Available online www.jocpr.com Journal of Chemical and Pharmaceutical Research, 2014, 6(10):18-26 Research Article ISSN : 0975-7384 CODEN(USA) : JCPRC5 18 DFT study of half-sandwich bis (tetramethylaluminate) lanthanide complexes Houria Bennaceur and Nadia Ouddai Laboratoire de chimie des matériaux et des vivants: Activité, Réactivité, University, Hadj Lakhdar, Batna, Algeria _____________________________________________________________________________________________ ABSTRACT Electronic structure of the half-sandwich complexes [Ln(AlMe 4 ) 2 Cp R ] with (Ln=Lu, Y, La), (Cp R = 1,3-(Me 3 Si) 2 C 5 H 3 and C 5 Me 5 ), has been investigated using density functional theory method at the ZORA/PW91/TZP level. The study reveals that the twist angle θ decreases with increasing ionic radii and the effect of substitution,1, 3-(Me 3 Si) 2 C 5 H 3 on the occupied molecular orbitals, ensuring a great stability. The quantum theory of atoms in molecules (AIM) and energy decomposition analysis indicate that the substitution 1, 3-(Me 3 Si) 2 C 5 H 3 increases the degree of covalency in the bonding Cp R Ln (Lu +3 , Y +3 , La +3 )–(AlMe 4 ) 2 . According to the Pearson terminology, The La(AlMe 4 ) 2 (1,3- (Me 3 Si) 2 C 5 H 3 ) complex shows the higher acidity. Keywords: lanthanides, Cyclopentadienyl ligands, DFT, Half-Sandwich, Acidity Strength, AIM, Dipole moment _____________________________________________________________________________________________ INTRODUCTION Lanthanide complexes have very rich and diversified coordinating properties and reactivities, and have been vastly used in organic and polymer synthesis [1]. Monocyclopentadienyl or half-sandwich complexes have recently attracted considerable attention in organorare-earth metal chemistry [2-4]. The rare earth metals usually adopt the +3 oxidation state as the most stable oxidation state [5]. Recently, the complexes half-sandwich bis(tetramethylaluminate) lanthanide complexes of the type Ln(AlMe 4 ) 2 Cp R containing various substituted cyclopentadienyl ancillary ligands have been synthesized and characterized by X-ray structure analysis [6-8]. These complexes are active in isoprene polymerization as precatalyst with boron-containing cocatalysts, such as [Ph 3 C] [B (C 6 F 5 ) 4 ], [PhNMe 2 H][B-(C 6 F 5 ) 4 ], or B(C 6 F 5 ) 3 produces initiators for the fabrication of trans -1, 4-polyisoprene [6]. Within this framework, we found interesting to consider a series of half-sandwich complexes [Ln(AlMe 4 ) 2 Cp R ), Ln=(Lu, Y, La) and Cp R = ( 1,3-(Me 3 Si) 2 C 5 H 3 , C 5 Me 5 )] (see scheme 1) to understand some peculiar geometries, proprieties and chemical reactivity. The aim of our work is also to investigate further the nature of bonding between metal and ligand. In our study we will make use of density functional theory (DFT) calculations. DFT is an effective tool for the determination of structural arrangements of organometallic molecules [9]. EXPERIMENTAL SECTION Computational Method Our calculations were performed using the Amsterdam density functional (ADF) program developed by Baerends and co-workers [10]. Electron correlation was treated within general gradient approximation with the PW91 functional [11]. The atom electronic configurations were described by a triple ζ Slater type orbital (STO) basis set for H 1s, and 2s and 2p for C, 3s and 3p for Al, and Si, augmented with 2p single-ζ polarization functions for H atoms, with 3d single-ζ polarization functions for C and 4p single-ζ polarization functions for Al and Si. The atomic basis set of the lanthanide atoms is the following: a triple ζ -STO for the outer 4f, 5d, and 6s orbitals, a frozen core