Organometallics 2007, 26, 6243-6247
6243
A Comparison of Isomers: trans- and
cis-Dicyanobis(para-ethylisocyanobenzene)Platinum
Anthony G. Dylla,† Daron E. Janzen,‡ Marie K. Pomije,*,† and Kent R. Mann*,§
Department of Chemistry and Geology, Minnesota State UniVersity, Mankato, Mankato, Minnesota 56001,
and Department of Chemistry, UniVersity of Minnesota, Minneapolis, Minnesota 55455
ReceiVed August 9, 2007
We report the synthesis and characterization of trans-Pt(p-CN-C6H4-C2H5)2(CN)2 and compare the
properties to the previously reported cis isomer, cis-Pt(p-CN-C6H4-C2H5)2(CN)2. These geometric isomers
exhibit textbook differences in spectroscopic and vapochromic properties, especially in the solid-state.
Introduction
Experimental Section
General Considerations and Materials. All solvents used were
ACS reagent grade and dried over molecular sieves prior to use.
[Pt(p-CN-C6H4-C2H5)4][Pt(CN)4] was prepared by a modification
of the method reported by Buss and Mann.1 The sample of cis-Pt-
(p-CN-C6H4-C2H5)2(CN)2 (cis-PtC2) was available from a previ-
ous study.1
trans-Pt(CN-p-C6H4-C2H5)2(CN)2 (trans-PtC2). A mixture of
[Pt(p-CN-C6H4-C2H5)4][Pt(CN)4] (0.201 g, 0.197 mmol) and
hydrocarbon-stabilized CHCl3 (25 mL, 0.31 mol) was stirred at
reflux under a nitrogen atmosphere for 5 h. The remaining solid
was removed by filtration, and the soluble product was purified by
chromatography (silica gel, 85:15 CH2Cl2/CH3CO2C2H5). The first
fraction was collected and rotary evaporated to afford a reddish-
purple powder (0.080 g, 0.157 mmol, 79.9%). mp 174 °C (dec).
1H NMR (300 MHz, rt, CD2Cl2): δ 7.54 (d, J ) 8.4 Hz, 2 H, Ph),
7.37 (d, J ) 8.4 Hz, 2 H, Ph), 2.74 (q, J ) 7.7 Hz, 2 H, CH2), 1.26
(t, J ) 7.7 Hz, 3 H, CH3). 13C NMR (75 MHz, rt, CD2Cl2): δ
149.9 (isocyanide; Ph), 129.9 (isocyanide; Ph), 127.7 (isocyanide;
We recently reported the synthesis and vapochromic sensing
capability of cis-Pt(p-CN-C6H4-C2H5)2(CN)2.1 This neutral
complex was formed from the thermal rearrangement of the
isomeric double-salt complex [Pt(p-CN-C6H4-C2H5)4][Pt-
(CN)4]. We are investigating these types of platinum complexes
due to their vapochromic properties,2 which have potential for
use in chemical sensors and other optoelectronic devices.3 Here
we report the synthesis and characterization of the trans isomer
of Pt(p-CN-C6H4-C2H5)2(CN)2 and compare it to the previ-
ously reported cis-Pt(p-CN-C6H4-C2H5)2(CN)2. This is the first
well-characterized trans isomer of the Pt(isocyanide)2(CN)2
family of compounds4 and presents a textbook example of the
differences in properties that geometric isomers can exhibit.
* Author to whom correspondence should be addressed. Email: marie.
pomije@mnsu.edu and mann@chem.umn.edu.
195Pt-13
C
Ph), 122.8 (isocyanide; Ph), 112.7 (m, J
) 490 Hz), 29.4
† Minnesota State University, Mankato.
(isocyanide; CH2), 15.4 (isocyanide; CH3). 195Pt NMR (64.5 MHz,
‡ The College of St. Catherine, St. Paul, MN.
§ University of Minnesota.
rt, CD2Cl2, external reference K2PtCl4 in D2O, δ -1624): δ -4698
(m, J
N ) 94 Hz). FTIR (ATR, ZnSe crystal): νCNR 2231 cm-1
(1) Buss, C. E.; Mann, K. R. J. Am. Chem. Soc. 2002, 124, 1031.
(2) (a) Nagel, C. C. U.S. Patent 4,834,909, 1989. (b) Mann, K. R.; Daws,
C. A.; Exstrom, C. L.; Janzen, D. E.; Pomije, M. U.S. Patent 5,766,952,
1998.
195Pt-14
(vs); νCN 2142 cm-1 (m). UV-vis (ATR, cubic zirconia crystal,
film cast from dichloromethane solution): λmax ) 568 nm. Emission
(thin film, λexc ) 397.6 nm) λmax ) 668 nm. HRFAB-MS:
(calculated) 532.1077; (found) 532.1066 (M + Na)+.
