Reaction of Selenium with Bromine (Se:Br ⴝ 1:1) in Acetonitrile in the
Presence of Tetramethylammonium Bromide: Synthesis and Crystal Structure of
[(CH
3
)
4
N]
2
[Se
16
Br
18
], the Salt of a Unique Bromoselenate(I) Anion
Vitalijus Janickis*
,a
, Karl Wilhelm Törnroos
b
, Max Herberhold
c
, Jon Songstad
b
, and Wolfgang Milius
c
a
Kaunas, Lithuania, Faculty of Chemical Technology, Kaunas University of Technology
b
Bergen, Norway, Department of Chemistry, University of Bergen
c
Bayreuth, Germany, Laboratory of Inorganic Chemistry, University of Bayreuth
Received April 16th, 2002.
Abstract. Red crystals of [(CH
3
)
4
N]
2
[Se
16
Br
18
](1) were isolated
when selenium and bromine were allowed to react in acetonitrile
solution in the presence of tetramethylammonium bromide. The
salt 1 crystallizes in the monoclinic space group P 2
1
/n with the cell
dimensions a ⫽ 12.1876(4) A
˚
,b⫽ 18.9670(4) A
˚
,c⫽ 12.2390(4)
A
˚
, β ⫽ 91.908(2) ° (123 K). In the solid state structure the
[Se
16
Br
18
]
2⫺
anion consists of two [Br(Se
2
Br
2
)
4
]
⫺
subunits which
are related by an inversion centre and connected by 4 weak Se⫺Br
bonds (3.2588(9) A
˚
and 3.3887(9) A
˚
, respectively). Each
Umsetzung von Selen mit Brom (Se:Br ⴝ 1:1) in Acetonitril in Gegenwart von
Tetramethylammonium-bromid: Synthese und Kristallstruktur von
[(CH
3
)
4
N]
2
[Se
16
Br
18
], dem Salz eines neuartigen Bromoselenat(I)-Anions
Inhaltsübersicht. Rote Kristalle von [(CH
3
)
4
N]
2
[Se
16
Br
18
](1) ließen
sich isolieren, wenn Selen und Brom in Acetonitril-Lösung in Ge-
genwart von Tetramethylammonium-bromid zur Reaktion ge-
bracht wurden. Das Salz 1 kristallisiert in der monoklinen Raum-
gruppe P 2
1
/n mit den Zellkonstanten a ⫽ 12.1876(4) A
˚
,b⫽
18.9670(4) A
˚
,c⫽ 12.2390(4) A
˚
, β ⫽ 91.908(2)° (123 K). In der
Festkörperstruktur besteht das Anion [Se
16
Br
18
]
2⫺
aus zwei
[Br(Se
2
Br
2
)
4
]
⫺
Untereinheiten, die über ein Inversionszentrum in
Zusammenhang stehen und über 4 schwache Se⫺Br Bindungen
Introduction
Selenium and bromine form the binary compounds Se
2
Br
2
,
SeBr
2
and SeBr
4
. In addition, Se
3
Br
2
and Se
4
Br
2
may be
obtained by disproportionation of Se
2
Br
2
. The binary sel-
enium(II) dibromide, SeBr
2
, has not been isolated, although
it is the parent compound of a series of complexes with
bromide ions. Examples of known dianionic bromoselen-
ate(II) complexes (cf. [7]) are the nearly square-planar,
mononuclear [SeBr
4
]
2⫺
ion [1,2], the dinuclear [Se
2
Br
6
]
2⫺
* Prof. Dr. Vitalijus Janickis
Faculty of Chemical Technology
Kaunas University of Technology
Radvile
`
nu
¸
str. 19, LT-3028 Kaunas, Lithuania
FAX: ⫹370 7 451582
E-Mail: vitalijus.janickis@ctf.ktu.lt
Z. Anorg. Allg. Chem. 2002, 628, 1967⫺1974 WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 0044⫺2313/02/628/1967⫺1974 $ 20.00⫹.50/0 1967
monoanionic subunit may be regarded as built up of 4 Se
2
Br
2
mol-
ecules, coordinated to a central bromide ion at distances of
3.0731(9)⫺3.1061(9) A
˚
. The structure of the [Se
16
Br
18
]
2⫺
dianion
can also be formally derived from the known [Se
4
Br
6
]
2⫺
dianion
which uses each of its two bridging bromo ligands for coordination
of 3 additional Se
2
Br
2
molecules.
Keywords: Selenium; Bromoselenates(I); Crystal structure; Tetra-
methylammonium ion
(3.2588(9) bzw. 3.3887(9) A
˚
) miteinander verknüpft sind. Jede der
beiden monoanionischen Untereinheiten lässt sich aus 4 Se
2
Br
2
-
Molekülen aufbauen, die (mit Abständen von 3.0731(9) bis
3.1061(9) A
˚
) an ein zentrales Bromid-Ion koordiniert sind. Die
Struktur des Dianions [Se
16
Br
18
]
2⫺
kann formal auch aus dem be-
kannten Dianion [Se
4
Br
6
]
2⫺
abgeleitet werden, wenn an die beiden
brückenständigen Bromo-Liganden zusätzlich jeweils 3 Moleküle
Se
2
Br
2
angelagert werden.
ion consisting of two edge-sharing distorted SeBr
4
squares
[1,3], the trinuclear [Se
3
Br
8]
2⫺
ion consisting of three edge-
sharing square planar SeBr
4
units [4], the tetranuclear ion
[Se
4
Br
14
]
2⫺
which is formed from two parallel planar Se
2
Br
6
units connected via two linear bromo bridges [4,5] , and the
pentanuclear ion [Se
5
Br
12
]
2⫺
, consisting of a central square
planar SeBr
4
unit with two of its trans-edges being shared
with additional pairs of square planar SeBr
4
units [4].
In contrast to monoselenium dibromide, SeBr
2
, the bi-
nary compound Se
2
Br
2
is stable both as liquid and in the
solid state. It may exist in the modifications α- and β-Se
2
Br
2
which have been characterized by low-temperature crystal
structure analyses [6].
Selenium reacts with bromine in acetonitrile solution,
and when the Se/Br
2
ratio is 2.0, the product is mainly
Se
2
Br
2
: