Abstract
Electronic spectra of copper(II) complexes and (L-2-[2-hydroxy-phenil]-4,4-diphenyl-1,2-dihydro-4H-3,1-benzoxazine, Ac –) (L) in chloroform are studied. It is shown that complex has rhombic bipyramid polyhedron and complex has tetragonal pyramidal polyhedron of copper ion. Results of definition of geometry for complexes in solution correlate with structure of solid complexes.
1. Introduction
4H-3,1-benzoxazines and their derivatives are used in biology and medicine [1–4]. These compounds have pharmacological activity at very low toxicity. Dihydrobenzoxazines are capable of transformation in the azomethyne tautomeric forms (Schiff base form); it is most strongly pronounced in compounds where the azomethine form is stabilized by intermolecular H-bonds [3] or complexion with transition metal ions [4].
It is known [4] that complex of transition metals with biologically active ligands possesses higher biological activity and low toxicity in comparison with ligands. So the research complex of transition metals with derivatives benzoxazine is actual.
The aim of this paper is the definition of a structure of complex compounds of copper(II) with 2-[2-hydroxy-phenil]-4,4-diphenyl-1,2-dihydro-4H-3,1-benzoxazine (L):
in chloroform by methods of molecular spectroscopy and comparison of the received results to X-ray data for a solid binuclear complex of copper(II) with L, described earlier [5].
2. Experimental Section
Synthesis of complexes was carried out by direct interaction of ethanol solutions of copper acetate with L following the reported procedure [5, 6]. Solutions of complexes were prepared in chloroform. The electronic spectra of complexes (C = 10-2 moldm-1) were recorded on IKS-14A (LOMO) spectrophotometer in 1 cm cuvette. The absorption spectrum of the studied complex was fitted to Gaussian components using program [7]. The relative root-mean-square errors for CuL2 and Cu2L2Ac2 are 0.19% and 0.21%, respectively. The ESR spectra were recorded on JES FA-300 spectrometer at room temperature. IR spectra of solid complexes were recorded on INFRALUM FT-02 spectrometer as KBr pellets by standard methods.
3. Results and Discussion
The studying of complexes CuL2 [6] paves the grounds to assume the presence of polyhedron structure Cu[O4N2] with formation tetragonal or rhombic bipyramid. Reasons for reduction of molecule symmetry are change of lengths of bonds metal ligand and change of corners between them. Division of the electronic spectrum of complex CuL2 in chloroform (Figure 1) components allows to isolate four Gaussian components, as the parameters (Table 1) correspond to d-d transitions of copper(II) ion.
For the offered structure of complexes relating to the group of symmetry (Figure 2(a)) -orbital of copper(II) will correspond to the indecomposable representations [8] for for , and .
(a)
(b)
Considering close values of oscillator forces for the given transitions (Table 1), we considered two cases of their possible splitting in ligands field (Figure 2(a)): variant 1: ; variant 2: .
Variants with arrangement of -orbital lower and -orbital were not examined, as they do not answer the experiment (energy -orbital can be less energy and -orbitals only in case of absence or very weak field of axial ligands).
Under terms of angular overlap model (AOM) [8] energy of d-orbital is possible to be expressed as:
Comparing differences of the d-orbital energy, we determine of parameters AOM (Table 2), on algorithm described in [8].
The analysis of the calculated values of AOM parameters allows to consider structure of variant (2) more preferabl as the number of obvious parities is carried out for it, typical for coordinating connections of copper(II) with N- and O-containing donors groups, namely, (where ) as nitrogen forms stronger covalence connections, 3-5 for all donors atoms and [8].
Thus, it is possible to consider that the data of electronic spectroscopy testifies a structure of coordination polyhedron in the form of rhombic bipyramid in a solution proved by the data of IR and ESR spectra of solid complexes.
In the IR spectra of complexes (Table 3) band of absorption stretching vibrations of N–H band is absent. the maximum of band of absorption of stretching vibration of O–H bond is displaced to 3530–3450 cm-1. It is explained by the contribution of the band stretching vibration O–H bond of the three phenylcarbinol fragments and the absence of a band of absorption of O–H bond of phenol group. It is possible to explain this fact to that in coordination with the azomethine form ligand participates. That is confirmed also by occurrence of intensive band of absorption in the region of 1620–1590 cm-1 in IR spectra of complexes.
Participation of atom of oxygen of phenolic group in coordination proves to be true by the presence of IR spectra of complexes in the region of 600–560 cm-1 of band of absorption which according to [8] is carried by us to stretching vibration of Cu–O bonds. Bands of absorption in the region of 470–450 cm-1 which is absent in spectra ligands, it is necessary to carry [9] stretching vibration of Cu–N bond.
According to spectra ESR of powder of CuL2, axial symmetry of the nearest environment of an ion of copper is observed, parameters of spin-Hamiltonian () correspond to a plane structure of coordination unit with a transarrangement oxi and azomethin groups [10, 11]. In the ESR spectrum of CuL2 in a chloroform the hyperfine structure from atom of copper and superhyperfine structure from atoms of nitrogen are observed.
Presence of five lines of superhyperfine structure with a parity of intensity and a constant of 14.40 cm-1 on high field component hyperfine structure confirms the coordination of two atoms of nitrogen in an equatorial plane of the complex, being in transposition under the relation to each other.
According to the data [5] for binuclear complex Cu2L2Ac2 (coordination polyhedron—the deformed square pyramid) the splitting of initial levels in approach of symmetry is presented on Figure 2(b). It is necessary to expect three partially resolved d-d transitions in the electronic spectrum: variant ; variant . Transition will have the minimal force of the oscillator, and according to data of the spectrum analysis (Figure 3) variant 2 is preferable.
As seen from the electronic spectrum of the solution of the complex (Figure 3) in the field of d-d transitions of the ion of copper(II), the spectrum has corresponded to structure of variant (2). Energy of d-orbital is determined by expressions [8]: The results of calculation of the angular overlap model parameters are given in Table 2.
Thus, the complex has already existed in a solution in the form binuclear molecules: [Cu2L2Ac2]. Formation of crystal structure of a solid complex occurs at the expense of the formation of connection between the second oxygen atom of the carboxylic group of the acetates anion and the atom of hydrogen of three phenylcarbinol groups and there is subsequent “chess” packing of formed structural units [5].