Crystal structures and quantum chemical calculations of dichloro[4-(dimethylamino)phenyl]arsine and tris[4-(dimethylamino)phenyl]arsine

Article abstract of DOI:10.1016/j.molstruc.2017.08.020

Dichloro[4-(dimethylamino)phenyl]arsine (1) and tris[4-(dimethylamino)phenyl]arsine (2) were synthesized and characterized using single crystal X-ray diffraction studies, NMR spectroscopy, IR spectroscopy and elemental analyses techniques. The X-ray struc

Full text of DOI:10.1016/j.molstruc.2017.08.020

Journal of Molecular Structure 1149 (2017) 560e568
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Crystal structures and quantum chemical calculations of dichloro[4-
(dimethylamino)phenyl]arsine and tris[4-(dimethylamino)phenyl]
arsine
,
b
,
,
Mutasem Z. Bani-Fwaz a *, Ahmed E. Fazary a c, Gerd Becker b
a Department of Chemistry, Faculty of Science, King Khalid University, P. O. Box 9004, Abha, 61413, Saudi Arabia
b
€
Institut für Anorganische Chemie, Universitat Stuttgart, Pfaffenwaldring 55, D-70569, Stuttgart, Germany
c Egyptian Organization for Biological Products and Vaccines [VACSERA Holding Company], 51 Wezaret El-Zeraa St., Agouza, Giza, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Dichloro[4-(dimethylamino)phenyl]arsine (1) and tris[4-(dimethylamino)phenyl]arsine (2) were syn-
thesized and characterized using single crystal X-ray diffraction studies, NMR spectroscopy, IR spec-
troscopy and elemental analyses techniques. The X-ray structure analysis of 1 (P1, triclinic, Z ¼ 4;
R1 ¼ 0.0478) revealed two crystallographically independent molecules in the asymmetric part of the unit
cell. The average AseCl bond (220.6 p.m.) is found to be slightly longer than that of arsenic(III) chloride
(216.1 or 216.2 p.m.), but to be rather similar to that in the orthorhombic modification of chlorobis[2,4,6-
tris(trifluoromethyl)phenyl]arsine (219.2 p.m.). Mean AseCaryl (191.7 p.m.) and CaryleN bond lengths
Received 30 June 2017
Received in revised form
4 August 2017
Accepted 6 August 2017
Available online 10 August 2017
This paper is dedicated to the memory of
Professor Gerd Becker, who passed away on
10 January 2017.
(135.9 p.m.) suggest extended electronic interactions between the dichloroarsanyl group, the p-electron
system of the arene ring and the nitrogen lone pair. In both molecules the nitrogen atoms are found in a
planar coordination sphere; the sums of bond angles vary only slightly between 359.1ꢀ for 1a and 359.9ꢀ
for 1b. In contrast to these observations, sums of bond angles of 292.7ꢀ for 1a and 293.98ꢀ for 1b indicate
a pyramidal coordination sphere at arsenic. As well, the X-ray structure analysis of 2 (P1, triclinic, Z ¼ 2;
R1 ¼ 0.0347) reveals bond lengths and angles at arsenic (AseC 194.9 p.m., CeAseC 99.3ꢀ, AseCeC 121.3ꢀ)
as to be expected and obtained for similar compounds such as triphenyl arsine or triphenyl arsine de-
rivatives. The sums of angles at two of the nitrogen atoms amount to values of 353.6ꢀ and 356.1ꢀ and
deviate significantly from the value of the third (348.1ꢀ). Hence, two of three dimethylamino groups are
found to be almost planar, whereas the third group shows a coordination sphere which has to be clas-
sified as an intermediate between trigonal planar and trigonal pyramidal. The molecule shows a high
degree of C3 pseudosymmetry; the sum of angles at arsenic amounts to 298.0ꢀ. The average CaryleN bond
Keywords:
Arsine complexes
Crystal structure
Quantum chemical calculations
length (139.0 p.m.) suggests an interaction of the nitrogen lone pair with the p-system of the arene ring
but it turns out to be much weaker than in dichloro[4-(dimethylamino)phenyl]arsine (1). Additionally,
quantum chemical calculations were performed on several para substituted dichlorophenyl arsine
compounds in order to ascertain optimized structural data and to shed some light onto these phe-
nomena. Indeed, the aforementioned shortening of the NeCipso bond to 135.9 p.m. can only in part be
attributed to the well-known electronic interaction between the lone pair at nitrogen and the anti-
bonding p* orbitals of the adjacent CipsoeCortho bonds e on an average, these two distances are signifi-
cantly elongated by 1.7 p.m. with respect to the standard value (140 p.m.).
© 2017 Elsevier B.V. All rights reserved.
1. Introduction
It was known that, the first organyloxoarsine compound was
prepared as early as 1858 by A. von Baeyer [1]. The preparation of
[4-(dimethylamino)phenyl]oxoarsine and insoluble tris[4-(dime-
thylamino)phenyl]arsine from the dichloro[4-(dimethylamino)
phenyl]arsine compound or its hydrochloride was reported and the
* Corresponding author. Department of Chemistry, Faculty of Science, King Khalid
University, P. O. Box 9004, Abha, 61413, Saudi Arabia.
E-mail addresses: banifawaz@yahoo.com, mbanifawaz@kku.edu.sa (M.Z. Bani-
Fwaz), aefazary@gmail.com, afazary@kku.edu.sa (A.E. Fazary), becker@iac.uni-
stuttgart.de (G. Becker).
http://dx.doi.org/10.1016/j.molstruc.2017.08.020
0022-2860/© 2017 Elsevier B.V. All rights reserved.

