The variability of hydrogen-bonded supramolecular assemblies in crystalline picrates prepared from ferrocenyl-substituted β-aminoalcohols

Article abstract of DOI:10.1016/j.jorganchem.2008.01.036

Ferrocene-based β-aminoalcohols FcCH₂NHCR₂CH₂OH (R = H, 1a; R = Me, 1b) and (S)-FcCH₂NHCH(CHMe₂)CH₂OH (1c; Fc = ferrocenyl) react with 2,4,6-trinitrophenol (Hpic) under proton transfer to afford the corresponding ammonium picrates 2a-c. In the crystal, these picrates associate predominantly via N-H?O and O-H?O bifurcated hydrogen bonds between the NH₂⁺ and OH groups in the aminoalcohol chain as the donors and the phenoxide and NO₂ oxygen atoms of the picrate anion as the acceptors. Compounds 2a and 2b form closed dimeric assemblies [1nH]₂[pic]₂ (n = a, b) around the crystallographic inversion centres. By contrast, their chiral analogue 2c gives rise to monomeric units [1cH][pic] (albeit through similar interactions), that further aggregate into infinite linear chains via N-H?O hydrogen bonds. The formed assemblies are interconnected by the soft C-H?O hydrogen bonds and via π?π stacking interactions of the picrate ions.

Full text of DOI:10.1016/j.jorganchem.2008.01.036

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 1779–1786
www.elsevier.com/locate/jorganchem
The variability of hydrogen-bonded supramolecular assemblies
in crystalline picrates prepared from ferrocenyl-substituted
b-aminoalcohols
a,
a
a
b
´
´
ˇ a
´ ˇ
´
ˇ
ˇ
*
Petr Steˇpnicˇka , Martin Zabransky , Martin Lamac , Ivana Cısarova , Petr Nemec
a Charles University in Prague, Faculty of Science, Department of Inorganic Chemistry, Hlavova 2030, 128 40 Prague, Czech Republic
b Charles University in Prague, Faculty of Mathematics and Physics, Department of Chemical Physics and Optics,
Ke Karlovu 3, 121 16 Prague, Czech Republic
Received 21 December 2007; received in revised form 22 January 2008; accepted 23 January 2008
Available online 2 February 2008
Abstract
Ferrocene-based b-aminoalcohols FcCH2NHCR2CH2OH (R = H, 1a; R = Me, 1b) and (S)-FcCH2NHCH(CHMe2)CH2OH (1c;
Fc = ferrocenyl) react with 2,4,6-trinitrophenol (Hpic) under proton transfer to afford the corresponding ammonium picrates 2a–c.
+
In the crystal, these picrates associate predominantly via N–Hꢀ ꢀ ꢀO and O–Hꢀ ꢀ ꢀO bifurcated hydrogen bonds between the NH2 and
OH groups in the aminoalcohol chain as the donors and the phenoxide and NO2 oxygen atoms of the picrate anion as the acceptors.
Compounds 2a and 2b form closed dimeric assemblies [1nH]2[pic]2 (n = a, b) around the crystallographic inversion centres. By contrast,
their chiral analogue 2c gives rise to monomeric units [1cH][pic] (albeit through similar interactions), that further aggregate into infinite
linear chains via N–Hꢀ ꢀ ꢀO hydrogen bonds. The formed assemblies are interconnected by the soft C–Hꢀ ꢀ ꢀO hydrogen bonds and via
pꢀ ꢀ ꢀp stacking interactions of the picrate ions.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Ferrocene; Aminoalcohols; Picrates; Chirality; Crystal structure
1. Introduction
combine high chemical stability with unique physicochem-
ical properties of the ferrocene framework [2]. However,
the number of ferrocene compounds that have been utilised
in creating supramolecular architectures remains rather
low and, above all, limited to few ligand classes. The typi-
cal examples include ferrocene-based carboxylic acids [3],
alcohols [4] and heterocycles [5]. This initiated our interest
in the preparation of polar ferrocene derivatives that are
capable of forming multiple hydrogen bonds [6]. We chose
these compounds mainly because of the fairly high stability
and better predictability of the hydrogen-bonded assem-
blies as compared to systems featuring the relatively
weaker C–Hꢀ ꢀ ꢀX (X = heteroatom or p-system) and pꢀ ꢀ ꢀp
interactions [7].
The design and preparation of ordered metal–organic
solids from organometallic precursors represent an attrac-
tive approach towards new functional materials [1].
Despite the recent effort, the synthesis of defined crystalline
materials is still far from rational and typically relies on
spontaneous self-assembly of molecular building blocks
via non-covalent interactions. Hence, the synthesis of
defined building blocks and studies into their structural
properties are desirable in order to provide a sound base
for their subsequent use in the preparation of crystalline
materials.
Polar ferrocene derivatives appear to be particularly
suitable precursors to defined crystalline materials as they
In our previous work, we had focused on ferrocenyl-
methanol derivatives substituted with phosphorus groups
at the ferrocene unit [8] and, later, turned to compounds
with b–hydroxyamine pendant chains. So far, we have
*
Corresponding author. Fax: +420 221 951 253.
