- Email: [email protected]
metal ratio in related Cu–Ca complexes
Polyhedron 26 (2007) 4209–4215 www.elsevier.com/locate/poly
Varying the metal/metal ratio in related Cu–Ca complexes Fatima Zohra Chiboub Fellah a,b, Jean-Pierre Costes a,*, Franc¸oise Dahan a, Carine Duhayon a, Jean-Pierre Tuchagues a a
Laboratoire de Chimie de Coordination du CNRS, UPR 8241, lie´e par conventions a` l’Universite´ Paul Sabatier et a` l’Institut National Polytechnique de Toulouse, 205 route de Narbonne, 31077 Toulouse Cedex, France b Universite´ Abou baker Belkaid, Faculte´ des Sciences, De´partement de Chimie, BP 119, 13000 Tlemcen, Algeria Received 23 April 2007; accepted 11 May 2007 Available online 26 May 2007
Abstract We demonstrate with the help of structural determinations and spectroscopic data that the nuclearity of Cu–Ca complexes derived from compartmental Schiff base ligands does not depend on the ionic radius of calcium. The main factors governing these reactions are the different affinities of the calcium ions for the anionic species present in solution: the tetradentate O2O2 coordination site of the ligand and the nitrato ions. Because these affinities do vary upon going from calcium to lanthanide ions, it is not possible to use the template effect of the trinuclear Cu–Ca–Cu complexes in order to prepare the corresponding Cu–Ln–Cu complexes. 2007 Elsevier Ltd. All rights reserved. Keywords: Compartmental Schiff base ligands; 3d-Alkaline-earth heterometallic complexes; Dinuclear Cu–Ca complexes; Trinuclear Cu–Ca–Cu complexes; Single-crystal X-ray structures; Magnetic properties
1. Introduction In the last decade, we have been interested in the magnetic properties of heterodinuclear 3d–4f complexes. Most of them were obtained by using compartmental Schiff base ligands able to coordinate the 3d cation in their inner N2O2 coordination site while a larger outer O2O2 site was prone to link the lanthanide cation. It has been demonstrated in the literature that such metal–salicylaldimine complexes may lead to different types of ion selective transport reagents [1,2]. Furthermore, several structural determinations dealing with alkali and lanthanide metal ions indicate that the resulting complexes do have mainly a 1/1 3d/alkali or 3d/lanthanide ratio [3–6]. Surprisingly, it appears that 3d/alkaline-earth/salicylaldimine complexes have a 2/1 metal ratio [7,8]. This is why we considered the case of calcium that can be easily replaced by lanthanide ions and that has an ionic radius similar to *
Corresponding author. Tel.: +33 561 175822; fax: +33 561 553003. E-mail addresses: [email protected], [email protected] (J.-P. Costes). 0277-5387/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2007.05.019
these ions. It was expected that use of the template effect of calcium should lead to novel complexes with different 3d/4f ratios. It has also been emphasized that the number of carbon atoms involved in the diimine chain of the precursor 3d compounds has a crucial influence on the behaviour of these Schiff base complexes. For example, a metal complex with three carbon atoms in the diimine chain leads to a more flexible O2O2 site which can accommodate ions of different sizes in contrast to complexes with a two carbon atoms chain which are more constrained, as demonstrated in the case of alkali metal ions [3]. Such complexes have also been used as single-source precursors for the MOCVD deposition of heterometallic materials [8]. A variation of the 3d/alkaline-earth ratio would give a supplementary interest to these complexes. In the present paper, we show that reaction of calcium ions with metal aldimine complexes results in the formation of entities with a 2/1 Cu/Ca ratio but that it is also possible to isolate complexes with a 1/1 Cu/Ca ratio. Unfortunately, replacement of calcium by lanthanide ions has not led to the expected 2/1 Cu/Ln entities. Only the previously described 1/1 Cu/Ln complexes have been
4210
F.Z. Chiboub Fellah et al. / Polyhedron 26 (2007) 4209–4215
isolated in good yields whatever the ratio between the trinuclear 2/1 Cu/Ca complex and the lanthanide ion. An explanation for the failure of the template effect has been put forward. 2. Experimental 2.1. Materials The metal aldimine complexes, L1Cu Æ H2O [9], L Cu Æ 2H2O [10] (L1H2: N,N 0 -ethylenedi(3-methoxysalicylideneimine); L2H2: N,N 0 -2,2-dimethylpropylenedi(3-methoxysalicylideneimine)), were prepared as previously described. Ca(NO3)2 Æ 4H2O, Ca(OH)2, Ba(OH)2 Æ 8H2O, Sr(OH)2 Æ 8H2O, 2,2,6,6-tetramethyl-3,5-heptanedione (Aldrich) were used as purchased. High-grade solvents were used for the syntheses of complexes. 2
2.2. Syntheses 2.2.1. Complexes 2.2.1.1. L1CuCa(thd)2 Æ MeOH (1). A mixture of L1Cu Æ H2O (0.41 g, 1 · 103 mol) and Ca(OH)2 (0.15 g, 2 · 103 mol) in methanol (20 mL) was stirred for 15 min and then filtered off. Addition of tetramethylheptanedione (0.38 g, 2 · 103 mol) under stirring yielded a red precipitate that was filtered off 30 min later and dried. Yield: 0.3 g (36%). Anal. Calc. for C41H60CaCuN2O9: C, 59.4; H, 7.3; N, 3.4. Found: C, 59.4; H, 7.2; N, 3.4%. Characteristic IR absorptions (KBr): 3434, 2957, 1634, 1604, 1558, 1548, 1475, 1449, 1419, 1309, 1242, 1223, 1081, 987, 974, 961, 856, 741, 643, 609 cm1. Mass spectrum (FAB+, 3-nitrobenzyl alcohol matrix): m/z = 612 (100), [L1CuCa(thd)]+. Crystals suitable for a X-ray study were obtained from a dichloromethane/methanol solution. They contain a dichloromethane molecule. Use of Sr(OH)2 Æ 8H2O or Ba(OH)2 Æ 8H2O in place of Ca(OH)2 with the same experimental process and the same amount of the copper complex precursor yielded the corresponding complexes. 2.2.1.2. L1CuSr(thd)2 (2). Yield: 0.36 g (43%). Anal. Calc. for C40H56CuN2O8Sr: C, 56.9; H, 6.7; N, 3.3. Found: C, 56.3; H, 6.6; N, 3.2%. Characteristic IR absorptions (KBr): 2941, 1644, 1603, 1546, 1475, 1446, 1322, 1242, 1219, 1087, 987, 978, 968, 856, 743, 724, 646, 607 cm1. Mass spectrum (FAB+, 3-nitrobenzyl alcohol matrix): m/z = 660 (100), [L1CuSr(thd)]+. 2.2.1.3. L1 CuBa(thd)2 (3). Yield: 0.5 g (56%). Anal. Calc. for C40H56BaCuN2O8: C, 53.8; H, 6.3; N, 3.1. Found: C, 53.5; H, 6.3; N, 3.1%. Characteristic IR absorptions (KBr): 2937, 1634, 1604, 1547, 1475, 1446, 1314, 1246, 1224, 1083, 988, 968, 855, 736, 644, 608 cm1. Mass spectrum (FAB+, 3-nitrobenzyl alcohol matrix): m/z = 710 (100), [L1CuBa(thd)]+.