M.Z. Bani-Fwaz et al. / Journal of Molecular Structure 1149 (2017) 560e568
561
isolation of crystals suitable for an X-ray structure determination
was repeatedly attempted but only crystals of tris[4-(dimethyla-
mino)phenyl]arsine could be obtained by storing a solution of the
crude product of [4-(dimethylamino)phenyl]oxoarsine in chloro-
form at ꢁ13 ꢀC [2e4] (Scheme S1). Many compounds of such a
composition are now known to be oligomeric in nature [5,6]. Doak
and coworkers [7] repeatedly failed to confirm the synthesis of [4-
(dimethylamino)phenyl]oxoarsine as described by Michaelis and
Rabinerson [2]. Among different possibilities to prepare arylarsonic
acids [8], by far the most widely applicable method is the Bart re-
action. It involves the interaction of a diazonium compound with an
alkaline metal arsenite(III) in the presence of copper(I) and cop-
per(II) salts, powdered silver or copper itself. The Bart reaction has
been improved by a number of research groups; in the Scheller
modification [8] primary arylamines are dissolved in an alcoholic
solution of sulphuric acid and arsenic(III) chloride, diazotized at
takes on a yellow colour. While stirring is continued for 50e60 min,
the mixture is heated in a water bath to complete the reaction. After
4 h cooling to ambient temperature the previously liquid product
starts to solidify and becomes a highly viscous yellow wax. It is
repeatedly placed under vacuum to remove all volatile materials
and finally dissolved in 50 mL of acetonitrile. Storing the solution
for several days at ꢁ13 ꢀC affords colourless to pale yellow crystals
of dichloro[4-(dimethylamino)phenyl]arsine. Yield 85% (17.0 g,
63.9 mmol); mp. 112 ꢀC. Elemental analysis: C8H10AsCl2N (Table S1),
Calc.: C 36.12%; H 3.79%; N 5.27%; Cl 26.66%. Found: C 35.82%; H
3.65%;
N
5.08%; Cl 26.74%. NMR (solution in CD3CN). 1H
(250.134 MHz):
d
¼ 3.02 (s, CH3eN; 6H);
d
¼ 7.54 (d, C6H4;
3J(H,H) ¼ 8.30, 2H);
d
¼ 7.82 ppm (d, C6H4; 3J(H,H) ¼ 8.30 Hz, 2H). 13
C
{1H} (62.896 MHz):
d
¼ 46.78 (s, CH3eN);
d
¼ 122.0 (s, eCeCeN);
d
¼ 130.88 (s, slightly broadened, ipso-CeAs);
d
¼ 131.22 (s,
eCeCeAs);
d
¼ 144.32 ppm (s, ipso-CeN). IR (Nujol mull between
0
ꢀC with the calculated amount of sodium nitrite in water and
[cmꢁ1]): 1591 (vs), 1201 (m), 1082 (vs), 1127 (m), 1065
~
CsBr disks; n
subsequently reacted with the arsenic(III) compound by addition of
a catalytic amount of copper(I) chloride [8]. As far as a predictable
synthesis of tris[4-(dimethylamino)phenyl]arsine is concerned, the
compound could be prepared in 21% yield by Tomaschewski [9]
reacting three equivalents of 4-dimethylaminophenyl lithium
with arsenic(III) chloride at ꢁ20 ꢀC in diethyl ether. Treatment of
tris(phenylmercapto)arsine with the same lithium reagent for 6 h
at ambient temperature by Wada et al. [10] afforded the product in
an essentially improved yield of 73%. Our methods applied to
prepare dichloro[4-(dimethylamino)phenyl]arsine as well as tris[4-
(dimethylamino)phenyl]arsine are both based on the early studies
of Michaelis and Rabinerson (Scheme S1) [2].
Our current research now is to widen the scope of different
starting materials such these arsines. These interest comes from
that the oligomeric organyloxoarsines such as methyl derivate
(H3CeAsO)4: might be of importance in the chemotherapy of can-
cer [11], and have been crystallised as a cyclic tetramer (RAsO)4 [12]
as well as stabilized as (CH3AsO)8 in the coordination sphere of MII
ions [13]. Moreover tris[4-(dimethylamino)phenyl]arsine used as
ligand in coordination chemistry instead of triphenylphosphine
and -arsine in the CO-substitution reactions of cyclopentadienyl-
(dicarbonyl) iron thiocarboxylate complexes [14] as well as the
substitution reactions fordichloro [4-(dimethylamino) phenyl]
arsine lead to different starting materials in our current research
now. The present study is concerned with obtaining crystallo-
graphic date and quantum chemical calculations of dichloro [4-
(dimethylamino) phenyl]arsine (1) and tris[4-(dimethylamino)
phenyl]arsine (2) compounds that can provide a quantitative basis
for discussing the molecular structures, as well as the differences,
that arise in these studies.
(m), 1014 (m), 993 (m), 832 (s), 807 (s), 722 (vs), 632 (m), 604 (s),
575 (w), 548 (vs), 514 (s), 502 (w), 381 (s, br), 366 (s, br).
2.3. Preparation of Tris[4-(dimethylamino)phenyl]arsine
The reaction conditions for the preparation of tris[4-(dimethy-
lamino)phenyl]arsine is similar to the preparation of dichloro[4-
(dimethylamino)phenyl]arsine except for the temperature of the
reaction mixture in which affords colourless cuboids of tris[4-
(dimethylamino)phenyl]arsine at ambient temperature. The sub-
sequent procedure may now be performed under aerobic condi-
tions. Here again with vigorous stirring it is dissolved in 300 mL of
cold distilled water. To the solution, from which insoluble material
has been removed by filtration, are slowly added with stirring 85 g
(2.13 mol) of anhydrous sodium hydroxide until a solid starts to
precipitate. The suspension thus formed is allowed to stand over-
night at ꢁ13 ꢀC, then the insoluble product is filtered off. After
adhering solvent has been removed with repeated evaporation the
solid is recrystallized from 15 mL of chloroform. Cooling to ꢁ13 ꢀC
affords colourless cuboids of tris[4-(dimethylamino)phenyl]arsine.
Yield 46% (5.0 g, 11.5 mmol); mp. 243 ꢀC. Elemental analysis:
C
24H30AsN3 (Table S2), Calc.: C 66.20%; H 6.94%; N 9.65%, Found: C
65.99%; 6.85%;
H
N
9.52%. NMR (solution in CDCl3): 1H
(250.134 MHz):
d
¼ 2.92 (s, CH3eN; 18H);
d
¼ 6.67 (d, C6H4;
3J(H,H) ¼ 8.74 Hz, 6H);
d
¼ 7.20 ppm (d, C6H4; 3J(H,H) ¼ 8.74 Hz, 6H).
