Synthesis and crystal structure of a solvate of arsenic 4,6-dimethyl-8-quinolinethiolate

Article abstract of DOI:10.1007/s10593-012-0946-x

A crystallosolvate of arsenic 4,6-dimethyl-8-quinolinethiolate, As[4,6-Me₂C₉H₄NS]₃·CHCl₃ has been synthesized. The molecular and crystalline structures of the compound have been determined by X-ray structural analysis. The influence of the composition and structure of the ligand on the geometry of the coordination environment of the central arsenic atom in the investigated crystal structures of intracomplex compounds of 8-quinolinethiols is discussed. Grant: The authors are grateful to the Latvian Council of Science for financial support of the investigation.

Full text of DOI:10.1007/s10593-012-0946-x

Chemistry of Heterocyclic Compounds, Vol. 47, No. 12, March, 2012 (Russian Original Vol. 47, No. 12, December, 2011)
SYNTHESIS AND CRYSTAL STRUCTURE OF A SOLVATE
OF ARSENIC 4,6-DIMETHYL-8-QUINOLINETHIOLATE*
1
2
1
1
1
E. Silina ***, S. Belyakov , J. Ashaks **, L. Pech **, and D. Zaruma
A crystallosolvate of arsenic 4,6-dimethyl-8-quinolinethiolate, As[4,6-Me C H NS] ·CHCl has been
2
9
4
3
3
synthesized. The molecular and crystalline structures of the compound have been determined by X-ray
structural analysis. The influence of the composition and structure of the ligand on the geometry of the
coordination environment of the central arsenic atom in the investigated crystal structures of
intracomplex compounds of 8-quinolinethiols is discussed.
Keywords: 8-quinolinethiolates, intracomplex arsenic compounds, molecular and crystal structure.
The present study is a continuation of systematic investigations of the structure of intracomplex
compounds of 8-quinolinethiol, summarized in [1-3]. Investigation results usually are in agreement with the well
established role of the cation in the organization of the crystal structure of the substance. However, among the
crystal structures of 8-quinolinethiolates there are groups of ligands, the composition and structure of which
influence the geometry of the coordination environment of the cation. The most marked effect on the
environment of the cation and also on the physicochemical properties of the corresponding complexes are
demonstrated by ligands with a substituent in position 2 of the quinoline nucleus [4]. Thus the presence of a
methyl group in this position leads, as a result of steric hindrances, to a tetrahedrally distorted planar
environment (2S+2N) for the central atom in 2-methyl-8-quinolinethiolates of palladium and platinum [5, 6] in
comparison with the planar centrosymmetric complexes Pd(C H NS) [7] and Pt(C H NS) [8]. In turn, the
9
6
2
9
6
2
structural similarity of 2-phenyl-8-quinolinethiolates of transition (Co, Ni) and non-transition (Zn, Hg) metals
with the distorted tetrahedral environment (2S+2N) of the central atoms with complex compounds described
above, is caused by an intramolecular π-π interaction of the quinoline nucleus of one ligand with the phenyl ring
of another ligand of the same complex [9].
It seemed of interest to investigate the effect of composition and structure of the ligand in intracomplex
compounds of partial valent p-elements of the V group, As(III), Sb(III), and Bi(III), in which the environment
of the central atom is determined not only by the nature of the cation, but also by the overall interaction of
the lone electron pair (LEP) of the cation and ligand. In the example of the obtained new complex
As(4,6-Me C H NS) ·CHCl (1) and the previously investigated complexes As(C H NS) (2) [10], (3) [11],
2
9
4
3
3
9
6
3
_
*
*
*
______
Dedicated to the memory of Academician E. Lukevics.
*Deceased.
**To whom correspondence should be addressed, e-mail: elga@nki.lv.
1
Institute of Inorganic Chemistry, Riga Technical University, 34 Miera St., Salaspils LV-2169, Latvia.
Latvian Institute of Organic Synthesis, 21 Aizkraukles St., Riga LV-1006, Latvia; e-mail: serg@osi.lv.
2
_
_________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1847-1853, December, 2011.
Original article submitted May 23, 2011.
544
0009-3122/12/4712-1544©2012 Springer Science+Business Media, Inc.
1

