Chemical and electrochemical formation of pseudorotaxanes composed of alkyl(ferrocenylmethyl)ammmonium and dibenzo[24]crown-8

Protonation of p-xylylaminomethylferrocene (1) and n-hexylaminomethylferrocene (2) by HCl and NH(4)PF(6) forms the ferrocenylmethyl(alkyl)ammonium salt. Inclusion of the compounds by dibenzo[24]crown-8 (DB24C8) produces [2]pseudorotaxanes, [(DB24C8)(1-H)](+)(PF(6)) and [(DB24C8)(2-H)](+)(PF(6)), respectively. X-ray diffraction of the former product indicates an interlocked structure composed of the axis and the macrocyclic molecule. Intermolecular N-H...O and C-H...O interactions and stacking of the aromatic planes are observed. [(DB24C8)(1-H)](+)(PF(6)), in the solid state, is characterized by IR spectroscopy and elemental analyses. A similar reaction of 1,1'-bis(p-xylylaminomethyl)ferrocene (3) forms a mixture of [2] and [3]pseudorotaxanes, [(DB24C8)(3-H(2))](2+)(PF(6))(2) and [(DB24C8)(2)(3-H(2))](2+)(PF(6))(2). The latter product having two DB24C8 molecules is isolated and characterized by X-ray crystallography. Formation of these pseudorotaxanes in a CD(3)CN solution is evidenced by (1)H NMR and mass spectrometry. Electrochemical oxidation of 1-3 at 0.4 V (vs Ag(+)/Ag) in the presence of TEMPOH (1-hydroxy-2,2,6,6-tetramethylpiperidine) and DB24C8 affords the corresponding pseudorotaxanes. The ESR spectrum of the reaction mixture indicates the formation of a TEMPO radical in high yield. Details of the conversion of the dialkylamino group of the ligand to the dialkylammonium group are investigated by using a flow electrolysis method linked to spectroscopic measurements. The proposed mechanism for the reaction involves the ferrocenium species, formed by initial oxidation, which undergoes electron transfer from nitrogen to the Fe(III) center, producing a cation radical at the nitrogen. Transfer of hydrogen from TEMPOH to the cation radical and inclusion of the resulting dialkylammonium species by DB24C8 yields the pseudorotaxanes.     

Synthesis and characterization of Pd(II) Complexes with bis-pyridinium and isoquinolinium N-ylides: moderate C-H...O=C intramolecular hydrogen bonds as source of conformational preferences

The bis(N-ylide) Pd(II) complexes cis-[PdX2[eta2-[C(H)NCxHy]2CO]] (X=I, NCxHy=NC5H5, 2a; X=Br, NCxHy=NC5H5 and NC5H3-2,3-Me2, 2c, isoquinolinium NC9H7, 2d) have been prepared by reaction of the corresponding bis-pyridinium salts with Pd(OAc)2 (1:1 molar ratio). Compounds 2 react with AgClO4 and Tl(acac) (1:1:1 molar ratio) to give the acetylacetonato derivatives [Pd(acac-O,O'[eta2-[C(H)NCxHy]2CO]]ClO4 (3a, c, d). In compounds 2 and 3, the bis-ylide is bonded as a C,C-chelate ligand through the two ylidic Calpha atoms. The reaction is stereoselective, and only one diastereoisomer is observed (meso form, RS/SR). The origin of the observed stereoselectivity lies with the establishment of intramolecular C-H...O=C hydrogen bonds between the ortho protons of the pyridine or isoquinoline fragments and the carbonyl oxygen, as it has been shown by density functional theory (DFT) calculations (B3LYP level) and Bader analysis of the electron density on model pyridinium ylides. Despite the inherent weakness of the C-H...O=C bonds, the results show that in these N-ylides the hydrogen bonds are stronger than expected and should be classified as moderate H bonds.     