13C{1H} (50.323 MHz):
d
¼ 40.38 (s, CH3eN);
d
¼ 112.64 (s,
eCeCeN);
(s, eCeCeAs);
CsBr disks;
d
¼ 126.71 (s, slightly broadened, ipso-CeAs);
d
¼ 134.46
d
¼ 150.35 ppm (s, ipso-CeN). IR (Nujol mull between
[cmꢁ1]): 3547 (w), 2664 (m), 2336 (w), 2086 (w), 1918
~
n
(w), 1890 (w), 1752 (w), 1701 (w), 1624 (w), 1591 (vs), 1546 (m),
1497 (vs), 1198 (vs), 1166 (vs), 1088 (s), 1049 (vs), 1000 (s), 942 (vs),
885 (m), 807 (vs), 755 (s), 722 (vs), 663 (w), 628 (w), 570 (w), 522
(vs).
2. Experimental section
2.1. General considerations
2.4. Preparation of [4-(Dimethylamino)phenyl]oxoarsine and
Dimethyl[4-(dichloroarsanyl)phenyl]ammonium chloride
All details about chemicals, materials, solvents, instruments,
techniques [15e17], and software programs used to solve crystal
structures [18e20] used in this work could be found in Supple-
memntary Information attached in a separate file with this research
article.
Three methods of preparation of [4-(dimethylamino)phenyl]
oxoarsine applied [5e7,21], and the preparation of Dimethyl[4-
(dichloroarsanyl)phenyl]ammonium chloride could be found in
Supplememntary Information attached in a separate file with this
research article.
2.2. Preparation of Dichloro[4-(dimethylamino)phenyl]arsine
It is recommended that the preparation be carried out free of
solvent under an atmosphere of argon. 9.5 mL (9.1 g, 75 mmol) of
N,N-dimethylaniline are added dropwise within 20 min with stir-
ring at 0 ꢀC to 6.3 mL (13.6 g, 75 mmol) of arsenic(III) chloride.
Gaseous hydrogen chloride is evolved and the solution gradually
2.5. Crystal data, measuring techniques, and general
crystallographic information
Storing solutions of dichloro[4-(dimethylamino)phenyl]arsine
(1) in acetonitrile and of tris[4-(dimethylamino)phenyl]arsine (2)

562
M.Z. Bani-Fwaz et al. / Journal of Molecular Structure 1149 (2017) 560e568
in chloroform for a period of three days to two weeks at ꢁ13 ꢀC
afforded colourless to slightly yellow plates or colourless cuboids,
respectively, both suitable for an X-ray structure analysis. A crystal
and details of data collection have been summarized in Table S3.
Selected bond lengths and bond angles as well as torsion angles
[27] can be taken from Table 2 (Table S4). Details concerning the
least-squares planes of these molecules are given in Table S5. Final
atomic coordinates as well as equivalent isotropic and anisotropic
displacement parameters have been listed in Tables S6 and S7,
respectively. In regard to the numbering Figs. 1 and 2, one should
notice that the atoms of the two independent molecules a and b in
the unit cell of compound 1 (Fig. 1) differ in the first integer n (n ¼ 1
or 2) following the element symbol, whereas in compound 2 (Fig. 2)
the atoms of the three substituents at the central atom As3 are
characterized by the integers n ¼ 3, 4 and 5.
of the approximate dimensions 0.7
ꢂ
0.5
ꢂ
0.1 mm (1)//
0.65 ꢂ 0.6 ꢂ 0.5 mm (2) was selected, covered with polyfluorinated
€
polyether oil (RS 3000, Riedel-de-Haen), transferred to an automatic
Syntex P21 diffractometer and cooled to
of ꢁ100
ꢀC. A least squares fit using the positions of 38//35
selected reflections in a range of 9.56 < 2
< 24.25ꢀ//15.54 <
< 25.76ꢀ supplied correct unit cell dimensions. The complete
a
temperature
3
q
2
q
data set was collected with graphite monochromatized Mo-Ka-ra-
diation at a scanning rate ranging from 4.00 to 29.30 deg minꢁ1. As
derived from the unit cell parameters and the lack of systematic
absences, both compounds crystallize in one of the two triclinic
The X-ray structure determination of dichloro[4-(dimethyla-
mino)phenyl]arsine (1) shows the compound to crystallize triclinic
in the centrosymmetric space group P1 and to comprise two in-
dependent molecules a and b in the asymmetric unit. Molecular
models are depicted in Fig. 1. Apart from nearly identical bond
lengths and angles (Table 2) in molecules a and b, even the orien-
tations of the dichloroarsinyl groups with their trigonal pyrami-
dally coordinate arsenic atoms and the planar dimethylamino
substituents in positions 1 and 4, respectively, are found to be very
similar relative to the central arene rings. On the whole the ge-
ometry of both molecules approaches largely pseudosymmetry m
in that the atoms of the total 4-di-methylaminophenyl unit form a
common plane which roughly bisects the Cln1eAsmeCln2 angle
(Table 2). Obviously the following discussion is based mainly on
average values. In order to calculate the length of a polar single
bond from covalent radii, differences in the electronegativity values
of the two atoms concerned have to be taken into consideration. For
such a correction the following methods are usually applied e the
original one set up by Schomaker and Stevenson [28], and a partially
improved one published about twenty years ago by Blom and
Haaland [29]. Inserting Pauling's covalent radii [26] of 77, 99 and
121 p.m. for the elements carbon, chlorine and arsenic and perti-
nent AlredeRochow electronegativities [30] of 2.50, 2.83 and 2.20
into the SchomakereStevenson equation and applying correction
factors of 8 and 4 for the AseC and AseCl distance [26], respec-
tively, result in calculated bond lengths of 196 and 217 p.m. With
the same starting parameters the method of Blom and Haaland [29]
actually leads to identical values of 196 and 216 p.m.
space groups; P1, however, was chosen over P1 [22] on the strength
of E-value statistics and a successful refinement of the structures.
Programs of the software package SHELXTL version 5.10 [18e20]
were employed to solve the phase problem with statistical
(direct) methods and to refine the atomic coordinates as well as at
first the isotropic and subsequently the anisotropic displacement
parameters of all heavier atoms by full matrix least squares calcu-
lations. Furthermore, program XP also included in this package was
used for an analysis of the molecular geometry and the preparation
of drawings. Calculation of the quality factors R1 and wR2 using
measured values with F > 4s (Fo); scattering factors for the neutral
atoms C, As, and Cl from D. T. Cromer and J. B. Man [23] and for the
hydrogen atoms from R. F. Stewart, E. R. Davidson and W. T.