2.2.1.4. (L1Cu)2Ca(NO3)2 Æ 2H2O (4). A mixture of L1Cu Æ H2O (0.41 g, 1 · 103 mol) and Ca(NO3)2 (0.24 g, 1 · 103 mol) in methanol (15 mL) was stirred for three hours. The precipitate which appeared was filtered off and dried. Yield: 0.31 g (65%). Anal. Calc. for C36H40CaCu2N6O16: C, 46.0; H, 4.1; N, 8.6. Found: C, 45.6; H, 3.9; N, 8.4%. Characteristic IR absorptions (KBr): 3459, 1642, 1626, 1606, 1450, 1412, 1384, 1314, 1247, 1224, 1083, 979, 962, 857, 752, 740, 648, 609 cm1. Mass spectrum (FAB+, 3-nitrobenzyl alcohol matrix): m/z = 880 (2.5), [(L1Cu)2Ca(NO3)]+, 818 (3.6), [(L1Cu)2Ca]+, 491 (100), [(L1Cu)Ca(NO3)]+. The following complexes were prepared similarly with use of the corresponding salts. 2.2.1.5. (L1Cu)2Ba(NO3)2 Æ 2H2O (5). Yield: 0.38 g (70%). Anal. Calc. for C36H40BaCu2N6O16: C, 40.1; H, 3.7; N, 7.8. Found: C, 39.7; H, 3.6; N, 7.7. Characteristic IR absorptions (KBr): 3434, 1631, 1603, 1449, 1474, 1450, 1384, 1301, 1243, 1226, 1080, 986, 966, 853, 740, 646, 609 cm1. Mass spectrum (FAB+, 3-nitrobenzyl alcohol matrix): m/z = 978 (32.0), [(L1Cu)2Ba(NO3)]+, 916 (19.3), [(L1Cu)2Ba]+, 589 (100), [(L1Cu)Ba(NO3)]+. 2.2.1.6. (L1Cu)2Ba(ClO4)2 (6). Caution: Due to their explosive character, perchlorate salts should be handled with care and in very low amounts. Acetone was used as solvent. Yield: 0.4 g (74%). Anal. Calc. for C36H36BaCl2Cu2N4O16: C, 38.7; H, 3.2; N, 5.0. Found: C, 39.6; H, 3.2; N, 4.9%. Characteristic IR absorptions (KBr): 1647, 1666, 1604, 1550, 1472, 1443, 1392, 1301, 1243, 1222, 1120, 1081, 1055, 1046, 981, 977, 966, 854, 737, 641, 628, 620 cm1. Mass spectrum (FAB+, 3-nitrobenzyl alcohol matrix): m/z = 1017 (48.6), [(L1Cu)2Ba(ClO4)]+, 916 (34.2), [(L1Cu)2Ba]+, 626 (100), [(L1Cu)Ba(ClO4)]+. 2.2.1.7. L1CuMg(H2O)(NO3)2 (7). Yield: 0.5 g (90%). Anal. Calc. for C18H20CuMgN4O11: C, 38.9; H, 3.6; N, 10.1. Found: C, 39.0; H, 3.6; N, 9.9%. Characteristic IR absorptions (KBr): 3401, 1638, 1601, 1556, 1474, 1440, 1384, 1316, 1243, 1221, 1082, 977, 964, 858, 742, 642, 611 cm1. Mass spectrum (FAB+, 3-nitrobenzyl alcohol matrix): m/z = 475 (100), [(L1Cu)Mg(NO3)]+. 2.2.1.8. (L2Cu)2Ca(NO3)2 Æ H2O (8). Yield: 0.34 g (65%). Anal. Calc. for C42H50CaCu2N6O15: C, 48.2; H, 4.8; N, 8.0. Found: C, 47.9; H, 4.6; N, 7.8%. Characteristic IR absorptions (KBr): 3419, 1617, 1558, 1472, 1384, 1312, 1229, 1170, 1082, 1067, 983, 855, 742, 646, 623 cm1. Mass spectrum (FAB+, 3-nitrobenzyl alcohol matrix): m/z = 966 (28.5), [(L2Cu)2Ca(NO3)]+, 902 (20.2), [(L2Cu)2Ca]+, 533 (100), [(L2Cu)Ca(NO3)]+. 2.3. Physical measurements Elemental analyses were carried out at the Laboratoire de Chimie de Coordination Microanalytical Laboratory
F.Z. Chiboub Fellah et al. / Polyhedron 26 (2007) 4209–4215
in Toulouse, France, for C, H, and N. IR spectra were recorded on a GX system 2000 Perkin–Elmer spectrophotometer; samples were run as KBr pellets. Mass spectra (FAB+) were recorded in dmf as solvent and 3-nitrobenzyl alcohol matrix with a Nermag R10-10 spectrometer. Magnetic data were obtained with a Quantum Design MPMS SQUID susceptometer. All samples were 3 mm diameter pellets molded from ground crystalline samples. Magnetic susceptibility measurements were performed in the 2– 300 K temperature range in a 0.1 T applied magnetic field, and diamagnetic corrections were applied by using Pascal’s constants [11]. The magnetic susceptibilities have been computed by exact calculations of the energy levels associated to the spin Hamiltonian through diagonalization of the full matrix with a general program for axial symmetry,[12] and with the MAGPACK program package [13,14]. Least-squares fittings were accomplished with an adapted version of the function-minimization program MINUIT [15]. 2.4. Crystallographic data collection and structure determination for [L1Cu(CH3OH)Ca(thd)2] (1) and [(L2Cu)2Ca(NO3)2] (8) Crystals suitable for X-ray analyses were obtained by slow evaporation of the corresponding methanol solutions. Data were collected at 160 K for 1 on a IPDS STOE diffractometer and at 180 K for 8 on an Xcalibur Oxford Diffraction diffractometer using graphite-monochromated Mo ˚ ) and equipped with Ka radiation sources (k = 0.71073 A Oxford Cryosystems Cryostream Cooler Devices. 46 391 reflections were collected for 1, 43 468 for 8, of which
Table 1 Summary of crystal data and refinement details for 1 and 8 Empirical formula C42H62CaCl2CuN2O9 M 913.49 Temperature (K) 160 ˚) Wavelength (A 0.71073 Crystal system monoclinic Space group P21/n ˚) a (A 12.594(1) ˚) b (A 14.661(1) ˚) c (A 25.276(3) b () 95.14(1) ˚ 3) V (A 4648.2(7) Z 4 q(calc) 1.31 lMo (mm1) 0.747 Crystal size (mm) 0.15 · 0.30 · 0.50 h Range () 2.14–25.98 Reflections collected/ 46 391/9047 unique Reflection parameters 506 Maximum and minimum 0.89 and 0.76 transmission Ra 0.058 (I P 1.2r(I)) 0.070 (I P 1.2r(I)) wRb ˚ 3) Dqmax and Dqmin (e A 0.62 and 0.63 P P a R ¼ jjF o j jF c jj= jF o j. P P b 2 2 2 wR ¼ ½ wjF o j jF c j = wjF 2o j2 1=2 .
C42H50CaCu2N6O15 1046.06 180 0.71073 orthorhombic Pccn 20.948(3) 10.579(1) 20.858(2) 4622.5(10) 4 1.50 1.10 0.06 · 0.10 · 0.18 3.36–29.07 43 468/6185 287 0.94 and 0.82 0.083 (I P 3r(I)) 0.081 (I P 3r(I)) 1.79 and 1.13
4211
Table 2 Selected bond lengths and angles for 1 and 8 Complex 1 Cu–O2 Cu–O3 Cu–N2 Cu–N1 Cu–O9 Ca–O1 Ca–O2 O2–Cu–O3 Cu–O2–Ca Complex 8 Cu–O2 Cu–O3 Cu–N2 Cu–N1 Cu–O5 Ca–O2 0 Ca–O4 0 O2–Cu–O3 Cu–O2–Ca O1–Ca–O1 0
1.892(3) 1.895(3) 1.916(5) 1.922(5) 2.416(3) 2.666(3) 2.488(3) 83.8(1) 103.5(1)
1.949(4) 1.942(4) 1.972(4) 1.958(5) 2.854(5) 2.379(4) 2.479(4) 79.8(2) 109.2(2) 86.8(2)
Ca–O3 Ca–O4 Ca–O5 Ca–O6 Ca–O7 Ca–O8 O2–Ca–O3 Cu–O3–Ca
Ca–O1 Ca–O2 Ca–O3 Ca–O4 Ca–O1 0 Ca–O3 0 O2–Ca–O3 Cu–O3–Ca O4–Ca–O4 0
2.444(3) 2.724(3) 2.365(3) 2.310(3) 2.336(3) 2.369(3) 61.7(1) 105.1(1)
2.446(4) 2.379(4) 2.415(4) 2.479(4) 2.446(4) 2.415(4) 62.8(1) 108.1(1) 89.0(2)
Sym op: 0 , x + 1/2, y + 5/2, z.
