Mechanism of the catalytic transformation of cyanopyridine isomers into pyridinecarboxamide isomers by magnesium phthalocyanine

Article abstract of DOI:10.1016/j.poly.2012.02.028

Three intermediate magnesium phthalocyanine complexes with 2-, 3- and 4-pyridiniecarboxamide, MgPc(2-pyridinecarboxamide), MgPc(3-pyridinecarboxamide) and (MgPc)₂(4-pyridinecarboxamide), were obtained during the catalytic transformation of the respective cyanopyridine isomers in presence of magnesium phthalocyanine. These complexes were obtained in the crystalline form and their structures were determined by the X-ray single crystal analysis. In MgPc(2-pyridinecarboxamide) and MgPc(3-pyridinecarboxamide) the Mg centre of MgPc is 4 + 1 coordinated by the oxygen atom of amide groups of axially coordinated 2- or 3-cyanopyridnine isomers. In the third complex the 4-pyridinecarboxanide acts as an O,N- bridging ligand forming 4 + 1 O- and N-coordinated (MgPc)₂(4-pyridinecarboxamide) supramolecular complex. Owing to the Mg...O interaction of the electropositive Mg-centre of MgPc molecule with oxygen atom of amide group of 2- and 3-pyridinecarboxamide axial ligands, the Mg atom is significantly displaced (～0.5 ) from the plane defined by the four isoindole N atoms of Pc(2-) macrocycle. In the (MgPc) ₂(4-pyridinecarboxamide) complex the O,N- ligand bridges two MgPc units, therefore the interaction of Mg centre from both MgPc units causes the deviation of the Mg atoms by 0.472(2) and 0.413(2) from the N₄-plane, respectively for Mg-O-coordinated and Mg-N-coordinated. The interactions of Mg with the axial ligand (Mg...O and Mg...N) lead a distortion of a planar Pc(2-) macrocycle to the saucer-shape form. Some remarks on the transformation mechanism of the CN group of cyanopyridine isomers into amide group of respective pyridinecarboxamide isomers have been made. The calculated three-dimensional molecular electrostatic potential maps are helpful for understanding the transformation mechanism as well as for better understanding the organisation and the arrangement of the molecules in solid-state (crystal).

Full text of DOI:10.1016/j.poly.2012.02.028

Polyhedron 38 (2012) 75–87
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Mechanism of the catalytic transformation of cyanopyridine isomers
into pyridinecarboxamide isomers by magnesium phthalocyanine
⇑
Jan Janczak
Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Okólna 2 str. P.O. Box 1410, 50-950 Wrocław, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Three intermediate magnesium phthalocyanine complexes with 2-, 3- and 4-pyridiniecarboxamide,
MgPc(2-pyridinecarboxamide), MgPc(3-pyridinecarboxamide) and (MgPc)2(4-pyridinecarboxamide),
were obtained during the catalytic transformation of the respective cyanopyridine isomers in presence of
magnesium phthalocyanine. These complexes were obtained in the crystalline form and their structures
were determined by the X-ray single crystal analysis. In MgPc(2-pyridinecarboxamide) and MgPc(3-pyri-
dinecarboxamide) the Mg centre of MgPc is 4 + 1 coordinated by the oxygen atom of amide groups of axi-
ally coordinated 2- or 3-cyanopyridnine isomers. In the third complex the 4-pyridinecarboxanide acts as
an O,N- bridging ligand forming 4 + 1 O- and N-coordinated (MgPc)2(4-pyridinecarboxamide) supramo-
lecular complex. Owing to the Mgꢀ ꢀ ꢀO interaction of the electropositive Mg-centre of MgPc molecule with
oxygen atom of amide group of 2- and 3-pyridinecarboxamide axial ligands, the Mg atom is significantly
displaced (ꢁ0.5 Å) from the plane defined by the four isoindole N atoms of Pc(2-) macrocycle. In the
(MgPc)2(4-pyridinecarboxamide) complex the O,N- ligand bridges two MgPc units, therefore the interac-
tion of Mg centre from both MgPc units causes the deviation of the Mg atoms by 0.472(2) and 0.413(2) Å
from the N4-plane, respectively for Mg–O-coordinated and Mg–N-coordinated. The interactions of Mg
with the axial ligand (Mgꢀ ꢀ ꢀO and Mgꢀ ꢀ ꢀN) lead a distortion of a planar Pc(2-) macrocycle to the sau-
cer-shape form. Some remarks on the transformation mechanism of the C„N group of cyanopyridine iso-
mers into amide group of respective pyridinecarboxamide isomers have been made. The calculated three-
dimensional molecular electrostatic potential maps are helpful for understanding the transformation
mechanism as well as for better understanding the organisation and the arrangement of the molecules
in solid-state (crystal).
Received 20 December 2011
Accepted 13 February 2012
Available online 8 March 2012
Keywords:
Magnesium phthalocyanine
4 + 1 Coordinated MgPc derivatives
Crystal structure
Transformation mechanism
Ab-initio calculations
Molecular electrostatic potential
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
Pc ring (ꢁ0.5 Å) [5], although the ab-initio molecular orbital calcu-
lations predict its planarity [6,7]. In the crystal, the electropositive
Metallophthalocyanines with the general formula of MPc
(M = divalent metal, Pc = C32H16N82ꢂ) exhibit relatively high stabil-
ity to chemical and thermal treatments [1]. However, the magne-
sium phthalocyanine is exceptional and unusual [2]. Although,
MgPc is thermally stable, chemically is active, what was proved
by the fact that in the ambient atmosphere it gives complexes with
the compositions of (MgPc)2O2 and (MgPc)2N2 [3]. The formation
of these complexes is reversible and strongly depends on the tem-
perature. The instability of the b-MgPc and its unusual behaviour
in relation to the other b-M(II)Pc complexes such as MnPc, FePc,
NiPc, CuPc and ZnPc is related with differences in their crystal
structure [4]. Although, MgPc crystallises, similar to other M(II)Pc
complexes, in the monoclinic system, the MgPc molecule, in con-
trast to other M(II)Pc molecules, is not planar. The electropositive
Mg centre of MgPc is significantly displaced from the N4-plane of
Mg centre of MgPc interacts with the N-azamethine atom of the
neighbour leading to the displacement of Mg from the N4-plane
(Scheme 1).
Thus, in the crystal the Mg centre of MgPc accommodates the
4 + 1 coordination. The difference in the crystal structure of MgPc
relative to other M(II)Pc complexes is useful in the activation and
catalytic transformation of organic compounds, especially the
cyanocompounds.
In particular, it has been shown that magnesium phthalocya-
nine during annealing process with phthalonitrile forms 4 + 1 coor-
dinated complex with the composition of MgPc(C6H4(CN)2) [8].
This complex is thermally moderately stable and with increasing
temperature releases phthalonitrile molecule in its active form
that undergoes trimerisation to the tris(2-cyanophenyl)-1,3,5-
triazine [9]. Further investigations of the catalytic activation and
transformation of the cyano group (C„N) in the organic cyano-
compounds by MgPc lead to obtaining the 2,4,6-tris(2-pyridyl)-
1,3,5-triazine and 2,4,6-tris(4-pyridyl)-1,3,5-triazine as a result of
⇑
Tel.: +48 71 343 5021; fax: +48 71 344 1029.
E-mail address: j.janczak@int.pan.wroc.pl
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.02.028

