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ISSN 00360236, Russian Journal of Inorganic Chemistry, 2011, Vol. 56, No. 5, pp. 680–686. © Pleiades Publishing, Ltd., 2011. Original Russian Text © V.V. Davydov, V.I. Sokol, N.V. Rychagina, R.V. Linko, Yu.V. Shklyaev, V.S. Sergienko, 2011, published in Zhurnal Neorganicheskoi Khimii, 2011, Vol. 56, No. 5, pp. 728–734.

COORDINATION COMPOUNDS

Synthesis, Crystal Structure, and Spectra of the Trichloromethane Solvate of Nickel(II) 9(E)Phenanthrene9,10Dione[(1Z) 3,3Dimethyl3,4Dihydroisoquinolin1(2H)ylidene]Hydrazonate V. V. Davydova, V. I. Sokolb, N. V. Rychaginaa, R. V. Linkoa, Yu. V. Shklyaevc, and V. S. Sergienkob a

Peoples Friendship University, ul. MiklukhoMaklaya 6, Moscow, 117198 Russia Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninskii pr. 31, Moscow, 117907 Russia c Institute of Technical Chemistry, Ural Branch, Russian Academy of Sciences, ul. Lenina 13, Perm, 614600 Russia b Kurnakov

Received March 15, 2010

Abstract—The complex [Ni(LH)2] ⋅ CHCl3 (I), where L–H is the (9E)phenanthrene9,10dione[(1Z) 3,3dimethyl3,4dihydroisoquinolin1(2H)ylidene]hydrazone anion (L), was synthesized for the first time. The crystal structure of I was solved. The L–H and L–H' anions exist as cis and transisomers and are linked to the central Ni2+ atom in a tridentate chelating mode giving rise to two conjugated fivemembered metal rings of different composition (NiN3C and NiONC2) at each anion. The Ni2+ coordination polyhe dron is a highly distorted octahedron whose axial positions are occupied by N(3) and N(3)' atoms. The ver tices of the tetrahedrally distorted equatorial base of the octahedron are occupied by the N(1) and N(1)' atoms of the dihydroisoquinoline fragment (A) and the O(1) and O(1)' atoms of the phenanthrenequinone fragment (B). Complex I occurs as the cisisomer. The conformations of the L–H anions in I and the L mol ecules in L ⋅ H2O do not differ much. The randomly disordered CHCl3 solvent molecules in I occupy crystal voids between the centrosymmetric dimeric associates. Spectroscopic (IR and UV–Vis) characteristics of I were obtained. DOI: 10.1134/S003602361105007X

During systematic studies of biologically active 3,4dihydroisoquinoline and 9,10phenanthrene quinone derivatives, we obtained previously unknown (9E)phenanthrene9,10dione[(1Z)3,3dimethyl 3,4dihydroisoquinolin1(2H)ylidene]hydrazone (L) [1]. The L molecule having four donor centers (nitro gen and oxygen atoms) is potentially a polydentate ligand. Depending on the position of the active hydro gen atom and the rotation of the dihydroisoquinoline A

2

1

N

N N

fragment (A) relative to the phenanthrenequinone fragment (B) around the exocyclic N–C bond, the L molecule can exist as 13 different isomers. Quantum chemical PPP calculations [1] showed that three iso mers are most stable (Scheme 1). XRay diffraction study of the crystal hydrate L ⋅ H2O (II) showed [1] that molecule L occurs as isomer а (cis, trans) in the crystal.

N

H 3

O

H O

N

N

N N

N

H O

B

а (cis, trans)

b (scis, cis)

b (strans, cis)

Scheme 1.

It was shown [1, 2] that the reaction of L with the crystal hydrates of Cu(II), Co(II), and Ni(II) halides

in the presence of acetone or alcohol may result in the compounds (LH)[CuBr2] and (LH)Br, where LH is

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SYNTHESIS, CRYSTAL STRUCTURE, AND SPECTRA OF THE TRICHLOROMETHANE

681

Table 1. Selected bond lengths (d) and bond angles (ω) in the structures of I and II d, Å Bond

Ni–O(1) Ni–N(1) Ni–N(3) N(1)–C(1) N(2)–C(1) N(2)–N(3) N(3)–C(12) O(1)–C(13)

I

II

L–H

L–H'

L

L'

