Inorganica Chimica Acta 357 (2004) 4265–4272
www.elsevier.com/locate/ica
Dinickel(II), dizinc(II) and dilead(II) complexes of a
pyridazine-containing Schiff-base macrocycle
Carsten D. Brandt a, Paul G. Plieger a, Robert J. Kelly a, Duncan J. de Geest a,
Dietmar K. Kennepohl a,b, Simon S. Iremonger a, Sally Brooker a,*
b
a
Department of Chemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand
Centre for Science, Athabasca University, 1 University Drive, Athabasca, Alberta, Canada T9S 3A3
Received 11 May 2004; accepted 12 June 2004
Available online 6 August 2004
Abstract
The study of the mid-late first row transition metal co-ordination chemistry of the pyridazine-containing Schiff-base macrocycle L1
[derived from the (2 + 2) condensation of 3,6-diformylpyridazine and 1,3-diaminopropane] has been completed. Transmetallation
reactions of [Pb2(4 + 4)](ClO4)4 (1) under appropriate conditions have led to the formation of the following complexes,
[Ni2L1(NCS)2(SCN)2] (3), [{Pb2L1}2(l3-OH)2](ClO4)6 (4), and [Zn2L1(CH3CN)4](ClO4)4 (5 Æ 4CH3CN), all of which have been structurally characterised. The analogous triflate salt of 5, [Zn2L1](CF3SO3)4 (6), can only be obtained by template reaction, as transmetallation of 1 with Zn(CF3SO3)2 Æ 6H2O gave 5, albeit in reduced yield. Attempts to synthesise pure [Fe2L1(CH3CN)4](ClO4)4 (7) using
the transmetallation procedure, from either [Pb2(4 + 4)](ClO4)4 or [Zn2L1(CH3CN)4](ClO4)4, were unsuccessful. The electrochemical
studies carried out on [Zn2L1](ClO4)4 (5) revealed multiple reduction processes and associated oxidations, but no processes
corresponding to oxidation of 5.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Macrocycle; Pyridazine; Structure determination; Electrochemistry; Schiff base
1. Introduction
In recent papers, we have reported the lead templated
synthesis of the pyridazine-containing Schiff-base macrocycle L1 (Scheme 1) [1,2], its dimanganese(II) complex,[2] and its dicopper(II) and dicobalt(II) complexes
which have unusual electrochemical properties and interesting magnetic behaviour [3–9]. In these complexes, the
pyridazine moieties doubly bridge the two metal ions, an
arrangement which is well known to mediate magnetic
exchange [9–11]. Tuning the coordination sphere of
the dicobalt(II) complexes led us to obtain the first exam-
ple of an exchange coupled spin crossover complex of cobalt [5,8]. This result fuelled our interest in the
development of single molecules, and arrays of molecules, which might ultimately be able to be developed
as nanoswitches due to their bistability (low () high
spin). A memory device based on magnetic properties
would require a spin-transition with hysteresis [12,13]:
increasing the communication between the metal ions is
N
N
N
N
N
N
N
N
*
Corresponding author. Tel.: +64 3 479 7919; fax: +64 3 479
7906.
E-mail address: [email protected] (S. Brooker).
0020-1693/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.06.013
Scheme 1. Pyridazine-containing Schiff-base macrocycle L1.
4266
C.D. Brandt et al. / Inorganica Chimica Acta 357 (2004) 4265–4272
one way to promote this [14]. Whilst numerous examples
of spin crossover complexes involving cobalt are known
[15–20], the vast majority of examples are of iron [21–29],
so we decided to pursue the iron(II) chemistry of L1. For
completeness, we also prepared a dinickel(II) complex of
L1 and, as an electrochemical probe for our earlier dicobalt [4] and dicopper [3,6,7] complexes, the dizinc(II)
complex. Finally, crystals of a lead(II) complex of the
(2 + 2) macrocycle L1 {as opposed to the dilead(II) complex of the (4 + 4) macrocycle which was structurally
characterised some time ago [1]} were obtained, and
the X-ray crystal structure determined. In this paper,
we present the structures of the resulting dinickel(II), dilead(II), and dizinc(II) complexes [Ni2L1(NCS)2(SCN)2]
(3), [{Pb2L1}2(l3-OH)2](ClO4)6 (4) and [Zn2L1(CH3CN)4](ClO4)4 (5 Æ 4CH3CN), along with the electrochemical study carried out on 5.
the isolation of [Ni2L1(NCS)2(SCN)2] (3), which is
insoluble in water. The IR spectrum of 3 shows the expected absorbance at 1640 cm1, characteristic of the
Schiff-base bonds in the macrocycle. The presence of
two bands due to the NCS-stretches, at 2088 and 2056
cm1, indicates that two different binding modes are
present. Unambiguous assignment of these bands is
not possible due to the narrow range of wavenumbers
observed for the variety of possible co-ordination modes
of thiocyanates [30], however, these are consistent with
the presence of S-bound and N-bound thiocyanate ions,
respectively (see later).