76
J. Janczak / Polyhedron 38 (2012) 75–87
MgPc
o
d-block M(II)Pc
Na
M
o
o
M(II)-N interaction
a
N
N
N
o
o
o
=
Na
Na
o
o
b
N
o
Na
Scheme 1. Intermolecular M(II)ꢀ ꢀ ꢀNa interaction in crystal of MgPc and other M(II)Pc complexes.
catalytic trimerisation of 2- and 4-cyanopyridine isomers [10]. In
the case of third isomer, i.e. 3-cyanopyridine, the transformation
process in the presence of MgPc leads to the 2-(3-pyridyl)-1,3,8-
triazanaphthalene [11]. Additionally, it has been stated that MgPc
under moist atmosphere forms the aquamagnesium phthalocya-
nine – MgPc(H2O). Depending on the crystallisation condition,
the MgPc(H2O) complex crystallises in the three crystallographic
modifications [12–14].
The aquamagnesium phthalocyanine transforms the cyano
group into the amide group in the organic cyano compounds. For
example, it has been stated that 1,3-dicyanobenzene transforms
into 3-cyanobenzamide in presence of MgPc(H2O) [15]. The 3-cya-
nobenzamide forms also in the reaction of MgPc in presence of
water, however, the mechanism of the activation and transforma-
tion of the cyano group(s) is still not clear. Therefore, in the present
work, the intermediate products obtained during transformation of
the cyanopyridine isomers into their amides have been investi-
gated. Some remarks on the activation of the cyano group by MgPc
and MgPc(H2O) and the mechanism transformation in amide will
be discussed. The intermediate products have been isolated in
the crystalline forms and their crystal structures were determined.
well as with a Perkin-Elmer 240 elemental analyser. Found for
the MgPc complex with nicotinamide (1): Mg, 3.55; C, 69.43; N,
21.15; O, 2.40 and H, 3.47%. Anal. Calc. for C38H22N10MgO: Mg,
3.36, C, 69.27; N, 21.26; O, 2.43; H, 3.36%. Found for the MgPc com-
plex with isonicotinamide (2): Mg, 3.41; C, 69.56; N, 21.20; O, 2.50;
H, 3.33%. Anal. Calc. for C76H44N20Mg2O2: Mg, 3.36, C, 69.27; N,
21.26; O, 2.43; H, 3.36%.
The reaction between the MgPc(H2O) and 2-cyanopyridine iso-
mer in the same thermal conditions has been also performed, how-
ever in this case besides the blue-violet crystals of MgPc complex
with 2-pyridinecarboxamide (3), the colourless needle single crys-
tals of 2-pyridinecarboxamide were obtained.
2.3. Single crystal X-ray data collection and structure determination
Violet single crystals of MgPc complex with 3-pyridinecarboxa-
mide (1) and with 4-pyridinecarboxamide (2) as well as colourless
single crystal of 2-pyridinecarboxamide (3) were used for data col-
lection at 295 K on
equipped with two-dimensional CCD area detector. The graphite
monochromatised Mo K radiation (k = 0.71073 Å) and the -scan
technique ( = 1°) were used for data collection. Data collection
a four-circle KUMA KM4 diffractometer
a
x
D
x
2. Experimental
and reduction along with absorption correction were performed
using CrysAlis software package [16]. The structure was solved by
direct methods using SHELXS-97 [17], which revealed positions of al-
most all non-hydrogen atoms. The remaining atoms were located
from subsequent difference Fourier syntheses. The structure was
refined using SHELXL-97 [17] with the anisotropic thermal displace-
ment parameters. The hydrogen atoms of phthalocyaninate(2-)
ring were refined with the riding model, H atoms of pyridinecarb-
oxamide isomers were constrained. Visualisation of the structure
was made with the Diamond 3.0 program [18]. Details of the data
collection parameters, crystallographic data and final agreement
parameters are collected in Table 1. Selected geometrical parame-
ters for 1, 2 and 3 crystals are listed in Tables 2–4, respectively.
2.1. Materials
Magnesium phthalocyanine was obtained by procedure de-
scribed previously [5]. 2-Cyanopyridine, 3-cyanopyridine and 4-
cyanopyridine (99.9% purity of all isomers) were obtained from
Sigma–Aldrich Co. and were used as received.
2.2. Preparation of MgPc complex with 3-pyridinecarboxamide (1),
with 4-pyridinecarboxamide (2) and with 2-pyridinecarboxamide (3)
The b-MgPc crystalline form was converted into hydrated form
of MgPc(H2O) by the procedure described previously [12]. The
identification of the aqua complex of MgPc(H2O) was performed
on a STOE powder diffractometer with linear PSD detector [16].
The powder diffraction pattern is consistent with the triclinic mod-
ification of MgPc(H2O) [12]. The obtained MgPc(H2O) in a such way
was used in the reaction with the cyanopyridine isomers. The
MgPc(H2O) was mixed in the molar proportion of 1:5 with 3-cya-
nopyridine or 4-cyanopyridine and pressed into pellets (each of
ꢁ1 g), degassed and sealed off in the glass ampoule. Next the am-
poules were heated at the temperature of 80 °C (hot zone of the
furnace) for one day. After such processing the well-developed sin-
gle crystals were obtained. The excess of the unreacted 3-cyano-
pyridine or 4-cyanopyridine, which in the reactions were as
reactants and as recrystallisation medium, was removed from the
samples under vacuum. Elemental analyses of the 1 and 2 com-
plexes were carried out on a energy dispersive spectrometer as
2.4. Thermogravimetric measurements
Thermal analysis was carried out on a Linseis L81 thermobal-
ance apparatus with Pt crucibles. The initial sample mass was
about 20 mg. Powder Al2O3 was used as a reference. The measure-
ments were performed under static air and recorded at the heating
rate of 5 °C minꢂ1
.
2.5. X-ray powder diffraction measurement
The rest of the sample left after thermogravimetric analysis was
measured on a STOE diffractometer equipped with a linear PSD
detector [19] using Cu Ka1 radiation (k = 1.54060 Å) at room
temperature.

