C. Ruiz-Pꢁrez et al.
0.026(1) cmꢀ1 and g=1.98(1). The calculated curve (solid
line in Figure 11) matches quite well the experimental data
over the whole temperature range. This very-weak ferro-
magnetic interaction is visualised by the magnetisation
versus H data at 2.0 K, which is slightly above the Brillouin
function for a magnetically isolated gadoliniumACTHNUTRGNE(UNG III) ion with
g=2.0, both tending to a saturation value of 6.7 mB (inset of
Figure 11).
At first sight, the different nature of the weak magnetic
coupling between the GdIII ions in 2 (antiferromagnetic) and
3 (ferromagnetic) seems a bit surprising because of the same
bridging groups [m-oxo(carboxylate) and carboxylato in the
syn–syn conformation] provide the exchange pathways in
them. The subtle difference is the occurrence of two syn–syn
carboxylato bridges in 2 versus only one in 3. This circum-
stance is certainly responsible for the shortening of the
angle at the oxo(carboxylate) bridge (h), 109.2(2)8 (2) and
111.8(3) and 111.2(3)8 (3). Previous magneto-structural stud-
ies on compounds containing the double m-oxo(carboxylate)
Experimental Section
Materials and physical characterisations: Methanetriacetic acid (H3tmc)
was prepared by using a method reported previously.[28] The compounds
were characterised by using 1H NMR (at 400 and 300 MHz) and
13C NMR (at 75 MHz) spectra, the chemical shifts are reported relative
to internal Me4Si, at room temperature. Column chromatography was
performed on silica gel, 60 ꢈ and 0.2–0.5 mm. The intermediate organic
compounds were visualised by using UV light and vanillin with acetic
and sulfuric acids in ethanol with heating. All solvents were purified by
standard techniques.[29] Reactions requiring anhydrous conditions were
performed under a dinitrogen atmosphere. Anhydrous magnesium sulfate
was used for drying solutions. The rest of reagents and solvents used in
the synthesis of compounds 1–3 were purchased from commercial sources
and used without further purification. Single crystals of 1 and 2 were
grown in silica gel medium through the techniques described by
Henish,[30] whereas those of compound 3 were obtained in hydrothermal
conditions. Elemental analyses (C and H) were performed on an EA
1108 CHNS-O microanalytical analyser. Magnetic susceptibility measure-
ments on polycrystalline samples of 1–3 were performed in the tempera-
ture range of 1.9–300 K by using a Quantum Design SQUID magnetome-
ter. The measurements in all compounds were made with a field of 100 G
between 1.9 and 50 K, and 10000 G in the range of 50 K to RT. Diamag-
netic corrections of the constituent atoms were estimated from Pascalꢆs
constants[31] to be ꢀ196ꢉ10ꢀ6 (1), ꢀ170ꢉ10ꢀ6 (2) and ꢀ131ꢉ
10ꢀ6 cm3 molꢀ1 (3) per one GdIII ion. Experimental susceptibilities were
also corrected for the magnetisation of the sample holder.
digadoliniumACHTUNGTRENNUNG(III) core suggest that there exists an antiferro-
magnetic interaction when the angle Gd-O-Gd is small, and
ferromagnetic when it is greater.[25] The magnetic behaviour
of compounds 2 and 3 follows this prediction. This agree-
ment is also observed when looking at the previous cases in
which the m-O(1);k2O(1),O(2)/double syn–syn carboxylato
(2)[26] or the m-O(1);k2O(1),O(2)/single syn–syn carboxylato
(3)[27] bridge occur.
Preparation of dimethyl-3-cyanomethyleneglutarate: A mixture of di-
methyl-1,3-acetonedicarboxylate (10 g, 57.4 mmol), cyanoacetic acid
(6.38 g, 86.1 mmol), ammonium acetate (0.77 g, 1.2 mmol), dry benzene
(50 mL) and acetic acid (3.4 mL) was refluxed under stirring for 24 h
using a Dean-Stark to remove water the formed in the reaction azeotrop-
ically. The reaction mixture was cooled and washed with water (2ꢉ
15 mL) and then with a saturated NaHCO3 solution (2ꢉ10 mL). The
aqueous washings were extracted with ether (2ꢉ20 mL) and the com-
bined organic layers were dried over MgSO4, filtered, concentrated and
purified by silica gel flash-chromatography, yielding dimethyl-3-cyanome-
Conclusions
1
thyleneglutarate (10.3 g, 90% yield) as an oil. H NMR (CDCl3): d=3.36
Three novel gadoliniumACTHNUTRGNEU(GN III) compounds (1–3) have been
(d, J=1.2 Hz, 2H), 3.59 (s, 2H), 3.69 (s, 3H), 3.70 (s, 3H), 5.49 ppm (s,
1H); 13C NMR (CDCl3): d=39.6 (t), 41.4 (t), 52.8 (q), 52.8 (q), 103.4 (d),
115.8 (s), 152.2 (s), 169.3 (s), 169.5 ppm (s); LRMS (EI): m/z: (%): 197
[M+] (0.5), 166 (71), 165 (100), 138 (23), 80 (38); HRMS (EI): m/z:
calcd: C9H11NO4 [M+]: 197.0688; found: 197.0695.
synthesised and single crystals suitable for X-ray analysis
have been obtained. They are the first examples that illus-
trate the use of methanetriacetic acid, as a scaffold for the
construction of MOFs. Compounds 1 and 2 have layered
structures, the former being a 63-hcb network, whereas the
latter can be viewed as a condensation of 1 in bilayers to
build (4862) sheets. In 3 the 3D framework is of the nia-type,
Preparation of methanetriacetic acid: A mixture of the a,b-unsaturated
cyanide (10 g, 50.7 mmol) and Pd(OH)2 (200 mg) in MeOH (150 mL)
was placed under H2 atmosphere. The reaction mixture was vigorously
stirred until TLC showed complete conversion to the dimethyl-3-(cyano-
methyl)pentanedioate. The mixture was filtered through a pad of Celite.
The solvent was removed under reduced pressure and the residue was
used without further purification. A 60 mL 5m NaOH solution was
added to the residue oil leading a two-phase system. The mixture was
heated and vigorously stirred for 2 h. After cooling, the clear solution
was acidified with 5m sulfuric acid and then evaporated to dryness. The
solid was extracted several times with diethyl ether and the combined ex-
tracts were dried with MgSO4. After filtration, the evaporation of the sol-
vent afforded the tricarboxylic acid as a white solid (9.35 g, 96% yield
from the dimethyl-3-cyanomethileneglutarate). 1H NMR ([D6]acetone):
d=2.50 (d, J=6.4 Hz, 6H), 2.67 ppm (m, 1H); 13C NMR ([D6]acetone):
d=28.4 (d), 36.6 (t), 172.8 ppm (s); elemental analysis calcd (%) for
C7H10O6 (190.0): C 44.21, H 5.30; found: C 44.22, H 5.99.
where both the [GdACHTUNGTRENNUNG
(H2O)]3+ ions and the mta3ꢀ ions act as
six-fold nodes. The complexes 1 and 2 have been obtained
in a gel medium varying slightly the pH value, whereas 3
was prepared by hydrothermal synthesis. This result sup-
ports that high-pressure preparative routes favour high di-
mensional architectures.
Concerning the magnetic properties, a relationship be-
tween the nature of the magnetic coupling and the type of
bridge that links the GdIII centres has been proposed on the
basis of magneto-structural data for digadoliniumACTHUNTGRNEUNG(III)
motifs with carboxylate-type ligands.[24] Compounds 2 and 3
exhibit weak antiferro- [J=ꢀ0.0063 cmꢀ1 (2)] and ferromag-
netic [J=+0.026 cmꢀ1 (3)] interactions that agree with the
above prediction.
Complex [GdACHTNUTRGNENUG(mta)HCATUGNTRNE(NGUN H2O)3]n·4nH2O (1): An aqueous solution of NaOH
was poured into a 0.07m solution of methanetriacetic acid [H2O (3 mL)
and ethanol (4 mL)] for which the pH was adjusted to 5.08. Afterwards,
tetramethoxysilane (0.7 mL) was added to the resulting solution. The
mixture was introduced into test tubes, covered, and stored for one day
at room temperature to allow the formation of the gel. Once the gel has
been formed, an aqueous solution of gadolinium
ACHTUNGERTN(NUNG III) nitrate hexahydrate
0.1m (2.5 mL) was placed on the gel, care being taken to avoid damaging
4044
ꢅ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 4037 – 4047