Dual-mode "co-conformational" switching in catenanes incorporating bipyridinium and dialkylammonium recognition sites

Three [2]catenanes and three [3]catenanes incorporating one or two pi-electron-rich macrocyclic polyethers and one pi-electron-deficient polycationic cyclophane have been synthesized in yields ranging from 4 to 38%. The pi-electron-rich macrocyclic components possess either two 1,4-dioxybenzene or two 1.5-dioxynaphthalene recognition sites. The pi-electron-deficient cyclophane components incorporate two bipyridinium and either one or two dialkylammonium recognition sites. The template-directed syntheses of these catenanes rely on i) pi...pi stacking interactions between the dioxyarene and bipyridinium recognition sites, ii) C-H...O hydrogen bonds between some of the bipyridinium hydrogen atoms and some of the polyether oxygen atoms, and iii) C-H...pi interactions between some of the dioxyarene hydrogen atoms and the aromatic spacers separating the bipyridinium units. The six catenanes were characterized by mass spectrometry and by both 1H and 13C NMR spectroscopy. The absorption spectra and the electrochemical properties of the catenanes have been investigated and compared with those exhibited by the component macrocycles and by related known catenanes. Broad and weak absorption bands in the visible region, originating from charge-transfer (CT) interactions between electron-donor and electron-acceptor units, have been observed. Such charge-transfer interactions are responsible for the quenching of the potentially fluorescent excited states of the aromatic units of the macrocyclic polyether components. The redox behavior of these novel compounds has been investigated and correlations among the observed redox potentials are illustrated and discussed. The catenanes undergo co-conformational switching upon one-electron reduction of the two bipyridinium units. One of them--in its reduced form--can be also switched by acid/base inputs and exhibits AND logic behavior. The co-conformational rearrangements induced by the redox and acid/base stimulations lend themselves to exploitation in the development of molecular-level machines and logic gates.     

New hybrid [2]catenanes based on a 4,4'-bipyridinium ligand

The self-assembly-mediated synthesis of metallomacrocycles 4a and 4b from (en)M(NO3)2 (M = Pd, Pt) and bipyridinium ligand 3 is described. The reaction is templated by disodium p-phenyldiacetic dicarboxylate, which is inserted into the macrocyclic cavity. Similarly, the self-assembly process between ligand 3, (en)M(NO3)2 (M = Pd, Pt), and the macrocyclic polyether 6 resulted in the formation of hybrid catenanes 7a and 7b. In the [2]catenanes, the circumrotation of the macrocyclic polyether through the cavity of the metallocycle is slow on the 1H NMR time scale.     

New palladium(II) and platinum(II) complexes with the model nucleobase 1-methylcytosine: antitumor activity and interactions with DNA

Palladium and platinum complexes with the model nucleobase 1-methylcytosine (1-Mecyt) of the types [Pd(N-N)(C6F5)(1-Mecyt)]ClO4 [N-N = bis(3,5-dimethylpyrazol-1-yl)methane (bpzm), bis(pyrazol-1-yl)methane (bpzm), N,N,N',N'-tetramethylethylenediamine (tmeda), or 2,2'-bipyridine (bpy)] and [M(dmba)(L')(1-Mecyt)]ClO4 [dmba = N,C-chelating 2-(dimethylaminomethyl)phenyl; L' = PPh(3) (M = Pd or Pt), DMSO (M = Pt)] have been obtained. Palladium and platinum complexes of the types cis-[M(C6F5)2(1-Mecyt)2] (M = Pd or Pt) and cis-[Pd(L')(C6F5)(1-Mecyt)2]ClO4 (L' = PPh(3) or t-BuNC) have also been prepared. The crystal structures of [Pd(bpzm)(C6F5)(1-Mecyt)]ClO4, [Pt(dmba)(DMSO)(1-Mecyt)]ClO4, cis-[Pd(C6F5)2(1-Mecyt)2], and cis-[Pd(t-BuNC)(C6F5)(1-Mecyt)2]ClO4 have been established by X-ray diffraction. There is extensive hydrogen bonding (N-H...O, C-H...F or C-H...O) in all the compounds. There are also intermolecular pi-pi interactions between pyrimidine rings of adjacent chains in [Pd(C6F5)2(1-Mecyt)2]. DNA adduct formation of the new complexes synthesized was followed by circular dichroism and electrophoretic mobility. Atomic force microscopy images of the modifications caused by the complexes on plasmid DNA pBR322 were also obtained. Values of IC(50) were also calculated for the new complexes against the tumor cell line HL-60. At a short incubation time (24 h) almost all new complexes were more active than cisplatin.     

