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1.
Dalton Trans ; 53(24): 10220-10225, 2024 Jun 17.
Artigo em Inglês | MEDLINE | ID: mdl-38828484

RESUMO

Bis-silylenes do not only act as strong chelating σ-donor ligands, but also exhibit cooperative behaviour in the activation of small molecules. Three different P-Si containing molecules were prepared from the reaction between tBuCP and different bis-silylenes, which are bridged by ferrocenediyl, diaminobenzene, or o-carborane.

2.
Angew Chem Int Ed Engl ; : e202405319, 2024 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-38656624

RESUMO

The general synthesis of heteroleptic acyclic silylenes with a bulky carbazolyl substituent (dtbpCbz) is detailed and a series of compounds with a chalcogenide substituent of the type [(dtbpCbz)SiE16R] (E16R=OtBu, SEt, SePh, TePh) is reported. With the bulky carbazolyl substituent present, the chalcogenide moiety can be very small, as is shown by incorporating groups as small as ethyl, phenyl or tert-butyl. For the first time, the electronic properties of the silylene can be tuned along a complete series of chalcogenide substituents. The effects are clearly visible in the NMR and UV/Vis spectra, and were rationalised by DFT computations. The reactivity of the heaviest chalcogenide-substituted silylenes was probed by reactions with trimethylphosphine selenide and the terphenyl azide TerN3 (Ter=2,6-dimesitylphenyl).

3.
Inorg Chem ; 63(4): 1997-2004, 2024 Jan 29.
Artigo em Inglês | MEDLINE | ID: mdl-38207101

RESUMO

The reactivity of the base-free bromosilylene dtbpCbzSiBr (dtbpCbz = 1,8-bis(3,5-di-tert-butylphenyl)-3,6-di-tert-butylcarbazolyl) toward carbodiimides and azides was studied in order to generate base-stabilized and base-free silaimidoyl bromides, respectively. The steric bulk of carbodiimides and azides allows control over the reactivity. While with small substituents such as tert-butyl or adamantyl, the reactions cannot be stopped at the Si═N stage, with large substituents, they lead to C-H activation in the product. The Dipp substituent (Dipp = 2,6-diisopropylphenyl) allowed the isolation of the silaimidoyl bromide dtbpCbzSi(Br)NDipp and its CNDipp-coordinated analogue. The reactivity of the Si═N double bond species was studied with respect to cycloaddition and donor exchange reactions.

4.
Chem Asian J ; 18(21): e202300698, 2023 Nov 02.
Artigo em Inglês | MEDLINE | ID: mdl-37702378

RESUMO

Phosphaketenes of divalent group 14 compounds can potentially serve as precursors for the synthesis of heavy multiple-bond systems. We have employed the dtbp Cbz substituent (dtbp Cbz=1,8-bis(3,5-ditertbutylphenyl)-3,6-ditertbutylcarbazolyl) to prepare such phosphaketenyltetrylenes [(dtbp Cbz)EPCO] (E=Ge, Sn, Pb). While the phosphaketenyltetrylenes are stable at ambient conditions, they can be readily decarbonylated photolytically. For the germylene and stannylene derivatives, dimeric diphosphene-type products [(dtbp Cbz)EP]2 (E=Ge, Sn) were obtained. In contrast, photolysis of the phosphaketenylplumbylene, via isomerisation of the [(dtbp Cbz)PbP] intermediate to [(dtbp Cbz)PPb], afforded an unsymmetric and incompletely decarbonylated product [(dtbp Cbz)2 Pb2 P2 CO] formally comprising a [(dtbp Cbz)PPb] and a [(dtbp Cbz)PbPCO] moiety.

5.
ACS Omega ; 8(33): 30442-30449, 2023 Aug 22.
Artigo em Inglês | MEDLINE | ID: mdl-37636904

RESUMO

The high thermal conductivity of polycrystalline diamond makes it ideally suited for thermal management solutions for gallium nitride (GaN) devices, with a diamond layer grown on an aluminum nitride (AlN) interlayer atop the GaN stack. However, this application is limited by the thermal barrier at the interface between diamond and substrate, which has been associated with the transition region formed in the initial phases of growth. In this work, in situ spectroscopic ellipsometry (SE) is employed to monitor early-stage microwave plasma-enhanced chemical vapor deposition diamond growth on AlN. An optical model was developed from ex situ spectra and applied to spectra taken in situ during growth. Coalescence of separate islands into a single film was marked by a reduction in bulk void fraction prior to a spike in sp2 fraction due to grain boundary formation. Parameters determined by the SE model were corroborated using Raman spectroscopy and atomic force microscopy.

