JOURNAL OF RARE EARTHS, Vol. 28, Spec. Issue, Dec. 2010, p. 83 Corresponding author: S. P. SINHA (E-mail: la2lu@yahoo.com) DOI: 10.1016/S1002-0721(10)60369-9 Comparison between the theoretical models and experimental structures of some octacoordinated Ln(III)-bis-dipyridyl-bis-dichloroacetato-diaquo complexes and their phenanthroline analogues S. P. SINHA 1 , Alfredo M. SIMAS 2 , Gustavo L. C. MOURA 2 (1. SRD, 6565 Willowick Pl., Dayton, OHIO 45459-3005, U.S.A.; 2. Departamento de Quimica Fundamental, CCEN, Universidade Federal de Pernambuco, 50590-470, Recife, PE, Brazil) Received 26 September 2010; revised 10 November 2010 Abstract: The title complexes were modeled using the semiempirical MOPAC and the newly developed SPARKLE paramerters of the lan- thanides. The calculated bond distances and angles agreed well with those found from crystal structure measurements. This technique allows us to screen a large number of molecules and get structural information within a very short time. Keywords: lanthanide complex; theoretical models; octacoordination; dipyridyl; phenanthroline; MOPAC; SPARKLE; rare earths Since the discovery of the bis-dipyridyl [1–3] and the bis-phenanthroline [4,5] complexes of the lanthanides with chlorides and nitrates, several crystal structures [6–8] of these and with other anions have been reported. Recently, Lu Weimin and coworkers [9] , isolated and studied the crystal structures of several lanthanide complexes with dichloroace- tate as anions, having composition, [Ln(III)-bis-(N-N)-bis dichloroacetate-diaquo] + where N–N is 2,2 ’ -dipyridyl(I) or 1,10-phenanthroline(II). Er-(dipyridyl I), Er-(phenanthroline II) and Eu-(phenan- throline II) complexes were found to be octacoordinated, with both heterocyclic ligands acting as a bidentate and the two dichloroacetate ions acting as monodentate. The other two coordination sites are occupied by the water molecules producing a slightly distorted square antiprismatic geometry around the lanthanide ions. It was of interest to model these octacoordinated com- plexes using the recently parameterized Ln(III) ions [10–12] as Sparkles in the domain of MOPAC and compare the struc- tures and bond parameters. This semiemperical approach has great advantage in screening a large number of analogous structures hundred times faster than the ab-initio methods and it also generates good coordination geometry, bond lengths and bond angles. 1 Method of calculation PM3 Sparkle parameter for the lanthanides (M(III) ions) [10–12] and PM3 parameters of C, O, F, and H were used to study the lanthanide complexes and the adducts using MOPAC 2009 [13] . 2 Results and discussion 2.1 [Er(dipy I) 2 (dichloroacetate) 2 (OH 2 ) 2 ] 1+ Our calculated model (Fig. 1) agrees with that of Lu and coworkers [9] in its geometry (distorted square antiprism) and the Er–O and Er–N distances. Howerver, in the calculated minimized geometry, the mode of coordination of the two dipyridyl ligands differ from that experimentally found [9] . In the crystal structure, the two dipyridyl moieties occupy the edges of the upper and lower square faces of the anti- prism, whereas in our calculated model one of the dipyridyl moiety is coordinated to one edge of a square face and the Fig. 1 Calculated square antiprismatic structure of the [Er(dipy) 2 (dichloroacetate) 2 (OH 2 ) 2 ] 1+ complex