Research of nickel(II) complexes with aroyl hydrazones of 5,5-dimethyl-2,4-dioxogexane acid ethyl ester ergashov Mansur Yarashovich

RESULTS AND ITS DISCUSSION

This communication discusses the study of the composition and structure of nickel(II) complex compounds prepared on the basis of H₂L₁–H₂L⁶. The results of elemental analysis and spectroscopic studies allowed us to assign the following structure to the compounds:

A=NH₃: X=N(CH₃)₂(NiL¹·NH₃); OCH₃(NiL²·NH₃);CH₃ (NiL³·NH₃); H(NiL⁴·NH₃), Br(NiL⁵·NH₃), NO₂(NiL⁶·NH₃); A= Py, X=NO₂(NiL⁶·3Py).

The composition and structure of the obtained complexes have been established by elemental analysis, IR and NMR spectroscopy. The IR spectrum of the NiL³‧ NH₃ complex compound differs from the spectrum of the H₂L³ ligand in that it lacks absorption bands in the ranges of 1660–1700 and 3400 cm^–1. This indicates the deprotonation of the ligand upon complex formation. In many respects, the IR spectrum of the NiL³ ‧NH₃ complex is identical with the IR spectra of previously studied nickel(II) complex compounds [6, 7].

The IR spectrum of the NiL³‧NH₃ complex also contains absorption bands at 3375, 3337, 3280, and 3170 cm^–1, which are attributed to _s and _as vibrations of the coordinated NH₃ molecule. It is also necessary to note the presence in the spectrum of the compound of an intense band in the region of 1730 cm^-1, which is due to _(С=О) of the ester substituent. In the IR spectrum of the complex, a number of bands of medium and strong intensity in the region of 1400–1620 cm^–1 should be associated with predominantly stretching and bending vibrations of the system of conjugation of one and a half bonds in five- and six-membered metallocycles [8].
We have studied the effect of pyridine upon recrystallization in its medium. In contrast to previously grown similar single crystals of the NiL·NH₃ type, single crystals have been isolated, which differs sharply in its molecular structure [3, 4] with the octahedral structure NiL⁶·3Py (composition NiC₃₂H₃₄N₆O₆)₂, as a result of which the environment of the Ni(II) ion reaches six with a set of Ni(trans-N₄O₂) donor atoms. Previously, we obtained such changes in the coordination sphere from a square planar through a square pyramidal to a six coordination octahedral structure using the example of both mononuclear copper(II) complexes and heterobinuclear complexes of nickel(II) and copper(II) [3].
The conclusions about the structure of the complex with the tridentate coordination of the ligand dianion, drawn from the results of the IR spectrum, have been previously verified by X-ray diffraction analysis for the grown single crystal of the NiL⁶∙NH₃ complex [4, 5]. In contrast to NiL⁶∙NH₃, the environment of the ion in the NiL⁶∙3Py crystal reaches octahedral due to the replacement of ammonia by pyridine in the equatorial plane and additional coordination of two pyridine molecules to axial positions (Fig. 1) with a set of donor Ni(trans-N₄O₂) atoms.
The isolated (NiC₃₂H₃₄N₆O₆)₂ single crystals were subjected to X-ray diffraction analysis on an Xcalibur, Oxford Diffraction automatic diffractometer (CuК_-radiation, graphite monochromator, -scanning, 2_max=50^o.

Fig. 1. Molecular structure of the complex compound NiL⁶∙3Py with para-nitrobenzoylhydrazone 5,5-dimethyl-2,4-dioxohexanoic acid ethyl ester.
(NiC₃₂H₃₄N₆O₆)₂ crystals are triclinic with unit cell parameters: a=9.5826(5); b=14.1432(6); c=26.1557(13) Ǻ; =76.300(4)^o; =89.447(4)^o; =73.234(4)^o; V=3291.0(3) Ǻ³; _{( calc.)}= 1.659 г/см³; Z=2, пр.гр. P-1; ρ(calc.) =1.327 г/см³; μ, мм^–1= 1.28; Scan area by θ,grad=3.4–76.2; Index area h=−11≤h≤ 11, k=–17≤k ≤14, l=–32≤l≤ 32; R₁, wR₂ (I>2σ(I)= 0.0513, 0.145; Δρ_max, Δρ_min(e Å⁻³)= 0.46–0.48.
The remainder of the ligand molecule is coordinated by two oxygen atoms and a nitrogen atom of the hydrazone fragment. Fourth place in the planar square of the trans-N₂O₂ coordination site and two axial positions are occupied by three pyridine molecules, bringing the environment of the central ion to an octahedral one. The Ni–O(1) bond lengths, 2.0665 Å and Ni–O(2), 2.025 Å, are close to similar bond lengths in previously studied nickel complex compounds with the trans- N₂O₂ coordination sphere [4–7]. The Ni–N(1)(1.981(2) Å) distance of the metal chelate is significantly shorter than the three bonds of the donor base Ni–N(4) (2.092 Å), Ni–N(5) (2.164(2) Å), and Ni–N (6) (2.154(2) Å).
The central nickel atom deviates by 0.0272 Å from the “average” plane of the five-membered NiN(1)N(2)C(1)O(2) metallocycle compared to the six-membered plane of NiN(1)C(8)-C(10)O (2)C(11)(0.0081 Å). This can be explained by the greater internal tension of the bonds of the five-membered cycle compared to the six-membered one. Almost flat five- and six-membered conjugated metallocycles are almost coplanar with each other, which has been previously discussed in [8–10]. When comparing the structure of donor pyridine molecules coordinated around the Ni(II) ion in the complex, the Py molecule with the set of N(4)C(18)C(19)C(20)C(21)C(22) atoms is the flattest in comparison with the other two pyridine molecules coordinated into axial positions. This is explained, in our opinion, by the formation of a d--dative bond between the d-electrons of the Ni(II) ion and the -orbital of the pyridine molecule. The packing of structural units in the crystal of the NiL⁶·3Py molecule is shown in fig. 2.

Fig. 2. Projections of the crystalline packing of NiL⁶3Py molecules on the ac plane.
The PMR spectra of the studied complexes provide the following information. The NMR spectrum of the NiL^4.NH₃ compound in a CCl₄+DMSO-d₆ solution with a substituted -ketoester aroylhydrazone is very similar to the spectra of nickel complexes with various acyl- and aroylhydrazones of -diketones, -ketoaldehydes, and -ketoesters [4].
It should be noted that the signals from the protons of the ethyl radical of the ester С₂Н₅ООС group clearly manifest themselves in the form of a triplet and from three protons of the –CH₃ group are recorded at  1.36 ppm, and the protons of the –CH₂ group resonate as a quadruplet at  4.28 m. etc., respectively, with intensity as 3:2 and with VSWR JAB=7Hz. Signals from a single vinyl proton are observed at δ 5.03 ppm, and nine protons of the tert- C₄H₉ β-group resonate as a clear singlet at δ 1.00 ppm. Multiplet signals from protons of aromatic nuclei of the hydrazone fragment of the molecule resonate in the region of weak fields with centers at δ 7.14 and 7.67 ppm. The type of signals is somewhat complicated due to their overlap. The signal from the protons of the coordinated ammonia molecule in the form of a singlet with an intensity of 3H has been recorded at δ 2.07 ppm.

Figure 3. PMR spectrum of NiL4·NH3 complex compound in CCl4+DMSO-d6 solution

4.