6.
Chem Rev ; 123(16): 10468-10526, 2023 Aug 23.
Artigo em Inglês | MEDLINE | ID: mdl-37556842

RESUMO

Heteroatom-centered diradical(oid)s have been in the focus of molecular main group chemistry for nearly 30 years. During this time, the diradical concept has evolved and the focus has shifted to the rational design of diradical(oid)s for specific applications. This review article begins with some important theoretical considerations of the diradical and tetraradical concept. Based on these theoretical considerations, the design of diradical(oid)s in terms of ligand choice, steric, symmetry, electronic situation, element choice, and reactivity is highlighted with examples. In particular, heteroatom-centered diradical reactions are discussed and compared with closed-shell reactions such as pericyclic additions. The comparison between closed-shell reactivity, which proceeds in a concerted manner, and open-shell reactivity, which proceeds in a stepwise fashion, along with considerations of diradical(oid) design, provides a rational understanding of this interesting and unusual class of compounds. The application of diradical(oid)s, for example in small molecule activation or as molecular switches, is also highlighted. The final part of this review begins with application-related details of the spectroscopy of diradical(oid)s, followed by an update of the heteroatom-centered diradical(oid)s and tetraradical(oid)s published in the last 10 years since 2013.

7.
Chemistry ; 29(60): e202302311, 2023 Oct 26.
Artigo em Inglês | MEDLINE | ID: mdl-37489573

RESUMO

Silacycles are ubiquitous building blocks. Small silacycles can typically be expanded catalytically. A silirane, silirene and phosphasilirene as well as a siletane and a silolene were prepared starting from the base-free bromosilylene [(dtbp Cbz)SiBr] (dtbp Cbz=1,8-bis(3,5-ditertbutylphenyl)-3,6-ditertbutylcarbazolyl). As these heterocycles were derived from a dicoordinated silylene, they are susceptible to reactions with an external base. The three-membered silacycles readily undergo non-catalysed ring expansion reactions with isonitriles yielding the related four-membered silacycles. Surprisingly, the ring-expanded derivatives of the silirane undergo up to two further isomerisation reactions, first by enamine formation and then by another ring expansion. DFT computations were utilised to gauge the scope of this reactivity pattern. Three-membered silacycles should essentially universally undergo a ring expansion with isonitriles, while for four-membered silacycles, only very few instances are predicted to accommodate more challenging kinetic requirements of this ring expansion. Larger silacycles lack the ring strain energy required for this ring expansion reaction and are not expected to be expanded.

8.
Inorg Chem ; 62(26): 10249-10255, 2023 Jul 03.
Artigo em Inglês | MEDLINE | ID: mdl-37341997

RESUMO

The silanide SiH3- is an archetypical anion. Its metathesis chemistry is, however, still underdeveloped. We have conveniently prepared the barium silanide complex [(dtbpCbz)BaSiH3]8 with a bulky carbazolide ligand by reaction of the corresponding barium amide with phenyl silane in a good yield. The silanide complex was then used in various metathesis reactions, displaying distinct reactivity toward different substrates. Toward organic substrates such as carbodiimide or benzophenone, the silanide acted as a hydride surrogate, and formamidinate or diphenylmethoxide ligands were formed. Toward the monocoordinated cation [(dtbpCbz)Ge]+, transfer of SiH3- was observed, and the decomposition of the silylgermylene [(dtbpCbz)GeSiH3] was studied. For the heavier, more easily reducible congeners [(dtbpCbz)Sn]+ and [(dtbpCbz)Pb]+ as substrates, [(dtbpCbz)SiH3] was obtained under elimination of elemental Sn and Pb, so that formally SiH3+ was transferred to the dtbpCbz- ligand.

