Synthesis and structural characterization of neutral higher-coordinate silicon(IV) complexes with tridentate dianionic chelate ligands

The neutral pentacoordinate silicon(IV) complexes 8 and 9 with an SiO2N3 skeleton and the neutral hexacoordinate silicon(IV) complex 10.1/2 CH3CN with an SiO4N2 skeleton were synthesized, starting from tetra(cyanato-N)silane or tetra(thiocyanato-N)silane. Compounds 8 and 9 contain one tridentate dianionic ligand derived from 4-[(2-hydroxyphenyl)amino]pent-3-en-2-one and two monodentate singly charged cyanato-N or thiocyanato-N ligands bound to the silicon(IV) coordination center, whereas the silicon(IV) center of 10 is coordinated by two of these tridentate dianionic ligands. All compounds were characterized by single-crystal X-ray diffraction and solid-state and solution NMR spectroscopy. To get more information about the stereochemistry of the compounds studied, the experimental investigations were complemented by computational studies.     

Neutral hexa- and pentacoordinate silicon(IV) complexes with SiO(6) and SiO(4)N skeletons

The neutral heteroleptic hexacoordinate silicon(IV) complexes 4 and 5 (SiO(6) skeletons) and the neutral pentacoordinate silicon(IV) complexes 7-9 (SiO(4)N skeletons) were synthesized, starting from the hexacoordinate precursor 2 and the pentacoordinate precursor 6, respectively. In these reactions, two monoanionic cyanato-N ligands are replaced by one dianionic bidentate O,O-chelate ligand. Compounds 4, 5, and 7-9 were characterized by single-crystal X-ray diffraction and solid-state and solution NMR spectroscopy. The chiral silicon(IV) complexes 4, 5, 7, and 8 were obtained as racemic mixtures, whereas 9 was isolated as a cocrystallizate consisting of the two diastereomers, (C,S)-9 and (A,S)-9 (ratio 1:1). The stereodynamics of 5 and 8 were studied by variable-temperature (1)H NMR experiments.     

Dianionic complexes with hexacoordinate silicon(IV) or germanium(IV) and three bidentate ligands of the hydroximato(2-) type: syntheses and structural characterization in the solid state

Reaction of Si(OMe)(4) with acetohydroxamic acid or benzohydroxamic acid and HNMe(2) (molar ratio 1:3:2) in MeCN yielded dimethylammonium fac-tris[acetohydroximato(2-)]silicate (fac-5) and N,N-dimethylacetamidinium fac-tris[benzohydroximato(2-)]silicate (fac-8), respectively. Reaction of Si(OMe)(4) with benzohydroxamic acid and HNMe(2) (molar ratio 1:3:2) or ethane-1,2-diamine (molar ratio 1:3:1) in MeOH gave dimethylammonium fac-tris[benzohydroximato(2-)]silicate-methanol (fac-6.MeOH) and ethane-1,2-diammonium mer-tris[benzohydroximato(2-)]silicate-dimethanol (mer-9.2MeOH), respectively. Reaction of Ge(OMe)(4) with benzohydroxamic acid and HNMe(2) (molar ratio 1:3:2) in MeOH resulted in the formation of dimethylammonium fac-tris[benzohydroximato(2-)]germanate-methanol (fac-7.MeOH). Single-crystal X-ray diffraction studies showed that the Si(Ge)-coordination polyhedra of the racemic hexacoordinate silicon (germanium) compounds fac-5, fac-6.MeOH, fac-7.MeOH, fac-8, and mer-9.2MeOH are distorted octahedra. All compounds were additionally characterized by solid-state VACP/MAS NMR studies ((13)C, (15)N, (29)Si). The structural investigations were complemented by computational studies of the dianions of fac-5 and mer-5.     

Synthesis and characterization of neutral cis-hexacoordinate bis(beta-diketonate) silicon(IV) complexes

Three new neutral cis-hexacoordinate bis(beta-diketonato) silicon(IV) complexes, (thd)2SiX2, where X = Me (1), tBuO (2), and tAmO (3), and thd = 2,2,6,6-tetramethyl-3,5-heptanedionato, were synthesized in high yield. Single crystal X-ray crystallographic analysis revealed that 1 was monomeric with cis-hexacoordinate octahedral geometry on the silicon and oxygen atoms. Crystal data: empirical formula C24H46O4Si, crystal system monoclinic; space group P2(1)/n; unit cell dimensions a = 10.4195(5) A, b = 19.7297(10) A, c = 13.6496(7) A; beta = 102.6590(10) degrees; Z = 4. Variable temperature NMR confirmed (thd)2SiX2 maintained cis-geometry in solution by observing two distinct methyl proton resonances (of thd) at room temperature or low temperatures. These compounds show potential for use as low temperature silicon oxide CVD precursors for transition metal silicate high kappa gate dielectrics.     

