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Synthesis and characterization of new unsaturated macrobicyclic and bis(macrocyclic) copper(II) complexes containing N–CH2–N linkages
Inorganica Chimica Acta 357 (2004) 605–610 www.elsevier.com/locate/ica
Note
Synthesis and characterization of new unsaturated macrobicyclic and bis(macrocyclic) copper(II) complexes containing N–CH2–N linkages Shin-Geol Kang
a,*
, Junghoon Song a, Jong Hwa Jeong
b
a
b
Department of Chemistry, Daegu University, Gyeongsan 712-714, South Korea Department of Chemistry, Kyungpook National University, Daegu 702-701, South Korea Received 11 April 2003; accepted 25 June 2003
Abstract New copper(II) complexes [CuL2 ]2þ (L2 ¼ 7,7,9-trimethyl-1,3,6,10,13-pentaazabicyclo[11,2,11:13 ]hexadec-9-ene) and [Cu2 (L3 ) (H2 O)2 ]4þ have been prepared by the reaction of [CuL1 ]2þ (L1 ¼ 5,5,7-trimethyl-1,4,8,11,14-pentaazatetradce-7-ene) and formaldehyde. The mononuclear complex [CuL2 ]2þ has a square-planar coordination geometry with a 5–6–5–6 chelate ring sequence and is relatively stable even in low pH at room temperature. The dinuclear complex [Cu2 (L3 )(H2 O)2 ]4þ consists of two unsaturated 15membered pentaaza macrocyclic units (7,7,9-trimethyl-1,3,6,10,13-pentaazacyclopentadec-9-ene) that are linked together by a ]. Each macrocyclic unit of [Cu2 (L3 )(H2 O)2 ]4þ methylene group in a tilted face-to-face arrangement [Cu Cu distance: 7.413(2) A contains one four-membered chelate ring and has a severely distorted octahedral coordination polyhedron. The dinuclear complex is quite stable in aqueous solutions containing an excess of formaldehyde or in dry acetonitrile but is decomposed to [CuL1 ]2þ and [CuL2 ]2þ in pure water. Ó 2003 Published by Elsevier B.V. Keywords: Bis(macrocyclic) complexes; Macrobicyclic complexes; Dinuclear complexes; Four-membered chelate rings; Copper(II) complexes
1. Introduction The design and synthesis of new types of polyaza macrocyclic compounds have received much attention because of their interesting chemical properties [1–3]. In order to synthesize such compounds, several synthetic strategies have been employed. In particular, metal-directed condensation reactions involving coordinated amines and formaldehyde are useful for the preparation of various types of saturated macrocyclic and bis(macrocyclic) complexes containing N–CH2 –N linkages [4–15]. For instance, the copper(II) and/or nickel(II) complexes of L4 , L5 , L6 and L7 can be prepared by the reaction of Eqs. (1)–(4) [10–13]. Although the N–CH2 –N linkages in organic compounds
*
Corresponding author. Tel.: +82-53-850-6443; fax: +82-53-8506449. E-mail address: [email protected] (S.-G. Kang). 0020-1693/$ - see front matter Ó 2003 Published by Elsevier B.V. doi:10.1016/j.ica.2003.06.006
are unstable unless both of the nitrogen atoms are tertiary [10,16], those at the six-membered chelate rings of square-planar complexes, such as [ML4 ]2þ (M ¼ Cu(II) or Ni(II)) [10], [ML5 ]2þ [11], and [M2 L7 ]4þ [12], are quite stable even at low pH. This has been attributed to the coordination of the secondary nitrogen atom(s) to the metal ion. On the other hand, the –NH–CH2 –NH linkage at the fourmembered chelate ring of the octahedral complex [NiL6 ]2þ is unstable in acid solutions, though it is quite stable in neutral aqueous solution [13]. Some other nickel(II) complexes of polyaza macrocycles containing a N–CH2 –N linkage at a four-membered chelate ring have been also prepared and investigated [13,14]. As far as we know, however, copper(II) complexes of such ligands are not reported to date. Herein, we report the preparation of two copper(II) complexes [CuL2 ]2þ and [Cu2 (L3 )(H2 O)2 ]4þ from the reaction of [CuL1 ]2þ with formaldehyde. Interestingly,
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the dinuclear complex [Cu2 (L3 )(H2 O)2 ]4þ , in which two unsaturated 15-membered macrocyclic units containing a four-membered chelate ring are linked together by a N–CH2 –N linkage, is readily hydrolyzed even in a neutral aqueous solution at room temperature and is eventually decomposed to [CuL1 ]2þ and [CuL2 ]2þ .
2. Experimental 2.1. Measurement Infrared spectra were recorded on a Shimadzu IR-440 spectrophotometer, electronic absorption spectra were measured with a Shimadzu UV-160A spectrophotometer, and conductance measurements with a Metrohm Herisau Conductometer E518. FAB-mass spectra and elemental analyses were performed at the Korea Basic Science Institute, Daegu, Korea. 2.2. Safety note Perchlorate salts of transition metal complexes with organic ligands are often explosive and should be handled with caution. 2.3. Preparation of [CuL2 ](PF6 )2 [CuL1 ](ClO4 )2 was prepared as described previously [15]. A water–methanol (2:1) solution (30 ml) of [CuL1 ](ClO4 )2 (2.0 g, 4.0 mmol) and an excess of 35% formaldehyde (2.0 ml) was refluxed for 1 h. The resulting solution was rotary evaporated to dryness. The residue was dissolved in minimum volume of water. An excess amount of NH4 PF6 was added to the solution, and the solvent was evaporated at room temperature. A red precipitate was filtered, washed with cold water, and recrystallized from hot water. Yield: 80%. Anal. found: C, 26.94; H, 4.55; N, 11.08. Calc. for C14 H29 N5 CuP2 F12 : C, 27.08; H, 4.71; N, 11.28%. FAB mass (m/z): 476 ([M– PF6 ]þ ) and 330 ([M–2PF6 –H]þ ). IR (Nujol mull): 3260 (vN–H), 3230 (vN–H), 1660 (vC@N), and 850 (v PF6 ) cm1 . 2.4. Preparation of [Cu2 (L3 )(H2 O)2 ](ClO4 )4 2H2 O
M2þ þ 2NH2 ðCH2 Þ2 NH2 þ 2MeNH2 þ 4HCHO ! ½ML4
2þ
ðM ¼ Cu or NiÞ
ð1Þ
M2þ þ 2NH2 ðCH2 Þ2 NHðCH2 Þ2 NH2 þ 4HCHO ! ½ML5
2þ
ð2Þ
2M2þ þ 5H2 ðCH2 Þ2 NH2 þ 2MeNH2 þ 8HCHO ! ½M2 L7
2þ
ð3Þ
Ni2þ þ 2NH2 ðCH2 Þ2 NHðCH2 Þ3 NH2 þ 3HCHO ! ½NiL6
2þ
ð4Þ
To a water–methanol (2:1) solution (30 ml) of [CuL1 ](ClO4 )2 (2.0 g, 4.0 mmol) was added an excess amount of 35% formaldehyde solution (2.0 ml). The mixture was stirred for 20 h at room temperature, and then an excess amount of NaClO4 was added to the resulting red-purple solution. A red-purple solid, which precipitated by evaporating the solvent at room temperature, was filtered and washed with methanol. The crude product often contains small amount (< 5%) of [CuL2 ](ClO4 )2 as a by-product. The product was recrystallized from water-acetonitrile at room temperature. Yield: 50%. Anal. Found: C, 29.08; H, 5.89; N, 12.60%. Calc. for C27 H66 N10 Cu2 Cl4 O20 : C, 28.96; H, 5.94; N, 12.51%. FAB mass (m/z): 947 ([M–4H2 O– ClO4 ]þ ), 848 ([M–4H2 O–2ClO4 –H]þ ). IR (Nujol mull,): 3500 (vO–H), 3270 (vN–H), 3250 (vN–H), 3200 (vN–H), and 1670 (vC@N) cm1 .
