Central Sn Research Articles

How tin metal prevents verdoheme ring opening? Comparative study of various nucleophiles

The inhibitory role of tin metal in the verdoheme ring opening mechanism has been investigated using B3LYP method. Nucleophilic additions of OH −, NH 2 −, and CN − to three possibly six, five, and four coordinate verdoheme complexes of tin(IV) have been employed as model reactions. The results of calculations suggest that nucleophilic attacks to tin(IV) verdohemes does not result in the opening of the macrocycle, being in excellent agreement with experimental reports. In six coordinate tin(IV) verdoheme complex the formation of open ring helical complexes is favorable thermodynamically but not kinetically. In this coordination state, tin has no coordination role. Thus, direct addition of nucleophiles to the positive oxo-carbon centers and formation of a closed ring hydroxy compound is proposed for blocking the conversion of verdoheme to biliverdin. Contrary to zinc and iron analogues, in five and four coordinate pathways, such addition to oxo-carbons does not proceed toward stable open chain helical products. This is because formation of these complexes is unfavorable both thermodynamically and kinetically. It has been determined that in the latter pathways a closed ring compound is formed as final product by adding nucleophiles to tin atoms. It has been thus shown that high affinity of ligands for binding to both the fifth and sixth coordination sites of the highly charged Sn(IV) center is responsible for inhibiting the conversion of verdoheme complexes to biliverdin compounds. Results indicate that high tendency of tin(IV) metal to increase coordination state plays a crucial role in preventing verdoheme ring opening. These key points have been corroborated with the results obtained from molecular orbital calculations.

FEEDBACK EFFECTS OF FIRST SUPERNOVAE ON THE NEIGHBORING DARK MATTER HALOS

The first-generation stars in the $\Lambda$CDM universe are considered to have formed in dark halos with total masses in the range $\sim 10^{5}-10^{7}M_sun$ at $z \sim 20-50$. These stars expected to be very massive and in some cases they end their lives as the first supernovae (SNe). We explore the problem of whether star formation in low mass dark halos (< 10^{7} M_sun) was triggered or suppressed by the SN feedback from neighboring star-forming halos. We take into consideration mainly two effects by the SN shock: one is the evacuation of gas components from the halos and the other is the promotion of H_2 formation because of the enhanced ionization degree by shock heating. Combining above effects, we find that the star formation activities in the neighboring dark matter halos (M < 10^{7} M_sun) are basically suppressed in case they are located close to the SN center, because of the gas evacuation effect. The critical distance within which the gas is blown away falls within the range $\sim 0.3-1.5$kpc depending on the SN energy and the halo mass. In addition, we find there is very little window in the parameter space where star formation activities in dark halos are induced or promoted by neighboring SN.

Silver aggregates and twofold-coordinated tin centers in phosphate glass: A photoluminescence study

The optical properties of silver species in various oxidation and aggregation states and of tin centers in melt-quenched phosphate glasses have been assessed by optical absorption and photoluminescence (PL) spectroscopy. Glasses containing silver and tin, or either dopant, were studied. Emission and excitation spectra along with time-resolved and temperature-dependent PL measurements were employed in elucidating the different emitting centers observed and investigating on their interactions. In regard to silver, the data suggests the presence of luminescent single Ag + ions, Ag +–Ag + and Ag +–Ag 0 pairs, and nonluminescent Ag nanoparticles (NPs), where Ag +–Ag 0→Ag +–Ag + energy transfer is indicated. Tin optical centers appear as twofold-coordinated Sn centers displaying PL around 400 nm ascribed to triplet-to-singlet electronic transitions. The optically active silver centers were observed in glasses where 8 mol% of both Ag 2O and SnO, and 4 mol% of Ag 2O were added. Heat treatment (HT) of the glass with the high concentration of silver and tin leads to chemical reduction of ionic silver species resulting in a large volume fraction of silver NPs and the vanishing of silver PL features. Further characterization of such heat-treated glass by transmission electron microscopy and X-ray photoelectron spectroscopy appears consistent with silver being present mainly in nonoxidized form after HT. On the other hand, HT of the glass containing only silver results in the quenching of Ag +–Ag 0 pairs emission that is ascribed to nonradiative energy transfer to Ag NPs due to the positioning of the pairs near the surface of NPs during HT. In this context, an important finding is that a faster relaxation was observed for this nanocomposite in relation to a heat-treated glass containing both silver and tin (no silver pairs) as revealed by degenerate four-wave mixing spectroscopy. Such result is attributed to Ag NP→Ag +–Ag 0 plasmon resonance energy transfer. The data thus indicates that energy transfer between Ag +–Ag 0 pairs and NPs is bi-directional.

