Erwin Weiss

Die kristall- und elektronenstruktur des methyllithiums

Zusammenfassung Es wurde die Kristallstruktur des Methyllithiums bestimmt. Die kubisch-raumzentrierte Elementarzelle ( a = 7.241 ≐ 0.01 A; Raumgruppe I 4 3 m ) enthalt 8 CH 3 Li. Je vier Lithiumatome bilden regulare Tetraeder mit gleichen Li-Li-Abstanden 2.56 A; uber der Mitte jeder Tetraederflache befindet sich eine Methylgruppe, dessen Kohlenstoffatom Vierzentren-Bindungen mit den drei benachbarten (2.28 A) Lithiumatomen bildet. Die Elektronenstruktur dieser Tetraeder wird im Rahmen der Theorie der Molekulzustande behandelt. Dabei werden die 2 s - und 2 p -Zustande der Lithiumatome berucksichtigt. Es wird gezeigt, dass vier stark bindende Molekulzustande — ein nicht entarteter und drei entartete — existieren, in denen sich die acht zur Verfugung stehenden Elektronen gerade unterbringen lassen. Anschliessend werden intermolekulare Wechselwirkungen zwischen den einzelnen Tetraeder-Einheiten und ihr Zusammenhang mit den physikalischen Eigenschaften von Methyl- und Athyllithium diskutiert.

Über metall-alkyl-verbindungen ☆: XII. verfeiner ung der kristallstruktur des methyllithiums

Abstract The crystal structure of methyllithium has been refined from X-ray powder data. The cubic unit cell ( a = 7.24 °A, space group I 4 3 m contains two tetrameric units of (CH 3 Li) 4 with the following refined bond distances: Li-Li: 2.6 8 °A; C-Li: 2.3 1 °A (within each tetramer) and C-Li: 2.3 6 °A (between two tetramers). In addition to former results the H atoms could be located.

Dicarbonyl-η5-methylcyclopentadienyl-manganio-bis[dicarbonyl-η5-methylcyclopentadienyl-manganio(MnMn)]germanium, [(η5-CH3C5H4)Mn(CO)2]3Ge und bis[dicarbonyl-η5-methylcyclopentadienyl-manganio]-germanium, [η5-CH3C5H4Mn(CO)2]2Ge. Neuartige verbindungen mit einer bzw. Zwei MnGe-Doppelbindungen

Abstract By treatment of K[(η5-CH3C5H4)Mn(CO)2GeH3] with acetic acid [(η5-CH3C5H4)Mn(CO)2]2Ge is formed. An X-ray analysis shows a linear MnGeMn system. The compound is also a first example for MnGe double bonds. The molecule is centrosymmetric, i.e. the ligands on the Mn atoms are in trans position. The reaction of K[(η5-CH3C5H4)Mn(CO)2GeH3] with Hg2+ ions yields small amounts of [(η5-CH3C5H4)Mn(CO)2]3Ge, which also contains a GeMn(CO)2Cp moiety. In addition a Cp(CO)2MnMn(CO)2Cp unit is attached to the Ge atom through two GeMn single bonds, thus forming a triangular Mn2Ge ring.

Verfeinerung der kristallstruktur von dicyclopentadienylmagnesium, (η-C5H5)2Mg

Abstract The crystal structure of Cp 2 Mg has been re-determined. Refined values for MgC and CC distances are 2.304(8) and 1.39(2) A respectively. In the crystalline state the two parallel rings of Cp 2 Mg have a staggered conformation in contrast to the results obtained from electron diffraction in the gaseous phase. Metal—carbon distances of various Cp 2 M compounds are compared with respect to the bond character.

Über metallalkyl- und -arylverbindungen : XXIII. Darstellung und kristallstruktur des (methyllithium)4(N,N,N′,N′-tetramethylethylendiamin)2

Abstract Methyllithium and N,N,N′,N′ -tetramethylethylendiamine (tmeda) react with formation of (MeLi) 4 (tmeda) 2 . A single-crystal X-ray diffraction study (tetragonal space group 4 2 / n ; a = b 1149, c 902 pm; 605 reflections; R 0.082) reveals that the methyllithium tetramers persist. These units show almost ideal T n symmetry and are linked through Li—tmeda—Li bridges. Bond distances for LiLi(256–257 pm) and LiC(Me)(223–227 pm) are of particular interest because so far only less accurate values for non-complexed methyllithium were available from powder data.