Synthesis and structural characterisation of neutral pentacoordinate silicon(IV) complexes with a tridentate dianionic N,N,S chelate ligand

A series of novel neutral pentacoordinate silicon(IV) complexes with SiClSN(2)C, SiBrSN(2)C, SiSN(3)C, SiSON(2)C, SiS(2)N(2)C, SiSeSN(2)C and SiTeSN(2)C skeletons (compounds 1-12) was synthesised, starting from PhSiCl(3), PhSiBr(3), PhSi(NCO)(3), MeSiCl(3) or C(6)F(5)SiCl(3). Compounds 1-12 contain (i) a tridentate dianionic N,N,S chelate ligand (derived from 2-{[(pyridin-2-yl)methyl]amino}benzenethiol), (ii) a phenyl, methyl or pentafluorophenyl group and (iii) a monodentate monoanionic ligand (Cl, Br, NCO, NCS, N(3), OS(O)(2)CF(3), OPh, SPh, SePh, TePh). The pentacoordinate silicon(iv) complexes 1-12 were characterised by elemental analyses, NMR spectroscopic studies in the solid state and in solution and crystal structure analyses. These experimental investigations were complemented by computational studies.     

Synthesis and characterization of some novel ruthenium(II) complexes containing thiolate ligands

Reactions of the ruthenium complexes [RuH(CO)Cl(PPh₃)₃] and [RuCl₂(PPh₃)₃] with hetero-difunctional S,N-donor ligands 2-mercapto-5-methyl-1,3,5-thiadiazole (HL¹), 2-mercapto-4-methyl-5-thiazoleacetic acid (HL²), and 2-mercaptobenzothiazole (HL³) have been investigated. Neutral complexes [RuCl(CO)(PPh₃)₂(HL¹)] (1), [RuCl(CO)(PPh₃)₂(HL²)] (2), [RuCl(CO)(PPh₃)₂(HL³)] (3), [Ru(PPh₃)₂(HL¹)₂] (4), [RuCl(PPh₃)₃(HL²)] (5), and [RuCl(PPh₃)₃(HL³)] (6) imparting κ²-S,N-bonded ligands have been isolated from these reactions. Complexes 1 and 4 reacted with diphenyl-2-pyridylphosphine (PPh₂Py) to give neutral κ¹-P bonded complexes [RuCl(CO)(κ¹-P-PPh₂Py)₂(HL¹)] (7), and [Ru(κ¹-P-PPh₂Py)₂(HL¹)₂] (8). Complexes 1-8 have been characterized by analytical, spectral (IR, NMR, and electronic absorption) and electrochemical studies. Molecular structures of 1, 2, 4, and 7 have been determined crystallographically. Crystal structure determination revealed coordination of the mercapto-thiadiazole ligands (HL¹-HL³) to ruthenium as κ²-N,S-thiolates and presence of rare intermolecular S-S weak bonding interaction in complex 1.     

Synthesis and characterization of hexacoordinate cobalt(III) complexes bearing three C,O-bidentate ligands

Hexacoordinated Co(III) complexes bearing three C,O-bidentate ligands (9a and 9b) were prepared from 1-bromo-2-(p-tolyloxymethyl)benzene (8a) and 1-bromo-2,6-bis(p-tolyloxymethyl)benzene (8b), respectively. Both complexes were stable in air at room temperature. X-ray analyses revealed that the structures of both complexes were essentially the same. According to variable temperature ¹H NMR study, it was found that the two oxygen ligands on the same aromatic ring of 9b interchanged with each other.     

Preparation and structural characterization of organotin(IV) complexes with ligands containing a hetero {N} atom and a hydroxy group or hydroxy and carboxyl groups

Twenty-two n-butyltin(IV) and t-butyltin(IV) complexes of ligands containing an -OH (-CO) group or -OH and -COOH groups and an aromatic {N} donor atom were prepared by metathetical reactions. On the basis of the FT-IR and Mössbauer spectroscopic data, molecular structures were assigned to these compounds. The binding sites of the ligands were identified by means of FT-IR spectroscopic measurements, and it was found that in most cases the organotin(IV) moiety reacts with the phenolic form of these ligands. In the complexes with -OH and -COOH functions, the -COOH group is coordinated to the organotin(IV) centres in a monodentate manner. The ¹¹⁹Sn Mössbauer and the FT-IR studies support the formation of trigonal bipyramidal (TBP) and octahedral (O_h) molecular structures. Furthermore, X-ray diffraction analysis has been performed on the n-butyltin(IV)- and t-butyltin(IV)-8-quinol 8-olato-O,N single crystals. The hexacoordinated tin centres exhibit cis-octahedral geometry in both complexes.     

Synthesis and characterization of new organotin(IV) complexes with polyfunctional ligands

New mono-, di- and tri-organotin(IV) derivatives containing the neutral bis(2-pyridylthio)methane ligand, [(pyS)₂CH₂] and tris(2-pyridylthio)methane ligand, [(pyS)₃CH] have been synthesized from reaction with SnR_nCl_4−n (R = Me, ⁿBu, Ph and Cy, n = 1-3) acceptors. Mono-nuclear adducts of the type {[(pyS)₂CH₂]R_nSnCl_4−n} and {[(pyS)₃CH]R_nSnCl_4−n} have been obtained and characterized by elemental analyses, FT-IR, ESI-MS, multinuclear (¹H and ¹¹⁹Sn) NMR spectral data. The ¹H and ¹¹⁹Sn NMR and ESI-MS data suggest for the triorganotin(IV) derivatives a complete dissociation of the compounds in solution. The mono- and di-organotin(IV) derivatives show a greater stability in solution, and their spectroscopic data are in accordance with the existence of six-coordinated RSnCl₃N₂ or R₂SnCl₂N₂ species.     

Zwitterionic and anionic multinuclear pentacoordinate silicon(IV) complexes with bridging (R,R)-tartrato(4-) ligands and SiO5 skeletons: synthesis and reactivity in aqueous solution

Two nutrients in one molecule: A zwitterionic λ(5)Si,λ(5)Si'-disilicate (1) was synthesized and characterized. It contains ligands that exclusively derive from natural products ((R,R)-tartaric acid, choline). Hydrolysis of 1 yields 2, which shows a remarkable kinetic stability in water. Upon dissolution of 1 and 2 in water, the nutrients choline and orthosilicic acid are formed by hydrolysis.     

Synthesis and structural characterization of centrosymmetric multinuclear nickel(II) complexes with neutral tetradentate N6-ligand

A neutral tetradentate ligand L1 [L1?=?3,6-bis(pyrazol-1-yl)-pyridazine] reacts with Ni(ClO₄)₂·6H₂O and undergoes counterion exchange with PF ^?₆ to give di- and tetranuclear complexes [Ni₂(L1)₂(CH₃CN)₄](PF₆)₄·4H₂O (1) and [Ni₄(L1)₄(µ-OH)₄](ClO₄)₄·2H₂O (2), respectively. The presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as base controls the nuclearity of the complex formation. Both complexes were structurally characterized by physicochemical and spectroscopic techniques. Their crystal structures revealed that both complexes are centrosymmetric and adopt slightly distorted octahedral geometry. Complex 1 crystallizes in monoclinic space group C2/c as the Ni(II) center is octahedrally bound to L1 in a trans-isomer arrangement. Complex 2 crystallizes in tetragonal space group I4₁/amd with four L1 and four hydroxy bridging ligands linked to Ni(II) center in cis-isomer arrangement. Cyclic voltammograms of complexes 1 and 2 were measured under Ar and CO₂. Under CO₂, the quasireversible peaks of both complexes become irreversible and a current enhancement occurs under reduction.

     

Synthesis and structural characterization of novel zinc(II) and cadmium(II) complexes with pyridine-phosphine chalcogenide ligands

New pyridine-phosphine chalcogenide ligands, tris[2-(2-pyridyl)ethyl]phosphine sulfide 1a and tris[2-(2-pyridyl)ethyl]phosphine selenide 1b, react with zinc(II) and cadmium(II) chlorides in EtOH at room temperature to afford complexes of compositions 2ZnCl₂·2L (2, L = 1a) and 3CdCl₂·2L (3a,b, L = 1a,b) in high yields. The solid-state structure of complexes 2, 3 has been proved by X-ray analysis data. Complex 2 is a centrosymmetric dimer, where two atoms of zinc are bonded by two bridging pyridine-phosphine sulfide ligands through N atoms. Complexes 3a,b exist as polymeric chains with each bridging ligand acting as a chelate N,S- or N,Se-donor to one cadmium(II) center and as a pyridine N-donor to the next cadmium(II) center.     

