3-Phenyl-N,N,N′,N′-tetra­methyl-1-ethyne-1-carboximidamidium bromide

The reaction of 3,3,3-tris­(dimethyl­amino)-1-phenyl­prop-1-yne with bromine in pentane yields the title compound, C13H17N2 +·Br−. The acetyl­enic bond distance [1.197 (2) Å] is consistent with a C C triple bond. The amidinium C=N bonds [1.325 (2) and 1.330 (2) Å] have double-bond character and the positive charge is delocalized between the two dimethyl­amino groups

1,1,2,2-Tetra­kis(dimethyl­amino)­ethane-1,2-diium bis­(tetra­phenyl­borate) acetone disolvate

The title compound, C10H24N4 2+·2C24H20B−·2C3H6O, crystallizes with two acetone solvent mol­ecules per asymmetric unit. In the dication, both amidinium units are twisted about the central C—C single bond by 63.8 (3)° and the positive charges are delocalized over both N—C—N planes

Investigations on reactivity, structure and dynamic of ionic closo-dodecaborates

Das Ziel der Arbeit war die Synthese, der strukturelle Aufbau, die Reaktivität und das dynamische Verhalten von salzartigen closo-Dodekaboraten im Festkörper mit Methoden der Röntgenbeugung an Einkristallen und der Festkörper-NMR-Spektroskopie an polykristallinen Pulverproben aufzuklären. Ausgehend von der ionischen Verbindung Cs2[B12H12] war es möglich, durch elektrophile Substitution die Wasserstoffatome des [B12H12]2–-Clusters gegen Halogenatome teilweise oder vollständig zu ersetzen. Durch Ionenaustauschtechniken gelang es die Cs+-Kationen gegen beliebige andere anorganische Kationen des Periodensystems zu ersetzen, was zusätzlich eine Vielfalt von bisher in der Literatur nur wenig bekannten Kristallstrukturen lieferte. Betrachtet man sich die [B12X12]2–-Anionen (X = H, Cl - I) genauer, so bilden die zwölf Boratome nahezu ein Ikosaeder, das von zwölf exo-ständigen Atomen in ebenfalls ikosaedrischer Weise terminiert wird. Liegen in Lösung freie [B12X12]2–-Anionen mit ihrer höchstmöglichen Symmetrie unverzerrt vor, so kann ein Ikosaeder im kristallinen Festkörper keine fünfzählige Drehachse realisieren und eine Verringerung der Anionensymmetrie ist deshalb zwingend. Dies hat eine Verzerrung des Ikosaeders zur Folge. Untersuchungen zum thermischen Abbau der closo-Dodekaborate mittels differenzthermoanalytischer Methoden (DTA/TG) belegen weiterhin die hohe thermische Stabilität dieser Verbindungsklasse. An einigen synthetisierten closo-Dodekaboraten wurden zusätzlich 11B-Festkörper-NMR-Untersuchungen vorgenommen. Im Vordergrund stand die Messung von temperaturabhängigen 11B-NMR-Pulverspektren unter statischen sowie Magic-Angle-Spinning-Bedingungen (MAS). Zusätzlich führte man temperaturabhängige Spin-Spin- und Spin-Gitter-Relaxationsexperimente durch, um die dynamischen Effekte im Festkörper genauer zu studieren. Die Befunde stützen die Annahme, daß in den meisten Fällen schon bei Raumtemperatur eine isotrope Reorientierungsbewegung der [B12H12]2–-Cluster stattfindet. Bei der Aufnahme von temperaturabhängigen statischen 11B-NMR-Spektren (sowohl protonenentkoppelt als auch nicht entkoppelt) sind Veränderungen an den Linienprofilen zu beobachten. Während bei höheren Temperaturen die dipolaren (11B-11B, 11B-10B, 11B-1H) als auch die quadrupolaren Wechselwirkungen durch die Dynamik ausgemittelt sind (isotrope Linie) wird bei tiefen Temperaturen ein 11B-Pulverspektrum mit einer charakteristischen Aufspaltung detektiert, die Bewegung der B12-Cluster scheint demnach eingefroren zu sein. Durch entsprechende Computer-Simulationen war es möglich, Rückschlüsse auf die Art des Bewegungsmechanismus der B12-Ikosaeder zu ziehen (Vier-Site-Sprungprozess) und diesbezüglich die Aktivierungsenergien für die Bewegung der Cluster-Anionen den in den entsprechenden Modellverbindungen zu bestimmen.The aim of this work was to clear up the synthesis, structure, reactivity and dynamic behavior of ionic closo-dodecaborates [B12X12]2– (X = H, Cl - I) in the solid state. Main object of the investigations was the structure determination of these salt-like solids with X-ray single crystal methods and solid state NMR spectroscopy on powder samples. In all compounds isolated, cage-like [B12X12]2– anions (X = H, Cl - I) are found in which twelve boron atoms form nearly a perfect icosahedron, that is icosahedrally surrounded by twelve hydrogen or halogen atoms. While in solution free [B12X12]2– anions with the highest possible symmetry are present, in the crystalline solid an icosahedron cannot realize a five fold axis of rotation and therefore a decrease of the anion symmetry by distortion is necessary. Investigations on the thermal decomposition of the ionic closo-dodecaborates show a high thermal stability for these compounds. For solid state 11B NMR investigations the solvent free dodecahydro-closo-dodecaborates of the heavy alkali metals M2[B12H12] (M = K, Rb, Cs and NH4) and [N(CH3)4]2[B12H12] as well the perhalogenated cesium salts Cs2[B12X12] (X = Cl, Br, I) were used as model compounds. Main interest was to study the influence of the cations and the present substituents at the boron cluster on the molecular mobility of the [B12X12]2– anions in the crystalline solid. Therefore the measurement of temperature-dependent 11B NMR spectra under static and magic angle spinning conditions held priority. Furthermore temperature dependant spin-spin- und spin-lattice relaxation measurements were performed for more accurate studies of the dynamic effects in the solids. The solid state NMR results support the prediction, that at room temperature a fast isotropic reorientation motion of the [B12H12]2– clusters takes place in the crystal lattice. Measurements of temperature dependant, static 11B NMR spectra (proton-decoupled as well as not decoupled) exhibit drastic changes only by cooling. At higher temperatures the dipolar (11B-11B, 11B-10B, 11B-1H) and quadrupolar interactions are averaged by the molecular mobility of the cluster anions (isotropic central signal), while at lower temperatures a 11B powder pattern with a characteristic dipolar splitting is observed. The movement of the B12-Cluster seems to be frozen on NMR time scale. During additional computer simulations it was possible to obtain more information about the molecular reorientation process of the [B12H12]2– icosahedra. As basis for the simulation of the spectra, a four site jump model was used. Here, a good agreement between the theoretical and experimental spectra can be obtained and the dynamics of the [B12H12]2– anions could be sufficiently described. From the temperature dependence of the rate constants, the kinetic parameters and thus the activation energies for the four site jump process of the [B12H12]2– cluster in their heavy alkali metal salts have been determined

