2.1 Preparation of tris(oxalato)-metallate salts
Tris(oxalato)-metallate anions have been synthesised for use as counter-ions in the charge-transfer salts investigated in this thesis. Tris(oxalato)-metallate anions are ideal since the metal centre can easily be changed, accompanied by only very small changes in the structure o f the anion. Therefore the magnetic properties o f the series o f BEDT-TTF charge-transfer salts with these anions can be investigated with various magnetic moments in an isostructural series. Tris(oxalato)-metallate anions are convenient for use in electrocrystallisation as it is possible to synthesise them with various counter-cations which are therefore soluble in a range o f solvents.
Composition o f the prepared tris(oxalato)-metallates were checked by elemental analysis. Carbon, hydrogen and nitrogen analyses were performed at University College London Micro Analytical Laboratory.
2.1.1 Tris(oxalato)-complexes of 3d metals
The first superconductor containing paramagnetic 3d moments was a charge-transfer
salt o f BEDT-TTF with tris(oxalato)-ferrate*° anions,
j5"-(BEDT-TTF)4[(H3 0)Fe(C2 0 4)3] C6H5CN*’l This was the first example o f
superconductivity and localised paramagnetism being observed in a molecular lattice and it is only reasonable to assume that other 3d tiis(oxalato)-metallate anions may yield isostructural salts o f this compound and so allow a study o f the effect o f changing the magnetic moment on the superconductivity. In order to prepare such compounds a range o f tris(oxalato)-complexes o f 3d metals was synthesised as starting materials.
___________________________________ Experimental___________________________________ Z L h l (NH43Ti2(C^4plOHAP^
3(NH4>2HC2 0 4 + 2TiCl3 + IOH2O (NH4)3[Ti2(C2O4)3].10H2O + 3NH4CI + 3HC1
To a solution o f acid ammonium oxalate (18.00g) in H2O (250ml), titanium
trichloride (12.35g) was added. The solution was stirred for 2 hours. Ethanol (100ml) was added to precipitate the white product, which was recrystallised 3 times from H2O giving white needles. Calculated for (NH4)3Ti2(C2 0 4 ) 3 IOH2O, %: C 12.13, H
5.43, N 7.07; Found, %: C 12.53, H 5.44, N 8.77. Yield = 13.49g (63%). Z L L 2 (NH^3Cr(C204s.3H2(P^
( N H4)2C r2 0? + 7 H 2 C 2 O 4 + 2 ( N H 4 ) 2 C 2 0 4 2 ( N H 4 ) 3 [ C r ( C 2 0 4 ) 3 ] . 3 H 2 0 + 6 C O 2 + H 2 O
To a solution o f ammonium oxalate monohydrate (4.436g) and oxahc acid dihydrate
(13.75g) in H2O (800ml), powdered ammonium dichromate (4.07g) was added in
small portions with vigorous stirring. When the reaction had ended, the solution was evaporated nearly to dryness and left to crystallise by solvent evaporation. The product was recrystallised from H2O and gave dark green crystals. Calculated for
(NH4)3Cr(C2 0 4)3.3H2 0, %: C 16.99, H 4.28, N 9.90; Found, %: C 16.91, H 4.23, N
10.04. Yield = 11.09g (81%). Z 1.L 3 KiCr(C204^2H2(P^
K 2 C r2 0 7 + 7H2C2O4 + 2K2C2O4 2 K 3 [C r(C 2 0 4 )3 ].2 H 2 0 + 6 C 0 2 + 3 H 2 0
To a solution o f potassium oxalate monohydrate (5.75g) and oxalic acid dihydrate
(13.75g) in H2O (800ml), powdered potassium dichromate (4.75g) was added in
small portions with vigorous stirring. When the reaction had ended, the solution was evaporated nearly to dryness and left to crystallise by solvent evaporation. The product was recrystallised from H2O and gave dark green crystals. Calculated for
___________________________________ Expérimental___________________________________ K3Cr(C2 0 4)3.2H2 0, %: C 15.33, H 0.85, N 0.00; Found, %: C 15.17, H 1.08, N 0.00.
Yield = 13.49g (86%).
2.L L 4 (NH43Fe(C/)4)3^3H^^
Fe2(S04)3 + 3BaC204 Fe2(C204>3 + 3BaS04
Fe2(C204)3 + 3(NH4)2C204 + 6H20 2(NH4)3[Fe(C204)3].3H20
Barium oxalate was prepared by mixing barium chloride (40g) and sodium oxalate (23.44g) in H2O (500ml) and stirring for 3 hours. The white solid was then filtered
and washed with H2O. A suspension o f barium oxalate (20g), ferric sulphate (lOg)
and ammonium oxalate (8.424g) was made in H2O (240ml) and refluxed for 24 hours
with constant stirring. After filtering and washing the precipitate with H2O, the filtrate
was evaporated to 50ml and left to crystallise by solvent evaporation. The dark green
crystals which formed were recrystallised 3 times fi'om H2O. Calculated for
(NH4)3Fe(C2 0 4)3.3H2 0, %: C 16.79, H 4.23, N 9.81; Found, %: C 17.00, H 3.93, N
9.94. Yield = 17.54g (91%). 2A.1.5 KsFe(C204)j.3H2(F^
Fe2(S04>3 + 3BaC204 Fe2(C204>3 + 3BaS04
F e2( C2 0 4)3 + 3 K 2 C 2 O 4 + 6 H 2 O 2 K 3 [ F e ( C 2 0 4 ) 3 ] . 3 H 2 0
Barium oxalate was prepared by adding barium chloride (40g) and sodium oxalate (23.44g) to H2O (500ml) and stirring for 3 hours. The white solid was then filtered
and washed with H2O. Barium oxalate (25g), ferric sulphate (12.5g) and potassium
oxalate (13.65g) were mixed in H2O (300ml) and refluxed for 24 hours. After filtering
and washing the precipitate with H2O, the filtrate was evaporated to 50ml and left to
crystallise by solvent evaporation. The light green crystals which formed were recrystallised 3 times fi'om H2O. Calculated for KsFe(C2 0 4)3.3H2 0, %: C 14.67, H
___________________________________ Experimental___________________________________ Z l.1 .6 (N H 4 ^ C ^ 4 ^ 3 .5 H 0 > ^
Co(CO)3 + H2C2O4 C0C2O4 + H2O + CO2
2C0C2O4 + 4(NH4>2C2 0 4 + PbQz + 4HC2H3O2 2(NH4)3[Co(C2 0 4)3].3.5H2 0 + 2NH4C4H3O2
+ Pb(C2H3Q2)2 + 2H20
Cobalt carbonate (11.90g) was added to a solution o f oxalic acid (12.60g) and
ammonium oxalate (29.16g) in H2O (250ml) at 70®C. When the solution has cooled to
40®C, lead dioxide (11.95g) was added slowly with vigorous stirring, followed by dropwise addition o f glacial acetic acid (25ml). The solution was stirred for a further hour over which time the colour changed from red to dark green. The excess lead oxide was filtered off, and the ammonium tris(oxalato)-cobaltate was precipitated by the addition o f ethyl alcohol (250ml) and the dark green crystals were recrystallised fi’om H2O. Calculated for (NH4)3Co(C2 0 4)s 3H2O, %: C 16.72, H 4.21, N 9.25;
Found, %: C 16.43, H 4.89, N 12.90. Yield = 24.12g (66%). 2.1.2 Tris(oxalato)-complexes of 4d metals
By replacing the 3d ion in j?'-(BEDT-TTF)4[(H3 0)Fe(C2 0 4)3].C6H5CN with a 4d
example, such as ruthenium or rhodium, it may be possible to alter the structure and properties vrithin this set o f charge-transfer salts. Synthesis o f these 4d tris(oxalato)-metallate anions proved more demanding than the 3d ones.