9 5 3 9 5 3
As(4-MeC H NS) (4) [12], and As(4-MeOC H NS) (5)*, the effect of the composition and structure of methyl-
and methoxy-8-quinolinethiol ligands on the formation of the coordination sphere of the central arsenic atom has
been shown.
Fig. 1. General view of the As(4,6-Me C H NS) ·CHCl complex with designation of atoms.
2
9
4
3
3
TABLE 1. Some Characteristic Bond Lengths (l) and Values of Valence
Angles (ω) in Complex 1.
Bond
l, Å
2.2699(8)
Angle
, deg.
75.11(6)
As(1)–S(1)
As(1)–S(2)
As(1)–S(3)
As(1)···N(1a)
As(1)···N(1b)
As(1)···N(1c)
S(1)–C(8)
S(1)–As(1)–N(1a)
S(2)–As(1)–N(1b)
S(3)–As(1)–N(1c)
S(1)–As(1)–S(2)
S(1)–As(1)–S(3)
S(2)–As(1)–S(3)
N(1a)–As(1)–N(1b)
N(1a)–As(1)–N(1c)
N(1b)–As(1)–N(1c)
S(3)–As(1)–N(1a)
S(1)–As(1)–N(1b)
S(1)–As(1)–N(1c)
S(3)–As(1)–N(1b)
As(1)–Se(1)–C(8)
2.2861(8)
2.3262(8)
2.637(1)
3.236(1)
3.051(1)
1.772
65.34(5)
67.38(7)
94.16(3)
82.22(4)
97.25(3)
75.27(8)
133.60(9)
67.79(9)
156.91(6)
144.06(6)
147.75(7)
127.46(6)
104.7
1
.767(2)1.775(2)*
1.315
.310(3)1.322(3)*
1.367
.364(2)1.372(3)*
1.422
.420(3)1.424(3)*
N(1)–C(2)
N(1)–C(9)
C(9)–C(10)
1
1
1
1
03.5(1)–106.42(8)*
_
______
Limits of variation of lengths of similar bonds and valence angles in ligands
L(a), L(b), L(c).
*
_
*
______
E. Ya. Silina, S. V. Belyakov, J. V. Ashaks, L. J. Pech, and D. E. Zaruma, Zh. Neorg. Khim., in press.
1
545

Compound As[4,6-Me C H NS] was obtained as a colorless amorphous powder. Recrystallization of
2 9 4 3
the substance from a chloroform–ethanol mixture was accompanied by inclusion of a molecule of chloroform
into the crystals. The molecular and crystal structures of the complex As(4,6-Me C H NS) ·CHCl (1) were
2
9
4
3
3
determined by X-ray structural analysis (Fig. 1).
In the complex the arsenic atom and the sulfur atoms of three ligands form bonds close in lengths to
As(1)–S, l = 2.2941 Å (Table 1). They are somewhat longer than the sum of the covalent radii of the atoms
av
(
R +R = 2.28 Å [13]), but somewhat shorter than the mean As–S bond length in the structures of complexes
As S
2
-5 (2.3010 to 2.3179 Å [10-12]). The As–S bond lengths are in agreement with the data of the Cambridge
Structural Database (version 5.26). The As(1)–S bonds are disposed roughly at right angles S–As(1)–S
ω = 91.21º), and the disposition of the atoms in the (As(1)+3S) fragment may be characterized as an
(
av
insignificantly distorted trigonal pyramid with the arsenic atom at the vertex. The As(1) atom deviates from the
S plane by -1.301(1) Å.
The interatomic As N distances in complex 1 are different and significantly exceed the sum of the
3
…
…
covalent radii of the atoms (R +R = 1.976 Å [13]). The As(1) N(1a) distance is found to be within the limits
As
N
…
of the As N distances in complexes 2-5, which correspond approximately to a value between the sums of the
covalent and van der Waals radii (r +r = 3.3 [14] and 3.576 Å [15]) and is interpreted as weak coordination
As
N
bond, which closes the metallacycle. The As(1)···N(1b) and As(1)···N(1c) distances are closer to the sum of the
van der Waals radii. It may be considered that in this case closing of the corresponding metallacycles does not
occur, in favor of which is also the large deviation of the As(1) atom position from the mean square planarity of
the corresponding quinoline nuclei (-1.748(1) (L(b)) and 1.468(1) (L(c)) as distinct from -0.737(1) Å (L(a))).
Hence in complex 1, similarly to complex 2, one ligand is bidentate (S, N), and the remaining two are
monodentate (S). However, as will be shown later, a directed weak second interaction As(1)···N could not be
excluded.
The values of the N–As(1)–N angles also differ strongly, Δ = 65.8º (Table 1). The values obtained are in
agreement with those in complex 2, but crucially differ from the approximately tetrahedral angles in complexes
3
and 5 (Table 2) characteristic of the symmetrical isomer of octahedral complexes [16]. In complex 1,
…
TABLE 2. Lengths and Configurations of Weak As N Coordination
Bonds in Complexes 1-5
Complex Distance As···N, Å
N–As–N angle, deg.
Coordination polyhedron of As atom
1
2
3
4
5
2.637(1)
67.79(9)
75.27(8)
133.60(9)
"Swing" (3S + N) or ψ-trigonal
bipyramid (3S + N + E)
3
3
.0501(1)
.236(1)
*
*
*
*
2.491(4)
73.0(1)
87.0(1)
133.2(2)
"Swing" (3S + N) or ψ-trigonal
bipyramid (3S + N + E)
2
3
.801(4)
.422(4)
2.641(3)
104.1(1)
106.3(1)
109.6(1)
Distorted octahedron (3S + 3N)
or one-capped ψ-octahedron
(3S + 3N + E)
2
2
.692(5)
.719(4)
2.524(4)
80.8(1)
115.2(2)
112.8(1)
Trigonal bipyramid (3S + 2N)
or ψ-octahedron (3S + 2N + E)
2
2
.672(2)
.964(2)
2.688(3)
110.12(9)
110.12(9)
110.12(9)
Distorted octahedron (3S + 3N)
or one-capped ψ-octahedron
(3S + 3N + E)
2
2
.688(3)
.688(3)
_
*
______
Data on complex 2 are taken from [10], for 3 from [11], for 4 from [12],
for 5 from unpublished work by the authors (see footnote on p. 1545).
1
546

the sum of the N–As(1)–N angles, equal to 276.6º is the least of all found in complexes 2-5. The As(1) atom
emerged from the plane of 3N by 1.013(1) Å. In the space between the As–N vectors, localization is possible for
the stereochemically reactive LEP, which prevents closure of two metallacycles.
The coordination bond As(1)···N(1a) is disposed in an approximately trans position to the weaker
As(1)–S(3) bond. In accordance with the discussed geometric parameters the coordination polyhedron of the
As(1) atom may be characterized as a "swing" (3S+N). However, analysis of all the angle values in the As(1)
…
atom environment (Table 1), taking into account possible weak secondary interactions As(1) N(1b) and
As(1)···N(1c), enabled the disposition of the S(1), S(3), N(1a), N(1b), and N(1c) atoms to be interpreted
geometrically as the strongly distorted base of a pentagonal pyramid. In such a case the coordination polyhedron
of the As(1) atom is a distorted pentagonal pyramid (3S+3N) with sulfur atom S(2) at the vertex or a
ψ-pentagonal bipyramid with sulfur atom S(2) and LEP at the vertices. The deviation of the pyramid base atoms
from its mean-square plane was 0.007(1) Å for atom S(1), 0.042(1) for S(3), -0.411(3) for N(1a), 0.699(3) for
N(1b), and 0.696(3) Å for N(1c). The central As(1) atom is deviated by -0.037(3) Å from the base of the
pyramid, but atom S(2) on the opposite side is deviated by 2.267(1) Å. In the trans position the S(2) atom (angle
…
S(2)–As(1) C(5a) 169.9º) has a shortened contact As(1)···C(5a) (1-x, -y, 2-z) with length of 3.489(2) Å. A pair
…
…
of contacts As(1) C(5a) joins the complexes into dimers (Fig. 2). Contact As(1) H(5a) does not satisfy the
criterion for a weak intramolecular hydrogen bond involving LEP proposed in [11].
Fig. 2. Dimer of complex 1.
The dihedral angle between the planes S(1)–As(1)–N(1a) and S(2)–As(1)–N(1b) was 85.78(3)º, between
the planes S(1)–As(1)–N(1a) and S(3)–As(1)–N(1c) was 164.56(4)º, and between the planes S(2)–As(1)–N(1b)
and S(3)–As(1)–N(1c) was 108.37(3)º. The dihedral angles between the bend of the five-membered rings S, As,
N, C, C along the N···S line were 26.22(8)º, 121.07(3)º, 127.7(1)º in the ligands L(a), L(b), and L(c),
respectively. The chelate ring –S(1)–As(1)···N(1a)–C(9a)–C(8a)– has an "envelope" conformation, the deviation
of the As(1) atom from the mean-square plane carried through the remaining atoms of the ring was -0.928(3) Å.
The S–C bond lengths of complex 1 (Table 1) were insignificantly greater than the standard lengths of a
2
sesqui S–C(sp ) bond (1.76 Å) [17]. The values of valence angles of the As(1)–S–C(8) type were somewhat less
than the value of an ideal tetrahedral angle.
The 4,6-dimethyl-8-mercaptoquinoline molecules have the usual structure (Table 1). The methyl groups
are localized in the ligand plane. The structure of the CHCl molecule is characterized by the bonds C(1')–Cl
3
o
close in lengths from 1.741(3) to 1.746(4) Å and values of the valence angles Cl–C(1')–Cl from 109.6(2) to
11.3(2) . The CHCl molecules are packed as centrosymmetric dimers with intermolecular contacts Cl(1')···Cl(1')
o
1
3
(
-x, 1-y, 2-z) with a length of 3.481(1) Å (2r = 3.50 Å [14]).
Cl
The general shape of the complex, which is characterized by the dihedral angles between the mean-
square plane of the quinoline ligands L(a)/L(b), L(a)/L(c), and L(b)/L(c) equal to 35.9(1)º, 36.2(1)º, and 3.9(1)º,
1
547

