(m), 1287 (m), 1210 (w), 1107 (vs), 907 (w), 766 (m), 625 (m).
Molar conductance, (MeCN solution) KM/ohm-1cm2mol-1: 220 .
UV-vis (MeCN solution) (lmax/nm (e/L mol-1cm-1)): 605 (447),
376 (11 489), 323 (17 849), 274 (32 965).
(0.065 g, 1 mmol) in MeOH (10 mL) and the mixture was stirred
for 30 min, yielding a greenish precipitate of complex 4. The
solid was isolated, washed with cold methanol–water and dried
under vacuum over P4O10. All analytical data and spectroscopic
characterization indicates the formation of complex 4.
[Cu4(L)2(OH)2(H2O)2](NO3)2·4H2O (2b·4H2O). This com-
plex was synthesized by following the above procedure us-
ing Cu(NO3)2·3H2O (0.63 g, 2.61 mmol). Anal. calcd for
C44H66Cu4N10O18: C 41.38, H 5.21, N 10.97, Cu 19.90%. Found:
C 41.22, H 5.28, N 10.76, Cu 19.86%. IR (KBr)n/cm-1: 3420
(b), 1635 (s), 1600 (m), 1448 (m) 1384 (vs), 1198 (m), 767 (m).
Molar conductance, (CH3CN solution) KM/ohm-1cm2mol-1: 218.
UV-vis (MeCN solution) (lmax/nm (e/L mol-1cm-1)): 590 (482),
372 (18 172), 318(15 121), 271(22 704), 227(29 700).
Method 3. To a MeCN (10 mL) solution of complex 2a/2b
(0.389/0.383 g; 0.3 mmol), was added slowly a solution of NaN3
(0.078 g, 1.2 mmol) in MeOH (10 mL) and the mixture was
stirred for 30 min to yield a greenish precipitate of 4. The
solid was isolated, washed with cold methanol–water and dried
under vacuum over P4O10. All analytical data and spectroscopic
characterization indicate formation of 4.
Method 4. To a MeCN–DMF (1 : 1 v/v, 20 mL) solution of
complex 3a/3b (0.404/0.381 g; 0.3 mmol), was added slowly a
solution of NaN3 (0.039 g, 0.6 mmol) in MeOH (5 mL) and the
mixture was stirred for 30 min to yield a greenish precipitate
of 4. The solid was isolated, washed with cold methanol–water
and dried under vacuum over P4O10. All analytical data and
spectroscopic characterizations support formation of complex 4.
[Cu4(L)2(N3)2(H2O)2](ClO4)2·H2O (3a·H2O). To a solution of
Cu(ClO4)2·6H2O (0.97 g, 2.62 mmol) in MeOH (15 mL) was added
for 15 min under stirring another solution of NaN3 (0.085 g,
1.31 mmol) in MeOH (15 mL). Then, a solution of H2L (0.5 g,
1.31 mmol) in CHCl3–MeOH (1 : 1 v/v, 30 mL) was added
to the above mixture followed by addition of Et3N (0.36 mL,
2.611 mmol). The system was stirred for 1 h and produced
a green precipitate. The solid was isolated, washed with cold
methanol, and dried under vacuum over P4O10. The yield was
75%. Anal. calcd for C44H58Cl2Cu4N14O15: C 39.20, H 4.34, N
14.55, Cu 18.85%. Found: C 39.24, H 4.18, N 14.22, Cu 18.76%.
IR (KBr) n/cm-1: 3420 (vs), 2077 (vs), 1634 (vs), 1600 (m), 1539
(m), 1448 (m), 1310 (m), 1093 (vs), 765 (m), 623 (m). Molar
conductance, (MeCN solution) KM/ohm-1cm2mol-1: 240. UV-
vis (MeCN solution) (lmax/nm (e/L mol-1cm-1)): 598 (875), 373
(16 215), 309 (18 385), 274 (29 165).
Results and discussion
Synthesis and characterization
The ligand H2L is prepared (Scheme S1)† from the appropriate
piperazine diamine, from its reaction with 2 mol of salicylaldehyde,
in 87% yield.15 The molecule has been fully characterized (see
Experimental) and its single-crystal X-ray diffraction structure
reveals that the piperazine backbone exists in the chair-a,a confor-
mation (Scheme 2, B), i.e., with the nitrogen lone pairs available
for metal ion coordination axially directed. The coordination
behaviour of this piperazine containing ligand is expected to be
distinct from the analogous hexadentate donor, where the cyclic
amine is replaced by an ethylenediamine bridge.20 In particular,
the piperazine moiety confers a higher rigidity to the ligand,
decreasing the degrees of freedom to the structure of possible
ensuing metal complexes.