9047 independent (Rint = 0.08) for 1 and 6185 (Rint = 0.13) for 8. Multiscan absorption corrections were applied (Tmin–max = 0.76–0.89 for 1, 0.82–0.94 for 8). The structures were solved by direct methods using SIR92 [16], and refined by means of least-squares procedures on F using the programs of the PC version of CRYSTALS [17]. Atomic scattering factors were taken from the International tables for X-ray crystallography [18]. All non-NO3 groups and non-hydrogen atoms were refined anisotropically. The maximum and minimum peaks on the final difference Fourier maps were 0.62 and 0.63 e A3 for 1, 1.79 and 1.13 e A3 for 8. Drawings of the molecule were performed with the program CAMERON [19]. Crystal data collection and refinement parameters are given in Table 1, and selected bond distances and angles are gathered in Table 2. 3. Results 3.1. Syntheses Reaction of the N,N 0 -ethylenedi(3-methoxysalicylideneiminato) copper complex with calcium, strontium and barium hydroxide in the presence of 2,2,6,6-tetramethyl3,5-heptanedione (thd) yielded a series of complexes formulated L1CuCa(thd)2 (1), L1CuSr(thd)2 (2) and L1CuBa(thd)2 (3), which are characterized by a 1/1 copper/alkaline-earth ratio. At variance, using alkaline-earth nitrate or perchlorate yielded complexes characterized by the 2/1 copper/alkalineearth ratio, (L1Cu)2Ca(NO3)2 Æ 2H2O (4), (L1Cu)2Ba(NO3)2 Æ 2H2O (5), (L1Cu)2Ba(ClO4)2 (6). The copper complex involving the more flexible N,N 0 -2,2-dimethylpropylenedi(3-methoxysalicylideneiminate) L2 ligand yielded a
4212
F.Z. Chiboub Fellah et al. / Polyhedron 26 (2007) 4209–4215
similar entity (L2Cu)2Ca(NO3)2 Æ H2O (8), with again a 2/1 ratio. The only exception to this 2/1 ratio occurred with magnesium ions that yielded the L1CuMg(NO3)2 Æ H2O complex (7). The different ionic radius of magnesium is most probably responsible for the change in Cu/alkaline-earth ratio. 3.2. Spectroscopic data The infrared spectra of the structurally determined complexes 1 and 8 are of prime interest for the study of the remaining entities. The mCN bands of the coordinated ligands are observed at 1604 and 1617 cm1 for 1 and 8, respectively. A strong band at 1384 cm1 is attributable to the monodentate NO3 anion in 8 [20], while a strong band at 1634 cm1 may be assigned to the coordinated keto functions of the thd ligands in 1 [21]. Mass spectra also yield interesting information. The three L1CuM(thd)2 complexes display very similar mass spectra (FAB+). In all mass spectra we observe peaks corresponding to the [L1CuM(thd)]+ ions. They appear at m/ z = 612 for 1 (M = Ca), 660 for 2 (M = Sr), and 710 for 3 (M = Ba). A different spectral pattern characterizes complex 8 with peaks at m/z = 964, 902 and 533, attributable to [(L2Cu)2Ca(NO3)]+, [(L2Cu)2Ca]+ and [L2CuCa(NO3)]+, respectively. If the peaks at 964 and 533 u are expected, the peak at 902 u is more surprising for it suggests a change in the oxidation state of the metal ions. Such an observation has been previously made [22]. Complexes 4 and 5 show similar peaks at 1017, 916 and 626, and 978, 916 and 589 u, respectively. For these three complexes, although it should be underlined that the most intense peak corresponds to the [L1CuM(NO3)]+ ion, the presence of peaks at 1017 (4) 978 (5) and 964 (8) lm confirms their trinuclear character. Complex 7, L1CuMg(NO3)2(H2O), where [L1CuMg(NO3)]+ is the only cationic species observed, is an exception. 3.3. Structural determinations The molecular structure of 1 is built from isolated dinuclear complex molecules [L1Cu(CH3OH)Ca(thd)2]. A perspective view of this dinuclear molecule with the corresponding labeling scheme is depicted in Fig. 1 while significant bond lengths and angles appear in Table 2. In each bimetallic unit, the CuII and CaII cations occupy the inner N2O2 and outer O2O2 sites, respectively. The two ions are doubly bridged to each other by phenoxo oxygen ˚ . The copper atoms, with a Cu Ca distance of 3.460(1) A is surrounded by five donor atoms. The equatorial N2O2 donors afforded by L1 are nearly coplanar and the axial position is occupied by the methanol oxygen atom at ˚ from the copper ion. While the copper ion is 2.416(3) A located in the N2O2 mean plane, the calcium ion is located ˚ out of this plane. The five-membered ring 0.741(2) A formed by the diimine moiety chelating the copper ion is in a d conformation. The Cu–O bond lengths do not differ significantly from the values reported for similar complexes
Fig. 1. Molecular structure of [L1Cu(CH3OH)Ca(thd)2] (1). The thermal ellipsoids are drawn at the 30% probability level.
[3,4]. The eight-coordinate Ca cation is surrounded by four oxygen atoms belonging to the Schiff base and by four oxygen atoms brought by two tetramethylheptanedionato anions acting as bidentate g2 chelating auxiliary ligands. The two longer Ca–O bonds involve the OMe side arms ˚ ) while the shorter ones concern (2.666(3) and 2.724(3) A the keto oxygen atoms from the thd ligands (from ˚ ); the Ca–O bonds involving the phe2.310(3) to 2.369(3) A noxo oxygen atoms are comprised in between these values ˚ ). p–p stacking interactions estab(2.444(3) and 2.488(3) A lished between the aromatic cycles located around the copper coordination spheres are responsible for the presence of ˚ ) and large short intermolecular Cu(1) Cu(1) 0 (3.819(1) A 0 ˚ Ca(1) Ca(1) (8.951(2) A) distances. The molecular structure of complex 8, along with the atom labeling scheme, is depicted in Fig. 2, while the rele-
Fig. 2. Molecular structure of (L2Cu)2Ca(NO3)2 Æ H2O (8). The thermal ellipsoids are drawn at the 30% probability level.
F.Z. Chiboub Fellah et al. / Polyhedron 26 (2007) 4209–4215
4213
Fig. 3. Fragment of the 1D chain resulting from the g1:l nitrato bridging for 8.
