Low temperature NO disproportionation by Mn porphyrin. Spectroscopic characterization of the unstable nitrosyl nitrito complex MnIII(TPP) (NO)(ONO)

Article abstract of DOI:10.1039/b404491f

Reaction of NO gas with sublimed layers of the Mn^IITPP (TPP = meso-tetraphenylporphyrinato^2-) at low temperature leads to nitric oxide disproportionation. UV-Vis and FTIR spectroscopy with isotopically substituted nitrogen oxides rev

Full text of DOI:10.1039/b404491f

Low temperature NO disproportionation by Mn porphyrin.
Spectroscopic characterization of the unstable nitrosyl nitrito complex
MnIII(TPP)(NO)(ONO)
Garik G. Martirosyan,a Arsen S. Azizyan,a Tigran S. Kurtikyan*ab and Peter C. Ford*c
a Armenian Research Institute of Applied Chemistry (ARIAC), 375005, Yerevan, Armenia
b Molecular Structure Research Centre NAS, 375014, Yerevan, Armenia. E-mail: tkurt@msrc.am
c
Department of Chemistry and Biochemistry, University of California, Santa Barbara, California, 93106.
E-mail: ford@chem.ucsb.edu
Received (in West Lafayette, IN, USA) 5th March 2004, Accepted 20th April 2004
First published as an Advance Article on the web 24th May 2004
Reaction of NO gas with sublimed layers of the MnIITPP (TPP
= meso-tetraphenylporphyrinato22) at low temperature leads
to nitric oxide disproportionation. UV-Vis and FTIR spectros-
copy with isotopically substituted nitrogen oxides revealed
formation of the unstable species identified as trans-
MnIII(TPP)(NO)(ONO).
asymmetric and symmetric modes of coordinated NO2 are
located12,5a in vicinity of 1440 and 1300 cm 21, much closer to each
other than in Mn(TPP)(NO)(X). On the other hand Ru(TPP)-
(NO)(ONO), for which X-ray structure revealed nitrito coor-
dination,5b shows IR bands at 1522 and 930 cm21. The Ru(TPP)-
(NO)(ONO) complex obtained in sublimed layers13 demonstrates
IR bands at 1844, 1516 and 928 cm21, which were shifted to 1810,
1492 and 908 cm21 respectively upon 15NO substitution.5a
Notably, the latter isotopic shifts are exactly the same as for
complex (1). Thus, the literature data and spectroscopic results lead
to the conclusion that NO has dispropotionated to give N2O14 and
The discovery that nitric oxide plays key roles in mammalian
biology has stimulated renewed interest in chemistry of the
reactions of NO with transition metal ions, especially with models
of metalloproteins.1 The ability of certain transition metal com-
plexes to promote NO disproportionation to form N2O and metal-
nitrite have long been known.2 However among the various
metalloporphyrin nitrosyls studied, only ruthenium and osmium
porphyrins revealed further reactivity with excess NO. These
complexes disproportionate NO to form nitrous oxide and rela-
tively stable at room temperature nitrosyl-nitrito species
M(P)(NO)(ONO) (P = various porphyrinato dianions).3 On the
other hand, to our knowledge only one manganese compound has
been reported to facilitate NO disproportionation.4 Here we give
evidence for nitric oxide disproportionation mediated by sublimed
layers of Mn(TPP) at low temperature. We also report the first IR
and UV-vis characterization of the unstable manganese nitrosyl
nitrito complex Mn(TPP)(NO)(ONO).
a
compound we have formulated as trans-coordinated
Mn(TPP)(NO)(ONO) (Scheme 1). In this interpretation the band at
1812 cm 21 corresponds to the n(N·O) stretch of the linear nitrosyl
and three latter bands belongs to the O-bonded nitrite group.
Indeed, the n(N·O) band lies within the conventional region
reported for linear metal-NO porphyrin complexes with axially
coordinated anions.11b The bands at 1480, 971 and 822 cm 21 are
also consistent with ranges reported3,11 for nitrito coordinated
ONO2 and should be assigned to n(NNO), n(N–O) and d(ONO)
modes.
The evidence of the formation of (1) upon reaction the low-
temperature layers of MnTPP(NO) with excess NO was also
Low temperature sublimed layers of MnII(TPP) on the KBr or
CaF2 plates were obtained from the parent compound MnII
(TPP)(B) (B = piperidine or pyridine) as described previously.5a
Thin layers of the metallo-tetraarylporphyrins sublimed onto a low-
temperature (77 K) surface are sponge-like6a and have high
microporosity that allows potential ligands to diffuse easily across
the bulk.6b The species thus formed are convenient for spectro-
scopic studies due to absence of solvent interference.
Exposure of sublimed layers of MnII (TPP) at 77 K to an excess
of clean7 NO displays formation of the NO dimer with strong IR
bands at 1853 and 1754 cm21 and known mononitrosyl complex
Mn(TPP)(NO)8a with n(NO) at ~ 1740 cm21, overlapping with the
asymmetric NO dimer stretch.9 Gradually warming the sample and
keeping the temperature constant at 130 K leads to dramatic
changes in the IR spectra. Concomitant with decreased intensity of
the bands for the NO dimer and Mn(TPP)(NO), new bands
correlated in intensities grew in at 2221 (not shown), 1818, 1480,
971 and 822 cm21 (Fig. 1). The band centered at 2221 cm21
undoubtedly represents the n3 vibration of N2O,10 while the band at
1818 cm21, which shifts to 1812 cm21 as it reaches maximum
intensity was assigned to the n(NO) of a MnIII(TPP)(NO)(X)
complex (1), where X is an anion. This assignment is consistent
with the literature data on the spectroscopic manifestation of the
6-coordinate manganese nitrosyl complexes with anionic ligands.8a
When MnII(TPP) was exposed to excess of 15NO the analogous
bands appeared at lower frequencies: 2152, 1778, 1455, 950 and
818 cm 21. These shifts indicate that all new bands are due to
nitrogen oxides and suggest that X is coordinated NO2 anion.
Infrared spectroscopy is very diagnostic in differentiating
Fig. 1 IR spectra at 77 K: (a) Mn(TPP)(NO) formed by exposure of
Mn(TPP) to NO (P = 5 Torr) for 10 min at 100 K followed by exhaustive
high vacuum pumping, (b) Mn(TPP)(NO)(ONO) formed by exposure of
Mn(TPP) to NO (ca. P = 15 Torr) at 77 K followed by annealing 130 K, (c)
the same with 15NO. n1 vibration of N2O denoted by asterisk.10
2
between N-bound nitro or O-bound nitrito NO2 coordination.11a
Indeed, for the nitrosyl nitro complex FeTPP(NO)(NO2) the
Scheme 1
1488
C h e m . C o m m u n . , 2 0 0 4 , 1 4 8 8 – 1 4 8 9
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