In an early attempt to make a copper(I) complex of
L1 [6,7], we treated 1 with [Cu(CH3CN)4]PF6. To our
surprise the structure determination carried out on the
few single crystals obtained shows that, though ring contraction from the (4 + 4) to the (2 + 2) macrocycle has occurred, the expected transmetallation of the lead(II) ions
by copper(I) ions did not occur. Instead, a small amount
of the doubly hydroxo-bridged dimeric dilead(II) complex of the (2 + 2) macrocycle, [{Pb2L1}2(l3-OH)2](ClO4)6 (4), formed (Scheme 3). The mechanism is
unclear, and we have not attempted to repeat the reaction or to obtain 4 in a different way. Dicopper(I), tetracopper(I) grid and mixed valent dicopper complexes
have been isolated and fully characterized [6,7].
The synthetic target [Zn2L1](ClO4)4 (5) was pursued
for two main reasons. Firstly, it provided an electrochemical blank for comparison with the electrochemically active dicobalt [4] and dicopper [3,6,7] complexes
of L1 and, secondly, the complex itself was of interest
as a starting material for transmetallation reactions.
2. Results and discussion
2.1. Synthesis
[Pb2(4 + 4)](ClO4)4 (1) was synthesised according to
the published procedure [2]. Treatment of 1 with four
equivalents of Ni(NO3)2 Æ 6H2O leads to the expected
ring contraction from the (4 + 4) to the (2 + 2) macrocycle and yields a red crystalline product (Scheme 2). The
microanalysis results indicate that it has the general formula [Ni2L1](NO3)2(ClO4)2 (2), but all attempts to purify the compound proved unsuccessful. Derivatisation of
2 with an excess of sodium thiocyanate in water allowed
4+
N
N
N
N
N
Ni
N
N
N
N
N
N
4+
4 Ni(NO3)2·6H2O
N
N
N
N
4 Fe(ClO4)2·6 H2O
N
N
CH3CN
N
N
N
N
CH3CN
N
N
N
N
N
L
L
Ni
L
L
Pb
Pb
N
N
N
N
Fe
4+
N
Fe
L
2 ClO4
2 NO3
L
L
N
L
4 ClO4
7
2
4 ClO4
10 eq NaNCS
4 Zn(ClO4)2·6H2O
1
H2O
4 Zn(CF3SO3)2·6H2O
2 Fe(ClO4)2·6H2O
CH3CN
CH3CN
CH3CN
NCS
SCN
4+
N
N
N
N
N
Ni
N
N
N
N
N
N
N
N
Zn
Ni
NCS
N
N
ex. NaCF3SO3
4+
N
Zn
N
N
N
N
Zn
N
CH3CN
N
N
Zn
N
SCN
3
4 CF3SO3
4 ClO4
6
5
Scheme 2. Summary of transmetallation reactions of [Pb2(4 + 4)](ClO4)4 (1) presented in this paper (L = CH3CN).
C.D. Brandt et al. / Inorganica Chimica Acta 357 (2004) 4265–4272
4+
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Pb
4267
6+
N
N
N
N Pb N
H O
Pb
N Pb N
N
N
N
N Pb N
O H
N
Pb N
N
N
6 ClO4
4 ClO4
1
4
3
Scheme 3. Formation of [{Pb2L1}2(l -OH)2](ClO4)6 Æ CH3CN (4 Æ 2CH3CN).
Complex 5 was prepared using the standard transmetallation protocol. Transmetallation of 1 with
Zn(ClO4)2 Æ 6H2O gives analytically clean 5 in 90% yield.
Attempts to form the potentially less explosive triflate
analogue, [Zn2L1](CF3SO3)4 (6), by either a transmetallation reaction on 1 or a metathesis reaction on 5, were
unsuccessful (Scheme 2): in both cases only 5 was isolated, albeit in reduced yield. In contrast, the template
synthesis of 6 from 3,6-diformylpyridazine and 1,3diaminopropane in the presence of Zn(CF3SO3)2 Æ 6H2O
did result in the isolation of the triflate analogue 6
(Scheme 4). Unfortunately, the yield of [Zn2L1]
(CF3SO3)4 (6) is poor due to an unidentified oily product
which is present along with the desired crystalline product and is hard to remove.
The infrared spectrum of 5 exhibits a sharp C‚N
stretch at 1647 cm1, and no evidence of either primary
amine stretches (typically 3400–3330 and 3330–3250
cm1) or C‚O stretches [31]. There are bands present
for pyridazine ring stretches (1582 and 1550 cm1).
The perchlorate bands observed (1102 and 625 cm1)
show no signs of peak splitting, therefore the perchlorate ions are not expected to show any significant interactions with the [Zn2L1]4+ cation. Complex 5 was fully
characterized by proton and carbon NMR spectroscopy. The FAB mass spectrum indicates, and X-ray
analysis confirms, that ring contraction from the
(4 + 4) to the (2 + 2) macrocycle has occurred. This has
been observed before in Schiff base chemistry [32–34]
and, in particular, in all of the pyridazine Schiff base
macrocyclic chemistry carried out to date [2–7,9].
For the synthesis of an iron(II) analogue, a similar
procedure to that used for 3 was employed. Transmetallation of 1 with 4 equivalents of Fe(ClO4)2 Æ 6H2O leads
to a colour change to deep purple, indicating the formation of a low spin iron(II) complex. Crystallisation from
CH3CN/TBME yields purple crystalline solid which was
initially believed to be [Fe2L1(CH3CN)4](ClO4)4 (7).
Unfortunately, the IR-spectrum shows a peak at 1718
cm1 indicating the presence of some C‚O bonds.
