borohydride (0.076 g, 2 mmol) in small portions over 1 h causing a
moments slightly higher than the spin only value [290 K: = 2.98
B per nickel]; weak overall coupling is again evident.
red colour to develop. The solution was stirred for 2 h, then brought
to reflux for 5 min. After cooling to room temperature the deep red
solution was acidified with 1 M hydrochloric acid (ca. 7 cm3) until
pH = 1 and then the solvent was removed in vacuo. The resulting
brown oily residue was dissolved in saturated sodium chloride
solution (50 cm3) and to this was added 1 M sodium hydroxide
(ca. 5 cm3) until pH = 10. The aqueous solution was extracted
with chloroform (4 × 30 cm3), the organic extracts combined, dried
over anhydrous sodium sulfate, filtered and the solvent removed in
vacuo to give a deep brown oil (0.298 g, 86%). H (300 MHz, solvent
CDCl3, reference TMS): 8.51 (2H, s, H14), 7.58 (2H, s, H12), 7.48
(2H, s, H4), 7.18 (2H, s, H11), 7.13 (2H, d, H13), 4.10 (4H, s, H6),
3.01 (~10H, multiplet, H8, H9 and amine NH). C (75 MHz, solvent
CDCl3, reference solvent): 160.1 (C5), 159.8 (C10), 149.0 (C14),
136.2 (C12), 126.1 (C4), 123.1 (C11), 121.1 (C13), 52.9 (C6), 48.7
(C8), 38.2 (C9). This was usually used without further purification
but if desired purification of this oil could be achieved by convert-
ing it to the dihydrochloride salt, (H2L2)Cl2 as follows. The oil was
dissolved in dry ethanol (60 cm3), acidified with two equivalents of
concentrated hydrochloric acid and the solvent removed in vacuo
yielding a deep brown powder. This was washed with hot isopro-
pyl alcohol (3 × 10 cm3), filtered and dried in vacuo to give the
dihydrochloride salt as a white powder (0.087, 21%); mp 195 °C
(decomp.). Found: C, 55.7; H, 6.3; N, 19.8. C20H26N6Cl2·ꢀH2O re-
quires: C, 55.8; H, 6.3; N, 19.5%. IR (KBr disk, inter alia) max/cm−1
3250, 2946, 2762, 2668, 2452, 1593, 1476, 1436, 1057, 1004, 769.
H (300 MHz, solvent D2O, reference DSS): 8.39 (2H, d, H14), 7.79
(2H, t, H12), 7.76 (2H, s, H4), 7.36 (2H, d, H11), 7.30 (2H, t, H13),
4.60 (4H, s, H6), 3.54 (4H, t, H8), 3.22 (4H, t, H9). C (75 MHz,
solvent D2O, reference DSS) 158.5 (C5), 157.5 (C10), 151.2 (C14),
141.8 (C12), 131.4 (C4), 127.2 (C11), 126.0 (C13), 52.0 (C6), 49.8
(C8), 35.4 (C9). FAB m/z (fragment): 349 (L2H+).
Conclusions
The incorporation of 3,6-diformylpyridazine into Schiff-base ligand
systems in recent years has allowed a renewed and varied investi-
gation of the pyridazine moiety and its ability to act as a bridge in
transition metal complexes, both in macrocyclic complexes and,
more recently, in acyclic complexes. The reactions of transition
metal perchlorate salts with the new acyclic pyridazine-containing
L1 and L2 ligands have led to dimetallic complexes in which the
two incorporated metal(II) ions are bridged in the equatorial plane
by the pyridazine unit and an anion (hydroxide, thiocyanate or
azide). Single-crystal X-ray structure determinations carried out on
four of these complexes proved this to be the case. Strong antiferro-
magnetic exchange was exhibited by the dicopper(II) complex 1,
which is typical of hydroxide-bridged systems, the pyridazine
bridge playing a minor role in the exchange. Competition between
the pyridazine (antiferromagnetic) and 1,1-bridging azide group
(ferromagnetic) resulted in the observed overall weak antiferro-
magnetic exchange for the dinickel(II) complex 7. Electrochemical
investigation of the complexes revealed quasi- or irreversible pro-
cesses, in contrast to the reversible processes observed in the related
macrocyclic complexes. The electrochemical potentials of these
processes in the acyclic complexes, when compared with the cor-
responding Cu(II) and Co(II) L3 macrocyclic complexes, revealed
that the potentials at which the equivalent reductions and, in the case
of cobalt, oxidations, occur are substantially more negative for the
acyclic complexes. This decreased stabilisation of the lower oxida-
tion states is attributed to the presence of one less pyridazine ring
in the acyclic complexes as compared to the related macrocyclic
complexes, and to the lack of the macrocyclic ring.
[Cu2L1(-OH)](ClO4)3 (1). To a stirred yellow solution of L1
(0.300 g, 0.877 mmol) in dry acetonitrile (27 cm3), was added a blue
solution containing Cu(ClO4)2·6H2O (0.650 g, 1.754 mmol) in dry
acetonitrile (26 cm3). The resulting intense blue–green solution was
stirred for 4 h after which it was reduced in volume to ca. 20 cm3. 1
was isolated as a mixture of cyan powder and intense purple single
crystals by vapour diffusion of diethyl ether into the reaction solu-
tion. This mixture was filtered off, mechanically separated and the
two samples dried in vacuo. The powder and crystals were shown to
be identical by elemental analysis (0.460 g, 58%). Found: C, 30.6; H,
2.5; N, 10.8. C20H21N6Cl3O13Cu2 requires: C, 30.5; H, 2.7; N, 10.7%.