S.-G. Kang et al. / Inorganica Chimica Acta 357 (2004) 605–610 Table 1 Crystal data and structure refinement for [Cu2 (L3 )(H2 O)2 ](ClO4 )4 2H2 O Chemical formula Formula weight Crystal size (mm) Crystal system, space group a (A) b (A) c (A) b (°) 3 ) V (A Z Temperature (°C) q (calc.) (g cm3 ) F000 l (mm1 ) h range (°) Index ranges Reflections collected/unique Data/restraints/parameters GOF on F 2 Final R indices [ I > 2rðIÞ] R indices (all data)
C27 H66 Cl4 Cu2 N10 O20 1119.78 0:45 0:40 0:35 monoclinic, P 21 =a 18.6571(8) 13.1133(9) 19.2297(9) 103.967(4) 4565.6(4) 4 20(2) 1.623 2320 1.250 1.90–26.04 0 6 h 6 22, 16 6 k 6 0, 23 6 l 6 23 8854/8445 [Rint ¼ 0:0208] 6853/0/558 1.072 R1 ¼ 0:064, wR2 ¼ 0:181 R1 ¼ 0:129, wR2 ¼ 0:204
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ing modes. Hydrogen atoms of water molecules were not located since their plausible positions were not found. Crystal data, data collection, and refinement for the complex are listed in Table 1.
3. Results and discussion 3.1. Synthesis
2.5. Crystal structure analysis A single crystal of [Cu2 (L2 )(H2 O)2 ](ClO4 )4 2H2 O was mounted on a thin glass fiber, and intensity data were collected on an Enraf-Nonius CAD4 Diffractometer equipped with monochromated Mo Ka (k ¼ 0:71073 A) radiation. Unit cell dimensions with estimated standard deviations were determined by least-squares using 25 well-centered reflections. Data reduction was carried out using a Molen program package [17a]. The intensities of the reflections were corrected for Lorentz and polarization effects and empirical absorption corrections were applied based on W scans [17a]. The structure in P 21 =a was determined by direct methods and refined by fullmatrix least-squares using S H E L X S -97 and S H E L X L -97 program packages [17b,17c]. All non-hydrogen atoms were refined anisotropically except disordered atoms of anions. Hydrogen atoms were constrained by using rid-
The reaction of [CuL1 ]2þ with formaldehyde was largely influenced by the temperature. As expected from the reaction of Eq. (2) [11], [CuL2 ]2þ was prepared as the only product by refluxing a water–methanol solution of [CuL1 ]2þ and formaldehyde. On the other hand, the main product prepared from the reaction at room temperature was the bis(macrocyclic) complex [Cu2 (L3 ) (H2 O)2 ]4þ (see Section 2). The proposed routes to form the complexes are shown in Scheme 1, which are similar to those reported for the complexes of L4 and L5 [10,11]. It is likely that [CuL1 ]2þ initially reacts with formaldehyde to produce the 15-membeded macrocyclic complex (A) as an intermediate. One of the secondary amino groups at the HN–CH2 –NH linkage of A reacts with additional formaldehyde to form the iminium ion (B), which readily undergoes the intramolecular condensation to yield [CuL2 ]2þ at an elevated temperature. On the other hand, the intermolecular condensation of A and B forms [Cu2 (L3 )(H2 O)2 ]4þ at room temperature. It is interesting to find that the only reagent for the cyclization and linking of [CuL1 ]2þ to form the bis(macrocyclic) complex is formaldehyde. The nickel(II) complex of L6 containing the HN– CH2 -NH linkage is stable in the solid state and in aqueous solutions [13]. In the present work, however, all attempts to isolate A as a solid were unsuccessful. 3.2. Crystal structure of [Cu2 (L3 )(H2 O)2 ](ClO4 )4 2H2 O The ORTEX drawing of [Cu2 (L3 )(H2 O)2 ]4þ with the atomic numbering scheme is shown in Fig. 1. The
Scheme 1.
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Fig. 1. An ORTEX drawing of [Cu2 (L3 )(H2 O)2 ]2þ in [Cu2 (L3 )(H2 O)2 ] (ClO4 )4 2H2 O with the atomic numbering scheme.