Hydrothermal Synthesis and Crystal Structure of a New Polyoxovanadate: [Mn(en)3]2en0.5[HV8VV8IVO38(Cl)]·4.5H2O (en = Ethylenediamine)

A new compound has been synthesized under hydrothermal conditions and characterized by IR, elemental analysis, XPS and single-crystal X-ray diffraction analysis. The title compound [Mn(en)3]2en0.5[HV16O38(Cl)]·4.5H2O crystallizes in monoclinic, space group C2/c, with a = 17.016(4), b = 18.858(4), c = 18.872(4) (A), β = 93.667(4)°, V = 6043(2) (A)3, Z = 4, Dc = 2.242 g/cm3, Mr = 2040.12, F(000) = 4020, μ = 2.895 mm-1, Rint = 0.0921, R = 0.0649 and wR = 0.1325. Single-crystal X-ray structure analysis indicates that the title compound consists of a polyanion [HV8VV8IVO38(Cl)]4( cage, two [Mn(en)3]22 cations, four and a half lattice waters and a half ethylenediamine. In addition, intermolecular O-H…N,O-H…O and C-H…O and C-H…O hydrogen bonds link the molecules together to form a three-dimensional structure.     

Very strong C-H...O, N-H...O, and O-H...O hydrogen bonds involving a cyclic phosphate.

Very short C-H...O, N-H...O, and O-H...O hydrogen bonds have been generated utilizing the cyclic phosphate [CH2(6-t-Bu-4-Me-C6H2O)2]P(O)OH (1). X-ray structures of (i) 1 (unsolvated, two polymorphs), 1...EtOH, and 1...MeOH, (ii) [imidazolium](+)[CH2(6-t-Bu-4-Me-C6H2O)2PO2](-)...MeOH [2], (iii) [HNC5H4-N=N-C5H4NH](2+)[(CH2(6-t-Bu-4-Me-C6H2O)2PO2)2](2-)...4CH3CN...H2O [3], (v) [K, 18-crown-6](+)[(CH2(6-t-Bu-4-Me-C6H2O)2P(O)OH)(CH2(6-t-Bu-4-Me-C6H2O)2PO2)](-)...2THF [4], (vi) 1...cytosine...MeOH [5], (vii) 1...adenine...1/2MeOH [6], and (viii) 1...S-(-)-proline [7] have been determined. The phosphate 1 in both its forms is a hydrogen-bonded dimer with a short O-H...O distance of 2.481(2) [triclinic form] or 2.507(3) A [monoclinic form]. Compound 2 has a helical structure with a very short C-H...O hydrogen bond involving an imidazolyl C-H and methanol in addition to N-H...O hydrogen bonds. A helical motif is also seen in 5. In 3, an extremely short N-H...O hydrogen bond [N...O 2.558(4) A] is observed. Compounds 6 and 7 also exhibit short N-H...O hydrogen bonds. In 1...EtOH, a 12-membered hydrogen-bonded ring motif, with one of the shortest known O-H...O hydrogen bonds [O...O 2.368(4) A], is present. 1...MeOH is a similar dimer with a very short O(-H)...O bond [2.429(3) A]. In 4, the deprotonated phosphate (anion) and the parent acid are held together by a hydrogen bond on one side and a coordinate/covalent bond to potassium on the other; the O-H...O bond is symmetrical and very strong [O...O 2.397(3) A].     