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supported by changes in the UV-Vis spectra (Fig. 2). Formation of
the nitrosyl and nitrosyl-nitrito complexes was first monitored by
FTIR spectroscopy (using CaF2 plates), and then absorption spectra
of the same samples cooled to 77 K were recorded. The spectrum of
Mn(TPP)(NO) displays absorption bands at 539, 573 and 612 nm
while that of (1) shows strong absorbance at 546 nm and shoulders
at 578 and 618 nm. Although the absorption in this region cannot be
measured with precision due to contribution of Mn(TPP)(NO)
(seen in IR spectra), the strong band at 476 nm is characteristic for
all MnIII(TPP) nitrosyl complexes.8a,c The same oxidation state
may be suggested for manganese ion in (1). The low-temperature
spectra of MnII(TPP) and Mn(TPP)(NO) are in good agreement
with those observed earlier in frozen solutions.8a,b However, NO
disproportionation was not detected in those studies, possibly
because excess NO was expelled before solution cooling. In the
present case maintaining the Mn(TPP)(NO) under excess NO at 77
K for a lengthy period does not lead to any changes in optical or
FTIR spectra. Only when the sample was warmed above 100 K
were reactions leading to Mn(TPP)(NO)(ONO) observed.
It has been established that positions of the some porphyrin
vibrations in the axial complexes of Fe(TPP) can serve as a markers
of the spin and oxidation states of iron center.15 The bands in the
range 1350–1330 cm21, which belong to n(Ca–Cm) mixed with
n(Cm–phenyl), and porphyrin core deformation mode at 469–432
cm21 lies at higher wavelengths in low-spin complexes. We have
reported similar behavior of these bands in our studies of dioxygen
and nitrate complexes of Mn(TPP).16 Indeed, in MnII(TPP) these
bands lie at 1343 and 428 cm21. Formation of Mn(TPP)(NO)
complex leads to a high to low spin state transition8a as indicated by
shifts of these bands to 1349 and 454 cm21, respectively. Upon
generation of (1) there is no further shift of these bands, indicating
that the Mn center remains in the low spin state. This suggestion is
in agreement with literature data on the spin states of the
6-coordinated manganese nitrosyl porphyrins complexes with
anionic ligands.8a
supported by FTIR and UV-Vis spectroscopy and low-spin state of
the manganese ion is suggested. The characterized nitrosyl-nitrito
complex is stable at low temperature conditions. Exhaustive
evacuation of nitric oxide at 130 K does not affect the relative
intensities and positions of the NO and NO2 bands, but warming to
room temperature leads to decomposition of (1). Under the same
experimental conditions we have measured FTIR spectra of the Fe,
Co, Cu, Ni and Zn TPP complexes upon exposure to excess NO.
Except for formation of the known mononitrosyls of Fe and Co
TPP, none of these compounds revealed further reactivity toward
nitric oxide disproportionation.
This work was supported by the CRDF (Grant 12919). Visiting
Fellowship of TSK at UCSB supported by Petroleum Research
Fund is greatly appreciated.
Notes and references
1 (a) A. R. Butler and D. L. H. Williams, Chem. Soc. Rev., 1993, 233; (b)
P. C. Ford, J. Bourassa, K. Miranda, B. Lee, I. Lorkovic’, S. Boggs, S.
Kudo and L. Laverman, Coord., Chem. Rev., 1998, 171, 185; (c) L.