complex consists of two unsaturated 15-membered pentaaza macrocyclic units that are linked together by a methylene group in a tilted face-to-face arrangement. The two units exhibit similar structural features. The is much longer than Cu(1) Cu(2) distance (7.413(2) A) the sum of van der Waals radii of the atoms. Selected bond distances and angles are listed in is Table 2. The C(8)–N(3) bond distance (1.27(2) A) corresponding to the C@N double bond. As expected from Jahn–Teller distortion of trans-octahedral copper(II) complexes [18–20], the Cu(1)–N(5) and Cu(1)– respectively) Ow(1) distances (2.672(6) and 2.538(8) A, are much longer than the in-plane Cu(1)–N distances One of the most remarkable (1.988(7)–2.027(7) A). structural features of the complex is that the Cu(1)–N(5) distance is distinctly longer than the Cu(1)–Ow(1) dis longer tance. The Cu(1)–N(5) distance is also ca. 0.54 A than the longest Ni–N (one of the nitrogen atoms of the HN–CH2 –NH linkage at the four-membered chelate of [NiL6 ](ClO4 )2 [13]. ring) bond distance (2.132(2) A) shorter than the However, the distance is ca. 0.65 A Ni N(uncoordinated tertiary nitrogen atom at the of six-membered chelate ring) distance (3.319(7) A) 10 10 [NiL ](ClO4 )2 (L ¼ 3-methyl-1,3,5,8,12-pentaazacyclotetradecane) [9]. It can be suggested that the N(5) atom Table 2 and angles (°) for [Cu2 (L3 )(H2 O)2 ] Selected bond distances (A) (ClO4 )4 2H2 O Cu(1)–N(1) Cu(1)–N(3) Cu(1)–N(5) Cu(2)–N(6) N(2)–C(4) N(5)–C(14)
2.027(7) 1.988(7) 2.672(6) 2.672(6) 1.498(8) 1.469(9)
Cu(1)–N(2) Cu(1)–N(4) Cu(1)–Ow(1) Cu(2)–Ow(2) N(3)–C(8) N(6)–C(14)
2.008(6) 2.004(6) 2.538(8) 2.524(8) 1.27(2) 1.460(9)
is coordinated to the metal ion very weakly. When the N(5) and Ow(1) atoms belong to the coordination sphere, the macrocyclic unit has a severely distorted octahedral coordination geometry with a four-membered chelate ring; the N(1)–C(1)–N(5) linkage is involved in the four-membered ring. The N(1)–Cu(1)–N(5) angle (59.4(2)°) is distinctly smaller than the N–Ni–N angle (66.1(2)°) involved in the four-membered chelate ring of [NiL6 ](ClO4 )2 [13]. This indicates that the angle distortion of the four-membered chelate ring is severer than that of the nickel(II) complex. The N(4)–Cu(1)– N(5) angle (75.3(2)°) is smaller than the other N–Cu(1)– N angles of the five-membered chelate rings. The C–N(5)–C bond angles (114.3(7)–115.6(7)°) deviate from ideal tetrahedral angle. The N(5)–C(14)–N(6) angle (120.7(6)°) is much larger than the ideal tetrahedral angle. This may be attributed to the severe steric hindrance caused by the 15-membered macrocyclic units. The N(1)– Cu(1)–N(3) and N(2)–Cu(1)–N(4) angles are close to 180°, whereas the N(5)–Cu(1)–Ow(1) angle (139.5(2)°) is largely deviated from 180°. The Cu(1)–Ow(1) bond is not perpendicular to the CuN4 plane with N(1)–Cu(1)-Ow(1) and N(2)–Cu(1)–Ow(1) angles of 84.7(3)° and 87.2(2)°, respectively. 3.3. Characterization The infrared and FAB mass spectra of [CuL2 ](PF6 )2 and [Cu2 (L3 )(H2 O)2 ](ClO4 )4 2H2 O as well as the elemental analyses are listed in Section 2. The values of molar conductance (Table 3) indicate that the monoTable 3 Electronic absorption spectral data of the copper(II) complexesa Complex
kmax (nm) (e, M1 cm1 )
[CuL1 ](ClO4 )2 b [CuL2 ](PF6 )2
620(124) 618(110)c 514(145) 490(130)c 510(170)d 490e 515(170) 516(165)c 530(165)d 515e 500(80) 498(76)d 535(185) 486(151)c 506(147) 507(158)d 565 572(124) 519e
[Cu2 (L3 )(H2 O)2 ](ClO4 )4 2H2 O [CuL4 ](ClO4 )2 f [CuL5 ](ClO4 )2 g [Cu2 (L7 )]4þ [CuL8 ]2þh [Cu2 (L9 )]4þi [CuL11 (MeCN)2 ]2þj a
N(1)–Cu(1)–N(2) N(1)–Cu(1)–N(4) N(2)–Cu(1)–N(3) N(3)–Cu(1)–N(4) N(1)–Cu(1)–Ow(1) N(5)–Cu(1)–Ow(1) N(3)–C(10)–C(11) C(1)–N(5)–C(14) C(14)–N(5)–C(13)
85.7(3) 96.3(3) 92.9(2) 85.1(3) 84.7(3) 139.5(2) 108.0(8) 115.6(7) 115.1(6)
N(1)–Cu(1)–N(3) N(1)–Cu(1)–N(5) N(2)–Cu(1)–N(4) N(4)–Cu(1)–N(5) N(2)–Cu(1)–Ow(1) C(1)–N(5)–Cu(1) N(5)–C(13)–C(12) C(1)–N(5)–C(13) N(6)–C(14)–N(5)
178.6(3) 59.4(2) 177.8(3) 75.3(2) 87.2(2) 81.9(4) 112.5(7) 114.3(7) 120.7(6)
In water at 20 °C unless otherwise specified. Ref. [15]. c Measured in nitromethane. d Measured in acetonitrile. e Nujol mull. f Ref. [10]. g Ref. [11]. h Ref. [21]. i Ref. [22]. j Ref. [18]. b
KM (X1 mol1 cm2 ) 230 250d
440 540d
S.-G. Kang et al. / Inorganica Chimica Acta 357 (2004) 605–610
nuclear and dinuclear complexes are 1:2 and 1:4 electrolytes, respectively. In the electronic absorption spectra (Table 3) of the complexes, the d–d transition bands are observed at much shorter wavelengths than that of the non-macrocyclic complex [CuL1 ]2þ [15]. The spectra of [CuL2 ](PF6 )2 are comparable with those of the square-planar complexes [CuL4 ]2þ and [CuL5 ]2þ with a 5-6-5-6 chelate ring sequence [10,11]. The electronic spectrum of [Cu2 (L2 )(H2 O)2 ](ClO4 )4 2H2 O measured in water, nitromethane, or Nujol mull shows a d–d transition band at ca. 515 nm. The wavelength is quite similar to that of the trans-octahedral complex [CuL11 (MeCN)2 ]2þ (519 nm) (L11 ¼ 3,14-dimethyl2,6,13,17-tetraazatrcyclo[16.4.0.07:12 ]docosane) [18] but is ca. 50 nm shorter than those of 15-membered tetraaza macrocyclic copper(II) complexes, such as [CuL8 ]2þ (565 nm) and [Cu2 L9 ]4þ (572 nm), with a 5-6-5-7 chelate ring sequence [21,22]. This supports the crystallographic observation that each macrocyclic unit of [Cu2 (L2 ) (H2 O)2 ](ClO4 )4 2H2 O has a distorted octahedral coordination geometry with relatively long axial Cu–N and Cu–O (H2 O) bonds. 