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The structures and interactions in four new hydrates of substituted piperidines have been studied using X-ray crystallography and quantum chemistry. The piperidine ring substitution leads to a significant reduction in the number of hydrates compared with the parent amine, with 4-methylpiperidine yielding a hemihydrate and a trihydrate; 4-chloropiperidine a monohydrate and a trihydrate, (where the architecture is similar to 4-methylpiperidine trihydrate). Despite many attempts, it did not prove possible to crystallize hydrates with higher molar amine : water ratios. Therefore, trihydrates are probably the most hydrated crystals to be obtained at ambient pressure for both amines. Both trihydrates create identical water layers of the L4(6)5(7)6(8) type and the main structural difference is the arrangement of hydrogen bonds between water layers and amines. Despite this, both trihydrates have the same melting temperature (263 K) and as supported by lattice energy calculations. Chlorine⋯chlorine contacts have no significant impact on the stabilization of the 4-chloropiperidine monohydrate or the 4-chloropiperidine trihydrate. Periodic DFT-D3 calculations show that the energies of the water layers are identical in both cases, and the summed hydrogen bond energies (although arranged differently) are similar. Moreover, in the case of trihydrates, which have a 2-D topology of water⋯water interactions, it is possible to perform DFT calculations for separate layers and to determine the contribution of those interaction energies to the cohesive energy of the whole crystals.

In this work, we thoroughly analyze the structural behavior of 3-pyrroline (unsaturated analogue of pyrrolidine) in the context of generating possible clathrate hydrates. The crystals of neat amine...

The understanding and control of proton transfer reactions between acid–base pairs in the solid state are two of the main challenges for the crystal engineering community. The ability to control pr...

In this Article, a number of single crystal structures of piperidine hydrates are presented. While the lower hydrates, i.e., containing 1/2 or 2 water molecules per amine, present features characteristic for well-defined structures of cocrystals, the higher hydrates (8.1, 9 3/4, 11) have properties more similar to clathrate hydrates with the organic molecules enclosed in cages. However, in these systems some weak hydrogen bonds between piperidine and the water framework exist; thus they cannot be considered as pure host–guest structures. The property of piperidine to crystallize with water giving full enclathration of the amine is compared with the ability of nonionic chaotropes to generate clathrate hydrate-like structures. According to the obtained crystal structures of higher hydrates of piperidine, this amine behaves more like a chaotrope. This finding is supported by Raman spectra in the solid state.

Lewis acid-base adducts of the general type R2Zn(4-tBuPy)x (R = Me 1, iPr 2, tBu 3, Cp* 4; x = 1, 2) were obtained in high yields from reactions of ZnR2 with the Lewis base 4-tBu-Pyridine. Compounds 1–4 were characterized by multinuclear NMR (1H, 13C) and IR spectroscopy and elemental analyses, 1 and 4 also by X-ray diffraction at single crystals.

The β-diketiminate zinc hydride MesnacnacZnH (1) reacts with CO(2), C(Ni-Pr)(2) and t-BuNCO at ambient temperature with insertion into the Zn-H bond and subsequent formation of the corresponding formato (2), formamido (3) and formamidinato (4) complexes.

This is the peer reviewed version of the following article: Angew. Chem. 2009,121, 821-824 which has been published in final form at: https://doi.org/10.1002/ange.200803736 Version of Record online: 15 December 2008

Monosubstituted amidinate complexes [RC(NR′)2]ECl2 [E = Sb, R = tBu, R′ = iPr 1, Cy 2, 2,6‐iPr2C6H3 (Dipp) 3; R = nBu, R′ = iPr 4; E = Bi, R = tBu, R′ = iPr 5, Dipp 6] were prepared in high yields by salt elimination reactions of ECl3 with Li amidinates. 1–6 were characterized by elemental analyses, NMR and IR spectroscopy and single‐crystal X‐ray diffraction. In addition, computational calculations were performed to clarify the different bonding modes in 1 and 5. Dedicated to Prof. Dietmar Seyferth on the occasion of his 80th birthday.