ˇ
E-mail address: stepnic@natur.cuni.cz (P. Steˇpnicˇka).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.01.036

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P. Steˇpnicˇka et al. / Journal of Organometallic Chemistry 693 (2008) 1779–1786
1780
R
R
HN
HN
OH
OH
Fe
Fe
1a R = H
1b R = CH3
1c
Scheme 1.
prepared and structurally characterised a series of ferro-
cene carboxamides bearing 2-hydroxyethyl groups at the
amide nitrogens [9], and reported the crystal structures of
ferrocene b-aminoalcohol 1b (Scheme 1) and its ammo-
nium salts [10].
Fig. 1. UV–Vis spectra of 2c (solid line) and 2,4,6-trinitrophenol (dashed
line) in methanol solutions (c = 5 ꢁ 10ꢂ5 M, optical path 10 mm) and the
spectrum of solid 2c (dotted line; diffuse reflectance mode, a powdered
sample was diluted with BaSO4).
Because the latter study revealed a pronounced effect of
the anion on the crystal assembly, we decided to study also
the influence of the substituents at the aminoalcohol chain
in a series of ammonium salts featuring the same anion. As
the anion source we chose 2,4,6-trinitrophenol (picric acid)
which is known to form well-defined crystalline salts with
amines and, simultaneously, possesses a number of poten-
tial hydrogen-bond acceptors. In this contribution we
describe the preparation and crystal structures of picrates
from aminoalcohols 1a–c (Scheme 1). In addition, we pres-
ent the results of UV–Vis spectroscopic and second har-
monic generation (SHG) measurements for the chiral
picrate obtained from 1c.
displays a broad maximum shifted by about 80 nm to lower
energies. This shift probably reflects the formation of pꢀ ꢀ ꢀp
interacting assemblies in the solid state (see below) that
either open new pathways for optical electron transfer pro-
cesses or at least influence the distribution of the energy
levels.
Since many ferrocene derivatives [2c,13] including sup-
ramolecularly assembled ones [13e] as well as picric acid
and its salts or adducts [14] exert non-linear optical proper-
ties, we have tested the chiral picrate 2c for second-
harmonic generation (SHG) efficiency. Indeed, the
compound showed some frequency doubling when irradi-
ated at 800 nm. However, a powdered sample (size fraction
75–125 lm) of 2c was found to have SHG efficiency of only
1.1% that of urea.
2. Results and discussion
2.1. Syntheses and characterisation
Aminoalcohols 1a–c (Scheme 1), readily available from
ferrocenecarboxaldehyde and the respective b-aminoalco-
hols [10,11], react smoothly with 2,4,6-trinitrophenol
(Hpic) under proton transfer to afford the respective
ammonium picrates 2a–c. Upon slow addition of hexane,
the picrates separate directly from the reaction solution
as air-stable, burgundy red crystalline solids.
Because of the known sensitivity of picrates to heating,
impact or friction, we have firstly studied the thermal stabil-
ity of the compounds to avoid possible problems. Fortu-
nately, compounds 2a–c are thermally rather stable,
decomposing above ca. 150 °C. When heated in an open test
tube, they vigorously decompose leaving dark voluminous,
soot-like residua. On the other hand, they can be pulverised
in a mortar without any appreciable decomposition.
As the mixing of the yellow (Hpic) and orange (amino-
alcohols) educts in ethyl acetate affords yellow solutions
from which deep red crystalline products separate, we have
investigated the spectral properties of the 1c-picric acid
model system in the UV–Vis region. Fig. 1 indicates that
the spectra of picric acid and compound 2c are practically
identical, showing a band at 354 nm and a shoulder at
around 400 nm [12]. By contrast, the spectrum of solid 2c
2.2. Molecular structures of 2a–c
Views of the molecular structures of 2a–c are shown in
Figs. 2–4, respectively, and the selected geometric parame-
ters are summarised in Table 1 and in Fig. 5. In all three
cases, the geometry of the ferrocene units is regular, show-
ing nearly identical Fe–Cg (see Table 1 for definitions) and
negligible tilts. The interatomic distances and angles within
the protonated aminoalcohol pendant chains are similar
and also compare favourably with the data reported for
unprotonated 1b and its bromide and dihydrogenphos-
phate salts [10]. The most notable difference is seen in the
conformation of the aminoalcohol chain. The torsion
angles at the C11–N1 and C12–C13 bonds change by only
ca. 10° in the whole series, whilst the torsion angle
C11–N1–C12–C13 varies broadly from ca. 76° for 2b to
ca. 180° for 2a. This is, however, the likely consequence
of the crystal packing effects: Whereas the torsion around
the C12–C13 bond controls the orientation of the polar
groups, which is kept near to synclinal, the rotation along
the C11–N1 bond may facilitate the accommodation of the

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P. Steˇpnicˇka et al. / Journal of Organometallic Chemistry 693 (2008) 1779–1786
1781
O6
O1
O7
O7
H1O
O8
N4
C16
C13
N4
C15
C25
C24
N3
O8
O2
O3
C13
O1
C26
C21
N2
C14
H1O
O3
C25
C12
H1N
C26
O2
C23
H2N
O6
O5
O5
C12
N1
C24
C22
C21
N1
H1N
N3
H2N
C22
C23
N2
O4
O4
C11
C2
C11
C5
C5
C1
C3
C1
C2
C3
C4
Fe
Fe
C4
C6
C7
C10
C7
C6
C10
C9
C8
C8
C9
Fig. 2. The molecular structure of 2a. Displacement ellipsoids are drawn
with 30% probability.