Theoretical investigations on the hydrolysis pathway of tin verdoheme complexes: elucidation of tin’s ring opening inhibition role

In order to obtain a better molecular understanding of inhibitory role of tin metal in the verdoheme ring opening process, hydrolysis of three possibly six, five, and four coordinate verdoheme complexes of tin(IV) and (II) have been studied using DFT method. The results of calculations indicate that, in excellent accord with experimental reports, hydrolysis of different possibly coordinated tin(IV) and (II) verdohemes does not lead to the opening of the macrocycle. Contrary to iron and zinc verdohemes, in five and four coordinate verdoheme complexes of tin(IV) and (II), formation of open ring helical complexes of tin are unfavorable both thermodynamically and kinetically. In these pathways, coordination of hydroxide nucleophile to tin metal due to the highly charged, exclusive oxophilicity nature of the Sn center, and high affinity of Sn to increase coordination state are proposed responsible as inhibiting roles of tin via the ring opening. While, in saturated six coordinate tin(IV) and (II) verdoheme complexes the ring opening of tin verdohemes is possible thermodynamically, but it is not predicted to occur from a kinetics point of view. In the six coordinate pathway, tin plays no coordination role and direct addition of hydroxide nucleophile to the positive oxo-carbon centers and formation of closed ring hydroxy compounds is proposed for preventing the verdoheme ring opening. These key points and findings have been corroborated by the results obtained from atomic charge analysis, geometrical parameters, and molecular orbital calculations. In addition, the results of inhibiting ring opening reaction of tin verdoheme complexes could support the great interest of tin porphyrin analogues as pharmacologic means of chemoprevention of neonatal jaundice by the competitive inhibitory action of tin porphyrins on heme oxygenase.

Structural and spectral studies of 3-(2-hydroxyphenylimino)-1-phenylbutan-1-one and its diorganotin(IV) complexes

Abstract Two diorganotin(IV) complexes of the general formula R2Sn[Ph(O)C CH-C(Me) N–C6H4(O)] (R = Ph, 1a; R = Me, 1b) have been synthesized from the corresponding diorganotin(IV) dichlorides and the ligand, 3-(2-hydroxyphenylimino)-1-phenylbutan-1-one (1) in methanol at room temperature in presence of triethylamine. Both compounds have been characterized by elemental analyses, IR and 1H, 13C, 15N, 119Sn NMR spectra. The structures of the free ligand and the complexes have been confirmed by single crystal X-ray diffraction. There are three independent molecules in the crystal structure of the ligand 1 and in all three the O-bound proton is transferred to the imine nitrogen and makes an intramolecular N–H⋯O hydrogen bond with the carbonyl oxygen. In turn this makes an intermolecular hydrogen bond with the phenolic H atom. The crystal structure of 1 is trigonal and a new polymorph; triclinic and monoclinic forms have already been published. In 1a, the central tin atom adopts distorted trigonal–bipyramidal coordination geometry whereas in dimeric 1b it is distorted octahedral when including the intermolecular Sn–O(phenolic) bond [2.7998(20) A]. The δ (119Sn) values for the complexes 1a and 1b are −306.6 and −127.9 ppm, respectively, thus indicating penta-coordinated Sn centres in solution.

Pushing and Pulling a Sn Ion through an Adsorbed Phthalocyanine Molecule

Molecule-based functional devices on surfaces may take advantage of bistable molecular switches. The conformational dynamics and efficiency of switches are radically different on surfaces compared to the liquid phase. We present a design of molecular layers which enables bistable switching on a surface and, for the first time, demonstrate control of a single switch in a dense and ordered array at the spatial limit. Up and down motion of a central Sn ion through the frame of a phthalocyanine molecule is achieved via resonant electron or hole injection into molecular orbitals.

Organotin meclofenamic complexes: Synthesis, crystal structures and antiproliferative activity of the first complexes of meclofenamic acid – Novel anti-tuberculosis agents

The complexes [Me(2)(Meclo)SnOSn(Meclo)Me(2)](2) (2) and [Ph(3)Sn(Meclo)] (3) where HMeclo is meclofenamic acid, N-(2,6-dichloro-m-tolylanthranilic acid)], have been prepared and structurally characterized by means of vibrational, (1)H and (13)C NMR spectroscopies. The crystal structure of complexes (2) and (3) have been determined by X-ray crystallography. Three distannoxane rings are present to the dimeric tetraorganodistannoxane of planar ladder arrangement of (2). The structure is centro symmetric and features a central rhombus Sn(2)O(2) unit two additional tin atoms linked at the oxygen atoms. Five- and six-coordinated tin centers are present in the dimer distannoxane. X-ray analysis of (3) revealed a penta-coordinated structure containing Ph(3)Sn coordinated to the chelated carboxylato group. The polar imino hydrogen atom participates in intra-molecular hydrogen bonds. Complexes (2) and (3) are self-assembled via pi-->pi, C-H-pi, stacking interactions and intra-molecular hydrogen bonds. Meclofenamic acid and [Ph(3)Sn(Meclo)] have been evaluated for antiproliferative activity in vitro against three human cancer cell lines: MCF-7 (human breast cancer cell line), T24 (bladder cancer cell line), A-549 (non-small cell lung carcinoma) and a mouse L-929 (a fibroblast-like cell line cloned from strain L). The [Ph(3)Sn(Meclo)] complex exhibited high cytotoxic activity against all the cancer cell lines. Meclofenamic and [Ph(3)Sn(Meclo)] were tested for anti-mycobacterial activity against Mycobacterium tuberculosis H37Rv. The [Ph(3)Sn(Meclo)] complex was found to be a promising anti-mycobacterial lead compound, displaying high activity against M. tuberculosis H37Rv.

Reactivity in the confined spaces of zeolites: the interplay between spectroscopy and theory to develop structure–activity relationships for catalysis

The Lewis acid properties of a series of isolated and well-defined Sn centers in different micro- and mesoporous materials have been investigated by means of DFT calculations and IR spectroscopy of probe molecules, and the results have been related to the experimentally measured catalytic activity of these materials for different reactions. Different types of Sn centers have been detected and modelled: inactive fully coordinated Sn atoms in framework positions that weakly interact with Lewis bases, and highly active strong Lewis acid sites associated with Sn centers with one or two hydrolyzed Sn-O-Si bridges. The relative amount of strong and weak sites depends on the zeolite structure, and can be modified by the catalyst pre-treatment conditions. On the other hand, it has been established that Sn-containing mesoporous materials obtained either by direct synthesis or by post-synthesis incorporation of Sn, show a similar distribution of centers. Finally, the influence of solvent and free space available around the active site on the diastereoselectivity of the cyclization of citronellal to isopulegol were investigated, and some hints were obtained on how to improve the catalyst performance.

Labile ligands on some Lewis super acids: a computational study

Lewis super-acids, like Sn(OTf)(4) or In(OTf)(3), OTf = CF(3)SO(3)(-), are efficient catalysts for cycloisomerization reactions. We report here a study on the coordination of ligands (or of solvent molecules) around such catalysts at density functional theory level. Using the Sn-based compound as an example, we consider the interaction with several molecules, usually nearby in reaction conditions. These include nitromethane, esters and diesters, dimethylsulfoxide, and so on. We establish a ladder of interaction strengths and show that dimethylsulfoxyde molecules can displace triflate ligands from the metallic center. This leads to the main conclusions that solvent molecules directly coordinate Sn centers and that non-coordinating triflates are potentially free in solution despite their anionic characteristic.

Complete 1H and 119Sn NMR spectral assignment for an asymmetric di[dihydroxotin(IV)] bis‐porphyrin supramolecular host and its corresponding tetraacetato complex

The full (1)H and (119)Sn NMR spectral assignments for a di[dihydroxotin(IV)] bis-porphyrin supramolecular host I and for the di[diacetatotin(IV)] complex II are presented. Despite the lack of varied chemical functionality in these molecules, all of their 64 proton environments are non-equivalent. This is due to the asymmetry afforded by the Tröger's base (methanodiazocine) bridge between the porphyrin and quinoxalinoporphyrin macrocycles. The methanodiazocine bridge imparts chirality and concavity on the host framework and the quinoxalino link to one porphyrin macrocycle results in a negation of C(2) symmetry. The anisotropy of the aromatic porphyrin and quinoxalinoporphyrin macrocycles results in good dispersion for all 60 signals of the host framework and for the four ligands bound in the axial positions of the tin(IV) centres. The full assignment of the (1)H NMR spectra for these systems was achieved using dqf-COSY, NOESY, ROESY, (1)H-(119)Sn HMQC, (1)H-(13)C HSQC and (1)H-(13)C HMBC spectroscopy at temperatures that optimised dispersion. The (1)H-(119)Sn HMQC was particularly useful in this assignment. The (119)Sn chemical shift is sensitive to the functionality of the porphyrin and to the nature of the axial ligation, and the (119)Sn centre couples to both the ligand protons and the beta-pyrrolic protons. This allows unequivocal identification of the spin systems associated with each metal centre.

Synthesis, characterization and catalytic properties of diorganotin derivatives. Crystal and molecular structure of the first complex of 2-(2-methyl-3-nitroanilino)benzoic acid of 1,2:3,4-di-μ2-2-(2-methyl-3-nitroanilino)benzoato- O, O-1,3-bis-2-(2-methyl-3-nitroanilino)benzoato- O-1,2,4:2,3,4-di-μ3-oxo-tetrakis[di-methyltin(IV)

The complexes [Me 2(MNAB)SnOSn(MNAB)Me 2] 2 ( 2) and [Me 2Sn(MNAB) 2] ( 3), where HMNAB is 2-(2-methyl-3-nitroanilino)benzoic acid, ( 1), have been prepared and structurally characterized by means of vibrational, 1H and 13C NMR spectroscopies. The crystal structure of [Me 2(MNAB)SnOSn(MNAB)Me 2] 2 has been determined by X-ray crystallography. Three distannoxane rings are present to the dimeric tetraorganodistannoxane of planar ladder arrangement. The structure is centro-symmetric and features a central rhombus Sn 2O 2 unit with two additional tin atoms linked at the O atoms. Six-coordinated tin centers are present in the dimmer distannoxane. This structure is self-assembled in one dimensional infinite chain via intermolecular hydrogen bonds, π → π and C–H → π stacking interactions. The polar imino hydrogen atom participates in intramolecular hydrogen bonds. The catalytic activity of the prepared complexes in transesterification reactions has been studied. The diorganotin complexes efficiently catalyze the transesterification reaction of 2-phenylethanol without addition of free ligand or any promoting additive.

Catena-Poly[[diphenylpropyltin(IV)]-μ-chloroacetato-κ2O:O′

The title compound, [Sn(C3H7)(C6H5)2(C2H2ClO2)]n, comprises polymeric carboxyl­ate-bridged spiral chains with two monomer formula units in the asymmetric unit. Both Sn centres exhibit similar distorted trigonal–bipyramidal [C3SnO2] coordination, with the O atoms of the carboyxlate ligands in trans positions.

Synthesis, spectroscopic characterization, and crystal structures of two chlorodiorganotin(IV) 4-(2-methoxyphenyl)piperazine-1-carbodithioates

Two chlorodiorganotin(IV) complexes of 4-(2-methoxyphenyl)piperazine-1-carbodithioate (MPPDA) have been synthesized by 1:1 mole-ratio reactions of the parent acid (MPPDAH) with Me 2SnCl 2 or Et 2SnCl 2 in dry methanol. The products have been characterized by Raman and multinuclear NMR ( 1H, 13C and 119Sn) spectroscopy, elemental analysis, and mass spectrometry. Single-crystal X-ray diffraction studies indicate that both complexes have distorted trigonal bipyramidal geometries around the central Sn atom.

Bis(μ-disulfur dinitrido)bis[diphenyltin(IV)

The title compound, [Sn2(C6H5)4(N2S2)2], exists as a centrosymmetric binuclear dimer with the SnIV centres in distorted trigonal bipyramidal geometry and a central Sn2N2 core.

Structural chemistry of organotin(IV) complexes

The amazing structural diversity in organotin compounds is discussed in the systems containing -O and -S donor ligands. It is demonstrated that there exist a fascinating range of structural diversity for organotin(IV) complexes, including differences in coordination number and molecular geometry. The difference in structure is correlated with the nature of tin and ligand bonded R groups. Despite the large number of different structures found in organotin(IV) carboxylates, there is limited range of coordination geometries about the Sn atom. The four coordinated Sn atom in triorganotin(IV) complexes is invariably distorted tetrahedral and five coordinated Sn is distorted trigonal bipyramidal. A large range has been observed for diorganotin carboxylate structures, where five, six and seven coordinate geometries have been reported. The Sn atom in mono-organotin has only been demonstrated to exist in distorted octahedral geometries (the single exception being a pentagonal bipyramidal geometry). In the case of organotin(IV) complexes of S donor ligands, it has been shown that there exists a rich diversity in Sn atom geometries and coordination modes of the sulfur donor ligands themselves. As in related carboxylate systems, the assignment of coordination numbers to the Sn centers in some compounds is controversial. As a general trend, it has been shown that, the overall coordination number at the Sn atom decreases with the increasing number of organic substituents at the Sn atom. This phenomenon is usually achieved by increased asymmetry in the mode of coordination of the sulfur donor ligands.

