H. Rieskamp

Bio: H. Rieskamp is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 12 citations.

Dioxofluoro-oxalato-vanadat: ein fünffach koordiniertes, monomeres Komplexion des Vanadins(V)

Abstract: (NH4)2VO2F(C2O4) kristallisiert in der Raumgruppe P21/c mit 4 Formeleinheiten pro Elementarzelle und a = 11,362(2), b = 9,503(2), c = 7,190(1) A und β = 96,02(2)° Der R-Wert mit 1046 Reflexen betragt 0,038 Im komplexen Anion ist Vanadin verzerrt trigonal-bipyramidal von 2 Sauerstoffatomen, dem Fluoratom und dem Oxalation als zweizahnigem Liganden koordiniert Das Zentralatom, Fluor und die Oxalatgruppe liegen in einer Ebene Die sehr kurzen Abstande in der cis-Dioxogruppe betragen 1,617(4) bzw 1,614(4) A bei einem Winkel von 107,5(2)°, die V–O(Oxalat)-Abstande 2,016(4) und 2,031(4) A, der Vanadin-Fluor-Abstand 1,893(3) A Die Schwingungen νas bzw νsVO2 liegen bei 930 bzw 948 cm−1 Die weiteren Banden des Schwingungsspektrums werden ebenfalls zugeordnet Dioxofluorooxalatovanadate: a Monomeric, Fivefold Coordinated Complex Ion of Vanadium(V) (NH4)2VO2F(C2O4) crystallises in the space group P21/c with 4 formula units per unit cell and a = 11362(2), b = 9503(2), c = 7190(1) A und β = 9602(2)° 1046 reflection data were refined to R = 0038 In the complex anion vanadium is trigonal bipyramidally coordinated by two terminal oxygen atoms in cis position, fluorine and a bidentate oxalate ion The coordination polyhedron is highly distorted The very short bonds in the dioxo-group forming an angle of 1075° have lengths of 1617(4) and 1614(4) A The V—O (oxalate) distances are 2016(4) and 2031(4) A, the V—F distance is 1893(3) A The vibrations νas VO2 and νsVO2 are observed at 930 and 948 cm−1, respectively The remaining bands of the vibrational spectra are also assigned

Trigonal Bipyramidal or Square Pyramidal Coordination Geometry? Investigating the Most Potent Geometry for Vanadium Phosphatase Inhibitors

Abstract: The five-coordinate geometry is an important factor in phosphoryl group transfer, particularly for phosphate ester hydrolysis. In the following review we analyze the five-coordinate geometries for a range of VO4X coordination spheres with regard to their structure from the point of view of square pyramidal or trigonal bipyramidal geometries. The actual differences for the coordination environment of the reported small molecule structures are compared to the coordination environment of vanadate complexed to a protein tyrosine phosphatase (PTP) with four coordinating O atoms and one S atom. These considerations demonstrate that actual differences between the coordination environments are very small and presumably less critical than generally anticipated. This analysis suggests that it is a combination of structural and electronic properties leading to the perfect combination of reactivity and stability for the potent protein phosphatase inhibitor complex, thus confirming the fact that some other geometries have been reported.

Tetramere Dioxo‐oxalato‐Komplexe des Vanadins(V). Die Kristallstruktur von K[VO2(C2O4)] · 2H2O

Abstract: Die roten Dioxo(oxalato)vanadate(V), M1[VO2(C2O4)] nH2O (M1 = Na, K, NH4, Rb, 1/2Sr) enthalten, wie durch eine Rontgenstrukturanalyse an K[VO2(C2O4)] 2H2O ermittelt wird, das tetramere, cyclische Anion [{VO2(C2O4)}4(H2O)2]4−. Alle Vanadinatome sind oktaedrisch von einem endstandigen und zwei verbruckenden Sauerstoffatomen, von einem Wassermolekul und einem Oxalat-Ion als zweizahnigem Ligand koordiniert. Je 2 Oktaeder sind uber eine gemeinsame Kante zu einem Paar verknupft; zwei Paare bilden dann uber zwei einfache Sauerstoffbrucken (Spitzenverknupfung) die tetramere Einheit. Tetrameric Dioxo(oxalato)vanadates(V). The Crystal Structure of K[VO2(C2O4)] · 2H2o The red compounds M1 [VO2(C2O4)] · nH2O (M1 = Na, K, NH4, Rb, 1/2 Sr) contain, as has been shown by X-ray crystal structure analysis, the tetrameric, cyclic anion [{VO2(C2O4)}(H2O)2]4−. Each vanadium atom is octahedrally coordinated by one terminal and two bridging oxygen atoms, one water molecule, and a bidentate oxalate ligand. Pairs of VO6-octahedra are formed by sharing an edge. Two pairs are then joined together by sharing vertices.

Molecular Modeling of Vanadium−Oxo Complexes. A Comparison of Quantum and Classical Methods

Abstract: A force field for vanadium−oxos was developed and tested with a variety of complexes with coordination numbers of 5 or 6 and formal oxidations states of +4 or +5 on the metal. Similarly, a semiempirical quantum mechanical method for transition metals was extended to vanadium. In this research soft and hard ligands were studied, as were ligands coordinated through single, multiple, and dative bonds. Despite the diversity of vanadium coordination chemistry, generally good modeling is achieved in a fraction of the time with less computational resources using molecular mechanics and semiempirical quantum mechanics. The L4V4+O and L5V5+O groups were emphasized given their prevalence and importance. In general, the predictive ability was superior for the former structural motif. The combination of molecular mechanics and semiempirical quantum calculations provide an effective and efficient tool for analysis of the steric and electronic energy differences between isomers.

Synthesis, structure and spectra of ammonium (salicylaldehydes s-methyltiosemic arbazonato) dioxovanadate(v) monohydrate

Abstract: Crystals of ammonium (salicylaldehyde S-methylthiosemicarbazonato)dioxovanadate(V)monohydrate, NH4[VO2L]·H2O were synthesized from ammonia–ethanol solution of VCl3 and salicylaldehyde S-methylthiosemicarbazone (H2L). They belong to the monocyclic system, space group P21/c, a, = 5.864(2), b = 16.382(7), c = 13.931(5)A, β = 97.60(3)°, Dm = 1.62, Dc = 1.63. The position of the vanadium atom was determined on the basis of the distribution of Patterson function, coordinates of the other atoms on the basis of Fourier synthesis. Vanadium occurs in the complex within the VO2 + group, lacking d-electrons. The coordination polyhedron has the form of a deformed square pyramid. The bands in infrared spectrum indicate the existence of valence oscillations of O=V=O group. Absorption spectra of the complex and ligand were calculated from the measured reflectance spectra by the application of Kubelka-Munk theory. Two out of the seven absorption maxima in the spectrum, result from intraligand transitions and the ...