Heteropolytopic arsanylarylthiolato ligands: cis-trans isomerism of nickel(II), palladium(II), and platinum(II) complexes of 1-AsPh2-2-SHC6H4.

Heteropolytopic arsanylthiolato ligands 1-AsPh(2)-2-SHC(6)H(4) (AsSH), PhAs(2-SHC(6)H(4))(2) (AsS(2)H(2)), and As(2-SHC(6)H(4))(3) (AsS(3)H(3)) have been prepared by lithiation-electrophilic substitution procedures. The 2:1 reaction of AsSH with NiCl(2)·6H(2)O, Na(2)[PdCl(4)], and [PtI(2)(cod)] (cod = 1,5-cyclooctadiene) in the presence of NEt(3) afforded the square-planar complexes trans-[Ni{(AsS)-κ(2)S,As}(2)] (1), cis-[Pd{(AsS)-κ(2)S,As}(2)] (2), trans-[Pd{(AsS)-κ(2)S,As}(2)] (3), and cis-[Pt{(AsS)-κ(2)S,As}(2)] (4). In the cases of nickel and platinum, only one isomer was isolated.

Heteropolytopic phosphanylarylthiolato ligands: formation of cis isomers of nickel(II), palladium(III) and platinum(III) complexes with 1-P(Biph)-2-SHC6H4 (Biph = 1,1'-biphenyl-2,2'-diyl).

Reaction of the ditopic phosphanylarylthiol 1-P(Biph)-2-SHC(6)H(4) (BiphPSH, Biph = 1,1'-biphenyl-2,2'-diyl), prepared by lithiation-electrophilic substitution, with NiCl(2)·6H(2)O, Na(2)[PdCl(4)] and [PtI(2)(cod)] (cod = 1,5-cyclooctadiene) in a 2:1 ratio and in the presence of NEt(3) led to formation of exclusively cis isomers of the square-planar complexes cis-[M{(1-P(Biph)-2-S-C(6)H(4))-κ(2)S,P}(2)] ([M{(BiphPS)-κ(2)S,P}(2)]; M = Ni (1), Pd (2), Pt (3)). Density functional calculations support the assumption that this is probably due to intramolecular π-π interaction of the biphenyl groups, which results in enhanced stability of the cis isomers. Compound 1 is the first example of a structurally characterised mononuclear cis-bis(phosphanylthiolato)nickel(III) complex.

Theoretical study of structural patterns in CH₂OP₂ isomers.

DFT calculations have been performed on the derivatives of formula CH₂OP₂ to determine their total energy, the relative energy between the isomers and their geometry. Among compounds with a P-C-P linkage, the most stable one is the 2-hydroxy-1,2-diphosphirene II.1, a three-membered heterocycle with a P=C unsaturation.

Computational investigation of the histidine ammonia-lyase reaction: a modified loop conformation and the role of the zinc(II) ion.

Possible reaction intermediates of the histidine ammonia-lyase (HAL) reaction were investigated within the tightly closed active site of HAL from Pseudomonas putida (PpHAL). The closed structure of PpHAL was derived from the crystal structure of PpHAL inhibited with L-cysteine, in which the 39-80 loop including the catalytically essential Tyr53 was replaced. This modified loop with closed conformation was modeled using the structure of phenylalanine ammonia-lyase from Anabaena variabilis (AvPAL) with a tightly closed active site as a template.

Butterfly and rhombus structures for binuclear cobalt carbonyl sulfur and phosphinidene complexes of the type Co2(CO)6E2 (E = S, PX).

Theoretical studies on Co(2)(CO)(6)(PX)(2) derivatives (X = H, Cl, OH, OMe, NH(2), NMe(2)) predict the lowest energy structures to be butterfly structures containing five two-electron two-center bonds in the central Co(2)P(2) unit. Among these butterfly structures the energy increases as the unique bond forming the "body" of the butterfly changes from Co-Co to Co-P and then P-P. Higher energy rhombus structures are also found for Co(2)(CO)(6)(PX)(2) with only Co-P bonds in the Co(2)P(2) framework without any Co-Co or P-P bonds.