J. Janczak / Polyhedron 38 (2012) 75–87
77
Table 1
Crystallographic data for 1, 2, and 3.
Complex
1
2
3
Formula
Molecular weight
T (K)
C
38H22N10OMg
C76H44N20O2Mg2
1317.93
295(2)
monoclinic
P21/c (No. 14)
12.291(2)
C88H52N24O2Mg2
1554.38
295(2)
monoclinic
P21/n (No. 14)
12.703(3)
658.97
295(2)
triclinic
P1 (No. 2)
9.080(1)
Crystal system
ꢀ
Space group
0
a (AÅ)
0
13.188(2)
14.882(3)
22.769(5)
23.003(5)
18.630(4)
15.402(3)
b (AÅ)
0
c (AÅ)
a
b (°)
(°)
114.67(2)
93.73(1)
100.73(3)
6325(2)
95.18(3)
c
(°)
107.85(2)
1502.6(6)
0
3630.1(13)
V (ÅA3)
Z
2
4
2
Dcalc/Dexp [g cmꢂ1
]
1.456/1.45
0.112
0.44 ꢃ 0.17 ꢃ 0.12
0.9492/0.9851
16541/7295/5573
0.0267
1.384/1.375
0.107
0.38 ꢃ 0.22 ꢃ 0.12
0.9646/0.9886
57746/16440/8833
0.0459
1.396/1.36
0.105
0.28 ꢃ 0.25 ꢃ 0.21
0.8760/0.9341
36558/7589/3013
0.1154
l
(mmꢂ1
)
Crystal size (mm3)
Tmin/Tmax
Total/unique/observed reflections
Rint
R [F2 > 2
r
(F2)]a
0.0459
0.0956
0.0503
0.0693
0.0780
0.1858
wR [F2 all reflections]b
S
1.006
0.266, ꢂ0.215
1.001
0.350, ꢂ0.217
1.004
0.198, ꢂ0.215
0
Residual electron density,
D
qmax
,
D
qmin (e ÅAꢂ3
)
P
P
a
R = ||Fo| ꢂ |Fc||/ Fo.
P
P
2
1=2
2
wR ¼ f ½wðF2o ꢂ F2c Þ ꢄ= wF4og ; wꢂ1
¼
r2ðF2oÞ þ ðaPÞ where P ¼ ðFo2 þ 2F2c Þ=3. The a parameter is 0.0334 for 1, 0.0127 for 2 and 0.033 for 3.
b
Table 2b
Table 2a
Hydrogen-bond geometry (Å, °) for MgPc(nicotinamide) – (1).
Comparison of the X-ray and ab-initio geometrical parameters (Å, °) for MgPc(nic-
otinamide) –(1).
D–HꢀꢀꢀA
D–H
HꢀꢀꢀA
2.303(15)
2.092(10)
DꢀꢀꢀA
2.969(2)
2.979(2)
D–HꢀꢀꢀA
130.5(14)
165.0(16)
X-ray
Ab-initio
N9–H1ꢀꢀꢀN1i
0.902(9)
0.909(9)
N9–H2ꢀꢀꢀN5ii
Mg–N2
Mg–N4
Mg–N6
Mg–N8
Mg–O1
O1–C33
N9–C33
C33–C34
N2–Mg–N4
N4–Mg–N6
N6–Mg–N8
N8–Mg–N2
O1–Mg–N2
O1–Mg–N4
O1–Mg–N6
O1–Mg–N8
2.0424(15)
2.0221(17)
2.0356(15)
2.0379(16)
1.9772(15)
1.236(2)
1.316(2)
1.486(2)
88.07(6)
86.37(6)
87.78(6)
86.05(6)
99.96(6)
102.24(6)
105.88(6)
104.15(7)
166.78(14)
122.10(18)
ꢂ2.2(2)
2.048
2.064
2.049
2.041
2.026
1.263
1.342
1.486
87.31
87.29
87.92
88.03
102.08
101.31
101.80
101.59
138.22
121.52
ꢂ12.70
0.416
5.19
Symmetry codes: (i) x + 1, y, z; (ii) ꢂx + 1, ꢂy + 2, ꢂz + 1.
the 3-21G basis set assuming the geometry resulting from the
X-ray diffraction study as the starting structure. As convergence
criterions the threshold limits of 0.00025 and 0.0012 a.u. were ap-
plied for the maximum force and the displacement, respectively.
3. Results and discussion
3.1. Synthesis
C33–O1–Mg
O1–C33–N9
The catalytic transformation of the C„N group of cyanopyri-
dine isomers into amide group in presence of water and MgPc
according to the reaction yielding the respective pyridinecarboxa-
O1–C33–C34–C35
Deviation of Mg from N4-plane
Dihedral angle N4/N2,C1–C8
Dihedral angle N4/N4,C9–C16
Dihedral angle N4/N6,C17–C24
Dihedral angle N4/N8,C25–C32
Dihedral angle N4/axial py ring
Dihedral angle amide/py ring of axial ligand
0.460(2)
1.3(1)
mide isomers has been performed at about 100 °C. In results the a-
1.6(1)
2.7(1)
1.2(1)
71.9(1)
9.41
5.00
4.09
86.30
13.59
picolinamide, nicotinamide and isonicotinamide in the crystalline
form were obtained. The lattice parameters of the obtained crystals
are in agreement with that of the literature data [23–25]. The cat-
alytic transformation of the C„N group takes place through some
steps with the intermediate active products. The high affinity of
MgPc to water with the formation of aquamagnesium phthalocya-
nine [10] is useful for explanation of the transformation C„N into
amide groups. However, the intermediate steps are unknown. To
expiation of the transformation mechanism, the thermal reaction
has been performed at about 80 °C. At this conditions the electro-
positive Mg centre of MgPc interacts with electronegative oxygen
atom of water molecule (see also Section 3.5 reporting the molec-
ular electrostatic potential) forming the aqua complex of
MgPc(H2O) that interacts with the C„N group of cyanopyridine
isomers as illustrate the Scheme 2 below.
3.1(1)
2.6. Theoretical calculations
Ab-initio molecular orbital calculations with full geometry opti-
misation of MgPc(nicotinamide) and (MgPc)2(isonicotinamide) as
well as the cyanopyridine isomers and pyridinecarboxamide iso-
mers were performed with the GAUSSIAN98 program package [20].
All calculations were carried out with the DFT level using the
Becke3-Lee–Yang–Parr correlation functional (B3LYP) [21,22] with

78
J. Janczak / Polyhedron 38 (2012) 75–87
Table 3
Table 4
Comparison of the X-ray and ab-initio geometrical parameters (Å, °) for (MgPc)2(iso-
nicotinamide) – (2).
Comparison of the X-ray and ab-initio geometrical parameters (Å, °) for MgPc complex
with 2-pyridinecarboxamide – (4).
X-ray
Ab-initio
X-ray
Ab-initio
Mg1–N2
Mg1–N4
Mg1–N6
Mg1–N8
Mg1–N9
Mg2–N22
Mg2–N24
Mg2–N26
Mg2–N28
Mg2–O1
O1–C70
C70–N10
C67–C70
N2–Mg1–N4
N4–Mg1–N6
N6–Mg1–N8
N8–Mg1–N2
N2–Mg1–N9
N4–Mg1–N9
N6–Mg1–N9
N8–Mg1–N9
N22–Mg2–N24
N24–Mg2–N26
N26–Mg2–N28
N28–Mg2–N22
O1–Mg2–N22
O1–Mg2–N24
O1–Mg2–N26
O1–Mg2–N28
C70–O1–Mg2
O1–C70–N10
O1–C70–C67–C68
Deviation of Mg1 from N4-plane
Deviation of Mg2 from N4-plane
Angle between N4/N4 planes
Dihedral angle N4/N2,C1–C8
Dihedral angle N4/N4,C9–C16
Dihedral angle N4/N6,C17–C24
Dihedral angle N4/N8,C25–C32
Dihedral angle N4/axial py ring
Dihedral angle amide/py ring of axial ligand
Dihedral angle N4/N22,C33–C40
Dihedral angle N4/N24,C41–C48
Dihedral angle N4/N26,C49–C56
Dihedral angle N4/N28,C57–C64
Dihedral angle N4/axial py ring
2.043(2)
2.027(2)
2.034(2)
2.036(2)
2.187(2)
2.032(2)
2.029(2)
2.058(2)
2.045(2)
1.966(2)
1.205(2)
1.384(2)
1.457(2)
87.95(8)
87.41(8)
87.83(8)
87.23(8)
97.26(9)
111.77(8)
105.86(9)
91.84(8)
87.08(8)
87.53(8)
86.20(8)
86.68(8)
100.41(8)
104.57(9)
107.34(8)
101.63(8)
155.8(2)
115.7(3)
ꢂ32.8(3)
0.413(2)
0.473(2)
55.22(2)
5.0(1)
2.046
2.043
2.043
2.045
2.174
2.045
2.044
2.041
2.043
2.036
1.256
1.344
1.501
88.31
87.79
88.38
87.71
97.72
102.11
103.59
98.99
87.68
88.00
87.98
87.88
98.11
100.21
104.52
101.53
173.68
121.48
ꢂ18.41
0.376
0.393
65.59
4.70
Mg–N2
Mg–N4
Mg–N6
Mg–N8
Mg–O1
O1–C38
N10–C38
N2–Mg–N4
N4–Mg–N6
N6–Mg–N8
N8–Mg–N2
O1–Mg–N2
O1–Mg–N4
O1–Mg–N6
O1–Mg–N8
C38–O1–Mg
2.040(4)
2.038(5)
2.039(4)
2.041(5)
2.017(4)
1.321(12)
1.406(16)
86.6(2)
2.049
2.045
2.045
2.049
2.017
1.266
1.332
87.65
87.76
87.65
87.65
98.87
104.30
104.31
98.88
141.78
126.21
0.00
86.67(19)
86.4(2)
86.4(2)
99.09(17)
106.82(19)
109.68(19)
101.29(18)
118.93(13)
125.5418)
ꢂ21.10(3)
0.503(3)
5.2(2)
12.3(2)
6.8(2)
2.8(2)
13.3(2)
O1–C38–N9
O1–C38–C37–C33
Deviation of Mg from N4-plane
Dihedral angle N4/N2,C1–C8
Dihedral angle N4/N4,C9–C16
Dihedral angle N4/N6,C17-C24
Dihedral angle N4/N8,C25–C32
Dihedral angle N4/axial py ring
Dihedral angle amide/py ring of axial ligand
0.412
3.49
4.91
4.91
3.49
90.00
0.00
20.2(2)
interact each other (Scheme 3) forming the (MgPc)2(isonicotina-
mide) supramolecular complex that cocrystallises with the re-
leased isonicotinamide yielding the crystal 2. The solvated
isonicotinamide molecules in the crystal 2 are disordered.
In the case of 2-cyanopyridine the transformation process of cy-
ano into amide groups runs in the same way as for 3-cyanopyridine.
However, during prolonged thermal processing at 80° two different
crystals, besides the blue-violet crystals of MgPc complex with 2-
pyridinecarboxamide (3), the colourless needle single crystals of
2-pyridinecarboxamide were obtained. The lattice parameters of
the crystal of 2-pyridinecarboxamide are in agreement with the lit-
erature data [23]. The X-ray single crystal analysis of the crystal 3
indicates that the crystals are built up of besides the complex of
MgPc(2-pyridinecaroxamide) also from 2,4,6-tris(20-pyridine)-
1,3,5-triazine and MgPc(H2O) molecules. At used thermal condition
these three different molecules MgPc(2-pyridinecaroxamide),
2,4,6-tris(20-pyridine)-1,3,5-triazine and MgPc(H2O) cocrystallise
yielding crystal 3. The catalytic trimerisation of 2-cyanopyridine
into 2,4,6-tris(20-pyridine)-1,3,5-triazine by MgPc is known and
has been earlier reported [10]. The formation of the O,N-bridged
MgPc-complex as for the isonicotinamide due to the steric hin-
drance of large MgPc molecules is impossible in the case of 2-pyri-
dinecarboxamide and 3-pyridinecarboxamide (nicotinamide).
7.0(1)
2.5(1)
2.9(1)
59.9(1)
51.9(1)
2.6(1)
3.5(1)
5.3(1)
4.81
7.09
4.71
87.50
19.59
6.89
5.40
5.70
2.2(1)
41.2(1)
5.19
75.90
H2N
CN
O
H2 O
MgPc
N
N
The interaction of MgPc(H2O) with nitrogen atom of C„N group
containing the lone-pair of electrons leads to the proton transfer
with the formation of the active forms of MgPc(OHꢂ) and
C6H4C+@NH (Scheme 2c). These oppositely charged intermediate
units interact each other (Scheme 2d) forming C@O bond. Simulta-
neously the proton transfer from oxygen atom to nitrogen atom
takes place. At the used thermal condition (ꢁ80 °C) the Mg O
coordinating bond is preserved and therefore during prolonged
thermal processing the intermediate MgPc(nicotinamide) (Scheme
2e) could be isolated in the crystalline form (crystal 1). Thermal
decomposition of the MgPc(nicotinamide) complex with formation
of isonicotinamide and free MgPc.
3.2. Thermal analysis
Thermogravimetric analyses of the solid-state samples 1, 2 and
3 are shown in Fig. 1. TG analysis of 1 shows that the MgPc(nico-
tinamide) complex decomposes at ꢁ140 °C. At this temperature
it loses the coordinated nicotinamide molecule and transforms in
the b-MgPc. The weight loss of ꢁ18.5% agrees well with the ex-
pected value of 18.53% related with the loss of nicotinamide mol-
ecule. TG analysis of the solid-state sample of 2 shows that this
complex undergoes a stepwise decomposition on heating. At first
at temperature of about 115 °C the starting sample of (MgPc)2
(isonicotinamide)ꢀ(isonicotinamide) loses the disordered solvated
In the case of 4-cyanopyridine isomer the transformation of
C„N into amide groups takes place in the similar way. However,
at used thermal condition two MgPc(isonicotinamide) molecules
isonicotinamide molecule, then at about 157 °C the
mide MgPc complex loses the O,N-bridged isonicotinamide
l-isonicotina-

