A novel tetranuclear cubic cage, [Tl4(μ3-dcp)4] {Hdcp=2,4-dichlorophenol}, new short Cl?Cl interactions, thermal, fluorescence, structural and solution studies

Article abstract of DOI:10.1016/j.inoche.2007.06.017

The single crystal X-ray analysis of a novel Tl^I complex of 2,4-dichlorophenol (Hdcp) ligand shows that the complex has a tetranuclear cubic cage as a result of bridging ligands dcp^- with basic repeating of [Tl(μ₃-dcp)] units. There are four thallium atoms with similar coordination spheres in the cubic cage. These thallium atoms contain irregular coordination sphere with stereo-chemically active lone pair. The thermal stability of [Tl₄(μ₃-dcp)₄] was studied by thermal gravimetric (TG) and differential thermal analyses (DTA). The compound [Tl₄(μ₃-dcp)₄] is luminescent in the solution state with emission maxima at 397 nm. The results of studies of the stoichiometry and formation of [Tl₄(μ₃-dcp)₄] complex in DMF solution were found to be in support of their solid state stoichiometry.

Full text of DOI:10.1016/j.inoche.2007.06.017

Inorganic Chemistry Communications 10 (2007) 1189–1193
www.elsevier.com/locate/inoche
A novel tetranuclear cubic cage, [Tl4(l3-dcp)4]
{Hdcp=2,4-dichlorophenol, new short ClÁ Á ÁCl interactions,
thermal, fluorescence, structural and solution studies
*
Kamran Akhbari, Ali Morsali
Department of Chemistry, Faculty of Sciences, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Islamic Republic of Iran
Received 9 May 2007; accepted 18 June 2007
Available online 29 June 2007
Abstract
The single crystal X-ray analysis of a novel TlI complex of 2,4-dichlorophenol (Hdcp) ligand shows that the complex has a tetranu-
clear cubic cage as a result of bridging ligands dcpÀ with basic repeating of [Tl(l3-dcp)] units. There are four thallium atoms with similar
coordination spheres in the cubic cage. These thallium atoms contain irregular coordination sphere with stereo-chemically active lone
pair. The thermal stability of [Tl4(l3-dcp)4] was studied by thermal gravimetric (TG) and differential thermal analyses (DTA). The com-
pound [Tl4(l3-dcp)4] is luminescent in the solution state with emission maxima at 397 nm. The results of studies of the stoichiometry and
formation of [Tl4(l3-dcp)4] complex in DMF solution were found to be in support of their solid state stoichiometry.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: 2,4-Dichlorophenol; Thallium; Tetranuclear cage
The TlI compounds are interesting and frequently dis-
cussed in considering the ‘‘stereo-chemical activity’’ of
valence shell electron lone pairs, potential ability to form
metal–metal bonds and also complexes with aromatic
hydrocarbons [1–27]. The Tl ion is nonspherical, with
its inert pair (6s2) partially hybridized leading to the for-
mation of a local dipole that may strongly affect cat-
ionÁ Á Áligand interactions. This ‘‘inert-pair effect’’ has, in
a general way, been explained by Pitzer [28] and by
Pykko¨ and Desclaux [29] as a relativistic effect causing
the outers electrons to be more strongly attracted to the
nucleus than normally expected. In p-block cations with
an ns2 np0 electronic configuration, lone pairs of elec-
trons may thus play a prominent role in controlling the
structures and chemical behavior. In inorganic salts, the
lone pair is manifested by a distortion of regular coordi-
nation geometries by a substantial elongation of certain
bonds, as exemplified in, for example, TlF [30],
Tl[CuAsO4], Tl[CuPO4] [31] or TlZn(PO3)3 [32]. In several
organometallic compounds, the stereo-active lone pair is
manifested by a ‘‘half-naked’’ cation, with ligands only
coordinating one hemisphere, as observed in the crystal
structures of complexes between Tl(I) and tris(pyraz-
olyl)borate, where the lone pair occupies the fourth
position of a tetrahedron bis(pyrazolyl)phosphinate [33],
with an obvious gap in the coordination sphere due to
the lone pair, and also in [Tl2(l-Htdp)2(l-H2O)]n
(H2tdp = 4,4-thiodiphenol) [34]. Although, in most of
thallium compounds the lone pair is stereo-chemically
active [35] but there are several compounds in which
the lone pair is inactive [36,37]. In this work we wish to
examine the structural characteristics of the novel Tl(I)
complex with the ligand 2,4-dichlorophenol (Hdcp), in
addition thermal, emission and solution studies of this
compound were done. Complexes of this ligand are
very sparse and our search shows that compound
[Tl4(l3-dcp)4] is the first complex of this ligand with short
and very interesting ClÁ Á ÁCl interactions that make this
compound as a coordination polymer.
