Force field parameters used to describe the conformation of coordination compounds involving transition metals are generally derived by a trial-and-error procedure, until a somehow satisfying agreement between the calculated and observed conformations of a few members of a class of related compounds is reached. It is shown in this paper that a more general and less biased alternative is available, applicable to many structures at a time. Genetic Algorithms will effectively optimize force field parameters in an automatic way, on the basis of a potentially exhaustive set of all the structural data available for a given class of compounds. The feasibility of this procedure has been demonstrated by the derivation of force field parameters describing the conformational behaviour of tripod-Mo(CO)(3) compounds [tripod RCH2C(CH2X)(CH2Y)(CH(2)Z), X,Y,Z = PR'R ")] by simultaneous optimization based on the structure of ten individual molecules. With the force field parameters relevant to the organic part of these compounds taken from MM2*,the parameters involving contributions from the Mo center were refined. The agreement between observed and calculated structures is characterized by an rms deviation of around 0.3 Angstrom for the ten structures contained in the data base. To assess the validity of this approach, the conformational space of CH3C(CH2PPh2)(3)Mo(CO)(3) was explored exhaustively, A contour diagram representing the relative energy of the molecule with respect to the rotational positions of its phenyl groups was found to effectively reproduce the scatter of these conformational parameters as earlier derived from an analysis of 82 relevant compounds. - As a further assessment, the conformational space of CH3C[CH2P(o-Tol)(2)](3)Mo(CO)(3), which was not included in the data base, has been analyzed. It is found that the structure corresponding to the global energy minimum corresponds to that observed in the crystal with an rms deviation of only 0.3 a. The novel approach to problems of this type - Genetic Algorithms had not previously been applied in this context - thus appears promising.

The energy decay function for an excited donor molecule surrounded by acceptors in diffusional motion is computed for a finite-size donor and arbitrary characteristics of the boundary. We evaluate the donor-acceptor---pair diffusion function via a Green-function approach for the Feynman-Kac equation in Laplace space. Quick and stable numerical solutions for the acceptor-averaged pair diffusion function, and thereby the energy decay functions, can be obtained, thus allowing model parametrization from time-resolved fluorescence measurements.

The energy transfer from excited donors to acceptors is enhanced by molecular motion. We present rate constants for processes due to exchange and multipolar interactions. The expressions explicitly incorporate the boundary conditions, which are decisive: for rapid motion the decay is diffusion controlled for absorbing and diffusionindependent for reflecting boundaries.

Molecular motion enhances the energy transfer from excited donors to diffusing acceptors. We present the decay law for transfer processes mediated by dipolar and quadrupolar interactions. From the expansions in the diffusion coefficients, valid for short times, expressions tor longer times are obtained through Padé approximation.

In a recent work [K. Allinger and A. Blumen, J. Chem. Phys. 72, 4608 (1980)] we derived expressions for the energy decay of an excited donor due to its interactions with moving acceptors. As we show here, this approach is related to path-integral methods which occur in different fields. We apply the formalism to interactions mediated by exchange. Analytic expressions are found for the decay due to acceptors moving slowly or rapidly on the time scale of the energy transfer. If the motion is frozen we retrieve the decay law for acceptors imbedded randomly in a solid matrix [A. Blumen, J. Chem. Phys. 72, 2632 (1980)]. For slow diffusive motion, as in the three-dimensional dipolar case [M. Yokota and O. Tanimoto, J. Phys. Soc. Jpn. 22, 779 (1967)], the decay may be expressed by means of a power series in the diffusion coefficients. Here we obtain the coefficients of the series from a recurrence formula and present the first ten terms. An approximate, compact formula for the decay law is also given. In the rapid motion case the decay law depends on the distance of nearest approach between donor and acceptors, but not on the details of the motion.

This paper studies the decay law of the excitation of a donor molecule, due to its microscopic long range interactions with moving acceptor molecules. Particular attention is given to the case of acceptor molecules randomly dispersed in a host liquid. From a general approach we derive an exact ensemble averaged formula for the decay of the donor excitation as a function of the molecular motion. The expression obtained is valid for all types of microscopic molecular interactions and for arbitrary ratios of acceptors to inert molecules; from this formula we determine the energy decay for motions which are slow or rapid relatively to the microscopic energy transfer times. If the motion is frozen, we retrieve the decay law valid for acceptors imbedded randomly in a solid matrix [A. Blumen and J. Manz, J. Chem. Phys. (to be published)]. For slow molecular displacements, which obey the Langevin equations of Brownian motion, the diffusion dependent decay law is presented; in the case of low acceptor concentration and multipolar interactions the expression reduces to the Yokota and Tanimoto result [J. Phys. Soc. Jpn 22, 779 (1967)], generalized to spaces of arbitrary dimensions. In the case of rapid motion, the decay becomes motion independent, and is not diffusion controlled.

The complex η-diiminobis(pentacarbonylchromium) crystallizes from THF solutions as red crystals, which are only stable under THF vapour and decompose to an amorphous solid on reduction of the THF partial pressure.

