Trigonal Bipyramidal Structure Research Articles

New Di- and Triorganotin(IV) Tyrosylalaninates as Models for Metal—Protein Interactions: Synthesis, Structural Characterization, and Potentiometric Studies of Tyrosylalanine, Glycyltyrosine, and Glycylisoleucine with Di- and Trimethyltin(IV) Moieties in Aqueous Medium

Di- and triorganotin(IV) derivatives of tyrosylalanine (H2Tyr-Ala) with general formula R2Sn(Tyr-Ala) (where R = Me, n-Bu, n-Oct, and Ph) and R3Sn(HTyr-Ala) (where R = Me and Ph) have been synthesized and structurally characterized in the solid state as well as in solution on the basis of various spectroscopic techniques, namely. FT-IR, multinuclear (1H, 13C and 119Sn) NMR and 119Sn Mössbauer. These investigations suggest that tyrosylalanine in R2Sn(Tyr-Ala) acts as dianionic tridentate ligand coordinating through carboxylate oxygen [–C(O)O−], amino (–NH2), and (CO)Npeptide- nitrogen, while in the case of R3Sn(HTyr-Ala), the ligand acts as monoanionic bidentate coordinating through –C(O)O− and –NH2, and the polyhedron around tin in R2Sn(Tyr-Ala) and R3Sn(HTyr-Ala) is a distorted trigonal-bipyramidal. Equilibrium (pH-metric) studies of the interaction of Me2Sn(IV)2+ and Me3Sn(IV)+ with dipeptides namely, tyrosylalanine (H2Tyr-Ala), glycyltyrosine (H2Gly-Tyr), and glycylisoleucine (H2Gly-Ile), in aqueous solution (I = 0.1 M KNO3, 298 K) have also been carried out. The concentration distribution of the various complex species in solution has been evaluated as a function of pH. It has been found that in these dipeptides, [–C(O)O−, N−, NH2] coordinated complexes are dominant in the neutral pH range with a trigonal-bipyramidal structure. The complex species formed are water soluble in the pH range 2.7–10.5. In all of the studied systems, no polymeric species have been detected in the experimental pH range. Beyond pH 8.0, significant amounts of hydroxo species, namely. Me3Sn(OH) and Me2Sn(OH)2, are formed.

The Beryllium Pentamer: Trailing an Uneven Sequence of Dissociation Energies

Recent high-resolution spectroscopic studies by Merritt, Bondybey, and Heaven (Science 2009, 324, 1548) have heightened the anticipation that small beryllium clusters will soon be observed in the laboratory. Beryllium clusters are important discrete models for the theoretical study of metals. The trigonal bipyramidal Be(5) molecule is studied using high-level coupled cluster methods. We obtain the optimized geometry, atomization and dissociation energies, and vibrational frequencies. The c~CCSDT(Q) method is employed to compute the atomization and dissociation energies. In this approach, complete basis set (CBS) extrapolations at the CCSD(T) level of theory are combined with an additive correction for the effect of iterative triple and perturbative quadruple excitations. Harmonic vibrational frequencies are obtained using analytic gradients computed at the CCSD(T) level of theory. We report an atomization energy of 129.6 kcal mol(-1) at the trigonal bipyramid global minimum geometry. The Be(5)→Be(4)+Be dissociation energy is predicted to be 39.5 kcal mol(-1). The analogous dissociation energies for the smaller beryllium clusters are 64.0 kcal mol(-1) (Be(4)→Be(3)+Be), 24.2 kcal mol(-1) (Be(3)→Be(2)+Be), and 2.7 kcal mol(-1) (Be(2)→Be+Be). The trigonal bipyramidal Be(5) structure has an equatorial-equatorial bond length of 2.000 Å and an axial-equatorial distance of 2.060 Å. Harmonic frequencies of 730, 611, 456, 583, 488, and 338 cm(-1) are obtained at the CCSD(T)/cc-pCVQZ level of theory. Quadruple excitations are found to make noticeable contributions to the energetics of the pentamer, which exhibits a significant level of static correlation.

Why Are SiX5– and GeX5– (X = F, Cl) Stable but Not CF5– and CCl5–?

The possible existence of the CF(5)(-), CCl(5)(-), SiF(5)(-), SiCl(5)(-), GeF(5)(-), and GeCl(5)(-) anions has been investigated using ab initio methods. The species containing Si and Ge as central atoms were found to adopt the D(3h)-symmetry trigonal bipyramidal equilibrium structures whose thermodynamic stabilities were confirmed by examining the most probable fragmentation channels. The ab initio re-examination of the electronic stabilities of the SiF(5)(-), SiCl(5)(-), GeF(5)(-), and GeCl(5)(-) anions [using the OVGF(full) method with the 6-311+G(3df) basis set] led to the very large vertical electron detachment (VDE) energies of 9.316 eV (SiF(5)(-)) and 9.742 eV (GeF(5)(-)), whereas smaller VDEs of 6.196 and 6.452 eV were predicted for the SiCl(5)(-) and GeCl(5)(-) species, respectively. By contrast, the high-symmetry and structurally compact anionic CF(5)(-) and CCl(5)(-) systems cannot exist due to the strongly repulsive potential predicted for the X(-) (F(-) or Cl(-)) approaching the CX(4) (CF(4) or CCl(4)). The formation of weakly bound CX(4)···X(-) (CF(4)···F(-) and CCl(4)···Cl(-)) anionic complexes (consisting of pseudotetrahedral neutral CX(4) with the weakly tethered X(-)) might be expected at low temperatures (approaching 0 K), whereas neither CX(5)(-) (CF(5)(-), CCl(5)(-)) systems nor CX(4)···X(-) (CF(4)···F(-) and CCl(4)···Cl(-)) complexes can exist in the elevated temperatures (above 0K) due to their susceptibility to the fragmentation (leading to the X(-) loss).

Fluoroborylene ligands in binuclear ruthenium carbonyls: Comparison with their iron analogues

The qualitative aspects of the chemistry of the fluoroborylene iron and ruthenium carbonyls M(BF)(CO)m (m=4, 3) and M2(BF)2(CO)n (n=7, 6) (M=Fe, Ru) are predicted to be very similar. For Ru(BF)(CO)4 the trigonal bipyramidal structures with the BF group in an equatorial position and in an axial position are both found with the equatorially substituted isomer lying ∼2kcal/mol below the axially substituted isomer. For the coordinately unsaturated Ru(BF)(CO)3 both singlet and triplet structures are found derived from the equatorially substituted Ru(BF)(CO)4 structure by removal of an equatorial CO group. The structures for the binuclear derivatives Ru2(BF)2(CO)n (n=7, 6) provide examples of lower energy structures with bridging BF groups relative to similar structures with bridging CO groups. The lowest energy Ru2(BF)2(CO)7 structure has two bridging BF groups and one CO group and is qualitatively similar to the well-known Fe2(CO)9 structure with three bridging CO groups. All of the structures of the unsaturated Ru2(BF)2(CO)6 within 30kcal/mol of the global minimum have two bridging groups. The structure with one bridging CO group and one bridging BF group lies ∼16kcal/mol above the global minimum with two bridging BF groups again showing the preference for bridging BF groups over bridging CO groups. A triplet Ru2(BF)2(CO)6 structure with two bridging BF groups was also found but at the high energy of ∼26kcal/mol above that of the corresponding singlet global minimum. This singlet–triplet splitting is much larger than the singlet–triplet splitting of the corresponding Fe2(BF)2(CO)6.

Solid‐State and Solution Structure of a Hypervalent AX5 Compound: Sb(C6F5)5

Eliminating restraints: a trigonal-bipyramidal structure has been found to be the energetically favored geometry of the hypervalent AX(5) molecule Sb(C(6)F(5))(5) in the solid state and also in fluid solution, where molecules move freely and no crystal packing effects operate.