Self-complementary

Three [3]catenanes with cavities large enough to accommodate aromatic guests have been designed and synthesized (yields = 5-20 %) by means of kinetically controlled self-assembly processes. The X-ray structural analysis of one of three [3]catenanes confirmed the presence of a rectangular cavity (dimensions = 7 x 11 A) lined by pi-electron-rich recognition sites and hydrogen-bond acceptor groups. In spite of their apparently ideal recognition features, none of these [3]catenanes bind guests incorporating a pi-electron-deficient bipyridinium unit. However, the template-directed syntheses of the [3]catenanes also produce, in yields of 2-23%, [2]catenanes incorporating a 1,5-dioxynaphtho[38]crown-10 interlocked with a bipyridinium-based tetracationic cyclophane. The X-ray structural analyses of two of these [2]catenanes revealed that a combination of [pi...pi] and [C-H...pi] interactions is responsible for the formation of supramolecular homodimers in the solid state. 1H NMR spectroscopic investigations of the four [2]catenanes demonstrated that supramolecular homodimers are also formed (Ka= 17-31M(-1), T= 185 K) in (CD3)2CO solutions. Dynamic 1H NMR spectroscopy revealed that the 1,5-dioxynaphtho[38]crown-10 and tetracationic cyclophane components in the four [2]catenanes and in the three [3]catenanes circumrotate (deltaGc(not equal to) = 9-14 kcal mol(-1)) through each other's cavity in (CD3)2CO. Similarly, the 1,5-dioxynaphthalene and the bipyridinium ring systems rotate (deltaGc(not equal to) =10-14 kcal mol(-1)) about their [O...O] and [N...N] axes, respectively, in solution.     

Syntheses and characterizations of palladium-based molecular triangle/square compounds and hybrid composites with polyoxometalates

Syntheses and characterizations of a Pd-based molecular triangle and square and hybrid composites with polyoxometalates are examined. The equilibrium between the Pd-based molecular triangle [(en*)Pd(4,4'-bpy)]3(NO3)6 and square [(en*)Pd(4,4'-bpy)]4(NO3)8 largely depends on the solvents, and both compounds have successfully been isolated: [(en*)Pd(4,4'-bpy)]3(NO3)6.3.5DMSO, monoclinic Cc (No. 9), a = 19.8210(2) A, b = 34.3667(5) A, c = 27.5484(4) A, beta = 89.9420(10) degrees , V = 18765.5(4) A3; [(en*)Pd(4,4'-bpy)]4(NO3)8, monoclinic C2/c (No. 15), a = 45.6921(16) A, b = 8.7721(8) A, c = 36.719(3) A, beta = 126.509(2) degrees , V = 11829.4(14) A3. The reactions of the Pd-based molecular triangle/square with [W6O19]2-, [W10O32]4-, and [alpha-SiW12O40]4- form [[(en*)Pd(4,4'-bpy)]4[ supersetW6O19]][W6O19]3, [[(en*)Pd(4,4'-bpy)]4[ supersetW6O19]](NO3)6, [[(en*)Pd(4,4'-bpy)]4[ supersetW10O32]][W10O32], [(en*)Pd(4,4'-bpy)]4[W10O32]2, and [(en*)Pd(4,4'-bpy)]4[alpha-SiW12O40]2. The molecular square does not encapsulate the largest [alpha-SiW12O40]4-, but it does encapsulate [W6O19]2- and [W10O32]4-. The isolation of [W6O19]2- and [alpha-SiW12O40]4- from the mixture by use of the molecular square is possible by utilizing the quite different solubility of [[(en*)Pd(4,4'-bpy)]4[ supersetW6O19]](NO3)6 and [(en*)Pd(4,4'-bpy)]4[alpha-SiW12O40]2 formed in DMSO. The size-selective encapsulation property of supramolecules may open the new way to rationalize isolation methods of the useful polyoxometalates.     

