Hydrogen-bonded chain structure of a six-coordinate 5,10,15,20-tetraphenylporphinatomanganese(III) complex

Article abstract of DOI:10.1016/S0020-1693(00)00360-1

In methanolic solutions, disproportionation of the TCNQ anion radical to neutral TCNQ⁰ and the dianion TCNQ^2- followed by aerobic oxidation of TCNQ^2- results in the formation of methyl-4-dicyanomethylene benzoate anion (MDCB^-). This anion coordinates to the manganese(III) atom of 5,10,15,20-tetraphenylporphinatomanganese(III) leading to the complex whose X-ray crystal structure is reported. The crystal had the monoclinic space group P2₁/n with unit cell dimensions a = 13.327(3), b = 20.236(6), c = 16.914(5) ? and β = 92.26(2)°. An important driving force behind the crystal packing is a hydrogen bonding interaction between non-identical ligands of adjacent molecules.

Full text of DOI:10.1016/S0020-1693(00)00360-1

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Inorganica Chimica Acta 315 (2001) 107–111
Note
Hydrogen-bonded chain structure of a six-coordinate
,10,15,20-tetraphenylporphinatomanganese(III) complex
5
a
a
a
b
a,
Jonathan P. Hill , Julio Santiago , Takushi Sugino , Motoo Shiro , Yo Shimizu *
a
Department of Organic Materials, Osaka National Research Institute (ONRI), AIST-MITI, Midorigaoka, Ikeda, Osaka 563-8577, Japan
b
Rigaku Corporation X-ray Research Laboratory, 3-9-12 Matsubara-cho, Akishima, Tokyo 196, Japan
Received 8 July 2000; accepted 6 October 2000
Abstract
0
2−
In methanolic solutions, disproportionation of the TCNQ anion radical to neutral TCNQ and the dianion TCNQ
by aerobic oxidation of TCNQ
followed
2
−
−
results in the formation of methyl-4-dicyanomethylene benzoate anion (MDCB ). This anion
coordinates to the manganese(III) atom of 5,10,15,20-tetraphenylporphinatomanganese(III) leading to the complex whose X-ray
crystal structure is reported. The crystal had the monoclinic space group P2 /n with unit cell dimensions a=13.327(3),
1
b=20.236(6), c=16.914(5) A and i=92.26(2)°. An important driving force behind the crystal packing is a hydrogen bonding
,
interaction between non-identical ligands of adjacent molecules. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Manganese(III) complexes; X-ray crystal structures; Hydrogen bonding interaction
1
. Introduction
that axial ligands have on the physical shape of the
porphyrin macrocycle and, more crucially, the effect
these ligands have on the electronic structure of the
metal atom (i.e. low spin or high spin) [15]. Further-
more, recent studies have revealed the crystal structures
of substituted TPPMn complexes with TCNQ anion
Manganese porphyrin complexes are of great impor-
tance because of their potential magnetic [1] and cata-
lytic properties [2,3] whilst salts of the TCNQ anion
radical are usually considered because of their low
electrical resistivities [4] (although magnetic studies of
some of these materials have been undertaken [5,6]).
Previously, several manganese–organic radical com-
plexes have been synthesized and their crystal structures
and magnetic properties determined [7–9]. In particu-
lar, oxidation of tetraphenylporphinatomanganese(II)
by tetracyanoethylene yields complexes having poly-
meric chain-like structures and long range magnetic
order at depressed temperatures [10,11]. Additionally,
stereochemistry of metalloporphyrins has been studied
extensively, not least because of its importance in the
reactivity of hemoproteins [12–14]. Many complexes
have been prepared in order to understand the influence
[16,17]. In this work, we describe the synthesis and
crystal structure of a six-coordinate tetraphenylporphi-
natomanganese(III) complex of methyl 4-(dicyano
methylene) benzoate.
2
. Experimental
2.1. Synthesis
Tetraphenylporphyrin (TPP) was purchased from
Aldrich and the chloromanganese(III) complex was pre-
pared by an ordinary method. TPP (1 g, 1.62 mmol)
and manganese(II) chloride tetrahydrate (650 mg, 3.3
mmol) were dissolved in dry N,N-dimethylformamide
*
Corresponding author. Tel.: +81-727-519 525; fax: +81-727-
(
50 ml) and the solution stirred at 100°C for 3 h. The
5
19 628.
E-mail address: yo@onri.go.jp (Y. Shimizu).
course of the reaction was monitored by TLC
0
020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(00)00360-1