9.
Dalton Trans ; 52(20): 6712-6721, 2023 May 22.
Artigo em Inglês | MEDLINE | ID: mdl-37129049

RESUMO

In order to study the effects of silylene ligands on the catalytic activity of carbonyl hydrosilylation catalyzed by cobalt phosphine complexes, readily available model catalysts are required. In this contribution, a comparative study of the hydrosilylation of aldehydes and ketones catalyzed by tris(trimethylphosphine) cobalt chloride, CoCl(PMe3)3 (1), and bis(silylene) cobalt chloride, Co(LSi:)2(PMe3)2Cl (2, LSi: = {PhC(NtBu)2}SiCl), is presented. It was found that both complexes 1 and 2 are good catalysts for the hydrosilylation of aldehydes and ketones under mild conditions. This catalytic system has a broad substrate scope and selectivity for multi-functional substrates. Silylene complex 2 shows higher activity than complex 1, bearing phosphine ligands, for aldehydes, but conversely, for ketones, the activity of complex 1 is higher than that of complex 2. It is worth noting that in the process of mechanistic studies the intermediates (PMe3)3Co(H)(Cl)(PhH2Si) (3) and (LSi:)2(PMe3)Co(H)(Cl)(PhH2Si) (4) were isolated from the stoichiometric reactions of 1 and 2 with phenylsilane, respectively. Further experiments confirmed that complex 3 is a real intermediate. A possible catalytic mechanism for the hydrosilylation of carbonyl compounds catalyzed by 1 was proposed based on the experimental investigation and literature reports, and this mechanism was further supported by DFT studies. The bis(silylene) complex 4 showed complicated behavior in solution. A series of experiments were designed to study the catalytic mechanism for the hydrosilylation of carbonyl compounds catalyzed by complex 2. According to the experimental results, the hydrosilylation of aldehydes catalyzed by 1 proceeds via a different mechanism than that of the analogous reaction with complex 2 as the catalyst. In the case of ketones, complex 4 is a real intermediate, indicating that both 1 and 2 catalyze the reaction by the same mechanism. The molecular structures of 3 and 4 were determined by single crystal X-ray diffraction analysis.

10.
Chem Sci ; 14(18): 4769-4776, 2023 May 10.
Artigo em Inglês | MEDLINE | ID: mdl-37181779

RESUMO

Insertion and functionalization of gallasilylenes [LPhSi-Ga(Cl)LBDI] (LPh = PhC(NtBu)2; LBDI = [{2,6-iPr2C6H3NCMe}2CH]) into the cyclo-E5 rings of [Cp*Fe(η5-E5)] (Cp* = η5-C5Me5; E = P, As) are reported. Reactions of [Cp*Fe(η5-E5)] with gallasilylene result in E-E/Si-Ga bond cleavage and the insertion of the silylene in the cyclo-E5 rings. [(LPhSi-Ga(Cl)LBDI){(η4-P5)FeCp*}], in which the Si atom binds to the bent cyclo-P5 ring, was identified as a reaction intermediate. The ring-expansion products are stable at room temperature, while isomerization occurred at higher temperature, and the silylene moiety further migrates to the Fe atom, forming the corresponding ring-construction isomers. Furthermore, reaction of [Cp*Fe(η5-As5)] with the heavier gallagermylene [LPhGe-Ga(Cl)LBDI] was also investigated. All the isolated complexes represent rare examples of mixed group 13/14 iron polypnictogenides, which could only be synthesized by taking advantage of the cooperativity of the gallatetrylenes featuring low-valent Si(ii) or Ge(ii) and Lewis acidic Ga(iii) units/entities.

11.
Dalton Trans ; 52(8): 2214-2218, 2023 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-36762566

RESUMO

The base-free carbazolyl bromosilylene RSiBr (R = 1,8-bis(3,5-di-tert-butyl-phenyl)-3,6-di-tert-butyl-carbazolyl) reacts with (η2-C2H4)Pt(PPh3)2 and Pt(PCy3)2 to form platinasilacyclobutane R(Br)Si(C2H4)Pt(PPh3)2 (1) and silylene platinum complex R(Br)SiPt(PCy3)2 (2), respectively. When silylene complex 2 is treated with C2H4, the six-membered metallasilacycle R(Br)Si(C2H4)2Pt(PCy3)2 (3) is obtained. All compounds are characterised by XRD and multinuclear NMR spectroscopy.

