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Computational Insight into the PNP-Lariat Ether Complexes with Some Alkali and Alkaline Earth Metal Cations

Supramolecular host-guest chemistry has attracted the growing attention of numerous researches over the past decades. The lariat ethers, the crown ethers having a side arm attached to the macrocycic system, were found to display very interesting cation-binding properties.1 In this work a complexation of some alkali and doubly- charged alkaline earth metal cations with PNP- lariat ethers [N3P3R4O(CH2CH2O)4] (R=H(1), NMe2(2), NC(NMe2)2(3)) in the gas phase has been studied by the DFT B3LYP/6-311+G(3df, 2p)//B3LYP/6-31+G(d, p) quantum chemical method. The obtained computational results indicate that these ligand structures act as efficient and very selective scavengers of Li+, Na+, K+, Be2+, Mg2+ and Ca2+ cations, exhibiting gas phase cation affinities in a wide range of 64.2 – 496.1 kcal mol-1. The cation affinity of the hosts has been found to be significantly amplified by attaching the electron-donating group to the P3N3 ring. The Bader's topological analysis of the electron density distribution function has been preformed for the studied complexes with the aim to gain more insight into their bonding properties. It was found that the coordination bonds of the s-block metal centers with the N/O atoms in the studied complexes possess the predominantly ionic character, except those of Be2+ metal cations with the N atoms that coorespond to the intermediate type of interactions. The charge donation from the PNP-lariat ether to the metal cation was established from the orbital population analysis. The amount of charge transfered from the host to the metal cation has found to be particularly significant in the complexes with alkaline earth metal cations. The structural features of considered PNP-lariat ethers complexes are provided and will be discussed. The calculated IR and UV-VIS absorption spectra of the selected complexes will be presented. References 1.G. W. Gokel, Chem. Soc. Rev., 21 (1992) 39. 2.I. Despotović, manuscript in preparation.

PNP-lariat ether ; complexes ; metal cations

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