Reactions of the monomeric β-diketiminate zinc complex (Mes)NacNacZnMe (MesNacNac = {[2,6-(2,4,6-Me3-C6H2)N(Me)C)]2CH}) with ROH (R = Me, Et, i-Pr) yielded the corresponding zinc alcoholates [(Mes)NacNacZnOR]2 (R = Me 1, Et 2, i-Pr 3). In addition, the reaction of (Mes)NacNacZnCl with various reducing agents such as K-graphite, K, or Na gave the Zn(II) complex [(Mes)NacNac]2Zn 4. 1 - 4 were characterized by elemental analyses, mass and multinuclear (1H, 13C{1H}) NMR spectroscopy (1H, 13C), and by single crystal Xray analysis. Dedicated to Prof. Gerd Meyer on the occasion of his 60th birthday.

Nine new cocrystals of para-phenylenediboronic or para-hydroxyphenylboronic acids with a series of aromatic N-oxides are reported. All of the complexes form centrosymmetric crystal structures. They are stabilized by an extended net of hydrogen bonds further supported by effective π-stacking interactions. In the studied structures four main synthons were distinguished. Only in the 3,10-phenanthroline-3-N-oxide and 3,10-N,N-dioxide cocrystals from the series, an acid–acid dimeric motif characteristic for arylboronic acid crystals was observed. The majority of the obtained cocrystals exhibit layered architectures, where the N-oxide molecules are separated by boronic acid slabs. Furthermore, most of the cocrystals form hydrates, where water molecules play the role of a “molecular glue”. Water contribution to the lattice stability is significant, and energy gain per water molecule ranges from 66.8 to 117.6 kJ·mol–1. The cocrystal cohesive energies seem to be more favorable when compared to the corresponding va...

Cyclobutylamine (cBA) and its four new hydrates were crystallized using an in situ crystallization technique with a focused infrared laser beam procedure on a single crystal diffractometer. Two groups of hydrates, separated by a gap, can be identified: the “lower hydrates” (the known hemi- and new monohydrate) plus the “higher hydrates”: (6 3/7, approximately 7 1/2 and 9 1/2). The “lower hydrates” are fully ordered structures with well-defined stoichiometries; in contrast the “higher hydrates” are severely disordered with water molecules organized into three-dimensional networks, similar to clathrate hydrate type sI (hydrate 7 1/2) and sH (hydrates 6 3/7 and 9 1/2). The latter two structures can be considered as extensions of the hexagonal clathrate hydrate sH with addition of water segments in a manner which preserves the hexagonal/trigonal symmetry of the lattice, changing only the c axis of the unit cell. Such a variation is commonly used in engineering for modifying standard structures to “extended” v...

The crystals of new ambient pressure, high temperature (HT) polymorphs of neat pyrrolidine hemi- and hexahydrates were obtained using the IR laser assisted in situ crystallization method. They were subsequently investigated by single crystal X-ray diffraction and Raman spectroscopy. The transition from HT form to the known low temperature (LT) polymorph of the amine was monitored by X-ray powder diffraction. Although the investigated amine is an analogue to tetrahydrofuran (THF) which forms a stable clathrate hydrate, both binary pyrrolidine hydrates are dissimilar to the THF hydrate. The hexahydrate of pyrrolidine represents a class of semiclathrates where “guest” molecules are incorporated in the water framework. While cooling it undergoes a phase transition to the fully ordered phase. At higher temperatures the structure contains disordered pyrrolidine and water molecules. The latter adopts the same type of disorder as typical for H-disordered ice polymorphs (e.g., Ih, Ic, ...) and most clathrate hydrates.

Calculations at various levels of theory with different methods and respective evaluations confirm that the twist conformation (C2) is preferred for tetrahydrothiophene (THT) in the gas phase. In the crystalline phase, achieved by a laser assisted crystallization device, THT has C1 symmetry (slightly distorted C2 symmetry) in the chiral space group P212121. This is obviously a packing effect caused by the nonsymmetrical arrangement of neighboring molecules. The distortion from C2 symmetry costs very little energy as confirmed by computational methods in the gas phase. Only one enantiomer of the chiral THT is found in the cell which requires spontaneous crystallization, which results in a racemic mixture of crystals, or a racemization occurs prior to/during nucleation or in the “embryonic” state. The racemization happens by a mechanism that can be described as a partial pseudo rotation within a five-membered mono-heterocycle with a C2–CS–C2′ transition (C2 and C2′ are enantiomers) maintaining the heteroato...