3.4. Solution behavior The mononuclear complex [CuL2 ](PF6 )2 is relatively stable against decomposition even at low pH; the electronic absorption spectra of the complex (2.0 103 M) in 0.3 M HClO4 solution indicated that only less than 2% of the complex was decomposed in 10 h at room temperature. This behavior is similar to the behaviors observed for various 14-membered polyaza macrocyclic complexes, such as [CuL4 ]2þ and [CuL5 ]2þ [10,11]. On the other hand, [Cu2 (L3 )(H2 O)2 ](ClO4 )4 2H2 O is readily decomposed in the acid solution. The pseudo firstorder rate constant (k) for the decomposition reaction of the dinuclear complex (2.0 103 M) measured in 0.3 M HClO4 solution was found to be 1.2 104 s1 at 25 °C. However, the reaction rate is distinctly slower than that of [NiL6 ]2þ (k ¼ 4:5 103 s1 in 0.3 M HClO4 ) [13] or [CuL1 ]2þ (k ¼ 0:1 s1 in 0.3 M HClO4 ) [15]. All efforts to isolate the free ligand L3 from the acid solution of [Cu2 (L3 )(H2 O)2 ](ClO4 )4 2H2 O were unsuccessful. Polyaza macrocyclic ligands containing N–CH2 –N linkages are readily decomposed to several fragments when they are removed from the coordination sphere [12,13]. Somewhat interestingly, [Cu2 (L3 )(H2 O)2 ](ClO4 )4 2H2 O is unstable in pure water even at room temperature. This was confirmed by the visible absorption spectra (Fig. 2) measured at 25 °C. The spectrum (curve e) measured after 142 h was similar to that of a mixture of [CuL1 ]2þ and [CuL2 ]2þ . The addition of an excess NaClO4 to the resulting solution produced perchlorate salts of the mononuclear complexes; the two complexes were isolated selectively by fractional recrystallizations.
609
Fig. 2. Visible absorption spectra of [Cu2 (L3 )(H2 O)2 ](ClO4 )4 (2.0 103 M) in water at 25 °C. Curve a is the first spectrum, and b, c, d, and e are the spectra measured after 22, 41, 74, and 142 h, respectively. The spectrum measured after 2 weeks was quite similar to curve e.
It is clear that the dinuclear complex is decomposed to [CuL1 ]2þ and [CuL2 ]2þ in water. At an elevated temperature (ca. 60 °C), the reaction was found to complete within 2 h. It should be noted that the dinuclear complex is quite stable in aqueous solutions containing an excess of formaldehyde or in dry acetonitrile even at 60 °C. This strongly supports the suggestion that, in the absence of formaldehyde, [Cu2 (L3 )(H2 O)2 ]4þ readily reacts with water to yield the intermediates A and B (see Scheme 1). Further hydrolysis of A forms [CuL1 ]2þ and HCHO, whereas the intramolecular condensation of B produces [CuL2 ]2þ . The present observation is quite different from that that reported for [NiL6 ]2þ , which is stable in a neutral aqueous solution [13]. The instability of [Cu2 (L3 )(H2 O)2 ]4þ in water is not clearly understood at this time. However, it can be suggested that the easy hydrolysis may be connected to the relatively weak Cu– N(5) and Cu–N(6) bonds and/or to the severe angle distortion about the nitrogen atoms of the four-membered chelate rings.
4. Conclusion This work has shown that [Cu2 (L3 )(H2 O)2 ]4þ and [CuL2 ]2þ can be prepared by controlling the reaction temperature of [CuL1 ]2þ and formaldehyde. To our knowledge, [Cu2 (L3 )(H2 O)2 ]4þ is a rarely prepared dinuclear bis(macrocyclic) copper(II) complex, in which two unsaturated 15-membered macrocyclic units are linked together by a N–CH2 –N linkage. The dinuclear complex is quite stable in aqueous solutions containing formaldehyde or in dry acetonitrile but is decomposed to [CuL1 ]2þ and [CuL2 ]2þ in pure water.
Acknowledgements This work was supported in part by the research grant of Daegu University (2003).
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(b) S.-G. Kang, K. Ryu, S.-K. Jung, C.-S. Kim, Bull. Korean Chem. Soc. 17 (1996) 331; (c) M.R. Suissa, C. Romming, J. Dale, Chem. Commun. (1997) 113; (d) S.V. Rosokha, Y.D. Lampeka, J. Chem. Soc., Chem. Commun. (1991) 1077; (e) S.V. Rosokha, Y.D. Lampeka, I.M. Maloshtan, J. Chem. Soc., Dalton Trans. (1993) 631; (f) R.W. Hay, J.M. Armstrong, M.M. Hassan, Trans. Met. Chem. 17 (1992) 270; (g) R.W. Hay, J.A. Crayston, T.J. Cromie, P. Lightfoot, D.C.L. de Alwis, Polyhedron 16 (1997) 3557. (a) P.V. Bernhardt, G.A. Lawrance, S. Luther, M. Maeder, M. Rossignoli, Inorg. Chim. Acta 306 (2000) 1; (b) P.V. Bernhardt, P. Comba, B.L. Elliott, G.A. Lawrance, M. Maeder, M.A. OÕLeary, G. Wei, E.N. Wilkes, Aust. J. Chem. 47 (1994) 1171, and references cited therein; (c) M. Rossignoli, P.V. Bernhardt, G.A. Lawrance, M. Maeder, Aust. J. Chem. 50 (1997) 529; (d) P.V. Barnhardt, E.J. Hayes, Inorg. Chem. 37 (1998) 4214; (e) M. Shakir, A.K. Mohamed, S.P. Varkey, O.S.M. Nasman, Z.A. Siddiqi, Polyhedron 14 (1995) 1277. L. Fabbrizzi, A.M.M. Lanfred, P. Pallavicini, A. Perotti, A. Taglietti, F. Ugozzoli, J. Chem. Soc., Dalton Trans. (1991) 3263. M.P. Suh, S.-G. Kang, Inorg. Chem. 27 (1988) 2544. (a) M.P. Suh, W. Shin, S.-G. Kang, M.S. Lah, T.M. Chung, Inorg. Chem. 28 (1989) 1602; (b) M.P. Suh, S.-G. Kang, T.-M. Chung, Bull. Korean Chem. Soc. 11 (1990) 206. S.