Chemischer InformationsdienstVolume 6, Issue 35 Physical Organic Chemistry ChemInform Abstract: KRISTALL- UND MOLEKUELSTRUKTUR DES DIIMIN-KOMPLEXES N2H2(CR(CO)5)2.2THF G. HUTTNER, G. HUTTNERSearch for more papers by this authorW. GARTZKE, W. GARTZKESearch for more papers by this authorK. ALLINGER, K. ALLINGERSearch for more papers by this author G. HUTTNER, G. HUTTNERSearch for more papers by this authorW. GARTZKE, W. GARTZKESearch for more papers by this authorK. ALLINGER, K. ALLINGERSearch for more papers by this author First published: September 2, 1975 https://doi.org/10.1002/chin.197535073AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume6, Issue35September 2, 1975 RelatedInformation

Angewandte Chemie International Edition in EnglishVolume 13, Issue 12 p. 822-823 Communication Structure of Diimine: X-ray Diffraction Analysis of N2H2[Cr(CO)5]2·2THF† Univ.-Doz. Dr. Gottfried Huttner, Corresponding Author Univ.-Doz. Dr. Gottfried Huttner Anorganisch-Chemisches Laboratorium der Technischen Universität 8 München 2, Arcisstrasse 21 (Germany)Anorganisch-Chemisches Laboratorium der Technischen Universität 8 München 2, Arcisstrasse 21 (Germany)Search for more papers by this authorDipl.-Chem. Wolfgang Gartzke, Dipl.-Chem. Wolfgang Gartzke Anorganisch-Chemisches Laboratorium der Technischen Universität 8 München 2, Arcisstrasse 21 (Germany)Search for more papers by this authorKurt Allinger, Kurt Allinger Anorganisch-Chemisches Laboratorium der Technischen Universität 8 München 2, Arcisstrasse 21 (Germany)Search for more papers by this author Univ.-Doz. Dr. Gottfried Huttner, Corresponding Author Univ.-Doz. Dr. Gottfried Huttner Anorganisch-Chemisches Laboratorium der Technischen Universität 8 München 2, Arcisstrasse 21 (Germany)Anorganisch-Chemisches Laboratorium der Technischen Universität 8 München 2, Arcisstrasse 21 (Germany)Search for more papers by this authorDipl.-Chem. Wolfgang Gartzke, Dipl.-Chem. Wolfgang Gartzke Anorganisch-Chemisches Laboratorium der Technischen Universität 8 München 2, Arcisstrasse 21 (Germany)Search for more papers by this authorKurt Allinger, Kurt Allinger Anorganisch-Chemisches Laboratorium der Technischen Universität 8 München 2, Arcisstrasse 21 (Germany)Search for more papers by this author First published: December 1974 https://doi.org/10.1002/anie.197408221Citations: 27 † This work was supported by the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie, and the Leibniz-Rechenzentrum der Bayerischen Akademie der Wissenschaften. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat No abstract is available for this article. References 1 N. Wiberg, H. Bachhuber, and G. Fischer, Angew. Chem. 84, 889 (1972); Angew. Chem. internat. Edit. 11, 829 (1972). 2 N. Wiberg, G. Fischer, and H. Bachhuber, Chem. Ber. 107, 1456 (1974). 3(a) D. Sellmann, J. Organometal. Chem. 44, C46 (1972); D. Sellmann, A. Brandl, and R. Endell, J. Organometal. Chem. 49, C22 (1973); Angew. Chem. 85, 1121 (1973); Angew. Chem. internat. Edit. 12, 1019 (1973); (b) Angew. Chem. internat. Edit. 85, 1122 (1973), and Angew. Chem. internat. Edit. 12, 1019 (1973), respectively. 4 We thank Dipl.-Chem. A. Brandl for preparing samples of the crystals. 5 According to IR spectroscopic investigations [3 b], the N2H2 ligand in the unsolvated complex (1) has a symmetry deviating from the trans configuration. 6 A much shorter N = N distance has been observed in bis(trimethylsilyl)diimine: M. Veith and H. Bärnighausen, Acta Crystallogr., in press. 7 F. A. Cotton and D. C. Richardson, Inorg. Chem. 5, 1851 (1966). 8 The chromium-nitrogen distance in cis-Cr(diene)CO3 [6] is possibly changed compared to a normal Cr—Nsp distance by strains in the chelate system: F. A. Cotton and M. B. LaProde, J. Amer. Chem. Soc. 91, 7000 (1969). 9 F. B. Boer and J. W. Turley, J. Amer Chem. Soc 91, 1371 (1969). 10 D. A. Dietrich, I. C. Paul, and D. Y. Curtin, Chem. Common. 1970, 1710. 11 In the case of the complexes [(R2PC2H4PR2)2MX2]N2H2 with R= alkyl, aryl: X=halogen; and MMo, W, described by Chatt et al., only the presence of a hydrazido ligand (=N-NH2) has so far been detected: G. A. Heath, R. Mason, and K. M. Thomas, J. Amer. Chem. Soc. 96, 259 (1974). Citing Literature Volume13, Issue12December 1974Pages 822-823 ReferencesRelatedInformation

dl-Phenylalaninpolypeptide werden unter verschiedenen Bedingungen aus dem N-Carbonsäureanhydrid dargestellt. Die Viskositätserhöhung, die sie in Lösung von Nitrobenzol, Dichloressigsäure und Benzol hervorrufen, wird bestimmt. Es besteht keine Beziehung zwischen dem mittleren Polymerisationsgrad der Polypeptide und den Viskositätseigenschaften ihrer Lösungen. In allen untersuchten Fällen scheint eine starke Aggregation der Polypeptidmolekel in Lösung vorzuliegen.

Es wird die Geschwindigkeit der Kohlendioxydabspaltung aus d,l-Phenylalanin-N-carbonsäureanhydrid unter dem Einfluß von N-Äthylglycindiäthylamid und p-Chloranilin in Nitrobenzol- und Benzollösung gemessen. Das Kohlendioxyd wird nach Absorption in Natronlauge durch Leitfähigkeitsmessung quantitativ bestimmt. Die Geschwindigkeitskonstanten für Start- und Wachstumsreaktion der Polypeptidbildung werden angegeben. An einigen der erhaltenen Polypeptide werden Endgruppenbestimmungen ausgeführt und ein Vergleich mit dem kinetisch zu erwartenden Endgruppengehalt durchgeführt.