J. Janczak / Polyhedron 38 (2012) 75–87
79
NH
C
N
C
+
(a)
H
H
(b)
Mg
Mg
Mg
O
O
+ H2O
+
+
H
N
N
(c)
NH2
NH
C
NH2
C
C
H
O
O
Mg
Mg
O
+
Mg
N
N
N
(f)
(d)
(e)
Scheme 2. Transformation mechanism of 3-cyanopyridine to nicotinamide.
O
NH2
NH2
C
N
NH2
NH2
C
C
C
+
Mg
O
Mg
+
Mg
O
O
N
N
N
Mg
Scheme 3. Formation of the (MgPc)2(isonicotinamide) supramolecular complex from the MgPc(isonicotinamide).
of both Mg–O and Mg–N bonds than that in the 1 and 3 complexes
0
-4
(MgPc(nicotinamide) and MgPc(2-pyridinecarboxamide)).
0
3
-5
3.3. Description of the structures
1
2
-10
-15
-20
-25
-30
-35
3.3.1. MgPc complex with 3-pyridinecarboxamide – (1)
-8
The molecular structure of MgPc(nicotinamide) is shown in
Fig. 2. The electropositive Mg centre of MgPc is equatorially coor-
dinated by four isoindole N atoms of phthalocyaninate(2-) macro-
cycle and axially by oxygen atom of amide group of nicotinamide
molecule. Thus the coordination environment of the Mg atom is
similar to that found in several chlorophyll derivatives [26–28],
i.e. Mg is equatorially bound by four N atoms of pyrrole rings
and by O atom in an axial position. Owing to the interaction of
the electropositive Mg centre of MgPc (about + 0.5, [29]) with axi-
ally coordinated electronegative O atom of nicotinamide molecule
is significantly displaced from the N4-isoindole plane of the Pc(2-)
macrocycle. The displacement of the Mg centre from the N4-plane
is comparable to that observed in other five-coordinated magne-
sium phthalocyanine derivatives [30–40], and is smaller by
ꢁ0.15 Å from that observed in 4 + 1-coorinated aquamagnesium
-12
-16
-20
40
80
120
160
200
Temperature [oC]
Fig. 1. Thermograms for the solid-state samples of 1, 2 and 3.
molecule. The respective weight losses agree well with the ex-
pected value of 9.26% related with the loss of solvated isonicotina-
mide molecule and 18.52% related with the loss of both
isonicotinamide molecules (solvated and bridged). TG analysis of
solid-state sample of 3 shows that this complex decomposes at
almost the same temperature as complex 1. At this temperature
from the sample
3
[MgPc(2-pyridinecarboxamide)ꢀ(MgPcH2O)ꢀ
(2,4,6-tris(20-pyridyl)-1,3,5-triazine)] loses the coordinated 2-pyri-
dinecarboxamide, 2,4,6-tris(20-pyridyl)-1,3,5-triazine and water
molecules, which are disordered in the crystal. In all samples, the
thermal process leading to the loss of coordinated and solvated
molecules and conversion of the rest samples into MgPc in the
b-form that was confirmed by the X-ray powder diffraction
experiment on a STOE powder diffractometer. The thermal decom-
position of the complexes 1 and 3 (MgPc(nicotinamide) and
MgPc(2-pyridinecarboxamide)) correlate well with the strength
of the axial Mg–O bonds. The higher temperature decomposition
of the (MgPc)2(isonicotinamide) complex is related with the bridg-
ing effect of the O,N-coordinated isonicotinamide by two MgPc
molecules. Thus the releasing of the O,N-bridged isonicotinamide
molecule from the complex needs greater energy for the breaking
Fig. 2. View of the molecular structure of MgPc(nicotinamide). Displacement
ellipsoids are drawn at the 50% probability level.