2-Acetyl-1,1,3,3-tetramethylguanidine

In the molecule of the title compound, C7H15N3O, the central C atom is surrounded in a nearly ideal trigonal–planar geometry by three N atoms. The C—N bond lengths in the CN3 unit are 1.3353 (13), 1.3463 (12) and 1.3541 (13) Å, indicating an intermediate character between a single and a double bond for each C—N bond. The bonds between the N atoms and the terminal C-methyl groups all have values close to that of a typical single bond [1.4526 (13)–1.4614 (14) Å]. In the crystal, the guanidine molecules are connected by weak C—H...O and C—H...N hydrogen bonds, generating layers parallel to the ab plane

N-[3-(Benzyldimethylazaniumyl)propyl]-N′,N′,N′′,N′′-tetramethylguanidinium bis(tetraphenylborate)

In the crystal structure of the title salt, C17H32N42+·2C24H20B−, the C—N bond lengths in the CN3 unit of the guanidinium ion are 1.323 (4), 1.336 (5) and 1.337 (5) Å, indicating partial double-bond character in each. The C atom of this unit is bonded to the three N atoms in a nearly ideal trigonal–planar geometry [N—C—N angles = 117.7 (4), 120.9 (3) and 121.4 (3)°] and the positive charge is delocalized in the CN3 plane. The bonds between the N atoms and the terminal C-methyl groups of the guanidinium moiety all have values close to a typical single bond [1.452 (5)–1.484 (6) Å]. In the crystal, C—H...π interactions are present between guanidinium H atoms and the phenyl rings of both tetraphenylborate ions. This leads to the formation of a two-dimensional supramolecular pattern along the ab plane