Template-directed synthesis of kinetically and thermodynamically stable molecular necklace using ring closing metathesis

We report the template-directed synthesis of a well-defined, kinetically stable [5]molecular necklace with dialkylammonium ion (R(2)NH(2)(+)) as recognition site and DB24C8 as macrocycle. A thread containing four dialkylammonium ions with olefin at both ends was first synthesized and then subjected to threading with an excess amount of DB24C8 to form pseudo[5]rotaxane, which in situ undergoes ring closing metathesis at the termini with second generation Grubbs catalyst to yield the desired [5]molecular necklace. The successful synthesis of [5]molecular necklace is mainly attributed to the self-assembly and dynamic covalent chemistry which allows the formation of thermodynamically most stable product. The self-assembly of the DB24C8 ring onto the recognition site known as templating effect was driven by noncovalent stabilizing interactions like [N(+)-H···O], [C-H···O] hydrogen bonds as well as [π···π] interactions which is facilitated in non-polar solvents. The reversible nature of olefin metathesis reaction makes it suitable for dynamic covalent chemistry since proof-reading and error-checking operates until it generates thermodynamically the most stable interlocked molecule. Riding on the success of [5]molecular necklace, we went a step further and attempted to synthesize [7]molecular necklace using the same protocol. This led to the synthesis of another thread with olefin at both ends but having six dibenzylammonium ions along the thread. However, the extremely poor solubility of this thread containing six secondary ammonium ions limits the self-assembly process even after we replaced the typical PF(6)(-) counter anion with a more lipophilic BPh(4)(-) anion. Although the poor solubility of the thread remains the bottleneck for making higher order molecular necklaces yet this approach of "threading-followed-by-ring-closing-metathesis" for the first time produces kinetically and thermodynamically stable, well-defined, homogeneous molecular necklace which was well characterized by one-dimensional, two-dimensional, variable temperature proton NMR spectroscopy and ESI mass spectroscopy.     

A versatile template for the formation of [2]pseudorotaxanes. 1,2-Bis(pyridinium)ethane axles and 24-crown-8 ether wheels

Linear 1,2-bis(pyridinium)ethane 'axles' and macrocyclic 24-membered crown ether 'wheels' (, and ) combine to form [2]pseudorotaxanes. These interpenetrated adducts are held together by N+...O ion-dipole interactions, a series of C-H...O hydrogen bonds and pi-stacking between electron-poor pyridinium rings of the axle and electron-rich catechol rings of the wheel. 1H NMR spectroscopy was used to identify the structural details of the interaction and to determine the thermodynamics of the binding process in solution. Analysis of nine of these adducts by single crystal X-ray crystallography allowed a detailed study of the non-covalent interactions in the solid state. A wide variety of structural changes could be made to the system. The versatility and potential of the template for the construction of permanently interlocked structures such as rotaxanes and catenanes is discussed.     

Mononuclear (Pd, Pt), heterodinuclear (PdAg, PtAg), and tetranuclear (Pd2Ag2, Pt2Ag2) 1,1-ethylenedithiolato complexes

lp;&-5q;1 The reactions of [Tl2[S2C=C[C(O)Me]2]]n with [MCl2L2] (1:1) or with [MCl2(NCPh)2] and PPh3 (1:1:2) give complexes [M[eta2-S2C=C[C(O)Me]2]L2] [M = Pt, L2 = 1,5-cyclooctadiene (cod) (1); L2 = bpy, M = Pd (2a), Pt (2b), L = PPh3, M = Pd (3a), Pt (3b)] whereas with MCl2 and QCl (2:1:2) anionic derivatives Q2[M[eta2-S2C=C[C(O)Me]2]2] [M = Pd, Q = NMe4 (4a), Ph3P=N=PPh3 (PPN) (4a'), M = Pt, Q = NMe4 (4b)] are produced. Complexes 1 and 3 react with AgClO4 (1:1) to give tetranuclear complexes [[ML2]2Ag2[mu2,eta2-(S,S')-[S2C=C[C(O)Me]2]2]](ClO4)2 [L = PPh3, M = Pd (5a), Pt (5b), L2 = cod, M = Pt (5b')], while the reactions of 3 with AgClO4 and PPh3 (1:1:2) give dinuclear [[M(PPh3)2][Ag(PPh3)2][mu2,eta2-(S,S')-S2C=C[C(O)Me]2]]]ClO4 [M = Pd (6a), Pt (6b)]. The crystal structures of 3a, 3b, 4a, and two crystal forms of 5b have been determined. The two crystal forms of 5b display two [Pt(PPh3)2][mu2,eta2-(S,S')-[S2C=C[C(O)Me]2]2] moieties bridging two Ag(I) centers.     