The [2.2]paracyclophane moiety is used as a spacer to connect the ends of a hex-3-ene-1,5-diyne unit, a p-system that on thermolysis usually cycloaromatizes to a benzene ring (Bergman cyclization). For the preparation of the pseudo-geminally-bridged system 9, the diacetylene 3 was chain-extended to the diol 16, which after conversion to the pseudo-geminal dibromide 17 was ring-closed by treatment with LiHMDS/HMPA to the [2.2]paracyclophane enediyne 9. Whereas the McMurry coupling of the pseudo-ortho bisaldehyde 24 resulted in the formation of the hexa-dienyne-bridged cyclophane 27, the pseudo-ortho-bridged hydrocarbon 11 was obtained by preparing first the diol 28 from 24, converting the latter into the dioxolane 29, which in the last step furnished the olefin 11 by treatment with Tf2O/EtN(iPr)2. The authentic Bergman product 10 of the pseudo-gem-bridged hexenediyne 9 was synthesized by a conventional sequence starting from the ethynyl formyl substrate 18. Since the pseudo-ortho-enediyne-bridged hydrocarbon 11 is thermally labile, its benzannelated derivate 34 was prepared. No classical Bergman cyclization reactions could be observed for any of the [2.2]paracyclophane-bridged hexenediynes prepared here. In the pseudo-gem-series the fulvenes 14 and 15 were the only products that could be identified under thermal conditions (McMurry coupling); the benzannelated substrate 34 gave the benzoful-vene-bridged cyclophane 36 on photolysis. Bergman cyclizations yielding fulvene derivatives are extremely rare. The mechanism of the cyclization of 9 and 34 is discussed, using compliance constants. The structure assignments of the hydrocarbons synthesized in this study are based on spectroscopic studies as well as X-ray structural analyses for 9, 10, 11, 27, and 34.

Crystal structure of benzene–acetylene co-crystal was analysed based on calculated energies of intermolecular interactions between basic molecules located in asymmetric part of unit cell and their neighbours belonging to their first coordination sphere. It is demonstrated that the basic structural motif of the crystal is represented by infinite chains formed by the hydrogen-bonded benzene and acetylene molecules. Energy of interaction of the basic pair of molecules to neighbours within the chain is 2.2 times higher than the energy of interactions with molecules of any neighbouring chain. This ratio almost does not depend on method of calculation of interaction energy. Also, results of calculations were compared with analysis of topology of electron density distribution in crystal. The possibility to find the basic structural motif of the crystal based on properties of intermolecular bond critical points is demonstrated.

Trichloromethyl thiocyanate, CCl3SCN, was structurally studied in both the gas and crystal phases by means of gas electron diffraction (GED) and single-crystal X-ray diffraction (XRD), respectively. Both experimental studies and quantum chemical calculations indicate a staggered orientation of the CCl3 group relative to the SCN group. This conclusion is supported by the similarity of the C-SCN bond length to that of the anti-structure of CH2ClSCN (Berrueta Martínez et al. Phys. Chem. Chem. Phys. 2015, 17, 15805-15812). Bond lengths and angles are similar for gas and crystal CCl3SCN structures; however, the crystal structure presents different intermolecular interactions. These include halogen and chalcogen type interactions, the geometry of which was studied. Characteristic C-Y⋯N angles (Y=Cl or S) close to 180° provide evidence for typical σ-hole interactions along the halogen/chalcogen-carbon bond in N⋯Cl and N⋯S, intermolecular units. Crystallize the difference: The crystal and gas-phase structures of CCl3SCN are studied by X-ray and gas electron diffraction techniques. In both phases, the CCl3 group presents a staggered orientation relative to the SCN group. Different intermolecular interactions are detected in the solid phase, including halogen- and chalcogen-type interactions. Fil: Berrueta Martinez, Yanina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; Argentina Fil: Rodriguez Pirani, Lucas Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; Argentina Fil: Erben, Mauricio Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; Argentina Fil: Boese, Roland. Universität Duisburg Essen; Alemania Fil: Reuter, Christian G.. Universität Bielefeld; Alemania Fil: Vishnevskiy, Yury V.. Universität Bielefeld; Alemania Fil: Mitzel, Norbert W.. Universität Bielefeld; Alemania Fil: Della Védova, Carlos Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; Argentina