IR (KBr disk, inter alia) max/cm−1: 3512, 3061, 2955, 2916, 2856,
1633, 1606, 1565, 1480, 1440, 1096, 799, 629. H (300 MHz, 233 K,
solvent CD3CN, reference external TSP): ~10.85 (2H, br, H6), ~9.35
(2H, br, H14), 8.15 (2H, s, H4), 8.23 (2H, t, H12), 7.99, 7.85 (2H, d,
H11, H13), ~5.0 (4H, br, H8), 3.48 (4H, s, H9). C (75 MHz, solvent
CD3CN, reference external TMS): 166.2 (C3), 159.4 (C10), 149.4
(C8), (140.7, 140.4) (C1, C7), 132.9 (C9), 51.0 (C4), 34.8 (C5).
FAB m/z (fragment): 822 ([Cu2L1(-OH)(H2O)2(ClO4)3]+); 724
([Cu2L1(-OH)(H2O)2(ClO4)2]+); 688 ([Cu2L1(-OH)(ClO4)2]+);
671([Cu2L1(ClO4)2]+);588([Cu2L1(-OH)(ClO4)]+).m(CH3CN) =
347 mol−1 cm2 −1 (cf. 340–420 mol−1 cm2 −1 for a 3:1 electrolyte
Experimental
Starting materials and reaction procedures
As reported previously except for the following.11,13 3,6-Diformyl-
pyridazine was synthesised according to the published procedure.13 2-
(2-Aminoethyl)pyridine (Aldrich, 95%) was distilled under vacuum
before use and o-aminophenol (Riedel-de Haen) was used without
further purification. The magnetic measurements were carried out on
a Quantum Design MPMS5 SQUID Instrument as described earlier.8
Other measurements were carried out as described previously.13
CAUTION! Whilst no problems were encountered in the course
of this work, perchlorate mixtures are potentially explosive and
should therefore be handled with appropriate care.
L1. To a stirred yellow solution of 3,6-diformylpyridazine
(0.780 g, 5.7 mmol), in dry acetonitrile (60 cm3), was added a
clear colourless solution of 2-(2-aminoethyl)pyridine (1.400 g,
11.4 mmol) in dry acetonitrile (40 cm3). The resulting clear golden
yellow solution was stirred overnight during which time the colour
intensified. The solution was then reduced to dryness in vacuo to
give the impure ligand L as a light fawn solid in quantitative yield.
This was usually used without further purification, but could be
purified by recrystallisation from dichloromethane or benzene by
vapour diffusion of pentane; mp 110 °C. Found: C, 69.6; H, 6.2;
N, 24.5. C20H20N6 requires: C, 69.7; H, 5.9; N, 24.4%. IR (KBr
disk, inter alia) max/cm−1: 3043, 3013, 2927, 2881, 2857, 1643,
1588, 1568, 1474, 1431, 765. H (300 MHz, solvent CDCl3, refer-
ence TMS): 8.61 (2H, s, H6), 8.56 (2H, d, H14), 8.15 (2H, s, H4),
7.58 (2H, t, H12), 7.17 (2H, d, H11), 7.12 (2H, d of d, H13), 4.17
(4H, t, H8), 3.23 (4H, t, H9). C (75 MHz, solvent CDCl3, reference
CDCl3): 159.8 (C6), 159.1 (C5), 157.3 (C10), 149.2 (C14), 136.1
(C12), 124.4 (C4), 123.4 (C11), 121.3 (C13), 60.9 (C8), 39.0 (C9).
FAB m/z (fragment): 345 (C20H21N6); 252 (C14H14N5).
in CH3CN).26
max(CH3CN) = 542 nm ( = 224 dm3 mol−1 cm−1).
max(H2O) = 541 nm ( = 153 dm3 mol−1 cm−1); = 0.4 B per Cu
[Gouy and Evans method (CH3CN)].
General procedure for copper halide derivatives 2–4
To a stirred blue–green solution of 1 was added the appropriate tet-
raethylammonium halide which resulted in the formation of a fine
dark green (2 or 3) or brown (4) precipitate. This mixture was stirred
overnight after which time the precipitate was filtered off, washed
with dry acetonitrile (10 cm3) and dried in vacuo.
[Cu2L1(-OH)Cl2]ClO4 (2). Yield: 0.030 g, 51%. Found: C,
36.4; H, 3.3; N, 13.0. C20H21N6Cl3O5Cu2 requires: C, 36.5; H, 3.2; N,
12.8%. IR (KBr disk, inter alia) max/cm−1: 3407, 3072, 2926, 1630,
L2. To a stirred room-temperature yellow solution of L1 (0.344 g,
1 mmol), in dry acetonitrile (50 cm3), was added solid sodium
2 1 6 2
D a l t o n T r a n s . , 2 0 0 4 , 2 1 5 7 – 2 1 6 5