Crystal structure of a trinuclear complex of zinc(II) with 2,6-Di-tert-butyl-p-quinone 1′-phthalazinylhydrazone

Article abstract of DOI:10.1134/S0022476614030123

2,6-Di-tert-butyl-p-quinone 1′-phthalazynylhydrazone (HL) is synthesized; the total energies and geometry of the possible hydrazone tautomeric forms are calculated by quantum chemical methods. The hydrazone phthalazone tautomer is shown to be the most stable, which is well consistent with the ¹H NMR spectroscopic data for hydrazone. An X-ray crystallographic analysis is performed of the hydrazone-based Zn(II) trinuclear complex, in which zinc atoms are linked by the diazine bridge of the phthalazine cycle and two pivalate bridges. The geometric properties of the monodeprotonated hydrazone residue in the complex are similar to the calculated data for the phthalazone hydrazone tautomeric form.

Full text of DOI:10.1134/S0022476614030123

Journal of Structural Chemistry. Vol. 55, No. 3, pp. 475-480, 2014.
Original Russian Text © 2014 A. E. Gol’dberg, M. A. Kiskin, L. D. Popov, S. I. Levchenkov, I. N. Shcherbakov, Yu. P. Tupolova, V. A. Kogan.
CRYSTAL STRUCTURE OF A TRINUCLEAR COMPLEX
OF ZINC(II) WITH 2,6-DI-TERT-BUTYL-p-QUINONE
1ꢀ-PHTHALAZINYLHYDRAZONE
A. E. Gol’dberg,1 M. A. Kiskin,1 L. D. Popov,2
S. I. Levchenkov,3 I. N. Shcherbakov,2
Yu. P. Tupolova,2 and V. A. Kogan2
UDC 539.27:544.18:546.46:547.556.93
2,6-Di-tert-butyl-p-quinone 1ꢀ-phthalazynylhydrazone (HL) is synthesized; the total energies and geometry
of the possible hydrazone tautomeric forms are calculated by quantum chemical methods. The hydrazone
1
phthalazone tautomer is shown to be the most stable, which is well consistent with the H NMR
spectroscopic data for hydrazone. An X-ray crystallographic analysis is performed of the hydrazone-based
Zn(II) trinuclear complex, in which zinc atoms are linked by the diazine bridge of the phthalazine cycle and
two pivalate bridges. The geometric properties of the monodeprotonated hydrazone residue in the complex
are similar to the calculated data for the phthalazone hydrazone tautomeric form.
DOI: 10.1134/S0022476614030123
Keywords: hydrazones, tautomerism, 1-hydrazine phtalazine, zinc(II) complex, X-ray crystallography,
density functional theory.
1-Hydrazinephthalazine and its derivatives, as well as 1,4-dihydrazinephthalazines, are known to act as N-donor
chelating–bridging ligands in the complexation with transition metal ions [1]. The possibility of their transition to the ion
form allows one to obtain molecular binuclear complexes with inorganic metal salts (cobalt(II), nickel(II), and copper(II)),
where metal centers are linked by chelating–bridging molecules of hydrazine phthalazine derivatives and contribute to the
coordination of monodentate ligands, solvent molecules, and/or inorganic anions [2-10]. The metal skeleton of these systems
can be enhanced by adding other bridging ligands (e.g., carboxylate anions, which are known to facilitate the formation of
polynuclear systems of a molecular and polymeric structure) into the reaction systems [11-13].
This article presents the results of synthesizing a new trinuclear complex Zn3(Piv)4L2 on the basis of zinc(II) pivalate
([Zn(Piv)2]n) and 2,6-di-tert-butyl-4-(phthalazine-1(2H)-ylidenehydrazono)cyclohexa-2,5-dienone (HL).
EXPERIMENTAL
The HL hydrazone compound was synthesized using commercially available 2,6-di-tert-butyl-para-quinone
(Aldrich) and 1-hydrazinephthalazine hydrochloride (Alfa Aesar). Polymeric zinc(II) pivalate was synthesized by a well-
known technique described in [14].
1Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, Russia. 2Southern
3
Scientific Center, Russian Academy of Sciences, Rostov-on-Don, Russia. Chemistry Department, Southern Federal
University, Rostov-on-Don, Russia; s.levchenkov@gmail.com. Translated from Zhurnal Strukturnoi Khimii, Vol. 55, No. 3,
pp. 505-510, May-June, 2014. Original article submitted March 20, 2013; revised June 8, 2013.
0022-4766/14/5503-0475 © 2014 by Pleiades Publishing, Ltd.
475

