ? 11

Reactions in water between the di-sodium salt of amino terepthalic acid (C₈H₃NO₄Na₂) and a lanthanide chloride lead to a family of 3D-coordination polymers with general chemical formula [Ln(C₈H₃NO₄)(C₈H₄NO₄), O]_∞ where Ln = La-Eu (except Pm) and 8 ? n ? 11. All these compounds are isostructural. High quality single crystals of [Ln(C₈H₃NO₄)(C₈H₄NO₄), nH₂O]_∞ with Ln = La-Sm (except Pm) and 8 ? n ? 11 have been obtained by slow diffusion in agar-agar gels. The crystal structure has been solved for the Nd-containing compound. This compound crystallizes in the cubic system, space group Ia-3 (no. 206) with a = 26.8056(5) Å. The crystal structure can be described as the juxtaposition of large channels with square cross-section.The channels are filled by highly disordered crystallization water molecules. The dehydration of the compounds by freeze-drying is possible and most of the crystallization water molecules can be removed without destruction of the molecular skeleton. The partially dehydrated compounds have general chemical formula [Ln(abdc)(Habdc), 2H₂O]_∞ with Ln = La-Eu except Pm. The porosity of the Nd-containing compound has been estimated by computational methods to 2170 m² g⁻¹. This dehydrated compound reversibly binds water when exposed to wet atmosphere restoring the initial hydrated phase.     

Oxidative nuclease activity of ferromagnetically coupled μ-hydroxo-μ-propionato copper(II) complexes [Cu3(L)2(μ-OH)2(μ-propionato)2] (L = N-(pyrid-2-ylmethyl)R-sulfonamidato, R = benzene, toluene, naphthalene)

Three doubly-bridged, trinuclear copper(II) compounds with hydroxo and carboxylato bridges, ^∞₁[Cu₃(L1)₂(μ-OH)₂(μ-propionato)₂](1), [Cu₃(L2)₂(μ-OH)₂(μ-propionato)₂(DMF)₂] (2) and ^∞₁{[Cu₃(L3)₂(μ-OH)₂(μ-propionato)₂]} [Cu₃(L3)₂(μ-OH)₂(μ-propionato)₂(DMF)₂]} (3) [HL1 = N-(pyrid-2-ylmethyl)benzenesulfonylamide, HL2 = N-(pyrid-2-ylmethyl)toluenesulfonylamide, HL3 = N-(pyrid-2-ylmethyl)naphthalenesulfonylamide], have been synthesized and characterized. 1 is built from [Cu₃(L1)₂(μ-OH)₂(μ-propionato)₂] clusters. Each unit contains three copper(II) with two different coordination environments: the terminal centers are square-base pyramidal whereas the central copper is square planar. 2 presents a similar square-base pyramidal geometry in the terminal centers, but the central copper is six-coordinate. 3 shows an unusual 1D coordination polymer comprised of two distinct building blocks: one similar to that found in 1 and the other similar to that found in 2. The magnetic susceptibility measurements (2-300 K) reveal a ferromagnetic interaction between the Cu(II) ions with J values of 76.0, 55.0, and 48.0 cm⁻¹ for 1, 2, and 3, respectively. Emission spectroscopy, thermal denaturation, viscosimetry and cyclic voltammetry show an interaction of the complexes with DNA through the sugar-phosphate backbone. All three Cu(II) complexes were found to be very efficient agents of plasmid DNA cleavage in the presence of ascorbato or mercaptopropionic acid. Both the kinetics and the mechanism of the cleavage reaction have also been examined.     