Die kristallstruktur des dimethylmagnesiums

Zusammenfassung Die Kristallstruktur des Dimethylmagnesiums wurde rontgenographisch ans Pulveraufnahmen ermittelt. Dimethylmagnesium bildet wie Dimethylberyllium hochmolekulare Ketten in einem rhombischen Gitter ( a = 6.00; b = 11.48; c = 5.45 A; wahrscheinliche Raumgruppe Ibam-D 26 2k ). Die Mg-Mg-Abstande in den Ketten betragen 2.73 A; die Metallatome sind durch je zwei Methylbrucken verknupft (Mg-C-Abstand 2.24 A), so dass jedes Metallatom etwa tetraedrisch von vier Methylgruppen umgeben ist. Aus den gefundenen Abstanden lasst sich auf eine gegenuber Dimethylberyllium verfestigte Bindung in den Ketten schliessen, wodurch die geringere Fluchtigkeit der Magnesiumverbindung erklart wird.

Verfeinerung der kristallstruktur von dicyclopentadienylkobalt, (η5-C5H5)2Co

Abstract The crystal structure of Cp 2 Co has been refined. Both cyclopentadienyl rings are parallel to each other and in a staggered conformation. The average CC distance is 1.41(1) A and the CoC distance 2.096(8) A.

Über metallalkyl und arylverbindungen

Abstract The title compound has been prepared and investigated by X-ray diffraction (monoclinic space group P 2 1 / n , Z = 4, 2456 reflexions, R = 0.07). The structure resembles that of Ph 3 CLi ⋯ tmeda (tmeda = N,N,N′,N′ -tetramethylethylenediamine) and can be described as a contact ion pair of a triphenylmethyl carbanion and a sodium ion coordinated to the bidentate ligand tmeda. The Na ion has close contacts to several C atoms of the π-carbanion (264 pm to the central C(methyl) atom, 288–309 pm to two adjacent C atoms of two phenyl groups). A further short distance (296 pm) exists between Na and a p -C(phenyl) atom of a neighbouring carbanion. Each carbanion is planar in its central part but has twisted and elongated phenyl groups.

Carbonyl-eisen-komplexe von pentafulvenen

Abstract The structures and spectroscopic properties (IR, NMR) of coordination compounds formed by the reaction of diphenylfulvene, dimethylfulvene and diethylfulvene with Fe 2 (CO) 9 are reported. Single-crystal X-ray diffraction studies of bis(dimethylfulvene)pentacarbonyldiiron and diphenylfulvenepentacarbonyldiiron have been made. The covalent single-bond radius of iron in the η-cyclopentadienyldicarbonyliron and η-allyltricarbonyliron group has been found to be 1.38 A. Chemical bonding in diphenylfulvenepentacarbonyldiiron and 6-dimethylaminofulvenylfulvenepentacarbonyldiiron has been studied using the simple HMO-model.

Über metallalkyl- und aryl-verbindungen ☆: XXXV. Zur struktur von allyllithium. Darstellung und kristallstruktur einer monomeren allyllithium-verbindung, allyl(pentamethyldiethylentriamin)lithium, LiC3H5(Me2NC2H4N(Me)C2H4NMe2)

Abstract Allyl(pentamethyldiethylenetriamine)lithium represents the first example of a crystalline monomeric allylithium complex. An X-ray diffraction investigation at 117 K revealed the precise structure of the LiC3H5 unit. The structural data show qualitative agreement with the results of previous theoretical calculations. Contrary to theory, however, asymmetrical bonding of the allyl group to lithium is observed, giving Li to terminal C atom distances of 225.5(5) for LiC(1) and 272.0(4) pm for LiC(3). The C3H5 unit is not planar. The central H(2) atom is bent slightly towards the Li atom; all terminal H atoms are bent in the opposite direction, particularly H(11) and H(31) which are anti to H(2).