Simpson [24]; full-matrix least squares refinement on F2; several
cycles of refinement with complete matrix and following difference
Fourier synthesis; minimizing of the function Sw (Fo2 e Fc2)2. The
quality factors are defined by the following formulas with m
(number of reflections) and n (number of parameters):
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
P
P
jFo ꢁ jFcjj
wðFo ꢁ jFcjÞ2
P
R ¼ R1 ¼
wR ¼
P
wFo2
Fo
vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
u
u
t
À
Á
À
Á
P
P
2
2
w Fo2 ꢁ Fc2
w Fo2 ꢁ Fc2
wR2 ¼
GOF ¼
À
Á
P
2
ðm ꢁ nÞ
w Fo2
The anisotropic displacement parameters Uij (10ꢁ23 m2) refer to
To allow, however, a careful discussion of the molecular pa-
rameters of dichloro[4-(dimethylamino)phenyl]arsine (1) and to
obtain an answer to whether or not there is a distinct p-conjugation
the expression: e[e2
p
2 (a*2 h2 U11 þ b*2 k2 U22 þ c*2 l2 U33 þ 2b* c*
k l U23 þ 2a* c* h l U13 þ 2 a* b* h k U12)]; the equivalent isotropic
parameters Ueq (10ꢁ23 m2) are calculated from the anisotropic
between the dimethylamino and the dichloroarsinyl substituent
across the arene ring, a second basis will have to be created in that
these values are compared with those of simple parent compounds
such as arsenic(III) chloride or trimethyle and triphenylarsine
together with the heteroleptic species (H3C)3-nAsCln and (H5C6)3-
nAsCln (n ¼ 1 or 2), respectively. For arsenic(III) chloride AseCl bond
lengths of 216.1 and 216.2 p.m. have been determined from its
microwave spectrum [31] and a gas electron diffraction experiment
[32]. Analogous studies on trimethylarsine reveal AseC distances of
195.9 [33] and 198 p.m. [34], whereas X-ray structure de-
terminations at ambient temperature give values of 194.9 [35] and
195.7 p.m. [36] for triphenylarsine. Remarkably, these AseCl and
AseC bond lengths obtained from experiments tally very well with
the results of Blom and Haaland [29]. Since, however, the AseCl and
AseC distances of the heteroleptic chloromethyle and chlor-
ophenylarsines are only partially available from the literature,
quantum chemical calculations [37] using ab-initio methods at the
MP2/6e311þþG** level or DFT methods at the B3LYP/6e311þþG**
level have been carried out to create a third basis and to fill the gap.
Additionally, the high quality of the ab-initio calculations in
particular allows a corroboration of experimental results. In this
P P
values applying the formula Ueq ¼ 1/3
jUija*i aj*ai.aj (a is real-
i
cell and a* reciprocal-cell length [25]. Therefore the equivalent
isotropic Ueq value is defined as one-third of the trace of the
orthogonalized Uij tensor [25]. The structures solved from the
crystallographic data of the compounds 1 and 2 were deposited to
the Cambridge Crystallographic Data Centre (CCDC) under numbers
1537949 and 1537950, respectively. For the data set of compound 1,
the application of a j-scan absorption correction turned out to be
necessary. The introduction of anisotropic displacement parame-
ters resulted in an improvement of the R-values from 0.1087//
0.2989 to 0.0649//0.1809. Finally, the positions of all hydrogen
atoms could be located on a difference Fourier map; the refinement
of these co-ordinates as well as their isotropic displacement pa-
rameters ended in reasonable values.
3. Results and discussion
3.1. Structural analyses
For both compounds 1 and 2, crystallographic parameters [26]

M.Z. Bani-Fwaz et al. / Journal of Molecular Structure 1149 (2017) 560e568
563
Table 1
Selected Bond Lengths (pm) and Bond Angles (ꢀ) as well as Torsion Angles for dichloro[4-(dimethylamino)phenyl]arsine (1) and tris[4-(dimethylamino)phenyl]arsine (2).
a) Bond lengths
1 a
1 b
Mean
2
2
2
Mean
m ¼ 1
m ¼ 2
m ¼ 3
m ¼ 3
m ¼ 3
n ¼ 1
n ¼ 2
n ¼ 3
n ¼ 4
n ¼ 5
AsmeCn1
AsmeCln1
AsmeCln2
NneCn4
NneCn7
NneCn8
191.9(4)
221.5(1)
219.3(1)
135.9(5)
145.3(5)
145.4(6)
191.5(4)
221.4(2)
220.1(2)
135.9(5)
145.4(6)
145.3(6)
191.7
220.6
195.6(2)
194.0(2)
195.0(2)
194.9
135.9
145.4
139.7(3)
145.5(4)
145.7(4)
138.6(3)
144.9(3)
144.3(3)
138.7(3)
143.9(4)
144.3(4)
139
144.8
b) Bond angles
1 a
1 b
Mean
2
2
2
Mean
99.3
m ¼ 1
m ¼ 2
m ¼ 3
m ¼ 3
m ¼ 3
n ¼ 1
n ¼ 2
n ¼ 3
n ¼ 4
n ¼ 5
Cn1eAsmeC(nþ1)1
Cn1eAsmeC(nþ2)1
Cn1eAsmeCln1
Cn1eAsmeCln2
Cln1eAsmeCln2
Cn4eNneCn7
98.5(1)
99.3(1)
100.2(1)
97.3(1)
100.5(1)
94.8(5)
120.0(3)
121.0(3)
118.1(4)
359.1
98.6(1)
98.9(1)
96.5(6)
120.1(4)
121.3(4)
118.5(4)
359.9
98.8
95.7
120.6
117.0(2)
117.1(2)
114.0(2)
348.1
118.6(2)
118.6(2)
116.4(2)
353.6
119.4(2)
119.4(2)
117.3(3)
356.1
118.4
Cn4eNneCn8
Cn7eNneCn8
118.3
359.5
115.9
352.6
P
Na
c) Torsion anglesb
1a
1 b
2
2
2
m ¼ 1
m ¼ 2
m ¼ 3
m ¼ 3
m ¼ 3
n ¼ 1
n ¼ 2
n ¼ 3
n ¼ 4
n ¼ 5
4n4
4n2
4n1
4n3c
C51eAs3eC31eC36
81.4
e101.1
0.8
C31eAs3eC41eC46
C31eAs3eC41eC42
C51eAs3eC41eC42
EPeAs3eC41eC46
90.9
e83.7
17.5
C41eAs3eC51eC56
C41eAs3eC51eC52
C31eAs3eC51eC52
EPeAs3eC51eC56
89.6
e94.6
5.9
C51eAs3eC31eC32
C41eAs3eC31eC32
EPeAs3eC31eC36
e47.7
e38.5
e40.2
a
Sum of angles at nitrogen.
b
c
The torsion angle AeBeCeD is defined as positive if, when viewed along the BeC bond, atom A must be rotated clockwise to eclipse atom D [27].