Synthesis and structural characterization of nickel(II) hexaazamacrotetracyclic complexes with phthalate ligands

Highly crosslinked polymeric networks formed by cyclodextrins (CD) have recently been shown to be highly versatile nanosponge systems, being for instance very efficient both for drug delivery and for pollutants removal. Here we report some molecular simulation results for dry and hydrated CD nanosponge models aimed to study their swelling behavior. We also report simulation results about the water mobility in these systems in terms of the calculated diffusion coefficient of “free” and of “bound” water molecules confined within the nanosponge cavities. Furthermore, we also suggest the presence of surface-constrained water molecules temporarily bound to the network surface but eventually set free in the bulk.     

Synthesis,characterization, and thermal properties of silicon(IV) compounds containing amidinate ligands as CVD precursors

The title compounds of the type R-C(=NⁱPr) (-N′ ⁱPrSiMe₃) (with R = Me or ⁿBu) as potential chemical vapor deposition (CVD) precursors have been synthesized and characterized by ¹H, ¹³C, and ²⁹Si NMR spectroscopy as well as by EI-MS and elemental analysis where necessary. Thermal properties, including stability, volatility, transport behavior, and vapor pressure, were evaluated by thermogravimetric analysis to confirm that they are suitable for the CVD procedure. Deposition was accomplished in a hot wall CVD reactor system, which qualitatively verified the ability of these compounds as CVD precursors.     

Synthesis,spectroscopic and structural characterisation of vanadium(IV) and oxovanadium(IV) complexes with arsenic donor ligands

The reaction of o-C₆H₄(AsMe₂)₂ with VCl₄ in anhydrous CCl₄ produces orange eight-coordinate [VCl₄{o-C₆H₄(AsMe₂)₂}₂], whilst in CH₂Cl₂ the product is the brown, six-coordinate [VCl₄{o-C₆H₄(AsMe₂)₂}]. In dilute CH₂Cl₂ solution slow decomposition occurs to form the V^III complex [V₂Cl₆{o-C₆H₄(AsMe₂)₂}₂]. Six-coordination is also found in [VCl₄{MeC(CH₂AsMe₂)₃}] and [VCl₄{Et₃As)₂]. Hydrolysis of these complexes occurs readily to form vanadyl (VO²⁺) species, pure samples of which are obtained by reaction of [VOCl₂(thf)₂(H₂O)] with the arsines to form green [VOCl₂{o-C₆H₄(AsMe₂)₂}], [VOCl₂{MeC(CH₂AsMe₂)₃}(H₂O)] and [VOCl₂(Et₃As)₂]. Green [VOCl₂(o-C₆H₄(PMe₂)₂}] is formed from [VOCl₂(thf)₂(H₂O)] and the ligand. The [VOCl₂{o-C₆H₄(PMe₂)₂}] decomposes in thf solution open to air to form the diphosphine dioxide complex [VO{o-C₆H₄(P(O)Me₂)₂}₂(H₂O)]Cl₂, but in contrast, the products formed from similar treatment of [VCl₄{o-C₆H₄(AsMe₂)₂}_x] or [VOCl₂{o-C₆H₄(AsMe₂)₂}] contain the novel arsenic(V) cation [o-C₆H₄(AsMe₂Cl)(μ-O)(AsMe₂)]⁺. X-ray crystal structures are reported for [V₂Cl₆{o-C₆H₄(AsMe₂)₂}₂], [VO(H₂O){o-C₆H₄(P(O)Me₂)₂}₂]Cl₂, [o-C₆H₄(AsMe₂Cl)(μ-O)(AsMe₂)]Cl·[VO(H₂O)₃Cl₂] and powder neutron diffraction data for [VCl₄{o-C₆H₄(AsMe₂)₂}₂].     

