Spin-crossover and liquid crystal properties in 2D cyanide-bridged Fe II-MI/II metalorganic frameworks

Article abstract of DOI:10.1021/ic101304v

Novel two-dimensional heterometallic Fe(II)-M(Ni^II, Pd ^II, Pt^II, Ag^I, and Au^I) cyanide-bridged metalorganic frameworks exhibiting spin-crossover and liquid crystal properties, formulated as {FeL₂

Full text of DOI:10.1021/ic101304v

10022 Inorg. Chem. 2010, 49, 10022–10031
DOI: 10.1021/ic101304v
Spin-Crossover and Liquid Crystal Properties in 2D Cyanide-Bridged FeII-MI/II
Metalorganic Frameworksr
,‡
†
§
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||
,†
M. Seredyuk,†,^ A. B. Gaspar,* V. Ksenofontov, Y. Galyametdinov, M. Verdaguer, F. Villain, and P. Gutlich*
€
†
€
Institut fu€r Anorganische und Analytische Chemie, Johannes-Gutenberg-Universitat, Staudinger-Weg 9,
‡
ꢀ
´
ꢀ
D-55099 Mainz, Germany, Institut de Ciencia Molecular (ICMOL)/Departament de Quımica Inorganica,
ꢀ
ꢀ
Universitat de Valencia, Edifici de Instituts de Paterna, Apartat de Correus 22085, 46071 Valencia, Spain,
§Kazan Physical Technical Institute, Russian Academy of Science, Sibirsky Tract 10/7, 420029, Kazan, Russia,
||
ꢁ
ꢁ
and Institut Parisien de Chimie Moleculaire, UMR CNRS 7201, FR-CNRS 2769, Universite Pierre et Marie
Curie, 4 place Jussieu, case courrier 42, 75252 Paris Cedex 05, France. ^ On leave from Kiev National University
Received June 29, 2010
Novel two-dimensional heterometallic Fe(II)-M(NiII,PdII,PtII,AgI, and AuI) cyanide-bridged metalorganic frameworks exhibiting
spin-crossover and liquid crystal properties, formulated as {FeL2[MI/II(CN)x]y} sH2O, where L are the ligands 4-(4-
alkoxyphenyl)pyridine, 4-(3,4-dialkoxyphenyl)pyridine, and 4-(3,4,5-trisalkoxyphenyl)pyridine, have been synthesized and
3
characterized. The physical characterization has been carried out by means of EXAFS, X-ray powder diffraction, magnetic
€
susceptibility, differential scanning measurements, and Mossbauer spectroscopy. The 2D Fe(II) metallomesogens undergo
incomplete and continuous thermally induced spin transition at T1/2 ≈ 170 K and crystal-to-smectic transition above 370 K.
Introduction
magnetic field,1a,e or guest absorption/desorption4). In the HS
and LS states, SCO compounds manifest differences in mag-
netism, optical properties, dielectric constant, color, and struc-
ture. These characteristics have made the SCO phenomenon
one of the most interesting application-oriented examples of
bistability in molecular materials.2b-d,4c,e,f,5
The SCO phenomenon has recently been investigated in the
framework of other materials of technological interest such as
liquid crystals.5 Materials combining spin-crossover and liquid
crystalline behavior may lead to a number of advantages in
practical applications, for example, processing spin-crossover
materials in the form of thin films, enhancement of spin
transition signals, switching and sensing in different tempera-
ture regimes, or the achievement of photo- and thermochro-
mism in Fe(II)-containing liquid crystals. The change of color
is certainly a phenomenon which is of interest in the field of
liquid crystals. The interest lies in the necessity of color change
in a number of applications in liquid crystals such as passive
blocking filters, laser addressed devices, polarizers based on
dichroic effects, or the utility of thermochromism.6
Spin-crossover (SCO) compounds represent a type of func-
tional molecular material with labile electronic configurations
switchable between the high-spin (HS) and low-spin (LS) states
in response to external stimuli (temperature,1 pressure,2 light,3
r Dedicated to Professor Wolfgang Kaim on the occasion of his 60th birthday.
*To whom correspondence should be addressed. E-mail: ana.b.gaspar@
uv.es (A.B.G.).
€
(1) (a) Gutlich, P.; Goodwin, G. Top. Curr. Chem. 2004, 233; 234; 235. (b)
Gaspar, A. B.; Ksenofontov, V.; Seredyuk, M.; G€utlich, P. Coord. Chem. Rev. 2005,
249, 2661. (c) Real, J. A.; Gaspar, A. B.; Munoz, M. C. Dalton Trans. 2005, 2062. (d)
Real, J. A.; Gaspar, A. B.; Niel, V.; Munoz, M. C. Coord. Chem. Rev. 2003, 236, 121.
~
~
(e) G€utlich, P.; Hauser, A.; Spiering, H. Angew. Chem., Int. Ed. 1994, 33, 2024.
€
(2) (a) Gutlich, P.; Ksenofontov, V.; Gaspar, A. B. Coord. Chem. Rev.
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2005, 249, 1811. (b) Galet, A.; Gaspar, A. B.; Munoz, M. C.; Bukin, G. V.;
Levchenko, G.; Real, J. A. Adv. Mater. 2005, 17, 2949. (c) Kahn, O.; Martinez, J.
Science 1998, 279, 44. (d) Kahn, O.; Krober, C.; Jay, C. Adv. Mater. 1992, 4, 718.
(3) (a) Decurtins, S.; Gutlich, P.; Kohler, C. P.; Spiering, H.; Hauser, A.
Chem. Phys. Lett. 1984, 105, 1. (b) Trzop, E.; Cointe, M. B. L.; Cailleau, H.;
Toupet, L.; Molnar, G.; Bousseksou, A.; Gaspar, A. B.; Real, J. A.; Collet, E. J.
Appl. Crystallogr. 2007, 40, 158. (c) Letard, J. F. J. Mater. Chem. 2006, 16,
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Bousseksou, A.; Varret, F. Science 1995, 268, 265. (b) Neville, S. M.; Halder,
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Moubaraki, B.; Murray, K. S.; Kepert, C. J. J. Am. Chem. Soc. 2008, 130, 2869. (c)
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Agustí, G.; Ohtani, R.; Yoneda, K.; Gaspar, A. B.; Ohba, M.; Munoz, M. C.; Kitagawa,
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J. L. Metallomesogens; VCH: Weinheim, Germany, 1996. (c) Donnio, B.; Bruce,
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Chem. Soc. 2009, 131, 12106. (e) Ohba, M.; Yoneda, K.; Agusí, G.; Munoz, M. C.;
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r
pubs.acs.org/IC
Published on Web 09/30/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 21, 2010 10023
Scheme 1. Structure of Fe(II) Metallomesogens under Study and Their Codesa
a The roman numerals above the arrows indicate the scattering pathways at the iron K edge (I, II, III) and nickel K edge (IV, V, III) observable in the
EXAFS Fourier transforms. b In parentheses are given the numbers of the crystal water molecules deduced from TGA.
Recently, we have illustrated the strategies developed in
order to achieve interplay/synergy between spin transition
and liquid crystal transition.5,7 The synthesized Fe(II) me-
tallomesogens exhibit different types of interplay between
both phase transitions. A classification according to the
analysis of the magnetic and structural data has led to the
distinction of three types of interplay, namely, type i, systems
with coupling between the electronic structure of the iron(II)
ions and the mesomorphic behavior of the substance; type ii,
systems where both transitions coexist in the same tempera-
ture region but are not coupled due to competition with the
dehydration (release of crystal water on heating); type iii,
systems where both transitions occur in different temperature
regions and therefore are uncoupled.
that lead to the isolation of the corresponding Fe(II) metallo-
mesogens formulated as {FeL2[MII/I(CN)x]y}, where L are the
ligands 4-(4-alkoxyphenyl)pyridine, 4-(3,4-dialkoxyphenyl)-
pyridine, and 4-(3,4,5-trisalkoxyphenyl)pyridine. We shall
present and discuss the characterization of their spin-cross-
over and liquid crystal properties. Scheme 1 shows the struc-
ture of Fe(II) metallomesogens under study and their codes.
Experimental Section
Synthesis of Compounds. Starting reagents and solvents were
obtained commercially from Aldrich or Across and used as re-
ceived. The synthesis of [N(t-Bu)4]2[MII(CN)4] (MII = Ni, Pd, Pt)
and [N(t-Bu)4][MI(CN)2] (MI = Ag, Au) is described by Seredyuk
et al.9 The synthesis of ligands is summarized in Scheme 2.
Compounds 4-(4-methoxyphenyl)pyridine (4A),4-(3,4-dimethoxy-
phenyl)pyridine (34A), and 4-(3,4,5-trismethoxyphenyl)pyridine
(345A) were prepared using Suzuki-coupling according to the
synthetic procedure described by Manley et al.10
Compound 4A. Yield 74%. Found: C, 77.83; H, 6.04; N, 7.37.
C12H11NO requires: C, 77.81; H, 5.99; N, 7.56. m/z (EI): 185.1
[M]þ (100%), 170.0 (M-CH3)þ (35%). 1H NMR δH (400 MHz,
CDCl3): 8.56 (2H, dd, J = 2.0, 5.8 Hz, PyH2,6), 7.56 (2H, dd, J=
1.2, 8.6 Hz, PhH2,6), 7.43 (2H, dd, J=2.0, 5.8 Hz, PyH3,5), 6.98
(2H, dd, J=1.2, 8.6 Hz, PhH3,5), 3.83 (3H, s, OCH3). 13C NMR
δC (100 MHz, CDCl3): 158.4, 150.1, 146.7, 127.5, 125.9, 125.9,
115.8, 55.9.
So far, these investigations have been centered in mono-
nuclear7b,c and one-dimensional Fe(II) metallomesogens.7a,8 In
this regard, we aimed to explore the possibility to achieve simi-
lar physical properties by modifying chemically the two-dimen-
sional cyanide-bridged Hoffman-like Fe(II) SCO polymers
{Fe(4-Phpy)2[MII/I(CN)x]y} sH2O (4PhyPy = 4-phenylpyri-
3
dine; MII=Ni, Pd, Pt; MI=Ag, Au).9 These complexes were
synthesized and studied because they might be well suited for
grafting the liquid crystal chemical functionality without sub-
stantial perturbation of the polymeric arrays. Here, we report
the chemical modification of these Fe(II) coordination polymers
Compound 34A. Yield 61%. Found: C, 72.53; H, 6.03; N,
6.50. C13H13NO2 requires: C, 72.54; H, 6.09; N, 6.51. m/z (EI):
215.2 [M]þ (100%). 1H NMR δH (400 MHz, CDCl3): 8.58 (2H,
dd, J=1.2, 4.6 Hz, PyH2,6), 7.43 (2H, dd, J=1.2, 4.6 Hz, PyH3,5),
7.19 (1H, dd, J=0.2, 8.4 Hz, PhH6), 7.10 (1H, J=0.2 Hz, PhH2),
6.93 (1H, J=8.4 Hz, PhH5), 3.92 (3H, s, OCH3), 3.90 (3H, s,
OCH3). 13C NMR δC (100 MHz, CDCl3): 149.9, 149.8, 149.3,
147.9, 130.6, 121.0, 119.4, 111.4, 109.7, 55.8.
(7) (a) Seredyuk, M.; Gaspar, A. B.; Ksenofontov, V.; Reiman, S.;
€
Galyametdinov, Y.; Haase, W.; Rentschler, E.; Gutlich, P. Chem. Mater.
2006, 18, 2513. (b) Seredyuk, M.; Gaspar, A. B.; Ksenofontov, V.; Galyametdinov,
Y.; Kusz, J.; G€utlich, P. J. Am. Chem. Soc. 2008, 130, 1431. (c) Seredyuk, M.; Gaspar,
A. B.; Ksenofontov, V.; Galyametdinov, Y.; Kusz, J.; G€utlich, P. Adv. Funct. Mater.
2008, 18, 2089.
(8) Seredyuk, M.; Gaspar, A. B.; Ksenofontov, V.; Galyametdinov, Y.;
€
Verdaguer, M.; Villain, F.; Gutlich, P. Inorg. Chem. 2008, 47, 10232.
(9) Seredyuk, M.; Gaspar, A. B.; Ksenofontov, V.; Verdaguer, M.;
(10) Manley, P. W.; Acemoglu, M.; Marterer, W.; Pachinger, W. Org.
Process Res. Dev. 2003, 7, 436.
€
Villain, F.; Gutlich, P. Inorg. Chem. 2009, 48, 6130.

10024 Inorganic Chemistry, Vol. 49, No. 21, 2010
Seredyuk et al.
Scheme 2. Synthesis of the Ligands 4-Cn, 34-C12, 345-C12a
a Reagents and conditions: (i) a, K2CO3, Pd(ac)2, (o-tol)3P, (CH3OCH2)2, 80 ꢀC, 14 h; (ii) HBr48%/CH3COOH (1:1), reflux, 2 h; (iii) CnH2nþ1Br,
K2CO3, DMF, 100 ꢀC, 8 h.
Compound 345A. Yield 54%. Found: C, 68.57; H, 6.22; N,
5.69. C14H15NO3 requires: C, 68.56; H, 6.16; N, 5.71. m/z (EI):
245.1 [M]þ (100%). 1H NMR δH (400 MHz, CDCl3): 8.65 (2H,
dd, J = 0.8, 7.0 Hz, PyH2,6), 7.47 (2H, dd, J = 0.8, 7.0 Hz,
PyH3,5), 6.83 (2H, s, ArH), 3.94 (6H, s, OCH3), 3.91 (3H, s,
OCH3). 13C NMR δC (100 MHz, CDCl3): 153.6, 149.9, 148.2,
138.8, 133.7, 121.4, 104.1, 60.8, 56.1.
Compounds 4-(4-hydroxyphenyl)pyridine (4B), 4-(3,4-dihy-
droxyphenyl)pyridine hydrobromide dihydride (34B), and
4-(3,4,5-trishydroxyphenyl)pyridine hydrobromide semihy-
dride (345B) were prepared from compounds 4A, 34A, and
345A, respectively, by ether cleavage according to the procedure
described by Gessner et al.11
Compound 4-C12. Yield 92%. Found: C, 81.31; H, 9.81; N,
4.16. C23H33NO requires: C, 81.37; H, 9.80; N, 4.13. m/z (EI):
339.2 [M]þ (100%), 171.0 [M - C12H25]þ (98%). 1H NMR δH
(400 MHz, CDCl3): 8.57 (2H, dd, J = 2.0, 5.8 Hz, PyH2,6), 7.54
(2H, dd, J = 1.2, 8.6 Hz, PhH2,6), 7.43 (2H, dd, J = 2.0, 5.8 Hz,
PyH3,5), 6.95 (2H, dd, J = 1.2, 8.6 Hz, PhH3,5), 3.97 (2H, t, J =
4.2 Hz, OCH2), 1.78 (2H, quin, OCH2CH2), 1.50-1.20 (18H, m,
CH2), 0.84 (3H, t, J = 4.2 Hz). 13C NMR δC (100 MHz, CDCl3):
159.9, 149.9, 147.7, 129.8, 127.9, 120.8, 114.9, 67.9, 31.7, 29.5,
29.4, 29.2, 29.1, 29.0, 25.8, 22.5, 13.9.
Compound 4-C18. Yield 83%. Found: C, 82.06; H, 10.77; N,
3.21. C29H45NO requires: C, 82.21; H, 10.71; N, 3.31. m/z (EI):
423.4 [M]þ (46%), 171.0 [M - C18H37]þ (100%). 1H NMR δH
(400 MHz, CDCl3): 8.57 (2H, dd, J = 2.0, 5.8 Hz, PyH2,6), 7.54
(2H, dd, J = 1.2, 8.6 Hz, PhH2,6), 7.42 (2H, dd, J = 2.0, 5.8 Hz,
PyH3,5), 6.95 (2H, dd, J = 1.2, 8.6 Hz, PhH3,5), 3.96 (2H, t, J =
4.2 Hz, OCH2), 1.77 (2H, quin, OCH2CH2) 1.50-1.20 (30H, m,
CH2), 0.84 (3H, t, J = 4.2 Hz). 13C NMR δC (100 MHz, CDCl3):
159.9, 149.9, 147.7, 129.8, 127.8, 120.8, 114.8, 67.9, 31.7, 29.5,
29.4, 29.2, 29.0, 25.8, 22.5, 13.9.
Compund 4B. Yield 95%. Found: C, 77.19; H, 5.30; N, 8.30.
C11H9NO requires: C, 77.17; H, 5.30; N, 8.18. m/z (EI): 171.0
1
[M]þ (100%). H NMR δH (400 MHz, CDCl3): 9.8 (1H, br,
OH), 8.48 (2H, d, J = 5.5 Hz, H2,6 Py), 7.60 (2H, d, J = 8.6 Hz,
H2,6 Ph), 7.55 (2H, d, J = 5.5 Hz, H3,5 Py), 6.84 (2H, d, J = 8.6
Hz, H3,5 Ph). 13C NMR δC (100 MHz, CDCl3): 158.9, 150.3,
147.1, 128.3, 127.8, 120.5, 116.3.
Compound 34B HBr 2H2O. Yield 86%. Found: C, 43.33; H,
Compound 34-C12. Yield 78%. Found: C, 80.18; H, 10.90; N,
2.60. C35H57NO2 requires: C, 80.25; H, 10.97; N, 2.67. m/z (EI):
523.7 [M]þ (100%). 1H NMR δH (400 MHz, CDCl3): 8.57 (2H,
dd, J = 1.2, 4.6 Hz, PyH2,6), 7.43 (2H, dd, J = 1.2, 4.6 Hz,
PyH3,5), 7.17 (1H, dd, J = 0.2, 8.4 Hz, PhH6), 7.10 (1H, J = 0.2
Hz, PhH2), 6.91 (1H, J = 8.4 Hz, PhH5), 4.01 (4H, m, OCH2),
1.80 (4H, quin, J = 4.2 Hz, OCH2CH2), 1.46-1.22 (36H, m,
CH2), 0.84 (6H, m, CH3). 13C NMR δC (100 MHz, CDCl3):
150.2, 149.8, 149.3, 147.9, 130.6, 120.9, 119.6, 113.6, 112.5, 69.4,
69.1, 31.7, 29.5, 29.4, 29.2, 29.1, 29.0, 25.8, 22.5, 13.9.
3
3
4.07; N, 4.61. C11H14BrNO4 requires: C, 43.44; H, 4.46; N, 4.61. m/z
(EI): 215.2 [M]þ (100%). 1H NMR δH (400 MHz, CDCl3): 8.38
(2H, dd, J=1.2, 4.6 Hz, PyH2,6), 7.84 (2H, dd, J=1.2, 4.6 Hz,
PyH3,5), 7.10 (1H, dd, J = 0.2, 8.4 Hz, PhH6), 7.04 (1H, J =
0.2 Hz, PhH2), 6.82 (1H, J = 8.4 Hz, PhH5). 13C NMR δC
(100 MHz, CDCl3): 156.2, 148.1, 144.4, 140.0, 125.5, 122.2,
121.2, 116.3, 114.6.
Compound 345B HBr 0.5H2O. Yield 98%. Found: C, 44.78;
3
3
H, 3.92; N, 4.75. C11H11BrNO3.5 requires: C, 45.07; H, 3.78; N,
4.78. m/z (EI): 203.1 [M]þ (100%). 1H NMR δH (400 MHz,
CDCl3): 8.27 (2H, dd, J=1.0, 7.0 Hz, PyH2,6), 7.57 (2H, dd, J =
1.0, 7.0 Hz, PyH3,5), 6.44 (2H, s, PhH2,6). 13C NMR δC (100 MHz,
CDCl3): 144.8, 139.6, 124.2, 121.7, 107.3.
Compound 345-C12. Yield 60%. Found: C, 79.78; H, 11.40;
N, 2.11. C47H81NO3 requires: C, 79.72; H, 11.53; N, 1.98. m/z
(EI): 707.4 [M]þ (70%). 1H NMR δH (400 MHz, CDCl3): 8.65
(2H, dd, J = 1.0, 6.1 Hz, PyH2,6), 7.48 (2H, dd, J = 1.0, 6.1 Hz,
PyH3,5), 6.82 (2H, s, PhH2,6), 4.06 (6H, m, OCH2), 1.85 (6H, m,
Compounds 4-Cn (n = 6, 12, 18), 34-C12, and 345-C12 were
obtained from the corresponding precursors 4B, 34B, and
345B by the synthetic procedure analogous to the preparation
of alkylated 5-(alkoxy)picolinaldehydes described by Seredyuk
et al.7b
OCH2CH2), 1.53-1.28 (54H, m, CH2), 0.90 (9H, m, CH3). 13
C
NMR δC (100 MHz, CDCl3): 153.5, 149.8, 148.4, 139.2, 133.0,
121.3, 105.6, 73.4, 69.2, 31.7, 30.1, 29.5-29.2, 25.9, 22.5, 13.9.
General Synthetic Procedure for Compounds 1-22. To a hot
Compound 4-C6. Yield 90%. Found: C, 80.06; H, 8.31; N, 5.43.
C17H21NO requires: C, 79.96; H, 8.29; N, 5.49. m/z (EI): 255.1 [M]þ
solution of an alkylated ligand (1.22 mmol) and FeCl2 2H2O
3
(0.10 g, 0.61 mmol) in hot ethanol was added dropwise a solu-
tion of [N(t-Bu)4]2[MII(CN)4] (MII = Ni, Pd, Pt) (0.61 mmol) or
[N(t-Bu)4][MI(CN)2] (MI = Ag, Au) (1.22 mmol) in ethanol,
which was immediately accompanied by the formation of a
precipitate. The mixture was stirred for 15 min and then
centrifuged. After that, the solution was decanted and the rest
washed with ethanol and centrifuged. The precipitate was dried
in vacuo.
1
(100%), 171.0 [M - C6H13]þ (93%). H NMR δH (400 MHz,
CDCl3): 8.56 (2H, dd, J = 2.0, 5.8 Hz, PyH2,6), 7.55 (2H, dd, J =
1.2, 8.6 Hz, PhH2,6), 7.43 (2H, dd, J = 2.0, 5.8 Hz, PyH3,5), 6.96
(2H, dd, J = 1.2, 8.6 Hz, PhH3,5), 3.97 (2H, t, J = 4.2 Hz, OCH2),
1.78 (2H, quin, OCH2CH2) 1.50-1.25 (6H, m, CH2), 0.84 (3H, t,
J =4.2 Hz). 13C NMR δC (100 MHz, CDCl3): 159.9, 149.8, 147.7,
129.8, 127.9, 120.8, 114.9, 67.9, 31.3, 28.9, 25.5, 22.4, 13.8.
Compound 1. 4-C6 (0.31 g), [N(t-Bu)4]2[Ni(CN)4] (0.28 g).
C38H44FeN6NiO3 requires: C, 61.07; H, 5.93; N, 11.25. Found:
C, 61.42; H, 5.63; N, 11.26
(11) Gessner, W.; Brossi, A.; Rong-sen, S.; Abell, C. W. J. Med. Chem.
1985, 28, 311.

Article
Compound 2. 4-C18 (0.52 g), [N(t-Bu)4]2[Ni(CN)4] (0.28 g).
C55H77FeN6NiO3 requires: C, 68.70; H, 8.55; N, 7.75. Found: C,
68.85; H, 8.89; N, 7.69
Compound 3. 4-C12 (0.41 g), [N(t-Bu)4]2[Ni(CN)4] (0.28 g).
C50H67FeN6NiO2,5 requires: C, 66.24; H, 7.45; N, 9.27. Found:
C, 66.68; H, 7.42; N, 8.78
Compound 4. 34-C12 (0.64 g), [N(t-Bu)4]2[Ni(CN)4] (0.28 g).
C74H118FeN6NiO6 requires: C, 68.25; H, 9.13; N, 6.45. Found:
C, 68.56; H, 9.06; N, 6.45
Compound 5. 345-C12 (0.87 g), [N(t-Bu)4]2[Ni(CN)4] (0.28 g).
C97H163FeN6NiO8 requires: C, 70.36; H, 9.92; N, 5.08. Found:
C, 69.84; H, 9.62; N, 4.97
Compound 6. 4-C18 (0.52 g), [N(t-Bu)4]2[Pd(CN)4] (0.42 g).
C55H77FeN6O3Pd requires: C, 63.98; H, 7.52; N, 8.14. Found:
C, 64.02; H, 7.55; N, 8.48
Compound 7. 4-C12 (0.41 g), [N(t-Bu)4]2[Pd(CN)4] (0.42 g).
C49H65FeN6O3Pd requires: C, 62.06; H, 6.91; N, 8.86. Found:
C, 62.40; H, 7.02; N, 8.48
Compound 8. 34-C12 (0.64 g), [N(t-Bu)4]2[Pd(CN)4] (0.42 g).
C74H115FeN6O4,5Pd requires: C, 67.18; H, 8.76; N, 6.35. Found:
C, 67.67; H, 8.43; N, 6.07
Inorganic Chemistry, Vol. 49, No. 21, 2010 10025
edge was calibrated with the strong absorption peak of metallic
iron foil at 7111.2 eV. A water-cooled Si(111) channel-cut crystal
was used as a monochromator. The intensities of the incident and
transmitted X-rays were recorded using ionization chambers. The
mass of the sample was calculated to obtain a product a ꢀ d of
about 2.5 for energies just above the absorption K edge of iron (a is
the linear absorption coefficient, and d is the thickness of the pellet).
The calculated amount of the sample was ground, mixed with
crystalline cellulose, and pressed into a 13-mm-diameter and about
1-mm-thick pellet. A closed-cycle He cryostat was used for variable
temperature measurements. The temperature was measured with a
Si diode placed close to the sample. The data acquisition time for
each data point was 1 s. EXAFS data analysis was performed with
the program EXAFS98.12a,b This standard analysis includes linear
pre-edge background removal, a Lengeler-Eisenberg spectrum
normalization, and reduction from the absorption data μ(E) to the
EXAFS spectrum χ(k) with
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2mε
k ¼
ðE - E0Þ
2
ðpÞ
where E0 is the energy threshold, taken at the absorption maximum
(7130 ( 1 eV). The radial distribution function F(R) was calculated
Compound 9. 345-C12 (0.87 g), [N(t-Bu)4]2[Pd(CN)4] (0.42
g). C97H165FeN6O9Pd requires: C, 67.67; H, 9.66; N, 4.88.
Found: C, 67.51; H, 9.29; N, 5.10
Compound 10. 4-C18 (0.52 g), [N(t-Bu)4]2[Pt(CN)4] (0.48 g).
C55H77FeN6O3Pt requires: C, 58.92, H, 6.92, N, 7.50. Found: C,
58.84, H, 6.53, N, 7.64
3
by Fourier transformation of k w(k) χ(k) in the 2-14 A-1 range;
˚
w(k) is a Kaiser-Bessel apodization window with smoothness
coefficient τ = 3. After Fourier filtering, the first single shell
Fe-N6 was fitted in the 4-12 A-1 range to the standard EXAFS
˚
formula, in a single scattering scheme:
"
Compound 11. 4-C12 (0.41 g), [N(t-Bu)4]2[Pt(CN)4] (0.48 g).
C49H65FeN6O3Pt requires: C, 56.75; H, 6.32; N, 8.10. Found: C,
57.16; H, 6.46; N, 7.94
Compound 12. 34-C12 (0.64 g), [N(t-Bu)4]2[Pt(CN)4] (0.48 g).
C74H116FeN6O5Pt requires: C, 62.56; H, 8.23; N, 5.92. Found:
C, 62.25; H, 7.79; N, 6.31
Compound 13. 345-C12 (0.87 g), [N(t-Bu)4]2[Pt(CN)4]
(0.48 g). C97H163FeN6O8Pt requires: C, 65.00; H, 9.17; N,
4.69. Found: C, 65.46; H, 9.12; N, 4.74
Compound 14. 4-C18 (0.52 g), [N(t-Bu)4][Ag(CN)2] (0.49 g).
C91H136Ag2FeN7O3,5 requires: C, 66.01; H, 8.28; N, 5.92.
Found: C, 66.03; H, 8.60; N, 6.16
X
Ni
R2i
2 2
kχðkÞ ¼ - S02
jðFπ, kÞje- 2σ k e- 2Ri=λðkÞ sinð2kRi
i ¼ 1:5
#
þ 2D1ðkÞ þ ΨðkÞÞ
where S20 is the inelastic reduction factor, N is the number of
nitrogen atoms at distance R from the iron center, λ(k) is the mean
free path of the photoelectron, σis the Debye-Waller factor, giving
the width of the Fe-N distance distribution, ∂1(k) is the central
atom phase shift, and |(Fπ,k)| and ψ(k) are the amplitude and
phase of the nitrogen backscattered wave. The curve-fitting analysis
for the first coordination sphere of the iron was performed with the
Compound 15. 4-C12 (0.41 g), [N(t-Bu)4][Ag(CN)2] (0.49 g).
C73H100Ag2FeN7O3,5 requires: C, 62.48; H, 7.18; N, 6.99.
Found: C, 62.24; H, 7.15; N, 6.92
Round Midnight12c code after Fourier filtering in the 0.7-2.0 A
˚
Compound 16. 34-C12 (0.64 g), [N(t-Bu)4][Ag(CN)2] (0.49 g).
107H167Ag2FeN7O7 requires: C, 66.41; H, 8.70; N, 5.07.
range of the EXAFS spectrum. Spherical-wave theoretical ampli-
tudes and phase shifts calculated by the McKale12d,e code were
used. Since theoretical phase shifts were used, we fitted the energy
threshold E0 (ΔE0). The goodness of fit was given by
C
Found: C, 66.76, H, 8.72, N, 5.03
Compound 17. 345-C12 (0.87 g), [N(t-Bu)4][Ag(CN)2] (0.49
g). C143H241Ag2FeN7O11 requires: C, 68.53; H, 9.69; N, 3.91.
Found: C, 68.36; H, 9.79; N, 3.62
Compound 18. 4-C6 (0.31 g), [N(t-Bu)4][Au(CN)2] (0.60 g).
C55H65Au2FeN7O4 requires: C, 49.37; H, 4.90; N, 7.33. Found:
C, 49.41; H, 4.97; N, 7.43
Compound 19. 4-C18 (0.52 g), [N(t-Bu)4][Au(CN)2] (0.60 g).
C91H136Au2FeN7O3,5 requires: C, 59.60; H, 7.47; N, 5.35.
Found: C, 59.21; H, 7.31; N, 4.93
Compound 20. 4-C12 (0.41 g), [N(t-Bu)4][Au(CN)2] (0.60 g).
C73H99Au2FeN7O3 requires: C, 55.76, H, 6.35, N, 6.24. Found:
C, 56.17, H, 5.98, N, 6.53
P
2
½kχexpðkÞ - kχthðkÞꢁ
Fð%Þ ¼
2
P
½kχexpðkÞꢁ
Variable-temperature magnetic susceptibility measurements
of samples 1-22 (20-30 mg) were recorded with a Quantum
Design MPMS2 SQUID susceptometer equipped with a 7 T
magnet, operating at 1 T and at temperatures from 1.8-400 K.
The susceptometer was calibrated with (NH4)2Mn(SO4)2
3
12H2O. Experimental susceptibilities were corrected for dia-
magnetism of the constituent atoms by the use of Pascal’s
Compound 21. 34-C12 (0.64 g), [N(t-Bu)4][Au(CN)2] (0.60 g).
C73H115Ag2FeN6O6 requires: C, 60.71; H, 8.03; N, 5.82. Found:
C, 60.89; H, 8.52; N, 5.59
€
constants. Mossbauer spectra were recorded in transmission
geometry with a 57Co/Rh source kept at room temperature and
a conventional spectrometer operating in the constant-accelera-
tion mode. The samples were sealed in a Plexiglas sample holder
and mounted in a nitrogen-bath cryostat. The Recoil 1.03a
Compound 22. 345-C12 (0.87 g), [N(t-Bu)4][Au(CN)2] (0.60 g).
143H238Au2FeN7O9,5 requires: C, 64.64; H, 9.03; N, 3.69. Found:
C
C, 64.54; H, 9.09; N, 3.60
€
Physical Characterization. The iron K-edge X-ray absorption
near-edge structures (XANES) and extended X-ray absorption
fine structures (EXAFS) spectra were recorded in the conven-
tional transmission mode on beamline A1 at the German
Electron Synchrotron, DESY, Hamburg. The spectrum was
recorded from 6970 to 7997 eV. The energy scale at the iron K
Mossbauer Analysis Software (Dr. E. Lagarec; http://www.
isapps.ca/recoil/) was used to fit the experimental spectra.
DSC measurements were performed on a Mettler model DSC
822e calibrated with metallic indium and zinc. An overall
accuracy of 0.2 K was estimated in the temperature control
and 2% in the heat flow. DSC profiles were recorded at the rate

10026 Inorganic Chemistry, Vol. 49, No. 21, 2010
Seredyuk et al.
Figure 1. Normalized XANES spectra of compounds 2 and 6.
of 10 K/min and analyzed with Netzsch Proteus software
(NETZSCH-Geraetebau GMBH, http://www.e-thermal.com/
proteus.htm).
Figure 1 shows the normalized edge spectra of complexes
2 and 6 at different temperatures. In both complexes, the
energy of the K edge is shifted to lower energy on heating the
sample, demonstrating the increased Fe-N distances asso-
ciated with the LS to HS spin transition. The radial distribu-
tions for 2 and 6 at low and high temperatures are presented
in Figure 2. The first shell (I) is formed by nitrogen atoms
which belong to bridging tetracyanide groups in the equa-
torial plane and to axial pyridine molecules or oxygen atoms
of water molecules. The second shell (II) includes carbon
atoms of cyanide groups and of pyridine molecules. The
third one (III) is essentially due to heavy Ni/Pd atoms of the
[Ni(CN)4]2-/[Pd(CN)4]2- groups. Using a simple scattering
model, we could analyze quantitatively the first shell of
neighbors I, which reflects the structural changes accompa-
nying the spin transition (Table 1). The fitted bond distances
for the first FeN6 coordination shell compare well with those
of related iron(II) polymers in both spin states.9 For 2, XAS
was used to explore changes at the iron K edge at different
temperatures and at the nickel K edge at 250 K. Both sets of
data show similar patterns with three dominant peaks
attributed to the first three coordination shells (Figure 3).
Like in the previously reported parent Ni compound,9 peak
III at the iron K edge is more intense than at the nickel K
edge. On the other hand, peak II at the iron K edge is less
intense than the one at the nickel K edge (V). This is
essentially similar to previously reported observations9 and
indicates a slight tilt of the [Ni(CN)4]2- groups such that the
angle Fe-C-N deviates from 180ꢀ while the Ni-C-N
angle is perfectly aligned.13a This fact leads to a focusing
effect on N in the case of the nickel K edge experiment and
low intensity of the Fe peak in the case of the Fe K edge
experiment (Figure 3). On the other hand, at the Fe K edge,
the focusing effect on Ni through the carbon atom intensifies
the signal of Ni in the Fourier transform but not on the C
(peak II is much less intense than peak V). At the Ni K edge,
the peaks in the Fourier transform are assigned to four
High-resolution powder diffraction patterns were collected in the
Debye-Scherrer mode on the high-resolution powder diffract-
ometer at ID31 of the European Synchrotron Radiation Facility
(ESRF, Grenoble) coupled with a liquid nitrogen cryostat. The sam-
ples were sealed in lithium borate glass capillaries of diameter 0.5 mm
(Hilgenberg glass No. 50) and rotated around θ in order to im-
prove the spatial averaging. The exact wavelength and the zero point
were determined from well-defined reflections of a silicon standard
˚
(λ = 0.29941892 ( 0.00009008 A). At ID31, nine crystal analyzers
[nine Ge(111) crystals separated by 2ꢀ intervals] with nine Na(Tl)I
scintillation counters were used simultaneously. The incoming beam
was monitored using an ion chamber for normalization purposes in
order to take the decay of the primary beam into account.
IR spectra were recorded at 293 K using a Bruker Tensor 27
Spectrometer in the range of 400-4000 cm-1. Elemental ana-
lyses were done on a Vario EL Mikro Elementanalysator.
TGA measurements were performed on a Mettler Toledo
TGA/SDTA 851, in the 300-680 K temperature range in a
nitrogen atmosphere with a rate of 10 K/min. Microanalysis was
done by using PV 9760 EDAX Microanalysis with a PHILIPS
XL 30 ESEM scanning electron microscope.
Results and Discussion
X-Ray Absorption Spectroscopy (XAS and EXAFS).
Structural Characterization of 2 and 6. In the family of
Hofmann-like polymers of iron(II) with monodentate li-
gands, the X-ray single-crystal structure is known for {Fe-
(py)2[Ni(CN)4]} and related compounds,13 whereas EXAFS
characterization of the {Fe(4-PhPy)2[MII(CN)4]} sH2O
3
compounds was reported by us recently.9 The fragment of
the 2D polymeric structure sketched in Scheme 1 consists of
iron(II) ions surrounded by pyridine moieties and bridging
tetracyanidenickelate anions. Since it is impossible to obtain
single crystals of compounds 1-22 suitable for X-ray dif-
fraction, we have used extended X-ray absorption fine
structure (EXAFS) spectroscopy for their structural char-
acterization.
˚
carbon atoms of cyanide ligands (mean distance =1.88 A)
for the first shell, to the cyanide nitrogen atoms for the
(12) (a) Michalowicz, A. EXAFS98 pour la Mac. In Logiciels pour la
ꢁ ꢁ
Chimie; Societe Franc-aise de Chimie: Paris, 1991; p 102. (b) Michalowicz, A. J.
second shell, and to Fe atoms for the third shell, visible at ca.
˚
Phys. IV France 1997, 7, 235. (c) Michalowicz, A. Round Midnight. In Logiciels
4.7 A. The analysis of the Ni-C shell is given in Table 2.
At the Fe K edge, 6 has the same first coordination shell
ꢁ ꢁ
pour la Chimie; Societe Franc-aise de Chimie: Paris, 1991; p 116. (d) McKale,
A. G.; Knapp, G. S.; Chan, S. K. Phys. Rev. B 1986, 33, 841. (e) McKale, A. G.;
Veal, B. W.; Paulikas, A. P.; Chan, S.-K.; Knapp, G. S. J. Am. Chem. Soc. 1988,
110, 3763–3768.
(13) (a) Kitazawa, T.; Gomi, Y.; Takahashi, M.; Takeda, M.; Enomoto,
M.; Miyazaki, A.; Enoki, T. J. Mater. Chem. 1996, 6, 119. (b) Kitazawa, T.;
Eguchi, M.; Takeda, M. Mol. Cryst. Liq. Cryst. 2000, 341, 1331. (c) Real, J. A.;
˚
as 2 (six nitrogen neighbors, Fe-N distance is 1.96 A in
the LS state and ca. 2.16 A in the HS state, see Table 1)
˚
and the same second shell consisting of carbon atoms of
CN groups and pyridines. The third shell of the heavy Pd
˚
atom appears at about 4.8 A. The significant intensity of
~
Gaspar, A. B.; Munoz, M. C. Dalton Trans. 2005, 2062.

Article
Inorganic Chemistry, Vol. 49, No. 21, 2010 10027
Figure 2. Fourier transforms of the iron K-edge EXAFS signal for 2 and 6 at low and high temperatures. I, II, and III correspond to Fe-N, Fe-C, and
Fe-M (M = Ni or Pd) distances, respectively.
Figure 3. Comparison of Fourier transforms of the EXAFS spectra at
Ni and Fe K edges of complex 2 at 250 K.
Figure 4. Dependence of the interlayer distance d on the length of single
alkyl substituents in 1-3-2.
Table 1. Best Fit for Structural Parameters of the First Coordination Shell (I) of
2 and 6
compound T/K NHS NLS RHS/A RLS/A σHS/A σLS/A ΔE/eV F/%
˚
˚
˚
˚
2
6
80
250 5.8 0.2 2.18
80 4.7 1.3 2.15
250 6.0 2.17
4.8 1.2 2.16
1.95 0.088 0.065 -1.3 8.8
1.95 0.088 0.065 -0.3 7.9
1.96 0.088 0.065 -0.3 6.0
0.088
1.7 3.2
the last peak is due to the focusing effect on linear cyanide
bridges.14
X-Ray Powder Diffraction (XRPD) for 1-22. The
XRPD patterns of compounds 1-22 were measured at
300 K (SFigure 1, Supporting Information). The patterns
of derivatives 1 and 3 with C6 and C12 single alkyl chains,
respectively, are of poor quality, reflecting the low crys-
tallinity of the samples. Lengthening of alkyl substituents
leads to resolution of the peaks ascribed to the (10), (20),
(30), and (40) reflections, revealing a well-defined layered
structure in 2. In the diffractogram, high order reflections
disappear with an increasing number of substituents up to
two and three; however, the intensity of the alkyl halo
increases. In the patterns of all compounds, peaks at 2θ ≈
17.5 and 25.0ꢀ are also observed with corresponding d
Figure 5. Dependence of the intrerlayer distance d on the number of
ligand substituents with increasing number of alkyl chains in 3-4-5.
Table 2. Best Fit for Structural Parameters of the First Coordination Shell (V) of
2 at 250 K
C
R /A
C
˚
˚
N
σ /A
ΔE/eV
-0.15
F/%
4
1.88
0.057
2.2
Table 3. Interlayer Distances d for 1-22
˚
subst. d/A subst. d/A subst. d/A subst. d/A subst. d/A
˚
˚
˚
˚
1
2
3
4
5
26.9
40.6
33.8
51.3
55.8
18
19
20
21
22
19.9
30.0
24.2
24.5
37.2
˚
spacings of 5.10 and 3.55 A, respectively, originating from
6
7
8
9
42.4
34.6
49.0
54.4
10
11
12
13
42.0
33.5
49.6
53.7
14
15
16
17
30.4
25.4
31.2
36.9
a face-centered monomeric unit of the Fe-M polycya-
nide array in the HS state (Table 3). Similar patterns have
been previously observed for Prussian blue thin films.15
A comparison of the interlayer distances in derivatives 1,
3, and 2 with C6, C12, and C18 single alkyl chains, respec-
tively, shows a linear increase of the interlayer distance by
of alkyl chains equal to 26.1ꢀ (Figure 4). In the series 3-4-5
with one, two, and three C12-alkyl chains per ligand mole-
cule, respectively, the simple dependence of the interlayer
distance on the number of alkyl substituents is not observed
(Figure 5). Since the chemical analysis does not reveal a
deviation of the composition from the expected one, we can
anticipate that in all compounds the Fe(II) ions are co-
ordinated by cyano groups and ligand molecules, except
˚
1.14 A per methylen group, which corresponds to a tilt angle
(14) Yokoyama, T.; Murakami, Y.; Kiguchi, M.; Komatsu, T.; Kojima,
N. Phys. Rev. B: Condens. Matter 1998, 58, 14238.
(15) Yamamoto, T.; Umemura, Y.; Sato, O.; Einaga, Y. J. Am. Chem.
Soc. 2005, 127, 16065.

10028 Inorganic Chemistry, Vol. 49, No. 21, 2010
Seredyuk et al.
Table 4. The Stretching Frequencies ν(CN) in 1-22
subst.
ν/cm-1
subst.
ν/cm-1
subst.
ν/cm-1
subst.
ν/cm-1
subst.
ν/cm-1
1
2
3
4
5
2172
2150
2154
2155
2168
18
19
20
21
22
2172
2171
2172
2172
2170
6
7
8
9
2167
2166
2170
2168
10
11
12
13
2165
2166
2168
2166
14
15
16
17
2161, 2063
2168, 2069
2164, 2075
2165, 2078
anions [Ag(CN)2]- and [Ag(L)(CN)2]- with three-coordi-
nated silver atoms, analogously to the structurally character-
ized 3-bromo- and 3-iodopyridine-based complexes described
by Munoz et al.18 and pyridine complexes of [Ag(CN)2]-.19
~
Accordingly, the higher frequency of the ν(CN) band is
assigned to the CN groups bonded to double coordinate Ag
atoms without an attached pyridine molecule. The second
band is assigned to the [Ag(CN)2]- groups where each triply
coordinate Ag atom bears a ligand molecule. Expectedly,
in the IR spectra of the [Au(CN)2]--based complexes, the
splitting of the CN band is not observed, reflecting the absence
of bonding between ligand molecules and dicyanoaurate
groups.
A confirmation that formed networks are heterometallic is
also found by EDXA spectroscopy (energy-dispersive X-ray
microanalysis). A scan of powdered samples shows both Fe
and M peaks. The quantitative analysis of the integrated
areas of the multiplex scans yields an Fe/M ratio of 1:1 ( 5%
(MII = Pd, Ni, or Pt) or 1:2 ( 5% (MI = Ag or Au).
Magnetic Susceptibility Measurements. The thermal
dependence of the product χMT (χM being the molar suscep-
tibility and T the temperature) for compounds 1-22 is
displayed in Figure 7. The temperature dependence of the
Figure 6. The total maximal length of the bond Fe-N and the stretched
ligand 4(4-dodecyloxyphenyl)pyridine with the alkyl chain in all-trans
configuration.
terminal sites. Comparing the cross sections of a monomeric
2
unit (51 A , from X-ray data of {Fe(py)2[Ni(CN)4]}13a) and
˚
magnetic susceptibility was recorded at a rate of 2 K min-1
.
of two all-trans alkyl chains of the ligand 34-C12 (18 ꢀ 2 =
2
˚
36 A ) or three alkyl chains of the ligand 345-C12 (18 ꢀ 3 =
The χMT value for all compounds at room temperature is
near 3.50 cm3 K mol-1, which reveals the HS configuration
of Fe(II) ions. In all compounds except for [Ag(CN)2]-
derivatives, an incomplete gradual HSTLS transition with
T1/2 ≈ 170 K is observed accompanied by a pronounced
change of color [from yellow (HS) to red (LS)]. This feature
is indicative of weakly cooperative character of the tran-
sition, contrary to the parent compounds where abrupt
transitions with hysteresis up to 40 K were found.9 An
explanation for the observed behavior could be the
absence of appreciable interactions between Fe centers,
whereas in the parent compounds it is mediated by strong
π-π interactions between pyridine and phenyl rings of
the ligand molecules.9 In all compounds, the decrease of
the susceptibility below 30 K is due to the zero field
splitting of the Fe(II) ions with the ground state S = 2.20
The magnetic behavior of the silver derivatives is
unique in the series. While in the majority of the com-
pounds, ca. 50% of Fe(II) ions undergo transition to the
LS state, in the Ag compounds, this value is nearly 10%.
The explanation must be looked for in the bonding of an
additional ligand molecule to the bridging [Ag(CN)2]-
groups, which can substantially change the strength of the
ligand field at the Fe(II) center and insert sterical hin-
drance for the transformation of the HS polymeric layer
to a more compact one with LS Fe(II) ions.
2
54 A ), we assume that in the second case the alkyl chains
˚
must be perpendicular to the plane formed by the polycya-
nide framework.16 Indeed, the theoretically estimated sum
of lengths of two ligand molecules 4-C12 (also 34-C12 and
345-C12) in the stretched form (Figure 6) together with the
˚
two bond lengths Fe-N is equal to ca. 52 A, and this is in a
good agreement with the experimentally found d values (see
Table 3). In the case of 4, the difference in relative cross-
sectional areas occupied by the alkyl chains and a mono-
meric unit of the polymeric framework is compensated by a
chain axis tilt with an estimated angle equal to 10.6ꢀ.
From the analysis of the XRPD data, one can conclude
that a common structural feature among all homologues
of the series is a similar layered structure, and adoption on
melting of a smectic mesophase at ca. 350-375 K.
IR Spectroscopy and EDXA Data. The formation of
Fe-NtC-M bridges in polynuclear complexes 1-22 is
evidenced by the stretching vibrations of the cyanide ligands.
The IR data are summarized in Table 4. The ν(CN) modes
are shifted to higher frequencies analogously to the parent
compounds, confirming the formation of the polymeric het-
erometallic structures.17 In the spectra of the [Ag(CN)2]--
based compounds, two CN bands are observed which differ
by about 100 cm-1. This fact and the ratio Fe/L=1:3 deduced
from the CHN analysis data point at the presence of bridging
(16) Dorset, D. L. Crystallography of the polymethylene chain: an inquiry
into the structure of waxes: Oxford University Press: Oxford, U. K., 2005.
(17) (a) Zhan, S.-z.; Guo, D.; Zhang, X.-y.; Du, C.-x.; Zhu, Y.; Yang,
R.-n. Inorg. Chim. Acta 2000, 298, 57. (b) Nakamoto, K. Infrared and Raman
spectra of inorganic and coordination compounds; John Wiley: New York, 1986.
(18) Munoz, M. C.; Gaspar, A. B.; Galet, A.; Real, J. A. Inorg. Chem.
2007, 46, 8182.
(19) Bowmaker, G. A.; Junk, P. C.; Skelton, B. W.; White, A. H. Z.
Naturforsch., B: Chem. Sci. 2004, 59, 1277.
(20) Carlin, L. R. Magnetochemistry; Springer: Berlin, 1986.

Article
Inorganic Chemistry, Vol. 49, No. 21, 2010 10029
Figure 7. Thermal variation of the χMT product from magnetic measurements of compounds 1-22 (a-e). LIESST effect upon irradiation at 4 K with
subsequent increase in temperature for compound 3 (f).
Irradiation of the pristine compound 3 at 4 K with a
green laser (λ = 514 nm) causes partial photoconversion
of the LS molecules into a metastable HS state. As an
example, in Figure 7f, the LIESST effect21 is shown for
complex 3, where the critical temperature of relaxation
which favors the HS configuration of the Fe(II) ion in
the whole temperature range. The size of the quadrupole
splitting reflects the extent of structural distortion of the
[FeN6-xOx] chromophor. The electric field gradient
(EFG) determining the size of the quadrupole splitting
is the sum of two contributions. One arises from noncubic
valence electron distribution at the SCO iron center and is
denoted as (EFG)val. The other one, denoted as (EFG)lat,
arises from structural distortions within the [FeN6-xOx]
chromophor and/or substitution of nitrogen atoms by O
atoms of coordinated water molecules, both effects lead-
ing to symmetry lowering to lower than cubic. As the two
contributions to the total EFG have opposite signs, the
observed quadrupole splitting ΔEQ is small (large) in the
case of large (small) (EFG)lat.
T
LIESST is 40 K.
The heating of the compounds up to 400 K and sub-
sequent cooling do not reveal any considerable changes in
their magnetic behavior due to melting or dehydration.
€
Mossbauer Spectroscopy Data. The temperature de-
€
57
pendence of the Fe Mossbauer spectra of 1-13 has
been studied in the low- and high-temperature regions.
€
Values of the Mossbauer parameters from a least-squares
fit are listed in Table 5. The variation of the molar frac-
tions, A, compares well with the data deduced from the
magnetic susceptibility measurements. A representative
spectrum of 3 (Figure 8) and of 1, 2, and 4-13 (SFigure 3,
Supporting Information) at 80 K consists of one LS and
three HS doublets. The HS doublets are most probably
related to the presence of terminal Fe(II) sites in relatively
small polymeric particles. In this case, a coordination
polyhedron of the type [FeN6-xOx] must be realized
The Au-containing compounds (18-22) have also been
€
characterized by Mossbauer spectroscopy. The spectra,
however, showed poor resolution in nearly all cases due
to an insufficient signal-to-noise ratio because of strong
K-edge absorption in gold atoms, which weakens the
€
14.4 keV Mossbauer γ radiation. Nevertheless, a qualita-
tive analysis of the spectra was possible. The area frac-
tions of the HS and LS resonance signals estimated from
the spectra matched well the results from the magnetic
measurements.
€
€
(21) (a) Decurtins, S.; Gutlich, P.; Kohler, C. P.; Spiering, H.; Hauser, A.
ꢀ
Chem. Phys. Lett. 1984, 105, 1. (b) Letard, J.-F. J. Mat. Chem. 2006, 16, 2550.

10030 Inorganic Chemistry, Vol. 49, No. 21, 2010
Seredyuk et al.
57
a
€
Table 5. Least-Squares-Fitted Fe Mossbauer Spectra for 1-13
compound
T/K
doublet
ΔEq/mm s-1
δ/mm s-1
Γ
1/2/mm s-1
A/%
1
80
LS
0.485(15)
1.058(71)
1.141(28)
1.101(68)
0.457(25)
1.1686(69)
1.162(74)
0.4567(83)
1.248(24)
1.273(33)
1.239(32)
0.5(14)
0.225(33)
1.54(16)
2.162(79)
2.80(17)
0.253(38)
1.264(14)
2.95(15)
0.23(10)
1.35(10)
1.86(11)
2.93(21)
0.3(28)
0.195(28)
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
51.9(36)
13.6(40)
25.2(46)
9.3(38)
23.52(96)
73.2(13)
3.3(10)
HS1
HS2
HS3
LS
HS1
HS2
LS
HS1
HS2
HS3
LS
HS1
HS2
HS3
LS
HS1
HS2
HS3
LS
HS1
HS2
HS3
LS
HS1
HS2
HS3
LS
HS1
HS2
HS3
LS
HS1
HS2
HS3
LS
HS1
HS2
HS3
LS
HS1
HS2
HS3
LS
HS1
HS2
HS3
LS
2
3
85
80
68.31(79)
14.9(19)
10.9(19)
5.97(80)
68.8(12)
14.4(33)
10.2(33)
6.6(14)
33.38(55)
24.76(97)
20.82(97)
21.04(75)
39.1(12)
22.0(10)
24.0(16)
15.7(68)
46.72(65)
15.7(63)
29.9(79)
7.7(19)
49.02(45)
22.85(96)
17.29(96)
10.83(43)
33.38(55)
24.76(97)
20.82(97)
21.04(75)
42.5(26)
15.4(44)
30.3(44)
11.8(25)
57.6(29)
15.9(46)
14.3(44)
12.2(28)
49.2(26)
15.4(34)
21.5(37)
13.9(27)
38.5(17)
26.1(26)
19.0(25)
16.4(22)
4
80
80
80
80
80
80
85
80
80
80
1.1(66)
2(13)
1.181(42)
1.164(45)
0.4696(75)
1.1893(77)
1.1733(69)
1.1380(63)
0.4965(82)
1.158(15)
1.192(18)
1.178(22)
0.5064(48)
1.154(12)
1.1693(84)
1.138(19)
0.4799(61)
1.1985(83)
1.230(12)
1.2076(97)
0.4696(75)
1.1893(77)
1.1733(69)
1.1380(63)
0.527(17)
1.06(49)
2.04(11)
2.865(99)
0.2312(97)
1.455(15)
2.167(21)
2.836(15)
0.24(1)
1.34(6)
1.96(9)
2.90(10)
0.2128(62)
1.24(4)
5
0.2
0.2
6
0.17(1)
0.20(5)
0.25(1)
0.273(65)
0.1751(55)
0.190(35)
0.248(33)
0.246(46)
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
7
1.76(5)
2.93(6)
8
0.2492(81)
1.316(20)
1.878(23)
2.984(20)
0.2312(97)
1.455(15)
2.167(21)
2.836(15)
0.155(55)
1.49(98)
1.87(48)
3.04(10)
0.20(4)
9
10
11
12
13
1.23(24)
1.282(51)
0.50(2)
1.30(7)
1.18(1)
1.22(5)
0.485(22)
1.177(44)
1.178(37)
1.234(44)
0.516(13)
1.120(26)
1.145(24)
1.138(25)
2.00(1)
1.15(2)
2.77(1)
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.244(28)
2.21(11)
1.373(74)
3.102(93)
0.148(46)
1.501(61)
2.193(66)
2.899(59)
HS1
HS2
HS3
0.2
0.2
0.2
a The values given in italics were fixed during fitting.
Differential Scanning Calorimetry (DSC) and Thermo-
gravimetric Analysis (TGA). The differential scanning
calorimetric measurements have been carried out on
pristine samples in the 175-400 K temperature range at
a rate of 10 K min-1. The temperature dependence of the
heat flow in the heating and cooling modes for 2-22 is
shown in SFigure 4 (Supporting Information). The en-
thalpy associated with the CrTSx transition estimated
from the DSC data is reported in STable 1 (Supporting
Information). For all compounds, the first heating pro-
cess reflects structure transformations due to dehydration
and concomitant annealing of the samples typical for
alkylated compounds. The consequent cooling and the
second heating runs give very similar curves, except
positions of the peak maxima. In compound 20, the peak
at 270 K might be attributed to pretransition phenomena
in the alkyl sublattice, while the peak near 360 K reflects
the transition of alkyl chains from an ordered to dis-
ordered quasi-liquid state. While in compounds 19 and 21
the melting points are well above 300 K, the Au-contain-
ing compound 22 undergoes a high-energetic phase tran-
sition at 270 K attributed to an intense peak in the DSC
profile and also confirmed by XRPD data (see SFigure 1,
Supporting Information). Analogous behavior is also
observed for the Ag analogue 17.
Thermally treated tetracyano Ni, Pd, and Pt derivatives
feature broad and poorly defined peaks. We can suggest
that the transformation of the ordered alkyl chains with
temperature is mechanically hindered due to tethering
alkyl chains to a rigid polycyanide framework. Contrary
to numerous reported metallomesogens, the melting of
5, for example, is a process reminiscent of low-energetic

Article
Inorganic Chemistry, Vol. 49, No. 21, 2010 10031
research and eventual applications. Investigations of the
pressure effect on the spin-crossover properties of an Fe(II)
metallomesogen were not yet reported. However, due to the
fluid nature of the metallomesogens, one can expect a
sensitive response to small pressure changes. Pressure allows
tuning of the thermal spin-crossover characteristics in a large
range of temperatures.2b,22 Indeed, application of hydrostatic
pressure could place the spin transition in the temperature
interval where the CrTSx transition occurs and may lead to
interplay/synergy between both phenomena.
Also interesting is thegrowth/deposition of a single layer of
these 2D polymers23 onto surfaces and the study of their
physical and chemical properties. These investigations are
prensently going on in our laboratories.
57
Figure 8. Fe Mossbauer spectrum of 3 at 80 K.
€
Acknowledgment. We acknowledge the financial help
from the Deutsche Forschungsgemeinschaft (Priority
Program 1137 “Molecular Magnetism”) and the Fonds
der Chemischen Industrie. A.B.G. thanks the Spanish
MEC for the project CTQ 2007-64727, the FGUVEG
(University of Valencia) for a research contract, and the
University of Valencia for work-visiting fellowships. We
second-order phase transitions, as follows also from the
gradual change of XRPD profiles with the temperature
(SFigure 2, Supporting Information).
Thermogravimetric measurements performed on 1-22
show that several samples release water below 400 K, and
others only above this temperature, but most of the
samples show two-step dehydration processes. There is
no clear influence of the content of solvent molecules on
the length of alkyl substituents or their number, which
points out that water molecules are not involved in
donor-acceptor or covalent bonding with any groups
of the coordination framework.
€
also thank Ms. E. Muth and Ms. P. Rader of the Max-
Planck-Institute for Polymer Research, Mainz, for their
help in performing TGA and DSC measurements. We are
grateful to Dr. R. Dinnebier and Dr. K. Sugimoto, Max-
Planck-Institute for Solid State Research, Stuttgart, and
Dr. I. Margiolaki for their help in performing high
resolution XRPD measurements at the European Syn-
chrotron Radiation Facility (ESRF). We also acknow-
ledge the support of the responsible scientist Dr. E. Welter
Conclusions
We have reported a novel family of 2D Fe(II) metallomeso-
gens exhibiting spin-crossover properties. In contrast with the
2D SCO parent compounds, where the observed spin transi-
tions are of the first order type and accompanied by large
hysteresis loops, the metallomesogens present incomplete and
continuous spin transition. The apparent loss of cooperativity
should be related to the lack of intermolecular contacts
between the [FeM(CN)4]¥ sheets. In the parent compounds,
there are strong π-πinteractions between pyridine and phenyl
rings of the ligand molecules of adjacent sheets that lead to
strongly cooperative spin transition phenomena.
In the reported metallomesogens, the photo- and thermally
induced spin transition and the CrTSx transition take place
at different temperature intervals and are consequently
classified into type iii. This should not be considered a
scientific drawback because it may open new possibilities of
€
from HASYLab, Dr. H. Ehrenberg, and Dominic Sturmer
from TU Darmstadt during the EXAFS measurements at
beamline A1 and A. Michalowicz for providing us with his
XAS analysis package.
Supporting Information Available: XRPD patterns of 1-22
at different temperatures. 57Fe Mossbauer spectrum of 1-13 at
€
80 K. Differential scanning calorimetry curves for 2-17 and
19-22. TGA analysis for 1-22. Enthalpy of the CrTSx transi-
tion estimated from the DSC data for 2-11. This material is
available free of charge via the Internet at http://pubs.acs.org.
€
(22) Gutlich, P.; Ksenofontov, V.; Gaspar, A. B. Coord. Chem. Rev. 2005,
249, 1811.
€
(23) Sakamoto, J.; van Heijst, J.; Lukin, O.; Schluter, A. Angew. Chem.,
Int. Ed. 2009, 48, 1030.