The NMR spectra, as well as the microanalysis, show
the compound to be contaminated. A different approach
to obtain 7, by the transmetallation of the dizinc(II)
complex of the (2 + 2) macrocycle (5) with two equivalents of Fe(ClO4)2 Æ 6H2O, was therefore tried. Again, a
purple crystalline material was obtained which was initially believed to be 7. However, metal ion analysis
clearly reveals that the transmetallation reaction was
incomplete, despite the intense colour of the product.
Attempts to obtain a pure sample of 7 by recrystallisation failed. The observation that the contaminated diiron(II) complex tended to slowly decompose in solution
(a problem unique to the iron complexes of L1), due
to hydrolysis and/or oxidation, meant that further attempts to obtain this compound were abandoned.
2.2. Crystal structures
Suitable crystals of 3 were grown by slow diffusion of
an aqueous solution of sodium thiocyanate into an
aqueous solution of 2 and the structure determined
(Fig. 1, Table 1). The compound possesses a centre of
2
N
O
N
4+
O
N
+2
+2
H2N
NH2
Zn(CF3SO3)2·6H2O
N
N
N
N
Zn
CH3CN
N
N
Zn
N
4 CF3SO3
6
Scheme 4. Synthesis of [ZnL1](CF3SO3)4 (6) via template reaction.
4268
C.D. Brandt et al. / Inorganica Chimica Acta 357 (2004) 4265–4272
Fig. 1. Perspective view of the molecular structure of the major (80%)
occupancy form of 3 (hydrogen atoms have been omitted for clarity).
Symmetry operation: a = 1 x, y, 1 z.
Table 1
Selected bond lengths, distances (Å) and angles (°) for
[Ni2L1(NCS)2(SCN)2] (3) and [Zn2L1(CH3CN)4](ClO4)4 (5 Æ 4CH3CN)
5 Æ 4CH3CN
3
M M
M–N(1)
M–N(2a)
M–N(3)
M–N(4)
M–N(20)
M–N(30)
M–S(30)
N(1)–M–N(2a)
N(1)–M–N(3)
N(3)–M–N(4)
N(2a)–M–N(4)
N(1)–M–N(20)
N(2a)–M–N(20)
N(3)–M–N(20)
N(4)–M–N(20)
N(1)–M–N(30)
N(2a)–M–N(30)
N(3)–M–N(30)
N(4)–M–N(30)
N(1)–M–S(30)
N(2a)–M–S(30)
N(3)–M–S(30)
N(4)–M–S(30)
3.817(2)
2.083(6)
2.068(6)
2.014(6)
2.030(7)
2.045(7)
3.8265(6)
2.1454(21)
2.1424(21)
2.0907(23)
2.0741(22)
2.1674(22)
2.1953(22)
2.491(3)
105.91(22)
79.93(27)
95.16(31)
78.97(27)
89.88(25)
91.82(24)
89.29(29)
91.15(27)
108.61(8)
77.28(9)
96.65(9)
77.41(9)
85.23(8)
92.46(8)
91.37(9)
95.86(9)
85.96(8)
88.50(8)
88.59(9)
93.12(8)
cyanates, one of which is N-bound, the other one Sbound. The S-bound thiocyanate is disordered between
two orientations such that it is 80% S-bound and 20%
N-bound. The differing co-ordination modes adopted
by the thiocyanates are consistent with the two observed
IR-bands. The Ni Ni distance is 3.817(2) Å.
A few colourless crystals of 4 Æ 2CH3CN suitable for
X-ray diffraction studies were grown by slow diffusion
of diethylether into the CH3CN reaction solution and
the crystal structure determined (Fig. 2, Table 2). The
asymmetric unit contains one molecule of CH3CN, three
perchlorate ions and the monomeric subunit of the dimeric complex, with the other half generated by inversion. The centre of symmetry is located in the centre
of the quadrangle Pb(2)–O(1)–Pb(2a)–O(1a).
The structure determination reveals a doubly l3-hydroxo-bridged dimer of complex dications, with the
macrocycle being significantly folded and the pyridazine
ring planes intersecting at an angle of 74.44(20)°. Both
lead atoms are located above their respective N4 mean
planes [Pb(1) 1.6652(28) Å, Pb(2) 1.7440(28) Å out of
plane]. However, the two lead centres are coordinated
in different co-ordination patterns. Each of them bonds
to four nitrogen donors, but while Pb(1) only bonds to
one hydroxide ion, Pb(2) possesses two hydroxide ions
in its co-ordination sphere. This leads to elongation of
the Pb(2)–N(2) and Pb(2)–N(3) bonds [2.789(6) and
2.737(6) Å, respectively]. The oxygen atom O(1) of the
hydroxide ion bridges the three lead atoms in an almost
symmetrical pattern [Pb(1)–O(1) 2.481(4) Å, Pb(2)–O(1)
2.431(4) Å, Pb(2a)–O(1) 2.486(4) Å]. There are several
weak lead-perchlorate interactions present in the structure. The six perchlorate ions fill the remaining space
between the two macrocyclic subunits and complete the
87.69(17)
92.89(17)
86.15(23)
90.91(20)
inversion located in the plane of the macrocycle between
the two metal centres. Each nickel(II) centre is found to
be octahedrally coordinated in an almost planar macrocycle, with angles subtended at the nickel(II) centre varying from 78.97(27)° to 105.91(22)°. The Ni–N(imine)
distances [2.014(6) and 2.030(7) Å] are slightly shorter
than the Ni–N(pyridazine) distances [2.083(6) and
2.068(6) Å]. The axial positions are occupied by thio-
Fig. 2. Perspective view of the molecular structure of 4 Æ 2CH3CN
(solvent molecules, hydrogen atoms and the remaining two perchlorate
ions have been omitted for clarity). Symmetry operation: a = x,
y + 1, z.
