7794 Inorganic Chemistry, Vol. 49, No. 17, 2010
Kurtikyan et al.
nitro complexes of nitroporphyrins are known for trans
nitrogen,6 oxygen,7 and phosphorus8 ligands. For sulfur
donors, however, to the best of our knowledge, no literature
reports are available to date.
In this paper, the six-coordinate nitrosyl and nitro com-
plexes of Co(TTP) with trans sulfur-containing ligands were
obtained and characterized by electronic and FTIR spectros-
copy in both layered solids and solutions and the equilibrium
constants of their complexation reactions are reported.
160 K for DMS and 170 K for THT), at which it was possible to
pumpout theexcessofthesulfur-donorligandswithoutdestroy-
ing the six-coordinate species. The FTIR spectra were then
measured at given temperatures to follow the decomposition
of the six-coordinate species as it warmed to room temperature.
The interaction of sulfur donors with Co(TTP)(NO) in a
toluene solution was carried out in an optical cryostat provided
with a 0.05 cm CaF2 cell. A measured quantity of Co(TTP)-
(NO) was fed into the airtight flask provided with a septum.
Known quantities of previously degassed solutions of sulfur
donors in toluene or the pure sulfur donor were transferred into
this flask by vacuum techniques. The solutions thus prepared
were transferred to an IR cell using an airtight Hamilton
syringe. The cell was then tightly closed and placed in the cryo-
stat. Over the course of the IR measurements, the 1280-
1320 cm-1 range, in which νs(NO2) values of Co(TPP)(NO2)6d
or (B)Co(TPP)(NO2)6e are observed, was also thoroughly in-
spected. There were no indications of Co(TTP)(NO) oxidation
during the study. The cell was then cooled using liquid nitrogen
vapors, and the FTIR spectra were taken at temperatures
controlled by a thermocouple that was in close contact with
the cell. Through changes in the flow rate of liquid nitrogen, it
was possible to maintain the temperature of solution at a given
temperature ((1 °C).
The sublimed layers of the nitro complexes Co(TTP)(NO2)
and Co(TTP)(15NO2) were obtained by supplying a low pres-
sure of NO2 (15NO2) on the amorphous layers of Co(TTP) as
described elsewhere.6d This procedure rapidly led to the forma-
tion of the nitro complex, which manifests itself by an intense
νs(NO2) band of coordinated NO2 at 1283 cm-1. The unreacted
NO2 was then pumped out, and a few torr of the sulfur donor
(DMS or THT) was introduced into the cryostat. This proce-
dure led to the fast formation of the six-coordinate nitro
complexes (L)Co(TTP)(NO2) (L = DMS, THT), which ap-
pear by the new set of NO2 vibrations. After the complete
disappearance of the five-coordinate nitro complex, the excess
of the base ligand was quickly pumped out to provide spectra of
the six-coordinated complexes uncomplicated by the presence
of sulfur donors adsorbed in the layer.
The solution studies of the nitro complexes were carried
out as follows. The weighed quantity of Co(TTP)(NO2)
scraped from the KBr substrate was dissolved in the mea-
sured quantity of solvent, as described for Co(TTP)(NO). In
the titration experiments, the measured quantities of sulfur
donors were added to the Co(TTP)(NO2) solution with an
airtight Hamilton syringe through the septum. The 1.00 cm
quartz and 0.05 cm cells with KBr windows were used for
UV-vis and FTIR measurements, respectively.
For study of the oxo-transfer reactivity of the six-coordinate
nitro complexes, measured quantities of the sulfur bases were
introduced into the cryostat with the layered Co(TTP)(NO2) at
room temperature. The layer was maintained under sulfur-
donor vapors overnight, after which the gaseous contents of the
cryostat was analyzed by FTIR spectroscopy and mass spectro-
metry. For the first purpose, the gaseous contents of the
cryostat was deposited through the vacuum connection to the
cold (77 K) KBr substrate of the second cryostat. Then the layer
was heated under vacuum to the temperatures at which the
sulfur donor was completely eliminated from the deposit and
the FTIR spectra of the possible oxidation products could be
measured. The mass spectrometric measurements were per-
formed using a residual gas analyzer. In this case, also the bulk
of the sulfur donor was pumped out at lowered temperatures,
and then the remaining gas was introduced into the chamber of
the gas analyzer through a needle valve.
Experimental Section
Co(TTP) was synthesized using a literature method.9 Before
the experiment, Co(TTP) was additionally purified by column
chromatography with dry alumina using reagent-grade chloro-
form as the eluent. Co(TTP)(NO) for solution experiments was
prepared by introducing a solid sample of Co(TTP) under a NO
atmosphere (∼100 Torr) for 2 h in an airtight flask connected
with a high-vacuum line. This procedure led to the formation
of an intense nitrosyl stretching band (v= 1680 cm-1, ε= 1100
M-1 cm-1 in toluene). NO (15NO) was purified by passing it
through KOH pellets and a cold trap (dry ice/acetone) to
remove the higher nitrogen oxides and trace quantities of water.
The purity was checked by IR measurements of the layer
obtained by the slow deposition of NO onto the cold substrate
of the optical cryostat (77 K). The IR spectrum did not show the
presence of N2O, N2O3, or H2O. 15NO with 98.5% enrichment
was purchased from the Institute of Isotopes, Republic of
Georgia, and was purified by the same procedures. Sulfur
donors dimethyl sulfide (DMS; 99%, Aldrich) and tetrahy-
drothiophene (THT; 99þ%, Aldrich) were freshly distilled over
sodium before use. Before their introduction into the cryostat,
they were degassed by multiple cycles of the freeze-pump-
thaw method. NO2 (15NO2) was obtained by oxidation of NO
(15NO) with an excess of pure dioxygen. After preliminary
drying under P2O5, it was purified by fractional distillation
using a low-temperature vacuum technique until a pure white
solid was obtained.
Sublimed layers of Co(TTP) were obtained on the cold (77 K)
KBr support of an optical cryostat according to a published
procedure.10 These layers were then heated to 250 K under a
dynamic vacuum (P ≈ 2 ꢀ 10-5 Torr), and NO (15NO) was
applied to the cryostat from a vessel provided with a mercury
manometer to measure the equilibrium pressure of the NO gas.
This procedure rapidly led to the formation of the nitrosyl
complex, which manifests itself by an intense NO stretching
band. The excess NO was pumped out, the layer was cooled to
120 K, and a few torr of the sulfur donor (DMS or THT) was
introduced into the cryostat. The layer was then slowly warmed
to 170 K, and the FTIR or UV-vis spectra were run at various
controlled temperatures measured by a thermocouple. This pro-
cedure was accompanied by the gradual disappearance of the
ν(NO) band at 1680 cm-1 and the appearance of the new NO
stretching band of the six-coordinate nitrosyl at lower wave-
numbers. After the complete disappearance of the five-coordi-
nate nitrosyl complex, the layer was cooled (to temperatures of
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The FTIR and UV-vis spectra were acquired on Nexus
(Thermo Nicolet) and “Specord M-40” (Carl Zeiss, Jena) or
Helios γ (Thermo Electron Corp.) spectrometers, respec-
tively, and mass spectra by an RGA-200 residual gas analyzer
(10) Kurtikyan, T. S.; Gasparyan, A. V.; Martirosyan, G. G.; Zhamkochyan,
G. H. J. Appl. Spectrosc. 1995, 62, 62-66 (Russian).