Phase transfer catalysis has been adapted to the synthesis of triisopropylcyclopentadiene isomers 1 in high yield and purity. Alkylation of sodium triisopropylcyclopentadienides with isopropyl bromide in tetrahydrofuran has been shown to be the currently most efficient way to generate tetraisopropylcyclopentadiene isomers 2, which give sodium tetraisopropylcyclopentadienide (3) upon metalation. The crucial step for the introduction of the fifth isopropyl group, the selective attack of an iminium salt at the tetraisopropylcyclopentadienide anion in the 5-position with generation of the corresponding 1,2,3,4-tetraisopropyl(6-dimethylamino)fulvene (4), has been carried out according to a published procedure. Addition of 1-naphthyllithium to the dimethylaminofulvene 4 yielded extremely bulky lithium dimethylamino(1-naphthyl)methyltetraisopropylcyclopentadienide (7). Pure 1,2,4,1′,2′,4′-hexaisopropylnickelocene (8) was obtained from sodium triisopropylcyclopentadienide and nickel(II) bromide. The tetraisopropy...

The synthesis and reactivity of heteroleptic zinc complexes of the type LZnX (X = Me, I) containing amidinate ligands L of varying steric bulk were investigated. Complexes of the type LZnMe, which were obtained from the homoleptic complexes L2Zn upon reaction with ZnMe2, react with iodine with subsequent formation of LZnI. Single-crystal X-ray structures of the amidinate zinc complexes [{MeC(Ni-Pr)2}ZnMe]2, 1, [{MeC(Ni-Pr)2}ZnI]2LiI(OEt)2, 3, [t-BuC(NDipp)2]ZnMe, 5, [t-BuC(NDipp)2]ZnMe(t-BuPy), 6, [{t-BuC(NDipp)2}Zn(μ-I)]2, 7, and [t-BuC{N(H)Dipp}2][Al{OC(CF3)3}4], 8, are reported.

Thirty-three different N,N-dialkyl- and N-alkyl-N-phosphorylalkyl-substituted carboxamides 9-17 were treated with unsubstituted as well as with 2-alkyl-, 2,2-dialkyl-, and 3-alkenyl-substituted ethylmagnesium bromides 6 in the presence of stoichiometric amounts of titanium tetraisopropoxide or methyltitanium triisopropoxide to furnish substituted cyclopropylamines 20-25 in 20-98% yield, depending on the substituents with no (1:1) to excellent (>25:1) diastereoselectivities. Generally higher yields (up to 98%) of the cyclopropylamines 20-28 without loss of the diastereoselectivity were obtained with methyltitanium triisopropoxide as the titanium mediator. Under these conditions, even dioxolane-protected ketones and halogen-substituted and chiral as well as achiral alkyloxyalkyl-substituted carboxamides could be converted to the correspondingly substituted cyclopropylamines with unsubstituted as well as phenyl- and a variety of alkyl-substituted ethylmagnesium bromides in addition to numerous heteroatom-containing (e.g., halogen-, trityloxy-, tetrahydropyranyloxy-substituted) Grignard reagents (62 examples altogether). The transformation of N,N-diformylalkylamines 54 with ethylmagnesium bromide in the presence of methyltitanium triisopropoxide to N,N-dicyclopropyl-N-alkylamines 55 can be brought about in up to 82% yield (6 examples). An asymmetric variant of the titanium-mediated cyclopropanation of N,N-dialkylcarboxamides has been developed by applying chiral titanium mediators generated from stoichiometric amounts of titanium tetraisopropoxide and chiral diamino or diol ligands, respectively. The most efficient chiral mediators turned out to be titanium bistaddolates that provided the corresponding cyclopropylamines with enantiomeric excesses (ee) of up to 84%. Evaluation of several silyl-based additives revealed that the reaction can also efficiently be carried out with substoichiometric amounts (down to 25 mol%) of the titanium reagent, as long as 2-aryl- or 2-ethenyl-substituted ethylmagnesium halides are used and a concomitant slight decrease in yields is accepted. The newly developed methodology was successfully applied for the preparation of analogues with cyclopropylamine moieties of known drugs and natural products such as the nicotine metabolite (S)-Cotinine as well as the insecticides Dinotefuran and Imidacloprid.

