Theoretical study of some pyrazole derivatives and rare earth metal complexes M.L. Kuznetsov a ,* , A.I. Dementiev a , S.V. Krasnoshchoikov b a Department of Chemistry, Moscow Pedagogical State University, 3, Nesvigskiy per., Moscow 119021, Russian Federation b Department of Chemistry, Moscow State University, Moscow, Russian Federation Received 2 June 1997; received in revised form 5 January 1998; accepted 20 February 1998 Abstract The theoretical study of some pyrazole derivatives and rare earth metal complexes was carried out. The equilibrium geometry of eight structures and modelling fragments was found by ab initio method (HF/6-31G HF/3-21G for Sc). The coordinational type of ligand was determined for a fragment of scandium complex taken as an example. After optimization, the Sc–O bond length was 2.17 A ˚ , and the Sc–N bond length was 2.98 A ˚ . So, the ligands examined were monodentate in complexes of transition metals with a carbonyl oxygen atom as the donor atom. Based on II and III structure calculations, the amidopyrine (Amy) geometry was estimated. Force constants, vibrational frequencies and scale factors of some pyrazole derivatives and transition metal complexes were calculated. The results obtained were used for the assignment of experimental vibrational frequencies.  1998 Elsevier Science B.V. All rights reserved. Keywords: Pyrazole derivatives; Transition metal complexes; Ab initio 1. Introduction Derivatives of the pyrazolone-5 are used widely in modern science and techniques. That is based on their special characteristics such as extract ability, extract colours suitable for photometric analyses and intense biological activity. These compounds display the majority of their valuable properties as ligands in transition metal complexes. The ligands with some probable coordination centres, for instance amidopyr- ine (Amy), attract special interest. There are many reports devoted to investigations of amidopyrine com- plexes with p- and d-elements [1,2]. However, the structure and spectral properties of these ligands and their complexes are not studied enough. So, there are no data about X-ray structure investigations of amidopyrine complexes with d- and f-metals, except for the report about the structure of [Gd(NO 3 ) 3 X2AmyXH 2 O]CH 3 CN [3], but the influ- ence of coordination on the ligand’s structure has not been studied. Also it is not clear up to now the mechanism of the amidopyrine molecule coordination. The amidopyrine molecule has several probable coordination centres: the carbonyl oxygen atom, two endocyclic nitrogen atoms and the exocyclic nitrogen atom. The Amy coordination through endocyclic nitrogen centres is hardly possible because of steric hindrance [4]. Parti- cipation of the carbonyl oxygen atom in coordination bonds is very probable and maintained by our Journal of Molecular Structure (Theochem) 453 (1998) 17–28 THEOCH 5588 0166-1280/98/$ - see front matter  1998 Elsevier Science B.V. All rights reserved. PII: S0166-1280(98)00140-7 * Corresponding author. E-mail: chemfak@centro.ru