2.107(3) 2.102(3) 1.994(3) 1.290(5) 1.402(5) 1.306(4) 1.335(5) 1.245(5)

2.086(3) 2.078(3) 1.993(3) 1.306(4) 1.408(4) 1.319(4) 1.333(5) 1.255(4)

1.344(8) 1.323(8) 1.361(7) 1.316(8) 1.246(8)

1.298(9) 1.358(8) 1.355(7) 1.316(9) 1.243(9)

123.8(6) 111.4(5)

123.4(6) 112.2(5)

116.9(5)

117.7(5)

127.0(8) 117.4(6) 119.0(6) 121.9(6) 118.3(6)

125.5(6) 119.2(6) 118.3(5) 121.7(6) 119.1(5)

ω, deg

Angle NiO(1)C(13) NiN(1)C(1) NiN(1)C(9) C(1)N(1)C(9) C(1)N(2)N(3) NiN(3)N(2) N(2)N(3)C(12) NiN(3)C(12) N(1)C(1)N(2) N(1)C(1)C(2) C(13)C(12)C(25) O(1)C(13)C(12) O(1)C(13)C(14)

111.2(3) 109.4(3) 131.5(3) 118.9(3) 110.6(3) 119.3(3) 122.5(3) 118.2(3) 122.9(3) 124.0(3) 121.0(4) 122.2(3) 119.8(3)

111.4(2) 110.8(3) 130.9(3) 117.2(3) 110.3(3) 119.3(2) 122.7(3) 117.9(2) 121.6(3) 125.1(3) 120.6(3) 121.6(3) 119.5(3)

the L molecule protonated at the exocyclic nitrogen atom. In the LH cation, the L molecule switches from isomeric form a (cis, trans) to form b (scis, cis) stabi lized by intramolecular hydrogen bonds. There are no published data concerning the synthesis and studies of metal complexes with L in which the ligand exists in the anionic (deprotonated) form. This paper describes the synthesis of the complex [Ni(L–H)2] ⋅ CHCl3 (I), where L–H is the deprotonated molecule L and pre sents the results of Xray diffraction and IR and UV– Visspectroscopic study of this compound. EXPERIMENTAL Synthesis of I. Compound L (0.3 mmol, 0.115 g) prepared by a reported procedure [1] was dissolved in chloroform (50 mL) and nickel(II) chloride (1.2 mmol, 0.156 g) was dissolved in water (20 mL). The obtained solutions were placed in a separating funnel, ethanol (5 mL) was added, and the mixture was stirred for several minutes until the color of the reaction mixture changed. After separation of the aqueous phase, the organic phase was partly concen trated in vacuum. The precipitate was filtered off, RUSSIAN JOURNAL OF INORGANIC CHEMISTRY

washed with ethanol, dried in vacuum, and recrystal lized from chloroform to give 0.064 g (49%) of the complex. For C50.7H40.7Cl2.1N6NiO2 anal. calcd. (%): C, 67.75; H, 4.53; N, 9.35; Cl, 8.28. Found (%): C, 68.21; H, 4.98; N, 8.38; Cl, 8.06. A single crystal of I was selected among the isolated crystals; its composition was determined more pre cisely in the Xray diffraction study. Crystaloptical phase analysis was performed by a reported procedure [3]. It was shown that the isolated crystalline compound is a single phase. XRay diffraction analysis. The crystals of com pound I (C51H41Cl3N6NiO2, FW = 934.96) formed as dark green plates belong to the monoclinic system. The lattice parameters: a = 17.511(4) Å, b = 12.329(3) Å, c = 21.336(5) Å, β = 103.00(7)°, V = 4488.5(7) Å3, ρcalc = 1.381 g/cm3, μCu = 26.50 cm–1, F(000) = 1928, Z = 4, space group Р21/n. The set of experimental data was obtained from a 0.10 × 0.50 × 0.30 mm single crystal at room tempera ture on a CAD4 EnrafNonius automated fourcircle diffractometer (CuKα radiation, graphite monochroma Vol. 56

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C(22)

C(23)

C(21) C(24) C(20) C(18)

C(4)

C(19)

C(5)

C(25) C(3)

N(2) C(12) N(3)

C(17) C(16)

O(1') C(15') C(14')

C(7) C(9') C(8)

Ni(1)

N(1') C(11)

C(13')

C(17')

C(18')

N(1)

C(10')

O(1) C(16')