Photoluminescent metal(II)-organic complexes with two distinct atropisomeric units from axially prochiral ligands through C-H?O hydrogen bonds (M = zinc, cobalt, nickel)

By taking advantage of rich-electron modification of pyridine-3,5-dicarboxylates, three photoluminescent isostructural metal-organic complexes, namely, [M(Hsmpdc)₂(H₂O)₄] · 6H₂O (smpdc = 2,6-dimethyl-4-(thiophen-2-yl)pyridine-3,5-dicarboxylate, M = Zn (1), Co (2) and Ni (3)), were synthesized and characterized by single crystal X-ray analyses. There are interesting hydrogen-bonded M²⁺(H₂O)₈ ionic clusters in the structures of title compounds. And of the most interesting is that S- and R-atropisomeric units are constructed from axially prochiral organic ligands through C-H?O hydrogen bonds. Strong photoluminescent emission at 543 nm with obvious red shift might make compound 1 a potentially photoactive solid-state material for its thermal and chemical stability.     

Phase studies of model biomembranes: Macroscopic coexistence of Lα + Lβ, with light-induced coexistence of Lα + Lo Phases

Phase diagrams of 3-component lipid bilayer mixtures containing cholesterol reveal major differences among the different types of lipids. Here we report that mixtures of cholesterol together with POPC and a high-melting temperature PC or sphingomyelin show different phase behavior from similar mixtures that contain DOPC or di-phytanoyl-PC instead of POPC. In particular, only one region of macroscopic phase coexistence occurs with POPC, a region of coexisting liquid disordered and solid phases, {Lα + Lβ}. Fluorescence microscopy imaging is useful for these studies, but is subject to artifactual light-induced domain formation, as reported by Ayuyan and Cohen [A.G. Ayuyan, F.S. Cohen, Lipid peroxides promote large rafts: Effects of excitation of probes in fluorescence microscopy and electrochemical reactions during vesicle formation, Biophys. J. 91 (2006) 2172-2183.]. This artifact can be attenuated by decreased illumination and low dye concentration. The use of the free radical scavenger n-propyl gallate can reduce the artifact, but this molecule enters the bilayer and itself perturbs the phase behavior. We suggest that the light-induced domain separation artifact might actually arise from pre-existing lipid clusters that are induced to coalesce, and therefore indicates highly nonrandom mixing of the lipid components.     

Cobalt complexes bridge with a (μ-X)(μ-carboxylato) unit (X = OH, N3): synthesis and structural studies

By using the hindered tris(pyrazolyl)borate ligand Tp^iPr2 (hydrotris(3,5-diisopropyl-1-pyrazolyl))borate, both mono- and binuclear complexes of cobalt [Tp^iPr2Co](X) (X = NO₃ and OBz) and [Tp^iPr2Co]₂(μ-X)(μ-OBz) (X = OH, N₃) were synthesized. The nitrato complex, [Tp^iPr2Co](NO₃) (1), which could be converted to (2), was prepared by reaction of KTp^iPr2 with hydrated Co(NO₃)₂ and its molecular structure was determined by X-ray crystallography. The dinuclear di(μ-hydroxo) complex, [Tp^iPr2Co]₂(μ-OH)₂ (2), which was obtained by treatment of 1 with aqueous NaOH, reacted with one equivalent of benzoic acid to give the (μ-benzoato)(μ-hydroxo) complex, [Tp^iPr2Co]₂(μ-OH)(μ-OBz) (3). X-ray crystallography shows the presence of both hydroxy and carboxylate group as bridging ligands and both cobalt metals are in five coordination environment in 3. The μ-azido complex, [Tp^iPr2Co]₂(μ-N₃)(μ-OBz) (5), was prepared by reaction of 3 with one equivalent of aqueous sodium azide. The spectroscopic studies suggested μ-1,1-bridging nature of group in this complex. The reaction of 2 with excess amount of benzoic acid resulted in the destruction of the bimetallic core to give the mononuclear carboxylato complex, [Tp^iPr2 Co](OBz) (4), which was characterized by X-ray crystallography.     