New oxo-bridge, mixed metal complex, [Fe2NiO(CH3CH2COO)6(H2O)3]·0.5H2O has been synthesized from the direct reaction between metal nitrate and propanoic acid and characterized by elemental analysis, infrared and electronic spectroscopy and single-crystal X-ray crystallography. This complex have a typical μ3-oxo trinuclear structure: (a) three metal atoms are situated in the apexes of the equilateral triangle; (b) μ3-oxygen atom and six propanoate ligands fulfill the bridge functions; (c) the monodentate water ligands complete the octahedral geometry of the metal ions. It crystallized in the triclinic, space group type P 1 ¯ . Two strong bands were observed in IR spectra at ∼1590 and ∼1420 (cm−1) stretching vibrations, the coordination mode of the carboxylate ligand can be assigned on the basis of the difference (Δν ⩽ 200 cm−1) of these two frequencies.

In linear-free-energy relations and free-energy relations substituents are characterized by so-called “electronic” parameters, σ1-parameters of substituents e. g. show direct correlations to Tolman's X1-parameters or our P-parameters. But by systematic variations at tetrahedral phosphorus we found a further set of Δ-parameters, by which representative substituents like -OMe/-SMe and -CMe3/-SiMe3 with nearly identical Xi- or P-parameters may be further characterized. The opposite influence of substituents on chemical behaviour is determined by the +/−sign of Δ-parameters. By the signs of P-and Δ-parameters with triphenylphosphane as standard alternative order factors like DO/ACC, EVEN/ODD and S/AS may be identified. Compensation phenomena by selforganisation alone make LFE-relations applicable. The importance of pattern recognition and consideration of absolute and relative control make general order control in chemical systems understandable (see next review).

An investigation of the feasibility of utilizing a specific, and previously largely unrecognized, hydrogen-bonded synthon for the design and preparation of co-crystals is reported. Structural evidence (i.e., > 12 000 instances) indicated the robustness of the cyclic R 2 4 (8) hydrogen-bonded motif containing, in most cases, four individual (either identical or different) molecules, in which the donor substituent (e.g., an amine) can provide two hydrogen-bond donors, and the acceptor (e.g., a carbonyl oxygen) can provide two hydrogen-bond acceptors. The energetic robustness of the motif with respect to chemical substitution and charge on the component molecules was investigated and confirmed in a series of fully optimized calculations at the MP2/6-31 + G(d) level. A proof-of-concept experiment to prepare a co-crystal between a prototypical ketone and a primary amine yielded the crystal structure reported herein, in which the hydrogen bonds between the co-crystal components indeed exhibit exclusively the designed and sought-after R 2 4 (8) motif.

Polynuclear amidinate zinc halide complexes of the general type{C[C(Ni-Pr)2ZnX]4} [X = Cl, 2; Br, 3; I, 4] were prepared in high yields via methyl/halide exchange reaction of {C[C(Ni-Pr)2ZnMe]4} (1a) with AlX3. 2−4 were characterized by elemental analysis, multinuclear NMR, and IR spectroscopy and single-crystal X-ray diffraction. Computational calculations of halide-substituted complexes {C[C(Ni-Pr)2ZnX]4} [X = F−I] were performed to clarify the influence of the halide atom on the structural parameters of the complexes and to elucidate their electronic structure and bonding situation. The capability of these halide-substituted complexes to serve as suitable starting reagents for further salt elimination reactions was proven by reaction of 2 with LiR (R = Me, n-Bu) and EtMgBr, which yielded the corresponding Zn-alkyl species {C[C(Ni-Pr)2ZnR]4} [R = Me, 1a; n-Bu, 5; Et, 6].

We report on the synthesis and the antimicrobial activity of 9-cyclopropyl-4-fluoro-6oxo[1,2,5]thiadiazolo[3,4-h]quinoline-5-carboxylic acid (16), representative of a new class of antibacterial agents structurally related to the clinically successful fluoroquinolones. The novel 6-fluoroquinolone (16) is herein prepared, in good yield, by thermal cyclocondensation of ethyl 7,8-diamino-9-cyclopropyl-4-fluoro-6-oxoquinoxaline-7-carboxylate with thionyl chloride, followed by acid-catalysed hydrolysis of the ester intermediate (15). Their structures were characterized by IR, MS, 1 H- and 13 C NMR spectra and X-ray crystal structure of 16 is presented. The antimicrobial evaluation against a broad panel of wild and resistant Grampositive and Gram-negative bacteria and fungal species demonstrated the high antibacterial activity of 16, even at the concentration of 0.015 µg mL -1 .