Density functional study of the sigma and pi bond activation at the Pd=X (X = Sn, Si, C) bonds of the (H2PC2H4PH2)Pd=XH2 complexes. Is the bond cleavage homolytic or heterolytic?

The mechanism for the activation of the sigma bonds, the O-H of H2O, C-H of CH4, and the H-H of H2, and the pi bonds, the C[triple bond]C of C2H2, C=C of C2H4, and the C=O of HCHO, at the Pd=X (X = Sn, Si, C) bonds of the model complexes (H2PC2H4PH2)Pd=XH2 5 has been theoretically investigated using a density functional method (B3LYP). The reaction is significantly affected by the electronic nature of the Pd=X bond, and the mechanism is changed depending on the atom X. The activation of the O-H bond with the lone pair electron is heterolytic at the Pd=X (X = Sn, Si) bonds, while it is homolytic at the Pd=C bond. The C-H and H-H bonds without the lone pair electron are also heterolytically activated at the Pd=X bonds independent of the atom X, where the hydrogen is extracted as a proton by the Pd atom in the case of X = Sn, Si and by the C atom in the case of X=C because the nucleophile is switched between the Pd and X atoms depending on the atom X. In contrast, the pi bond activation of C[triple bond]C and C=C at the Pd=Sn bond proceeds homolytically, and is accompanied by the rotation of the (H2PC2H4PH2)Pd group around the Pd-Sn axis to successfully complete the reaction by both the electron donation from the pi orbital to Sn p orbital and the back-donation from the Pd dpi orbital to the pi orbital. On the other hand, the activation of the C=O pi bond with the lone pair electron at the Pd=Sn bond has two reaction pathways: one is homolytic with the rotation of the (H2PC2H4PH2)Pd group and the other is heterolytic without the rotation. The role of the ligands controlling the activation mechanism, which is heterolytic or homolytic, is discussed.     

Investigations of coupling characters in ionic liquids formed between the 1-ethyl-3-methylimidazolium cation and the glycine anion

In this study, novel ionic liquids formed between the 1-ethyl-3-methylimidazolium cation [emim]+ and the glycine anion [Gly]- have been investigated theoretically. The relevant geometrical characteristics, energy properties, the characters of the intermolecular hydrogen bonds (H bonds), and the possibility of proton transfer as well as IR characteristics have been systematically discussed. The natural bond orbital (NBO) and atoms in molecule (AIM) analyses have also been applied to understand the nature of the interactions between ionic pairs in ionic liquids. The most stable geometries have been determined by analyzing the relative energies and interaction energies, where the C-H...O intermolecular H bonds involving the protons attached to the imidazolium ring have been found to possess partial covalent character in nature. Electron transfers from the lone pairs of the carbonyl O atom of [Gly]- to the C-H antibonding orbital of the [emim]+ can explain the elongation and red shift of the C-H stretching frequency. The interaction modes are more favorable when the carbonyl O atoms of [Gly]- interact with the C2-H of the imidazolium ring and the C-H of the methyl group through the formation of double H bonds. The origin of the high stability of the amino acid ionic liquids observed experimentally may be attributed to the nonexistence of the proton-transferred products (neutral pairs) together with the large energy needed for separation of the ionic pairs. Additionally, the characteristics of the IR spectra have been analyzed to demonstrate the variants of the molecular structure of the [emim]+[Gly]- ionic liquids.     

Preparation, solid-state characterization, and computational study of a crown ether attached to a squaramide

[structure: see text] Crystals of a disecondary squaramide covalently linked to a crown ether presents a great variety of inter- and intramolecular nonbonded interactions including C-H/pi contacts, C-H...O and N-H...O hydrogen bonds, and pi-pi stacking between squaramide rings. Latter interaction, the stacking between squaramide rings, can be considered as an experimental evidence for the proposed aromaticity of squaramide when it is forming hydrogen bonds, either as acceptor or donor.     