For a definition of torsion angle 4n3 see text in this paper.
Table 2
Bond Lengths and Angles Quantum Chemically Calculateda and Experimentally Determined for the Compounds (H3C)3-nAsCln and (H5C6)3-nAsCln (n ¼ 0 / 3) as well as
Me2NeC6H4eAsCl2 (1).
Compound
AseCl
AseC
CeAseC
CeAseCl
CleAseCl
calc.
exp.
calc.
exp.
calc.
exp.
calc.
exp.
calc.
exp
Me2NeC6H4eAsCl2 (1) 224.7b (av.) 220.6 (av.) 193.5
191.7
99.2
e
98.9 (av.)
e
97.6
e
94.8
e
(H3C)3As
e
e
196.9c
198.9b
195.7c
197.9b
194.7c
197.2b
e
195.9 [33]
198d [34]
e
96.4c
97.2b
96.4c
96.9b
e
96 [33]
96 [34]
(H3C)2AseCl
H3CeAsCl2
AsCl3
221.5c
225.4b
219.6c
223.2b
218.0c
221.3b
e
e
96.3c
97.0b
99.8c
100.7b
e
e
e
e
e
e
e
e
e
95.7c
96.4b
216.1 [31]
e
e
e
98.9c 98.4 [31]
99.7b
(H5C6)3Ase
(H5C6)2AseClg
e
198.1 (av.)b
194.9 (av.)f [35]
195.7 (av.)f [36]
99.9 (av.)c 99.7 (av.)f [35]
100.1 (av.)f [36]
e
e
e
225.7b
223.5b
218.0c
221.3b
226.0 [38] 197.1; 197.6b 196.0; 197.0 [38] 99.5b
105.0 [38]
e
98.3; 99.4b 94.0; 98.0 [38]
e
98.7b
e
e
H5C6eAsCl2
e
195.9b
e
e
98.5b
e
e
h
AsCl3
216.2 [32]
e
e
e
e
e
98.9c 98.6 [32]
99.7b
a
For details see discussion.
b
c
Calculated by DFT methods at the B3LYP/6e311þþG** level.
Calculated by ab-initio methods at the MP2/6e311þþG** level.
Value obtained from an early GED experiment of the year 1938.
Molecule of C3 symmetry.
Four independent molecules in the asymmetric unit.
Molecule of point group C1.
d
e
f
g
h
Molecule of point group Cs.
respect, already a short look at Table 2, where all relevant AseCl
and AseC bond lengths have been put together, makes evident that
all values calculated by ab-initio methods do not deviate signifi-
cantly from those experimentally determined. Unfortunately, DFT
methods give somewhat longer distances for arsenic(III) chloride,
trimethylarsine and both the chloromethylarsines; obviously these
values are less appropriate for
a
comparison. But for
dichlorophenyle and chlorodiphenylarsine [38] an excellent
agreement between experimentally determined values and those
calculated by DFT methods has been found. With regard to the
AseC distances, however, the well-known shortening of the
element carbon bond caused by a change in hybridization of the

564
M.Z. Bani-Fwaz et al. / Journal of Molecular Structure 1149 (2017) 560e568
parent compound arsenic(III) chloride exhibits the shortest bond
length of 216.1 p.m. [31]. This value is followed by the range of
dichloro(2-chlorophenyl)arsine opening with 218.3 p.m. from a gas
electron diffraction experiment [39] and closing with 226.0 p.m.
from an X-ray structure analysis on chlorodiphenylarsine [38].
Hence, the mean AseCl bond length of dichloro[4-(dimethylamino)
phenyl]-arsine (1, 220.6 p.m.) does not deviate from this range, but
to be rather similar to that in the orthorhombic modification of
chlorobis[2,4,6-tris(trifluoromethyl)phenyl]arsine (219.2 p.m.)
[40]. A completely different situation for the AseC bond lengths of
the two structurally independent molecules 1a and 1b. Both dis-
tances (191.9 and 191.5 p.m.) were found to be distinctly shorter
than a bond length of chlorodiphenylarsine (197 p.m.) as well as
dichloro(2-chlorophenyl)arsine (195.5 p.m.) [39] studied by gas
electron diffraction. Additionally, quantum chemical calculations
on different methylarsines using ab-initio methods at the MP2/
6e311þþG** level furnish a sequence of similar, but slightly
decreasing AseC distances starting with 196.9 p.m. trimethylarsine
and ending with 194.7 p.m. for dichloromethylarsine (Table 2).
These bond lengths are in close agreement with the standard value
of 196 p.m. derived by Blom and Haaland [29].
Without doubt the substantial shortening of the AseC bond
between the dichloroarsinyl unit and the phenyl substituents by 5.3
p.m. (197 vs. 191.7 p.m.) is caused by the dimethylamino in para-
position. Since those interactions are known to be interdependent,
the geometry of the dimethylamino group and especially the dis-
tance between the nitrogen and the ipso-carbon atom have to be
considered first and to be compared with values of parent com-
pound such as N,N-dimethylaniline. To the best of our knowledge,
however, the solid state structure have unfortunately not yet been
determined, but two electron diffraction studies of N,N-dimethy-
laniline have been performed. The first one published as early as
1965 [41] afforded an only rather vague molecular model in that the
planes of the arene ring and the dimethylamino group had been
assumed to be parallel and as far as bond lengths and angles are
concerned, merely average values had been reported. Some years
ago Novikov, Samdal and Vilkov [42] repeated the structure deter-
mination and achieved a substantial improvement by applying
highly discriminating quantum chemical calculations in order to
allow for low-frequency vibrations such as the inversion of the
dimethylamino group and its torsion round the NeCipso bond. The
most important results of the investigation to be mentioned in this
context are the experimental corroboration of the nearly trigonal
planar coordination sphere at nitrogen, a NeCipso bond length of
139.6 p.m. which is shortened by 6.4 p.m. in comparison to the
NeCmethyl distances (146.0 p.m.) and slightly elongated CipsoeCortho
bonds (140.9 p.m.); further data will be found in Table S8. The
strong shortening of the NeC bond to the ipso-carbon atom and a
Fig. 1. Stereoscopic views of both the independent molecules a and b of compound 1.