3.4. Magnetic properties The dinuclear complexes 1, 2, 3, 7, in which the copper ion is in presence of diamagnetic centres, behave as paramagnetic entities devoid of any intermolecular interactions. The intermolecular contacts established by p–p stacking in 1 are not able to transmit a magnetic interaction. The temperature dependence of the magnetic susceptibility for 8 in the 2–300 K temperature range is shown in Fig. 4 as the vMT versus T variation. The vMT product remains constant and equal to 0.77 cm3 mol1 K in the whole temperature range. Identical results have been obtained for the complexes 4 and 5. These results confirm that the copper ions are well isolated from each other by the alkaline-earth cations and that the bridging nitrato anions are not active. In complex 6, the decrease of the vMT product is due to weak antiferromagnetic interactions operating at low temperature. These interactions must be intermolecular for the previous complexes 4, 5 and 8 demonstrate clearly that there is
0.8
χMT (cm3mol-1K)
vant interatomic bonds lengths are collated in Table 2. The N2O2 donor set of (L2)2 is at the basal plane of the pentacoordinate copper cation, to which an oxygen atom of the nitrato anion is axially bonded. Cu(1) is displaced from the ˚ toward the aximean equatorial N2O2 plane by 0.128(2) A ally coordinated nitrato oxygen atom. The two Cu(OO)Ca cores including the two bridging phenoxo oxygen atoms are essentially planar and roughly orthogonal, with a ˚ yielding related Cu(1) Ca(1) separation of 3.5375(6) A 0 ˚ an intramolecular Cu(1) Cu(1) separation of 7.044(3) A II 0 through (Ca(1) ( :, x + 1/2, y + 5/2, z)). The Ca cation is eight-coordinate through two sets of four oxygen atoms from each L2Cu building unit, and linked to each copper ion by two phenoxo bridges. The shortest intermolecular ˚ for the nitCu(1) Cu(1) distance is equal to 5.212(1) A rato ion bridges two copper ions through the same oxygen atom, thus forming a 1D chain of trinuclear units (Fig. 3). As a consequence, the intermolecular Cu(1) Cu(1) 0 ˚ ) and Ca(1) Ca(1) (10.429(3) A ˚ ) distances are (9.127(1) A 1 large. This g :l nitrato bridging mode is not common [20].
0.6 0.4 0.2 0.0 0
20
40
60
80
100
T (K) Fig. 4. Thermal dependence of the vMT product for (L2Cu)2Ca(NO3)2 Æ H2O (8).
no significant intramolecular magnetic interaction through the alkaline-earth cations. They originate from the presence of perchlorate ions that are not able to bind copper at the axial coordination site: as the copper cations are thus in a square planar environment, intermolecular Cu Cu interactions through the phenoxo oxygen atoms must be responsible for such a weak interaction. Fitting the magnetic susceptibility data of 6 to the Bleaney–Bowers [23] equation for an exchange coupled pair of S = 1/2 spins with a 2J singlet–triplet energy gap yields an estimate of the intermolecular interaction equal toP0.75 cm1 with g = 2.05 P and an agreement factor R ( [(vMT)obs (vMT)calc]2/ [(vMT)obs]2) equal to 1 · 104 (see Fig. 4). 4. Discussion We have previously shown that compartmental Schiff base ligands resulting from the reaction of 3-methoxysalicylaldehyde with different diamines may yield discrete heterodinuclear 3d/4f complexes [5,10] with the 3d ion coordinated in the N2O2 site and the 4f ion in the O2O2 site. Very similar 3d/alkali-metal complexes have also been isolated, with the alkali-metal in the outer O2O2 coordination site [3,4]. The isolated complexes are formulated LMM 0 X or LMLnX3, L standing for the ligand, M for the 3d ion (most often Ni2+ and Cu2+), M 0 for Na+, Li+, K+, Ln
F.Z. Chiboub Fellah et al. / Polyhedron 26 (2007) 4209–4215
for the 4f ion and X for the anionic species (most often NO3 or ClO4). The presence of methoxy groups in the 3,3 0 positions of the Cu–salicylaldimine precursor complexes implies that these building units are potential ligands able to chelate metal ions in the plane of the donor atoms or to sandwich them between two sets of such Cu–salicylaldimine ligands, depending on the size of the M 0 or Ln cation. These O2O2 compartments can be preformed or can result from self-assembling of the 3d precursor complex in the presence of alkaline or lanthanide ions [4,10]. Another factor that affects the complexing ability is the number of carbon atoms involved in the imine bridge. With a 1,3-propylene bridge, metal ions linked to the outer O2O2 site are located in the plane of the four donor atoms while there is a lesser adaptability with a 1,2-ethylene bridge [3]. The third factor influencing the complexation stoichiometry originates from the anions present in the reaction medium. Indeed, these anions can compete with the precursor ligand-complex, depending on their affinity with the introduced metal ion. Concerning the outer O2O2 coordination site, it may be considered as a polyether in which a carbon atom spacer (O–CH2–CH2–O) has been replaced by a metal ion (O–M–O), as in metallacrowns [24]. In addition, the oxygen atoms linked to the metal ion are deprotonated and capable of better bonding than the ether-type oxygen atoms. Because calcium(II) ions have a chemistry closely related to that of lighter lanthanide ions, and are thus easily replaced by lanthanide ions [25], we have studied their reaction with the 3d precursor complexes. The analytical results and the structural determinations demonstrate that the isolated complexes may be formulated as [(L2Cu)2Ca(NO3)2], with a 2/1 3d/alkaline-earth ratio. This observation is really surprising for the previously studied 3d/alkaline or 3d/lanthanide complexes were characterized by a 1/1 ratio. This result is puzzling if we remember that the ionic radii of sodium, calcium and gadolinium ions span the same range of values, depending on their coordination number [25]. It is also worth noting that the flexibility of the L2 ligand used in the present case, with its three carbon atoms chain in the diimino fragment [3], is not a factor able to introduce a change in the Cu/Ca ratio. On the contrary, the magnesium ions, with their smaller ionic radius, yield a 1/1 Cu/Mg ratio even with the more rigid L1 ligand, while the barium ions, with their larger ionic radius, yield a 2/1 ratio in all cases. These data indicate that the ionic radius cannot be considered as the only factor responsible for the stoichiometry of the isolated complexes. In the present case, the results may be explained by the higher affinity of the alkaline-earth for the outer coordination site of the Cu–salicylaldimine precursor complex, a factor which prevails over the chelating power of the nitrato anions, thus yielding 2/1 entities which are not observed under similar experimental conditions in the case of lanthanide ions. In the latter case, the chelating effect of the nitrato anions toward the Ln ions is the most important factor, explaining why the observed 1/1 3d–4f ratio in the presence of nitrato anions is always obtained.
Increasing the number of oxygen atoms involved in the outer coordination site by introducing polyether-like chains does not modify the 3d/alkaline earth ratio, as reported earlier [7]. The only way to change this ratio is to introduce auxiliary ligands with a strong chelating ability, such as diketones. Then discrete species with a 1/1 3d/ alkaline earth ratio may be isolated, as demonstrated by the structural determination of the L1Cu(MeOH)Ca(thd)2 complex 1. Again the calcium ion is eight-coordinate, with two auxiliary thd ligands substituting one Cu–salicylaldimine building unit. Mass spectra data (FAB+) confirm the presence of these entities in solution. Peaks corresponding to the [L1CuM(thd)]+ ions appear at m/z = 612 (M = Ca), 660 (M = Sr) and 710 (M = Ba), thus demonstrating that the corresponding complexes are also obtained with larger alkaline-earth ions. Again, the only exception was observed for magnesium which failed to yield such a 1/1 complex. The magnetic data indicate that the copper ions are magnetically well isolated in the dinuclear (1, 2, 3, 7) and trinuclear (4, 5, 8) entities. The presence of a nitrato anion or a solvent molecule at the apical position of the copper coordination sphere prevents intermolecular interactions. Furthermore, the lack of magnetic interactions through the diamagnetic alkaline-earth cations of the trinuclear species is clearly evidenced by these results. Complex 6 behaves differently. From the magnetic results and UV– Vis data, we can conclude that the copper ions are in a square planar environment, the perchlorate anion being unable to enter the coordination sphere at an axial site, thus favouring intermolecular contacts which are responsible for the slight vMT decrease at low temperature corresponding to weak antiferromagnetic interactions (see Fig. 5). Up to now, we have not been able to obtain 3d–4f complexes in a 2/1 ratio with symmetrical Schiff base ligands, in presence of nitrato anions. As the 2/1 3d-alkaline-earth complexes are easily obtained, we have tried to use the template effect of the calcium ions to prepare the corresponding 2/1 3d-Ln complexes. It is known for a long time that such a replacement is possible [25]. Unfortunately all our experiments failed to yield the expected 3d–4f complexes, our attempts leading to the isolation of 1/1 3d–4f com0.9
χMT (cm3mol-1K)
4214
0.6
0.3
0.0 0
20
40
60
80
100
T (K) Fig. 5. Thermal dependence of the vMT product for (L1Cu)2Ba(ClO4)2 (6). The solid line is the best fit to the Bleaney–Bowers equation, see text.