TABLE 1. Main Bond Lengths (d, Å) and Angles (ω, deg) according to the Calculated Results for the HL
–
Molecule (tautomeric forms a–c) and L Monoanion in Complex 1 (atomic notation corresponds to that of complex 1 in Fig. 2)
–
–
Bond
HLa
HLb
HLc
L
Angle
HLa
HLb
HLc
L
N(1)–N(2)
N(1)–C(11)
N(2)–C(18)
N(3)–C(18)
N(3)–N(4)
N(4)–C(19)
1.350
1.295
1.370
1.320
1.354
1.316
1.346
1.310
1.323
1.392
1.323
1.317
1.445
1.355
1.504
1.230
1.491
1.353
1.444
1.357
1.311
1.316
1.415
1.254
1.409
1.398
1.389
1.424
1.367
1.416
1.391
1.396
1.366(2) C(20)–C(19)–C(32) 119.05
118.59
122.24
118.82
118.88
118.27
123.19
119.95 119.78(19)
121.99 121.6(2)
116.55 118.6(2)
123.11 119.21(19)
117.12 117.8(2)
121.28 122.6(2)
1.296(3) C(19)–C(20)–C(21) 122.00
1.339(3) C(20)–C(21)–C(26) 118.82
1.355(3) C(21)–C(26)–C(27) 119.07
1.351(3) C(26)–C(27)–C(32) 118.17
1.333(3) C(19)–C(32)–C(27) 122.89
C(19)–C(20) 1.446
C(20)–C(21) 1.353
C(21)–C(26) 1.502
1.429(3)
1.353(3)
1.490(3)
1.235(3)
1.484(3)
1.349(3)
1.426(3)
O(5)–C(26)
1.230
C(26)–C(27) 1.495
C(27)–C(32) 1.353
C(19)–C(32) 1.444
2,6-Di-tert-butyl-4-(phthalazine-1(2H)-ylidenehydrazono)cyclohexa-2,5-dienone (HL). 0.164 g (2 mmol)
sodium acetate was added to a hot suspension of 0.391 g (2 mmol) 1-hydrazinephthalazine hydrochloride in 20 ml EtOH. The
mixture was boiled for 10 min, and 0.44 g (2 mmol) 2,6-di-tert-butyl-para-quinone was added. The reaction mixture was
boiled under reflux for 4 h. Then 50 ml water was added, and the mixture was left overnight. The orange precipitate was
filtered and washed with water and ethanol. Recrystallized from DMFA.
Yield 0.396 g (55%); m.p. 207°C. Elemental analysis: gross formula C22H26N4O; calculated, %: C 72.90, H 7.23, N
–1
15.46; found, %: C 72.65, H 7.39, N 15.62. IR spectrum (Varian Scimitar 1000 FT-IR, nujol mull, ν, cm ): 3371 ν(NH),
1684 ν(C=O), 1636, 1597 ν(C=N). PMR spectrum (Varian Unity 300, CDCl3, δ, ppm, J, Hz): 10.928 s (1H, NH); 8.50-
8.60 m (1H, CHarom); 8.044 s (1H, CHarom); 7.70-7.80 m (2H, CHarom); 7.56-7.67 m (1H, CHarom); 8.094 d (1H, CHarom
,
J = 2.5 Hz); 7.101 d (1H, CHarom, J = 2.5 Hz); 1.328 s (9H, t-Bu); 1.356 s (9H, t-Bu). EAS (Varian Cary 5000, toluene, nm):
–1 –1
471 (ε = 34500 l·cm ·mol ).
Zn (Piv) L (1). A suspension of 0.035 g (0.1 mmol) HL and 0.030 g (0.11 mmol) [Zn(Piv)2]n in 30 ml MeCN was
3 4 2
stirred while heating (80°C) for 2 h. The resulting red fine-crystalline precipitate was washed with MeCN and DMFA.
Yield: 0.040 g (80%); m.p. > 250°C. Elemental analysis: gross formula C64H86N8O12Zn3; calculated, %: С 58.08, Н
–1
7.02, N 8.47; found, %: С 57.4, Н 7.3, N 8.6. IR spectrum (KBr, ν, cm ): 3600-3300 w, 2959 m, 2868 w, 1605 m, 1591 s,
1581 s, 1566 vs, 1546 s, 1506 m, 1485 s, 1461 m, 1453 m, 1423 s, 1402 s, 1377 vs, 1357 vs, 1331 s, 1307 vs, 1257 s, 1231 m,
1192 s, 1171 w, 1164 w, 1136 s, 1085 w, 1064 m, 1021 s, 960 vs, 938 m, 912 w, 899 w, 884 w, 799 w, 788 w, 760 m, 678 w,
616 w, 606 w, 544 vs, 436 w.
Quantum chemical calculations of the electronic and spatial structure of the HL hydrazone were conducted in
Gaussian′03 [15] within the density functional theory (DFT). The calculations used the B3LYP hybrid exchange–correlation
functional [16] with the Becke exchange part [17] and Lee–Yang–Parr correlation part [18]. The 6-311+G(d,p) split-valence
basis was used. The geometric structure of the molecules was optimized with respect to all natural variables with no
symmetry restrictions. Potential energy surface minima were identified for each structure by calculating the matrix of force
constants and normal vibration frequencies. The ChemCraft program [19] was used to prepare the data and presentation
images and visualize the calculated results. The total energies of the tautomeric forms and selected bond lengths and valence
angles are presented in Table 1.
476