C.D. Brandt et al. / Inorganica Chimica Acta 357 (2004) 4265–4272
4269
Table 2
Selected bond lengths, distances (Å) and angles (°) for of [{Pb2L1}2(l3OH)2](ClO4)6 Æ 2CH3CN (4 Æ 2CH3CN)
Pb(1)–N(1)
Pb(1)–N(6)
Pb(1)–N(7)
Pb(1)–N(8)
Pb(1)–O(1)
Pb(1)–O(12)
Pb(1)–O(21)
Pb(1)–O(24)
Pb(1)–O(33)
N(1)–Pb(1)–N(6)
N(6)–Pb(1)–N(7)
N(7)–Pb(1)–N(8)
N(1)–Pb(1)–N(8)
N(1)–Pb(1)–O(1)
N(6)–Pb(1)–O(1)
N(7)–Pb(1)–O(1)
N(8)–Pb(1)–O(1)
Pb(1)–O(1)–Pb(2)
Pb(1)–O(1)–Pb(2a)
Pb(2)–O(1)–Pb(2a)
2.625(5)
2.662(5)
2.553(5)
2.604(6)
2.481(4)
2.970
3.193
3.214
2.914
70.18(16)
63.68(17)
67.27(18)
63.04(19)
89.26(15)
68.63(14)
127.33(16)
150.97(17)
119.26(15)
122.11(16)
106.78(15)
Pb(2)–N(2)
Pb(2)–N(3)
Pb(2)–N(4)
Pb(2)–N(5)
Pb(2)–O(1)
Pb(2)–O(1a)
Pb(2)–O(12)
Pb(2)–O(14)
Pb(2)–O(31)
N(2)–Pb(2)–N(3)
N(3)–Pb(2)–N(4)
N(4)–Pb(2)–N(5)
N(2)–Pb(2)–N(5)
N(2)–Pb(2)–O(1)
N(3)–Pb(2)–O(1)
N(4)–Pb(2)–O(1)
N(5)–Pb(2)–O(1)
N(2)–Pb(2)–O(1a)
N(3)–Pb(2)–O(1a)
N(4)–Pb(2)–O(1a)
N(5)–Pb(2)–O(1a)
O(1)–Pb(2)–O(1a)
2.789(6)
2.737(6)
2.565(5)
2.615(5)
2.431(4)
2.486(4)
3.057
3.277
3.047
60.47(18)
65.43(18)
63.57(17)
69.42(16)
86.22(15)
146.69(16)
126.21(15)
69.49(14)
145.67(14)
135.04(16)
72.48(15)
77.61(15)
73.22(15)
co-ordination sphere of the four metal centres. Each
perchlorate ion adopts one of three different co-ordination modes. In the first one the Cl(2) perchlorate ion chelates to Pb(1). In the second co-ordination mode the Cl(3)
perchlorate ion bridges the lead(II) centres within the
same macrocycle. The last, Cl(1), perchlorate ion acts
as a bidentate chelate at Pb(2) and as a bridging ligand
between two lead(II) centres in different macrocycles
[Pb(1a) and Pb(2)]. The Pb–Operchlorate distances vary between 2.970 Å [Pb(1)–O(12)] and 3.277 Å [Pb(2)–O(14)].
Therefore, both lead atoms are surrounded by four nitrogen and five oxygen donors. There is also an extensive
hydrogen-bonding network between the perchlorate ions
and the solvent molecules present in the unit cell.
Crystals of [Zn2L1(CH3CN)4](ClO4)4 (5 Æ 4CH3CN)
suitable for X-ray diffraction studies were grown by slow
diffusion of diethylether into an CH3CN solution of
[Zn2L1](ClO4)4 (Fig. 3, Table 1). Complex 5 displays a
molecular structure similar to that reported for
[Co2L1-(H2O)4](ClO4)4 [8]. The asymmetric unit consists
of one half of each of two independent complexes with
the other halves generated by inversion. There are no
significant differences between the two macrocyclic complexes. The X-ray crystal structure of 5 Æ 4CH3CN reveals the presence of four bound CH3CN molecules.
These were not observed in the elemental analysis of
the complex. Drying under vacuum removes these co-ordinated molecules from the complex, a feature not
uncommon in this family of dimetallic L1 macrocycles.
The zinc(II) centres are in a distorted octahedral donor
environment, with angles subtended at the zinc(II) centres varying from 77.28(9)° to 108.61(8)°. The Zn Zn
Fig. 3. Perspective view of the molecular structure of 5 Æ 4CH3CN (only
one of the two independent molecules is shown and hydrogen atoms
and perchlorate ions have been omitted for clarity). Symmetry
operation: a = x + 2, y + 2, z + 1.
separations in 5 Æ 4CH3CN are 3.8265(6) and 3.8234(6)
Å. The macrocyclic ligand is nearly undistorted with
the metal centres sitting almost exactly in their respective N4 macrocyclic basal planes [Zn(1) 0.040(1) Å and
Zn(2) 0.017(1) Å out of plane]. The donors are all nitrogen atoms, consisting of two pyridazine and two imine
donors from the macrocycle and two co-ordinated
CH3CN molecules. The Zn–N(CH3CN) bonds are longer [2.1674(2) and 2.1953(22) Å] than the Zn–Nmacrocycle
bond lengths [2.0741(22)–2.1454(21) Å].