F.Z. Chiboub Fellah et al. / Polyhedron 26 (2007) 4209–4215
plexes equivalent to those previously characterized. This result confirms the ready replacement of calcium by lanthanide ions. Unfortunately, the template effect of the calcium ion is not able to give the expected trinuclear 3d–4f–3d entities.
4215
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ ccdc.cam.ac.uk. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.poly.2007.05.019.
5. Conclusion References It is well known that the lanthanide ionic radii depend on their coordination number and that they span the values of the calcium ionic radii. Furthermore, the Ln ions, which are the chameleons of coordination chemistry, replace with much ease the Ca ions in coordination compounds [25]. The present work demonstrates that this replacement is in fact easy but that it yields complexes with stoichiometries different from those of the starting 3d/Ca compounds. This behaviour is explained by the different affinities of the Ln and Ca ions for the anionic species present in the reaction medium: the tetradentate donor ligand and the nitrato anions. The alkaline-earth affinity for the outer coordination site of the metal–salicylaldimine complex prevails over the chelating power of the nitrato anions while the reverse is true for the lanthanide ions. Using auxiliary ligands such as diketones, which have a strong chelating power, allows to vary the 3d-alkaline earth ratio from 2/1 to 1/1. Playing with these different factors yields a large and rich palette to the synthetic chemist. This work demonstrates that synthesis of a desired complex is not always straightforward. Eventually, the possible variation of the 3d/alkaline-earth ratio gives a supplementary interest to these complexes as single-source precursors for the MOCVD deposition of heterometallic materials. Acknowledgements We thank Dr. A. Mari for his contribution to the magnetic measurements. F.Z.C.F. acknowledges the Algerian Ministry for Education and Research for an abroad doctoral grant. Appendix A. Supplementary material CCDC 638955 and 638956 contain the supplementary crystallographic data for 1 and 8. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/ conts/retrieving.html, or from the Cambridge Crystallo-
[1] A. Schepartz, J.P. McDevitt, J. Am. Chem. Soc. 111 (1989) 5976. [2] O.F. Schall, K. Robinson, J.L. Atwood, G.W. Gokel, J. Am. Chem. Soc. 113 (1991) 7434. [3] D. Cunningham, P. McArdle, M. Mitchell, N. Ni Chonchubhair, M. O’Gara, F. Franceschi, C. Floriani, Inorg. Chem. 39 (2000) 1639. [4] J.P. Costes, F. Dahan, J.P. Laurent, Inorg. Chem. 33 (1994) 2738. [5] J.P. Costes, F. Dahan, A. Dupuis, Inorg. Chem. 39 (2000) 165. [6] J.P. Costes, F. Dahan, W. Wernsdorfer, Inorg. Chem. 45 (2006) 5. [7] J.P. Costes, J.P. Laurent, P. Chabert, G. Commenges, F. Dahan, Inorg. Chem. 36 (1997) 656. [8] A.N. Gleizes, F. Senocq, M. Julve, J.L. Sanz, N. Kuzmina, S. Troyanov, I. Malkerova, A. Alikhanyan, M. Ryazanov, A. Rogachev, E. Dedlovskaya, J. Phys. IV France 9 (1999) 943. [9] R.H. Holm, M.J. O’Connor, Progr. Inorg. Chem. 14 (1971) 241. [10] J.P. Costes, F. Dahan, A. Dupuis, J.P. Laurent, Inorg. Chem. 36 (1997) 3429. [11] P. Pascal, Ann. Chim. Phys. 19 (1910) 5. [12] J.M. Clemente-Juan, C. Mackiewicz, M. Verelst, F. Dahan, A. Bousseksou, Y. Sanakis, J.-P. Tuchagues, Inorg. Chem. 41 (2002) 1478. [13] J.J. Borra´s-Almenar, J.M. Clemente-Juan, E. Coronado, B.S. Tsukerblat, Inorg. Chem. 38 (1999) 6081. [14] J.J. Borra´s-Almenar, J.M. Clemente-Juan, E. Coronado, B.S. Tsukerblat, J. Comput. Chem. 22 (2001) 985. [15] F. James, M. Roos, Comput. Phys. Commun. 10 (1975) 345. [16] A. Altomare, G. Cascarano, G. Giacovazzo, A. Guagliardi, M.C. Burla, G. Polidori, M. Camalli, J. Appl. Cryst. 27 (1994) 435. [17] P.W. Betteridge, J.R. Carruthers, R.I. Cooper, C.K. Prout, D.J. Watkin, J. Appl. Cryst. 36 (2003) 1487. [18] International Tables for Crystallography, vol. C, Kluwer Academic Publishers, Dordrecht, The Netherlands, 1992. [19] D.J. Watkin, C.K. Prout, L.J. Pearce, CAMERON, Chemical Crystallography Laboratory, Oxford, UK, 1996. [20] L.W. Yang, S. Liu, S.J. Rettig, C. Orvig, Inorg. Chem. 34 (1995) 4921. [21] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, fifth ed., Wiley, New York, 1997. [22] J.M. Miller, K. Balasanmugan, J. Nye, G.B. Deacon, N.C. Thomas, Inorg. Chem. 26 (1987) 560. [23] B. Bleaney, K.D. Bowers, Proc. R. Soc. London, Ser. A 214 (1952) 451. [24] M.S. Lah, V.L. Pecoraro, J. Am. Chem. Soc. 111 (1989) 7258. [25] J.C.-G. Bu¨nzli, in: R.S. Puche, P. Caro (Eds.), Rare Earths, Editorial Complutense, Madrid, 1998.
