Crystal Structure and Spectroscopic Behaviour of Oxoetoxo-bis(5,7-dichloro-8-hydroxyquinolinato)vanadium(V)

The title compound, a new example of an inorganic ester-like complex, was characterized by spectroscopic and X-ray crystallographic methods. It crystallizes in the triclinic space group P1 (a=9.413(2), b=10.595(3), c=11.783(2) A, α=103.59(2), β=101.98(2), γ=99.40(2)°, Z=2). The structure was solved employing 2902 independent reflections with I>2σ(I) by direct and Fourier methods and refined by a full-matrix least-squares fit to R1=0.049. Infrared and Raman spectra of the solid compound and the electronic absorption spectra of its acetonitrilic and ethanolic solutions were recorded and are briefly discussed.


Introduction
It is well known that a black, water insoluble complex of stoichiometry Q 2 VO(OH) is generated by reaction of vanadium(V) with 8-hydroxyquinoline (QH) [1±3].Giacomelli et al. suggested that this species should be considered as an inorganic analog of a carboxylic acid [4].According to this proposal, the species of composition Q 2 VO(OR), produced by its interaction with alcohols, may be classi®ed as esters.Although many such esters have so far been prepared, most of them are only scarcely characterized [3±9].
In continuation of our studies on vanadium complexes containing halogenated derivatives of 8-hydroxyquinoline as ligands [9,10], we have prepared esters derived from ``acids'' containing this type of ligands [9,11].Furthermore, in the case of the species derived from 5.7-dichloro-8-hydroxyquinoline, we have solved the crystal structure of the respective ethyl ester.
In this paper, we present the results of this structural study, complemented with some spectroscopic data.

Structural analysis
Crystal parameters and details of the applied re®nement procedures are given in Table 1, whereas Fig. 1 shows an ORTEP plot [12] of the structure including the atom labelling of the non-hydrogen atoms and their vibrational ellipsoids.
Atomic fractional coordinates and equivalent isotropic displacement parameters are listed in Table 2. Selected interatomic bonding distances and angles are compiled in Table 3; Fig. 2 shows a projection of the crystal packing.
The only similar structure which has so far been reported is that of the isopropyl ester of oxohydroxobis(8-hydroxyquinolinato)vanadium(V) [7].This compound presents an analogous structural arrangement with the VO(O±i±Pr) group in cis con®guration.The O±V±O angle of 101.9 is similar to that found in present study (102.7 ).The V±O distances to the oxo and etoxo ligands are slightly shorter in the present case.
The coordination sphere around the central vanadium(V) atom is a distorted octahedron constituted by the oxygen atoms located at 1.590(3) A Ê (terminal V=O bond) and 1.746(3)A Ê (etoxo bond), the oxygen atoms of the organic ligand, presenting practically the same bond distances (1.910(3) and 1.924(3)A Ê ), and the two nitrogen atoms of the ligands, whose bonding distances are signi®cantly different.The V±N bond trans to the oxo ligand is longer (2.319(3)A Ê ) than that located trans with respect to the etoxo ligand (2.203(3)A Ê ).This behaviour is also similar to that found in the previously investigated structure [7] and has been explained as a consequence of a kind of trans effect generated by the ester linkage [7].
The C±O and C±N±C distances are somewhat shorter in the present case than in the isopropoxo complex; in general the ring C±C bonds are not very different in both compounds despite the presence of the two chlorine atoms in the present case.The four C±Cl bonds are practically identical.

Vibrational spectra
To further characterize this new inorganic ester, we have also recorded its infrared and Raman spectra.Both spectra are very complex.The proposed assignments, based on data or related compounds [9, 10, 13±16] and on some general literature information [17] are presented in Table 4 and shall be brie¯y discussed.