*
Corresponding author. Tel.: +98 218011001; fax: +98 218009730.
E-mail address: morsali_a@yahoo.com (A. Morsali).
1387-7003/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2007.06.017

1190
K. Akhbari, A. Morsali / Inorganic Chemistry Communications 10 (2007) 1189–1193
Fig. 1. (a) ORTEP diagram, (b) view of the Tl environment; showing the tetranuclear cubic cage, (c) Space-filling representations of compound [Tl4(l3-
dcp)4]. (Tl = purple, O = red, C = gray, Cl = green). i: Àx, Ày + 1/2, z + 1/2; ii: x + 1/4, À y + 1/4, À z + 1/4; iii: Àx + 1/4, y + 3/4, Àz + 1/4.
atoms within the cage are 4.393(2), longer than the sum
Cl
[38] of van der Waals radii of two TlI. Hence, two metall-
ophilic TlÁ Á ÁTl interactions for Tl1 atoms in compound
Cl
OH
[Tl4(l3-dcp)4] may be considered. However, the Tl-ions in
this compound may be considered five-coordinate, the
resulting environment being as TlO3Tl2. In [Tl4(l3-dcp)4],
the lone pair of Tl(I) atoms is ‘‘active’’ in the solid state.
Indeed, the arrangement of O atoms suggests a gap or hole
in coordination geometry around the Tl(I) coordination
sphere (Fig. 1), a gap possibly occupied by a ‘‘stereo-
active’’ electron lone pair. Hence, the geometry of the near-
est coordination environment of every Tl(I) atoms is likely
to be caused by the geometrical constraints of coordinated
O and Tl atoms and by the influence of a stereo-chemically
‘‘active’’ electron lone pair on the metal. Four thallium
atoms and four oxygen atoms of dcpÀ anions form a new
interesting cage with distorted cubic geometry (Fig. 1).
These tetranuclear cubic cages act as nodes and are con-
nected through ClÁ Á ÁCl interactions to four other nodes
(Fig. 3), resulting in a two-dimensional network as shown
in Fig. 2. However, the other interesting feature of this
complex is that, there is the shortest ClÁ Á ÁCl interactions
(Fig. 2) with the distances of Cl3Á Á ÁCl3 [2 À x, 2 À y,
Hdcp
The reaction between 2,4-dichlorophenolate (dcpÀ) and
TlI(NO3) provided crystalline materials of the general for-
mula [Tl4(l3-dcp)4] [48]. Determination of the structure of
this compound by X-ray crystallography (Table S1 and
S2) showed the compound has a novel tetranuclear cubic
cage (Figs. 1 and 2)1 with four Tl+-ions and with coordina-
tion numbers of three. Tl atoms are coordinated with three
phenolic oxygen atoms with Tl–O distances of Àca. 2.50–
˚
2.75 A. The phenolic oxygen atom of the ‘‘dcp ’’ ligand
acts as bridging group (totally with three bonding interac-
tions) (Scheme 1).
There are interactions between the Tl1 and two other
thallium atoms in the cage. The distances between them
are 3.845(2) A, smaller than the sum of van der Waals radii
of two Tl(I) [9]. The distances between the other thallium
˚
1
For interpretation of colours in Figs. 1 and 2, the reader is referred to
˚
1 À z] = 3.233(2) A that is less than the sum of the van
the web version of this article.

K. Akhbari, A. Morsali / Inorganic Chemistry Communications 10 (2007) 1189–1193
1191
Fig. 2. A fragment of the two-dimensional layer in compound [Tl4(l3-dcp)4], showing the ClÁ Á ÁCl interactions. H atoms are omitted for clarity.
of the end residue. DTA curve displays two distinct exo-
thermic peaks at 316 and 573 ꢁC and two endothermic
peaks at 183 and 426 ꢁC (Fig. S1).
The fluorescence spectra of compound [Tl4(l3-dcp)4] has
been studied in DMF solution. The compound shows a
broad emission band with the maximum intensity at
397 nm upon excitation at 300 nm, (Fig. 3). This fluores-
cent emission can be tentatively assigned to MMCT and
Scheme 1.
the existence of thallium–thallium interactions in the solu-
˚
der Waals radii of two Cl atoms that is 3.6 A [39]. Indeed, it
is now realized that ClÁ Á ÁCl interactions can also play a sig-
nificant and predictable structure-determining role in the
chlorine-substituted phenolic metal ion complexes. Hence,
interhalogen interactions are capable of affecting the real-
ized crystalline architecture of solid organic compounds
decisively, and they may thus be used as tools in crystal
engineering [40–46]. It has been shown that the ClÁ Á ÁCl
interactions can be indicative of hypervalent (n–r*) Cl–Cl
contacts [47].
To examine the thermal stability of compound [Tl4(l3-
dcp)4], thermal gravimetric (TG) and differential thermal
analyses (DTA) were carried out between 30 and 700 ꢁC
in the static atmosphere of air. Compound [Tl4(l3-dcp)4]
melts at 183 ꢁC. TG curve exhibits a loss of weight between
Fig. 3. Electronic absorption of ligand Hdcp (a) Electronic absorption of
183 and 376 ꢁC with a mass loss of 19.9% (calcd 19.3%).
Because of formation of a weak bond between C–Cl, this
stage could be related to remove of Cl2 from this com-
pound. The next loss of weight correlated to decomposition
compound [Tl4(l3-dcp)4]. (b) Absorption: c = 1.36 · 10À4 mol lÀ1, DMF,
d = 1 cm for both ligand Hdcp and compound [Tl4(l3-dcp)4]. The
fluorescence spectra of [Tl4(l3-dcp)4] in DMF solution. Room tempera-
ture, kexc = 300 nm.

1192
K. Akhbari, A. Morsali / Inorganic Chemistry Communications 10 (2007) 1189–1193
tion state as there is not any similar emission for the free
ligand Hdcp upon the same excitation at 300 nm (Fig. 3),
the luminescent behavior observed for this complex also
indicates that the structure of this complex is kept in solu-
tion state [49–51].
retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.a-
c.uk. Supplementary data associated with this article can
be found, in the online version, at doi:10.1016/
j.inoche.2007.06.017.
The electronic absorption spectra of the ligand dcpÀ in
the presence of increasing concentration of thallium(I)
ion in DMF at room temperature are shown in Fig. S2.
As is obvious, the strong absorption of ligand at 287 nm
increases with increasing concentration of the metal ion.
The resulting absorbance (at 287 nm) against [Tl+]/[dcpÀ]
mole ratio plot, shown in the inset of Fig. S2, revealed a
distinct inflection point at metal-to-ligand molar ratio of
about 1, emphasizing the formation of a 1:1 complex in
solution. The formation and stoichiometry of the Tl+-dcpÀ
complex in DMF solution were also investigated by a con-
ductometric method. The conductivity of a 5.0 · 10À5 M
solution of thallium(I) nitrate solution in DMF was moni-
References
[1] H.M. Alvarez, P.A. Gillespie, C.D. Gause, Polyhedron 23 (2004) 617.
[2] R.P. Sharma, R. Bala, J. Mol. Struct. 249 (2005) 738.
[3] P. Pyykk, M. Straka, T. Tamm, Phys. Chem. Chem. Phys. 1 (1999)
3441.
[4] H. Schumann, C. Janiak, J. Pickardt, U. Borner, Angew. Chem., Int.
Ed. 26 (1987) 789.
[5] C. Janiak, R. Hofmann, J. Am. Chem. Soc. 112 (1990) 5924.
[6] P.H.M. Budzelaar, J. Boersma, Recl. Trav. Chim. Pays-Bas 109
(1990) 187.
[7] H. Schumann, C. Janiak, M.A. Khan, J.J. Zuckerman, J. Organomet.
Chem. 354 (1988) 7.
[8] H. Schmidbaur, W. Bublak, J. Riede, G. Muller, Angew. Chem., Int.
Ed. 24 (1985) 414.
[9] W. Frank, G. Korrell, G.J. Reiß, J. Organomet. Chem. 506 (1996)
293.
[10] S. Strauss, H.M.D. Noirot, O.P. Anderson, Inorg. Chem. 25 (1986)
3850.
[11] M.D. Noirot, O.P. Anderson, S.H. Strauss, Inorg. Chem. 26 (1987)
2216.
tored as
a
function of [dcpÀ]/[Tl+] mole ratio at
25.00 0.05 ꢁC and the resulting plot is shown in
Fig. S3. As it is seen, the initial conductivity is relatively
low, probably due to some degree of ion pairing which is
common in solvents with relatively low dielectric constant
like DMF. Addition of the ligand to the metal salt solution
then do not causes a variation in the solution conductivity
possessing a rather distinct inflection point at a molar ratio
of about 1, indicating the formation of a 1:1 Tl+-dcpÀ com-
plex in solution.
[12] M.A. Bandman, C.B. Knobler, M.F. Hawthorne, Inorg. Chem. 27
(1988) 2399.
[13] H. Schmidbaur, W. Bublak, B. Huber, J. Hofmann, G. Muller, Chem.
Ber. 122 (1989) 265.
For evaluation of the conditional formation constants,
the mole ratio data obtained by the two different physico-
chemical methods employed were fitted to the previously
reported equations [52,53] using a non-linear least-squares
curve fitting program KINFIT [54]. The conditional for-
mation constants of the complex were evaluated as
2.58 0.003 and 2.47 0.1 from the spectrophotometric
and conductometric methods, respectively.
[14] J. Beck, J. Strahle, Z. Naturforsch. 41b (1986) 1381.
[15] S.D. Waezsada, T. Belgardt, M. Noltemeyer, H.W. Roesky, Angew.
Chem., Int. Ed. 33 (1994) 1351.
[16] P. Ghosh, A.L. Rheingold, G. Parkin, Inorg. Chem. 38 (1999)
5464.
[17] T. Fillebeen, T. Hascall, G. Parkin, Inorg. Chem. 36 (1997) 3787.
[18] M.D. Noirot, O.p. Anderson, S.H. Strauss, Inorg. Chem. 26 (1987)
2216.
[19] A. Askarinejad, Ali Morsali, Helv. Chim. Acta 89 (2006) 265.
[20] A. Askarinejad, Ali Morsali, Inorg. Chem. Commun. 9 (2006) 143.
[21] A. Askarinejad, A. Morsali, J. Org. Chem. 691 (2006) 3563.
[22] A. Askarinejad, A. Morsali, Inorg. Chim. Acta 359 (2006) 3379.
[23] A. Askarinejad, A. Morsali, L.-G. Zhu, Solid State Sci. 8 (2006)
537.
[24] E. Craven, D. Mutlu, S. Lundberg, S. Temizdemir, H. Dechert, C.
Brombacher, C. Janiak, Polyhedron 21 (2002) 553.
[25] C. Janiak, Coord. Chem. Rev. 163 (1997) 107.
[26] A.-V. Mudring, F. Rieger, Inorg. Chem. 44 (2005) 6240.
[27] M.V. Childress, D. Millar, T.M. Alam, K.A. Kreisel, G.P.A. Yap,
L.N. Zakharov, J.A. Golen, A.L. Rheingold, L.H. Doerrer, Inorg.
Chem. 45 (2006) 3864.
In summary, a novel TlI tetranuclear cubic cage of 2,4-
dichlorophenol (Hdcp) ligand, [Tl4(l3-dcp)4], was synthe-
sized and characterized. These thallium atoms contain
irregular coordination sphere with stereo-chemically active
lone pair. The results of studies of the stoichiometry and
formation of [Tl4(l3-dcp)4] in DMF solution were found
to be in support of their solid state stoichiometry. This
compound has shown luminescent properties in DMF
solution.
[28] K.S. Pitzer, Acc. Chem. Res. 12 (1979) 271.
[29] P. Pyykko¨, J.P. Desclaux, Acc. Chem. Res. 12 (1979) 276.
[30] N.W. Alcock, H.D.B. Jenkins, J. Chem. Soc., Dalton Trans. (1974)
1907.
[31] P. Moser, H.M. Schwunck, W. Jung, Z. Anorg. Allg. Chem. 624
(1998) 1256.
Acknowledgement
Support of this investigation by Iran National Science
Foundation, INSF (Project Number 84118) is gratefully
acknowledged.
[32] A. El Abiad, B. Es-Sakhi, M. Mesnaoui, M. Maazaz, I. Belharouak,
P. Graveraeau, C. Parant, G. Wallez, G. Le Flem, J. Solid State
Chem. 154 (2000) 584.
Appendix A. Supplementary material
[33] (a) P.L. Jones, K.L.V. Mann, J.C. Jerrery, J.A. McCleverty, M.D.
Ward, Polyhedron 16 (1997) 2435;
CCDC 643425 contains the supplementary crystallo-
graphic data for [Tl4(l3-dcp)4]. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/
(b) D.A. Bardwell, J.C. Jerrery, J.A. McCleverty, M.D. Ward, Inorg.
Chim. Acta 267 (1998) 232.

K. Akhbari, A. Morsali / Inorganic Chemistry Communications 10 (2007) 1189–1193
1193
[34] K. Akhbari, Ali. Morsali, A.D. Hunter, M. Zeller, Inorg. Chem.
Commun. 10 (2007) 178.
[35] S.-H. Huang, R.-J. Wang, T.C.W. Mak, J. Chem. Soc., Dalton Trans.
(1991) 1379.
[46] E. Weber (Ed.), Design of Organic Solids, Topics in Current
Chemistry, vol. 198, Springer-Verlag, Berlin, Heidelberg, 1998.
[47] S. Herres-Pawlis, U. Florke, G. Henkel, Inorg. Chem. Commun. 9
(2006) 996.
[36] E.J. Fernandez, A. Laguna, J.M. Lopez-de-Luzuriaga, M. Monge, M.
Montiel, M.E. Olmos, Inorg. Chem. 46 (2007) 2953.
[48] 1 mmol (0.163 g) of 2,4-Dichlorophenol was dissolved in 20 ml
acetonitril and was mixed and refluxed with solution of 1 mmol
(0.057 g) KOH in 3 ml H2O, then a solution of 1 mmol (0.266 g) TlNO3
in 5 ml H2O was added to the mixture and was refluxed for 2 h. After
filtering it was allowed to evaporate for several days and then suitable
colourless crystals were obtained. The crystals were washed with
acetone and air dried, m.p. = 183 ꢁC, Yield: 0.161 g (44%). IR (selected
bands; in cmÀ1): 540 m, 606 m, 640 s, 715 vs, 809 s, 845 m, 1034 m, 1083
m, 1274 s, 1302 s, 1386 m, 1454 vs and 1563 m. Anal. calc. for
C6H3Cl2OTl: C, 19.65; H, 0.81; Tl, 55.68%; found; C, 19.80; H, 1.00.
[49] E.J. Fernandez, J.M. Lopez-de-Luzuriaga, M. Elena Olmos, J. Perez,
Inorg. Chem. 44 (2005) 6012.
´
´
[37] E.J. Fernandez, A. Laguna, J.M. Lopez-de-Luzuriaga, M.E. Olmos,
J. Pe´rez, Chem. Commun. (2003) 1760.
[38] F. Wiesbrock, H. Schmidbaur, J. Am. Chem. Soc. 125 (2003)
3622.
[39] H. Zhu, Z. Chu, D. Hu, W. Huang, S. Gou, Inorg. Chem. Commun.
10 (2007) 362.
[40] J.A.R.P. Sarma, G.R. Desiraju, Acc. Chem. Res. 19 (1986) 222.
[41] G.R. Desiraju, Crystal Engineering: The Design of Organic Solids,
Materials Science Monographs, vol. 54, Elsevier, Amsterdam,
1989.
[42] G.R. Desiraju, Angew. Chem., Int. Ed. Engl. 107 (1995) 2541.
[43] G.R. Desiraju, in: D.D. MacNicol, F. Toda, R. Bishop (Eds.),
Comprehensive Supramolecular Chemistry, vol. 6, Elsevier, Oxford,
1996, p. 1.
[44] G.R. Desiraju, J. Chem. Soc. Chem. Commun. (1997) 1475.
[45] A. Anthony, G.R. Desiraju, R.K.R. Jetti, S.S. Kuduva, N.N.L.
Madhavi, A. Nangia, R. Thaimattan, V.R. Thalladi, Cryst. Eng. 1
(1998) 1.
[50] E.J. Fernandez, J.M. Lopez-de-Luzuriaga, M. Monge, M.E. Olmos,
J. Perez, J. Am. Chem. Soc. 124 (2002) 5942.
[51] E.J. Fernandez, A. Laguna, J.M. Lopez-de-Luzuriaga, M. Montiel,
M.E. Olmos, J. Perez, Inorg. Chim. Acta. 358 (2005) 4293.
[52] M.R. Ganjali, A. Rouhollahi, A.R. Mardan, M. Shamsipur, J. Chem.
Soc., Faraday Trans. 94 (1998) 1959.
[53] A. Fakhari, M. Shamsipur, J. Incl. Phenom. 26 (1996) 243.
[54] V.A. Nicely, J.L. Dye, J. Chem. Educ. 49 (1971) 443.