-G. Kang, S.-K. Jung, J.K. Kweon, Bull. Korean Chem. Soc. 12 (1991) 219. S.-G. Kang, K. Ryu, S.-K. Jung, J.H. Jeong, Inorg. Chim. Acta 317 (2001) 314. M.P. Suh, J. Choi, S.-G. Kang, W. Shin, Inorg. Chem. 28 (1989) 1763. S.-G. Kang, J. Song, J.H. Jeong, Bull. Korean Chem. Soc. 20 (1999) 849. O. Barton, W.D. Ollis, Comprehensive Organic Chemistry, Pergamon Press, Oxford, England, 1979 (vol. 2, p. 83). (a) C.K. Fair, MOLEN, An Interactive Intelligent System for Crystal Structure Analysis, Enraf-Nonius, Delft, Netherlands, 1990; (b) G.M. Sheldrick, S H E L X S -97, Program for the Solution of Crystal Structure, University of G€ ottingen, G€ ottingen, Germany, 1990; (c) G.M. Sheldrick, S H E L X L -97, Program for Crystal Structure Refinement, University of G€ ottingen, G€ ottingen, Germany, 1997. (a) J.C. Kim, J.C. Fettinger, Y.I. Kim, Inorg. Chim. Acta 286 (1999) 67; (b) K.Y. Choi, I.-H. Suh, J.C. Kim, Bull. Korean Chem. Soc. 18 (1997) 1321. (a) P. Comba, S.M. Luther, O. Maas, H. Pritzkow, A. Vielfort, Inorg. Chem. 40 (2001) 2335; (b) A. McConnel, P. Lightfoot, D.T. Richens, Inorg. Chim. Acta 331 (2002) 143. M.Y. Udugala-Ganehenege, M.J. Heeg, L.M. Hryhorczuk, L.E. Wenger, J.F. Endicott, Inorg. Chem. 40 (2001) 1614. N.F. Curtis, S.R. Osvath, Inorg. Chem. 27 (1988) 305. P. Comba, P. Hilfenhaus, J. Chem. Soc., Dalton Trans. (1995) 3269.
Note
Synthesis and characterization of new unsaturated macrobicyclic and bis(macrocyclic) copper(II) complexes containing N–CH2–N linkages Shin-Geol Kang
a,*
, Junghoon Song a, Jong Hwa Jeong
b
a
b
Department of Chemistry, Daegu University, Gyeongsan 712-714, South Korea Department of Chemistry, Kyungpook National University, Daegu 702-701, South Korea Received 11 April 2003; accepted 25 June 2003
Abstract New copper(II) complexes [CuL2 ]2þ (L2 ¼ 7,7,9-trimethyl-1,3,6,10,13-pentaazabicyclo[11,2,11:13 ]hexadec-9-ene) and [Cu2 (L3 ) (H2 O)2 ]4þ have been prepared by the reaction of [CuL1 ]2þ (L1 ¼ 5,5,7-trimethyl-1,4,8,11,14-pentaazatetradce-7-ene) and formaldehyde. The mononuclear complex [CuL2 ]2þ has a square-planar coordination geometry with a 5–6–5–6 chelate ring sequence and is relatively stable even in low pH at room temperature. The dinuclear complex [Cu2 (L3 )(H2 O)2 ]4þ consists of two unsaturated 15membered pentaaza macrocyclic units (7,7,9-trimethyl-1,3,6,10,13-pentaazacyclopentadec-9-ene) that are linked together by a ]. Each macrocyclic unit of [Cu2 (L3 )(H2 O)2 ]4þ methylene group in a tilted face-to-face arrangement [Cu Cu distance: 7.413(2) A contains one four-membered chelate ring and has a severely distorted octahedral coordination polyhedron. The dinuclear complex is quite stable in aqueous solutions containing an excess of formaldehyde or in dry acetonitrile but is decomposed to [CuL1 ]2þ and [CuL2 ]2þ in pure water. Ó 2003 Published by Elsevier B.V. Keywords: Bis(macrocyclic) complexes; Macrobicyclic complexes; Dinuclear complexes; Four-membered chelate rings; Copper(II) complexes
1. Introduction The design and synthesis of new types of polyaza macrocyclic compounds have received much attention because of their interesting chemical properties [1–3]. In order to synthesize such compounds, several synthetic strategies have been employed. In particular, metal-directed condensation reactions involving coordinated amines and formaldehyde are useful for the preparation of various types of saturated macrocyclic and bis(macrocyclic) complexes containing N–CH2 –N linkages [4–15]. For instance, the copper(II) and/or nickel(II) complexes of L4 , L5 , L6 and L7 can be prepared by the reaction of Eqs. (1)–(4) [10–13]. Although the N–CH2 –N linkages in organic compounds
*
Corresponding author. Tel.: +82-53-850-6443; fax: +82-53-8506449. E-mail address: [email protected] (S.-G. Kang). 0020-1693/$ - see front matter Ó 2003 Published by Elsevier B.V. doi:10.1016/j.ica.2003.06.006
are unstable unless both of the nitrogen atoms are tertiary [10,16], those at the six-membered chelate rings of square-planar complexes, such as [ML4 ]2þ (M ¼ Cu(II) or Ni(II)) [10], [ML5 ]2þ [11], and [M2 L7 ]4þ [12], are quite stable even at low pH. This has been attributed to the coordination of the secondary nitrogen atom(s) to the metal ion. On the other hand, the –NH–CH2 –NH linkage at the fourmembered chelate ring of the octahedral complex [NiL6 ]2þ is unstable in acid solutions, though it is quite stable in neutral aqueous solution [13]. Some other nickel(II) complexes of polyaza macrocycles containing a N–CH2 –N linkage at a four-membered chelate ring have been also prepared and investigated [13,14]. As far as we know, however, copper(II) complexes of such ligands are not reported to date. Herein, we report the preparation of two copper(II) complexes [CuL2 ]2þ and [Cu2 (L3 )(H2 O)2 ]4þ from the reaction of [CuL1 ]2þ with formaldehyde. Interestingly,
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the dinuclear complex [Cu2 (L3 )(H2 O)2 ]4þ , in which two unsaturated 15-membered macrocyclic units containing a four-membered chelate ring are linked together by a N–CH2 –N linkage, is readily hydrolyzed even in a neutral aqueous solution at room temperature and is eventually decomposed to [CuL1 ]2þ and [CuL2 ]2þ .