80
J. Janczak / Polyhedron 38 (2012) 75–87
Table 5
Comparison of the Mg-coordination centre in 4 + 1 O-coordinated MgPc-complexes.
4 + 1 complexes MgPc-complexes
Displacement of the Mg atom from the N4-isoindole plane Average Mg–N bond length
Mg–O bond length
(Å)
References
(Å)
(Å)
MgPc(nicotinamide)
MgPc(H2O) (triclinic form)
0.460(2)
0.442(3)
2.0345
2.044
2.045
1.9772(15)
2.008(2)
2.056(3)
This work
[12]
[13]
MgPc(H2O) (monoclinic form, P21/ ꢁ0.47
a)
MgPc(H2O) (monoclinic form, P21) 0.489(4)
2.046
2.040
2.036
2.039
2.038
2.044
2.040
2.037
2.034
2.038
2.020
2.091(2)
2.022
[14]
[30]
[31]
[32]
[33]
[35]
[35]
[35]
[36]
[37]
[40]
MgPc(H2O).2py
0.496(4)
0.437(1)
0.492(2)
0.509(1)
0.488(2)
0.491(2)
0.492(2)
0.496(2)
0.486(2)
0.357(3)
MgPc(CH3OH)
2.033(1)
1.993(2)
1.971(2)
2.038(2)
2.016(2)
2.009(2)
2.029(2)
2.009(2)
2.1204(15)
MgPc(H2O)ꢀ2(C2H5)2NH
MgPc(H2O)ꢀC3H7NH2
(MgPc(H2O))2ꢀMEA
(MgPc(H2O))2ꢀ2MEA
(MgPc(H2O))2ꢀ3MEA
MgPc(H2O)ꢀ3Cl-py
MgPc(H2O)ꢀ4-picoline
(MgPc)2(dioxane)
porphyrinato complexes [41–43] and in chlorophyll deriv-
atives (Table 5) [26–28]. The four equatorial Mg–N bonds
[2.0221(17)ꢅ2.0424(15) Å] are longer than the axial Mg–O bond
[1.9772(15) Å] linking the nicotinamide molecule. The relation be-
tween the equatorial Mg–N and axial Mg–O bonds in the present
MgPc-complex is similar to that found in other 4 + 1 coordinated
MgPc-O-derivatives, in which the axial Mg–O bond is shorter than
the equatorial Mg–N bonds (Table 6). The opposite relation is ob-
served in both monoclinic forms (P21/a and P21) of MgPc(H2O)
and in (MgPc)2(dioxane) molecule, in which the dioxane molecule
bridges two MgPc molecules [40]. The interaction of the electro-
positive Mg centre with electronegative O atom of nicotinamide
leads to the distortion of Pc(2-) macrocycle from the planar confor-
mation to the saucer-shape geometry. The four isoindole moieties
of Pc(2-) macrocycle are inclined to the N4-plane by 1.3(1), 1.6(1),
2.7(1) and 1.2(1)°, respectively for the N2/C1–C8, N4/C9–C16, N6/
C17–C24 and N8/C25–C32 rings. The axial Mg–O bond is almost
perpendicular (88.9(2)°) defined by the four N-isoindole atoms of
Pc(2-) macrocycle. Although, axial Mg–O bond is perpendicular,
but the pyridine ring of isonicotinamide molecule is inclined by
7.1(2)° to this N4-plane. The amide group of isonictotinamide is
almost coplanar with the pyridine ring. The torsion angle of
O1–C33–C34–C35 describing the rotation of the amide group in
relation to the plane of pyridine ring around the C–C bond is equal
to ꢂ2.2(2)°. The ab-initio optimised conformation of the nicotin-
amide molecule also exhibits non-planar geometry, however the
amide group is significantly more rotated in relation to the pyri-
dine ring (23.4°).
mentioned above. The distances between the Pc(2-) macrorings
within the stacks allow for energetically favourable molecular
arrangement. The N–Hꢀ ꢀ ꢀN hydrogen bonds between the NH2
group and the azamethine N atom of the neighbouring MgPc(nico-
tinamide) molecules stabilise the stacking structure.
3.3.2. MgPc complex with 4-pyridinecarboxamide – (2)
The molecular structure of the MgPc complex with isonicotina-
mide is shown in Fig. 4. The isonicotinamide molecule bridges two
MgPc units via pyridine N-ring and O amide atoms forming
(MgPc)2(isonicotinamide) supramolecular complex. Thus the iso-
nicotinamide molecule is a bridging N,O-donor ligand. The interac-
tions of electronegative N and O atoms of isonicotinamide with
electropositive Mg centre of two MgPc molecules lead to the dis-
placements of the Mg atom in both MgPc molecules. The displace-
ment of Mg joined to the pyridine N ring atom is smaller
(0.413(2) Å) than the displacement of Mg linking the O atom of
amide groups (0.473(2) Å). The four equatorial Mg–N bonds with
Pc(2-) macrocycle in both MgPc units of (MgPc)2(isonicotinamide)
supramolecular complex are comparable in both MgPc units, but
the axial Mg–N bond (2.187(2) Å) is significantly longer than the
axial Mg–O bond (1.966(2) Å). Thus in the (MgPc)2(isonicotina-
mide) complex two type of 4 + 1 coordination of the Mg centre of
MgPc molecule, N and O coordination, is observed. The interaction
of the bridged isonicotinamide with Mg centre of two MgPc mole-
cules via pyridine N ring and O amide atoms leads to the distortion
of Pc(2-) macrocycle from planar conformation to the saucer-shape
geometry. The four isoindole moieties of MgPc linked to pyridine N
ring atom are inclined to the N4-plane by 5.0(2), 7.0(2), 2.5(2) and
2.9(2)° for the N2/C1–C8, N4/C9–C16, N6/C17–C24 and N8/C25–
C32 rings, respectively. In the other Pc(2-) ring, the four isoindole
moieties of MgPc linked to the O atom of amide group are inclined
to the N4-plane by 2.6(2)°, 3.5(2)°, 5.3(2)° and 2.1(2)° for the N22/
C33–C40, N24/C41–C48, N26/C49–C57 and N28/C58–C64 isoin-
dole rings, respectively. The dihedral angle between the N4 planes
of the (MgPc)2(isonicotinamide) complex is equal to 55.6(2)°. The
conformation of the bridging isonicotinamide molecule is twisted.
The planar amide group is rotated around the C–C bond by 32.8(3)°
in relation to the plane of pyridine ring. The conformation of the
free isonicotinamide molecule in the crystal is also twisted, how-
ever the rotation angle is different and depends on its crystal mod-
ifications. In the orthorhombic phase the rotation of planar amide
group along C–C bond in relation to the pyridine ring plane is equal
to 30.7(3)° [25], while in the known two monoclinic modifications
of isonicotinamide the rotation of amide group in relation to
pyridine ring is equal to ꢁ25° and ꢁ30° [44]. The gas-phase
The arrangement of MgPc(nicotinamide) molecules in the crys-
tal is mainly determined by the N–Hꢀ ꢀ ꢀN hydrogen bonds and
p–p
interaction and to a lesser degree by the van der Waals forces. Two
MgPc(nicotinamide) molecules interact each other by a pair of the
N–Hꢀ ꢀ ꢀN hydrogen bonds (Table 2b) into dimeric structure. The
dimeric structures of (MgPc(nicotinamide))2 are interlined via
additional N–Hꢀ ꢀ ꢀN hydrogen bonds forming a polymeric stacking
structure parallel to (110) crystallographic plane (Fig. 3). Within
the stack the p–p interactions between the back-to-back oriented
(MgPc(nicotinamide))2 dimers as well as in the dimers are
observed. The back-to-back saucer-shaped Pc(2-) macrorings be-
tween the dimers are separated by 3.543(2) Å, whereas in the di-
mer the Pc(2-) macrorings are separated by 3.383(2) Å (the
N4ꢀ ꢀ ꢀN4 distance). However, due to the sauce-shaped geometry of
the Pc(2-) macrorings the mean interplanar separation of 40-atoms
ring between the dimers is about 0.1 Å shorter, while the mean
interplanar separation between partially overlapped Pc(2-) macr-
orings in the dimer is longer 0.05 Å than the N4ꢀ ꢀ ꢀN4 distances