Varying the metal/metal ratio in related Cu–Ca complexes Fatima Zohra Chiboub Fellah a,b, Jean-Pierre Costes a,*, Franc¸oise Dahan a, Carine Duhayon a, Jean-Pierre Tuchagues a a
Laboratoire de Chimie de Coordination du CNRS, UPR 8241, lie´e par conventions a` l’Universite´ Paul Sabatier et a` l’Institut National Polytechnique de Toulouse, 205 route de Narbonne, 31077 Toulouse Cedex, France b Universite´ Abou baker Belkaid, Faculte´ des Sciences, De´partement de Chimie, BP 119, 13000 Tlemcen, Algeria Received 23 April 2007; accepted 11 May 2007 Available online 26 May 2007
Abstract We demonstrate with the help of structural determinations and spectroscopic data that the nuclearity of Cu–Ca complexes derived from compartmental Schiff base ligands does not depend on the ionic radius of calcium. The main factors governing these reactions are the different affinities of the calcium ions for the anionic species present in solution: the tetradentate O2O2 coordination site of the ligand and the nitrato ions. Because these affinities do vary upon going from calcium to lanthanide ions, it is not possible to use the template effect of the trinuclear Cu–Ca–Cu complexes in order to prepare the corresponding Cu–Ln–Cu complexes. 2007 Elsevier Ltd. All rights reserved. Keywords: Compartmental Schiff base ligands; 3d-Alkaline-earth heterometallic complexes; Dinuclear Cu–Ca complexes; Trinuclear Cu–Ca–Cu complexes; Single-crystal X-ray structures; Magnetic properties
1. Introduction In the last decade, we have been interested in the magnetic properties of heterodinuclear 3d–4f complexes. Most of them were obtained by using compartmental Schiff base ligands able to coordinate the 3d cation in their inner N2O2 coordination site while a larger outer O2O2 site was prone to link the lanthanide cation. It has been demonstrated in the literature that such metal–salicylaldimine complexes may lead to different types of ion selective transport reagents [1,2]. Furthermore, several structural determinations dealing with alkali and lanthanide metal ions indicate that the resulting complexes do have mainly a 1/1 3d/alkali or 3d/lanthanide ratio [3–6]. Surprisingly, it appears that 3d/alkaline-earth/salicylaldimine complexes have a 2/1 metal ratio [7,8]. This is why we considered the case of calcium that can be easily replaced by lanthanide ions and that has an ionic radius similar to *
Corresponding author. Tel.: +33 561 175822; fax: +33 561 553003. E-mail addresses: [email protected], [email protected] (J.-P. Costes). 0277-5387/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2007.05.019
these ions. It was expected that use of the template effect of calcium should lead to novel complexes with different 3d/4f ratios. It has also been emphasized that the number of carbon atoms involved in the diimine chain of the precursor 3d compounds has a crucial influence on the behaviour of these Schiff base complexes. For example, a metal complex with three carbon atoms in the diimine chain leads to a more flexible O2O2 site which can accommodate ions of different sizes in contrast to complexes with a two carbon atoms chain which are more constrained, as demonstrated in the case of alkali metal ions [3]. Such complexes have also been used as single-source precursors for the MOCVD deposition of heterometallic materials [8]. A variation of the 3d/alkaline-earth ratio would give a supplementary interest to these complexes. In the present paper, we show that reaction of calcium ions with metal aldimine complexes results in the formation of entities with a 2/1 Cu/Ca ratio but that it is also possible to isolate complexes with a 1/1 Cu/Ca ratio. Unfortunately, replacement of calcium by lanthanide ions has not led to the expected 2/1 Cu/Ln entities. Only the previously described 1/1 Cu/Ln complexes have been
4210
F.Z. Chiboub Fellah et al. / Polyhedron 26 (2007) 4209–4215
isolated in good yields whatever the ratio between the trinuclear 2/1 Cu/Ca complex and the lanthanide ion. An explanation for the failure of the template effect has been put forward. 2. Experimental 2.1. Materials The metal aldimine complexes, L1Cu Æ H2O [9], L Cu Æ 2H2O [10] (L1H2: N,N 0 -ethylenedi(3-methoxysalicylideneimine); L2H2: N,N 0 -2,2-dimethylpropylenedi(3-methoxysalicylideneimine)), were prepared as previously described. Ca(NO3)2 Æ 4H2O, Ca(OH)2, Ba(OH)2 Æ 8H2O, Sr(OH)2 Æ 8H2O, 2,2,6,6-tetramethyl-3,5-heptanedione (Aldrich) were used as purchased. High-grade solvents were used for the syntheses of complexes. 2
2.2. Syntheses 2.2.1. Complexes 2.2.1.1. L1CuCa(thd)2 Æ MeOH (1). A mixture of L1Cu Æ H2O (0.41 g, 1 · 103 mol) and Ca(OH)2 (0.15 g, 2 · 103 mol) in methanol (20 mL) was stirred for 15 min and then filtered off. Addition of tetramethylheptanedione (0.38 g, 2 · 103 mol) under stirring yielded a red precipitate that was filtered off 30 min later and dried. Yield: 0.3 g (36%). Anal. Calc. for C41H60CaCuN2O9: C, 59.4; H, 7.3; N, 3.4. Found: C, 59.4; H, 7.2; N, 3.4%. Characteristic IR absorptions (KBr): 3434, 2957, 1634, 1604, 1558, 1548, 1475, 1449, 1419, 1309, 1242, 1223, 1081, 987, 974, 961, 856, 741, 643, 609 cm1. Mass spectrum (FAB+, 3-nitrobenzyl alcohol matrix): m/z = 612 (100), [L1CuCa(thd)]+. Crystals suitable for a X-ray study were obtained from a dichloromethane/methanol solution. They contain a dichloromethane molecule. Use of Sr(OH)2 Æ 8H2O or Ba(OH)2 Æ 8H2O in place of Ca(OH)2 with the same experimental process and the same amount of the copper complex precursor yielded the corresponding complexes. 2.2.1.2. L1CuSr(thd)2 (2). Yield: 0.36 g (43%). Anal. Calc. for C40H56CuN2O8Sr: C, 56.9; H, 6.7; N, 3.3. Found: C, 56.3; H, 6.6; N, 3.2%. Characteristic IR absorptions (KBr): 2941, 1644, 1603, 1546, 1475, 1446, 1322, 1242, 1219, 1087, 987, 978, 968, 856, 743, 724, 646, 607 cm1. Mass spectrum (FAB+, 3-nitrobenzyl alcohol matrix): m/z = 660 (100), [L1CuSr(thd)]+. 2.2.1.3. L1 CuBa(thd)2 (3). Yield: 0.5 g (56%). Anal. Calc. for C40H56BaCuN2O8: C, 53.8; H, 6.3; N, 3.1. Found: C, 53.5; H, 6.3; N, 3.1%. Characteristic IR absorptions (KBr): 2937, 1634, 1604, 1547, 1475, 1446, 1314, 1246, 1224, 1083, 988, 968, 855, 736, 644, 608 cm1. Mass spectrum (FAB+, 3-nitrobenzyl alcohol matrix): m/z = 710 (100), [L1CuBa(thd)]+.