12.
Inorg Chem ; 61(49): 19710-19725, 2022 Dec 12.
Artigo em Inglês | MEDLINE | ID: mdl-36455154

RESUMO

Two new bisphosphine [PCP] pincer cobalt(III) hydrides, [(L1)Co(PMe3)(H)(Cl)] (L11, L1 = 2,6-((Ph2P)(Et)N)2C6H3) and [(L2)Co(PMe3)(H)(Cl)] (L21, L2 = 2,6-((iPr2P)(Et)N)2C6H3), as well as one new bissilylene [SiCSi] pincer cobalt(III) hydride, [(L3)Co(PMe3)(H)(Cl)] (L31, L3 = 1,3-((PhC(tBuN)2Si)(Et)N)2C6H3), were synthesized by reaction of the corresponding protic [PCP] or [SiCSi] pincer ligands L1H, L2H, and L3H with CoCl(PMe3)3. Despite the similarities in the ligand scaffolds, the three cobalt(III) hydrides show remarkably different performance as catalysts in alkene hydrosilylation. Among the PCP pincer complexes, L11 has higher catalytic activity than complex L21, and both catalysts afford anti-Markovnikov selectivity for both aliphatic and aromatic alkenes. In contrast, the catalytic activity for alkene hydrosilylation of silylene complex L31 is comparable to phosphine complex L11, but a dependence of regioselectivity on the substrates was observed: While aliphatic alkenes are converted in an anti-Markovnikov fashion, the hydrosilylation of aromatic alkenes affords Markovnikov products. The substrate scope was explored with 28 examples. Additional experiments were conducted to elucidate these mechanisms of hydrosilylation. The synthesis of cobalt(I) complex (L1)Co(PMe3)2 (L17) and its catalytic properties for alkene hydrosilylation allowed for the proposal of the mechanistic variations that occur in dependence of reaction conditions and substrates.


Assuntos
Alcenos , Cobalto , Cobalto/química , Alcenos/química , Ligantes , Catálise
13.
Chemistry ; 28(55): e202201963, 2022 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-35762907

RESUMO

The reaction of the dilithium salt of the enantiopure (S)-BINOL (1,1'-bi-2-naphthol) with two equivalents of the amidinate-stabilized chlorosilylene [LPh SiCl] (LPh =PhC(NtBu)2 ) led to the formation of the first example of a chiral cyclic silene species comprising an (S)-BINOL ligand. The reactivity of the Si=C bond was investigated by reaction with elemental sulfur, CO2 and HCl. The reaction with S8 led to a Si=C bond cleavage and concomitantly to a ring-opened product with imine and silanethione functional groups. The reaction with CO2 resulted in the cleavage of the CO2 molecule into a carbonyl group and an isolated O atom, while a new stereocenter is formed in a highly selective manner. According to DFT calculations, the [2+2] cycloaddition product is the key intermediate. Further reactivity studies of the chiral cyclic silene with HCl resulted in a stereoselective addition to the Si=C bond, while the fully selective formation of two stereocenters was achieved. The quantitative stereoselective addition of CO2 and HCl to a Si=C bond is unprecedented.

14.
Dalton Trans ; 51(13): 5218-5226, 2022 Mar 29.
Artigo em Inglês | MEDLINE | ID: mdl-35275153

RESUMO

The synthesis and characterisation of rare-earth metal complexes with redox-active formazanate ligands are described. Deprotonation of the neutral formazan ligand L1H (L1 = PhNNC(Ph)NNPh) with [Ln{N(SiMe3)2}3] (Ln = Y, Sm, Dy) resulted in homoleptic tris(formazanate) complexes with the general formula [(L1)3Ln] (Ln = Y (1), Sm (2), Dy (3)), in which the central metal atom is coordinated by six N atoms, revealing a propeller-type structure. To generate heteroleptic complexes, a novel formazan ligand L2H (L2 = {PhNNC(4-tBuPh)NNPh}) was employed. Salt metathesis by using the trivalent precursors [SmCp*2(µ-Cl)2K(thf)] (Cp* = η5-C5Me5) or [LnCp2Cl]2 (Cp = η5-C5H5, Ln = Dy, Yb) and [L2K(thf)] formed mono(formazanate) complexes, [L2SmCp*2] (4) and [L2LnCp2] (Ln = Dy (5), Yb (6)), respectively. Unexpectedly, a redox reaction occurred between [L2K(thf)] and the divalent ytterbium precursor, [YbI2(thf)2], generating the trivalent ytterbium complex [(L2)3Yb] (7). When the neutral formazan ligand (L2H) reacted with [SmCp*2(thf)2], the oxidised samarium complex 4 was formed. These novel compounds were fully characterised and their electrochemical properties were explored by cyclic voltammetry.