Re-visiting of 5-[( E)-2-(aryl)-1-diazenyl]-quinolin-8-ol with tweaking of Sn–Ph groups: Synthesis, spectroscopic characterization and X-ray crystallography

Reactions of sodium 5-[( E)-2-(aryl)-1-diazenyl]quinolin-8-olates (LH, where the aryl group is an R-substituted phenyl ring such that for L 1H: R = H; L 2H: R = 2′-CH 3; L 3H: R = 3′-CH 3; L 4H: R = 4′-CH 3; L 5H: R = 4′-OCH 3 and L 6H: R = 4′-OC 2H 5) with Ph 3SnCl in a 1:1 molar ratio yielded complexes of composition Ph 3SnL. The complexes have been characterized by 1H, 13C, 119Sn NMR, IR and 119mSn Mössbauer spectroscopic techniques in combination with elemental analyses. The crystal structures of Ph 3SnL 1 · 0.5C 6H 6 ( 1), Ph 3SnL 2 ( 2), Ph 3SnL 5 · C 6H 6 ( 5) and Ph 3SnL 6 · 0.5C 6H 6 ( 6) were determined. The results of the X-ray studies indicated that the benzene solvated compounds 1, 5 and 6 are distorted square pyramid, with one of the phenyl C atoms in the apex while the ligand arrangement around central Sn atom in 2 is distorted trigonal-bipyramidal, with a phenyl C and the oxinato N atoms in axial positions.

Di-μ(3)-oxido-bis-(μ(2)-quinaldato-κO:O)-bis-(quinaldato-κN,O)tetra-kis[di-n-butyl-tin(IV)

The title tetra­nuclear SnIV complex, [Sn4(C4H9)8(C10H6NO2)4O2], is a cluster built up by inversion symmetry around the central Sn2O2 ring. The coordination geometries of the Sn atoms involved can be classified into two types: the five-coordinate Sn atoms of the central Sn2O2 core have a trigonal–bipyramidal geometry, with axial positions occupied by a μ3-O atom and a μ2-O atom belonging to the nonchelating quinaldate ligand. The peripheral Sn atoms are six-coordinate, with a distorted octa­hedral geometry. The methyl group of an n-butyl ligand is disordered over two sites, with occupancies of 0.643 (12) and 0.357 (12).

(4-Amino-3-phenyl-5-thioxo-4,5-dihydro-1H-1,2,4-triazol-1-yl)triphenyltin(IV)

In the title complex, [Sn(C6H5)3(C8H7N4S)], all bond lengths and angles show normal values. The Sn centre is four-coordinated by three C atoms [Sn—C 2.119 (6)–2.133 (6) Å] and one N atom [Sn—N 2.107 (5) Å] in a distorted tetra­hedral geometry. The crystal packing exhibits no classical inter­molecular hydrogen bonds.

Enhanced UV-excited luminescence of europium ions in silver/tin-doped glass

Glasses containing silver, tin and europium were prepared by the melt-quenching technique with silver nanoparticles (NPs) being embedded upon heat treatment (HT). An intensification of Eu 3+ ions emission was observed for non-resonant excitation around 270 nm, corresponding to UV absorption in the material. Optical measurements suggest that light absorption occurs at single Ag + ions and/or twofold-coordinated Sn centers followed by energy transfer to europium which results in populating the 5D 0 emitting state in Eu 3+. After HT at 843 K, a quenching effect is observed on Eu 3+ luminescence with increasing holding time in the 350–550 nm excitation range. The quenching effect shows with the presence of Ag NPs which may provide multipole radiationless pathways for excitation energy loss in europium ions.

Static and dynamic disorder in organotin compounds: A bis(amido)stannylene coordinated by N, N′-diisopropyl-1,8-diamidonaphthalene

The root-mean-square amplitude of vibration of the tin atom in the bis(amido)stannylene Sn[1,8-(N i Pr) 2C 10H 6] has been determined from temperature-dependent 119Sn Mössbauer effect measurements over the range 98 < T < 225 K and compared with the U i, j value extracted from a single crystal X-ray diffraction study. The large difference in these values (at 238 K) is associated with the flexibility in the bonding between the Sn center and chelating diamido ligand in this complex.