2. Experimental 2.1. Measurement Infrared spectra were recorded on a Shimadzu IR-440 spectrophotometer, electronic absorption spectra were measured with a Shimadzu UV-160A spectrophotometer, and conductance measurements with a Metrohm Herisau Conductometer E518. FAB-mass spectra and elemental analyses were performed at the Korea Basic Science Institute, Daegu, Korea. 2.2. Safety note Perchlorate salts of transition metal complexes with organic ligands are often explosive and should be handled with caution. 2.3. Preparation of [CuL2 ](PF6 )2 [CuL1 ](ClO4 )2 was prepared as described previously [15]. A water–methanol (2:1) solution (30 ml) of [CuL1 ](ClO4 )2 (2.0 g, 4.0 mmol) and an excess of 35% formaldehyde (2.0 ml) was refluxed for 1 h. The resulting solution was rotary evaporated to dryness. The residue was dissolved in minimum volume of water. An excess amount of NH4 PF6 was added to the solution, and the solvent was evaporated at room temperature. A red precipitate was filtered, washed with cold water, and recrystallized from hot water. Yield: 80%. Anal. found: C, 26.94; H, 4.55; N, 11.08. Calc. for C14 H29 N5 CuP2 F12 : C, 27.08; H, 4.71; N, 11.28%. FAB mass (m/z): 476 ([M– PF6 ]þ ) and 330 ([M–2PF6 –H]þ ). IR (Nujol mull): 3260 (vN–H), 3230 (vN–H), 1660 (vC@N), and 850 (v PF6 ) cm1 . 2.4. Preparation of [Cu2 (L3 )(H2 O)2 ](ClO4 )4 2H2 O
M2þ þ 2NH2 ðCH2 Þ2 NH2 þ 2MeNH2 þ 4HCHO ! ½ML4
2þ
ðM ¼ Cu or NiÞ
ð1Þ
M2þ þ 2NH2 ðCH2 Þ2 NHðCH2 Þ2 NH2 þ 4HCHO ! ½ML5
2þ
ð2Þ
2M2þ þ 5H2 ðCH2 Þ2 NH2 þ 2MeNH2 þ 8HCHO ! ½M2 L7
2þ
ð3Þ
Ni2þ þ 2NH2 ðCH2 Þ2 NHðCH2 Þ3 NH2 þ 3HCHO ! ½NiL6
2þ
ð4Þ
To a water–methanol (2:1) solution (30 ml) of [CuL1 ](ClO4 )2 (2.0 g, 4.0 mmol) was added an excess amount of 35% formaldehyde solution (2.0 ml). The mixture was stirred for 20 h at room temperature, and then an excess amount of NaClO4 was added to the resulting red-purple solution. A red-purple solid, which precipitated by evaporating the solvent at room temperature, was filtered and washed with methanol. The crude product often contains small amount (< 5%) of [CuL2 ](ClO4 )2 as a by-product. The product was recrystallized from water-acetonitrile at room temperature. Yield: 50%. Anal. Found: C, 29.08; H, 5.89; N, 12.60%. Calc. for C27 H66 N10 Cu2 Cl4 O20 : C, 28.96; H, 5.94; N, 12.51%. FAB mass (m/z): 947 ([M–4H2 O– ClO4 ]þ ), 848 ([M–4H2 O–2ClO4 –H]þ ). IR (Nujol mull,): 3500 (vO–H), 3270 (vN–H), 3250 (vN–H), 3200 (vN–H), and 1670 (vC@N) cm1 .
S.-G. Kang et al. / Inorganica Chimica Acta 357 (2004) 605–610 Table 1 Crystal data and structure refinement for [Cu2 (L3 )(H2 O)2 ](ClO4 )4 2H2 O Chemical formula Formula weight Crystal size (mm) Crystal system, space group a (A) b (A) c (A) b (°) 3 ) V (A Z Temperature (°C) q (calc.) (g cm3 ) F000 l (mm1 ) h range (°) Index ranges Reflections collected/unique Data/restraints/parameters GOF on F 2 Final R indices [ I > 2rðIÞ] R indices (all data)
C27 H66 Cl4 Cu2 N10 O20 1119.78 0:45 0:40 0:35 monoclinic, P 21 =a 18.6571(8) 13.1133(9) 19.2297(9) 103.967(4) 4565.6(4) 4 20(2) 1.623 2320 1.250 1.90–26.04 0 6 h 6 22, 16 6 k 6 0, 23 6 l 6 23 8854/8445 [Rint ¼ 0:0208] 6853/0/558 1.072 R1 ¼ 0:064, wR2 ¼ 0:181 R1 ¼ 0:129, wR2 ¼ 0:204
607
ing modes. Hydrogen atoms of water molecules were not located since their plausible positions were not found. Crystal data, data collection, and refinement for the complex are listed in Table 1.
3. Results and discussion 3.1. Synthesis
2.5. Crystal structure analysis A single crystal of [Cu2 (L2 )(H2 O)2 ](ClO4 )4 2H2 O was mounted on a thin glass fiber, and intensity data were collected on an Enraf-Nonius CAD4 Diffractometer equipped with monochromated Mo Ka (k ¼ 0:71073 A) radiation. Unit cell dimensions with estimated standard deviations were determined by least-squares using 25 well-centered reflections. Data reduction was carried out using a Molen program package [17a]. The intensities of the reflections were corrected for Lorentz and polarization effects and empirical absorption corrections were applied based on W scans [17a]. The structure in P 21 =a was determined by direct methods and refined by fullmatrix least-squares using S H E L X S -97 and S H E L X L -97 program packages [17b,17c]. All non-hydrogen atoms were refined anisotropically except disordered atoms of anions. Hydrogen atoms were constrained by using rid-
The reaction of [CuL1 ]2þ with formaldehyde was largely influenced by the temperature. As expected from the reaction of Eq. (2) [11], [CuL2 ]2þ was prepared as the only product by refluxing a water–methanol solution of [CuL1 ]2þ and formaldehyde. On the other hand, the main product prepared from the reaction at room temperature was the bis(macrocyclic) complex [Cu2 (L3 ) (H2 O)2 ]4þ (see Section 2). The proposed routes to form the complexes are shown in Scheme 1, which are similar to those reported for the complexes of L4 and L5 [10,11]. It is likely that [CuL1 ]2þ initially reacts with formaldehyde to produce the 15-membeded macrocyclic complex (A) as an intermediate. One of the secondary amino groups at the HN–CH2 –NH linkage of A reacts with additional formaldehyde to form the iminium ion (B), which readily undergoes the intramolecular condensation to yield [CuL2 ]2þ at an elevated temperature. On the other hand, the intermolecular condensation of A and B forms [Cu2 (L3 )(H2 O)2 ]4þ at room temperature. It is interesting to find that the only reagent for the cyclization and linking of [CuL1 ]2þ to form the bis(macrocyclic) complex is formaldehyde. The nickel(II) complex of L6 containing the HN– CH2 -NH linkage is stable in the solid state and in aqueous solutions [13]. In the present work, however, all attempts to isolate A as a solid were unsuccessful. 3.2. Crystal structure of [Cu2 (L3 )(H2 O)2 ](ClO4 )4 2H2 O The ORTEX drawing of [Cu2 (L3 )(H2 O)2 ]4þ with the atomic numbering scheme is shown in Fig. 1. The
Scheme 1.