15.
Org Biomol Chem ; 20(14): 2873-2880, 2022 04 06.
Artigo em Inglês | MEDLINE | ID: mdl-35315476

RESUMO

An air- and moisture-stable helical radical with seven six- and five-membered rings arranged alternately was synthesized by cyclizations in a suitably ortho,ortho'-substituted terphenyl and re-establishment of its conjugation. Mesityl groups at the five-membered rings prevent radical reactions. This cyclopenta-fused polyaromatic hydrocarbon (CP-PAH) was characterized by X-ray crystallographic analysis, EPR and UV/Vis spectroscopy, and by cyclic voltammetry. Further properties and spectra were determined by quantum chemical calculation (spin densities, orbital energies, UV/Vis/NIR and ECD spectra). It turned out that this radical is best described with its radical centre being in the outer five-membered rings, which allows for the largest number of fully intact benzene rings. Its triradical character is rather small and can be neglected. The five-membered rings show significant antiaromatic character, which is highest in the central ring.


Assuntos
Hidrocarbonetos Aromáticos , Hidrocarbonetos Policíclicos Aromáticos , Carbono , Cristalografia por Raios X , Ciclização , Hidrocarbonetos Policíclicos Aromáticos/química
16.
Chemistry ; 28(1): e202103974, 2022 Jan 03.
Artigo em Inglês | MEDLINE | ID: mdl-34817892

RESUMO

The synthesis and full characterization of α-silylated (α-SiCPs; 1-7) and α-germylated (α-GeCPs; 11-13) phosphorus ylides bearing one chloride substituent R3 PC(R1 )E(Cl)R2 2 (R=Ph; R1 =Me, Et, Ph; R2 =Me, Et, iPr, Mes; E=Si, Ge) is presented. The molecular structures were determined by X-ray diffraction studies. The title compounds were applied in halide abstraction studies in order to access cationic species. The reaction of Ph3 PC(Me)Si(Cl)Me2 (1) with Na[B(C6 F5 )4 ] furnished the dimeric phosphonium-like dication [Ph3 PC(Me)SiMe2 ]2 [B(C6 F5 )4 ]2 (8). The highly reactive, mesityl- or iPr-substituted cationic species [Ph3 PC(Me)SiMes2 ][B(C6 F5 )4 ] (9) and [Ph3 PC(Et)SiiPr2 ][B(C6 F5 )4 ] (10) could be characterized by NMR spectroscopy. Carrying out the halide abstraction reaction in the sterically demanding ether iPr2 O afforded the protonated α-SiCP [Ph3 PCH(Et)Si(Cl)iPr2 ][B(C6 F5 )4 ] (6 dec) by sodium-mediated basic ether decomposition, whereas successfully synthesized [Ph3 PC(Et)SiiPr2 ][B(C6 F5 )4 ] (10) readily cleaves the F-C bond in fluorobenzene. Thus, the ambiphilic character of α-SiCPs is clearly demonstrated. The less reactive germanium analogue [Ph3 PC(Me)GeMes2 ][B{3,5-(CF3 )2 C6 H3 }4 ] (14) was obtained by treating 11 with Na[B{3,5-(CF3 )2 C6 H3 }4 ] and fully characterized including by X-ray diffraction analysis. Structural parameters indicate a strong CYlide -Ge interaction with high double bond character, and consequently the C-E (E=Si, Ge) bonds in 9, 10 and 14 were analyzed with NBO and AIM methods.