TABLE 2. Selected Interatomic Distances (d, Å) and Valence Angles (ω, deg) in Zn Atoms Coordination
Polyhedra in the Structure of 1
Bond
d
Angle
Bond
ω
ω
Zn(1)–N(2)
Zn(1)–N(4)
Zn(1)–O(1)
Zn(1)–O(3)
Zn(1)–O(4)
Zn(1)⋯Zn(2)
Zn(2)–N(1)
Zn(2)–O(2)
Zn(2)–O(4)
Zn(2)–N(1A)
Zn(2)–O(2A)
Zn(2)–O(4A)
2.007(2)
2.060(2)
1.926(2)
1.970(2)
2.572(2)
3.4000(3)
2.092(2)
2.111(2)
2.104(2)
2.092(2)
2.111(2)
2.104(2)
N(2)–Zn(1)–N(4)
N(2)–Zn(1)–O(1)
N(2)–Zn(1)–O(3)
N(2)–Zn(1)–O(4)
N(4)–Zn(1)–O(1)
N(4)–Zn(1)–O(3)
N(4)–Zn(1)–O(4)
O(1)–Zn(1)–O(3)
O(1)–Zn(1)–O(4)
77.66(7)
120.61(8)
115.08(7)
82.38(7)
O(3)–Zn(1)–O(4)
N(1)–Zn(2)–O(2)
N(1)–Zn(2)–O(4)
N(1)–Zn(2)–N(1A)
N(1)–Zn(2)–O(2A)
N(1)–Zn(2)–O(4A)
O(2)–Zn(2)–O(4)
O(2)–Zn(2)–O(2A)
O(2)–Zn(2)–O(4A)
55.60(7)
92.04(7)
92.26(7)
180.00(7)
87.96(7)
87.74(7)
89.82(7)
180.00(7)
90.18(7)
115.02(7)
106.80(7)
143.43(7)
115.05(8)
101.49(7)
X-Ray crystallographic study. The crystal of complex 1 has a red-brown color and prismatic habit; dimensions:
0.16×0.14×0.02 mm (C64H86N8O10Zn3, M = 1323.52); monoclinic; space group P21/n at T = 183(2) K: a = 10.5014(9) Å, b =
3
3
–1
9.7816(8) Å, c = 32.018(3) Å, β = 91.9220(10)°, V = 3287.1(5) Å , Z = 2, dx = 1.337 g/cm , F(000) = 1392, μ = 1.147 mm .
The unit cell parameters and the intensities of 27,442 reflections (Rint = 0.0507) were measured with a Bruker
Apex II diffractometer with a CCD detector (T = 183(2) K, MoK radiation, graphite monochromator, ω-scanning,
α
θmax = 28.39°) [20]. A semiempirical correction for X-ray absorption (Tmin/Tmax = 0.8378/0.9556) was made with SADABS
[21]. The structure was solved by the direct method and refined by full-matrix least squares in an anisotropic approximation
2
for nonhydrogen atoms against F . Hydrogen atoms were put into geometrically calculated positions and refined in the rider
hkl
model (Uiso(H) = 1.5Ueq(C) for tert-butyl groups; Uiso(H) = 1.2Ueq(C) for all the other fragments). The final divergence
factors R1 = 0.0388 and wR2 = 0.0938 for 6018 independent reflections with I > 2σ(I ) and R1 = 0.0652 and wR2 = 0.1092 for
all the 8212 independent reflections; 385 refinement parameters; GOOF = 1.039. All the calculations were made in the
SHELX-97 programs [22]. The main bond lengths and valence angles are given in Table 2. The atomic coordinates and
temperature factors have been deposited with the Cambridge Crystallographic Data Centre (No. 950157;
deposit@ccdc.cam.ac.uk; http://www.ccdc.cam.ac.uk/data_request/cif).
RESULTS AND DISCUSSION
The HL hydrazone was obtained by condensation of 1-hydrazine phthalazine and 2,6-di-tert-butyl-para-quinone and
1
identified by elemental analysis and IR and Н NMR spectroscopy.
Due to NH-proton mobility, the HL hydrazone can exist in three main tautomeric forms: phthalazonic (HLa),
hydrazonic (HLb), and azophenolic (HLc).
477