J. Janczak / Polyhedron 38 (2012) 75–87
81
Table 6
Selected ab-initio (B3LYP/6-311++G⁄⁄) geometrical parameters (Å, °) for 2-pyridinecarboxamide (a), nicotinamide (b) and isonicotinamide (c).
(a) 2-Pyridinecarboxamide
N1–C2
C3–C4
C5–C6
C2–C1
1.343
1.394
1.398
1.513
1.357
C2–C3
C4–C5
N1–C6
C1–O1
1.398
1.396
1.338
1.229
1
2
1
5
O
NH2
2
C1–N2
3
N1
6
O1–C1–N2
N2–C1–C2
N1–C2–C3
O1–C1–C2–C3
N2–C1–C2–N1
124.00
114.51
123.31
O1–C1–C2
N1–C2–C1
C2–N1–C6
121.49
117.60
117.89
4
0.20
0.19
(b) Nicotinamide
N1–C2
C3–C4
C5–C6
C3–C1
1.337
1.400
1.397
1.502
1.337
C2–C3
C4–C5
N1–C6
C1–O1
1.404
1.394
1.341
1.227
1
2
1
O
H2N
3
C1–N2
4
5
2
1
O1–C1–N2
N2–C1–C3
N1–C6–C5
O1–C1–C3–C2
N2–C1–C3–C2
(c) Isonicotinamide
N1–C2
C3–C4
C5–C6
C4–C1
C1–N2
O1–C1–N2
N2–C1–C4
C2–N1–C6
O1–C1–C4–C5
N2–C1–C2–N1
121.79
116.40
123.51
O1–C1–C3
N1–C2–C3
C2–N1–C6
121.81
123.79
117.49
N
6
ꢂ23.31
157.89
1.339
1.400
1.395
1.508
1.339
C2–C3
C4–C5
N1–C6
C1–O1
1.397
1.398
1.341
1.226
2
NH2
1
O
1
4
3
2
5
6
122.11
116.39
117.10
O1–C1–C4
N1–C2–C3
121.51
123.70
N
1
ꢂ21.79
159.21
conformation obtained by ab-initio MO calculations shown also its
non-planar conformation with the rotation angle of 21.9° of the
amide group in relation to the pyridine ring along the C–C bond.
The axial Mg2–O1 bond is almost perpendicular to the N4-plane
of Pc(2-) macroring (89.2(2)°), whereas the axial Mg1–N9 joining
the pyridine ring is significantly deviated from the orthogonal ori-
entation to the N4-plane of Pc(2-) macroring (81.7(2)°). In addition,
the axial Mg1–N9 bond is inclined to the plane of pyridine ring by
ꢁ20°. Thus the pyridine ring plane of isonicotinamide forms dihe-
dral angles of 59.9(2)° and 41.2(2)° with the N4 planes of Pc(2-)
rings of MgPc units joining the pyridine N ring and O amide atoms,
respectively.
The TG analysis of crystalline sample of 2 (Fig. 1 and Section 3.2)
clearly shows that, besides the (MgPc)2(isonicotinamide) supra-
molecules, the isonicotinamide molecules as solvated molecules
are present in the crystal. The refinement of the crystal structure
of 2 with the original data set was unable to localise the solvated
and disordered isonicotinamide molecules. Therefore, to localise
the solvated and disordered isonicotinamide molecule, the
SQUEEZE algorithm of the PLATON program has been used [45].
The SQUEEZE procedure suggests two positions at (0,0,0.5) and
(0,0.5,0) with ꢁ31 electrons in each for localisation of isonicotina-
mide molecule. Thus, the isonicotinamide molecule C5H4N–
C(O)NH2 having 64 electrons is disordered, and statistically occu-
pies both (0,0,0.5) and (0,0.5,0) positions with occupation factor
of ꢁ0.5.
The arrangement of (MgPc)2(isonicotinamide) supramolecules
in the crystal is mainly determined by the
p–p interactions and
by the van der Waals forces. The (MgPc)2(isonicotinamide) mole-
cules related by a combination of screw axis and the c plane are ar-
ranged in the back-to-back fashion with a distance of 3.619(3) Å
between the N4-planes of the back-to-back oriented Pc(2-) macro-
cycles (Fig. 5). Since the Pc(2-) macrorings exhibit saucer-shape
geometry, the mean interplanar separation between the 40-atoms
Fig. 3. Arrangement of MgPc(nicotinamide) molecules in the unit cell showing the
stacking structure. Dashed lines represent the N–Hꢀ ꢀ ꢀN hydrogen bonds. Symmetry
code as in Table 2b.

82
J. Janczak / Polyhedron 38 (2012) 75–87
Fig. 4. View of the molecular structure of (MgPc)2(isonicotinamide). Displacement ellipsoids are drawn at the 50% probability level.
Fig. 5. Arrangement of (MgPc)2(isonicotinamide) molecules in the unit cell showing the stacking structure.
rings of the back-to-back oriented Pc(2-) macrocycles is smaller by
ꢁ0.3 Å than the N4ꢀ ꢀ ꢀN4 value. Scheidt and Lee [46] examined the
overlap in neutral, structurally characterised, sterically unhindered
metal–porphyrinato complexes and discovered that the distribu-
tion of the overlap of the ligands is trimodal rather than continu-
ous. The mean interplanar separation between the 40 atoms
rings of ꢁ3.3 Å is shorter than the sum of the C atom van der Waals
3.3.3. MgPc(2-pyridinecarboxamide)ꢀ(MgPcH2O)ꢀ(2,4,6-tris(20-
pyridyl)-1,3,5-triazine) – (3)
The crystal structure of the crystal 3 is more complicated than
the structures of 1 and 2. The crystal of 3 id built up from three dif-
ferent molecules: MgPc(2-pyridinecarboxamide), MgPc(H2O) and
2,4,6-tris(20-pyridine)-1,3,5-triazine. The formation of 2,4,6-
tris(20-pyridyl)-1,3,5-triazine from 2-cyanopyridine in presence of
MgPc has been known and described previously [10]. However,
in the present crystal the asymmetric unit consists only of half of
each building molecules due to symmetry of the crystal. Thus they
radii of the
the distance of 3.08 Å at which the steric interactions between the
-aromatic ring system becomes predominantly repulsive.
p
-aromatic rings (ꢁ3.4 Å), but significantly longer than
p

J. Janczak / Polyhedron 38 (2012) 75–87
83
Fig. 6. View of two statistically orientations (a and b) of the MgPc(2-pyridinecarboxamide), (MgPcH2O) and (2,4,6-tris(20-pyridyl)-1,3,5-triazine) molecules in 3, and (c)
MgPc(2-pyridinecarboxamide)ꢀ(MgPcH2O)ꢀ(2,4,6-tris(20-pyridyl)-1,3,5-triazine) showing that the pyridyl ring N9,C33-C37 belongs to the coordinated 2-pyridinecarboxamide
as well as to 2,4,6-tris(20-pyridyl)-1,3,5-triazine molecules, and therefore the occupation factor of N9 and C37 (and its equivalent N9i and C37i) is 0.5 N + 0.5C. Symmetry
code: (i) 1 ꢂ x, 1 ꢂ y, ꢂz.
are disordered in the crystal. Fig. 6a and b illustrates the two pos-
sible orientations of the molecules in the crystal, while the Fig. 6c
is the superposition of the 6a and 6b. Therefore in the crystal of 3
the atoms of the MgPcO units as well as the pyridine ring of coor-
dinated 2-pyridinecarboxamide and one 20-pyridyl ring of the
2,4,6-tris(20-pyridine)-1,3,5-triazine molecule (see Fig. 6) lie at
the same positions, but the rest of the atoms of the 2,4,6-tris(20-
pyridine)-1,3,5-triazine molecule and the C–NH2 atoms of the
amide group of 2-pyridinecarboxamide are statistically distributed
over two positions related by the inversion centre. Due to the dis-
ordering the H atoms of 2,4,6-tris(20-pyridine)-1,3,5-triazine mole-
cule and the H atoms of NH2 and H2O were not localised.
MgPc-derivatives. The four isoindole units of Pc(2-) macrocycle
are inclined to the N4-isoindole plane by 5.2(2)°, 12.3(2)°, 6.8(2)°
and 2.8(2)°, respectively for the N2/C1–C8, N4/C9–C16, N6/C17–
C24 and N8/C25–C32 rings. The four equatorial Mg–N bonds
[2.038(5)–2.041(5) Å] are slightly longer than the axial Mg–O bond
[2.017(4) Å]. The relation between the equatorial Mg–N and axial
Mg–O bonds is observed in the most structures of 4 + 1 O-coordi-
nated MgPc-complexes. The axial Mg–O bond is almost perpendic-
ular (ꢁ88.5°) to the N4-plane of the Pc(2-) macrocycle. The
pyridine ring of coordinated 2-pyridinecarboxamide molecule is
inclined to the N4-plane of Pc(2-) macroring by 13.3(2)°. The amide
group of 2-pyridinecarboxamide molecule is rotated around the
C–C bond by 20.2(2)° in relation to the plane of pyridine ring.
The twisted conformation of the 2-pyridinecarboxamide molecule
is also observed in the crystal of pure 2-pyridinecarboxamide.
The Pc(2-) macroring of the MgPc(2-pyridinecarboxamide) mol-
ecule exhibits, similar as in the complexes 1 and 2, saucer-shape
geometry (Fig. 7), which is typical for the 4 + 1 coordinated