C(6)

C(1) C(11')

C(14) C(13)

C(15)

C(2)

C(1') N(3')

C(12') N(2') C(19')

C(7')

C(2')

C(3') C(25')

C(8') C(10) C(6') C(5')

C(20') C(4') C(21')

C(22')

C(24')

C(23')

Fig. 1. Structure of the molecule of complex [Ni(L–H)2] in the crystal of I.

tor, ω scan mode, 2θmах = 135°). Altogether 8138 reflec tions were recorded (Rint = 0.028, –21 ≤ h ≤ 20, 0 ≤ k ≤ 15, 0 ≤ l ≤ 25). The structure was solved by a direct method (SHELXS97) [4] and refined by leastsquares calcu lations in the fullmatrix anisotropic approximation (on F 2) for nonhydrogen atoms (SHELXL97) [5]. The positions of H atoms at C atoms were calculated geometrically (C–H, 0.96 Å) and included in the refinement with fixed positional and thermal parame ters UH that were 0.1–0.3 Å2 greater than the Uj parameters of the corresponding C atoms. The chloro form molecule in compound I is disordered. Analysis of the zero Fourier syntheses revealed additional peaks corresponding to the statistic position of each of the three independent Cl atoms in four positions. The multiplicities of the Cl positions were refined and fixed. In the final version, the parameters of the Cl atoms were refined in the isotropic approximation. The final refinement parameters: R1 = 0.086, wR2 = 0.238 for 5314 reflections with Fo ≥ 4σ(Fo); R1 = 0.117,

wR2 = 0.269 for all reflections; GOOF = 1.136. The residual electron density maximum and minimum are 1.212 and –0.707 еÅ–3, the extinction coefficient being 0.0012(3). Selected interatomic distances and bond angles are summarized in Table 1. The crystal data are deposited with the Cambridge Crystallographic Data Centre, no. CCDC 767473. IR spectra were recorded on an Infralum FT801 IR spectrometer in the range of 400–4000 cm–1 in the crystalline state (KBr pellets). The accuracy of fre quency determination depending on the band half width was ±0.1 cm–1. UV–Vis spectra were recorded on a Specord M40 spectrophotometer in ethanol and chloroform solu tions at concentrations of (7.0–9.6) × 10–5 mol/L in 1 cmthick quartz cells and in the polycrystalline state as mineral oil mulls.

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RESULTS AND DISCUSSION According to elemental analysis of the powder, the complex is described as [Ni(L–H)2] ⋅ nCHCl3 (n ≈ 0.7), and according to single crystal Xray diffraction data of I, the formula is [Ni(L–H)2] ⋅ CHCl3 (n = 1), i.e., the ligand occurs in the anionic (deprotonated) form (L–H). Previously [2], it was noted that L occurs in solu tion as a mixture of isomers а (cis, trans) and b (scis, cis) (Scheme 1), which differ by their UV–Vis spectra. Deprotonation of these isomers should lead to the same anion L–H in which the negative charge is delo calized in the conjugated chain N(1)–C(1)–N(2)– N(3)–C(12)–C(13)–O(1). Since the chelate com plexes have enhanced stability [6], the L–H anion might be expected to add to the Ni atom in the triden tate fashion (structures с and d, Scheme 2, which can be considered as the canonical structures of the same compound).

683

Table 2. Bond angle (ω) in the coordination polyhedron of nickel in structure I Angle

ω, deg

Angle

ω, deg

N(3)Ni(1)N(3')

168.6(1)

N(1)Ni(1)O(1')

91.1(1)

O(1)Ni(1)N(1)

155.5(1)

O(1)Ni(1)O(1')

89.7(1)

O(1')Ni(1)N(1')

156.1(1)

N(1)Ni(1)N(1')

98.3(1)

O(1)Ni(1)N(3)

77.9(1)

N(3)Ni(1)O(1')

93.0(1)

O(1')Ni(1)N(3')

78.4(1)

N(3')Ni(1)O(1)

94.4(1)

N(1)Ni(1)N(3)

77.6(1)

N(3)Ni(1)N(1') 110.5(1)

N(1')Ni(1)N(3')

77.7(1)

N(3')Ni(1)N(1) 109.9(1)

O(1)Ni(1)N(1')

90.7(1)

A

N

N

Ni

N

Ni N

N O

N O

Table 3. Selected torsion angles (τ) in structures I and II τ, deg

B Angle c

I L–H

d Scheme 2.