Crystal and molecular structure studies of 1′-Benzyl-8-(4-fluorobenzyl)-8-azaspiro[bicyclo-[3.2.1]octane-3,4′-imidazolidine]-2′,5′-dione

The title compound 1′-Benzyl-8-(4-fluorobenzyl)-8-azaspiro[bicyclo[3.2.1] octane-3,4′-imidazolidine]-2′,5′-dione, C₂₃H₂₃FN₃O₂ is synthesized and the structure is investigated by X-ray diffraction studies. The compound crystallizes in the triclinic crystal class in the P1 space group. The hydantoin ring adopts a planar conformation and is affected by the π conjugation. The pyrrolidine and piperidine rings in the bicyclo octane moiety adopt envelope and chair conformations respectively. The structure exhibits both inter- and intramolecular hydrogen bonds of the type N-H...O, C-H...O, and C-H...N. The oxygen atom in the hydantoin ring simultaneously accepts two hydrogen bonds to form a three-centered hydrogen bonding pattern.     

Influence of solvent and weak C-H...O contacts in the self-assembled [Pt2M4{CC(3-OMe)C6H4}8] (M = Cu, Ag) clusters and their role in the luminescence behavior

New alkynyl complexes [Pt2M4{CC(3-OMe)C6H4}8] (M = Ag 1, Cu 2) have been synthesized and their structures and properties compared to those of related [Pt2M4(CCPh)8] compounds. For the Pt-Ag derivatives, the X-ray structures of the discrete yellow solvate monomer, [Pt2Ag4{CC(3-OMe)C6H4}8].2THF ([1.2THF]), and the dark garnet unsolvated polymeric form, [Pt2Ag4{CC(3-OMe)C6H4}8](infinity) ([1](infinity)), are presented. The yellow form ([1.2THF]) exhibits a distorted octahedral geometry of the metal centers with the platinum atoms mutually trans and the four silver atoms in the equatorial plane. Pairs of Ag atoms are weakly bridged by THF molecules [mu-Ag2...O(THF)]. The garnet form ([1](infinity)) has an unprecedented infinite stacked chain of octahedral clusters linked by short Pt...Pt bonds (3.1458(8) A). In both forms, different types of weak C-H...O (OMe) hydrogen bonds are observed. For comparative purposes, we have also provided the crystal structures of the yellow monomer form, [Pt2Ag4-(CCPh)8].CHCl3, and the red dimer form, [Pt2Ag4(CCPh)8]2 (Pt-Pt 3.221(2) A). These clusters display intense photoluminescence in both solution and the solid state, at room temperature and 77 K. The emission observed for the yellow form [1.2THF] in the solid state is assigned to a 3MLM'CT [Pt(d)/pi(CCR) --> Pt(p(z))/Ag(sp)/pi(CCR)] state modified by Pt...Ag, Ag...Ag, and Ag...(THF) contacts. However, in the garnet form [1](infinity) and in 2, the emissions are related to the axial Pt-Pt bonds and are assigned as phosphorescence from a metal-metal-to-ligand charge-transfer (3MMLCT) excited state ([1](infinity)), or an admixture of a metal-metal (Pt-Pt) centered 3(dsigmap(z)sigma) and 3MMLCT excited state (2). For 1, a remarkable quenching and a shift to higher energies in the emission is observed on changing from CH2Cl2 to THF, and for both 1 and 2, the emission spectra at 77 K varies with the concentration, showing their tendency to stack even in glass.     