(3) Selected sensor references: (a) Drew, S. M.; Janzen, D. E.; Mann,
K. R. Anal. Chem. 2002, 74, 2547. (b) Albert, K. J.; Walt, D. R.; Gill, D.
S.; Pearce, T. C. Anal. Chem. 2001, 73, 2501. (c) Rakow, N. A.; Suslick,
K. S. Nature 2000, 406, 710. (d) Seker, F.; Meeker, K.; Kuech, T. F.; Ellis,
A. B. Chem. ReV. 2000, 100, 2505. (e) Dickinson, T. A.; White, J.; Kauer,
J. S.; Walt, D. R. Nature 1996, 382, 697. (f) Bohrer, F. I.; Sharoni, A.;
Colesniuc, C.; Park, J.; Schuller, I. K.; Kummel, A. C.; Trogler, W. C. J.
Am. Chem. Soc. 2007, 129, 5640. (g) Mansour, M. A.; Connick, W. B.;
Lachicotte, R. J.; Gysling, H. J.; Eisenberg, R. J. Am. Chem. Soc. 1998,
120, 1329. (h) Bailey, R. C.; Hupp, J. T. J . Am. Chem. Soc. 2002, 124,
6767. (i) Li, B.; Sauve´, G.; Iovu, M. C.; Jeffries-EL, M.; Zhang, R.; Cooper,
J.; Santhanam, S.; Schultz, L.; Revelli, J. C.; Kusne, A. G.; Kowalewski,
T.; Snyder, J. L.; Weiss, L. E.; Fedder, G. K.; McCullough, R. D.; Lambeth,
D. N. Nano Lett. 2006, 6, 1598. Selected electronic device applications
references: (j) Kunugi, Y.; Mann, K. R.; Miller, L. L.; Exstrom, C. L.
J. Am. Chem. Soc. 1998, 120, 589. (k) Kunugi, Y.; Miller, L. L.; Mann,
K. R.; Pomije, M. K. Chem. Mater. 1998, 10, 1487. (l) Kunugi, Y.;
Mann, K. R.; Miller, L. L.; Exstrom, C. L. U.S. Patent 6,160,267, 2000.
(m) Kunugi, Y.; Mann, K. R.; Miller, L. L.; Pomije, M. K. U.S. Patent
6,137,118, 2000.
(4) A thorough search of the Cambridge Structural Database (CSD
version 5.28, January 2007) reveals no examples of crystallographically
characterized trans-Pt(isocyanide)2(CN)2 structures. (a) trans-Pt(isocyanide)2-
(CN)2 isomers were reported based on KBr pellet IR spectra by Isci, H.;
Mason, W. R. Inorg. Chem. 1975, 14, 913. (b) trans-Pt(CNCH3)2(CN)2
isomer was detected by 195Pt NMR but not isolated or otherwise character-
ized in a report by Martellaro, P. J.; Hurst, S. K.; Larson, R.; Abbott, E.
H.; Peterson, E. S. Inorg. Chim. Acta, 2005, 358, 3377.
Infrared Spectroscopy. Infrared spectra were obtained by the
ATR (attenuated total reflectance) method using a Nicolet Magna-
FTIR System 550 spectrometer. The sample films were deposited
on a ZnSe trough HATR crystal purchased from PIKE Technolo-
gies. The films were cast from either CH2Cl2 or CHCl3 solutions.
Data were processed using OMNIC ESP v 4.1 software.
NMR Spectroscopy. NMR spectra were acquired on a Varian
Inova 300 MHz spectrometer operating at 64.457 MHz for 195Pt.
The 195Pt spectra were obtained at room temperature and externally
referenced to K2PtCl4 in D2O, δ -1624.0 ppm. A typical set of
parameters for the 195Pt experiments included: acquisition time )
0.164 s, relaxation delay ) 0.300 s, sweep width ) 400.0 kHz and
a 45° pulse. The 1H and 13C spectra were obtained at room
temperature using standard parameters and referenced to the residual
protonated solvent peaks (CH2Cl2 1H 5.32 ppm; 13C 54.0 ppm).
Visible Absorption Spectroscopy. Solid-state visible absorption
spectra were acquired at room temperature using a modification of
the apparatus reported by Drew, Mann, Marquardt, and Mann.5 Thin
(5) Drew, S. M.; Mann, J. E.; Marquardt, B. J.; Mann, K. R. Sens.
Actuators 2004, B97, 307.
10.1021/om7008167 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 11/07/2007