Fig. 4. The molecular structure of 2c. Displacement ellipsoids are drawn
with 30% probability.
Table 1
O4
a,b
˚
Selected distances and angles for 2a, 2b, and 2c (in A and °)
O5
N2
Parameter
2a
2b
2c
C14
C23
C22
Fe–Cg1
Fe–Cg2
\Cp1,Cp2
N1–C11
N1–C12
1.6445(8)
1.650(1)
1.7(1)
1.503(2)
1.487(2)
1.413(2)
177.9(1)
ꢂ179.9(1)
55.9(2)
1.6419(8)
1.6512(9)
1.1(1)
1.511(2)
1.525(2)
1.419(2)
168.3(2)
75.7(2)
1.6420(9)
1.646(1)
0.3(1)
1.518(2)
1.517(2)
1.430(2)
167.3(1)
ꢂ95.7(2)
48.8(2)
N3
C15
O3
O6
C24
C25
C12
O2
C26
O8
C21
H1N
H2N
N1
C13
H1O
O1
N4
O1–C13
C1–C11–N1–C12
C11–N1–C12–C13
N1–C12–C13–O1
Cp1ꢀ ꢀ ꢀPic
\Cp1,Pic
a
C11
O7
C1
C5
49.0(2)
5.127(1)
14.11(9)
4.7701(9)
11.64(9)
ca. 6.08
31.4(1)
C2
C10
C4
The ring planes are defined as follows: Cp1 = C(1–5), Cp2 = C(6–10),
Pic = C(21–26). Cg1, Cg2 and CgP denote their respective ring centroids.
Fe
C3
C9
C6
b
Interatomic distances for the picrate ions are summarised in Fig. 5.
C7
C8
˚
(1.243(2) A) [16], and 4,4-bis(2-hydroxyethyl)-1-oxa-4-azo-
˚
niacyclohexane (1.234(7) A) [17] as the cations.
Fig. 3. The molecular structure of 2b. Displacement ellipsoids are drawn
The planes of the nitro substituents show different rota-
tions from the plane of their parent aromatic ring. The
maximum dihedral angle is ca. 45° for the {N2O3O4}
group in 2a whereas the lowest rotation by ca. 5° is exerted
by the {N3O5O6} groups in 2a and 2c. The rotation of the
nitro groups is probably brought about by steric interfer-
ence between the phenoxide oxygen and its adjacent nitro
groups and also by crystal packing forces, e.g., hydrogen
bonding interactions, the formation of which may well
compensate a destabilisation resulting from a reduced con-
jugation of the p-systems.
Although the picrate aromatic ring does not deviate
much from coplanarity with the ferrocene cyclopentadienyl
Cp1 in both 2a and 2b, the rings are rather distant to allow
for an efficient pꢀ ꢀ ꢀp interaction. In the case of compound
2c, the distance and rotation of the ring planes are even less
favourable (Table 1).
with 30% probability.
bulky ferrocene moiety in the crystal (see the discussion of
the crystal packing).
The structures of the picrate counter ions in 2a–c are
similar (Fig. 5); the only statistically significant difference
in the interatomic distances is found among the C22–C23
bond lengths. The picrate moiety displays partial quinoid
character where the C–C bonds adjoining the phenoxide
carbon atom C21 are markedly longer than the remaining
inter-ring C–C bonds. The C21–O2 distance corresponds
well with the distances typically encountered in the crystal
structures of simple organic picrates, including the b-ami-
noalcohol-based ones possessing 2-hydroxyethanaminium
˚
(1.260 A) [15], (2-hydroxymethyl)trimethylammonium

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P. Steˇpnicˇka et al. / Journal of Organometallic Chemistry 693 (2008) 1779–1786
1782
Table 2
2a
2b
2c
O3
1.229(2)
1.229(2)
1.219(3)
O2
1.252(2)
1.254(2)
1.258(2)
O8
1.227(2)
1.228(2)
1.219(2)
a
˚
Summary of hydrogen bond parameters for 2a–c (in A and °)
D–Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
Angle at H
Compound 2a
1.445(2)
1.444(3)
1.443(3)
1.451(2)
1.446(3)
1.448(3)
1.225(2)
1.227(2)
1.234(3)
1.230(2)
1.231(2)
1.231(2)
C21
N4
N1–H1Nꢀ ꢀ ꢀO1i
N1–H1Nꢀ ꢀ ꢀO1
N1–H2Nꢀ ꢀ ꢀO2
O1–H1Oꢀ ꢀ ꢀO2i
O1–H1Oꢀ ꢀ ꢀO3i
C12–H12Aꢀ ꢀ ꢀO8
C12–H12Bꢀ ꢀ ꢀO6ii
2.748(2)
2.869(2)
2.778(2)
2.680(2)
3.140(2)
2.970(2)
3.234(2)
146
128
148
131
150
105
137
N2
1.455(2)
1.457(2)
1.458(2)
1.458(2)
1.459(2)
1.465(3)
C22
C26
O7
O4
1.380(2)
1.365(3)
1.371(2)
1.372(2)
1.377(3)
1.372(3)
C23
C25
Compound 2b
1.383(2)
1.384(3)
1.380(3)
1.390(2)
1.386(3)
1.385(3)
H25
H23
C24
N1–H1Nꢀ ꢀ ꢀO2
N1–H1Nꢀ ꢀ ꢀO3
N1–H2Nꢀ ꢀ ꢀO1
N1–H2Nꢀ ꢀ ꢀO1iii
O1–H1Oꢀ ꢀ ꢀO2iii
O1–H1Oꢀ ꢀ ꢀO8iii
C4–H4ꢀ ꢀ ꢀO4iv
2.849(2)
3.025(2)
2.697(2)
2.892(2)
2.670(2)
3.022(2)
3.430(3)
2.977(3)
3.255(2)
3.337(3)
3.285(3)
144
137
112
143
154
128
156
111
143
136
139
1.449(2)
1.447(3)
1.451(3)
N3
1.232(2)
1.236(2)
1.227(3)
1.230(2)
1.231(2)
1.229(3)
O5
O6
C13–H13Aꢀ ꢀ ꢀO8iii
C13–H13Aꢀ ꢀ ꢀO5v
C14–H14Aꢀ ꢀ ꢀO3
C15–H15Cꢀ ꢀ ꢀO3
˚
Fig. 5. Summary of the bond lengths for the picrate anions in 2a–c (in A).
2.3. Description of the crystal packing
Compound 2c
N1–H1Nꢀ ꢀ ꢀO2
N1–H1Nꢀ ꢀ ꢀO3
N1–H2Nꢀ ꢀ ꢀO1vi
O1–H1Oꢀ ꢀ ꢀO2
O1–H1Oꢀ ꢀ ꢀO8
C8–H8ꢀ ꢀ ꢀO7vii
C11–H11ꢀ ꢀ ꢀO6viii
a
2.852(2)
3.127(2)
2.777(2)
2.646(2)
2.816(2)
3.381(3)
3.438(3)
142
139
171
150
125
151
149
Views of the crystal packing of 2a are shown in Fig. 6
and the relevant geometric data are presented in Table 2.
The basic repeating unit in the crystal of 2a is constituted
by two ion-pairs [1aH][pic] that assemble into centrosym-
metric dimers (Fig. 6a). The cation–anion secondary bond-
ing in the resulting four-ion aggregate is accomplished
exclusively via a pair of three-centre hydrogen bonds from
the NH and OH protons at the aminoalcohol chain to the
D = donor, A = acceptor. Symmetry codes: (i) ꢂx, ꢂy, 1 ꢂ z; (ii) x, y,
ꢂ1 + z; (iii) ꢂ1 ꢂ x, 1 ꢂ y, ꢂz; (iv) ꢂx, 1/2 + y, 1/2 ꢂ z; (v) ꢂ1 + x, y, z;
(vi) 2 ꢂ x, 1/2 + y, 2 ꢂ z; (vii) 2 ꢂ x, 1/2 + y, 1 ꢂ z; (viii) 1 + x, y, 1 + z.
a
b
D
B
O3
A
O2
O1
O8
B
C13
A
N1
C12
C
C11
O6’
b
0,a
c
Fig. 6. (a) Principal intermolecular interactions in the structure of 2a. To avoid overlaps, the bulky ferrocenyl groups were replaced with filled black
circles. The hydrogen bonds are shown as dashed lines. Symmetry operations: A (x, y, z); B (ꢂx, ꢂy, 1 ꢂ z); C (x, y, ꢂ1 + z); D (ꢂx, ꢂy, 2 ꢂ z). (b) View
of the unit cell of 2a along the crystallographic a-axis.

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P. Steˇpnicˇka et al. / Journal of Organometallic Chemistry 693 (2008) 1779–1786
1783
picrate oxygen atoms (Oꢂ and NO2). The aminoalcohol
O5’
D
C11
chains are interconnected through the two-centre N1–
H2Nꢀ ꢀ ꢀO1 hydrogen bonds (Table 2).
C15
C12
A
O3
C13
O1
N1
The formed assembly is further linked to two adjacent
picrate ions generated by translation along the c-axis
(A ? C and B ? D in Fig. 6a). The adjacent picrate ions
interact via cooperative pꢀ ꢀ ꢀp stacking interactions of their
per-symmetry parallel benzene rings at the centroid–cen-
O2
C14
A
B
O8
B
0
˚
C
troid distance picꢀ ꢀ ꢀpic of 3.4076(8) A (the prime-labelled
plane is generated by the inversion operation (ꢂx, ꢂy,
Fig. 7. Intermolecular interactions in the structure of 2b. The ferrocenyl
groups were replaced with black circles and the hydrogen bonds are
indicated with dashed lines. Symmetry operations: A (x, y, z); B (ꢂ1 ꢂ x,
1 ꢂ y, ꢂz); C (ꢂx, 1 ꢂ y, ꢂz); D (ꢂ1 + x, y, z).
˚
2 ꢂ z); cf. interplanar distance = 3.29 A, ring slip-
˚
page = 0.90 A; pairs Aꢀ ꢀ ꢀD and Bꢀ ꢀ ꢀC in Fig. 6a) and by
thus enforced C–Hꢀ ꢀ ꢀO contacts between the picrate oxy-
gen atoms O6 and O8 and hydrogens at C12 (Table 2).
When combined, these interactions result into the forma-
tion of infinite chains along the crystallographic c-axis.
These chains are located in the ac plane at b = 0 and 1,
forming polar layers that are separated by non-polar
domains built up from the alternating ferrocene moieties
(Fig. 6b).
the N1–H2Nꢀ ꢀ ꢀO1 hydrogen bonds. The changed confor-
mation of the aminoalcohol chain together with re-orienta-
tion of the subunits allows for an increase in the number of
hydrogen bonding interactions. When compared with 2a,
the structure of 2b features an additional C–Hꢀ ꢀ ꢀO(pic)
contact per one molecule and, more importantly, an intra-
molecular N1–H2Nꢀ ꢀ ꢀO1 hydrogen bond that apparently
stabilises the conformation of the hydroxyammonium
chain.
The crystal assembly of 2b (Fig. 7, Table 2) resembles in
many regards the packing of its non-methylated analogue
2a. The observed differences seem to reflect increased steric
bulk of the polar hydroxyamine chain, which also results in
conformational changes. On going from 2a to 2b, the N1–
C12–C13–O1 angle becomes by ca. 7° smaller while the
C11–N1–C12–C13 angle drops from a value typical for
an antiperiplanar arrangement to synclinal (see Table 1).
Consequently, both methyl groups are directed away from
the OH and NH2 groups involved in hydrogen bonding
interactions.
Similarly to 2a, the key feature in the crystal assembly of
2b is a centrosymmetric dimer involving two [1bH][pic] ion-
pairs, where the cations and anions interact via bifurcated
N1–H1Nꢀ ꢀ ꢀO(pic) and O1–H1Oꢀ ꢀ ꢀO(pic) hydrogen bonds
whereas the hydroxyammonium chains are connected by
As in the case of 2a, the dimers of 2b aggregate with
picrate ions from the neighbouring units via cooperative
C–Hꢀ ꢀ ꢀO(pic) contacts and offset pꢀ ꢀ ꢀp stacking interac-
tions of the parallel aromatic rings (Fig. 7; Aꢀ ꢀ ꢀC and
˚
Bꢀ ꢀ ꢀD: centroid–centroid distance = 3.474(1) A, interpla-
˚
˚
nar separation = 3.39 A, offset of the planes = 0.75 A).
The crystal assembly of picrate 2c markedly differs from
its achiral counterparts mainly because the chiral com-
pound cannot form closed centrosymmetric assemblies
(Fig. 8a). Thus, instead of interacting with a pair of the cat-
ions (as in 2a and 2b), each picrate ion in 2c binds to a sin-
gle aminoalcohol moiety by two three-centre hydrogen
a
b
A
B
O3
E
O8
O2
G
C11’
C12’
O1’
N1’
C13’
F
H
c
C
D
a
0,b
Fig. 8. (a) View of the hydrogen-bonded chains in the structure of 2c. The ferrocenyl moieties are omitted for clarity. (b) A projection of the unit cell onto
the ac plane. The hydrogen bonds are indicated with dashed lines. Symmetry operations: A (x, y, z); B (x, 1 + y, z); C (2 ꢂ x, ꢂ1/2 + y, 2 ꢂ z); D (2 ꢂ x, 1/
2 + y, 2 ꢂ z); E (1 ꢂ x, ꢂ1/2 + y, 2 ꢂ z); F (1 + x, y, z); G (1 ꢂ x, 1/2 + y, 2 ꢂ z); H (1 + x, 1 + y, z).

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1784
bonds involving the phenoxide O2 and one oxygen atom
from both adjacent NO2 groups as the acceptors, and the
OH and NH protons as the donors. The formed ion pairs
associate linearly into infinite angular chains along the
crystallographic 21 screw axes by means of hydrogen bond
between the second NH proton and the hydroxyl oxygen
from an adjacent molecule (see Table 2 for hydrogen bond
parameters). Contrary to the previous cases, the structure
lacks any significant pꢀ ꢀ ꢀp interactions, the cross-linking
of the hydrogen-bonded chains being achieved through
the relatively softer C–Hꢀ ꢀ ꢀO interactions (Fig. 8b).
were measured with an automatic polarimeter Autopol
III (Rudolph Research) at room temperature. Positive
ion electron impact (EI+) mass spectra including the high
resolution (HR) measurements were performed with a
ZAB EQ spectrometer (VG Analytical). Melting points
were determined on a Kofler block.
The measurements of SHG efficiency were performed
using the Kurtz powder method [18] at 800 nm with pulse
Ti-sapphire laser (Tsunami, Spectra Physics; 90 fs pulse
width, 82 MHz repetition rate). For quantitative determi-
nation of the SHG efficiency, the intensity of the back-scat-
tered laser light at 400 nm was measured by a grating
spectrograph with a diode array (InstaSpec II, Oriel) and
its intensity was compared with that of a urea standard.
To minimise the influence of preferential orientation, the
experiments were performed on powdered samples (75–
125 lm particle size) loaded into a 5 mm glass cell with
the aid of a vibrator, and the measurements were repeated
on different areas of the sample.
3. Conclusions
In summary, the reaction of ferrocene aminoalcohols
1a–c with picric acid affords well defined and reasonably
stable crystalline picrates 2a–c. The chief force towards
intermolecular association of these salts are N–Hꢀ ꢀ ꢀO(pic)
and O–Hꢀ ꢀ ꢀO(pic) hydrogen bonds that are supported by
C–Hꢀ ꢀ ꢀO contacts and by offset pꢀ ꢀ ꢀp stacking interactions
of the parallel benzene rings. Whereas the former interac-
tions are typically responsible for the formation of closed
centrosymmetric assemblies or at least the basic repeating
unit such in 2c, the latter represent the means for a further
supramolecular aggregation. The formed structures are
rather compact, showing similar space filling efficiencies
(70.6% for 2b, 70.5% for 2b, and 68.7 for 2c). The density
of the picrates parallels the trend in space filling, being low-
est for the chiral representative, whose structure lacks the
cyclic aggregates.
Safety Note. CAUTION! Although we have not encoun-
tered any problems it should be noted that picrates are
potentially explosive and should be handled with care.
4.2. Syntheses
The aminoalcohols have been prepared by reduction of
the (non-isolated) intermediate imines resulting from con-
densation of ferrocenecarboxaldehyde with the respective
aminoalcohol. The preparation of 1a [11] and 1b [10] was
reported elsewhere; compound 1c was synthesised as
follows.
A closer look at the structures reveals that the phenox-
ide oxygen atom O2 always points towards the twisted ami-
noalcohol chain and forms the shortest hydrogen bonds
with the NH and OH protons. This indicates that electro-
static interactions play significant role in stabilisation of
the supramolecular arrays (e.g., via charge-support to the
hydrogen bonding interactions). Furthermore, it is evident
that the excess of the potential hydrogen bond donors in
the structures of 2a–c leads to preferential formation of
three-centre hydrogen bonds with bifurcated donors that
in turn give rise to structure-stabilising cyclic (chelate)
subunits.
4.2.1. Preparation of (S)-2-[(ferrocenylmethyl)amino]-3-
methyl-butan-1-ol (1c)
Ferrocenecarboxaldehyde (428 mg, 2.0 mmol) and (S)-
valinol (217 mg, 2.1 mmol) were dissolved in dry chloro-
form (20 mL; dried over K2CO3) and the resulting solution
was heated at reflux under argon for 90 min. Then, the
solution was cooled to room temperature, the solvent was
removed under vacuum and the red–brown residue imme-
diately re-dissolved in dry methanol (20 mL; distilled from
a MeONa solution). The methanolic solution was cooled in
an ice bath and treated slowly with solid NaBH4 (378 mg,
10 mmol over 30 min). After the addition was complete,
the mixture was stirred at 0 °C for 1 h and at room temper-
ature for 90 min. Then, it was quenched by addition of 10%
aqueous NaOH (20 mL) and extracted with dichlorometh-
ane (2 ꢁ 20 mL). The combined organic layer was washed
with brine (2 ꢁ 20 mL), dried over magnesium sulphate,
and evaporated, leaving the crude product as a yellow–
brown solid. Subsequent purification by column chroma-
tography (silica gel, dichloromethane–methanol 10:1) led
to the development of two bands: the first (minor) one con-
taining mostly ferrocenylmethanol, followed by the major
band of the aminoalcohol. Careful evaporation of the sec-
ond fraction afforded pure 1c as an amber oil, which slowly
solidifies to a brown solid. Yield: 457 mg (76%).
4. Experimental
4.1. Methods
NMR spectra were measured on a Varian UNITY Inova
400 spectrometer at 298 K. Chemical shifts (d/ppm) are
given relative to internal tetramethylsilane. IR spectra were
recorded on an FT-IR Nicolet Magna 760 instrument in
the range of 400–4000 cmꢂ1. UV–Vis spectra were recorded
with Unicam UV300 (solution) and on a Perkin–Elmer
Lambda 35 spectrometers (solid state). The samples were
dissolved in methanol or powdered and diluted with bar-
ium sulphate (Merck, white standard). Optical rotations

ˇ
P. Steˇpnicˇka et al. / Journal of Organometallic Chemistry 693 (2008) 1779–1786
1785
1
[aD]23 °C + 20.4° (c = 1.0, CHCl3). H NMR (400 MHz,
0.18 ꢁ 0.28 ꢁ 0.37 mm3; 2c: red prism, 0.23 ꢁ 0.23 ꢁ
0.30 mm3; and 2c: red bar, 0.10 ꢁ 0.27 ꢁ 0.60 mm3). Full-
3
CDCl3): d 0.91, 0.97 (2 ꢁ d, JHH = 6.8 Hz, 3H, CH2Me);
3
1.84 (octet, JHH = 6.8 Hz, 1 H, CHMe2), 2.47 (dt,
set diffraction data ( h
k
l, 2h 6 55°) were collected
3JHH = 4.2, 6.7 Hz, 1H, CHNH), 2.71 (br s, 2H, NH a
on a Nonius KappaCCD diffractometer equipped with
Cryostream Cooler (Oxford Cryosystems). The measure-
ments were performed using graphite-monochromatised
2
3
OH), 3.38 (dd, JHH = 10.7, JHH = 6.9 Hz, 1H, CH2OH),
3.52 and 3.56 (2 ꢁ d, 2JH = 12.9 Hz, 1H, AB system of
2
3
˚
FcCH2); 3.63 (dd, JHH = 10.7, JHH = 4.2 Hz, 1H,
CH2OH), 4.12 (m, 2H, C5H4), 4.13 (s, 5H, C5H5), 4.20 (vir-
tual t, 2H, C5H4). 13C{1H} NMR (100 MHz, CDCl3): d
18.52, 19.65 (CHMe2); 28.86 (CHMe2), 46.34 (FcCH2),
60.28 (CH2OH), 63.96 (CHNH), 67.80, 67.92, 68.09,
68.25 (CH of C5H4); 68.40 (C5H5), 86.51 (Cipso of C5H4).
IR (neat): m/cmꢂ1 3311 s, 3277 s, 3092 br, 2957 vs, 2932
m 2870 vs, 2825 vs, 2118 m, ca. 1550–1790 br m, 1466 s,
1438 s, 1385 s, 1361 m, 1332 w, 1308 w, 1234 m, 1196 m,
1104 vs, 1083 m, 1050 s, 1040 s, 998 vs, 976 s, 923 m, 914
m, 907 m, 857 s, 829 s, 816 vs, 809 vs, 752 w, 693 br w,
562 w, 537 w, 490 vs, 478 vs, 427 m. EI MS: m/z (relative
abundance) 302 (7), 301 (33, M+.), 299 (2), 215 (1), 200
(16), 199 (100, [FcCH2]+), 197 (6), 186 (2, FcH+), 165
(3), 147 (4), 135 (4), 121 (30, [C5H5Fe]+), 56 (13, Fe+).
Anal. Calc. for C16H23FeNO (301.2): C, 63.80; H, 7.70;
N, 4.65. Found: C, 63.26; H, 7.84; N, 4.42%.
Mo Ka radiation (k = 0.71073 A). Details on the data col-
lection, structure solution and refinement are given in
Table 3.
The structures were solved by direct methods (SIR-97
[19]) and refined by full-matrix least-squares routines on
F2 (SHELXL97 [20]). The non-hydrogen atoms were refined
with anisotropic displacement parameters. The nitrogen-
bonded (H1N and H2N) and hydroxyl (H1O) hydrogens
were located on the difference electron density maps and
refined as riding atoms with unconstrained isotropic dis-
placement parameters. All other hydrogen atoms were
included in the calculated positions and refined as riding
atoms.
Final geometric calculations were performed with a
recent version of PLATON program [21]. The numerical val-
ues were rounded with respect to their estimated standard
deviations (ESDs) given with one decimal; parameters
involving fixed hydrogen atoms are given without ESDs.
4.2.2. General procedure for the preparation of the picrates
Picric acid (23 mg, 0.10 mmol) was dissolved in a mini-
mum volume (ca. 1 mL) of ethyl acetate and the solution
was added to a concentrated solution of the respective
aminoalcohol 1 in the same solvent (0.10 mmol in ca.
1.5–2.5 mL). The resulting solution was carefully layered
with hexane (ca. 8 mL) and the mixture was allowed to
crystallise at +4 °C by diffusion for several days. The dark
red, crystalline picrates were isolated by suction, washed
with hexane and dried under reduced pressure.
Table 3
Crystallographic data, structure solution and refinement parameters for
2a–ca
Compound
2a
2b
2c
Formula
M (g molꢂ1
C19H20FeN4O8 C21H24FeN4O8 C22H26FeN4O8
488.24
Triclinic
)
516.29
530.32
Monoclinic
Crystal system
Space group
Monoclinic
P21/c (no. 14) P21 (no. 4)e
12.4417(2)
14.4118(2)
13.2273(2)
ꢀ
P1 (no. 2)
˚
a (A)
8.1689(2)
11.4123(3)
11.4843(3)
98.048(2)
103.220(2)
96.624(2)
1019.86(5)
2
10.7161(2)
10.9226(2)
10.6942(2)
(Ferrocenylmethyl)(2-hydroxyethyl)ammonium
picrate
˚
b (A)
(2a) was obtained from 1a (26 mg) and picric acid
(23 mg). Yield: 45.5 mg (93%). M.p. 163–164 °C (melting
with dec.). Anal. Calc. for C19H20O8N4Fe (488.24): C,
46.74; H, 4.13; N, 11.48. Found: C, 46.77; H, 3.99; N,
11.37%.
(Ferrocenylmethyl)[2,2-dimethyl-2-hydroxyethyl]ammo-
nium picrate (2b) was obtained from 1b (29 mg) and picric
acid (23 mg). Yield: 17 mg (33%). M.p. 159–161 °C (dec.).
Anal. Calc. for C21H24O8N4Fe (516.29): C, 48.85; H,
4.69; N, 10.85. Found: C, 48.82; H, 4.64; N, 10.71%.
(S)-(Ferrocenylmethyl)[2-(1-methylethyl)-2-hydroxyethyl]-
ammonium picrate (2c) was prepared similarly from 1c
(30 mg) and picric acid (23 mg). Yield: 47.5 mg (90%). M.p.
148–150 °C (melting), ca. 155 °C (dec.). [aD]23 °C ꢂ10°
(c = 1.0, MeOH). Anal. Calc. for C22H26O8N4Fe (530.32):
C, 49.82; H, 4.94; N, 10.57. Found: C, 50.46; H, 5.14; N,
10.08%.
˚
c (A)
a (°)
b (°)
c (°)
110.842(1)
108.807(1)
3
˚
V (A )
2216.55(6)
4
1.547
0.737
41444
1184.90(4)
2
1.486
0.692
20664
Z
Dcalc (g mLꢂ1
)
1.590
0.796
15849
l (Mo Ka) (mmꢂ1
Diffractions
collected
)
Independent/
observedb
4662/4275
5067/4152
5393/5036
diffractions
Rcint (%)
2.7
2.98
4.2
3.49
4.0
2.78
Rc observed
diffractions (%)
R, wRc all data (%)
3.33, 7.37
0.32, ꢂ0.52
4.69, 9.20
1.15,d ꢂ0.44
3.29, 6.28
0.31, ꢂ0.26
ꢂ3
˚
Dq (e A
)
a
Common details: T = 150(2) K.
Diffractions with I > 2r(I).
Definitions: Rint
b
c
P
P
2
=
|Fo ꢂ Fo2(mean)|/ Fo2, where Fo2(mean) is the
P
4.3. X-ray crystallography
average intensity of symmetry-equivalent diffractions. R = ||Fo| ꢂ |Fc||/
P
P
P
|Fo|, wR = [ {w(Fo ꢂ Fc2)2}/ w(Fo2)2]1/2
.
2
d
Crystals suitable for X-ray diffraction studies were
selected directly from the reaction batch (2a: red prism,
Residual electron density in vicinity of the iron atom.
e
Flack’s enantiomorph parameter: ꢂ0.01(1).

ˇ
P. Steˇpnicˇka et al. / Journal of Organometallic Chemistry 693 (2008) 1779–1786
1786
(b) I.S. Lee, D.M. Shin, Y.K. Chung, Cryst. Growth Des. 3 (2003) 521;
(c) D. Braga, M. Polito, M. Bracaccini, D. D’Addario, E. Tagliavini,
L. Sturba, Organometallics 22 (2003) 2142;
(d) D. Braga, M. Polito, D. D’Addario, E. Tagliavini, D.M. Proserpio,
F. Grepioni, J.W. Steed, Organometallics 22 (2003) 4532;
(e) R. Horikoshi, C. Nambu, T. Mochida, New J. Chem. 28 (2004) 26;
(f) T. Mochida, K. Okazawa, R. Horikoshi, Dalton Trans. (2006) 693;
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3364;
Acknowledgement
This work is as a part of the long-term research project
supported by the Ministry of Education of the Czech
Republic (No. MSM0021620857). The authors thank Ing.
K. Lang for recording the UV–Vis spectrum of solid 2c
and Ms. A. Jenisˇova for an assistance during the prepara-
tion of 1c.
´
(h) T. Mochida, F. Shimizu, H. Shimizu, K. Okazawa, F. Sato, D.
Kuwahura, J. Organomet. Chem. 692 (2007) 1834.
Appendix A. Supplementary material
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