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Fig. 1. An ORTEX drawing of [Cu2 (L3 )(H2 O)2 ]2þ in [Cu2 (L3 )(H2 O)2 ] (ClO4 )4 2H2 O with the atomic numbering scheme.
complex consists of two unsaturated 15-membered pentaaza macrocyclic units that are linked together by a methylene group in a tilted face-to-face arrangement. The two units exhibit similar structural features. The is much longer than Cu(1) Cu(2) distance (7.413(2) A) the sum of van der Waals radii of the atoms. Selected bond distances and angles are listed in is Table 2. The C(8)–N(3) bond distance (1.27(2) A) corresponding to the C@N double bond. As expected from Jahn–Teller distortion of trans-octahedral copper(II) complexes [18–20], the Cu(1)–N(5) and Cu(1)– respectively) Ow(1) distances (2.672(6) and 2.538(8) A, are much longer than the in-plane Cu(1)–N distances One of the most remarkable (1.988(7)–2.027(7) A). structural features of the complex is that the Cu(1)–N(5) distance is distinctly longer than the Cu(1)–Ow(1) dis longer tance. The Cu(1)–N(5) distance is also ca. 0.54 A than the longest Ni–N (one of the nitrogen atoms of the HN–CH2 –NH linkage at the four-membered chelate of [NiL6 ](ClO4 )2 [13]. ring) bond distance (2.132(2) A) shorter than the However, the distance is ca. 0.65 A Ni N(uncoordinated tertiary nitrogen atom at the of six-membered chelate ring) distance (3.319(7) A) 10 10 [NiL ](ClO4 )2 (L ¼ 3-methyl-1,3,5,8,12-pentaazacyclotetradecane) [9]. It can be suggested that the N(5) atom Table 2 and angles (°) for [Cu2 (L3 )(H2 O)2 ] Selected bond distances (A) (ClO4 )4 2H2 O Cu(1)–N(1) Cu(1)–N(3) Cu(1)–N(5) Cu(2)–N(6) N(2)–C(4) N(5)–C(14)
2.027(7) 1.988(7) 2.672(6) 2.672(6) 1.498(8) 1.469(9)
Cu(1)–N(2) Cu(1)–N(4) Cu(1)–Ow(1) Cu(2)–Ow(2) N(3)–C(8) N(6)–C(14)
2.008(6) 2.004(6) 2.538(8) 2.524(8) 1.27(2) 1.460(9)
is coordinated to the metal ion very weakly. When the N(5) and Ow(1) atoms belong to the coordination sphere, the macrocyclic unit has a severely distorted octahedral coordination geometry with a four-membered chelate ring; the N(1)–C(1)–N(5) linkage is involved in the four-membered ring. The N(1)–Cu(1)–N(5) angle (59.4(2)°) is distinctly smaller than the N–Ni–N angle (66.1(2)°) involved in the four-membered chelate ring of [NiL6 ](ClO4 )2 [13]. This indicates that the angle distortion of the four-membered chelate ring is severer than that of the nickel(II) complex. The N(4)–Cu(1)– N(5) angle (75.3(2)°) is smaller than the other N–Cu(1)– N angles of the five-membered chelate rings. The C–N(5)–C bond angles (114.3(7)–115.6(7)°) deviate from ideal tetrahedral angle. The N(5)–C(14)–N(6) angle (120.7(6)°) is much larger than the ideal tetrahedral angle. This may be attributed to the severe steric hindrance caused by the 15-membered macrocyclic units. The N(1)– Cu(1)–N(3) and N(2)–Cu(1)–N(4) angles are close to 180°, whereas the N(5)–Cu(1)–Ow(1) angle (139.5(2)°) is largely deviated from 180°. The Cu(1)–Ow(1) bond is not perpendicular to the CuN4 plane with N(1)–Cu(1)-Ow(1) and N(2)–Cu(1)–Ow(1) angles of 84.7(3)° and 87.2(2)°, respectively. 3.3. Characterization The infrared and FAB mass spectra of [CuL2 ](PF6 )2 and [Cu2 (L3 )(H2 O)2 ](ClO4 )4 2H2 O as well as the elemental analyses are listed in Section 2. The values of molar conductance (Table 3) indicate that the monoTable 3 Electronic absorption spectral data of the copper(II) complexesa Complex
kmax (nm) (e, M1 cm1 )
[CuL1 ](ClO4 )2 b [CuL2 ](PF6 )2
620(124) 618(110)c 514(145) 490(130)c 510(170)d 490e 515(170) 516(165)c 530(165)d 515e 500(80) 498(76)d 535(185) 486(151)c 506(147) 507(158)d 565 572(124) 519e
[Cu2 (L3 )(H2 O)2 ](ClO4 )4 2H2 O [CuL4 ](ClO4 )2 f [CuL5 ](ClO4 )2 g [Cu2 (L7 )]4þ [CuL8 ]2þh [Cu2 (L9 )]4þi [CuL11 (MeCN)2 ]2þj a
N(1)–Cu(1)–N(2) N(1)–Cu(1)–N(4) N(2)–Cu(1)–N(3) N(3)–Cu(1)–N(4) N(1)–Cu(1)–Ow(1) N(5)–Cu(1)–Ow(1) N(3)–C(10)–C(11) C(1)–N(5)–C(14) C(14)–N(5)–C(13)
85.7(3) 96.3(3) 92.9(2) 85.1(3) 84.7(3) 139.5(2) 108.0(8) 115.6(7) 115.1(6)
N(1)–Cu(1)–N(3) N(1)–Cu(1)–N(5) N(2)–Cu(1)–N(4) N(4)–Cu(1)–N(5) N(2)–Cu(1)–Ow(1) C(1)–N(5)–Cu(1) N(5)–C(13)–C(12) C(1)–N(5)–C(13) N(6)–C(14)–N(5)
178.6(3) 59.4(2) 177.8(3) 75.3(2) 87.2(2) 81.9(4) 112.5(7) 114.3(7) 120.7(6)
In water at 20 °C unless otherwise specified. Ref. [15]. c Measured in nitromethane. d Measured in acetonitrile. e Nujol mull. f Ref. [10]. g Ref. [11]. h Ref. [21]. i Ref. [22]. j Ref. [18]. b
KM (X1 mol1 cm2 ) 230 250d
440 540d
S.-G. Kang et al. / Inorganica Chimica Acta 357 (2004) 605–610