The two numbering schemes applied differ only in the first figure (n ¼ 1 or 2) following
the element symbols. Thermal ellipsoids are at 30% probability, hydrogen atoms have
been omitted for clarity.
carbon atom e.g. from sp3 to sp2 is not as pronounced as expected;
quite on the contrary, the mean AseC values determined for
trimethyle (195.9 p.m. [33]) and triphenylarsine (194.9 [35] and
195.7 p.m. [36]) were found to be almost identical.
The dependence of AseCl distances on the number of chlorine
atoms at arsenic becomes apparent not only from quantum
chemical calculations, but also from an inspection of some exam-
ples in a literature [31e36,38]. The different chloroarsines the
Fig. 2. Molecular model of compound 2 in stereoscopic view. Thermal ellipsoids are at 30% probability; hydrogen atoms have been omitted for clarity.

M.Z. Bani-Fwaz et al. / Journal of Molecular Structure 1149 (2017) 560e568
565
trigonal planar coordination sphere at nitrogen indicate an effective
electronic interaction between the free electron pair and the
value of the aniline derivative (139.6 p.m., Tables S4 and S8).
Moreover, nearly identical NeCphenyl and NeCmethyl distances of
138.7 and 145.1 p.m., respectively, obtained from quantum chem-
ical calculations on N,N-dimethylaniline, can also be taken for a
comparsion (Table S8).
p
-
system of the molecule, but the already mentioned NeCipso distance
(139.6 p.m.) is still longer than the bond lengths determined
experimentally (135.9 p.m.) and calculated quantum chemically
(137.6 p.m.) for dichloro[4-(dimethylamino)phenyl]arsine (1)
(Table S8).
The structural similarity between tris[4-(dimethylamino)
phenyl]arsine (2) and a standard compound such as N,N-dime-
thylaniline holds not only for the outer part of the molecule, as
elaborated just above but also for its arsenic centre. Despite various
substituents at the arene rings the average AseC bond lengths fall
into a rather small range from 195.4 p.m. obtained for tris(4-
methylphenyl)arsine [43] to 199.0 p.m. for the tris(2,5-
dimethylphenyl) derivative [44]. The series of average AseC dis-
tances starts with tris[4-(dimethylamino)phenyl]arsine (2; 194.9
p.m.) but is immediately followed by the almost identical nearly
values of triphenylarsine [36] (195.7 p.m.), tris[(4-chloro)phenyl]
arsine (195.8pm) [43] and tris[(4-methoxy)phenyl]arsine
(196.3pm) [44]. As expected, methyl groups or even bulkier sub-
stituents in positions 2 and 6 of the arene rings cause an elongation
of the average AseC distances up to values of 198.6 or 199.0 p.m.
published e.g. for tris(2,4,6-triisopropylphenyl)arsine [45] or
tris(2,5-dimethylphenyl)arsine [44], respectively. Tris[2-(dimethy-
laminomethyl)phenyl]arsine, however, has to be regarded as an
exception as three dimethylamino groups additionally coordinate
at the arsenic atom and increase its coordination number to 6
(AseC 198.2 p.m., [(2-Me2NCH2eC6H4)3As)]) [46]. Parallel to the
AseC bond elongation a widening of the CeAseC angles up to
107.6ꢀ in tris(2,4,6-trimethylphenyl)arsine [47] is observed. As a
summary, the following results have to be pointed out: The X-ray
structure analysis of tris[4-(di-methylamino)phenyl]arsine (2)
clearly demonstrates that the unusual shortening of the NeCphenyl
as well as the AseCphenyl bond lengths are restricted to dichloro [4-
(di-methylamino)phenyl]arsine (1) and disappear completely or at
least largely when the highly electronegative chlorine atoms at
arsenic are replaced by 4-(dimethylamino)phenyl substituents.
In order to allow a straightforward conformational analysis of
compound 2 the phenyl carbon atoms in ortho position to the
arsenic atom which are located closer to the nonbonding electron
pair (EP; free coordination site of the distorted tetrahedron at
arsenic) are attributed the designation Cn6 (n ¼ 3, 4, 5) (Fig. 2).
According to the rules set up by Cahn, Ingold and Prelog [27] the
torsion angle EPeAs3eCn1eCn6 (4n3, Fig. 3) has to be used to
define the partial conformation of an individual As3eCn1 bond.
Since, however, the position of the pseudoatom EP cannot be
established, the values of 4n3 cannot be determined directly and
have to be calculated from the relevant torsion angles 4n4, 4n2 and
4n1 (Table 1, Fig. 3) by applying the formula: 4n3:
[4(EPeAs3eCn1eCn6) ¼ e [180 e j4n4j e ½ (j4n2j þ j4n1j)].
The calculation results in torsion angles 4n3 of ꢁ47.7ꢀ, ꢁ38.5ꢀ
and ꢁ40.2ꢀ (Table 1). These values indicate a negative synclinal [48]
partial conformation at all As3eCn1 bonds and hence a helical
chirality of the molecule concerned (Fig. 2). Since the angles 4n3
are found to be very similar, a high degree of molecular C3 pseu-
dosymmetry is achieved. Furthermore, the planes of the arene rings
form an right-handed propeller; by the centres of inversion of space
The average values of the angles CleAseCl (95.7ꢀ) and CeAseCl
(98.8ꢀ, Table 1) correspond very well with relevant parameters
determined for arsenic(III) chloride (98.4ꢀ) and chlor-
odiphenylarsine (93.5ꢀ and 98.3ꢀ,Table 2). Additionally, quantum
chemical calculations on dichlorophenylarsine reveal very similar
values of 98.7ꢀ and 98.5ꢀ for the angles CleAseCl and CeAseCl,
respectively (Table 2). Furthermore, the structural data of the
dimethylamino groups of compound 1 and N,N-dimethylaniline
[42] are also found to be very similar. The average NeCmethyl bond
lengths are almost identical (145.4 vs 146.0 p.m.) and the mean
values of the angles CmethyleNeCmethyl (118.3ꢀ) and CmethyleNeC-
(120.6ꢀ) determined for compound 1 do not differ substan-
phenyl
tially from those of N,N-dimethylaniline (117.4ꢀ and 121.3ꢀ,
respectively; Table S8). The packing of the two crystallographically
different dichloro[4-(dimethylamino)phenyl]arsine molecules 1a
and 1b in the unit cell is depicted in stereoscopic view in Fig. S1. An
inspection of intermolecular distances reveals two short arsenic …
chlorine contacts of 362.6 (As1/Cl11) and 369.0 p.m. (As1/Cl22)
as well as a short arsenic … nitrogen contact of 348.2 p.m. (As/N1).