17.
Chem Commun (Camb) ; 57(93): 12532-12535, 2021 Nov 23.
Artigo em Inglês | MEDLINE | ID: mdl-34751692

RESUMO

We report details of our attempts to reduce the bulky carbazolyl diiodoalane [R-AlI2]. The reducing agents employed include KC8, Cp*2Co and the Mg(I) compound [(MesBDI)Mg]2. The use of KC8 allowed the spectroscopic observation of the alanediyl [R-Al]. With Cp*2Co as the reducing agent, the alanediyl [R-Al] was obtained as a crystalline material in low yield, but paramagnetic impurities remained. When diiodoalane [R-AlI2] was treated with [(MesBDI)Mg]2, no reduction but a 2 : 1 addition was observed.

18.
Nanoscale ; 13(23): 10555-10565, 2021 Jun 17.
Artigo em Inglês | MEDLINE | ID: mdl-34100512

RESUMO

Copper (Cu) as an excellent electrical conductor and the amphiphilic diblock copolymer polystyrene-block-poly(ethylene oxide) (PS-b-PEO) as a polymer electrolyte and ionic conductor can be combined with an active material in composite electrodes for polymer lithium-ion batteries (LIBs). As interfaces are a key issue in LIBs, sputter deposition of Cu contacts on PS-b-PEO thin films with high PEO fraction is investigated with in situ grazing-incidence small-angle X-ray scattering (GISAXS) to follow the formation of the Cu layer in real-time. We observe a hierarchical morphology of Cu clusters building larger Cu agglomerates. Two characteristic distances corresponding to the PS-b-PEO microphase separation and the Cu clusters are determined. A selective agglomeration of Cu clusters on the PS domains explains the origin of the persisting hierarchical morphology of the Cu layer even after a complete surface coverage is reached. The spheroidal shape of the Cu clusters growing within the first few nanometers of sputter deposition causes a highly porous Cu-polymer interface. Four growth stages are distinguished corresponding to different kinetics of the cluster growth of Cu on PS-b-PEO thin films: (I) nucleation, (II) diffusion-driven growth, (III) adsorption-driven growth, and (IV) grain growth of Cu clusters. Percolation is reached at an effective Cu layer thickness of 5.75 nm.

19.
Chemistry ; 27(30): 7998-8002, 2021 May 26.
Artigo em Inglês | MEDLINE | ID: mdl-33834548

RESUMO

In this work we detail our efforts to systematically generate stable dicoordinate CuII complexes. Initial experiments via metathesis reactions of a bulky potassium carbazolide (RK) with copper(II) salts indeed yielded a stable product, RCuOTf (1). However, subsequent attempts to grasp systematic synthetic access to complexes of the type RCuX (X=monoanionic ligand) proved difficult as many of the complexes rapidly decomposed in solution. By using triflate-related ligands such as ethyl sulfate and bistriflimide, the additional dicoordinate copper complexes RCuOSO3 Et (2), [RCu(THF)][Cu(NTf2 )2 ] (3) and RCuNTf2 (4) could be isolated. Spectroscopic indications corroborate more CuI than CuII character in all RCuX derivatives.

20.
ACS Appl Electron Mater ; 3(2): 813-824, 2021 Feb 23.
Artigo em Inglês | MEDLINE | ID: mdl-33644761

RESUMO

The performance of transistors designed specifically for high-frequency applications is critically reliant upon the semi-insulating electrical properties of the substrate. The suspected formation of a conductive path for radio frequency (RF) signals in the highly resistive (HR) silicon substrate itself has been long held responsible for the suboptimal efficiency of as-grown GaN high electron mobility transistors (HEMTs) at higher operating frequencies. Here, we reveal that not one but two discrete channels distinguishable by their carrier type, spatial extent, and origin within the metal-organic vapor phase epitaxy (MOVPE) growth process participate in such parasitic substrate conduction. An n-type layer that forms first is uniformly distributed in the substrate, and it has a purely thermal origin. Alongside this, a p-type layer is localized on the substrate side of the AlN/Si interface and is induced by diffusion of group-III element of the metal-organic precursor. Fortunately, maintaining the sheet resistance of this p-type layer to high values (∼2000 Ω/□) seems feasible with particular durations of either organometallic precursor or ammonia gas predose of the Si surface, i.e., the intentional introduction of one chemical precursor just before nucleation. It is proposed that the mechanism behind the control actually relies on the formation of disordered AlSiN between the crystalline AlN nucleation layer and the crystalline silicon substrate.

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