According to Xray diffraction data, the single crystal of complex I has the composition [Ni(L–Н)2] ⋅ CHCl3 (Fig. 1). In complex I, each of the two indepen dent ligands in the anionic form (L–H and L–H') is attached to nickel in the tridentate chelating mode through the isoquinoline N(1) atom of fragment (A), the azogroup N(3), and phenanthrenequinone O(1) atom of fragment (B) as the donor centers. Coordina tion of each of L–H and L–H in I closes two conju gated fivemembered chelate rings coupled at the N(3)–Ni and N(3)'–Ni bonds with different compo sitions, NiN3C and NiONC2. The same tridentate chelating attachment to the metal giving two conju gated chelate metal rings was found previously for the ligands composed, like L, of two cyclic fragments with donor centers connected by the azo group. An exam ple is a complex of bis(1(2thiazolylazo)2naphtho lato)nickel(II) [7]. The nickel coordination polyhedron in I is a highly distorted octahedron in which the axial positions are occupied by N(3) and N(3)' atoms. The vertices of the tetrahedrally distorted equatorial base of the coordi nation polyhedron are occupied by the N(1) and N(1)' atoms of fragments A and A' and the O(1) and O(1)' atoms of fragments B and B' occurring in the cisposi tions. Complex I thus exists as the cisisomer. RUSSIAN JOURNAL OF INORGANIC CHEMISTRY

II L–H'

L

L'

C(10)C(9)N(1)C(1) 160.5 156.0 78.1 –80.6 C(11)C(9)N(1)C(1) –80.5 –84.2 –161.7 160.6 N(1)C(1)N(2)N(3) –0.5 –5.0 2.6 –1.1 C(1)N(2)N(3)C(12) 177.8 –176.0 179.1 –179.1 N(2)N(3)C(12)C(13) 175.8 173.0 –178.2 –180.0 N(2)N(3)C(12)C(25) –2.6 –3.7 –1.1 3.8 N(3)C(12)C(13)O(1) –0.4 6.7 –15.9 11.7 O(1)C(13)C(14)C(15) 7.1 –3.8 4.61 –1.0

The octahedron distortion in I depends on both the flattened structure of L–H molecules (the N(1), N(3), and O(1) donor atoms are roughly coplanar) and the steric restrictions arising upon coordination of bulky organic ligands to the metal atom. Since the geometric parameters of the L–H and L–H' ligands are rather similar, in what follows we consider the average values. In the nickel coordination polyhedron, the bond angles are most distorted (Table 2). The equatorial base is shaped like a flattened tetrahedron; the oxygen atoms deflect from its mean plane (Δavg = ±0.431 Å) by ±0.448 Å, while the nitrogen atoms deflect by ±0.413 Å. Correspondingly, the opposing O–Ni–N bonds are markedly bent and the interring angles, O(1)NiN(1), are much smaller (155.8(1)° ± 0.3°) than the ideal val ues for a planar base. The N(3)NiN(3)' axial angle in Vol. 56

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C(1) N(2) N(3) C(12)

Fig. 2. Comparative conformation of the coordinated L–H ion in the crystal of I (continuous line) and the Lfree mol ecule in the crystal of II (dashed line).

the octahedron (168.6(1)°) also differs from 180°. The N(1)NiN(1)' (98.3(1)°) and O(1)NiO(1)' (89.7(1)°) angles between the atoms that occupy the cispositions in the base are distorted to a lesser extent. The mini mum values in the coordination polyhedron belong to the intracyclic angles, ONiN (78.2(1)° ± 0.3°) and NNiN (77.7(1)° ± 0.1°). The axial–equatorial angles vary over a broad range: 93.0(1)°–110.5(1)°. The distortions in the coordination polyhedron of complex I are also manifested as the difference between the Ni–N bond lengths. The Ni–N(3) bonds (1.994(3) ± 0.001 Å) with the atoms of the azo groups located at the centers of the L–H and L–H' ligands are, on average, 0.094 Å shorter than the Ni–N(1) bonds (2.090(3) ± 0.012 Å) with the nitrogen atoms of fragments A and A'. The NO(1) bond lengths in I are 2.097(3) ± 0.011 Å. During complexation, the conformation of the coordinated L–H and L–H' molecules does not change fundamentally as compared with the free Lfree molecule in L ⋅ H2O (II) [1]. The formation of chelate rings in complex I does not violate the flattened struc ture of the molecule. The ligands L–H in complex I occur as а isomers (cis, trans) (Scheme1), the same as

the molecule Lfree in structure II. However, upon the addition of ligands L–H and L–H' to the nickel atom, some geometric characteristics change: the dihedral angle between the mean planes of fragments A and B considerably increases (from 5.3° in Lfree to 16.0° in L–H and 24.6° in L–H'). Upon closure of four che late rings in complex I, which are nearly planar (Δavg = 0.021 Å; the folding angles at the Ni–N(3) and Ni– N(3)' bonds are 2.9° and 3.9°, respectively), the bond angles in the chain of bonds between fragments A and B considerably change. The torsion angles almost do not change (Table 3). Figure 2 shows the superimposi tion of the Lfree molecule in II (dashed line) onto the L–H anion in I (continuous line) with coinciding octaatomic planar fragments C(1)–C(8). In crystals of I, noticeable рπstacking interaction of the PD (paralleldisplaced) type occurs between the molecules of the complexes related by an inversion center (0 1/2 0) [8]. This stacking involves the plane parallel rings (D' and F') of the phenanthrenequinone fragments (B') of the ligand L–H' separated by the 3.45 Å distance optimal for the PD interactions with substantial overlap of the planes. In addition, there are short contacts between the molecules related by an inversion center, O(1)···H(18')–C(18') (C(18')–H, 0.97 Å; O(1)···H(18'), 2.47(5) Å; O(1)···C(18'), 3.386(6) Å; O(1)H(18')C(18'), 149(2)°). As a result, large dimeric associates are formed in the structure of I (Fig. 3). The ligand L–H, unlike L–H', is not involved in the PD interaction. This results in some difference between the conformations of two ligands manifested first of all as unequal dihedral angles between the like planar fragments. For example, due to the PD interac tion, the phenanthrenequinone fragment B' is mark edly more planar than fragment B in both complex I and molecule Lfree in the crystal of II. The dihedral angles (F'/D', 5.1°; F'/E', 4.0°; E'/D', 1.5°) are some what smaller than the corresponding angles in frag ment B of the L–H ligand (12.4°, 6.5°, and 6.0°) or in Lfree (8.8°, 3.5°, and 8.4°). The A'/B' dihedral angle in the L–H' ligand (24.5°) is, conversely, increased as compared with the corresponding A/B angle in L–H (16.0°) or in Lfree (5.3°). In addition, the L–H and L–H' ligands in structure I have significant difference in the deviations of the C(9) atom bonded to the methyl groups and the N(1) atom from the plane through C(1)–C(8) of fragments A and A'. The deviations of C(9) (–0.560 Å) and N(1) (–0.309 Å) in L–H are much smaller than 0.828 and 0.378 Å, respectively, in L–H' and in other nonplanar dihydroisoquinoline derivatives with different substituents where analogous deviations are, on average, 0.950 Å (C(9)) and 0.560 Å (N(1)) [1, 2]. The two ligands in complex I are approx imately perpendicular to each other: the dihedral angles are A/A', 81.5°, and B/B', 89.5°. The analogous bond lengths and bond angles in L–H and L–H' are nearly equal. However, the electron density distribution along the sixbond chain from


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C(17)

685

C(16)

C(18) C(15) C(19) C(20)

C(21) C(22)

C(14) C(5') C(6')

C(10')

C(4') N(1A)

C(13) C(2')

C(25)

N(2A)

C(12)

O(1)

C(23) C(24)

C(11')

N(3)

Ni(1A)

C(1')

C(9')

N(2')

N(1') Ni(1)

C(13')

N(3A)

N(3') C(12')

C(24')

C(14')

N(2)

C(22')

O(1') C(1)

N(1) C(9)

C(2)

C(15')

C(23')

C(16') C(17')

C(10)

C(3) C(8)

C(4)

C(11)

C(7) C(5)

C(6)

Fig. 3. Dimeric associates of the complex molecules in the crystal of I.

0

c

b

a

Fig.4. Packing of the structural units in the crystal of I (projected on the xy plane).