2.2.1.4. (L1Cu)2Ca(NO3)2 Æ 2H2O (4). A mixture of L1Cu Æ H2O (0.41 g, 1 · 103 mol) and Ca(NO3)2 (0.24 g, 1 · 103 mol) in methanol (15 mL) was stirred for three hours. The precipitate which appeared was filtered off and dried. Yield: 0.31 g (65%). Anal. Calc. for C36H40CaCu2N6O16: C, 46.0; H, 4.1; N, 8.6. Found: C, 45.6; H, 3.9; N, 8.4%. Characteristic IR absorptions (KBr): 3459, 1642, 1626, 1606, 1450, 1412, 1384, 1314, 1247, 1224, 1083, 979, 962, 857, 752, 740, 648, 609 cm1. Mass spectrum (FAB+, 3-nitrobenzyl alcohol matrix): m/z = 880 (2.5), [(L1Cu)2Ca(NO3)]+, 818 (3.6), [(L1Cu)2Ca]+, 491 (100), [(L1Cu)Ca(NO3)]+. The following complexes were prepared similarly with use of the corresponding salts. 2.2.1.5. (L1Cu)2Ba(NO3)2 Æ 2H2O (5). Yield: 0.38 g (70%). Anal. Calc. for C36H40BaCu2N6O16: C, 40.1; H, 3.7; N, 7.8. Found: C, 39.7; H, 3.6; N, 7.7. Characteristic IR absorptions (KBr): 3434, 1631, 1603, 1449, 1474, 1450, 1384, 1301, 1243, 1226, 1080, 986, 966, 853, 740, 646, 609 cm1. Mass spectrum (FAB+, 3-nitrobenzyl alcohol matrix): m/z = 978 (32.0), [(L1Cu)2Ba(NO3)]+, 916 (19.3), [(L1Cu)2Ba]+, 589 (100), [(L1Cu)Ba(NO3)]+. 2.2.1.6. (L1Cu)2Ba(ClO4)2 (6). Caution: Due to their explosive character, perchlorate salts should be handled with care and in very low amounts. Acetone was used as solvent. Yield: 0.4 g (74%). Anal. Calc. for C36H36BaCl2Cu2N4O16: C, 38.7; H, 3.2; N, 5.0. Found: C, 39.6; H, 3.2; N, 4.9%. Characteristic IR absorptions (KBr): 1647, 1666, 1604, 1550, 1472, 1443, 1392, 1301, 1243, 1222, 1120, 1081, 1055, 1046, 981, 977, 966, 854, 737, 641, 628, 620 cm1. Mass spectrum (FAB+, 3-nitrobenzyl alcohol matrix): m/z = 1017 (48.6), [(L1Cu)2Ba(ClO4)]+, 916 (34.2), [(L1Cu)2Ba]+, 626 (100), [(L1Cu)Ba(ClO4)]+. 2.2.1.7. L1CuMg(H2O)(NO3)2 (7). Yield: 0.5 g (90%). Anal. Calc. for C18H20CuMgN4O11: C, 38.9; H, 3.6; N, 10.1. Found: C, 39.0; H, 3.6; N, 9.9%. Characteristic IR absorptions (KBr): 3401, 1638, 1601, 1556, 1474, 1440, 1384, 1316, 1243, 1221, 1082, 977, 964, 858, 742, 642, 611 cm1. Mass spectrum (FAB+, 3-nitrobenzyl alcohol matrix): m/z = 475 (100), [(L1Cu)Mg(NO3)]+. 2.2.1.8. (L2Cu)2Ca(NO3)2 Æ H2O (8). Yield: 0.34 g (65%). Anal. Calc. for C42H50CaCu2N6O15: C, 48.2; H, 4.8; N, 8.0. Found: C, 47.9; H, 4.6; N, 7.8%. Characteristic IR absorptions (KBr): 3419, 1617, 1558, 1472, 1384, 1312, 1229, 1170, 1082, 1067, 983, 855, 742, 646, 623 cm1. Mass spectrum (FAB+, 3-nitrobenzyl alcohol matrix): m/z = 966 (28.5), [(L2Cu)2Ca(NO3)]+, 902 (20.2), [(L2Cu)2Ca]+, 533 (100), [(L2Cu)Ca(NO3)]+. 2.3. Physical measurements Elemental analyses were carried out at the Laboratoire de Chimie de Coordination Microanalytical Laboratory
F.Z. Chiboub Fellah et al. / Polyhedron 26 (2007) 4209–4215
in Toulouse, France, for C, H, and N. IR spectra were recorded on a GX system 2000 Perkin–Elmer spectrophotometer; samples were run as KBr pellets. Mass spectra (FAB+) were recorded in dmf as solvent and 3-nitrobenzyl alcohol matrix with a Nermag R10-10 spectrometer. Magnetic data were obtained with a Quantum Design MPMS SQUID susceptometer. All samples were 3 mm diameter pellets molded from ground crystalline samples. Magnetic susceptibility measurements were performed in the 2– 300 K temperature range in a 0.1 T applied magnetic field, and diamagnetic corrections were applied by using Pascal’s constants [11]. The magnetic susceptibilities have been computed by exact calculations of the energy levels associated to the spin Hamiltonian through diagonalization of the full matrix with a general program for axial symmetry,[12] and with the MAGPACK program package [13,14]. Least-squares fittings were accomplished with an adapted version of the function-minimization program MINUIT [15]. 2.4. Crystallographic data collection and structure determination for [L1Cu(CH3OH)Ca(thd)2] (1) and [(L2Cu)2Ca(NO3)2] (8) Crystals suitable for X-ray analyses were obtained by slow evaporation of the corresponding methanol solutions. Data were collected at 160 K for 1 on a IPDS STOE diffractometer and at 180 K for 8 on an Xcalibur Oxford Diffraction diffractometer using graphite-monochromated Mo ˚ ) and equipped with Ka radiation sources (k = 0.71073 A Oxford Cryosystems Cryostream Cooler Devices. 46 391 reflections were collected for 1, 43 468 for 8, of which
Table 1 Summary of crystal data and refinement details for 1 and 8 Empirical formula C42H62CaCl2CuN2O9 M 913.49 Temperature (K) 160 ˚) Wavelength (A 0.71073 Crystal system monoclinic Space group P21/n ˚) a (A 12.594(1) ˚) b (A 14.661(1) ˚) c (A 25.276(3) b () 95.14(1) ˚ 3) V (A 4648.2(7) Z 4 q(calc) 1.31 lMo (mm1) 0.747 Crystal size (mm) 0.15 · 0.30 · 0.50 h Range () 2.14–25.98 Reflections collected/ 46 391/9047 unique Reflection parameters 506 Maximum and minimum 0.89 and 0.76 transmission Ra 0.058 (I P 1.2r(I)) 0.070 (I P 1.2r(I)) wRb ˚ 3) Dqmax and Dqmin (e A 0.62 and 0.63 P P a R ¼ jjF o j jF c jj= jF o j. P P b 2 2 2 wR ¼ ½ wjF o j jF c j = wjF 2o j2 1=2 .
C42H50CaCu2N6O15 1046.06 180 0.71073 orthorhombic Pccn 20.948(3) 10.579(1) 20.858(2) 4622.5(10) 4 1.50 1.10 0.06 · 0.10 · 0.18 3.36–29.07 43 468/6185 287 0.94 and 0.82 0.083 (I P 3r(I)) 0.081 (I P 3r(I)) 1.79 and 1.13
4211
Table 2 Selected bond lengths and angles for 1 and 8 Complex 1 Cu–O2 Cu–O3 Cu–N2 Cu–N1 Cu–O9 Ca–O1 Ca–O2 O2–Cu–O3 Cu–O2–Ca Complex 8 Cu–O2 Cu–O3 Cu–N2 Cu–N1 Cu–O5 Ca–O2 0 Ca–O4 0 O2–Cu–O3 Cu–O2–Ca O1–Ca–O1 0
1.892(3) 1.895(3) 1.916(5) 1.922(5) 2.416(3) 2.666(3) 2.488(3) 83.8(1) 103.5(1)
1.949(4) 1.942(4) 1.972(4) 1.958(5) 2.854(5) 2.379(4) 2.479(4) 79.8(2) 109.2(2) 86.8(2)
Ca–O3 Ca–O4 Ca–O5 Ca–O6 Ca–O7 Ca–O8 O2–Ca–O3 Cu–O3–Ca
Ca–O1 Ca–O2 Ca–O3 Ca–O4 Ca–O1 0 Ca–O3 0 O2–Ca–O3 Cu–O3–Ca O4–Ca–O4 0
2.444(3) 2.724(3) 2.365(3) 2.310(3) 2.336(3) 2.369(3) 61.7(1) 105.1(1)
2.446(4) 2.379(4) 2.415(4) 2.479(4) 2.446(4) 2.415(4) 62.8(1) 108.1(1) 89.0(2)
Sym op: 0 , x + 1/2, y + 5/2, z.