From closo to isocloso structures and beyond in cobaltaboranes with 9 to 12 vertices.

Density functional theory (DFT) studies predict the dianions CpCoB(n-1)H(n-1)(2-) (n = 9, 10, 11, 12; Cp = eta(5)-C(5)H(5)) to have structures based on the most spherical deltahedra found in the isoelectronic boranes B(n)H(n)(2-). In the CpCoB(8)H(8)(2-) dianion the non-equivalent structures with the cobalt atom at a degree 4 vertex and at a degree 5 vertex are essentially degenerate in terms of energy (within approximately 1 kcal/mol). For the CpCoB(n-1)H(n-1)(2-) dianions (n = 10, 11, 12) the cobalt atom prefers energetically the vertices of the lowest possible degree (four for n = 10 and 11, five for n = 12).

Kinetic versus thermodynamic isomers of the deltahedral cobaltadicarbaboranes.

Synthesis of the deltahedral cobaltadicarbaboranes CpCoC(2)B(n-3)H(n-1) (n = 9, 10, 11, 12) typically leads initially to kinetically stable isomers with energies up to approximately 20 kcal/mol above the lowest energy isomers. Pyrolyses of these originally produced isomers typically results in isomerization to give more thermodynamically stable isomers. In this connection the relative stabilities of the CpCoC(2)B(n-3)H(n-1) (n = 9, 10, 11, 12) isomers have been investigated using density functional theory.

(Diethyl-enetriamine)bis-(theophyllinato)zinc(II) dihydrate.

In the title compound, [Zn(C(7)H(7)N(4)O(2))(2)(C(4)H(13)N(3))]·2H(2)O, the Zn(II) ion is penta-coordinated by three N atoms of the diethyl-enetriamine ligand and one N atom of each of the two theophyllinate anions in a distorted trigonal-bipyramidal geometry. The Zn-N distances range from 2.076 (3) to 2.

When arsine makes the difference: chelating phosphino and bridging arsinoarylthiolato gallium complexes.

The (organo)gallium compounds GaCl{(SC6H4-2-PPh2)-kappa2S,P}2 (1), Ga{(SC6H4-2-PPh2)-kappa2S,P}{(SC6H4-2-PPh2)-kappaS}2 (2), GaMe2{(SC6H4-2-PPh2)-kappa2S,P} (3), GatBu2{(SC6H4-2-PPh2)-kappa2S,P} (4), GatBu{(SC6H4-2-PPh2)-kappa2S,P}{(SC6H4-2-PPh2)-kappaS} (5), [GaMe2{(mu2-SC6H4-2-AsPh2)-kappaS}]2 (6), and GatBu{(SC6H4-2-AsPh2)-kappa2S,As}{(SC6H4-2-AsPh2)-kappaS} (7) were obtained from the reaction of 2-EPh2C6H4SH (E = P (PSH), As (AsSH)) with GaCl3 (1, 2) or GaR3 (R = Me, tBu; 3-7) in different molar ratios and under different reaction conditions. Compound 2 was also obtained from Li(PS) and GaCl3 (3.5:1).

Polyhedral structures with three-, four-, and five fold symmetry in metal-centered ten-vertex germanium clusters.

Studies using density functional theory (DFT) at the hybrid B3LYP level indicate that the relative energies of structures with three-fold, four-fold, and five-fold symmetry for centered 10-vertex bare germanium clusters of the general type M@Ge(10) (z) depend on the central metal atom M and the skeletal electron count. For M@Ge(10) clusters with 20 skeletal electrons the DFT results agree with experimental data on the isoelectronic centered 10-vertex bare metal clusters. Thus the lowest energy structure for Ni@Ge(10), isoelectronic with the known Ni@In(10) (10-), is a C(3v) polyhedron derived from the tetracapped trigonal prism.

PalladiumII and platinumII complexes with heteroditopic 10-(aryl)phenoxarsine (aryl = 2-C6H4OR, R = H, Me, Pr(i)) ligands: solvent-oriented crystallization of cis isomers.