respectively, differs significantly from those of complexes 3-5. The virtually parallel dispositions of ligands L(b)
and L(c) of complex 1 are caused by the π-π interaction of the aromatic systems (distance between the centroids
of the heterocycle N(1c), C(2c), C(3c), C(4c), C(9c), C(10c) and of the benzene ring C(5b), C(6b), C(7b), C(8b),
C(9b), C(10b) amounts to 3.479 Å).
The complexes As(4,6-Me C H NS) in the crystals are packed in layers parallel to the (0 1 0) plane
2
9
4
3
(
Fig. 3). The chloroform molecules link the ligands into layers, since the contacts Cl(1')···H(7b) (x, y, z) with
…
…
geometric parameters Cl(1') C(7b) 3.841(4) Å, Cl(1')···H(7b) 2.86 Å, Cl(1') H(7b)–C(7b) 168º in agreement
with [18], may be interpreted as weak C–H···Cl hydrogen bonds.
Fig. 3. Complexes 1 packing in crystal structure.
In conclusion, by comparing the investigated intracomplex compounds 1-5 it should be noted that in the
molecules described the coordination environment of the arsenic atom depends on the composition and structure
of the ligand. Since the structure of the main coordination polyhedron (As+3S) is unchanged, the existing weak
coordination As···N bonds determine the type of polyhedron. The lengths and configuration of these bonds may
be changed within wide limits both on going from one complex to another and in a single molecule. The
presence of methyl substituents in the second and sixth positions of the ligand leads in a complex to the
predominant role of weak (As···N, π-π) interactions in the formation of these intracomplex compounds.
EXPERIMENTAL
Synthesis of Complex As(4,6-Me C H NS) and Its Solvate (1). 20% Aqueous NaOH was added
2
9
4
3
dropwise to a solution of 4,6-dimethyl-8-mercaptoquinoline (0.50 g, 2.65 mmol) in ethanol (15 ml) and water
3 ml) with heating until the solution acquired a yellow color, after which the mixture was diluted with water to
0 ml. Separately As O (0.08 g, 0.40 mmol) was suspended in water (10 ml), 20% aqueous NaOH (several
(
5
2
3
drops) was added and the mixture was shaken until complete dissolution of the solid. The obtained arsenic
548
1

hydroxide solution was added to the first solution. The reaction mixture was neutralized by adding acetic acid
dropwise with stirring until a neutral reaction (pH 7), the precipitated colorless substance was filtered off,
washed with water, and air-dried. Yield 0.45 g (88%). Found, %: C 62.04; H 5.12; N 6.63; S 14.92.
C H N S As. Calculated, %: C 61.60; H 5.17; N 6.54; S 14.96.
3
3
30
3 3
Light-yellow monocrystals of solvate 1 were grown from a chloroform–ethanol, 1:1 mixture.
X-ray Structural Analysis of Compound 1. Parameters of the unit cell of the crystal and a diffraction
o
pattern were obtained from a monocrystal of compound 1 of size 0.170.160.05 mm at -80(2) C on a Bruker
Nonius Kappa CCD automatic diffractometer using scanning by φ and ω (λMoKα-radiation, graphite mono-
o
chromator) to 2θmax = 59 . Monocrystals of solvate 1 were monoclinic, space group was P2 /n. Crystal lattice
1
o
3
parameters: a = 16.4671(2), b = 12.0801(2), c = 17.9947(3) Å, β = 108.7908(7) , V = 3388.79(9) Å ,
M = 759.116, F(000) = 1552, μ = 1.45 mm , ρ
-
1
3
calc
= 1.488 g/cm , Z = 4. The molecular structure of the
compound was established by the direct method and was refined by a full-matrix least squares method on 6505
reflections with I > 3σ(I) to an R factor = 0.044 (wR = 0.110, GOOF = 1.083) in an anisotropic approximation
2
for the non-hydrogen atoms. The methyl groups hydrogen atoms positions were found from a difference
synthesis, the remaining H atoms coordinates were calculated geometrically. The coordinates of the hydrogen
atoms were refined with a "rider" model. The programs maXus and Denzo were used [19, 20]. The crystal
structure has been deposited in the Cambridge Crystallographic Data Center (CCDC 856937).
The authors are grateful to the Latvian Council of Science for financial support of the investigation.
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