1
08
J.P. Hill et al. / Inorganica Chimica Acta 315 (2001) 107–111
(
CH Cl –silica gel). Following completion of the reac-
lography. The spectral data for this compound are
summarized in Ref. [21] .
2
2
1
tion the solvent was removed under reduced pressure.
Chromatographic purification using a silica gel column
with chloroform eluant gave the chloromanganese com-
plex as a green amorphous powder (970 mg, 85%)
which was used in subsequent steps without further
purification.
2.2. Measurements
The infrared and UV–Vis spectra of producuts were
measured by Perkin–Elmer FT-IR spectrometer,
Paragon 1000 and Shimadzu UV-2500PC UV–Vis
recording spectrophotometer, respectively. The X-ray
diffraction measurement was carried out using Rigaku
RAXIS-IV imaging plate area detector with graphite
monochromated Mo Ka radiation.
A boiling solution of Li+TCNQ ((90 mg, 4.26
−
4
(
10
mol)) in methanol (20 ml) was carefully added to
a boiling solution of chloromanganese tetraphenylpor-
phyrin (300 mg, 4.25 (10
−
4
mol)) in methanol (30 ml).
The resulting mixture was reduced to half its volume
and allowed to cool to room temperature (r.t.) where-
after a black precipitate appeared. The precipitate was
filtered, washed sparingly with ice-cold methanol then
dried under reduced pressure (yield: 230 mg, 62%). The
remaining supernatant solution from the synthesis of
the TCNQ anion radical complex was set aside in a
vessel open to the air. After 3 weeks, most of the
methanol had evaporated and black crystals had ap-
peared on the walls of the vessel.
3
. Results and discussion
Scheme 1 briefly illustrates the reaction of TPPMnCl
(
1) [18] (whose crystal structure is already known [19])
+
’
−
2
with Li [TCNQ ] (giving 2) [20] and the subsequent
crystallization of product 3 where the anionic ligand is
methyl 4-(dicyanomethylene) benzoate.
Formation of the methyl 4-(dicyanomethylene) ben-
These crystals were subject to analysis by infrared
spectrophotometry and, subsequently, by X-ray crystal-
−
zoate anion (MDCB ) is explained by considering the
chemistry of the TCNQ anion radical in aerobic solu-
+
−
tions. Dissolution of Li (TCNQ ) results in the dis-
proportionation of TCNQ anion radical [21] into
0
2−
neutral TCNQ and TCNQ . The dianion then reacts
irreversibly with molecular oxygen giving 4-(di-
−
cyanomethylene) benzoyl cyanide anion (DCBC ) [22].
This benzoyl cyanide readily reacts with methanol [23]
yielding the benzoic acid ester group. The formation of
−
MDCB is summarized in Scheme 2. Oxidation of the
TCNQ anion radical by molecular oxygen has also
been reported to occur in the solid state [24] but the
+
−
Scheme 1. Synthesis of 2 and 3.
complex [TPPMn ][TCNQ ] is stable once precipi-
3
tated and dried .
One other consequence of the reaction in Scheme 2 is
that a manganese(III) cyanate or (more likely) isocya-
nate complex is implicated as a product. No attempt
has been made to isolate this but it may be easy to
observe by infrared spectroscopy, especially if it is
present as the isocyanate, because of the change in
1
For 3: Elemental Anal.: For C56H39N MnO ·5/4H O Calc.
6
3
2
(
(
Found %): C, 72.93 (72.87); H, 4.50 (4.20); N, 9.12 (9.13). UV–Vis
−
1
−3
−1
−1
5:1, CH Cl :CH OH) u nm
(m, dm
mol
cm ): 374(82 100)
2
2
3
3
99(60 300), 468(103 400), 517(6900), 565(12 300), 598 (9300). IR
−
1
(
KBr) (cm ): 2192, 2140 (CN(str)), 1704(CꢀO(str)), 1592 (Ar
CꢀC(str)), 1271 (CꢁOꢁC(str) asym), 1173 (CꢁOꢁC(str) sym), 1098
(
MeOH CꢁO(str)).
2
For 2: Elemental Anal.: For C56H32MnN8 Calc (Found %): C,
7
7.15 (77.02); H, 3.70 (3.77); N, 12.85 (12.89). UV–Vis (1:1,
−
1
−3
−1
−1
CH OH–CH CN) u nm
(m, dm
mol
cm ): 377(59 200),
3
3
4
5
01(61 700), 420(52 300), 469(69 700), 514(5600), 565(9600),
99(8000), 742(20 100), 761(16 700). IR (KBr) (cm ): 2183, 2121
−
1
+
−
−
Scheme 2. Formation of [TPPMn ][MDCB ]. DCBC =4-(di-
(CN (str)).
−
3
cyanomethylene)benzoyl cyanide anion, MDCB =methyl 4-(di-
No carbonyl infrared absorption appears in samples stored in air
for a 6-month period.
cyanomethylene)benzoate anion.