2.3. Electrochemical studies
Electrochemical investigations of the dizinc(II) complex 5 were carried out in CH3CN at a concentration
of 1 mmol L1 and were referenced to 0.01 mol L1
AgNO3 in CH3CN/Ag(s). As a further reference check,
ferrocene was added at the conclusion of each experiment: the Fc/Fc+ couple consistently occurred at E1/
2 = + 0.07 ± 0.01 V with DE = 0.07 V.
Owing to its instability, the free Schiff-base ligand has
not yet been isolated. Accordingly, the dizinc(II) complex
5 was studied as a reference compound to assist with
assigning electron transfer sites (metal vs ligand) for the
redox processes observed in the dicobalt [4,35] and dicopper [3,6,7] complexes of L1, zinc(II) being electroinactive
over the range of interest. The cyclic voltammogram of 5
in CH3CN is complex, giving multiple reduction processes and associated oxidations but no processes corresponding to oxidation of 5 (supplementary data).
A closer examination of the first reduction process by
reversing the scan at 0.80 V (Fig. 4) gives one reduction wave (Epc = 0.67 V) and two return oxidation
4270
C.D. Brandt et al. / Inorganica Chimica Acta 357 (2004) 4265–4272
the 290–1090 nm scan range and it corresponds to the
n ! p* transition [40,41].
4
2
0
3. Conclusion
I / µA
-2
-4
-6
-8
-10
-12
-1.00
-0.80
-0.60
-0.40
-0.20
0.00
0.20
0.40
0.60
E / V vs. 0.01 M AgNO3/Ag(s)
Fig. 4. Cyclic voltammogram of 5 in acetonitrile, scan rate 0.1 V s1.
waves (Epa = 0.56 and 0.46 V, respectively). A subsequent scan rate study showed these processes to be electrochemically quasi-reversible. Controlled potential
coulometry at E = 0.80 V indicated that this is a two
electron process (98% of 2e, If = 2.5% of Ii). Repeating
the cyclic voltammogram over the same range after
coulometry gives no waves at all, showing that the process is chemically irreversible. The chemically irreversible
two electron reduction process is ligand based and may
be due to the well known reduction of a pyridazine unit
to give a dihydropyridazine [36,37]. The second pyridazine ring in L1 may be reduced at slightly more negative
potentials, as it may be influenced by the reduction of
the first pyridazine ring [communication through the
zinc(II) metal centres]. The reduction of substituted
pyridazines is known to proceed via a complex series
of pH dependent processes [36,37], which could account
for the large number of reduction processes observed for
5 (supplementary data). The irreversible peak at
Epc = 1.92 V in the full scale cyclic voltammogram is
at a potential typical of the reduction of a Schiff-base
to a secondary amine (typical values 1.82 to 2.15 V
in CH3CN versus SCE) [38,39].
To try and further understand the two electron reduction process occurring between 0.40 and 0.80 V, a
spectroelectrochemical investigation was undertaken
during controlled potential electrolysis of 5 at 0.80 V
(supplementary data). After the passage of ca. one electron (94%), two absorbance maxima had developed,
k1 = 335 nm (e ca. 1382 mol1 L cm1) and k2 = 525 nm
(e ca. 983 mol1 L cm1). These two bands decreased
in absorbance during addition of the second electron
(92%), and a new absorbance maximum developed at
k3 = 414 (e ca. 1796 mol1 L cm1). There are many literature examples of substituted dihydropyridazines, however, very few have been investigated by UV–Vis
spectroscopy. Of those that have been investigated,
there is typically only one absorption maximum, between 370 and 447 nm (e = 150220 mol1 L cm1), in
These results, along with those reported in previous
papers, reveal the accommodating nature of the macrocycle L1. Its ability to co-ordinate all of the divalent metal
ions from Mn(II) to Zn(II) [as well as to Cu(I) and Pb(II)]
has led to the isolation of a wide range of interesting dinuclear, doubly pyridazine-bridged, complexes. In the case
of iron(II), neither the transmetallation of
[Pb2(4 + 4)](ClO4)4 nor of [Zn2L1](ClO4)4 was an effective
way to access the iron(II) complex and only very impure
[Fe2L1(CH3CN)4](ClO4)4 could be obtained. An atypical
problem for this series of complexes was the observation
that the diiron(II) complex tended to slowly decompose
in solution, due to hydrolysis and/or oxidation. These severe synthetic problems and the similar solubility of the
diiron(II) complex and the impurities prevented the isolation of pure [Fe2L1(CH3CN)4](ClO4)4.
4. Experimental
4.1. Materials
3,6-Diformylpyridazine was prepared according to a
slight modification of the published procedure [2].
[Pb2(4 + 4)](ClO4)4 (1) was synthesised according to the
literature preparation [2]. All reagents and solvents were
used as received, without further purification, unless
otherwise stated. CH3CN was refluxed over calcium hydride and distilled prior to use.
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.
4.2. Synthesis
4.2.1. [Ni2L1(NCS)2(SCN)2] (3)
To a suspension of [Pb2(4 + 4)](ClO4)4 (1) (151 mg, 0.1
mmol) in CH3CN (50 cm3) was added a solution of Ni(NO3)2 Æ 6H2O (118 mg, 0.4 mmol) in CH3CN (10 cm3).
The solution immediately darkened and a pale brown
precipitate formed. After a further 30 min at reflux temperature the solution was cooled and the insoluble nitrates removed by filtration. After removing the solvent
in vacuo the residue was redissolved in water (20 cm3)
and a 10-fold excess of solid NaNCS (80 mg, 1.0 mmol)
was added. On standing, dark red block crystals formed,
suitable for X-ray analysis (90.0 mg, 51%). Anal. Calc. for
C22H20N12S4Ni2: C, 37.9; H, 2.9; N, 24.1; S 18.4. Found
C, 37.5; H, 3.1; N, 24.1; S, 18.1%. IR (inter alia) m/cm1:
C.D. Brandt et al. / Inorganica Chimica Acta 357 (2004) 4265–4272
4271
3046, 3029(m), 2927, 2913, 2856, 2088, 2056, 1640, 1580,
1552. FAB mass spectrum: m/z 464 [Ni2(L1)]+.
(KBr disk) m/cm1: 1638, 1575, 1545, 1431, 1342, 1320, 1145,
1113, 1087, 885, 636, 626.
4.2.2. [Zn2L1](ClO4)4 (5)
To a yellow suspension of [Pb2(4 + 4)](ClO4)4 (251
mg, 0.17 mmol) in CH3CN (60 cm3) was added a solution of Zn(ClO4)2 Æ 6H2O (248 mg, 0.67 mmol) in
CH3CN. The resulting solution was refluxed for 30 minutes and evaporated in vacuo to ca. 40 cm3. Vapour diffusion of diethylether into the resulting solution yielded
slightly pink crystals of [Zn2(L1)(CH3CN)4](ClO4)4,
which on drying in vacuo gave [Zn2(L1)](ClO4)4 (267
mg, 90%). Anal. Calc. for C18H20N8Cl4O16Zn2: C,
24.7; H, 2.3; N, 12.8. Found: C, 24.8; H, 2.3; N,
12.5%. 1H NMR (CD3CN): d = 2.46 (m, 4H,
CH2CH2N), 4.51 (t, 8H, CH2CH2N), 8.97 (s, 4H, Harom),
9.02 (s, 4H, N‚CH); 13C NMR (CD3CN): d = 27.3,
58.4, 137.6, 151.8, 159.1. IR (KBr disk) m/cm1: 3424,
3067, 2928, 1647, 1582, 1550, 1441, 1344, 1102, 928,
884,
625.
FAB
mass
spectrum:
m/z
775
[Zn2(L1)(ClO4)3]+,
676
[Zn2(L1)(ClO4)2]+,
577
[Zn2(L1)ClO4]+. Km(CH3CN) = 375 mol1 cm2 X1 (cf.
340–420 for a 3:1 electrolyte in CH3CN) [42].
4.3. X-ray crystallography
4.2.3. [Zn2L1](CF3SO3)4 (6)
To a yellow solution of 3,6-diformylpyridazine (90.0
mg, 0.66 mmol) in CH3CN (20 cm3) was added a solution of Zn(CF3SO3)2 Æ 6H2O (312 mg, 0.66 mmol) in
CH3CN (20 cm3). To the resulting clear yellow solution,
1,3-diaminopropane (49.0 mg, 0.66 mmol) in CH3CN
(10 cm3) was added. The resulting pale yellow solution
was stirred overnight. The product was isolated as pale
pink crystals by vapour diffusion of diethylether into
the CH3CN solution, filtered off, and dried in vacuo to
give [Zn2(L1)](CF3SO3)4 (46.0 mg, 13%). Anal. Calc.
for C22H20N8S4F12O12Zn2 Æ 2H2O: C, 23.8; H, 2.2; N,
10.1; S, 11.5. Found: C, 24.0; H, 2.3; N, 10.1; S,
11.8%. IR (KBr disk) m/cm1: 3420, 3060, 2957, 1647,
1586, 1556, 1450, 1345, 1238, 1160, 1028, 959, 888, 638.
4.2.4. [Fe2L1(CH3CN)4](ClO4)4 (7)
A deep blue solution of Fe(ClO4)2 Æ 6H2O (191 mg,
0.53 mmol) in CH3CN (5 cm3) was added quickly to a
stirred pale pink solution of [Zn2(L1)](ClO4)4 (5) (231
mg, 0.26 mmol) in CH3CN (50 cm3). The resulting purple reaction mixture was left to stir for 4 h. After reduction of the volume to 20 cm3 the mixture was filtered.
The product was isolated by vapour diffusion of TBME
into the CH3CN solution. The purple crystalline material was filtered, washed with TBME and air-dried.