Synthesis and Structure Characterization of some Triorganotin Esters of Heteroaromatic Carboxlic Acid and Crystal Structure of Triphenyltin Esters 5-Chloro-6-Hydroxynicotinic Acid

Reactions of (R3Sn)2O (R=Ph, 2-ClC6H4CH2, 2-FC6H4CH2, 4-CNC6H4CH2) with 5-chloro-6-hydroxynicotinic acid in 1/2 stoichiometry yielded eight triorganotin compounds. These compounds have been characterized by elemental analysis, IR and NMR spectroscopy. The crystal structures of triphenyltin esters of 5-chloro-6-hydroxynicotinic acid were determined by single crystal X-ray diffraction. In the compound, the tin atoms are rendered five-coordinated in a trigonal bipyramidal structure by coordinating though the three phenyl carbon atoms and two oxygen atoms one from carboxylate and other from the phenolic hydroxide. The resulting structure is one-dimensional linear polymers through an interaction between the O atoms of phenolic hydroxide and tin atoms of an adjacent molecule.

Synthesis, structural elucidation and biological activities of organotin(IV) derivatives of (E)-3-(4-methoxyphenyl)-2-(4-chlorophenyl)-2-propenoic acid

A new series of di- and tri-organotin(IV) compounds with the general formula R4−n SnLn, where R = Me (1,2), Et (3), n-Bu (4,5), n-Oct (6), Ph (7) and L = (E)-3-(4-methoxyphenyl)-2-(4-chlorophenyl)-2-propenoate, were synthesized by reaction of silver salt of ligand or ligand acid with diorganotin dichloride/oxide and triorganotin chloride in 2:1 and 1:1 molar ratio, respectively. These compounds were characterized by elemental analyses, FT-IR, multinuclear (1H, 13C, 119Sn) NMR and mass spectrometry. The spectroscopic results revealed that all the diorganotin(IV) compounds possess trigonal bipyramidal structures in solution and octahedral geometry in the solid state around the tin atom. A linear polymeric trigonal bipyramidal structure in the solid state and a tetrahedral environment around the tin atom in non-coordinating solvents has been proposed for the triorganotin(IV) compounds. All synthesized compounds were tested in vitro against a number of microorganisms to assess their biocidal activity. These studies revealed that ligand acid and some of its organotin compounds show promising activity against different strains of bacteria and fungi but lowered than reference drugs.

Direct reaction of iodine-activated lanthanoid metals with 2,6-diisopropylphenol

Rare earth metals activated with ca. 2% iodine react directly with 2,6-diisopropylphenol (HOdip) in tetrahydrofuran (thf), 1,2-dimethoxyethane (dme), and dig-dme (dig = di(2-methoxyethyl) ether) to give solvated phenolate complexes [Ln(Odip)(3)(thf)(n)] (Ln = La, Nd, n = 3; Ln = Sm, Dy, Y, Yb, n = 2), [Eu(Odip)(μ-Odip)(thf)(2)](2), [Ln(Odip)(3)(dme)(2)] (Ln = La, Yb) and [La(Odip)(3)(dig)] in good yield for Ln = La, Nd, Eu but modest yield for smaller Ln metals under comparable conditions. However, increasing the excess of metal greatly increased the yield for Ln = Y. The synthetic method has general potential, at least for lanthanoid phenolates. Comparison redox transmetallation/protolysis (RTP) reactions between Ln metals, Hg(C(6)F(5))(2) and the phenol gave higher yields in shorter time and, for Eu, gave [Eu(Odip)(3)(thf)(3)] in contrast to an Eu(II) complex from Eu(I(2)). New [Ln(Odip)(3)(thf)(3)] complexes have fac-octahedral structures and [Ln(Odip)(3)(thf)(2)] monomeric five coordinate distorted trigonal bipyramidal structures with apical thf ligands. [Eu(Odip)(μ-Odip)(thf)(2)](2) is an unsymmetrical dimer with two bridging Odip ligands. One five coordinate Eu atom has distorted trigonal bipyramidal stereochemistry and the other is distorted square pyramidal. Whilst [La(Odip)(3)(dme)(2)] has irregular seven coordination with mer-Odip and chelating dme ligands, [Ln(Odip)(3)(dme)(2)] (Ln = Dy, Y (prepared by ligand exchange), Yb) are monomeric six coordinate with one chelating and one unidentate dme. A six coordinate fac-octahedral arrangement is observed in [La(Odip)(3)(dig)].