J.P. Hill et al. / Inorganica Chimica Acta 315 (2001) 107–111
109
+
−
Fig. 1. ORTEP diagram and numbering for [TPPMn ][MDCB ].
frequency of the nitrile absorption (in isocyanato com-
distorted octahedral geometry which is usual in the
six-coordinate manganese(III) complexes. The man-
,
ganese atom has a displacement of 0.073 A out from
the porphyrin least-squares plane towards the anionic
ligand. This value is similar to that of
−
1
plexes wCN occurs around 2220 cm ).
4
The X-ray crystal structure of 3 is shown in Fig. 1 .
The electronic spectrum of 3 indicates that the man-
ganese atom has an oxidation state of +3 (i.e. the
b-band is split into components at 468 and 380 nm).
This is supported by the sixfold coordination which is
usual for high spin manganese(III) porphyrin com-
plexes especially when crystallized from [strongly] coor-
TPPMn(N )(CH OH) (0.086 A) which has a similar
,
3
3
molecular structure. The porphine macrocycle has a
slight ruffling which is consistent with approximate S4
geometry although this deviation from planarity is not
as significant as in other metalloporphyrins [15]. The
mean perpendicular deviation from the porphine plane
dinating solvents [25]. The MnꢁN bond lengths, with
p
an average of 2.013 A
six-coordinate manganese(III) porphyrin [19,26]. Also,
the lengthened axial bonds (2.235 and 2.247 A for
,
, are typical for this type of
is 0.1 A.
,
,
−
The MDCB ligand is bound to the manganese atom
anionic and neutral ligand, respectively) indicate the
via atom N of one nitrile group although its negative
5
charge is usually formally represented on the methylene
carbon atom, C51. The reason for this coordination
mode lies with the delocalization of the charge over the
ligand and the consequent lowering in electron density
at C51 so that coordination is preferred through a
nitrile group. Also of importance are steric repulsions
which make end-on nitrile coordination preferable. It
should be noted that TPPMn(CN), in which there is a
4
Crystal data for 3: Black prismatic crystals, crystal dimensions:
0
1
A
,
.30×0.20×0.15 mm, monoclinic, space group P2 /n (no. 14); a=
1
3.327(3), b=20.236(6), c=16.914(5) A
,
, i=92.26(2)°; V=4527(1)
3
; Z=4. Data collection: Rigaku RAXIS-IV imaging plate area
detector/graphite monochromated Mo Ka radiation. The data were
collected at temperature of 2591°C to a maximum 2q value of 57.3°.
Structure was refined by direct methods and by expanded Fourier
techniques. Non-hydrogen atoms were refined anisotropically. Hydro-
gen atoms were included but not refined. The final cycle of the
full-matrix least-squares refinement was based on 6566 reflections
I\3|(I)). The standard deviation of an observation of the unit
weight was 1.36. The maximum and minimum of the final difference
Fourier map corresponded to 0.25 and −0.37 e A
tions were performed using the TEXSAN crystallographic programme
metal–carbon bond, is known [27]. The MnꢁN bond
5
(
length, at 2.247 A, is slightly shorter than in other
,
−
3
similar complexes [28] but this is consistent with the
,
. All calcula-
MnꢁN ꢁC52 bond angle of 161° which allows greater
5
of the Molecular Structure Corporation. R =0.039, R =0.058.
bonding overlap.
l
w

1
10
J.P. Hill et al. / Inorganica Chimica Acta 315 (2001) 107–111
Packing within the crystal is strongly influenced by a
In conclusion, X-ray crystallography was used to
determine the structure of the product from the oxida-
hydrogen bonding interaction between the non-identi-
cal ligands of neighbouring molecules. Thus, the closest
approach by the N atom to the O atom of a neigh-
’
−
tion of TCNQ in methanolic solution. The molecules
are arranged in a chain-like structure because of the
interaction between axial ligands. The geometry about
the manganese atom is similar to that of the azide
complex, TPPMn(N )(CH OH). We are currently in-
6
3
bouring molecule is just 2.655 A
responsible for the 0.1 A
,
. This may also be
shortening of the methanol
,
MnꢁO bond although variation in the bond lengths
3
3
3
vestigating the role, if any, of the manganese(III) por-
phyrin in the reaction described above and also, the
possibility of any synthetic utility for this system. The
basic aim, however, is to understand more fully the
magnetic properties of these complexes and accounts of
these will appear in due course.
between manganese(III) atom and neutral axial ligands
in six-coordinate complexes has previously been antici-
pated [26]. Inspection of the remaining non-bonded
contacts below 3.60 A did not reveal any other unusual
,
intermolecular interactions. Fig. 2 illustrates the chain-
like structure caused by hydrogen-bonding between ax-
ial ligands within crystals of 3.
It is still unclear whether the manganese porphyrin
plays any role in the reaction (e.g. by activation of
molecular oxygen [29]) but previous results demonstrate
that the mechanism shown in Scheme 2 does not re-
quire a catalyst to proceed [22]. However, initial studies
regarding the role of the porphyrin reveal that there is
an increase in the rate of decomposition of the TCNQ
anion radical in the presence of 1. This is possibly due
Acknowledgements
The authors would like to thank the Agency of
Industrial Science and Technology, Ministry of Interna-
tional Trade and Industry for the financial support
under the research project ‘Harmonized Molecular Ma-
terials’. J.P.H. and J.S. acknowledge the Science and
Technology Agency (STA) for providing STA
fellowship.
’
−
3+
2+
to the reduction (by TCNQ ) of Mn
to Mn
which would result in activation of molecular oxygen
via the formation of a TPPMn–O adduct [30,31].
2
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