The synthesis and characterization of 10-(o-alkoxyphenyl)phenoxarsines 2-ROC6H4As(C6H4)2O (R = H, Me, and Pri, As(C6H4)2O = phenoxarsine) and their platinum(II) and palladium(II) complexes cis-[PtCl2{2-PriOC6H4As(C6H4)2O-kappaAs}2] (1), trans-[PdCl2{2-PriOC6H4As(C6H4)2O-kappaAs}2] (2), cis-[PtCl2{2-HOC6H4As(C6H4)2O-kappaAs}2] (3), cis-[PdCl2{2-HOC6H4As(C6H4)2O-kappaAs}2] (4), cis-[PtI2{2-MeOC6H4As(C6H4)2O-kappaAs}2] (5), and trans-[PdCl2{2-MeOC6H4As(C6H4)2O-kappaAs}2] (6) are reported. The chelate complex cis-[Pt{2-OC6H4As(C6H4)2O-kappaAs,O}2] (7) is also described. The molecular structures of 1-4 and 7 were determined.

Interplay among tetrahedrane, butterfly diradical, and planar rhombus structures in the chemistry of the binuclear iron carbonyl phosphinidene complexes Fe2(CO)6(PX)2.

Density functional theory studies on a series of Fe2(CO)6(PX)2 derivatives show the tetrahedrane to be the most stable for the alkyl (X = Me, tBu), P-H (X = H), and chloro (X = Cl) derivatives. However, butterfly diradical and planar rhombus structures are found to be more stable than tetrahedranes for the amino (X = NH2, NMe2, and NiPr2) and aryloxy (R = 2,6-tBu2-4-Me-C6H2O) derivatives. For the chloro (X = Cl) and methoxy (X = OMe) derivatives energetically accessible bishomotetrahedrane Fe2(CO)6P2(mu-X)2 isomers are observed in which the X substituents on the phosphorus atoms interact with the iron atom to form two direct Fe-X bonds at the expense of two of the four Fe-P bonds.

1,3-Digermacyclobutanes with exocyclic C=P and C=P=S double bonds.

New 1,3-digermacyclobutanes, with two exocyclic C=PMes* bonds, and the corresponding first bis(methylenethioxo)phosphoranes with C=P(S)Mes* moieties have been synthesized.

Density functional theory study of twelve-atom germanium clusters: conflict between the Wade-Mingos rules and optimum vertex degrees.

Density functional theory (DFT) at the hybrid B3LYP level has been applied to Ge(12)(z) bare germanium clusters (z = -6, -4, -2, 0, +2, +4, +6) starting from 11 initial configurations. The Wade-Mingos rules are seen to have limited value in rationalizing the results since they frequently require vertex degrees higher than the optimum vertex degree of 4 for germanium. Thus the expected I(h) regular icosahedron is no longer the global minimum for Ge(12)(2-) although it remains a low energy structure for Ge(12)(2-) lying only 5.

Molecular rotors: design, synthesis, structural analysis, and silver complex of new [7.7]cyclophanes.

New molecular rotors, [7.7](2,6)pyridinocyclophanes (monomers and dimers) embedding 1,3-dioxanes in the bridges, were investigated by variable-temperature NMR, molecular modeling, and single-crystal X-ray diffractometry. The nitrogen-inside rotation of the pyridine ring is more hindered in the derivatives with longer distance between the bridges (i.

Butterfly diradical intermediates in photochemical reactions of Fe2(CO)6(mu-S2).

Photolysis of the tetrahedrane Fe2(CO)6(mu-S2) at 450 +/- 35 nm in a Nujol matrix at low temperatures gives an isomer characterized by its nu(CO) infrared frequencies. Comparison of these experimental frequencies with those calculated by density functional theory using the BP86 functional indicates this photoisomer to be the butterfly singlet diradical Fe2(CO)6S2 isomer in which the S-S bond of the tetrahedrane is broken but the Fe-Fe bond is retained. Photolysis at higher energies (420-280 nm) results in CO loss from this singlet butterfly diradical as indicated again by comparison of the experimental infrared nu(CO) frequencies with those calculated for an Fe2(CO)5S2 isomer of this type.

Co-complexes of ortho-dilithiated thiophenol or 2-trimethylsilylthiophenol with lithiated TMEDA molecules: synthesis, crystal structures and theoretical studies (TMEDA = N,N,N',N'-tetramethylethylenediamine).

When an excess of nBuLi was used in the ortho-dilithiation of thiophenol or 2-trimethylsilylthiophenol in the presence of TMEDA (TMEDA = N,N,N',N'-tetramethylethylenediamine), deprotonation of TMEDA occurred and crystals of [Li3{(2-S-C6H4)(CH2MeNCH2CH2NMe2)(TMEDA)}]2 (1) or [Li4{(2-S-3-SiMe3-C6H3)(CH2MeNCH2CH2NMe2)2(TMEDA)}] (2) were obtained. Molecular orbital calculations on gas-phase 1 and 2 at the DFT B3LYP/6-31G(d) level reproduce the experimental structures fairly well. In spite of the short Li.

DFT and the electromerism in complexes of iron with diatomic ligands.

A reliable procedure is proposed for assigning the electronic structures for large biologically-relevant systems, where the size of the model confines one to the use of density functional theory (DFT) methods, and where the risk of over-interpreting DFT-derived molecular orbitals and spin densities still exists. The proposed approach focuses on the use of the only DFT-derived parameter that is unanimously recognized to be reliable: the geometry. We examine DFT-derived O-O bond lengths in formally ferrous-dioxygen models, and compare them to bond lengths in free, non metal-bound, dioxygen, superoxide and peroxide moieties.

Periodic cages.

Various cages are constructed by using three types of caps: f-cap (derived from spherical fullerenes by deleting zones of various size), kf-cap (obtainable by cutting off the polar ring, of size k), and t-cap ("tubercule"-cap). Building ways are presented, some of them being possible isomerization routes in the real chemistry of fullerenes. Periodic cages with ((5,7)3) covering are modeled, and their constitutive typing enumeration is given.

Tin(IV) halide complexes of AsPh3) The structures of trans-SnCl4(AsPh3)2 and SnBr4(AsPh3).AsPh3.

The structures of two 1 : 2 adducts between tin(IV) halides and AsPh(3) have been determined. SnCl(4)(AsPh(3))(2) adopts a six-coordinate geometry at tin in which the two organoarsine donors are mutually trans. In contrast, SnBr(4)(AsPh(3))(2) is five-coordinate at tin and only one arsine is directly bonded to the metal, in an axial site of the trigonal bipyramid.

Influences of changes in multitopic tris(pyrazolyl)methane ligand topology on silver(I) supramolecular structures.

The reactions between silver tetrafluoroborate and the ligands 1,2,4,5-C(6)H(2)[CH(2)OCH(2)C(pz)(3)](4) (L1, pz = pyrazolyl ring), o-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2) (L2), and m-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2) (L3) yield coordination polymers of the formula (C(6)H(6)(-)(n)[CH(2)OCH(2)C(pz)(3)](n)(AgBF4)(m))( infinity ) (n = 4, m = 2, 1; n = 2, ortho substitution, m = 1, 2; meta substitution, m = 2, 3). In the solid state, L2 molecules dimerize by a pair of C-H.pi interactions, forming an arrangement that resembles the tetratopic ligand L1.

Computational study of the non-heme iron active site in superoxide reductase and its reaction with superoxide.

The ferrous square-pyramidal [Fe(NHis)4(SCys)] site of superoxide reductases (SORs) has been shown to reduce superoxide at a nearly diffusion-controlled rate. The final products of the reaction are hydrogen peroxide and the ferric hexacoordinated SOR site, with a carboxylate group from a conserved glutamate serving as the sixth ligand trans to the cysteine sulfur. A transient intermediate absorbing at approximately 600 nm in the reaction of the ferrous pentacoordinated site with superoxide has been proposed to be a ferric-(hydro)peroxo complex (Coulter, E.