Synthesis and solid-state structural characterisation of Pt(II,IV) bromide complexes containing bidentate organothiomethylpyridine heteroleptic ligands

A convenient synthetic method for the preparation of organothiomethylpyridine ligands 2-(RSCH₂)C₅H₄N (R = Ph (L¹), Me (L²)), 2-MeS–6-Me-C₅H₃N (L³), and 2-MeS–4-Me-C₅H₃N (L⁴) via the initial lithiation of substituted 2-picolines followed by the nucleophilic reaction with a diorganyldisulfide is described. The complexes [PtBr₂L] (L = L¹–L⁴) have been prepared in good to high yields as yellow solids with low solubility in organic solvents. The solid state structures of the complexes have been determined, showing the spatial arrangement of the complexes to depend significantly upon varying substituents within the ligand. The complexes undergo oxidation by bromine to form the tetravalent complexes [PtBr₄(L)] (L = L¹–L⁴). The solid state structures of [PtBr₄(L²)] and [PtBr₄(L₄)] have been determined, and shown to be monomeric with the ligand chelating the platinum centre.     

Luminescence of neutral and ionic gold(I) complexes containing pyrazole or pyrazolate-type ligands

A series of pyrazole (Hpz) and pyrazolate (pz⁻) Au(I) complexes of types [Au(Hpz^2R(n))(PPh₃)]⁺ (I), [Au(Hpz^2R(n))₂]⁺ (II), [Au(μ-pz^R(n))]₃ (III), [Au(pz^R(n)/2R(n))(PPh₃)] (IV), [AuCl(Hpz^R(n)/2R(n))] (V) and [(PPh₃)Au(μ-pz^R(n))Au(PPh₃)]⁺ (VI), R(n) and 2R(n) represent C₆H₄OC_nH_2n+1 substituents at the 3- or 3- and 5-positions of the heterocyclic ring, respectively, have been shown to be luminescent in the solid state at 77 K, independently of the presence or not of inter-metallic Au-Au interactions. The emission spectra of all complexes consist of structured bands in the region 395-500 nm, attributed to ligand-to-metal charge transfer (LMCT) transitions involving the Hpz or pz⁻ ligands, the pattern of bands of compounds being related with the molecular structure and/or the nature of the ligands. The thermal behaviour of several complexes of the types III, IV and V containing long-chain substituents (n ? 12) was examined by polarising light optical microscopy (POM). The derivative [AuCl(Hpz^R(12))] was proved to have liquid crystal properties exhibiting a mesophase SmA but the remaining complexes were not liquid crystal materials. This complex is one of the scarce examples of Au(I) derivatives exhibiting both liquid crystal and luminescent properties.     

Synthesis and characterization of cyclometalated iridium(III) complexes containing pyrimidine-based ligands

New pyrimidine derivatives (pyr) have been synthesized using palladium-catalyzed Suzuki coupling reaction. These compounds can undergo cyclometalation with iridium trichloride to form bis-cyclometalated iridium complexes, (pyr)₂Ir(acac) (acac = acetylacetonate; pyr = cyclometalated pyr). The substituents at the both cyclometalated phenyl ring and pyrimidine ring were found to affect both electrochemical and photophysical properties of the complexes. Computation results on these complexes are consistent with the electrochemical and photophysical data. The complexes are green-emitting with good solution quantum yields at ∼0.30. Light-emitting devices using these complexes as dopants were fabricated, and the device performance at 100 mA/cm² are moderate: 9 (17 481 cd/m², 4.8%, 18 cd/A, 5.1 lm/W); 10 (18 704 cd/m², 4.9%, 18.9 cd/A, 4.7 lm/W); 13 (20 942 cd/m², 5.4%, 21.0 cd/A, 6.1 lm/W).     

Synthesis and characterization of copper(II) hexaazamacrotetracyclic complexes containing organic ligands

Two mononuclear copper(II) complexes [Cu(L)(NO₂)](ClO₄) (1) and [Cu(L)(MO₄)]₂· 5H₂O (2) (L = 1,3,10, 12,16,19-hexaazatetracyclo[17,3,1,1^12.16,0^4.9]tetracosane) have been synthesized and their structures determined. Both compounds show a distorted square-pyramidal geometry with the two secondary and two tertiary amines of the macrocycle and one ligand coordinated at the axial position. Cyclic voltammetry of the complexes gives two one-electron waves corresponding to Cu^II/Cu^III and Cu^II/Cu^I processes. The electronic spectra and electrochemical behavior of the complexes are significantly affected by the nature of the organic ligands.