Since these distances do not deviate substantially from the relevant
sums of van-der-Waals radii (As/Cl 380, As/N 357 p.m. [26]),
strong intermolecular interactions which might increase the coor-
dination number of arsenic, have to be cluded. Taking into account
an analogous sum of 380 p.m. for arsenic and carbon, the same
conclusion holds for several short arsenic … carbon contacts found
in a range from 357.9 (As2/C23) or 361.1 p.m. (As/C14) and 375.6
(As2/C17) to 378.4 p.m. (As/C22).
At first, however, a molecular model of compound 2 will be
depicted stereoscopically in Fig. 2. As already indicated by a sum of
angles at arsenic of 298.0ꢀ and individual CeAseC values varying
only slightly between 98.5 and 100.2ꢀ (Table 1), the central atom is
found in a trigonal pyramidal environment. Previous to a necessary
but rather difficult analysis of the molecular conformation, how-
ever, the following discussion will focus first on the bonding situ-
ation at the dimethylamino groups and the AseC distances. As the
sums of angles at the nitrogen atoms N4 and N5 amount to values
of 353.6ꢀ and 356.1ꢀ, respectively, and hence deviate significantly
from the value of nitrogen atom N3 (348.1ꢀ, Table 1), only two of
three dimethylamino groups are considered to be almost planar.
The third one is found in an environment which has to be classified
as intermediate between trigonal planar and trigonal pyramidal.
Since for amines the barrier of a pyramidal inversion at nitrogen is
well known to be rather low, crystal packing effects may easily
account for the different geometry. Furthermore, the angles be-
tween the least-squares planes of the arene rings An and the
dimethylamino groups Bn (n ¼ 3 / 5, Table S5) fall into a rather
wide range from 35.9ꢀ (A3/B3) to 15.8ꢀ (A5/B5). Differing distances
of the two carbon atoms Cn7 and Cn8 to the least-squares planes An
of the arene rings give additional information about the twist of the
dimethylamino groups (Table S5); the difference in these two
values is highest again for the two carbon atoms C37 and C38 at
nitrogen atom N3. Irrespective of these minor deviations the
structural data of the dimethylamino groups of compound 2
correspond very well with parameters obtained for N,N-dimethy-
laniline by gas electron diffraction [42]. Especially the length of the
characteristic NeCphenyl bond which in comparsion to the average
NeCmethyl distance of 144.8 p.m. is shortened to 139.0 p.m. owing to
group P1 the enantiomeric molecule is generated (Fig. S2). The
packing of molecule (2) in the unit cell is illustrated in Fig. S2. An
inspection of tris[4-(dimethylamino)phenyl]arsine intermolecular
distances does not reveal any values exceeding the sum of appro-
priate van-der Waals radii.
3.2. Quantum chemical calculations
p
-conjugation with the arene ring, tallies with the appropriate
In the molecular structure of dichloro[4-(dimethylamino)

566
M.Z. Bani-Fwaz et al. / Journal of Molecular Structure 1149 (2017) 560e568
groups and the arene ring, respectively. Without doubt the initially
most important result of these quantum chemical studies was the
close agreement in the molecular parameters obtained from the
solid state structure analysis and from calculations on the gaseous
compound (Fig. S3; Table 2 and Table S8). The only major deviation
worth to be mentioned are differences of 5.0 and 3.1 p.m. in the
AseCl bond lengths (219.7 vs 224.7; 221.5 vs 224.6 p.m.), whereas
the distances between arsenic or nitrogen and the ipso-carbon
atoms C1 and C4, respectively, are found to be rather similar (191.7
vs 193.5; 135.9 vs 137.6 p.m.).
By analogy to N,N-dimethylaniline [42] the aforementioned
shortening of the NeCipso bond to 135.9 p.m. can be attributed to an
electronic interaction between the lone pair at nitrogen and the
antibonding p* orbitals of the adjacent CipsoeCortho bonds; on an
average these two distances are significantly elongated by 1.7 p.m.
(Table S8) with respect to the standard value (140 p.m.). Quite
obviously the interaction is intensified by structural features such
as the trigonal planar coordination sphere at nitrogen (Table S8)
and an almost perfect co-planarity of the arene ring with the
dimethylamino group; in both the crystallographically indepen-
dent molecules 1a and 1b the deviations come up to 12.6ꢀ and 1.6ꢀ
only (Table S5). The sp2-hybridization of the nitrogen atom is also
reflected in the results of the NBO hybridization analysis; s and p
character of all bonding orbitals involved vary only slightly be-
tween 0.3111 and 0.3695 and between 0.6298 and 0.6895,
respectively. This type of hybridization also implies an almost pure
p character of the lone pair (0.9939).
Further donor-acceptor interactions in the dichloro[4-(dime-
thylamino)phenyl]arsine (1) molecule are restricted to donating
effects within the arene ring; in particular, one has to emphasize
that such an interaction cannot be observed for bonds at the arsenic
atom. Therefore, an NBO charge analysis was performed to account
for the significant shortening of the AseCipso bond to 191.7 p.m. It
results in a high positive charge of 0.963 to be allocated to the
arsenic atom (Fig. S3a), whereas the adjacent ipso carbon atom
exhibits a rather high negative charge of ꢁ0.468. In comparison to
values of ꢁ0.404 and ꢁ0.260 calculated for the ipso-carbon atom of
dichlorophenylarsine (c) and the hydrogen bonded para carbon
atom of N,N-dimethylaniline (Fig. S4d), respectively, a considerable
increase in negative charge has to be noticed, whereas the positive
charge at the arsenic atom of dichlorophenylarsine (0.974; Fig. S4c)
turned out to be almost unchanged. The unusual shortening of the
AseCipso bond in dichloro[4-(dimethylamino)phenyl]arsine (1) may
therefore be essentially traced back to the unexpectedly high dif-
ference of 1.431 elementary charges and an enhanced electronic
attraction between arsenic and ipso carbon atom. The electronic
situation specified above can best be described in the sense of a
push-pull effect in that the dimethylamino substituents induces
(pushes) a negative charge at (to) the para carbon atom and this
charge is additionally increased by (pulled to) the dichloroarsinyl
group. The optimized Cartesian coordinates and total energies
[Hartrees] for all species could be found in Table S 9.