Heterodimetallic germanium(IV) complex structures with transition metals

The hydrothermal synthesis and structural characterization of a number of complex compounds containing the divalent tris(oxalato-O,O')germanate anion, [Ge(C2O4)3]2-, or the neutral bis(oxalate-O,O')germanium fragment, [Ge(C2O4)2], with transition-metal (M) cationic complexes of 1,10'-phenanthroline (phen) is reported: [M(phen)3][Ge(C2O4)3].xH2O [where M2+ = Cu2+ (1a and 1b), Fe2+ (2a and 2b), Ni2+ (3), Co2+ (4); x = 0.2 for 2b], [MGe(phen)2(mu2-OH)2(C2O4)2] [where M2+ = Cd2+ (5) and Cu2+ (6)]. The isolation of two polymorphs with Cu2+ (1a and 1b) and other pseudo-polymorphs for Fe2+ (2a and 2b) was rationalized based on slightly different molar ratios for the starting materials. All compounds have been characterized using EDS, SEM, vibrational spectroscopy (FT-IR and FT-Raman), thermogravimetry, and CHN elemental composition and their structure determined on the basis of single-crystal X-ray diffraction studies. The crystal packing of the different chemical moieties for each series of compounds was discussed on the basis of the various intermolecular interactions present (strong C-H...pi and weak C-H...O hydrogen-bonding interactions, C-H...pi and pi-pi contacts).     

Geometric isotope effect of various intermolecular and intramolecular C-H...O hydrogen bonds, using the multicomponent molecular orbital method

The geometric isotope effect (GIE) of sp- (acetylene-water), sp(2)- (ethylene-water), and sp(3)- (methane-water) hybridized intermolecular C-H...O and C-D...O hydrogen bonds has been analyzed at the HF/6-31++G level by using the multicomponent molecular orbital method, which directly takes account of the quantum effect of proton/deuteron. In the acetylene-water case, the elongation of C-H length due to the formation of the hydrogen bond is found to be greater than that of C-D. In contrast to sp-type, the contraction of C-H length in methane-water is smaller than that of C-D. After the formation of hydrogen bonds, the C-H length itself in all complexes is longer than C-D and the H...O distance is shorter than D...O, similar to the GIE of conventional hydrogen bonds. Furthermore, the exponent (alpha) value is decreased with the formation of the hydrogen bond, which indicates the stabilization of intermolecular C-H...O hydrogen bonds as well as conventional hydrogen bonds. In addition, the geometric difference induced by the H/D isotope effect of the intramolecular C-H...O hydrogen bond shows the same tendency as that of intermolecular C-H...O. Our study clearly demonstrates that C-H...O hydrogen bonds can be categorized as typical hydrogen bonds from the viewpoint of GIE, irrespective of the hybridizing state of carbon and inter- or intramolecular hydrogen bond.     

Synthesis, structure and reactivity of cuboidal-type cluster aqua complexes with W3PdS4 4+ core

The reaction of PdCl(2) with [W3S4(H2O)9]4+ in the presence of hypophosphorous acid in 2 M HCl gives cuboidal cluster [W3(PdCl)S4(H2O)9]3+ (1) which undergoes condensation and crystallises from Hpts solutions as edge-linked double cubane cluster [{W3PdS4(H2O)9}2](pts)(8).19H2O (pts = p-toluenesulfonate) (1'). The substitution of Cl- in (1) by different ligands was explored. The Pd atom in the cluster shows an exceptionally high reactivity in the isomerisation of the hydrophosphoryl H2P(O)(OH), HP(O)(OH)2, HPPh(O)(OH) and HPPh2(O) molecules into the corresponding hydroxo tautomers HP(OH)2, P(OH)3, PhP(OH)2 and Ph2P(OH) stabilised by coordination at Pd. The reactions were followed by UV-Vis spectrophotometry and 31P NMR. Formation constants of the 1 : 1 coordination of [M3(PdCl)S4(H2O)9]3+ (M = Mo, W) with HP(OH)2 and As(OH)3 were obtained. The structures of cucurbit[6]uril (C36H36N24O12, CUC[6]) adducts [W3(PdP(OH)3)S4(H2O)8Cl]-(C36H36N24O12)Cl3.12.5H2O (2), and [W3Pd(PhP(OH)2)S4(H2O)7Cl2]2(C36H36N24O12)Cl4.9H2O (3) were determined by single-crystal X-ray diffraction.