The elemental and spectroscopic analysis reveals the
purple material to be very contaminated. All attempts
to purify the material were unsuccessful. 1H NMR
(CD3CN): d = 2.40 (m, 4H, CH2CH2N), 4.46 (m, 8H,
CH2CH2N), 8.91 and 8.97 (each s, 8H, N‚CH and Harom);
13
C NMR (CD3CN): d=28.3, 59.5, 138.8, 152.9, 160.1. IR
Crystal data for [Ni2L1(NCS)4] (3) (brown block,
T = 163 K): C22H20N12S4Ni2, M = 698.16, monoclinic,
space group P21/c, a = 9.164(2), b = 10.765(5),
c = 13.987(3) Å, b = 92.36(3)°, U = 1378.7(8) Å3, Z = 2,
Dcalc = 1.682 g cm3, l = 1.71 mm1, F(0 0 0) = 712, 2633
reflections collected (3 < h < 26°), 2625 independent
(Rint = 0.0213), 2615 used in structure refinement;
R1 = 0.0569[I > 2r(I)]; wR2 = 0.2769 (all data), goodnessof-fit = 1.16 for 188 parameters and 8 restraints, largest
difference peak, hole = 0.963, 1.405 e Å3. The central
CH2 group is found to be disordered over two sites
70:30, one thiocyanate ion was found to be disordered
over two orientations (80% S-bound: 20% N-bound).
CCDC-231401.
Crystal data for [{Pb2L1}2(l3-OH)2](ClO46 Æ 2CH3CN (4 Æ 2CH3CN) (colourless plate, T = 163 K):
C36H42N20Cl6O26Pb4 Æ 2CH3CN, M = 1160.27, monoclinic, space group P21/n, a = 12.459(4), b = 16.243(6),
c = 17.727(6) Å, b = 103.252(5)°, U = 3492(2) Å3, Z = 2,
Dcalc = 2.207 g cm3, l = 9.934 mm1, F(0 0 0) = 2192,
43973 reflections collected (2.10 < h < 26.45°), 7088 independent (Rint = 0.0577), 7088 used in structure refinement; R1 = 0.0366[I > 2r(I)]; wR2 = 0.1049 (all data),
goodness-of-fit = 1.027 for 453 parameters and 0 restraints, largest difference peak, hole = 1.895, 3.288
e Å3. The 10 highest electron residues are located
around the heavy atoms at a distance of around 1 Å.
CCDC-231402.
Crystal
data
for
[Zn2L1(CH3CN)4](ClO4)4
(5 Æ 4CH3CN) (colourless plate, T = 148 K): C26H32N12
Cl4O16Zn2, M = 1041.18, triclinic, space group P 1,
a = 11.0867(3),
b = 11.6844(3),
c = 17.2672(5)
Å,
a = 87.1550(10)°, b = 87.2050(10)°, c = 65.1570(10)°,
U = 2026.37(10) Å3, Z = 2, Dcalc = 1.706 g cm3, l = 1.530
mm1, F(0 0 0) = 1056, 13370 reflections collected
(1.92 < h < 30.44°), 9754 independent (Rint = 0.0303),
9754 used in structure refinement; R1 = 0.0373[I > 2r(I)];
wR2 = 0.0979 (all data), goodness-of-fit = 0.911 for 494
parameters, largest difference peak, hole = 0.82, 0.66
e Å3. CCDC-231403.
X-ray data were collected on a Siemens four circle (3)
or Bruker SMART (4 Æ 2CH3CN and 5 Æ 4CH3CN) diffractometer (k = 0.71073 Å) and the structures solved
and refined using SHELXS [43,44] and SHELXL [45].
Acknowledgements
This work was supported by grants from the University of Otago and the Marsden Fund (Royal Society of
New Zealand). D.K.K. thanks Athabasca University for
4272
C.D. Brandt et al. / Inorganica Chimica Acta 357 (2004) 4265–4272
granting him study leave. We are grateful to Professor
W.T. Robinson and Dr. J. Wikaira (University of Canterbury) for the X-ray data collections.
Appendix A. Supplementary material
Supplementary data associated with this article can
be found in the online version at doi:10.1016/
j.ica.2004.06.013.
References
[1] S. Brooker, R.J. Kelly, G.M. Sheldrick, J. Chem. Soc., Chem.
Commun. (1994) 487.
[2] S. Brooker, R.J. Kelly, J. Chem. Soc., Dalton Trans. (1996) 2117.
[3] S. Brooker, R.J. Kelly, B. Moubaraki, K.S. Murray, Chem.
Commun. (1996) 2579.
[4] S. Brooker, R.J. Kelly, P.G. Plieger, Chem. Commun. (1998)
1079.
[5] S. Brooker, P.G. Plieger, B. Moubaraki, K.S. Murray, Angew.
Chem., Int. Ed. 38 (1999) 408 and front cover feature.
[6] S. Brooker, S.J. Hay, P.G. Plieger, Angew. Chem., Int. Ed. 39
(2000) 1968.
[7] S. Brooker, T.C. Davidson, S.J. Hay, R.J. Kelly, D.K. Kennepohl, P.G. Plieger, B. Moubaraki, K.S. Murray, E. Bill, E.
Bothe, Coord. Chem. Rev. 216–217 (2001) 3.
[8] S. Brooker, D.J. de Geest, R.J. Kelly, P.G. Plieger, B. Moubaraki,
K.S. Murray, G.B. Jameson, J. Chem. Soc., Dalton Trans. (2002)
2080.
[9] S. Brooker, Eur. J. Inorg. Chem. (2002) 2535 and front cover
feature.
[10] Y. Zhang, L.K. Thompson, M. Bubenik, J.N. Bridson, J. Chem.