Fig. 1. Structure of the most stable HL hydrazone form in
vacuum (atomic numbering corresponds to that of
complex 1 in Fig. 2).
Fig. 2. Structure of complex 1 (hydrogen atoms are not shown; thermal ellipsoids are drawn at 50% probability).
Since there are two signals from tert-butyl group protons in the PMR spectrum of HL (see Experimental), priority
can be given to one of the quinoid forms, i.e., HLа or HLb. As to the azophenolic form HLc, here one can expect a fast (in the
NMR time scale) rotation of the phenol moiety around the single bond N–C, whereupon the signals from the two t-Bu groups
in the PMR spectra must be detected as an 18-proton singlet. The available literature data lead us to assume that, as in the
case of other hydrazinephthalazine hyrdrazones [1, 23-27], the HL compound exists primarily as a phthalazone hydrazone
tautomer HLa.
To find evidence supporting this assumption, we calculated the electronic and spatial structure of the HLa–c
tautomers by quantum chemical methods within the density functional theory (DFT). The structure of the most stable HL
form is shown in Fig. 1; selected bond lengths and bond angles are given in Table 1. It follows from the calculated results that
the most stable HL form is the phthalazone hydrazone tautomer HLa, which is stabilized by a strong intramolecular hydrogen
bond N(2)–H…N(4). The hydrazonic HLb and azophenolic HLc tautomers are destabilized relative to HLa by 9.34 kcal/mol
and 15.13 kcal/mol, respectively.
The Zn3(Piv)4L2 (1) trinuclear complex was obtained in the reaction between HL and zinc(II) pivalate [Zn(Piv)2]n.
Previously, this reaction was carried out in MeCN, EtOH, and CH2Cl2 to produce, in all the cases, a fine-crystalline
478

precipitate that was low soluble in polar and nonpolar solvents. Single crystals of the resulting compound were obtained by
solvothermal recrystallization of the precipitate (DMFA, 140°C, 48 h).
The molecule of 1 is centrosymmetric; the Zn(2) atom is located at the center of inversion (Fig. 2). The zinc atoms
Zn(1) and Zn(2) (Zn⋯Zn distance is 3.4000(3) Å) are linked by two carboxylate groups and the phthalazine moiety of the L
ligand. The central Zn(2) atom has a distorted octahedral ZnN2O4 environment consisting of the N atoms of two L molecules
and the O atoms of four carboxylate groups (d(Zn–O) distances are 2.1038(18) Å and 2.1105(18) Å; d(Zn–N) is
2.0920(19) Å; Table 2). The peripheral Zn(1) atoms have a distorted tetrahedral ZnN2O2 environment due to the coordination
of the O atoms of two carboxylate groups (d(Zn–O) are 1.9261(18) Å and 1.9697(17) Å) and the azomethine and heterocyclic
N atoms of the hydrazinephthalazine moiety (d(Zn–N) are 2.0069(18) Å and 2.0605(18) Å).
The para-quinone moiety of the monodeprotonated L ligand in the Zn3(Piv)4L2 molecule has a quinoid form, which
is confirmed by the short (C(20)–C(21) 1.353(3) Å and C(27)–C(32) 1.349(3) Å) and long (C(19)–C(20) 1.429(3) Å, C(19)–
C(32) 1.426(3) Å, C(21)–C(26) 1.490(3) Å, and C(26)–C(27) 1.484(3) Å) carbon–carbon distances in the cycle. The short
lengths of C(26)–O(5) (1.235(3) Å) and C(19)–N(4) (1.333(3) Å) correspond to the double bonds C=O and C=N,
–
respectively [28]. The geometric properties of the L anion in 1 are very close to the calculated data for the phthalazone
hydrazone tautomeric form HLа (Table 1).
Thus, it is shown by PMR and quantum chemical methods that the product of the interaction of 1-hydrazine-
phthalazine and 2,6-di-tert-butyl-para-quinone HL has a phthalazone hydrazone tautomeric form, which is stabilized in the
Zn3(Piv)4L2 molecular complex. The compound Zn3(Piv)4L2 is the first example of a trinuclear complex on the basis of
1-hydrazine phthalazine and its derivatives, in which the metal skeleton is enhanced by strengthening the metal centers with
the bridging anions of pivalic acid.
The X-ray crystallographic analysis was conducted at the resource sharing center of the Institute of General and
Inorganic Chemistry (Moscow).
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