The adducts of aryliodinedifluorides ArfIF2, (Arf = C6F5; x-FC6H4, x = 2, 3, 4) and aryliodinedicyanide 4-FC6H4I(CN)2 with N-bases (phenanthroline, 2,2′-bipyridine, and quinoline) were isolated and characterized by their single crystal structure, Raman spectra, and their multi nuclear magnetic resonance spectra in solution. Their properties and their thermal decomposition are discussed with respect to the non-coordinated analogues.

Potassium isopropyl xanthate, (CH3)2CHOC(S)SK, reacts with methyl chloroformiate ClC(O)OCH3 to yield (methoxycarbonyl) (2-propoxythiocarbonyl) sulfide, (CH3)2CHOC(S)SC(O)OCH3. This novel xanthogen formate was characterized by 1H and 13C{1H} NMR spectroscopy, mass spectrometry and IR and Raman spectroscopy. The structure of a single crystal of (CH3)2CHOC(S)SC(O)OCH3 was determined by X-ray diffraction analysis at 173 K. The conformational properties have been studied by liquid IR and Raman spectroscopy, matrix isolation spectroscopy together with photochemical studies and quantum chemical calculations (HF and B3LYP methods with the 6-31+G* basis set). The analysis of the IR spectrum of liquid (CH3)2CHOC(S)SC(O)OCH3 suggests the presence of two conformers in equilibrium at room temperature. However, in the photochemical matrix study, an equilibrium of three conformers was detected. These forms were further characterized by theoretical calculations. Different photolysis products, such as CH3OC(O)SCH(CH3)2, OCS, CO, CO2 and CS2, were identified by matrix spectroscopy. The IR absorptions of CH3OC(O)SCH(CH3)2, for which literature data are scarce, were analysed in the light of the results of appropriate theoretical calculations. Copyright © 2009 John Wiley & Sons, Ltd.

Bis(pentafluorophenylxenonium) tetrafluoroterephthalate (1) was obtained by metathesis reactions of pentafluorophenylxenonium and tetrafluoroterephthalate salts. The availability of suitable solvents for the metatheses hampered the optimization of the reaction. The new xenon–carbon compound with two polar Xe–O bonds was characterized by NMR spectroscopy in solution and by Raman spectroscopy in the solid state. From (CF3)2CHOH/MeCN solutions single crystals were obtained with four alcohol molecules attached to 1 by hydrogen bridges. The thermal properties of the intrinsically unstable title compound are reported.

This is the peer reviewed version of the following article: Angew. Chem. 2009,121, 5859-5862 which has been published in final form at: https://doi.org/10.1002/ange.200902202 Version of Record online: 30 June 2009

This is the peer reviewed version of the following article: Angew. Chem. Int. Ed., 2009,48, 5748-5751, which has been published in final form at: https://doi.org/10.1002/anie.200902202 Version of Record online: 30 June 2009

The four-membered heterocyclic beta-propiothiolactone compound was isolated in a low-temperature inert Ar matrix, and the UV-visible (200or = lambdaor = 800 nm) induced photochemistry was studied. On the basis of the IR spectra, the formation of methylketene (CH(3)CHCO) was identified as the main channel of photodecomposition. The formation of ethene and thiirane, with the concomitant elimination of OCS and CO, respectively, was also observed as minor decomposition channels. The valence electronic structure was investigated by HeI photoelectron spectroscopy assisted by quantum chemical calculations at the OVGF/6-311++G(d,p) level of theory. The first three bands at 9.73, 9.87, and 12.06 eV are ascribed to the n''(S), n'(O), and pi''(CO) orbitals, respectively, denoting the importance of the -SC(O)- group in the outermost electronic properties. Additionally, the structure of a single crystal, grown in situ, was determined by X-ray diffraction analysis at low temperature. The crystalline solid [monoclinic system, P21/c, a = 8.1062(1) A, b = 10.3069(2) A, c = 10.2734(1) A, beta = 107.628(1) degrees, and Z = 8] consists of planar molecules arranged in layers. The skeletal parameters, especially the valence angles [angleC2-C1-S = 94.55(7) degrees, angleOC-C = 134.20(11) degrees, angleC-S-C = 77.27(5) degrees], differ from those typically found in acyclic thioester compounds, suggesting the presence of strong strain effects. The conventional ring strain energy was determined to be 16.4 kcal/mol at the G2MP2 level of calculation within the hyperhomodesmotic model.