84
J. Janczak / Polyhedron 38 (2012) 75–87
distance between the
p
p-clouds of the Pc(2-) macrocycle and the
-cloud of the 2,4,6-tris(20-pyridine)-1,3,5-triazine molecule is
longer than the half value of N4ꢀ ꢀ ꢀN4 distance and is equal to
ꢁ3.2 Å due to the sauce-shape conformation of the Pc(2-). Addi-
tionally, the back-to-back oriented Pc(2-) macrocycles with a sep-
aration of 3.705(3) Å between the N4ꢀ ꢀ ꢀN4 planes stabilise the
stacking structure along the b-axis (Fig. 7). Due to the saucer-shape
conformation of the Pc(2-) macrorings the mean interplanar sepa-
ration between the 40 atoms rings of back-to-back oriented Pc(2-)
units is shorter by ꢁ0.3 Å and is comparable to the sum of the C
atom van der Waals radii of the
p-aromatic rings (ꢁ3.4 Å) [47].
3.4. Gas-phase structures
The gas-phase geometries of MgPc(2-pyridinecarboxamide),
MgPc(nicotinamide) and (MgPc)2(isonicotinamide) complexes
were obtained by ab-initio full optimised molecular orbital calcula-
tions using the same basis set functions for all three molecules. The
difference between the energies of the fully optimised geometries
and that as in the crystals is 13.065 kJ molꢂ1 for the MgPc(2-pyri-
dinecarboxamide), 12.413 kJ molꢂ1 for MgPc(nicotinamide) and
23.399 kJ molꢂ1 for the O,N-bridging (MgPc)2(isonicotinamide)
complex. The ab-initio geometrical parameters are, in general, in
good agreement with those obtained from the X-ray structure
investigations. A selected ab-initio geometrical parameters for
these complexes are listed together with the X-ray values in Tables
2–4. A noticeable differences between the ab-initio and the X-ray
results in the coordination environment of the Mg centre are ob-
served. In all complexes, the deviation of the Mg centre from the
N4-plane of Pc(2-) macroring in the gas-phase is slightly smaller
than that obtained by the X-ray single crystal analysis. The sau-
cer-shape geometry of the Pc(2-) macrocycle in the gas-phase is
more pronounced for MgPc(nicotinamide) and (MgPc)2(isonicoti-
namide) molecules than that in the crystals. This is likely due to
Fig. 7. View of the molecular structure of MgPc(2-pyridinecarboxamide).
the
p–p cloud interactions between the back-to-back oriented
Pc(2-) macrorings (Tables 2–3) that lead to flattening of Pc(2-)
macrorings. Although, the optimised value of the axial Mg–O bond
length is slightly greater than the X-ray result for all complexes,
however the relation between the equatorial Mg–N and axial
Mg–O bonds is preserved as in the crystals. The greatest differ-
ences between the gas-phase and the X-ray geometries of MgPc-
complexes are observed for the orientation and the conformation
of the axial 2-, 3- and 4-pyridiniecarboxamide molecules. The X-
ray conformation of the axially ligated pyridinecarboxamide iso-
mers is twisted in all crystals, but in the gas-phase the twisting
conformation of the axial ligand is observed only for the MgPc(nic-
otinamide) and (MgPc)2(isonicotinamide) molecules, while in the
third MgPc(2-pyridinecarboxamide) complex the axial 2-pyridine-
carboxamide ligand exhibits a planar conformation. The ab-initio
optimised geometry of free 2-pyridinecarboxamide molecule also
exhibits a planar conformation (Table 6) with the NH2 group on
the side of pyridine N-ring atom. This conformation of 2-pyridine-
carboxamide molecule is stabilised by the intramolecular N–Hꢀ ꢀ ꢀN
interactions between the NH2 of amide group and the pyridine N-
ring atom [with a distance of 2.700 Å between donor–acceptor
Nꢀ ꢀ ꢀN]. The perpendicular orientation of the axial planar 2-pyridin-
ecarboxamide ligand in the MgPc(2-pyridinecarboxamide) mole-
cule in the gas-phase is stabilised by two intramolecular N–Hꢀ ꢀ ꢀN
interactions between the NH2 of amide group and the pyridine
N-ring atom and between the NH2 of amide group and the azame-
thine N atom of Pc(2-) macrocycle, since the axial ligand is copla-
nar with the Naza–Mg–Naza plane of MgPc unit. In the crystal due to
the intermolecular interactions the conformation of the axial
2-pyridinecarboxamide in the MgPc(2-pyridinecarboxamide)
complex is twisted (20.2(2)°), and the pyridine ring is inclined to
the N4-plane of Pc(2-) macroring by 13.3(2)°. A similar twisted
Fig. 8. Arrangement of MgPc(2-pyridinecarboxamide)ꢀ(MgPcH2O)ꢀ(2,4,6-tris(20-
pyridyl)-1,3,5-triazine) molecules in the unit cell showing the stacks along [010]
direction.
However, in the gas-phase, as shown the fully optimised molecular
orbital calculations, the 2-pyridinecarboxamide molecule exhibits
planar conformation. The planar conformation of the 2-pyridine-
carboxamide molecule in the gas-phase is stabilised by the intra-
molecular N–Hꢀ ꢀ ꢀN interactions between the amide and the
N-ring atom of pyridine with a distance of 2.700 Å between
Nꢀ ꢀ ꢀN (donorꢀ ꢀ ꢀacceptor).
The arrangement of the MgPc(2-pyridinecarboxamide),
MgPc(H2O) and 2,4,6-tris(20-pyridine)-1,3,5-triazine molecules in
the crystal is determined by the
p–p interactions and by the van
der Waals forces (Fig. 8). Two face-to-face oriented MgPcO units
of disordered MgPc(2-pyridinecarboxamide) and MgPc(H2O) mole-
cules are separated by a distance of 6.025(5) Å between the N4ꢀ ꢀ ꢀN4
of the Pc(2-) macroring. Between the face to face oriented MgPc(2-
pyridinecarboxamide) and MgPc(H2O) molecules is located the dis-
ordered 2,4,6-tris(20-pyridine)-1,3,5-triazine molecule, thus the

