Quantum chemical study of electronic and dynamic properties of metal and mixed non-stoichiometric clusters

The aim of this contribution is to show that quantum chemistry has suitable tools to extract the specific properties of small metallic and mixed non-stoichiometric clusters which cannot be obtained by extrapolation from the bulk properties to the atom. For this purpose, first the main features of the methods used for the calculations of the ground and excited states of clusters valid at zero temperature (T=0) will be sketched and the factors determining accuracy of results will be pointed out. The structural and optical response properties of cationic Na _n ⁺ clusters as a function of size will be presented and compared with experimental data. The series of non-stoichiometric alkali-halide clusters containing single and multiple excess electrons will serve as prototypes to study a possible “metal-insulator transition” and “segregation into metallic and ionic parts” in finite systems. Second, an outline of ab initio molecular dynamics methods based on gradient corrected density functional approach with gaussian basis used for determination of temperature dependent ground state properties will be presented. Different temperature behavior of distinct type of structures will be illustrated on an example of Li ₉ ⁺ cluster. Presented by V. Bonačić-Koutecky at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5, 1997. This work has been supported by the Deutsche Forschungsgemeinschaft (SFB 337, Energy transfer in molecular aggregates) and the Consiglio Nationale delle Ricerche (CNR, Rome).     

Highly Efficient Chirality Transfer from Diamines Encapsulated within a Self‐Assembled Calixarene–Salen Host

A calix[4]arene host equipped with two bis‐[Zn(salphen)] complexes self‐assembles into a capsular complex in the presence of a chiral diamine guest with an unexpected 2:1 ratio between the host and the guest. Effective chirality transfer from the diamine to the calix–salen hybrid host is observed by circular dichroism (CD) spectroscopy, and a high stability constant K_2,1 of 1.59×10¹¹ M ^?2 for the assembled host–guest ensemble has been determined with a substantial cooperativity factor α of 6.4. Density functional calculations are used to investigate the origin of the stability of the host–guest system and the experimental CD spectrum compared with those calculated for both possible diastereoisomers showing that the M,M isomer is the one that is preferentially formed. The current system holds promise for the chirality determination of diamines, as evidenced by the investigated substrate scope and the linear relationship between the ee of the diamine and the amplitude of the observed Cotton effects.