DNA aptamers bind specifically and selectively to (1 → 3)-β-d-glucans

(1 → 3)-β-d-Glucans are structural cell wall components of fungi, plants, and some bacteria and have been linked with human respiratory symptoms following aerosol exposure. A clear interpretation of the health impact of (1 → 3)-β-d-glucans is limited by the high cost and uncertainties associated with current glucan quantitation methods. The objective of this research is to develop DNA aptamers for the measurement of (1 → 3)-β-d-glucans. Aptamers are synthetic DNA functional binding molecules that fold into unique conformations, allowing them to bind specifically to their target. Through the in vitro selection process SELEX, we have produced aptamers that are able to bind with sub-micromolar affinity to curdlan, a linear unbranched form of (1 → 3)-β-d-glucans. These aptamers display high selectivity to curdlan and do not bind to non-(1 → 3)-β-d-polysaccharides, suggesting specificity for the β-(1 → 3)-glycosidic linkage. The aptamers produced here will enable the production of more cost-effective, less ambiguous assays for the environmental measurement of (1 → 3)-β-d-glucans.     

Functional properties of the newly observed γ-chain fetal hemoglobin variant Hb F-Monserrato-Sassari (HBG2:c.280T > C) or [γ93 (F9) Cys → Arg]

Background

HbF-Monserrato-Sassari is a newly discovered abnormal fetal hemoglobin observed in an apparently normal newborn baby during a hemoglobinopathies survey at birth in North Sardinian population.

Methods

Electrophoretic analysis of the cord blood lysate evidenced for an abnormal tetramer due to a mutated fetal globin chain. Electrospray ionisation-mass spectrometry and gene sequencing were used to identify the mutation. Oxygen binding ability of the variant Hb was determined.

Results

Sequencing of the γ globin genes revealed the TGT → CGT transition at codon 93 in one of the two ^Gγ genes, which leads to the Arg for Cys amino acid replacement at position 9 of the F α-helix. The amino acid substitution was confirmed by mass spectrometric analysis of the globin chains. Since modifications or substitutions at position β93 are known to affect the arrangement of a salt bridge at the α1β2 sliding contacts that are crucial for subunit cooperativity, the functional properties of the variant were studied to evaluate the effect of the replacement at the same position in the γ globin chain. With respect to normal HbF, the variant showed a significant increase in oxygen affinity and a slight decrease of both Bohr effect and cooperativity.

General significance

Result indicates a key role of the Cys γ93 residue for subunit cooperativity in the T → R transition of the HbF tetramer. Substitutions at the F9 position of the ^Gγ globin may result in stabilization of the high affinity R-state of the Hb tetramer. Because of the loss of Cys γ93 residue, this variant is considered to be potentially compromised in nitric oxide transport.     

Synthesis and electrochemical aspects of group 14 iron complexes of the type (η-C5H5)Fe(L)2ER3, L2 = (CO)2, (Ph2P)2CH2; E = C, Si, Ge, Sn

The dicarbonyl and diphosphine complexes of the type (η⁵-C₅H₅)Fe(L)₂ER₃ (L₂ = (CO)₂ (a), (Ph₂P)₂CH₂ (b); ER₃ = CH₃ (1a/b); SiMe₃ (2a/b), GeMe₃ (3a/b), SnMe₃ (4a/b)) were synthesized and studied electrochemically. Cyclic voltammetric studies on the dicarbonyl complexes 1a-4a revealed one electron irreversible oxidation processes whereas the same processes for the chelating phosphine series 1b-4b were reversible. The E_ox values found for the series 1a-4a were in the narrow range 1.3-1.5 V and in the order Si > Sn ≈ Ge > C; those for 1b-4b (involving replacement of the excellent retrodative π-accepting CO ligands by the superior σ-donor and poorer π-accepting phosphines) have much lower oxidation potentials in the sequence Sn > Si ≈ Ge > C. This latter oxidation potential pattern relates directly to the solution ³¹P NMR chemical shift data illustrating that stronger donation lowers the E_ox for the complexes; however, simple understanding of the trend must await the results of a current DFT analysis of the systems.     

Hydrogen bonding interaction between imidazolyl N-H group and peroxide: Stabilization of Mn(III)-peroxo complex TpMn(η-O2)(imH) (imH = 2-methylimidazole)

A mononuclear side-on peroxo managanese (III) complex, Tp^iPr2Mn(η²-O₂)(im^MeH) (3) was prepared by the reaction of [Tp^iPr2Mn(O)]₂ with excess amount of H₂O₂ in the presence of 2-methylimidazole (im^MeH). Its X-ray structure clearly demonstrated the involvement of intermolecular hydrogen bonding interaction between η²-peroxide and imidazolyl N-H functional group. Complex 3 was stable, green in color and unable to oxygenate triphenylphosphine and ethyl vinyl ether.     