nuclear and dinuclear complexes are 1:2 and 1:4 electrolytes, respectively. In the electronic absorption spectra (Table 3) of the complexes, the d–d transition bands are observed at much shorter wavelengths than that of the non-macrocyclic complex [CuL1 ]2þ [15]. The spectra of [CuL2 ](PF6 )2 are comparable with those of the square-planar complexes [CuL4 ]2þ and [CuL5 ]2þ with a 5-6-5-6 chelate ring sequence [10,11]. The electronic spectrum of [Cu2 (L2 )(H2 O)2 ](ClO4 )4 2H2 O measured in water, nitromethane, or Nujol mull shows a d–d transition band at ca. 515 nm. The wavelength is quite similar to that of the trans-octahedral complex [CuL11 (MeCN)2 ]2þ (519 nm) (L11 ¼ 3,14-dimethyl2,6,13,17-tetraazatrcyclo[16.4.0.07:12 ]docosane) [18] but is ca. 50 nm shorter than those of 15-membered tetraaza macrocyclic copper(II) complexes, such as [CuL8 ]2þ (565 nm) and [Cu2 L9 ]4þ (572 nm), with a 5-6-5-7 chelate ring sequence [21,22]. This supports the crystallographic observation that each macrocyclic unit of [Cu2 (L2 ) (H2 O)2 ](ClO4 )4 2H2 O has a distorted octahedral coordination geometry with relatively long axial Cu–N and Cu–O (H2 O) bonds. 3.4. Solution behavior The mononuclear complex [CuL2 ](PF6 )2 is relatively stable against decomposition even at low pH; the electronic absorption spectra of the complex (2.0 103 M) in 0.3 M HClO4 solution indicated that only less than 2% of the complex was decomposed in 10 h at room temperature. This behavior is similar to the behaviors observed for various 14-membered polyaza macrocyclic complexes, such as [CuL4 ]2þ and [CuL5 ]2þ [10,11]. On the other hand, [Cu2 (L3 )(H2 O)2 ](ClO4 )4 2H2 O is readily decomposed in the acid solution. The pseudo firstorder rate constant (k) for the decomposition reaction of the dinuclear complex (2.0 103 M) measured in 0.3 M HClO4 solution was found to be 1.2 104 s1 at 25 °C. However, the reaction rate is distinctly slower than that of [NiL6 ]2þ (k ¼ 4:5 103 s1 in 0.3 M HClO4 ) [13] or [CuL1 ]2þ (k ¼ 0:1 s1 in 0.3 M HClO4 ) [15]. All efforts to isolate the free ligand L3 from the acid solution of [Cu2 (L3 )(H2 O)2 ](ClO4 )4 2H2 O were unsuccessful. Polyaza macrocyclic ligands containing N–CH2 –N linkages are readily decomposed to several fragments when they are removed from the coordination sphere [12,13]. Somewhat interestingly, [Cu2 (L3 )(H2 O)2 ](ClO4 )4 2H2 O is unstable in pure water even at room temperature. This was confirmed by the visible absorption spectra (Fig. 2) measured at 25 °C. The spectrum (curve e) measured after 142 h was similar to that of a mixture of [CuL1 ]2þ and [CuL2 ]2þ . The addition of an excess NaClO4 to the resulting solution produced perchlorate salts of the mononuclear complexes; the two complexes were isolated selectively by fractional recrystallizations.
609
Fig. 2. Visible absorption spectra of [Cu2 (L3 )(H2 O)2 ](ClO4 )4 (2.0 103 M) in water at 25 °C. Curve a is the first spectrum, and b, c, d, and e are the spectra measured after 22, 41, 74, and 142 h, respectively. The spectrum measured after 2 weeks was quite similar to curve e.
It is clear that the dinuclear complex is decomposed to [CuL1 ]2þ and [CuL2 ]2þ in water. At an elevated temperature (ca. 60 °C), the reaction was found to complete within 2 h. It should be noted that the dinuclear complex is quite stable in aqueous solutions containing an excess of formaldehyde or in dry acetonitrile even at 60 °C. This strongly supports the suggestion that, in the absence of formaldehyde, [Cu2 (L3 )(H2 O)2 ]4þ readily reacts with water to yield the intermediates A and B (see Scheme 1). Further hydrolysis of A forms [CuL1 ]2þ and HCHO, whereas the intramolecular condensation of B produces [CuL2 ]2þ . The present observation is quite different from that that reported for [NiL6 ]2þ , which is stable in a neutral aqueous solution [13]. The instability of [Cu2 (L3 )(H2 O)2 ]4þ in water is not clearly understood at this time. However, it can be suggested that the easy hydrolysis may be connected to the relatively weak Cu– N(5) and Cu–N(6) bonds and/or to the severe angle distortion about the nitrogen atoms of the four-membered chelate rings.
4. Conclusion This work has shown that [Cu2 (L3 )(H2 O)2 ]4þ and [CuL2 ]2þ can be prepared by controlling the reaction temperature of [CuL1 ]2þ and formaldehyde. To our knowledge, [Cu2 (L3 )(H2 O)2 ]4þ is a rarely prepared dinuclear bis(macrocyclic) copper(II) complex, in which two unsaturated 15-membered macrocyclic units are linked together by a N–CH2 –N linkage. The dinuclear complex is quite stable in aqueous solutions containing formaldehyde or in dry acetonitrile but is decomposed to [CuL1 ]2þ and [CuL2 ]2þ in pure water.
Acknowledgements This work was supported in part by the research grant of Daegu University (2003).
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