Versatile Behavior of the Fluorophosphinidene Ligand in Iron Carbonyl Chemistry

Fluorophosphinidene (PF) is a versatile ligand found experimentally in the transient species M(CO)(5)(PF) (M = Cr, Mo) as well as the stable cluster Ru(5)(CO)(15)(μ(4)-PF). The PF ligand can function as either a bent two-electron donor or a linear four-electron donor with the former being more common. The mononuclear tetracarbonyl Fe(PF)(CO)(4) is predicted to have a trigonal bipyramidal structure analogous to Fe(CO)(5) but with a bent PF ligand replacing one of the equatorial CO groups. The tricarbonyl Fe(PF)(CO)(3) is predicted to have two low-energy singlet structures, namely, one with a bent PF ligand and a 16-electron iron configuration and the other with a linear PF ligand and the favored 18-electron iron configuration. Low-energy structures of the dicarbonyl Fe(PF)(CO)(2) have bent PF ligands and triplet spin multiplicities. The lowest energy structures of the binuclear Fe(2)(PF)(CO)(8) and Fe(2)(PF)(2)(CO)(7) derivatives are triply bridged structures analogous to the experimental structure of the analogous Fe(2)(CO)(9). The three bridges in each Fe(2)(PF)(CO)(8) and Fe(2)(PF)(2)(CO)(7) structure include all of the PF ligands. Other types of low-energy Fe(2)(PF)(2)(CO)(7) structures include the phosphorus-bridging carbonyl structure (FP)(2)COFe(2)(CO)(6), lying only ~2 kcal/mol above the global minimum, as well as an Fe(2)(CO)(7)(μ-P(2)F(2)) structure in which the two PF groups have coupled to form a difluorodiphosphene ligand unsymmetrically bridging the central Fe(2) unit.

Vibronic Model for Cooperative Spin-Crossover in Pentanuclear {[MIII(CN)6]2[M′ II(tmphen)2]3} (M/M′ = Co/Fe, Fe/Fe) Compounds

In this paper we present a microscopic model for the cooperative spin-crossover (SCO) phenomenon in crystals containing cyano-bridged pentanuclear clusters {[MIII(CN)6]2[M′ II(tmphen)2]3} (M/M′ = Co/Fe, 1; Fe/Fe, 2) with a trigonal bipyramidal (TBP) structure. The low-spin to high-spin (ls–hs) transition is considered as a cooperative phenomenon that is driven by the interaction of electronic shells of FeII ions with totally symmetric deformation of the local environment that is extended over the crystal lattice via the acoustic phonon field. Due to proximity of FeII ions in the cluster, the short-range intracluster interaction between these ions via the optical phonon field is included as well. The model takes into consideration also the spin–orbit coupling operating within the cubic 5T2(t24e2) term of the hs-FeII ions. For cluster 2 the Heisenberg-type exchange interaction between the hs-FeII and ls-FeIII ions is taken into account. The competition between short- and long-range interactions is shown to ...

Synthesis, characterization, crystal structures and in vitro antistaphylococcal activity of organotin(IV) derivatives with 5,7-disubstituted-1,2,4-triazolo[1,5-a]pyrimidine

New organotin(IV) complexes of 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine ( dbtp) and 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine ( dptp) with 1:1 and/or 1:2 stoichiometry were synthesized and investigated by X-ray diffraction, FT-IR and 119Sn Mössbauer in the solid state and by 1H and 13C NMR spectroscopy, in solution. Moreover, the crystal and molecular structures of Et 2SnCl 2(dbtp) 2 and Ph 2SnCl 2(EtOH) 2(dptp) 2 are reported. The complexes contain hexacoordinated tin atoms: in Et 2SnCl 2(dbtp) 2 two 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine molecules coordinate classically the tin atom through N(3) atom and the coordination around the tin atom shows a skew trapezoidal structure with axial ethyl groups. In Ph 2SnCl 2(EtOH) 2(dptp) 2 two ethanol molecules coordinate tin through the oxygen atom and the 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine molecules are not directly bound to the metal center but strictly H-bonded, through N(3), to the OH group of the ethanol moieties; Ph 2SnCl 2(EtOH) 2(dptp) 2 has an all-trans structure and the C–Sn–C fragment is linear. On the basis of Mössbauer data, the 1:2 diorganotin(IV) complexes are advanced to have the same structure of Et 2SnCl 2(dbtp) 2, while Me 2SnCl 2(dptp) 2 to have a regular all-trans octahedral structure. A distorted cis-R 2 trigonal bipyramidal structure is assigned to 1:1 diorganotin(IV) complexes. The in vitro antibacterial activities of the synthesized complexes have been tested against a group of reference pathogen micro-organisms and some of them resulted active with MIC values of 5 μg/mL, most of all against staphylococcal strains, which shows their inhibitory effect.

Stereomutation in Trigonal‐Bipyramidal Systems: A Unified Picture

Same difference: Berry pseutorotation (BPR) and Ugi turnstile rotation, which are generally treated as two distinctly different mechanisms for rearrangement of trigonal-bipyramidal structures, have been shown to be equivalent. Alternative mechanisms consist of sequences of pseudorotations proceeding in a single step.

Computational study on the mechanisms of action of the potential anticancer drug trans-isopropylaminedimethylaminedichloroplatinum (trans-IPADMADP) and its cis isomer with DNA purine bases

The monofunctional and bifunctional bindings of the potential anticancer drug trans-isopropylaminedimethylaminedichloroplatinum (trans-IPADMADP) and its cis isomer to purine base in DNA are explored by using density functional theory and IEF-PCM solvation models. The computed lowest free energy barrier in the aqueous solution is 14.0/11.6kcal/mol (from trans-Pt-chloroaqua complex to trans-/cis-monoadduct) for guanine(G), and 11.7/13.3kcal/mol (from trans-Pt-chloroaqua complex to trans-/cis-monoadduct) for adenine(A). Our calculations demonstrate that the trans reactant complexes (or isolated reactants) can generate trans- or cis-monoadducts via similar trigonal bipyramidal transition state structures, suggesting that the monoadducts can subsequently close to form the bifunctional intrastrand Pt–DNA adducts and simultaneously distort DNA in the similar way as cisplatin. Our calculations show that Pt(isopropylamine)(dimethylamine)G22+ head-to-head path has the lowest free energy of activation at 17.6kcal/mol, closely followed by the Pt(isopropylamine)(dimethylamine)GA2+ head-to-head path at 19.6kcal/mol when the monofunctional cis-Pt-G complex serves as the reactant; while the Pt(isopropylamine)(dimethylamine)G22+ head-to-tail adduct has the lowest barrier of 20.5kcal/mol, closely followed by the Pt(isopropylamine)(dimethylamine)GA2+ head-to-tail adduct at 23.0kcal/mol if the monofunctional trans-Pt-G complex is the reactant.The calculated relatively lower activation energy barrier than that of cisplatin theoretically confirm that trans-[PtCl2(isopropylamine)(dimethylamine)] is a potential anticancer drug as described by experiment.

Et2SnCl2 · H2O and the Trigonal–Bipyramidal Transition State of a SN2 Reaction

The title compound Et2SnCl2 · H2O was prepared and characterized by IR-spectroscopy and single crystal X-ray diffraction, showing the typical trigonal bipyramidal structure of a SN2 transition state with the water molecule in an axial position. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. GRAPHICAL ABSTRACT

Interaction of organotin(IV) moieties with nucleic acid constituent: Synthesis, structural characterization and anti-inflammatory activity of tri-i-propyltin(IV) and diorganotin(IV) derivatives of guanosine

Abstract Tri- i -propyltin(IV) and diorganotin(IV) derivatives of guanosine of the general formulae, i -Pr 3 Sn(HGuO).H 2 O and [R 2 Sn(O)(HGuO).H 2 O] n , where R = Me, n -Oct and Ph; H 2 GuO = Guanosine, have been synthesized by either sodium salt or azeotropic removal of water method. The bonding and coordination behavior in these derivatives are discussed on the basis of FT-IR, multinuclear 1 H, 13 C and 119 Sn NMR and 119 Sn Mossbauer spectroscopic studies. These investigations suggest that guanosine acts as monoanionic monodentate coordinating through O-2′ of the ribofuranose group. Diorganotin(IV) derivatives of guanosine have a polymeric structure with Sn O Sn bridges and cis -disposition of the organic groups in a distorted trigonal-bipyramidal geometry around the tin atom. 119 Sn Mossbauer and 119 Sn NMR spectral data of tri- i -propyltin(IV) derivative support a penta-coordinate distorted trigonal-bipyramidal structure having equatorial organic groups, and involving a water molecule and O-2′ of the ribofuranose group in the axial positions. Some extent of intermolecular hydrogen-bonding involving water or (OH) groups leading to some degree of polymerization could not be ignored. Tri- i -propyltin(IV) and diorganotin(IV) derivatives of guanosine exhibited very low anti-inflammatory activity (~ 7.51–9.21% inhibition) at 40 mg kg − 1 dose and LD 50 values > 200 mg kg − 1 in albino rats.

Of the Ortho Effect in Palladium/Norbornene-Catalyzed Reactions: A Theoretical Investigation

Mechanistic questions concerning palladium and norbornene catalyzed aryl-aryl coupling reactions are treated in this paper: how aryl halides react with the intermediate palladacycles, formed by interaction of the two catalysts with an aryl halide, and what is the rational explanation of the "ortho effect" (caused by an ortho substituent in the starting aryl halide), which leads to aryl-aryl coupling with a second molecule of aryl halide rather than to aryl-norbornyl coupling. Two possible pathways have been proposed, one involving aryl halide oxidative addition to the palladacycle, the other passing through a palladium(II) transmetalation, also involving the palladacycle, as previously proposed by Cardenas and Echavarren. Our DFT calculations using M06 show that, in palladium-catalyzed reaction of aryl halides, not containing ortho substituents, and norbornene, the intermediate palladacycle formed has a good probability to undergo transmetalation, energetically favored over the oxidative addition leading to Pd(IV). The unselective sp(2)-sp(2) and sp(2)-sp(3) coupling, experimentally observed in this case, can be explained in the framework of the transmetalation pathway since the energetic difference between aryl attack onto the aryl or norbornyl carbon of the palladacycle intermediate is quite small. On the other hand, according to the experimentally observed "ortho effect", selective aryl-aryl coupling only occurs in the reactions of ortho-substituted metallacycles. The present work offers the first possible rationalization of this finding. These in situ formed palladacycles containing an ortho substituent could more easily undergo oxidative addition of an aryl halide rather than reductive elimination from the transmetalation intermediate as a result of a steric clash in the transition state of the latter. The now energetically accessible Pd(IV) intermediate, featuring a Y-distorted trigonal bipyramidal structure, can account for the reported selective aryl-aryl coupling through a reductive elimination which is easier than aryl-norbornyl coupling. Thus, the steric effect represents the main factor that dictates the energetic convenience of the system to follow the Pd(IV) or the transmetalation pathway. Ortho substituents cause a higher energy transition state for reductive elimination from the transmetalation intermediate than for oxidative addition to the metallacycle palladium(II) and the pathway based on the latter predominates.

Chemistry of Four-Membered Ring Compounds Containing a Hypervalent Sulfur Atom and a Heteroatom at the Neighbor Positions

Title compounds containing tetracoordinated and pentacoordinated sulfur together with oxygen, nitrogen, or sulfur were successfully synthesized as stable compounds. They contain the Martin ligand, which is well known to be able to stabilize such highly coordinated main group compounds. X-ray crystallographic analyses revealed that they have distorted trigonal bipyramidal (TBP) or pseudo-TBP structures. In marked contrast to group 13–15 element analogues, which afford the corresponding alkenes upon heating, thermolyses of compounds bearing an oxygen or nitrogen atom gave the corresponding oxiranes or aziridine, suggesting the possibility that these compounds are intermediates of the Corey-Chaykovsky reaction of sulfur ylides with carbonyl compounds or imines. Thermolysis of 1λ4,2-dithietanes also gave the corresponding thiiranes. The stereochemistry (retention of configuration) of formation of these three-membered ring compounds is also described.

A DFT study of a novel oxime anticancer trans platinum complex: Monofunctional and bifunctional binding to purine bases

The first and second substitution reactions binding of the anticancer drug trans-[Pt((CH3)2CNOH)((CH3)2CHNH2)Cl2] to purine bases were studied computationally using a combination of density functional theory and isoelectric focusing polarized continuum model approach. Our calculations demonstrate that the trans monoaqua and diaqua reactant complexes (RCs) can generate either trans- or cis-monoadducts via identical or very similar trans trigonal-bipyramidal transition-state structures. Furthermore, these monoadducts can subsequently close by coordination to the adjacent purine bases to form 1,2-intrastrand Pt-DNA adducts and eventually distort DNA in the same way as cisplatin. Thus, it is likely that the transplatin analogues have the same mechanism of anticancer activity as cisplatin. For the first substitutions, the activation free energies of monoaqua complexes are always lower than that of diaqua complexes. The lowest activation energy for monoaqua substitutions is 16.2 kcal/mol for guanine and 16.5 kcal/mol for adenine, whereas the lowest activation energy for diaqua substitutions is 17.1 kcal/mol for guanine and 25.9 kcal/mol for adenine. For the second substitutions, the lowest activation energy from trans-monoadduct to trans-diadduct is 19.1 kcal/mol for GG adduct and 20.7 kcal/mol for GA adduct, whereas the lowest activation energy from cis-monoadduct to cis-diadduct is 18.9 kcal/mol for GG adduct and 18.5 kcal/mol for GA adduct. In addition, the first and second substitutions prefer guanine over adenine, which is explained by the remarkable larger complexation energy for the initial RC in combination with lower activation energy for the guanine substitution. Overall, the hydrogen-bonds play an important role in stabilizing these species of the first and second substitutions. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Coordination isomerism of the complex of o-methoxybenzoyl chloride with tetrachlorostannane. The results of ab initio calculations

Quantum-chemical calculations of three isomers of the o-methoxybenzoyl chloride complex with tetrachlorostannane and of their components were performed applying the RHF/3-21G* and MP2/3-21G* methods. It was found that a complex with trigonal-bipyramidal structure is formed, its formation occurred through the interaction of ester (not carbonyl) oxygen atom with tin atom. This complex eventually is transformed into the energetically more favorable cis-octahedral complex of the same composition. The tin atom in the latter complex interacts with two oxygen atoms. The reasons for the formation of energetically unfavorable complex of trigonal-bipyramidal structure is the almost equal probability of the existence of various possible forms of o-methoxybenzoyl chloride and therefore higher probability of the Sn atom to interact with the ester oxygen atom possessing a much more negative charge than the carbonyl oxygen.

Synthesis, structural characterization, and in vitro antimicrobial properties of salicylate and pyrazoline complexes of bismuth(III)

Displacement reactions of dichlorobismuth(III)pyrazolinates with oxygen donors such as sodium salicylate and acetate in 1 : 1 and 1 : 2 molar ratio in refluxing anhydrous benzene yields (C12H15N2OX)Bi(C6H4O3), (CH3COO)BiCl(C15H12N2OX), and (CH3COO)2Bi(C15H12N2OX) [C12H15N2OX = 3(2′-hydroxyphenyl)-5-(4-X-substituted phenyl) pyrazoline X = H in 1,5,9, CH3 in 2,6,10, OCH3 in 3,7,11, and Cl in 4,8,12, respectively, (C6H4O3) = salicylate and (CH3COO) = acetate]. Newly synthesized derivatives are brown solids, soluble in organic solvents like benzene, chloroform, and acetone. The compounds have been characterized by elemental analyses (C, H, N, Cl, and Bi), molecular weight measurements, and spectral (IR, 1H NMR, 13C NMR) studies. The (C12H15N2OX) and (C6H4O3) are bidentate while (CH3COO) is monodentate to bismuth(III), leading to a distorted trigonal bipyramidal structure. The complexes were screened against different bacteria and fungi showing potential antibacterial and antifungal activities.