Ionic metallomesogens derived from silver(I) bis-amine complexes: Structure and mesogenic behavior

Article abstract of DOI:10.1016/j.ica.2007.11.033

Complexes [Ag(NH₂R)₂]X, (X = NO₃, R = -C₆H₄-C_nH_2n+1-p, -C₆H₄-O-C_nH_2n+1-p, -CH₂-C₆H₄-O-C_nH_2n+1-p, n = 6, 8, 10, 12, 14; X = BF₄, R = -CH₂-C₆H₄-O-C_nH_2n+1-p, n = 6, 8, 10, 12, 14; X = OAc, R = -CH₂-C₆H₄-O-C₁₀H₂₁-p; X = CF₃SO₃, R = -CH₂-C₆H₄-O-C₁₀H₂₁-p) have been prepared. They all show S_A mesophases corresponding to two kinds of structures, already present in the solid state. The alkylaniline and alkoxyaniline derivatives adopt a bilayered structure where the cation has an extended centrosymmetric conformation. The benzylamine derivatives contain U-shaped cations giving rise to a bilayered structure which allows microsegregation of the organic part of the molecule from the inorganic Ag?(anion) part. Some degree of interdigitation of the terminal chains is observed for all the complexes with aryl containing ligands.

Full text of DOI:10.1016/j.ica.2007.11.033

Available online at www.sciencedirect.com
Inorganica Chimica Acta 361 (2008) 2270–2278
www.elsevier.com/locate/ica
Ionic metallomesogens derived from silver(I) bis-amine
complexes: Structure and mesogenic behavior
1
2
,1
*
´
´
´
Marıa del Carmen Lequerica , Marıa Jesus Baena , Pablo Espinet
IU CINQUIMA/Quı´mica Inorga´nica, Facultad de Ciencias, Universidad de Valladolid, E-47071 Valladolid, Spain
Received 20 September 2007; received in revised form 23 November 2007; accepted 23 November 2007
Available online 14 May 2008
Abstract
Complexes [Ag(NH2R)2]X, (X = NO3, R = –C6H4–CnH2n+1-p, –C6H4–O–CnH2n+1-p, –CH2–C6H4–O–CnH2n+1-p, n = 6, 8, 10, 12, 14;
X = BF4, R = –CH2–C6H4–O–CnH2n+1-p, n = 6, 8, 10, 12, 14; X = OAc, R = –CH2-C6H4–O–C10H21-p; X = CF3SO3, R = –CH2–
C6H4–O–C10H21-p) have been prepared. They all show SA mesophases corresponding to two kinds of structures, already present in
the solid state. The alkylaniline and alkoxyaniline derivatives adopt a bilayered structure where the cation has an extended centrosym-
metric conformation. The benzylamine derivatives contain U-shaped cations giving rise to a bilayered structure which allows microseg-
regation of the organic part of the molecule from the inorganic Agꢀ ꢀ ꢀ(anion) part. Some degree of interdigitation of the terminal chains is
observed for all the complexes with aryl containing ligands.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Liquid crystals; Metallomesogens; Bilayered mesophases; Silver complexes; Amine complexes
1. Introduction
n-alkylamines, [Ag(NH2–CnH2n+1-n)2]X, (X = NO3, BF4,
OAc) that are a very much related to this paper [7]. The
compounds displayed a thermotropic lamellar mesophase
corresponding to a bilayered arrangement of U-shaped
[Ag(NH2–CnH2n+1-n)2]+ cations sandwiching a layer of
anions. This kind of structure is reminiscent of that of
the biomembranes and can be found in other mesogenic
ionic systems [8]. In this work, we extend our study to silver
primary amine complexes with a rigid part in the amine
ligand (anilines and benzylamines) and alkyl or alkoxy ter-
minal chains (series 1–4). Complexes with different anions
were prepared for the benzylamine series (compounds 5
and 6) in order to test the anion influence on the properties
of the material. The complexes are labeled according to the
series they pertain and the length of the alkyl chain, as
follows:
Ionic mesogens are among the first liquid crystals sys-
tematically studied [1]. They combine the inherent proper-
ties of liquid crystals and those of the ionic compounds,
and have been used as ordered solvents, as catalysts and
templates for synthesis, as optical and ferroelectric systems,
as electronic or ionic conductors, and as membranes [2].
The term ‘‘ionic metallomesogens” refers to mesogens
based on ionic molecules bearing a transition metal. Exam-
ples can be found in several reviews [2b,3]. In general,
much attention has been paid to complexes with heterocy-
clic N-donor ligands, such as mono and poly-substituted
stilbazole silver complexes [4], pyridine carboxylates and
pyridine imine silver complexes [5].
Previously we have published studies on ionic metallo-
mesogens,[6] including silver amino complexes with
Series 1: [Ag(NH2–C6H4–CnH2n+1-p)2](NO3)
n = 6, 8, 10, 12, 14
*
Corresponding author. Tel./fax: +34 983 423 231.
Series 2: [Ag(NH2–C6H4–O–CnH2n+1-p)2](NO3)
n = 6, 8, 10, 12, 14
E-mail address: espinet@qi.uva.es (P. Espinet).
Facultad de Ciencias.
E. T. S. de Ingenieros Industriales.
1
2
0020-1693/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.11.033

M.del Carmen Lequerica et al. / Inorganica Chimica Acta 361 (2008) 2270–2278
2271
Series 3: [Ag(NH2–CH2–C6H4–O–CnH2n+1p)2](NO3)
2.3.1. Preparation of 4-n-alkoxybenzylamines H2n+1CnO–
C6H4–CH2NH2 (n = 6–14)
n = 6, 8, 10, 12, 14
Series 4: [Ag(NH2–CH2–C6H4–O–CnH2n+1-p)2](BF4)
n = 6, 8, 10, 12, 14
Compound 5: [Ag(NH2–CH2–C6H4–O–C10H21-p)2](OAc)
Compound 6: [Ag(NH2–CH2–C6H4–O–C10H21-p)2]
(CF3SO3)
To a suspension of 0.66 g (17.4 mmol) of LiAlH4 in
40 mL of dry diethylether under nitrogen atmosphere was
added dropwise a solution of 4.5 g (17.4 mmol) of the
corresponding 4-n-alkoxybenzonitrile in 20 mL of diethyl-
ether. The mixture was stirred for 1/2 h. Then, the flask
was cooled in an ice bath and water was added slowly to
destroy the excess of LiAlH4, followed by 15 mL of
H2SO4 6 N. The mixture was cleaned with 4 ꢁ 15 mL of
diethylether, the aqueous solution was cooled to 5 °C and
NaOH pellets were slowly added until ca. pH 11. The basic
solution was diluted with water (10 mL) and extracted with
diethylether (4 ꢁ 15 mL). The organic phases were collected
together, dried over anhydrous magnesium sulfate, filtered
off and evaporated to dryness. The amine was purified by
column chromatography with silica as stationary phase
and a mixture of CHCl3/EtOH (10:1) as eluent. Yield:
65–70%. Elemental Anal. Calc. for n = 6: C, 73.32; H,
10.21; N, 6.76. Found: C, 73.58; H, 9.90; N, 6.51%. Anal.
Calc. for n = 8: C, 76.55; H, 10.71; N, 5.95. Found: C,
76.90; H, 10.24; N, 5.72%. Anal. Calc. for n = 10: C,
77.51; H, 11.10; N, 5.32. Found: C, 77.78; H, 11.41; N,
4.81%. Anal. Calc. for n = 12: C, 78.29; H, 11.41; N, 4.81.
Found: C, 78.01; H, 10.93; N, 4.57%. Anal. Calc. for
n = 14: C, 78.94; H, 11.67; N, 4.38. Found: C, 78.54; H,
11.22; N, 4.10%. Spectroscopic data are for n = 10: mmax
(KBr)/cmꢂ1: 3280br. dH (300 MHz; CDCl3; Me4Si): 7.21
(2H), 6.86 (2H, AA0XX0 spin system, J 8.7, aromatic hydro-
gens) 3.94 (2H, t, J 6.6, –O–CH2-) 3.79 (2H, s, –Ph–CH2–
N); 1.51 (2H, br s –NH2) 1.81–0.86 (m, alkyl chain).
2. Experimental
2.1. General
Experimental procedures, analytical and spectroscopic
determinations, and optical and thermal mesophase stud-
ies, were as reported in reference 7. A Phillips Analytical
diffractometer equipped with a PW1710 generator was used
for the X-ray powder diffraction in solid state, using mono-
˚
chromatic Cu Ka radiation (k = 1.54 A). The samples were
held on a rectangular 20 ꢁ 15 mm aluminium sample
holder. The X-ray scanned from 3° to 70° 2h. XRD mea-
surements in the mesophase were carried out with a Philips
X’Pert PRO MPD X-ray diffractometer in th-th configura-
tion equipped with a PW3373 generator and a high temper-
ature chamber (Anton Paar HTK1200). Monochromatic
˚
Cu Ka radiation (k = 1.54 A) was used, and the samples
were held on circular 18 mm diameter and 0.4 mm depth
alumina sample holder coated with aluminium foil. Three
diffractograms were taken for each sample: the first at
25 °C in the solid state, the second 10 °C over the melting
point and the third 10 °C under the clearing point. The
X-ray area scanned from 2° to 50° 2h. Solvents were dried
and distilled prior to use. The silver salts and the 4-n-alky-
lanilines were obtained from commercial sources and used
without further purification.
2.3.2. Preparation of [Ag(NH2–C6H4-n-CnH2n+1)2](NO3)
To a solution of AgNO3 (0.255 g, 1.5 mmol) in aceto-
nitrile (ca. 15 mL), shielded from light, was added the
corresponding amine (3 mmol) and the mixture was stir-
red at room temperature for 4 h. The resulting solution
(n = 6, 8, 10) or white suspension (n = 12, 14) was con-
centrated under vacuum and cooled overnight in the free-
zer. The crystallized white product was collected by
filtration, washed with diethyl ether and dried under vac-
uum. The products were further purified by recrystalliza-
tion from acetonitrile/diethyl ether. Yields: 52–87%.
Elemental Anal. Calc. for n = 6: C, 54.97; H, 7.30; N,
8.01. Found: C, 54.95; H, 7.28; N, 8.05%. Anal. Calc.
for n = 8: C, 57.93; H, 7.99; N, 7.24. Found: C, 57.90;
H, 7.95; N, 7.25%. Anal. Calc. for n = 10: C, 60.37; H,
8.55; N, 6.60. Found: C, 60.32; H, 8.58; N, 6.68%. Anal.
Calc. for n = 12: C, 62.42; H, 9.02; N, 6.07. Found: C,
62.39; H, 8.76; N, 6.09%. Anal. Calc. for n = 14: C,
64.16; H, 9.42; N, 5.61. Found: C, 64.06; H, 9.50; N
5.64%. Spectroscopic data are for n = 10: mmax(KBr)/
cmꢂ1: 3421br m, 1618m, 1517s, 1384br s. dH (300 MHz;
CDCl3; Me4Si): 6.93 (4H), 6.81 (4H, AA0XX0 spin sys-
tem, J 8.3, aromatic hydrogens) 4.40 (4H, v br s, –
NH2); 2.43 (4H, t, J 7.7, –Ph–CH2–) 1.51–0.89 (m, alkyl
chain).
2.2. Computational methods
Calculations were carried out at the HF level of theory
as implemented in the GAUSSIAN 98.11 program [9]. Due
to the existence of an Ag atom a quasi-relativistic pseudo-
potential (LANL2DZ, Los Alamos potential) was used
where the basis functions for the valence s and p electrons
consist of the standard double-z basis set (notation HF/
LANL2DZ). Schematic representations of the structures
were obtained and analyzed by using the Spartan 4:1 pro-
gram [10].
2.3. Preparation of ligands and complexes
Literature procedures were used to synthesize 4-n-
alkoxyanilines [11], 4-n-alkoxybenzonitriles[12] and 4-n-
alkoxybenzylamines [13], although in this last case a
small variation on the method was introduced as speci-
fied below.

2272
M.del Carmen Lequerica et al. / Inorganica Chimica Acta 361 (2008) 2270–2278
2.3.3. Preparation of [Ag(NH2–C6H4–O-n-CnH2n+1)2]-
(NO3)
56.55; H, 7.87; N, 4.09%. Anal. Calc. for n = 12: C,
58.69; H, 8.55; N, 3.60. Found: C, 58.60; H, 8.13; N,
3.71. Anal. Calc. for n = 14: C, 60.50; H, 8.95; N, 3.36.
Found: C, 60.62; H, 8.74; N, 3.50%. Spectroscopic data
are for n = 10: mmax (KBr)/cmꢂ1: 3347m, 3300m, 1251s,
1036br. dH (300 MHz; CDCl3; Me4Si): 7.17 (4H), 6.84
(4H, AA0XX0 spin system, J 8.5, aromatic hydrogens),
3.91 (4H, t, J 6.6 Hz, –O–CH2–), 3.78 (4H, s, –Ph–CH2–
N), 2.91 (4H, br s, –NH2), 1.81–0.86 (m, alkyl chain).
The synthetic method is the same as for the alkylaniline
complexes above. For n = 6–10 a small amount of precip-
itate was formed during the reaction, which was removed.
Times of reaction were shorter (2 h) than for the alkyl ani-
line complexes in order to reduce decomposition. Yields:
40–70%. Elemental Anal. Calc. for n = 6: C 51.80, H
6.88, N 7.55. Found: C 51.90, H 6.69, N 7.56%. Anal. Calc.
for n = 8: C, 54.90; H, 7.55; N, 6.86. Found: C, 55.09; H,
7.48; N, 6.94%. Anal. Calc. for n = 10: C, 57.48; H, 8.14;
N, 6.28. Found: C, 57.31; H, 7.95; N, 6.31%. Anal. Calc.
for n = 12: C, 59.66; H, 8.62; N, 5.80. Found: C, 59.60;
H, 8.67; N, 5.80%. Anal. Calc. for n = 14: C, 61.53; H,
9.04; N, 5.38. Found: C, 61.70; H, 8.85; N, 5.31%. Spectro-
scopic data are for n = 10: mmax (KBr)/cmꢂ1: 3346m,
3282m, 1514s, 1364br s, 1243s. dH (300 MHz; CDCl3;
Me4Si): 6.85 (4H), 6.76 (4H, AA0XX0 spin system, J 8.8,
aromatic hydrogens), 3.88 (4H, t, J 6.6, –O–CH2–), 2.96
(4H, v br s, –NH2), 1.77–0.89 (m, alkyl chain).
2.3.6. Preparation of [Ag(NH2-CH2-C6H4–O-n-C10H21)2]-
(OAc)
The synthetic method was the same as for the BF4 com-
plex above described. Yield: 47%. Elemental Anal. Calc.: C,
62.33; H, 8.86; N, 4.03. Found: C, 62.48; H, 8.77; N, 4.07%.
mmax (KBr)/cmꢂ1
: 3448br, 1578s, 1513s, 1249s. dH
(300 MHz; CDCl3; Me4Si): 7.21 (4H), 6.86 (4H, AA0XX0
spin system, J 8.6, aromatic hydrogens), 3.94 (4H, t, J
6.5, –O–CH2–); 3.79 (4H, s, –Ph–CH2–N), 2.98 (4H, br s,
–NH2); 1.99 (3H, s, OOC-CH3), 1.80–0.95 (m, alkyl chain).
2.3.4. Preparation of [Ag(NH2-CH2–C6H4–O-n-Cn-
2n+1)2](NO3)
2.3.7. Preparation of [Ag(NH2–CH2–C6H4–O-n-C10H21)2]-
(CF3SO3)
H
To a suspension of the 4-n-alkoxybenzylamine (3 mmol)
The synthetic method was the same as above. Yield:
17%. Elemental Anal. Calc.: C, 53.63; H, 7.46; N, 3.57.
in 10 mL of acetonitrile was added a solution of AgNO3
(0.255 g, 1.5 mmol) in acetonitrile. After stirring for 4 h
shielded from light, the resulting suspension was concen-
trated (n = 6, 8) and then filtered off. The white solid was
washed with diethyl ether. Yields: 80–85 %. Elemental
analysis (%): Found: C 53.55, H 7.11, N 7.20; calc. for
n = 6: C 53.42, H 7.24, N 7.19. Found: C 56.26, H 7.53,
N 6.11; calc. for n = 8: C 56.24, H 7.87, N 6.56. Found:
C 58.63, H 8.06, N 6.17; calc. for n = 10: C 58.61, H
8.39, N 6.03. Found: C 60.32, H 8.49, N 5.69; calc. for
n = 12: C 60.62, H 8.84, N 5.58. Found: C 62.23, H 8.80,
N 5.12; calc. for n = 14: C 62.36, H 9.22, N 5.19. Spectro-
scopic data are for n = 10: mmax(KBr)/cmꢂ1: 3301m,
3247m, 1513s, 1368br s, 1250s, 1612m, 1584m. dH (300
MHz; CDCl3; Me4Si): 7.18 (4H), 6.83 (4H, AA0XX0 spin
system, J 8.6, aromatic hydrogens), 3.89 (4H, t, J 6.6, -O-
CH2-), 3.77 (4H, s, –Ph–CH2–N), 3.31 (4H, br s, –NH2),
1.78–0.89 (m, alkyl chain).
Found: C, 53.50; H, 7.22; N, 3.61%. mmax(KBr)/cmꢂ1
:
3301m, 3247m, 1513m, 1251vs, 1032s. dH (300 MHz;
CDCl3; Me4Si): 7.17 (4H), 6.84 (4H, AA0XX0 spin system,
J 8.6, aromatic hydrogens), 3.91 (4H, t, J 6.6, –O–CH2–),
3.79 (4H, s, –Ph–CH2–N), 3.03 (4H, br s, –NH2), 1.81-
0.86 (m, alkyl chain).
3. Results and discussion
3.1. Syntheses
The complexes were prepared by stoichiometric reaction
(1:2) of the silver salt AgX, (X = NO3, BF4, OAc, CF3SO3)
with the correspondent amine, in acetonitrile. The products
were isolated as white microcrystalline solids. They are
light sensitive in long and heavy exposures.
3.2. Mesogenic behavior
2.3.5. Preparation of [Ag(NH2-CH2-C6H4-O-n-CnH2n+1)2]
BF4
Optical microscopy with polarized light revealed that all
the complexes exhibit only a typical lamellar SA phase after
melting, characterized by focal conic, mielinic and homeo-
tropic textures [14]. Often (mostly in the benzylamine series
and for high clearing points) the persistence of the homeo-
tropic texture is large, and it has to be characterized by
rubbing the sample. The SA mesophase for the p-alkyl (1)
and p-alkoxyaniline (2) complexes is very viscous, and
traces of decomposition are observed at the melting point,
becoming more severe at the clearing point. Decomposition
after melting was heavier in alkoxyaniline than in alkylan-
iline complexes and a deep red coloration was observed,
probably due to the formation of oxidation products of
To a suspension of 4-n-decyloxybenzylamine (0.51 g,
1.94 mmol) in 10 mL of acetonitrile, shielded from light,
was added a solution of AgBF4 (0.97 mmol) in ca. 3 mL
of acetonitrile. A white precipitate was formed and after
30 min stirring CH2Cl2 was added to dissolve the precipi-
tate. The solution was filtered, concentrated, and then crys-
tallized by cooling in the freezer. The white solid collected
was washed with diethyl ether. Yields: 70–92 %. Elemental
Anal. Calc. for n = 6: C, 51.25; H, 6.95; N, 4.60. Found: C,
51.15; H, 6.74; N, 4.59%. Anal. Calc. for n = 8: C, 54.15; H,
7.57; N, 4.21. Found: C, 54.08; H, 7.32; N, 4.12%. Anal.
Calc. for n = 10: C, 56.60; H, 8.10; N, 3.88. Found: C,

M.del Carmen Lequerica et al. / Inorganica Chimica Acta 361 (2008) 2270–2278
2273
Table 1
the alkoxyaniline. Thus, for series 2, we cannot assign the
Thermal parameters for the silver amino complexes prepared
data of the SA mesophase observed as pertaining to the
starting complex, since they must be significantly altered
by the mixture with appreciable amounts of the decompo-
sition product. The p-alkoxybenzylamine complexes (series
3 and 4) are far more thermally stable than aniline deriva-
tives. Slight decomposition is observed only at the clearing
point.
The phase transition temperatures and transition enthal-
pies, measured by differential scanning calorimetry (DSC),
are collected in Table 1. Transition temperatures are plot-
ted in Fig. 1 for easy comparison.
In general, the mesogenic behavior of the silver aniline
or benzylamine complexes is similar for the four series to
that found previously for aliphatic amine derivatives: only
a SA mesophase and melting points increasing with the
length of the chain, higher for series 1–4 than for the com-
plexes with aliphatic amines, due to the presence of aro-
matic and dipolar interactions. The tetrafluoroborate
complexes (series 4) show much lower melting tempera-
tures and shorter ranges of mesophase than the nitrate
homologous (series 3). For complex 4.6 the mesophase is
monotropic.
Compound
n
Transition
T (°C)
DH (kJ molꢂ1
)
1a
6
8
C–C0
62.2
88.5
140
90.0
135
2.5
20.2
–
34.5
–
C0– SA
SA–Idec.
C–SA
b
SA–Idec.
10
12
14
6
C–SA
SA–Idec.
C–SA
SA–Idec.
C–SA
SA–Idec.
C–SA
SA–Idec.
C–SA
SA–Idec.
C–SA
SA–Idec.
95.4
135
101.0
127
102.1
119
70.2
144
82.9
135
87.5
124
98.8
130
91.6
99.6
115
80.0
83.7
115.2
78.3
129.1
89.1
137.1
94.8
135.4
99.7
133.5
(53.7)
43.4
70.7
95.1
80.9
112.6
55.2
59.5
83.5
112.3
89.1
116.1
39.6
76.7
30.9
38.7
15.7
40.6
–
57.9
–
69.4
–
26.2
–
43.8
–
57.3
–
71.7
–
b
b
b
2c
3d
4d
b
8
b
10
12
14
b
C–SA
b
SA–Idec.
C–C0
C0–SA
87.5e
–
b
SA–Idec.
6
C–C0
C0– SA
SA–I
C–SA
SA–I
C–SA
SA–I
C–SA
SA–I
C–SA
SA–I
C–I
33.8e
2.2
41.7
1.7
59.7
1.2
68.7
1.1
82.1
0.8
(30.5)
ꢂ1.6
38.0
1.3
55.5
1.2
4.0
Fig. 2 compares the thermal behavior of complexes hav-
ing the same cation, [Agꢂ(C10H21–O–C6H4–CH2–NH2)2]+
8
10
12
14
6
and differentꢂanions NO3 (3.10), BF4 (4.10), OAcꢂ (5)
ꢂ
and CF3SO3 (6) (see also Table 1). The nature, shape
and volume of the anions should influence the ionic pack-
ing and the electrostatic attractive forces between ions.
Consistent with the results found for n-alkylamines, the
planar nitrates seem to allow for stronger interactions with
the cations than the tetrahedral BF4ꢂ ions, both in the solid
state and in the melt. In addition, covalent Ag–O interac-
tions in the nitrates migh reinforce the lattice stability
[8b,15]. The planar but bulkier and less symmetric OAcꢂ
makes the interionic forces weaker, leading to a marked
reductioꢂn in both melting and clearing points. The bulkiest
CF3SO3 is not able to stabilize the mesophase after melt-
ing, although the hysteresis produced in the cooling process
leads to the formation of a mesophase before crystalliza-
tion occurs, observed in DSC. This monotropic mesophase
extends over a range of 35 °C and was assigned a SA struc-
ture according to the enthalpy change.
I–SA
C–SA
SA–I
C–SA
SA–I
C–C0
C0–C00
C00–SA
SA–I
C–SA
SA–I
C–SA
SA–I
C–C0
C0–I
8
10
12
0.8
52.3
0.9
72.7
0.7
54.6
2.4
14
10
10
5d
6d
47.3e
ꢂ1.4
I–SA
3.3. X-ray diffraction studies
a
Melting temperatures for the first heating.
Data from the microscope.
Melting temperatures for the first heating, fast run at 20 °C/min.
b
c
The similarity in mesophase properties of the com-
plexes reported here and the alkylamine complexes previ-
ously reported [7], does not imply structural similarity in
the mesophase. The molecules under study can adopt dif-
ferent shapes considering a sp3 hybridization for the amine
nitrogen and easy rotation around single C–C, C–N, or
Ag–N bonds. For aniline complexes in a U-shaped con-
formation the aromatic ring takes necessarily the chains
of the two ligands far from each other, and it is expected
that in a condensed phase the cations derived from ani-
lines will not adopt a U-shaped conformation, which
d
Melting temperatures for the second heating; data in parenthesis are
for the first heating.
e
Combined enthalpies.
would produce a worse molecular packing than an
extended conformation. However, for the bisbenzylamine
complexes molecular models suggest that extended or U-
shaped conformations are both compatible with a good
molecular packing.

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M.del Carmen Lequerica et al. / Inorganica Chimica Acta 361 (2008) 2270–2278
Crystal
Smectic A
150.0
125.0
100.0
75.0
50.0
25.0
n
8
10 12 14
6
8
10 12 14
Series1
6
8
10 12 14
6
8
10 12 14
6h 6c
8
10 12 14
6
8
10 12 14
Alkylamine NO3
Alkylamine BF4
Series 3
Series 4
Series 2
Fig. 1. Transition temperatures for the complexes (h = heating; c = cooling). Bis-n-alkylamine silver(I) complexes from Ref. [7] are plotted for
comparison.
Crystal
Smectic A
150.0
125.0
100.0
75.0
50.0
25.0
0.0
CF3SO3–
h
c
CF3SO3–
Fig. 3. Temperature dependence of the [Ag(NH2–C6H5–C10H21)2]NO3
diffractogram: (a) solid state; (b) near the melting point; (c) near the
clearing point. Reflections at 2h = 38° and 44° arise from metallic silver
planes (111) and (200), respectively [17].
NO3–
BF4–
AcO–
Anions
Fig. 2. Transition temperatures of the bis(4-n-decyloxybenzylamine) silver
(I) complexes (h = heating; c = cooling).
Although there are exceptions [16], for simple molecular
shapes and mesophases the solid state structure is fre-
quently related to the mesophase, and is a good starting
point to understand the mesogenic behavior. It was impos-
sible to obtain single crystals of the complexes suitable for
X-ray diffraction, so powder measurements were taken on
polycrystalline samples. All the diffraction diagrams exhibit
a simple diffraction pattern (see for instance Fig. 3a), also
similar to that shown by the bis-n-alkylamine silver com-
plexes, consisting of periodic reflections of (00l) planes.
This indicates a layered arrangement of cations with the sil-
ver centers defining a layer separated d(00l) from the nearest
equivalent silver layer. This interplanar distance should
depend on how the amine ligands in a cation are arranged
one respect to the other. In what follows we compare, for
each series of complexes, the observed d(00l) distance and
the calculated length of the cation (Lcalc), in order to decide
the most likely cation shape in the solid state.
XRD data were also taken on the mesophases in order
to see whether the arrangement in the mesophase was in
fact related to the solid. Three different SA arrangements
were considered [18]: SA1, when the molecules pack
together in monolayers; SA2, when arranged in bilayers;
and SAd, when there is some interdigitation in the bilayer.
All of them are characterized by a periodic XRD pattern
of (00l) reflections, as observed in the high temperature dif-
fractograms of Fig. 3b or c, but they can be distinguished
by comparing the interplanar spacing with the molecular
parameters. Table 2 collects d(00l) values for the four series
of complexes. They show a very good linear dependence

M.del Carmen Lequerica et al. / Inorganica Chimica Acta 361 (2008) 2270–2278
2275
Table 2
Experimental interplanar spacing (d(00l)) for the series studied
˚
Series
1
n
d(00l) (A)[19]
6
28.81
8
32.70
10
12
14
36.76
40.45
44.58
d(00l) = 1.01 (2n) + 16.30
r = 0.99948
2
3
4
7
30.56
35.27
38.84
43.03
9
11
13
15
47.08
d(00l) = 1.02 (2n) + 16.52
r = 0.99932
28.30
32.77
37.42
42.85
47.29
d(00l) = 1.20 (2n) + 11.29
r = 0.99945
30.62
35.25
39.49
43.60
48.43
7
9
11
13
15
Fig. 4. Minimum energy conformation and calculated length (Lcalc) of
four representative cations. (a) [Ag(NH2–C6H4–C6H13)2]+. (b) [Ag(NH2–
C6H4–OC6H13)2]+. (c) [Ag(NH2–CH2–C6H4–OC6H13)2]+. (d) [Ag(NH2–
C6H13)2]+.
7
9
11
13
15
d(00l) = 1.10 (2n) + 15.29
r = 0.99965
rotation around the N–Ag bond [22]. We will see later that
this variation is unimportant to our discussion: similarly to
the case of alkylamines, which are predicted a transoid cen-
trosymmetrical conformations in the gas phase, both kinds
of complexes adopt U-saped conformations for long alkyl
chains, in the solid state and in the mesophase [7].
The linear adjustment the total number of carbon atoms for the two
terminal chains (2n) is given; for alkoxy chains each oxygen counts as one
member.
The central graphic in Fig. 5 plots the values of Lcalc and
d(00l) in the solid for the n = 6 member of the four series.
The bis-n-hexylamine silver complex, known to be
U-shaped, is taken for reference. Taking these plots and
the expressions of d(00l) = f(2n) calculated in Table 2, two
different trends are suggested. The complexes derived from
anilines (series 1 and 2) show d-spacings close to but larger
than their corresponding cationic lengths in the extended
conformation, with l/CH2 values clearly shorter than
with the chain length. Assuming an all-trans conformation
in the alkyl chains (although random deviations are to be
expected), the slope of the line corresponds to the length
˚
per methylene group, l/CH2. A mean value of 1.26 A is
expected for a chain orientated parallel to the line defining
the molecular length,3 while smaller values for l/CH2 will
suggest tilting of the chains.
The theoretical molecular length (Lcalc) was taken as the
distance between the terminal CH3 groups from the mini-
mum energy conformation calculated for an isolated cat-
ions (gas phase), which have the expected all-trans
conformation. Fig. 4 shows the optimized conformations
for one representative cation (n = 6) of each series. The
transoid centrosymmetrical conformations calculated for
the alkyl (Fig. 4a) and alkoxy (Fig. 4b) aniline complexes
are in good agreement with the conformations usually
observed in single crystal XRD structures of a number of
related complexes lacking long chains [20]. The cisoid con-
formation found for the bis-benzylamine complex in the
gas phase (Fig. 4c) is unusual in solid state structures of
complexes lacking long chains [21]. Its calculated molecular
length is somewhat shorter than for the more commonly
found centrosymmetric conformation, easily accessible by
˚
1.26 A. On the contrary, in benzylamine derivatives the
spacing is shorter than the calculated length for the cation
in the cisoid conformation (even shorter than the transoid
˚
˚
conformation), and l/CH2 is closer to 1.26 A (1.20 A for
˚
series 3 and 1.10 A for series 4). This behavior is similar
to that reported for alkylamine silver complexes [7].
These results in the solid phase are compatible with a
cationic arrangement for series 1 and 2 close to that shown
in a bilayer arrangement of the cations with the amine
ligands extended in opposite sense in a centrosymmetric
conformation and the silver atoms in a plane. The interpla-
nar distance should be almost the same as the cation
length. A lamellar like mesophase is closely related to this
solid structure.
For the benzylamine complexes the graphic in Fig. 5
reveals a behavior similar to the n-alkylamine complexes,
and also that d(00l) is dependent on the anion size (the
3
˚
l/CH2 = dC–Csen55°; dC–C = 1.54 A.

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M.del Carmen Lequerica et al. / Inorganica Chimica Acta 361 (2008) 2270–2278
Fig. 5. Center: Plot of Lcalc and d(00l) values (solid state) for all the n = 6 members of the four series. The bis-n-hexylamine silver complex (Ref. [7]) is
included for comparison. Up and down, proposed arrangement in solid state for series 1 and 2 (up) and 3 and 4 (down).
Table 3
spacing increases for the bigger anion). This is consistent
X-ray diffraction data for selected silver complexes in the solid and in the
SA mesophase
with a U-shaped cation conformation (as observed for
the n-alkylamine complexes), not with the cation confor-
mation calculated in gas phase (Fig. 4c or its transoid con-
former), for which the d-spacing is not expected to be
affected by the anion size. The values of l/CH2 indicate a
parallel orientation of the chains respect to the line defining
Compound
Solid
Mesophase
˚
˚
˚
d(00l) (A)
d(00l) (A)
T (°C)
Dd(00l) (A)
1.8
1.10
3.8
3.10
4.8
4.10
32.70
36.76
32.77
37.42
34.21
39.49
18.28
23.75
27.20
20.00
29.44
31.30
30.48
32.70
29.35
31.60
18.45
22.80
27.00
17.80
100
105
90
100
80
90
40
56
50
3.26
5.46
2.29
4.72
4.86
7.89
ꢂ0.17
0.95
0.20
2.20
Lcalc, shorter for the tetrafluoroborate series due to the
occurrence of chain interdigitation. The diffraction dia-
grams show a lamellar cation distribution. These data sug-
gest an arrangement of the U-shaped benzylamine cations
of the type shown in with the anions located in the space
between contiguous silver atoms. Our results support that
the complexes of series 3 and 4 behave as amphiphiles
already in the solid state, where the preexistent separation
of microphases will be the driving force for the mesophase
formation upon melting.
Additional information from variable temperature
X-ray diffraction is given in Table 3. The diffraction exper-
iments were carried out on selected samples of series 1, 3
and 4 (n = 8, 10), excluding series 2 because of the marked
decomposition it suffers just after melting, for some nitrate
[Ag(NH2–C6H13)2]NO3
[Ag(NH2–C8H17)2]NO3
[Ag(NH2–C10H21)2]NO3
AgSC6H13
130
n-alkylamine compounds of reference 7 (n = 6, 8, 10), and
for the reference compound AgSC6H13 [16a]. For each
sample data were collected 10 °C above its melting point.
There is
a
striking difference Dd(00l) = d(00l)solid
ꢂ
d(00l)mesophase for series 1, 3, and 4, which is four to six times
bigger than the same difference in the nitrate n-alkylamine
silver complexes. This is not due to the high mesophase

M.del Carmen Lequerica et al. / Inorganica Chimica Acta 361 (2008) 2270–2278
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Acknowledgements
This work was sponsored by the D.G.I. (Project
´
CTQ2005-08729/BQU) and the Junta de Castilla y Leon
(Project VA099A05). We are indebted to Dr. D. Galisteo
(E.T.S.I.I. U. Valladolid) for the computational calcula-
tions and to E. Matesanz (C.A.I DRX, U. Complutense,
Madrid), S. Azpeleta and J. Arias (U. Valladolid) for help
with the powder diffraction experiments.
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