Fig. 3. Newman projection to specify the partial conformation of the individual
As3eCn1 bond. The bond As3eC41 has been selected as an example.
phenyl]arsine (1), unusual changes in bond lengths have been
noticed. Compared with standard values which, however, have to
be corrected to 144 and 194 p.m. for the Nsp2eCsp2 and AseCsp2
single bond, respectively. By inserting Pauling's covalent radii [26]
of 121, 77 and 74 p.m. for the elements arsine, carbon and nitro-
gen, and pertinent Alred-Rochow electronegativities [30] of 2.20,
2.50 and 3.07 into the Pauling's Modification of the Schomaker-
Stevenson rule lead actually to the values 146 and 196 p.m. and then
corrected to 144 and 194 p.m. by minus 2 p.m. for sp2 hybridization
[26]. The distances between the ipso-carbon atoms and nitrogen as
well as arsenic are both shortened to values of 135.9 and 191.7 p.m.
(Table 1). Additionally, relatively large fluctuations in the CeC bond
lengths from 137.2 to 142.4 p.m. within the arene ring (Tables S4
and 8) suggest substantial substituent effects. To throw light on
the aforementioned problems quantum chemical calculations were
performed [37] in particular with regard to population analyses on
a natural bond orbital (NBO) basis. By such a procedure information
on the allocation of atomic charges as well as the significance of
donor-acceptor interactions between Lewis-type natural bond or-
bitals is easily available. For all compounds to be studied NBO an-
alyses were accomplished by use of the hybrid density functional
method B3LYP [49] and the basis set 6e311þþG** [50]. From the
canonical molecular orbitals initially obtained by these calculations,
natural bond orbitals (NBOs) are derived applying mathematical
algorithms to receive representations of two- or three-centre bonds
and for lone pairs. As for dichloro[4-(dimethylamino)phenyl]arsine
(1) NBO analyses were performed using the results of the X-ray
structure determination as well as molecular parameters supplied
by quantum chemical calculations. In the case of the experimen-
tally based NBO analysis the atomic coordinates of the non-
hydrogen atoms were directly adopted from the last stage of the
crystal structure refinement, whereas standard values of 109 and
108 p.m. had to be ascribed to the CeH bond lengths of the methyl
3.3. NMR characterization
The 1H-NMR-spectrum of dichloro[4-(dimethylamino)phenyl]
arsine shows the typical AA'XX0-pattern of a 1,4-disubstituted arene
ring the four hydrogen atoms of which give rise to two doublets
(3J(H,H) ¼ 8.3 Hz) at 7.54 (3,5-H) and 7.79 p.m. (2,6-H). The singlet
at 3.1 ppm is assigned to the dimethylamino group. In the 13C{1H}
spectrum four singlets in the arene and one in the alkyl region are
noticed; they are tentatively assigned to the ipso-CeN (144.3),
CeCeAs (131.2), ipso-CeAs (130.9) and CeCeN carbon atoms
(122.0) as well as to the dimethylamino group (46.8 ppm). Tris[4-

M.Z. Bani-Fwaz et al. / Journal of Molecular Structure 1149 (2017) 560e568
567
(dimethylamino)phenyl]arsine obtained in 46% yield from an
analogous solvent free reaction of the same starting compounds
N,N-dimethylaniline and arsenic(III) chloride again in a ratio of 1:1,
but followed by a hydrolysis of the highly viscous yellow wax
formed first with sodium hydroxide and an accompanying redis-
tribution of the substituents at arsenic, crystallizes at ꢁ13 ꢀC from a
chloroform solution in colourless cuboids. As expected its NMR
spectra are found to be very similar to those of the dichloro de-
rivative: The hydrogen atoms in 3,5- and 2,6-positions of the
disubstituted arene ring become apparent as two doublets
(3J(H,H) ¼ 8.74 Hz) at 6.67 and 7.20 ppm, whereas the singlet at
2.92 ppm comes from the dimethylamino group. The singlets of the
13C{1H} spectrum at 150.4, 134.5, 126.7 (broadened), and 112.6 ppm
are again tentatively assigned in an analogous way to the carbon
atoms of the ipso-CeN, CeCeAs, ipso-CeAs and CeCeN moiety; the
resonance at 40.4 ppm springs from the (H3C)2N group. Chemical
shifts of the compounds 1 and 2 in comparison with some pa-
rameters of similar compounds [51] are summarized in Table S10.
dissertation (ISBN 978-3-86186-549-0) of the first author and a part
of his postdoctoral research work done in the laboratory of Pro-
€
fessor Gerd Becker at Institut für Anorganische Chemie, Universitat
Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.molstruc.2017.08.020.
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4. Conclusion
Our methods applied to prepare dichloro[4-(dimethylamino)
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are based on the early studies of Michaelis and Rabinerson. Without
doubt, the isolation of a hydrogen chloride free compound has to be
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occurs at ꢃ 0 ꢀC to give dichloro[4-(dimethylamino)phenyl]arsine,
while when the temperature arising to ambient temperature,
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(dimethylamino)phenyl]arsine. The X-ray structure analysis
revealed two crystallographically independent molecules in the
asymmetric part of the unit cell of dichloro[4-(dimethylamino)
phenyl]arsine. In both independent molecules the nitrogen atoms
are found in a planar coordination sphere. Apart from the molecular
data already discussed, the structure of dichloro[4-(dimethyla-
mino)phenyl]arsine (1, Fig. S5) attracts attention by unusual
changes in bond lengths. The high quality of the ab-initio calcula-
tions allows a corroboration of experimental results. Unfortunately,
DFT methods give somewhat longer distances for arsenic(III)
chloride, trimethylarsine and both the chloromethylarsines; obvi-
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dichlorophenyle and chlorodiphenylarsine an excellent agreement
between experimentally determined values and those calculated
by DFT methods has been found. Quantum chemical calculations
were performed also on dichloro[4-(dimethylamino)phenyl]arsine
(1), dichlorophenylarsine, and N,N-dimethylaniline to ascertain
optimized structural data and to shed some light onto these phe-
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(dimethylamino)phenyl]arsine (2, Fig. S5) and a standard com-
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