Synthesis of (β-phenylethynyl)-gem-diphenyltrifluorocyclotriphosphazene and its reaction with RCpCo(PPh3)2 [R = MeOC(O)]

Reaction of gem-diphenyltetrafluorocyclotriphosphazene with in situ generated lithiated phenylacetylene resulted in the formation of the first example of a gem-diphenyltrifluorophosphazene based alkyne (β-phenylethynyl)-gem-diphenyltrifluorocyclotriphosphazene (NPPh₂)(NPF₂)[NP(F)CCPh] 1. Reaction of this alkyne with η⁵-(MeOC(O)C₅H₄)Co(PPh₃)₂ resulted in the formation of a CpCo stabilized cyclobutadiene complex [η⁵-carbomethoxycyclopentadienyl][η⁴-1,3-bis(gem-diphenyltrifluorocyclotriphosphazenyl)-2,4-diphenylcyclobutadiene]cobalt 2, having two gem-diphenyltrifluorophosphazene moieties trans to each other on the cyclobutadiene ring. The reaction also yielded two structural isomers of the PPh₃ stabilized cobaltacyclopentadiene compounds 3 and 4 having gem diphenyl trifluorophosphazene moieties present in the 2,4 and 2,5 positions of the metallacycle. The reaction in addition yielded a novel spirocyclic phosphazacyclopentadiene compound bound to a CpCo unit in the η⁴-mode 5. All the compounds were characterized by ¹H, ¹³C, ³¹P and ¹⁹F NMR spectroscopy and compounds 2, 3 and 5 were also structurally characterized by X-ray crystallography.     

Copper(II) complexes based on a new chelating 4-(3,5-diphenyl-1H-pyrazol-1-yl)-6-(piperidin-1-yl)pyrimidine ligand: Synthesis and crystal structures. Lone pair-π, C-H···π, π-π and C-H···A (A = N, Cl) non-covalent interactions

A new bidentate chelating pyrazolylpyrimidine ligand bearing a strong electron-donating substituent, i.e. 4-(3,5-diphenyl-1H-pyrazol-1-yl)-6-(piperidin-1-yl)pyrimidine (L) (Scheme 1), has been synthesized and used to obtain the copper(II) complexes by reaction with CuCl₂. The molar ratio Cu:L = 1:2 leads to isolation of a complex having CuL₂Cl₂ empirical formula, while the molar ratio Cu:L = 1:1 gives a complex with CuLCl₂ empirical formula. The crystal structure of L as well as the structures of both complexes were studied by single crystal X-ray diffraction. The crystal structure of CuL₂Cl₂ compound is formed by trans-[CuL₂Cl₂] mononuclear molecules. Surprisingly, in contrast to the previous compound having molecular structure, the crystal structure of CuLCl₂ consists of mononuclear [CuL₂Cl]⁺ complex cations and dinuclear [Cu₂Cl₆]²⁻ anions. Thus, formula of CuLCl₂ complex can be represented as [CuL₂Cl]₂[Cu₂Cl₆]. In both complexes molecules of L adopt bidentate chelating coordination mode through N² atom of pyrazole and N³ atom of pyrimidine rings forming five-membered CuN₃C metallocycles. Owing to C-H···N interactions and π-π-stacking L molecules form 2D network. In the structure of trans-[CuL₂Cl₂] there exist double lone pair(N(piperidine))-π(pyrimidine) interactions and C-H···Cl contacts resulting in the formation of 1D chains. Layered 2D structure of [CuL₂Cl]₂[Cu₂Cl₆] results from C-H···Cl, C-H···π and double lone pair(Cl([CuL₂Cl]⁺ complex cation)-π(pyrimidine) interactions.