2,1.2.1 (NH4)3Ru(C204hL5HiC^^
RuQz + (NH4)2HC20 4 (NH4)3Ru(C204)3.1.5H2O
Hydrated ruthenium trichloride (lOg) was dissolved in 4M hydrochloric acid (100ml). Concentrated aqueous sodium hydroxide was added to precipitate hydrated
ruthenium dioxide, which was washed with H2O. The ruthenium dioxide was refluxed
in H2O (750ml) containing a large excess o f acid ammonium oxalate (45g). The
___________________________________ Experimental___________________________________ excess ammonium oxalate, which was separated by filtration. Methanol was added to the filtrate precipitating the remaining acid ammonium oxalate which was again separated by filtration. The filtrate was cooled in ice and ethanol was added until a yellow solid precipitated. The yellow crystals were recrystallised fi’om ethanol/water (3:1). Calculated for (NH4)3Ru(C2 0 4)3 1 5HzO, %: C 16.15, H 3.39, N 9.42; Found,
%: C 16.63, H 3.56, N 9.29. Yield = 8.24g (38%). 2 ,1 ,2 ,2 K 3 R u (C 2 O 4 h 4 .5 H 0 ^
RuCb + K2C2O4 K3Ru(C2 0 4)3.4.5H2 0
A solution o f hydrated ruthenium trichloride (5.0g) and potassium oxalate (11.8g) in water (100ml) was refluxed with constant stirring for 8 hours. The solution changed colour fi'om black to dark green. A black solid was obtained by addition o f the hot solution to ethanol (250ml) and this was filtered off whilst still warm. The crude product was dissolved in water (10ml) and the solution was poured into ethanol (100ml). The precipitate was collected by filtration and the filtrate tested with AgNOs for the presence o f chloride ions. No chloride ions were present after two reprecipitations. The product was recrystallised from H2O, and evaporation o f the
solvent over silica gel in a desiccator gave dark green needles. Calculated for K3Ru(C2 0 4)3.4.5H2 0, %: C 13.43, H 1.13, N 0.00; Found, %: C 10.37, H 1.20, N
0.14. Yield = 7.61g (56%).
2,1,Z3 (NH4)3Rh(C2O4h4,5H0^^
RhQz + (NH4)2HC204 (NH4)3Rh(C204)3.4.5H20
Rhodium oxide (5.06g) was added to a solution o f aqueous ammonium hydrogen
oxalate (6.96g) in H2O (20ml) and stirred for 1 hour. Ethanol was added to
precipitate yellow crystals, which were recrystallised three times from H2O. Yield =
___________________________________ Experimental___________________________________ 2.1.3 Tris(oxalato)-complexes of 4f metals
A non-anionic 4f tris(oxalato)-metallate complex was synthesised in an attempt to prepare BEDT-TTF charge-transfer salts with a higher magnetic moment than possible for 3d and 4d salts. The 4 f complex proved very simple to prepare in good yield and good crystallinity.
2.L3.1 Gd2(C2O4hlOH20^^^
2Gd(N0 3)3.6H2 0 + 3H2C2O4 Gd2(C2O4)3.10H2O + 6HNQ3
Gadolinium nitrate (1.8g) was dissolved in H 2 O (400ml). 6M H N O 3 (12ml) was
added followed by a solution o f oxalic acid (18g) in H2O (240ml), and the mixture
was stirred for 1 hour. The resultant solution was heated on a water bath for 3 hours after which the tris(oxalato)-metallate began to precipitate. On cooling, the white crystals were left to crystallise overnight, filtered and washed with H 2 O , and then with
ethanol. The white needles were recrystallised twice from H 2 O . Yield = 1.22g (81%).
2.1.4 Tris(oxalato)-complexes of main group metals
A number o f main group metals form tris(oxalato)-complexes which may be useful for preparing diamagnetic analogues o f the paramagnetic BEDT-TTF tris(oxalato)-salts. Preparation o f an isostructural diamagnetic salt would be useful for studying the transport properties in this series o f salts with no paramagnetic interactions in the compound.
2.L4.1 (NH4)3Al(C204h3H2(F^