N(1) to O(l) between fragments A and B in the L–H and L–H' anions in I differs somewhat from that in Lfree in II. In Lfree, the bond lengths in this chain from C(1) to C(13) correspond to sesquialteral bonds, i.e., the πelectron density is delocalized over these bonds. In I, the πelectron density in this chain is localized at the N(1)–C(1) (1.298(1) ± 0.002 Å), N(2)–N(3) (1.312 ± 0.007 Å), and C(13)–O(1) bonds (1.252(5) ± 0.003 Å), which is typical of the anionic form of the ligands (Scheme 2, d). Due to the drawingtogether RUSSIAN JOURNAL OF INORGANIC CHEMISTRY

effects induced by the formation of fivemembered chelate rings, the bond angles in this chain of bonds also change considerably in the L–H and L–H' anions. In I, the intracyclic angles, C(1)N(1)C(9) (118° ± 0.1°), N(1)C(1)N(2) (122.6° ± 0.4°), and N(3)C(12)C(13) (110.4° ± 0.1°), are markedly smaller than similar angles in Lfree (123.6° ± 0.2°, 126.3° ± 0.7°, and 112.0° ± 0.1°, respectively). The exocyclic angles N(2)N(3)C(12) in I are, conversely, increased to 122.7° ± 0.1°; in Lfree, this angle is 117.3° ± 0.4°. Vol. 56

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Figure 4 shows the packing of structural units in the crystals of I (projected onto the xy plane). The key structural units in the crystal are large centrosymmet rical dimeric associates (DA) in which, as noted above, the molecules of the complex are connected by the PD interactions between the planeparallel fragments D' and F' of one of the ligands (L–H'). The large DA located near the inversion center (0 1/2 0) occupy the whole space of the crystal; their length (~22 Å) deter mining the maximum crystal parameter of I. No addi tional intermolecular interactions occur between the DA in structure I. The voids between the DA are occu pied by the СНCl3 solvent molecules whose chlorine atoms are statistically disordered. One of the chlorine atoms has a shortened C–H···Cl contact. The UV–Vis spectrum of Lfree (ethanol) shows a longwavelength band (LB) with an absorption maxi mum at 465 nm. The addition of a solution of Ni salt in ethanol to a solution of L induces a bathochromic shift of the LB, and the spectrum exhibits two bands with maxima at 530 and 563 nm, which can be attrib π* transitions based on their intensity. uted to π The spectrum has isosbestic points, which is indicative of the existence of two forms of the compound in solu tion. Analogous doublet LB (531 and 566 nm) are also present in the UV–Vis spectra of the isolated complex as a chloroform solution and in the UV–Vis spectrum of the complex in the polycrystalline state (535 and 575 nm, mineral oil mulls). The IR spectrum of the polycrystalline complex (in KBr pellets) exhibits characteristic rather intense C–H

stretching bands for the aromatic rings and methyl and methylene groups in the region of 2852–3068 cm–1. The 1406–1604 cm–1 range exhibits bands that can be attributed to C=C, C=N, C=O, and N=N stretching vibrations. No bands are present in the stretching region of the carbonyl groups of 9,10phenanthrene quinone (1660–1720 cm–1) in the spectrum of the complex. REFERENCES 1. V. V. Davydov, V. I. Sokol, N. V. Rychagina, et al., Zh. Neorg. Khim. 54 (6), 958 (2009) [Russ. J. Inorg. Chem. 54 (6), 893 (2009)]. 2. V. I. Sokol, V. V. Davydov, N. V. Rychagina, et al., Zh. Neorg. Khim. 55 (5), 754 (2010) [Russ. J. Inorg. Chem. 55 (5), 700 (2010)]. 3. A. I. Ezhov, Crystal Optics (RUDN, Moscow, 1987) [in Russian]. 4. G. M. Sheldrick, SHELXS97. Programs for the Solution of Crystal Structures (Univ. of Göttingen, Göttingen, 1997). 5. G. M. Sheldrick, SHELXL97. Programs for the Refine ment of Crystal Structures (Univ. of Göttingen, Göttin gen, 1997). 6. Yu. A. Buslaev and E. G. Il’in, The Chemical Encyclo pedia (Sovetskaya entsiklopediya, Moscow, 1990), Vol. 2 [in Russian]. 7. M. Kurahashi, Acta Crystallogr., Sect. B 32, 1611 (1976). 8. C. Janiak, J. Chem. Soc., Dalton Trans., No. 22, 3885 (2000).


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