A description of ligand field effects in the Di-mu-Azido-Bis [{Azido(N,N-Diethylethylenediamine)}Copper(II)] compound by the simple overlap model

Journal of the Brazilian Chemical Society

Sargentelli, V.¹  UFPE, Recife, Brazil¹  Universidade de Marília, Marília, Brazil¹  UNESP, Araraquara, Brazil¹  Malta, O.L.¹  Mattioli, M.P.D.¹  Brito, H.F.¹  Mauro, A.E.¹  USP, São Paulo, Brazil¹ 

关键词: copper(II);    complexes;    amine ligands;    ligand field;   

DOI  :  10.1590/S0103-50531998000300007

学科分类：化学（综合）

来源: SciELO

【 摘 要 】

One of our research interests has been the synthesis and solid state structural characterization of copper complexes with bidentate amine ligands1-3. Structural and spectroscopic data concerning these complexes with pseudohalides, mainly the azido-group, have a great importance since they may be related to those of important biological systems such as copper-containing proteins4-6. The d9 ion is characteristically stereochemically flexible and, as a consequence, it may form distorted stereochemistries of difficult description. The spectroscopy of these systems turns out to be rather difficult and, in some cases, uncertain. Thus, electronic spectroscopy alone is not a definitive tool for identifying structure or corroborating X-ray structural data. In several instances a theoretical analysis of ligand field effects and spectral intensities in these complexes may be very useful. In this work we apply the simple overlap model (SOM)7,8 to describe ligand field effects in the complex [Cu(N3)2(N,N-diEten)]2 (N3 = azide; N,N-diEten = N,N-diethylethylenediamine), for which crystallographic data are available3. The aim is to describe theoretically the d-d transition energies and to get information on the ligand field strength in the complex.   Experimental The complex was prepared as described previously in the literature, together with a full X-ray crystallographic analysis3. Electronic spectra of ethanolic or acetone solutions of the compound were obtained in a HP-8425 dyode array spectrophotometer. As described previously in the X-ray crystallographic analysis3 , the structure of the complex consists of a centrosymmetric Cu2N2 unit whose N atoms belong to the azido bridges. Each copper atom is also surrounded by three nitrogen atoms, two from one N,N-diEten and one from the terminal azide. The five nitrogen atoms altogether occupy the vertices of a slightly distorded trigonal bipyramid and the azido bridge leads to a rather short Cu ... Cu distance of 3.37 Ã…. If the slight distortions are not considered we may assume a D3h site symmetry occupied by the copper. The molecular structure is shown in Fig. 1.   The UV electronic absorption spectrum of the compound in ethanolic solution, Fig. 2, shows two bands at 276 nm (e = 581 M-1cm-1) and 384 nm (e = 525 M-1cm-1 ), assigned to internal p ® p* transitions in the N3- anion9-11 , or to charge transfer transitions between the azide and copper ion (N3,p ® Cud). As can be seen in the acetone solution absorption spectrum shown in Fig. 3, in the visible region, one broad band is observed. By using a simulation program with gaussian line shapes12, only one component was identified in the d-d transition region, at 670 nm.     The Simple Overlap Model The splitting of the d levels in ligand fields have been successfully described by the angular overlap model (AOM) in terms of the anti-bonding character acquired by d orbitals in a chemical environment13. In this section we briefly outline the alternative approach based on the SOM.This model has been introduced and has been applied to the

【 授权许可】

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