Soc., Chem. Commun. (1993) 1375.
[11] T. Otieno, S.J. Rettig, R.C. Thompson, J. Trotter, Inorg. Chem.
34 (1995) 1718.
[12] O. Kahn, C.J. Martinez, Science 279 (1998) 44.
[13] H. Toftlund, Magnetism: A Supramolecular Function, Vol.
NATO ASI Series C, vol. 484, Kluwer Academic Press, The
Netherlands, 1996.
[14] J.A. Real, A.B. Gaspar, V. Niel, M.C. Muñoz, Coord. Chem.
Rev. 236 (2003) 121.
[15] A.B. Gaspar, M.C. Muñoz, V. Niel, J.A. Real, Inorg. Chem. 40
(2001) 9.
[16] R. Clerac, F.A. Cotton, K.R. Dunbar, T. Lu, C.A. Murillo, X.
Wang, J. Am. Chem. Soc. 122 (2000) 2272.
[17] R. Sieber, S. Decurtins, H. Stoeckli-Evans, C. Wilson, D. Yufit,
J.A.K. Howard, S.C. Capelli, A. Hauser, Chem. Eur. J. 6 (2000)
361.
[18] K. Heinze, G. Huttner, L. Zsolnai, P. Schober, Inorg. Chem. 36
(1997) 5457.
[19] P. Thuery, J. Zarembowitch, Inorg. Chem. 25 (1986) 2001.
[20] J. Zarembowitch, O. Kahn, Inorg. Chem. 23 (1984) 589.
[21] K. Nakano, N. Suemura, S. Kawata, A. Fuyuhiro, T. Yagi, S.
Nasu, S. Morimoto, S. Kaizaki, Dalton Trans. (2004) 982.
[22] B.A. Leita, B. Moubaraki, K.S. Murray, J.P. Smith, J.D. Cashion,
Chem. Commun. (2004) 156.
[23] M. Ruben, E. Breuning, J.-M. Lehn, V. Ksenofontov, F. Renz,
P. Gütlich, G.B.M. Vaughan, Chem. Eur. J. 9 (2003) 4422.
[24] J. Elhaı̈k, V.A. Money, S.A. Barrett, C.A. Kilner, I.R. Evans,
M.A. Halcrow, Dalton Trans. (2003) 2053.
[25] P.J. van Koningsbruggen, Y. Garcia, H. Kooijman, A.L. Spek,
J.G. Haasnoot, O. Kahn, J. Linares, E. Codjovi, F. Varret, J.
Chem. Soc., Dalton Trans. (2001) 466.
[26] O. Roubeau, J.M.A. Gomez, E. Balskus, J.J.A. Kolnaar, J.G.
Haasnoot, J. Reedijk, New J. Chem. 25 (2001) 144.
[27] P. Gütlich, Y. Garcia, H.A. Goodwin, Chem. Soc. Rev. 29 (2000)
419.
[28] P.A. Anderson, T. Astley, M.A. Hitchman, F.R. Keene, B.
Moubaraki, K.S. Murray, B.W. Skelton, E.R.T. Tiekink, H.
Toftlund, A.H. White, J. Chem. Soc., Dalton Trans. (2000)
3505.
[29] D.L. Reger, C.A. Little, A.L. Rheingold, M. Lam, T.L. Concolino, A. Mohan, G.J. Long, Inorg. Chem. 39 (2000) 4674.
[30] K. Nakamoto, Infrared and Raman Spectra of Inorganic Coordination Compounds. Part B, fifth ed., Wiley, New York, 1997.
[31] R.M. Silverstein, G.C. Bassler, T.C. Morrill, Spectrometric
Identification of Organic Compounds, fifth ed., Wiley, Singapore,
1991.
[32] S. Brooker, V. McKee, W.B. Shepard, L.K. Pannell, J. Chem.
Soc., Dalton Trans. (1987) 2555.
[33] S. Brooker, V. McKee, J. Chem. Soc., Chem. Commun. (1989)
619.
[34] S. Brooker, PhD thesis, University of Canterbury (Christchurch),
1989.
[35] C.D. Brandt, E.J.L. McInnes, S. Brooker, work in progress.
[36] H. Lund in Electrochemistry of the Carbon–Nitrogen Double
Bond, (editor S. Patai) Jerusalem, 1970.
[37] H. Lund, Adv. Heterocycl. Chem. 12 (1970) 213.
[38] A. Lomax, R. Hirasawa, A.J. Bard, J. Electrochem. Soc. 119
(1972) 1679.
[39] P. Gili, M.G.M. Reyes, P.M. Zarza, I.L.F. Machado, M.F.C.G.
de Silva, M.A.N.D.A. Lemos, A.J.L. Pombeiro, Inorg. Chim.
Acta 244 (1996) 25.
[40] P. De Mayo, M.C. Usselman, Can. J. Chem. 51 (1973) 1724.
[41] T. Severin, R. Adam, H. Lerche, Chem. Ber. 108 (1975)
756.
[42] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81.
[43] G.M. Sheldrick, Acta Crystallogr., Sect. A 46 (1990) 467.
[44] G.M. Sheldrick, Meth. Enzymol. 276 (1997) 628.
[45] G.M. Sheldrick, T.R. Schneider, Meth. Enzymol. 277 (1997)
319.