Cheng and G. B. Richter-Addo, in The Porphyrin Handbook, vol. 4, eds.
K. M. Kadish, K. M. Smith and R. Guilard, Academic Press, New York,
2000.
2 (a) F. Bottomley, Reactions of Coordinated Ligands, Plenum, New
York, 1989; (b) G. B. Richter-Addo and P. Legzdins, Metal Nirosyls,
Oxford University, New York, 1992.
3 P. C. Ford and I. M. Lorkovic’, Chem. Rev., 2002, 102, 993.
4 S. J. Lippard and K. J. Franz, J. Am. Chem. Soc., 1998, 120, 9034.
5 (a) T. S. Kurtikyan, G. G. Martirosyan, I. M. Lorkovic’ and P. C. Ford,
J. Am. Chem. Soc., 2002, 124, 1012; (b) K. M. Miranda, X. Bu, I. M.
Lorkovic’ and P. C. Ford, Inorg. Chem., 1997, 36, 4838.
6 (a) M. P. Byrn, C. J. Curtis, Y. Hsiou, S. I. Khan, P. A. Sawin, S. K.
Tendick, A. Terzis and C. E. Strouse, J. Am. Chem. Soc., 1993, 115,
9480; (b) T. S. Kurtikyan, A. V. Gasparyan, G. G. Martirosyan and G.
H. Zhamkochyan, J. Appl. Spectrosc., 1995, 62, 62 (Russ.).
7 The NO (15NO) used was purified by multiple passage through KOH
pellets column and metylbromide/liquid N2 cooled traps. The purity was
checked by GC and IR spectroscopy of the condensate obtained by low
rate deposition of NO on the cooled substrate of optical cryostat (77 K).
The N2O impurity in NO used was estimated less than 0.2% and no other
contaminants were revealed.
In summary, exposure of the low temperature sublimed layers of
MnII(TPP) to excess nitric oxide leads to disproportionation of NO
yielding a new MnIII(TPP)(NO)(ONO) species and releasing
nitrous oxide gas. Formation of the six-coordinate complex (1) is
8 (a) B. B Wayland, L. W. Olson and Z. U. Siddiqui, J. Am. Chem. Soc.,
1976, 98, 94; (b) M. Hoshino and S. Konishi, Chem. Phys. Lett., 1985,
115, 511; (c) L. J. Boucher, Coord., Chem. Rev., 1972, 7, 289.
9 L. Krim and N. Lacome, J. Phys Chem. A, 1998, 102, 2289.
10 A. Lapinski, J. Spanget-Larsen, J. Waluk and J. J. Radziszewski, J.
Chem. Phys., 2001, 115, 1757.
11 (a) K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 3rd ed., Wiley, New York, 1978; (b) G. R. A.
Wyllie and W. R. Scheidt, Chem. Rev., 2002, 102, 1067.
12 T. Yoshimura, Inorg. Chem. Acta, 1984, 83, 17.
13 (a) Such sublimed layers prepared from other Ru(P) precursors might
contain RuNRu dimers after sublimation.13b However that is unlikely to
be the case with the carbonyl precursor. (b) J. P. Collman, C. E. Barnes,
T. J. Collins and P. J. Brothers, J. Am. Chem. Soc., 1981, 103, 7030; J.
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14 The reaction gas was sampled by GC after each experiment. Depending
on the reaction conditions analysis show 7-15 fold growth of N2O
comparing with background contamination.
15 H. Oshio, T. Ama, T. Watanabe, J. Kincaid and K. Nakamoto,
Spectrochim. Acta, 1984, 40A, 863.
16 T. S. Kurtikyan, T. H. Stepanyan, G. G. Martirosyan and V. N.
Madakyan, Russ. J. Coord. Chem., 2000, 26, 345; T. S. Kurtikyan, G. G.
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Fig. 2 Optical absorption spectra at 77 K: dotted line – MnII(TPP), dashed
line – MnTPP(NO) formed by exposure of MnIITPP to the excess of nitric
oxide (P = 10 Torr) at 100 K, solid line – subsequent slow warming of the
MnTPP(NO) to 130 K.
C h e m . C o m m u n . , 2 0 0 4 , 1 4 8 8 – 1 4 8 9
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