Electronic spectra
The electronic absorption spectra of the ester in solutions of acetonitrile and ethanol are shown in Fig. 3.Both solutions are brown-reddish when freshly prepared, but their colour fades with time changing to green, probably caused by atmospheric humidity.The ethanolic solution is relatively more stable.
The two absorption bands at higher energies (210 and 258 nm in acetonitrile and 214 and 246 nm in ethanol) are assigned to intraligand transitions, probably superimposed by the O 3 V charge transfer involving the double bonded oxo group [13,16,20].The other two bands are related to ligand-to-metal charge transfer transitions involving the organic ligand.The higher energy band (326 nm in acetonitrile and 324 nm in ethanol) essentially involves the oxygen atom, whereas the other one (374 nm in acetonitrile and 394 nm in ethanol) may be related to the nitrogen atom [13].
The higher intensity of the 324 nm band in ethanol as compared to the respective transition in acetonitrile can be explained by the fact that in ethanol the free ligand presents also a band in this region.The generated wine-red solution was ®ltered and cooled to room temperature.After 24 h, crystal formation was observed.A number of well formed single crystals, suitable for a crystallographic study, were separated manually from the crystalline mass.The crystals were thermally stable up to ca. 220 C.

Crystal structure determination
Single crystal data collection was performed at 293(2) K on an Enraf-Nonius CAD-4 diffractometer using a dark red crystal plate of 0.05 mm in thickness parallel to 10 " 1.The plate was bounded by three pairs of opposite crystal faces: 0Y AE1Y 0Y AE1Y AE2Y AE1Y and AE1Y 0Y AE1, separated by 0.28, 0.21, and 0.20 mm, respectively.Unit cell parameters were re®ned by least-squares of [sin Âa! 2 , using 25 re¯ections in the 22.82 `2Â `39X28 range.Intensities were corrected for Lorentz and polarization effects as well as for absorption [21] (maximum and minimum transmission factors were 0.958 and 0.758).The crystal structure was solved by direct and Fourier methods and re®ned by full-matrix least squares techniques (programs used were SDP [22], SHELX-76 [23], SHELX-86 [24], and SHELX-93 [25]).All hydrogen atoms of the ligands and one of the alcohol methyl group were located in a difference Fourier map.However, they were all positioned on a stereochemical basis and included in the re®nement riding on the atom to which they are bonded (C-H distances of 0.93, 0.97, and 0.96 A Ê for CH, CH 2 , and CH 3 groups, respectively) with three independent isotropic thermal parameters, one common to the quinoline hydrogens (which converged to U 0X0534 A Ê 2 ), the second one common to the alcohol CH 2 hydrogens U 0X203 A Ê 2 ), and a third one common to the methyl hydrogens U 0X365 A Ê 2 ).During the re®nement, the CH 3 hydrogen atoms were allowed to rotate as a rigid group around the corresponding alcohol C±C bonds as to maximize the sum of the electron density at the three calculated hydrogen positions.The somewhat large U-values for the alcohol hydrogens are consistent with the observed trend of an increase of thermal parameters of the carbon atoms to which they are attached towards the free end of the group, suggesting relatively large vibrational movements of the alcohol moiety.
Tables containing complete information on bond distances, angles, and anisotropic thermal parameters for the non-H atoms are available from the authors up on request and have been deposited at the Fachinformationszentrum Karlsruhe GmbH, D-76344 Eggenstein-Leopoldshafen (FRG), from where they can be obtained referring to the deposition number CSD-59442, the names of the authors, and the citation of the paper.

Spectroscopic measurements
Infrared spectra were recorded with a Perkin Elmer 580 B spectrophotometer (KBr pellets).Raman spectra were obtained with an FRA 106 Raman accessory of a Bruker FTIR IF 66 spectrometer.The 1064 nm line of a Nd:YAG laser was used for excitation.Electronic absorption spectra were measured on a Hewlett-Packard 8453 diode array spectrophotometer using 1 cm quartz cells.

Fig. 1 .
Fig. 1.ORTEP drawing of C 20 H 13 O 4 N 2 Cl 4 V showing the non-H labelling and the vibrational ellipsoids at 30% probability

Fig. 2 .
Fig. 2. ORTEP projection of C 20 H 13 O 4 N 2 Cl 4 V crystal packing along a; the b axis is horizontal

Fig. 3 .
Fig. 3. Electronic absorption spectra of the ester in acetonitrile (A) and ethanol (B)

Table 1 .
Summary of crystal data, X-ray measurements, and structure re®nements

Table 2 .
Atomic coordinates (Â104and equivalent isotropic displacement parameters (A Ê 2 Â 10 3 for C 20 H 13 O 4 N 2 Cl 4 V; U(eq) is de®ned as one third of the trace of the orthogonalized U ij tensor

Table 4 .
Assignment of relevant IR and Raman bands (cm À1 vs: very strong; s: strong; m: medium; w: weak; vw: very weak; sh: shoulder