[Cu4(L)2(N3)2(H2O)2](NO3)2·H2O (3b·H2O). This complex
was synthesized by following the above procedure using
Cu(NO3)2·3H2O (0.63 g, 2.61 mmol). The yield was 73%. Anal.
calcd for C44H58Cu4N16O13: C 41.51, H 4.59, N 17.60, Cu 19.96%.
Found: C 41.42, H 4.62, N 17.48, Cu 19.88%. IR (KBr) n/cm-1:
3436 (b), 2049 (vs), 1637 (s), 1449 (m) 1384 (vs), 763 (m).
Molar conductance, (DMF solution) KM/ohm-1cm2mol-1: 145.
UV-vis (DMF solution) (lmax/nm (e/L mol-1cm-1)): 607 (863),
372 (16 102), 302 (14 587), 277(26 377).
Reactions of H2L with Cu(ClO4)2 or Cu(NO3)2 in a DMF–
MeOH solvent mixture containing NEt3 (1 : 2 : 2 molar ratio)
led upon slow evaporation to crystals of [Cu2L(DMF)2]X2 (1)
(X = ClO4, 1a; NO3, 1b) in high yield (Scheme 4). Complex
1a had been previously obtained by us through a different
route, resulting from in situ transformation of an imidazolidine
ligand.13 In contrast to the above, the same reactions performed in
CHCl3–MeOH (Scheme 4) produced the tetranuclear complexes
[Cu2L(N3)2]n (4).
Method 1. To a solution of H2L (0.5 g, 1.31 mmol) and Et3N
(0.36 ml, 2.62 mmol) in CHCl3–MeOH (1 : 1 v/v, 30 mL) was
added a solution of Cu(ClO4)2·6H2O (0.97 g, 2.62 mmol) MeCN–
MeOH (1 : 1 v/v, 30 mL). The mixture was stirred for 15 min
and then a solution of NaN3 (0.170 g, 2.62 mmol) in MeOH
(10 mL) was added. The mixture was stirred for a further 1 h to
give a green precipitate. The solid was isolated, washed with cold
methanol–water and dried under vacuum over P4O10. The yield
was 85%. Single crystals suitable for X-ray analysis were obtained
from MeCN after one week. Anal. calcd for C22H26Cu2N10O2: C
44.81, H 4.44, N 23.75, Cu 21.55%. Found: C 44.72, H 4.52, N
23.68%. IR (KBr) n/cm-1: 2061 (vs), 1634 (vs), 1600 (m), 1530 (m),
1448 (s), 1353 (m), 1196 (m), 770 (m), 754 (m). Molar conductance,
(DMF solution) KM/ohm-1cm2mol-1: 6. UV-vis (MeCN solution)
(lmax/nm (e/L mol-1cm-1)): 600 (540), 372 (11 735), 308 (11 596),
272 (28 328).
-
[Cu4(L)2(OH)2(H2O)2]X2·nH2O (X = ClO4 , n = 1, 2a·H2O; X =
-
NO3 , n = 4, 2b·4H2O) directly from the reaction mixture, also
in high yield (optimized for the 1 : 6 : 2 molar ratio). The
procedure used for the preparation of complexes of type 2 was
repeated employing the salt NaN3 instead of the base NEt3. The
products this time are proposed to be [Cu4(L)2(N3)2(H2O)2]X2·H2O
-
-
(3·H2O) (X = ClO4 , 3a; NO3 3b) and were obtained in high
yields as optimized using stoichiometric amounts of the reactants.
Elemental analysis and conductivity measurements together with
UV-vis spectroscopy and IR spectroscopy were used to fully
characterize these compounds, and were consistent with the above
=
formulations. The IR C N stretching frequencies of 1a and 1b
Method 2. To a DMF (10 mL) solution of complex 1a/1b
(0.425/0.387 g; 0.5 mmol), was added slowly a solution of NaN3
appear at 1615 and 1635 cm-1, respectively, whereas strong bands
-
-
corresponding to the ClO4 and NO3 show up at 1085 and
1354 | Dalton Trans., 2009, 1352–1362
This journal is The Royal Society of Chemistry 2009
©