ON POLYIODIDES OF COMPLEX CATIONS WITH 12-CROWN-4 AS LIGAND
Zehra Edis,
Theo Gilles, Karl-Friedrich Tebbe
Institut für Anorganische Chemie der Universität zu Köln,D-50939 Köln, Greinstraße 6, Germany, zehra.edis@uni-koeln.de
Keywords: polyiodides, triiodide,
pentaiodide, heptaiodide, 12-crown-4, crown ether complexes,
crystal structures, phase transitions
On modifying cationic size and shape polyiodide anions I2m+nn-
with varying iodine excess m and anionic charge n may be derived
as components of crystalline solids, which are formed by adding m
iodine molecules I2 und n iodide ions I-.
They may be nearly free or associated to networks with differing
coordination numbers of the iodide ions and various dimensions of
the iodine gratings [1]. The interatomic distances and angles
within the anionic iodine substructure cover a broad range with
pronounced accumulations depending on the structural patterns.
The widespread single charged anions I2n+1-
form a first set of polyiodide ions [2]. Recently an increasing
number of formally higher charged polyiodide ions of the
following rows I4n2-, I6n13-,
I8n24- have been made accessible [3].
Because of the comparatively weak interactions within the anionic
iodine substructure and the manifold possibilities of joining
iodine molecules and iodide ions together by using a few simple
basic patterns a systematic route for the deduction of
polyiodides with unusual composition and structure is not
obvious. Only the variation of cationic size, shape and charge
distribution and the recording of complete series of compounds
starting with the unavoidable triiodide and ending with the
limiting iodine richest compound seems to be successful. Crown
ethers and their low charged complexes particularly seem to be
suitable to precipitate such anions. Our team [3, 4, 5, 6, 7] and
other groups [8, 9, 10] have systematically investigated
polyhalides with sufficiently large crown ethers as ligands for a
long time. Such studies have now been extended to alkali
complexes with the hardly encapsulating ligand 12-crown-4
(1,4,7,10-tetraoxycyclododecan C8H16O4).
Triiodides like [Li(12-crown-4)(H2O)]I3 and
[M(12-crown-4)2]I3 with M = Na, K, Cs have
already been prepared and spectroscopically characterized [11].
Such compounds are much less stable than those with larger rings
(e.g. 18-crown-6 and its derivatives) because of dissociating the
weakly bound ligand. We completed the listing of compounds and
made accessible those with higher iodine contents. Without
exception all these (poly)iodides belong to the first row I2n+1-
with n = 0 (monoiodides), 1 (triiodides), 2 (pentaiodides) and 3
(heptaiodides). They have been characterized by analytical (CHN,
AAS), spectroscopic (MS, UV, IR, Raman), thermal (DSC, TG) and
X-ray diffraction (powder, single crystal) methods. In most cases
the ligands are burdened with some disorder. Crystal structures
will be presented, explained, compared and derived out of
suitable fragments of iodide-iodine gratings [12]. At least all
triiodides run through temperature dependent phase transitions.
This work is build upon earlier investigations of Dr. M.
El Essawi and coworkers. It was carried out within the framework
of the Graduiertenkolleg ´Klassifizierung von Phasenumwandlungen
kristalliner Stoffe aufgrund struktureller und physikalischer
Anomalien´ and was also supported by the Fonds der Chemischen
Industrie. Cand. chem. Oliver Schlüter, Marc Lamshöft and Iris
Krampitz assisted in preparing some compounds, Dipl.-Chem.
Carsten Wieczorrek in solving some crystal structures.
[M(C8H16O4)2]Ix
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M x RG Z a b c V Nref R1 wR2
a b g
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Li 3 Fddd 24 12.467 33.445 36.708 15306 3544 0.131 0.554
7 Pm3m 1 9.521 863.1 293 0.075 0.222
Na 1 Fddd 6 10.452 12.839 24.511 3289
3 P1- 2 8.505 14.275 12.213 1472 4204 0.047 0.067
89.71 84.57 68.01
5 Pnma 4 13.762 9.515 22.881 2996 2690 0.085 0.309
7 Pm3m 1 9.576 878.1
K 3 Pnma 4 13.547 22.642 8.904 2731 2476 0.068 0.213
P1- 2 9.254 12.900 13.713 1366.3 4442 0.045 0.116
117.22 107.54 90.66
5 P4/nbm 4 18.070 13.288 4339 2057
7 P1- 2 12.355 12.621 13.722 1761.8 5810 0.053 0.150
116.42 97.52 105.97
Rb 1 orhP 9.307 12.516 14.548 1694.6
3 P1- 2 10.694 11.598 12.718 1375.5 4529 0.049 0.150
71.00 86.97 67.71
5 P21/n 4 8.920 24.069 13.995 3104 5532 0.040 0.093
91.98
Cs 5 P1- 4 15.204 15.403 15.456 2874
67.90 65.15 64.24
7 I2/a 4 16.386 11.705 19.005 3467 2871 0.044 0.125
108.01
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