Four-coordinate Atoms Research Articles

Intramolecular Aminoalkene Hydroamination Catalyzed by Magnesium Complexes Containing Multidentate Phenoxyamine Ligands

The magnesium complexes L2MgiPr (L2 = 4-tert-butyl-6-(triphenylsilyl)-2-[bis((3-(dimethylamino)propyl)amino)methyl]phenoxyl) and L3MgiPr (L3 = 4-tert-butyl-6-(triphenylsilyl)-2-[benzyl((3-(dimethylamino)propyl)amino)methyl]phenoxyl) supported by potentially tetradentate and tridentate triphenylsilyl-substituted phenoxyamine ligands have been prepared and fully characterized. The X-ray crystallographic analysis of L2MgiPr confirmed a monomeric structure in which only one of the amine side arms is bound to the four-coordinate magnesium atom. The free and coordinated side arms in L2MgiPr undergo an exchange process at 25 °C in solution, while the phenoxydiamine complex L3MgiPr, on the other hand, shows no sign of fluxionality. Both complexes, as well as L1MgiPr (L1 = 4,6-di-tert-butyl-2-[bis((3-(dimethylamino)propyl)amino)methyl]phenoxyl), were shown to be competent catalysts in the cyclization of aminoalkenes. L2MgiPr exhibited the best catalytic activity, and both triphenylsilyl-substituted complexes display zero-order rate dependence on substrate concentration and first-order rate dependence on catalyst concentration, whereas the sterically less hindered complex L1MgiPr exhibits second-order rate dependence on substrate concentration. No Schlenk-type ligand redistributions were observed, and the catalytically active magnesium species was stable after prolonged heating to 120 °C, according to an NMR spectroscopic study.

Achieving Ferromagnetism in Single-Crystalline ZnS Wurtzite Nanowires via Chromium Doping

The magnetic properties of Cr-doped wurtzite ZnS nanowires were studied through first-principles computations. At a low doping concentration of 2.08% (one Cr atom in a 96-atom supercell), the Cr atom prefers to substitute for the surface four-coordinated Zn atom in the groove of the ZnS nanowire with a diameter of 1.2 nm; at a higher doping concentration of 4.17% (two Cr atoms in the 96-atom supercell), the Cr atoms preferably substitute for the surface four-coordinated Zn atom and its neighboring surface three-coordinated Zn atom. Irrespective of the sites that Cr atoms occupy, Cr atoms in ZnS nanowires are always ferromagnetically coupled to each other and antiferromagnetically coupled to the mediating S atom; moreover, the robust ferromagnetism is not sensitive to surface passivation. The ferromagnetism in Cr-doped ZnS nanowires is attributed to a double-exchange mechanism.

Substituted Diorganotin(IV) O,O’-Alkylene Dithiophosphates: Synthesis and Spectral Aspects

Six new substituted diphenyltin(IV) O,O′-alkylene dithiophosphates, (C6H5)2Sn(X)S(S) POGO [G = —CH2C(CH3)2CH2—, X = Cl (1), SCN (3), ClO4 (5); G = —CH2C (C4H9)(C2H5)CH2—, X = Cl (2), SCN (4), ClO4 (6)], were synthesized by the reaction of the corresponding ammonium salts of the O,O’-alkylene dithiophosphates with an appropriate organotin(IV) chloride. The compounds were characterized on the basis of elemental and spectral analyses (ESI mass spectrometry, IR, 1H, 13C, 31P, and 119Sn NMR). The presence of a four-coordinated Sn atom and monodentate O,O’-alkylene dithiophosphate moiety in compounds 1–4 as well as bidentate O,O’-alkylene dithiophosphate unit in compounds 5,6 is established.

Synthesis, structures and ε-caprolactone polymerization activity of aluminum N,N′-dimethyloxalamidates

Alkyl aluminum N,N′-dimethyloxalamidates R 4Al 2(dmoa) ( 1, R = Me; 2, R = Et; 3, R = i Bu; 4, R = t Bu) (dmoa-H 2 = N,N′-dimethyloxalamide) have been prepared and characterized. Molecular structures of the compounds 1 and 4 have been determined by X-ray crystallography. The centrosymmetric molecules of the compounds consist of one N,N′-dimethyloxalamidate unit bonded to two four-coordinated aluminum atoms. Each of the aluminum atoms is bonded to two alkyl groups, and oxygen and nitrogen atoms originating from two different amidate groups. A skeleton framework of the molecules of 1 and 4 consists of two fused AlNOC 2 heterocyclic rings, which are flat and positioned in one plane. It was shown that compounds 1– 3 were initiators in a process of ring opening polymerization (ROP) of ε-caprolactone. The compound 4 exhibited low activity in ROP.

Reversible formation of regular pentagonal dodecahedral (H2O)20in a 2D metal–organic framework

The regular pentagonal (H2O)20 dodecahedra has been found in the cavity of 2D [Ag6(Pra2biim)3]. It consists of two two-coordinated, eight three-coordinated and ten four-coordinated oxygen atoms accompanied by 28 surface hydrogen bonds and 12 apical hydrogen bonds. The reversible formation of the (H2O)20 cluster has been reported for the first time.

Synthesis and thermolytic behavior of tin(iv) formates: in search of recyclable metal–hydride systems

The synthesis and characterization of the series of organotin formates together with their thermolytic behavior are described. The diformate Bu(n)(2)Sn{OC(O)H}(2) (1) was synthesized by the reaction of Bu(n)(2)SnH(2) with formic acid. The triorganotin monoformate compounds R(3)SnOC(O)H (R = Cy (cyclohexyl)) 3, Mes, (mesityl, 2,4,6-trimethylphenyl) 4, and Dmp (2,6-dimethylphenyl 5) were obtained by the reaction of R(3)SnOH with formic acid. Their X-ray crystal structures along with that of the previously reported formate (PhCH(2))(3)SnOC(O)H (2) were determined. The diformate 1 exhibits an extended two-dimensional polymeric structure in which six-coordinate tin centers are linked by formate bridges. The tribenzyltin formate (2) possesses a chain structure in which the five-coordinate Sn(CH(2)Ph)(3) units are bridged by formate ions. The cyclohexyl derivative 3 was observed to have a similar structure. In contrast, the Mes and Dmp derivatives 4 and 5 support monomeric structures in which the four-coordinate tin atom is bound to an oxygen of the formate ligand. Heating the compounds in various high boiling solvents produced no decomposition up to 120 °C in the case of 1 and refluxing a solution of 2 or 3 in mesitylene or diglyme left the starting material mostly unchanged, although 3 decomposed to an insoluble orange solid in refluxing decalin. In contrast, the heating of 4 and 5 in refluxing mesitylene led to elimination of CO to give the tin hydroxides. The results are in contrast to the known thermolytic behavior of R(3)SnOC(O)H (R = Pr(n) or Bu(n)) complexes, which eliminate CO(2) to generate R(3)SnH. Compounds 3-5 are rare examples of structurally characterized tin formates.

Structural Investigation of (5-Amino-1,3,4-thiadiazolyl-2-thionato)trimethyltin(IV): 1D Chains Generated by Hydrogen Bonding

ABSTRACT The geometry of the four-coordinated Sn atom in the title compound, (CH3)3Sn(C2H2N3S2), is distorted tetrahedral with three Sn–C bonds and one Sn–S bond. Two crystallographically distinct molecules a and b within the asymmetric unit are hydrogen bonded. Intermolecular “N–H⋯N” hydrogen bond interactions generate infinite 1D chains consisting of alternating, centrosymmetric R2,2(8) and R4,2(10) rings.

Theoretical study of polyoxide clusters Sc20O30, P20O50, Ti20O30F20, and V20O30F20

The structural, electronic, and vibrational characteristics and energies of the isolated polyoxide clusters Sc20O30, P20O50, Ti20O30F20, and V20O30F20 and ammonia complexes Sc20O30 · nNH3 were calculated by the density functional theory B3LYP method with several basis sets. The computation results show that a fullerene-like closo structure Ih with oxygen bridges located above the midpoints of the edges of an empty [M20] dodecahedron is preferable for the Ti20O30F20 and V20O30F20 clusters with four-coordinate metal atoms protected by the outer M-F bonds. This structure with a cage diameter of ∼1 nm and the diameter of nearly planar decagonal faces (windows) of ∼0.5 nm is stable to dissociation into fragments and to strong geometric distortions and retains its closo shape when molecules like NH3 and anions like H− are attached to the cage. An analogous closo structure is favorable for the P20O50 cluster; however, in this structure, the [P20] cage is severely distorted and all 12 windows are strongly corrugated. For Sc20O30, the Ih dodecahedron with bare three-coordinate Sc atoms corresponds to a local minimum of the potential energy surface, which is 170–200 kcal/mol less favorable than compact puck-shaped isomers in which four- and five-coordinate metal atoms and three- and four-coordinate oxygen atom prevail. “Solvation” of the dodecahedral and puck-shaped Sc20O30 isomers by ammonia molecules strongly decreases the energy gap between the isomers; however, the dodecahedron Ih in all cases remains a high-lying intermediate. According to calculations, most polyoxides under consideration have a high electron affinity (comparable with or higher than that of fullerenes) and is able to add three to five or more alkali-metal atoms to form radical salts in which clusters are in the state of polyanions. Because of large sizes of the [M20] cages and their windows, the interior of the cage (as distinct from fullerenes) can accommodate a considerable number of atoms and several small molecules. The V20O30F20 cluster has 20 unpaired electrons and can be treated as a molecular magnet. The properties of the [M20] cages depend only slightly on the outer substituents. It is suggested that the pattern will be retained upon the substitution of OH groups for the F atoms and that the hydroxo-substituted clusters can bind to each other through hydrogen bridges and serve as building blocks for self-assembly into ordered nanometer and crystalline structures of various dimensions.

Aggregation of local hypervalent defects in amorphous selenium: Quantum-chemical modeling

Modeling of associated local diamagnetic defects generated in amorphous selenium by transformation of the continuous random network (CRN) was performed in the cluster approximation with inclusion of electron correlation effects at the second-order perturbation theory (MP2) level. It was shown that the participation of configurations involving four-coordinate atoms can lead to the formation of associated local defects that are as stable as the basic CNR elements.

Transfer of Amide and 2-Methoxyethoxy Groups and Sodium Encapsulation in the Reaction of TaCl3[N(TMS)2]2 with Sodium Bis(2-methoxyethoxy)aluminum Hydride: X-ray Structure of [NaAl{N(TMS)2}(OCH2CH2OMe)3

The reaction between the tantalum compound TaCl3[N(TMS)2]2 and the hydridic reducing agent sodium bis(2-methoxyethoxy)aluminum hydride (Vitride) has been investigated in toluene solution at room temperature and found to afford the dimeric aluminate complex [NaAl{N(TMS)2}(OCH2CH2OMe)3]2 as the sole isolable product. The molecular structure of the product establishes the existence of a four-coordinate aluminum atom and the formal transfer of the 2-methoxyethoxy and bis(trimethylsilyl)amide groups to the aluminate product. The aggregation of two NaAl{N(TMS)2}(OCH2CH2OMe)3 units serves to bind the two sodium cations in a crown-ether fashion through six ancillary oxygen atoms. The reaction between TaCl3[N(TMS)2]2 and the reducing agent Vitride has been examined and found to furnish the dimeric aluminate complex [NaAl{N(TMS)2}(OCH2CH2OMe)3]2 in low yields. X-ray diffraction analysis confirms the attendant transfer of the 2-methoxyethoxy and bis(trimethylsilyl)amide groups to the aluminate product, which exists as a dimer that encapsulates two sodium counter ions via the 2-methoxyethoxy appendages.

Bis{(E)-2-methoxy-6-[(4-methylphenyl)iminomethyl]phenolato}zinc(II)

The title compound, [Zn(C15H14NO2)2], contains a four-coordinate Zn atom located on a twofold rotation axis that exhibits a distorted tetra­hedral geometry by two phenolate O atoms and two azomethine N atoms of the Schiff base 2-methoxy-6-[(4-methyl­phen­yl)imino­meth­yl]phenolate ligands.

Polymerizing Cluster Helicates into High‐Connectivity Networks

Solvothermal reactions of CuII salts and 3,5-bis(4-pyridyl)pyrazole (HL) under various conditions gave three different types of crystalline compound, namely [Cu2(Cu5L6)]BF(4).5 H2O (1 a), [Cu2(Cu5L6)]ClO(4).5 H2O (1 b), and [Cu7(CN)2(Cu5L6)2][BF4]3 (2). 1 a and b were obtained in ethanol and NH3.H2O, whereas 2 was obtained in methanol and NH3.H2O. The three complexes were constructed by incorporating new pentanuclear copper(I) pyrazolate bis(triple helical) cluster helicates (Cu5L6) as the second building units (SBUs), in which as many as twelve 4-pyridyl N atoms are available for further coordination and construction of high-connectivity topological networks. In 1 a and b, seven 4-pyridyl N atoms are linked to three three-coordinated CuI atoms and four four-coordinated CuI atoms, which results in 3,4,7-connected networks. In 2, as many as eleven 4-pyridyl N atoms coordinate to eleven CuI atoms, which results in a 4,10-connected topological network. The increasing connectivity of the cluster nodes in 2 is closely related to the in situ-formed CN- anion bridge around the periphery of the pentanuclear cluster helicates. The luminescenct properties of these compounds were also investigated.

Catena-Poly[[dichloridocobalt(II)]-μ-1,3-di-4-pyridylpropane-κ2N:N′

In the title compound, [CoCl2(C13H14N2)]n, 1,3-bis­(4-pyrid­yl)propane (bpp) ligands bridge four-coordinate Co atoms, generating an extended one-dimensional zigzag chain. Both the Co and two Cl atoms in the tetrahedral coordination polyhedron lie on a mirror plane, while the bbp ligand is bis­ected through the central C atom in the chain by a second mirror plane. There are some π–π stacking inter­ations in the crystal structure, with inter­planar distances of 3.449 Å, which are responsible for the supra­molecular assembly.

The quantum-chemical determination of group contributions to the thermodynamic properties of organophosphorus compounds

The enthalpies of formation, entropies, and heat capacities of 95 organophosphorus derivatives calculated by nonempirical quantum-chemical methods were used to develop the additive method for estimating the thermodynamic properties of these compounds. 86 group contribution values were obtained for estimating the thermodynamic properties of diverse organic derivatives of phosphorus in the oxidation states 3 and 5 (three-and four-coordinate phosphorus atoms).

Synthesis, crystal structure, antibacterial assay and DNA binding activity of new binuclear Cu(II) complexes with bridging oxamidate

Two new binuclear copper complexes, [Cu 2(oxpn)(bpy)(pic)(H 2O)](pic) (1) and [Cu 2(oxpn)(Me 2bpy)(pic)](pic) (2) [H 2oxpn = N, N′-bis(3-aminopropyl)oxamide; Hpic = 2,4,6-trinitrophenol; bpy = 2,2′-bipyridine; Me 2bpy = 4,4′-dimethyl-2,2′-bipyridine], have been synthesized and characterized by elemental analyses, conductivity measurements, IR, UV–visible spectroscopy and single crystal X-ray analyses. Both complexes have similar molecular structures. In complex 1, the central two Cu(II) atoms are bridged by cis-oxpn 2− with the Cu1–Cu2 separation of 5.221 Å and the polyhedron of each copper atom is a square-pyramid. Similarly, complex 2 is a cis-oxpn 2−-bridged binuclear complex with the Cu1–Cu2 separation of 5.196 Å. Cu1(II) central atom situated in a tetrahedral geometry is four-coordinated and Cu(II) atom situated in a square-pyramidal geometry is five-coordinated. Hydrogen bonding interactions and π–π stacking interactions link the binuclear copper complex 1 or 2 into a 2D infinite network. The antibacterial assays indicate that the two complexes showed better activities than their ligands. The interactions of the two binuclear complexes with herring sperm DNA ( HS-DNA) have been studied by UV absorption titration, fluorescence titration and viscosity measurements. The results suggest that the two binuclear complexes bind to HS-DNA via an intercalative mode.

Theoretical study of polyoxide clusters B20O30, Al20O30, V20O50, Si20O30H20, and Si20O30F20

The structural, electronic, and vibrational characteristics and energies of the isolated polyoxide clusters B20O30, Al20O30, V20O50, Si20O30H20, and Si20O30F20 and their complexes with the H− ion and ammonia complexes Al20O30 · nNH3 have been calculated by the density functional theory B3LYP method with different basis sets. The computation results show that the symmetric closo structure Ih with oxygen bridges located above the centers of the faces of an empty [M20] dodecahedron is more favorable for V20O50, Si20O30H20, and Si20O30F20. For B20O30, the cage closo isomer is also more favorable than the other isomers, but its structure is severely distorted as compared to a dodecahedron and has a symmetry close to C3. For Al20O30, the Ih structure corresponds to a high-lying local minimum of the potential energy surface. For Al20O30, a set of unusual puckshaped isomers of symmetry Ci, with different numbers of four-coordinate atoms IVAl and three-coordinate atoms IIIO, was localized; these structures are more than 90 kcal/mol more favorable than the dodecahedron Ih. The most favorable isomer of Al20O30 contains twelve four-coordinate atoms IVAl and four five-coordinate atoms VAl. The energies of dissociation of the most favorable M20O30 clusters into the M2O3 (C2v) and M4O6 (Td) fragments and, in the case of Al20O30, also into the Al8O12 (Oh) and Al12O18 (D3d) fragments, have been estimated. The conclusion has been drawn that these clusters can, in principle, exist and can be experimentally detected in the isolated state. Analogous calculations have been performed for ammonia complexes Al20O30 · nNH3 with n varying from 1 to 20. The effect of solvation on the relative stability of the dodecahedral and puckshaped isomers of the Al20O30 cluster is observed. The isomers with ammonia molecules in their first coordination sphere become much closer to one another on the energy scale; however, the dodecahedron remains a considerably less favorable intermediate.

Neutron Diffraction Studies on a 4-Coordinate Hydrogen Atom in an Yttrium Cluster

A four-coordinate hydrogen atom has been unambiguously located, by single-crystal neutron diffraction for the first time, in the center of the tetrahedral metal complex Y4H8(Cp')4(THF) [Cp'=C5Me4(SiMe3)]. The core of the molecule consists of a tetranuclear cluster with one interstitial, one face-bridging, and six edge-bridging hydride ligands. The compound was prepared via the reaction of YCp'(CH2SiMe3)2(THF) with gaseous H2. Neutron data were collected on a 4 mm3 crystal at the Quasi-Laue diffractometer VIVALDI at ILL (Grenoble)1a and on an 8 mm3 crystal at the SXD diffractometer at ISIS (Didcot). The final agreement factor is R = 8.9% for 4171 reflections. The existence of 4-coordinate hydrogen now completes the series of high-connectivity hydride ligands located in the interstitial cavities of molecular cluster complexes. We had previously reported the existence of 6-coordinate hydrogen in the octahedral cavity of [HCo6(CO)15]- in 1979, and 5-coordinate hydrogen in the square pyramidal cavities of [H2Rh13(CO)24]3- in 1997, also via single-crystal neutron analyses.

Mono- and dinuclear silver(I) complexes of benzene- and pyridine-bearing 20-membered thiaoxaaza macrocycles

Two 20-membered penta- and hexadentate macrocycles containing one or two pyridine subunits, namely [20]aneNO 2S 2 ( L 1) and [20]aneN 2O 2S 2 ( L 2), have been synthesized. Reaction of L 1 with silver(I) nitrate afforded a unique 2:2 (M:L) disilver(I) complex [μ 2-Ag 2( L 1) 2](NO 3) 2 ( 1) in which two four-coordinate Ag atoms bridge two ligands to form a cyclic dimer. In contrast, an endo-dentate 1:1 monosilver(I) complexes [Ag L 2]X; [X = ClO 4 ( 2) or PF 6 ( 3)] which show isomorphous structures were obtained from the reactions of L 2 with silver(I) salts.

Synthesis and structure of silicon-containing N-methyland N-benzoylamides of diisopropylphosphoric acid

Diisopropyl N-benzoyl-N-(trimethylsilyl)phosphoramidate reacts with ClCH2SiMe2Cl under mild conditions to form diisopropyl N-benzoyl-N-[(chlorodimethylsilyl)methyl]phosphoramidate (III). Diisopropyl N-methyl-N-(trimethylsilyl)phosphoramidate with ClCH2SiMe2Cl affords an N-transsilylation product which does not rearrange into diisopropyl N-[(chlorodimethylsilyl)methyl]-N-methylphosphoramidate (XV) even under severe conditions (4 h, 130°C). Compound XV was prepared by the reaction of diisopropyl phosphorochloridate with N-[(methoxydimethylsilyl)methyl]-N-methylamine followed by treatment of diisopropyl N-[(methoxydimethylsilyl)methyl]-N-methylphosphoramidate with boron trichloride. Analysis of experimental and calculated 29Si chemical shifts points to a five-coordinate silicon atom in compound III and a fourcoordinate silicon atom in compound XV. According to B3LYP calculations with due regard to solvent effects, compound III is an isomer with a C=O→Si bond. By variation of substituents at silicon, phosphorus, and carbonyl carbon atoms, chelate structures with either C=O→Si or P=O→Si dative bonds can be obtained.

Bis(acetonitrile-κN)hexakis(μ2-4-amino-3,5-dimethyl-1,2,4-triazole-κ2N1:N2)tetrasilver(I) tetrakis(trifluoromethanesulfonate) acetonitrile disolvate

The centrosymmetric tetra­nuclear cluster of the title compound, [Ag4(C4H8N4)6(C2H3N)2](CF3SO3)4·2C2H3N, has four 4-amino-3,5-dimethyl-1,2,4-triazole N-heterocycles, each functioning as a bridge between two Ag atoms. Two of the Ag atoms are additionally coordinated by acetonitrile mol­ecules, so that there are three-coordinate Ag atoms in a trigonal–planar geometry and four-coordinate Ag atoms in a tetra­hedral geometry. There are no short hydrogen bonds between cations and anions.