J. Janczak / Polyhedron 38 (2012) 75–87
85
Table 7
Selected Milliken charges.
Atom
Mg
MgPc
1.076
H2O
MgPcH2O
0.978
2CNpy
3CNpy
4CNpy
MgPc2AP
0.993
MgPc3AP
0.978
(MgPc)2(4AP)
2AP
3AP
4AP
1.070 (Mg1),
0.991 (Mg2)
ꢂ0.563
O
ꢂ0.927
ꢂ0.624
ꢂ0.677
ꢂ0.722
ꢂ0.591
ꢂ0.679
ꢂ0.757
ꢂ0.568
ꢂ0.678
ꢂ0.762
ꢂ0.591
ꢂ0.506
ꢂ0.505
Nazamethine
Nisoidole
Pyridine
N-ring
N (C„N)
N (NH2)
ꢂ0.676
ꢂ0.791
ꢂ0.678
ꢂ0.764
ꢂ0.133
ꢂ0.531
ꢂ0.105
ꢂ0.491
ꢂ0.120
ꢂ0.505
ꢂ0.608
ꢂ0.768
ꢂ0.529
ꢂ0.783
ꢂ0.656
ꢂ0.761
ꢂ0.376
ꢂ0.524
ꢂ0.122
ꢂ0.513
ꢂ0.120
ꢂ0.501
2CNpy, 3CNpy and 4CNpy are 2-, 3- and 4-cyanopyridine isomers.
2AP, 2-pyridinecarboxamide; 3AP, nicotinamide; 4AP, isonicotinamide.
conformation of the molecule with the rotation angle of ꢁ19° of
amide group in relation to pyridine ring is observed in the crystal
of pure 2-pyridinecarboxamide [23].
For MgPc molecule the calculated 3D MESP map displays the
electrophilic region near the Mg centre on both side of the planar
MgPc molecule and the nucleophilic regions near the bridged
azamethine nitrogen atoms (Fig. 9a). In addition, the less positive
value of MESP than that near the Mg centre and less negative value
of MESP comparing to that of azamethine N bridges are observed
The rotation angle of the amide group in relation to pyridine
ring of the axial ligand in the gas-phase of MgPc(nicotinamide)
molecule is equal to 13.59° and is significantly greater than the
X-ray value (3.1(1)°), but smaller than that in the optimised free
nicotinamide molecule (see Table 6). In optimised free nicotin-
amide molecule and in the MgPc(nicotinamide) complex of both
phases (gas-phase and in the crystal) the NH2 group lies in oppo-
site side in relation to the pyridine N-ring atom. The greatest
differences in the rotation angle of amide group in relation to pyr-
idine ring of pyridinecarboxamide isomers between the gas-phase
and X-ray results are observed in the O,N-bridging (MgPc)2(isonic-
otinamide) supramolecular complex in which the X-ray value and
ab-initio values are 51.9(1) and 19.59°, respectively. In addition,
the differences in the orientation of the O,N-bridge between the
two MgPc units are observed (Table 3).
across the extended 18p-electron conjugation in the Pc macroring
and on the both side of the phenyl rings, respectively. Thus the
high affinity and instability of the MgPc crystals to water with
the formation of aquamagnesium phthalocyanine complex can be
understood. The interaction between MgPc and water molecule
takes place between the electropositive Mg centre of MgPc (blue
colour in Fig. 9a) with the lone pair of electrons of oxygen atom
of water molecule (red, Fig. 9b) forming in result the Mg–O coordi-
nating bond (Fig. 9c).
The MESP maps calculated for each cyanopyridine isomers
(Fig. 9d, e and f) display the regions of negative value of MESP near
the N atom of C„N groups as well as near the pyridine N ring
atom. However, the negative regions of MESP near the N atom of
C„N groups occupy larger space that that near the pyridine N
rings atom (Fig. 9d, e and f). The MESP maps of pyridinecarboxa-
mide isomers (Fig. 9g, h and i) display the large negative value of
MESP near the oxygen atom of amide group and smaller region
of negative MESP near the pyridine N ring atom, since the O atom
contains two lone pair of electron.
The interaction of MgPcH2O molecule (Fig. 9c) with the C„N
group of 2-, 3- and 4-cyanopyridine isomers (Fig. 9d, e and f)
mainly takes place between the H atoms of coordinated water mol-
ecule of MgPcH2O and the nitrogen atom of C„N group. This inter-
action leads to the proton transfer from water molecule of
MgPcH2O to the N atom of C„N group with formation of interme-
diate ionic MgPcOHꢂ and HN@C+–C5H4N units (see Scheme 2c).
These active intermediate units interact each other forming O–C
bond, simultaneously the proton of MgPcOHꢂ unit is transferred
to he nitrogen atom forming NH2. At used thermal conditions
(ꢁ80 °C) as shown the TG analysis the intermediate MgPc com-
plexes with 2-pyridinecarboxamide and nicotinamide are stable
and can be isolated in the crystalline form (crystals 1 and 3).
In the case of isonicotinamide the formed 1:1 complex of MgPc
with isonicotinamide at used conditions interact each other and
transform into a bridging (MgPc)2(isonicotinamide) complex (see
Scheme 3). The interaction between the MgPc(isonicotinamide)
monomers takes place between the electropositive Mg centre of
one molecule and the pyridine N ring atom of axially coordinated
isonicotinamide of the second one. Finally, one isonicotinamide
molecule form each two MgPc(isonicotinamide) molecules is re-
leased and a bridging (MgPc)2(isonicotinamide) complex is formed.
As shows the X-ray structure analysis, the released isonicotina-
mide cocrystallise with the (MgPc)2(isonicotinamide) complex
forming crystals of 2. The interaction between isonicotinamide
(Fig. 9i) and two MgPc molecules with the formation of
3.5. Molecular electrostatic potential
The electrostatic potential V(r) that the electrons or nuclei of a
molecule create at each point r in the surrounding space can be cal-
R
P
culated by the equation V(r) =
(ZA/(RA ꢂ r)) ꢂ
(
q
(r0)/|r0 ꢂ r|)dr,
A
where ZA is the charge on nucleus A having a position vector RA
and the
q
(r0) is the electron density function of the molecule. The
molecular electrostatic potential (MESP) maps have emerged as
powerful predictive and interpretative tools in fields such as chem-
istry, rational drug design, catalysis and intermolecular interac-
tions and organisation in solids [48–51].
The molecular electrostatic potential carry a wealth quantita-
tive and qualitative information and is widely used as a reactivity
map displaying the most probable regions of molecule for the elec-
trophilic attack of reagents and as distribution of the charge in the
molecule. The Milliken charges were calculated for each atoms of
molecules (reacting molecules, intermediate molecules and for
the final products of transformations 2-, 3- and 4-cyanopyridine
into 2-, 3- and 4-pyridinecarboxamide molecules) and the selected
values are summarised in Table 7.
The three dimensional MESP maps are obtained on the basis of
the DFT (B3LYP) optimised results and are illustrated in Fig. 9. The
calculated 3D MESP mapped onto the total electron density isosur-
face (0.008 e Åꢂ3) for each molecules. The colour code of MESP is in
the range of ꢂ0.05 (red) to 0.05 e Åꢂ1 (blue). Regions of negative
MESP are usually associated with the lone pair of electronegative
atoms, whereas the regions of positive MESP are associated with
the electropositive atoms. These calculated 3D MESP maps will
be helpful for understanding of the transformation mechanism of
C„N into amide groups of cyanopyridine isomers in presence of
magnesium phthalocyanine.

86
J. Janczak / Polyhedron 38 (2012) 75–87
Fig. 9. Three-dimensional molecular electrostatic potential (ꢂ0.05 e Åꢂ1, red and +0.05 e Åꢂ1, blue) mapped on the surface of total electron density (0.008 e Åꢂ3) for the
molecules: MgPc (a), H2O (b) MgPc(H2O) (c), 2-cyanopyridine (d), 3-cyanopyridine (e), 4-cyanopyridine (f), 2-pyridinecarboxamide (g), nicotinamide (h), isonicotinamide (i),
MgPc(2-pyridinecarboxamide) (j), MgPc(nicotinamide) (k) and (MgPc)2(isonicotinamide) (l) (colour online).
of Mg centre of MgPc with O atom of amide group is preferred than
that with pyridine N ring atom.
The 3D MESP maps for each studied here MgPc-derivatives
(Fig. 9j, k and l) are helpful for understanding the organisation of
molecules in solid-state (crystals). For example, the 3D MESP
O,N-bridged
l-isonicotinamide MgPc supramolecular complex is
sterically possible, in contrast to the interaction with 2-pyridine-
carboxamide or nicotinamide.
The MESP maps of 2-pyridinecarboxamide, nicotinamide and
isonicotinamide (Fig. 9g, h and i) clearly show that the interaction

J. Janczak / Polyhedron 38 (2012) 75–87
87
map of MgPc(nicotinamide) (Fig. 9k) displays the nucleophilic re-
gions near the pyridine N atom of the axial ligand (red) as well
as near the bridged azamethine nitrogen atoms of Pc(2-) macrocy-
cle and near the coordinated to the Mg centre of MgPc oxygen
atom of amide group, since only one of two lone pairs of electrons
forms the Mg O coordinating bond. The positive values of MESP
are observed near the all H atoms. As can be seen from the X-ray
molecular packing (Fig. 2) each MgPc(nicotinamide) molecule
bridges two neighbours via N–Hꢀ ꢀ ꢀN hydrogen bonds between
the NH2 group and the azamethine nitrogen atom of Pc(2-) macro-
cycle of the neighbours MgPc(nicotinamide) forming a stacking
structure. This mutually orientation of MgPc(nicotinamide) mole-
cules leads to the effective electrostatic interactions between the
azamethine N atom (red) with H atom of NH2 group of neighbour
forming the N–Hꢀ ꢀ ꢀN hydrogen bonds.
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223 336 033; or e-mail: deposit@ccdc.cam.ac.uk.
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This work was supported by the Ministry of Science and Higher
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Appendix A. Supplementary data
CCDC 859255, 859256 and 859257 contain the supplementary
crystallographic data for compounds 1, 2 and 3. For 2 the original
CIF (not SQUEEZED version) has been also deposited, No. CCDC
867352. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge