Table 1 Similarities between halogen bonding motifs of terminal
alkynes (left) and aryl iodides (right), showing how the I · · · p interaction
(bottom right) might have been predicted by consideration of the similar
alkynyl · · · p motif
Fig. 3 Solid-state packing of 3: hydrogen atoms and the ethyl groups
of the PEt3 ligands (orange) have been removed for clarity.
In order to establish whether the I · · · p interaction seen
above is a reproducible phenomenon, we next synthesised
Pt(PEt3)2(C≡C-p-C6H4–I)2 5. Crystallographic analysis reveals
that this structure also contains the same type of interaction,
but now occurring symmetrically at both ends of the molecule
(Fig. 4). The sheet of molecules thus formed have their platinum
atoms lying in the (–2 0 4) plane of the cell.
of 5.11 This is emphasised in Table 1, which illustrates known
similarities between the recognition properties of iodo and
alkyne groups and shows how the I · · · p interaction continues
this trend.
To summarise, we report:
(i) the first straightforward synthesis of mono- and unsym-
metric bis-alkynyl platinum compounds.
(ii) Identification of the I · · · p synthon as a halogen-bonding
interaction which mimics the ≡CH · · · p hydrogen bond.
(iii) That the influence of halogen-bonding on organic com-
pounds may be reproduced in the structures of inorganic mimics.
Notes and references
‡ Crystal structure data for 2, 3 and 5: 2: C21H34INP2Pt, M = 684.42,
¯
triclinic, space group P1 (no. 2), a = 8.609(2), b = 14.534(6), c =
◦
˚
19.817(9) A, a = 95.63(3), b = 90.51(3), c = 90.93(4) , U = 2467.1(16)
A , Z = 4, Dc = 1.843 g cm−3, l = 7.074 mm−1, T = 100, 27899
3
˚
reflections collected, 11193 unique data (Rint = 0.0314), R1 = 0.0363.
3: C28H38I1.14N0.86O1.72P2Pt, M = 815.71, monoclinic, space group P21/c
Fig. 4 Solid-state packing of 5: hydrogen atoms and the ethyl groups
of the PEt3 ligands (orange) have been removed for clarity.
◦
˚
(no. 14), a = 9.897(2), b = 28.205(6), c = 10.995(2) A, b = 91.19(3) ,
U = 3068.5(11) A , Z = 4, Dc = 1.765 g cm−3, l = 5.844 mm−1
,
3
˚
Within 3 and 5 the distance between the carbon atoms of the
T = 100, 29713 reflections collected, 7040 unique data (Rint = 0.0306),
R1 = 0.0385. 5: C28H38I2P2Pt, M = 885.41, monoclinic, space group
P21/c (no. 14), a = 9.4839(10), b = 15.0660(14), c = 11.1185(17)
˚
triple bond and the iodo atom is in the order of 3.4–3.7 A,
less than or equal to the sum of their van der Waals’ radii
◦
A, b = 97.685(9) , U = 1574.4(3) A , Z = 2, Dc = 1.868 g cm−3
,
3
˚
˚
˚
(3.68 A). The distance from the centre of the triple bond to
l = 6.533 mm−1, T = 173, 17917 reflections collected, 3618 unique
data (Rint = 0.0209), R1 = 0.0163. CCDC reference numbers 262633–
262635. See http://www.rsc.org/suppdata/dt/b5/b506025g/ for crys-
tallographic data in CIF or other electronic format.
˚
the iodine atom is 3.60 and 3.43 A, respectively, for 3 and
5. Clearly there is a halogen-bonding interaction between the
two, in which the p-system is the electron-donor and polarising
species.
1 CSD refcode IOBNIT01: G. R. Desiraju and R. L. Harlow, J. Am.
Chem. Soc., 1989, 111, 6757.
2 R. B. Walsh, C. W. Padgett, P. Metrangolo, G. Resnati, T. W. Hanks
and W. T. Pennington, Cryst. Growth Des., 2001, 1, 165.
3 J. M. A. Robinson, D. Philp, K. D. M. Harris and B. M. Kariuki,
New J. Chem., 2000, 24, 799.
4 CSD refcode ZONYIK: V. R. Thalladi, B. S. Goud, V. J. Hoy, F. H.
Allen, J. A. K. Howard and G. R. Desiraju, Chem. Commun., 1996,
401.
5 S. George, A. Nangia, C.-K. Lam, T. C. W. Mak and J.-F. Nicoud,
Chem. Commun., 2004, 1202.
6 C. J. Adams, L. E. Bowen, M. G. Humphrey, J. P. L. Morrall and
L. J. Yellowlees, Dalton Trans., 2004, 4130.
7 Cambridge Structural Database, Version 5.26, (November 2004); F. H.
Allen, Acta Crystallogr., Sect B, 2002, 58, 380.
8 CSD refcode DIACET: J. D. Dunitz, H. Gehrer and D. Britton, Acta
Crystallogr., Sect. B, 1972, 28, 1989.
9 CSD refcode XASWOD: F. Balavoine, D. Madec and C. Mioskowski,
Tetrahedron Lett., 1999, 40, 8351.
A search of the Cambridge Structural Database7 reveals
that it contains 39 structures containing both a carbon–carbon
triple bond and a terminal carbon–iodine bond. The iodo–p
interaction is present in three of these structures, and is thus not
newly discovered but has merely been overlooked in discussions
of halogen-bonding. Packing within the crystal structure of
1,2-diiodoacetylene8 adopts a similar motif to that seen for
5, reflecting the disposition of iodine atoms and triple-bonds
in both species; equally, the packing of 1-(ethynyl)-4-iodo-3-
(methylaminocarbonyl)benzene9 creates a zigzag similar to 3, as
both compounds contain a single iodo group and a carbon–
carbon triple bond at opposite ends of an approximately linear
molecule. The third example, 1,4-bis(4-tert-butylphenyl)-1,2-
diiodobut-1-en-3-yne,10 has a different arrangement of groups,
which creates a dimeric unit within the crystal.
Similarities between the recognition properties of organic
iodides and terminal alkynes have been reported before,11
and in this respect the iodo · · · p interaction discussed herein
is equivalent to the ≡CH · · · p synthon. As a result of this
equivalence, the structures of the 4-halogenoethynylbenzenes
(apart from the fluoro analogue) display the same motif as 3,12
and the packing of 1,4-diethynylbenzene is the same as that
10 CSD refcode RETRIR: J. Barluenga, I. Llorente, L. J. Alvarez-
Garcia, J. M. Gonzalez, P. J. Campos, M. R. Diaz and S. Garcia-
Granda, J. Am. Chem. Soc., 1997, 119, 6933.
11 J. M. A. Robinson, B. M. Kariuki, K. D. M. Harris and D. Philp,
J. Chem. Soc., Perkin Trans. 2, 1998, 2459.
12 H. C. Weiss, R. Boese, H. L. Smith and M. M. Haley, Chem.
Commun., 1997, 2403.
2 2 4 0
D a l t o n T r a n s . , 2 0 0 5 , 2 2 3 9 – 2 2 4 0