9047 independent (Rint = 0.08) for 1 and 6185 (Rint = 0.13) for 8. Multiscan absorption corrections were applied (Tmin–max = 0.76–0.89 for 1, 0.82–0.94 for 8). The structures were solved by direct methods using SIR92 [16], and refined by means of least-squares procedures on F using the programs of the PC version of CRYSTALS [17]. Atomic scattering factors were taken from the International tables for X-ray crystallography [18]. All non-NO3 groups and non-hydrogen atoms were refined anisotropically. The maximum and minimum peaks on the final difference Fourier maps were 0.62 and 0.63 e A3 for 1, 1.79 and 1.13 e A3 for 8. Drawings of the molecule were performed with the program CAMERON [19]. Crystal data collection and refinement parameters are given in Table 1, and selected bond distances and angles are gathered in Table 2. 3. Results 3.1. Syntheses Reaction of the N,N 0 -ethylenedi(3-methoxysalicylideneiminato) copper complex with calcium, strontium and barium hydroxide in the presence of 2,2,6,6-tetramethyl3,5-heptanedione (thd) yielded a series of complexes formulated L1CuCa(thd)2 (1), L1CuSr(thd)2 (2) and L1CuBa(thd)2 (3), which are characterized by a 1/1 copper/alkaline-earth ratio. At variance, using alkaline-earth nitrate or perchlorate yielded complexes characterized by the 2/1 copper/alkalineearth ratio, (L1Cu)2Ca(NO3)2 Æ 2H2O (4), (L1Cu)2Ba(NO3)2 Æ 2H2O (5), (L1Cu)2Ba(ClO4)2 (6). The copper complex involving the more flexible N,N 0 -2,2-dimethylpropylenedi(3-methoxysalicylideneiminate) L2 ligand yielded a
4212
F.Z. Chiboub Fellah et al. / Polyhedron 26 (2007) 4209–4215
similar entity (L2Cu)2Ca(NO3)2 Æ H2O (8), with again a 2/1 ratio. The only exception to this 2/1 ratio occurred with magnesium ions that yielded the L1CuMg(NO3)2 Æ H2O complex (7). The different ionic radius of magnesium is most probably responsible for the change in Cu/alkaline-earth ratio. 3.2. Spectroscopic data The infrared spectra of the structurally determined complexes 1 and 8 are of prime interest for the study of the remaining entities. The mCN bands of the coordinated ligands are observed at 1604 and 1617 cm1 for 1 and 8, respectively. A strong band at 1384 cm1 is attributable to the monodentate NO3 anion in 8 [20], while a strong band at 1634 cm1 may be assigned to the coordinated keto functions of the thd ligands in 1 [21]. Mass spectra also yield interesting information. The three L1CuM(thd)2 complexes display very similar mass spectra (FAB+). In all mass spectra we observe peaks corresponding to the [L1CuM(thd)]+ ions. They appear at m/ z = 612 for 1 (M = Ca), 660 for 2 (M = Sr), and 710 for 3 (M = Ba). A different spectral pattern characterizes complex 8 with peaks at m/z = 964, 902 and 533, attributable to [(L2Cu)2Ca(NO3)]+, [(L2Cu)2Ca]+ and [L2CuCa(NO3)]+, respectively. If the peaks at 964 and 533 u are expected, the peak at 902 u is more surprising for it suggests a change in the oxidation state of the metal ions. Such an observation has been previously made [22]. Complexes 4 and 5 show similar peaks at 1017, 916 and 626, and 978, 916 and 589 u, respectively. For these three complexes, although it should be underlined that the most intense peak corresponds to the [L1CuM(NO3)]+ ion, the presence of peaks at 1017 (4) 978 (5) and 964 (8) lm confirms their trinuclear character. Complex 7, L1CuMg(NO3)2(H2O), where [L1CuMg(NO3)]+ is the only cationic species observed, is an exception. 3.3. Structural determinations The molecular structure of 1 is built from isolated dinuclear complex molecules [L1Cu(CH3OH)Ca(thd)2]. A perspective view of this dinuclear molecule with the corresponding labeling scheme is depicted in Fig. 1 while significant bond lengths and angles appear in Table 2. In each bimetallic unit, the CuII and CaII cations occupy the inner N2O2 and outer O2O2 sites, respectively. The two ions are doubly bridged to each other by phenoxo oxygen ˚ . The copper atoms, with a Cu Ca distance of 3.460(1) A is surrounded by five donor atoms. The equatorial N2O2 donors afforded by L1 are nearly coplanar and the axial position is occupied by the methanol oxygen atom at ˚ from the copper ion. While the copper ion is 2.416(3) A located in the N2O2 mean plane, the calcium ion is located ˚ out of this plane. The five-membered ring 0.741(2) A formed by the diimine moiety chelating the copper ion is in a d conformation. The Cu–O bond lengths do not differ significantly from the values reported for similar complexes
Fig. 1. Molecular structure of [L1Cu(CH3OH)Ca(thd)2] (1). The thermal ellipsoids are drawn at the 30% probability level.
[3,4]. The eight-coordinate Ca cation is surrounded by four oxygen atoms belonging to the Schiff base and by four oxygen atoms brought by two tetramethylheptanedionato anions acting as bidentate g2 chelating auxiliary ligands. The two longer Ca–O bonds involve the OMe side arms ˚ ) while the shorter ones concern (2.666(3) and 2.724(3) A the keto oxygen atoms from the thd ligands (from ˚ ); the Ca–O bonds involving the phe2.310(3) to 2.369(3) A noxo oxygen atoms are comprised in between these values ˚ ). p–p stacking interactions estab(2.444(3) and 2.488(3) A lished between the aromatic cycles located around the copper coordination spheres are responsible for the presence of ˚ ) and large short intermolecular Cu(1) Cu(1) 0 (3.819(1) A 0 ˚ Ca(1) Ca(1) (8.951(2) A) distances. The molecular structure of complex 8, along with the atom labeling scheme, is depicted in Fig. 2, while the rele-
Fig. 2. Molecular structure of (L2Cu)2Ca(NO3)2 Æ H2O (8). The thermal ellipsoids are drawn at the 30% probability level.
F.Z. Chiboub Fellah et al. / Polyhedron 26 (2007) 4209–4215
4213
Fig. 3. Fragment of the 1D chain resulting from the g1:l nitrato bridging for 8.
3.4. Magnetic properties The dinuclear complexes 1, 2, 3, 7, in which the copper ion is in presence of diamagnetic centres, behave as paramagnetic entities devoid of any intermolecular interactions. The intermolecular contacts established by p–p stacking in 1 are not able to transmit a magnetic interaction. The temperature dependence of the magnetic susceptibility for 8 in the 2–300 K temperature range is shown in Fig. 4 as the vMT versus T variation. The vMT product remains constant and equal to 0.77 cm3 mol1 K in the whole temperature range. Identical results have been obtained for the complexes 4 and 5. These results confirm that the copper ions are well isolated from each other by the alkaline-earth cations and that the bridging nitrato anions are not active. In complex 6, the decrease of the vMT product is due to weak antiferromagnetic interactions operating at low temperature. These interactions must be intermolecular for the previous complexes 4, 5 and 8 demonstrate clearly that there is
0.8
χMT (cm3mol-1K)
vant interatomic bonds lengths are collated in Table 2. The N2O2 donor set of (L2)2 is at the basal plane of the pentacoordinate copper cation, to which an oxygen atom of the nitrato anion is axially bonded. Cu(1) is displaced from the ˚ toward the aximean equatorial N2O2 plane by 0.128(2) A ally coordinated nitrato oxygen atom. The two Cu(OO)Ca cores including the two bridging phenoxo oxygen atoms are essentially planar and roughly orthogonal, with a ˚ yielding related Cu(1) Ca(1) separation of 3.5375(6) A 0 ˚ an intramolecular Cu(1) Cu(1) separation of 7.044(3) A II 0 through (Ca(1) ( :, x + 1/2, y + 5/2, z)). The Ca cation is eight-coordinate through two sets of four oxygen atoms from each L2Cu building unit, and linked to each copper ion by two phenoxo bridges. The shortest intermolecular ˚ for the nitCu(1) Cu(1) distance is equal to 5.212(1) A rato ion bridges two copper ions through the same oxygen atom, thus forming a 1D chain of trinuclear units (Fig. 3). As a consequence, the intermolecular Cu(1) Cu(1) 0 ˚ ) and Ca(1) Ca(1) (10.429(3) A ˚ ) distances are (9.127(1) A 1 large. This g :l nitrato bridging mode is not common [20].
0.6 0.4 0.2 0.0 0
20
40
60
80
100
T (K) Fig. 4. Thermal dependence of the vMT product for (L2Cu)2Ca(NO3)2 Æ H2O (8).
no significant intramolecular magnetic interaction through the alkaline-earth cations. They originate from the presence of perchlorate ions that are not able to bind copper at the axial coordination site: as the copper cations are thus in a square planar environment, intermolecular Cu Cu interactions through the phenoxo oxygen atoms must be responsible for such a weak interaction. Fitting the magnetic susceptibility data of 6 to the Bleaney–Bowers [23] equation for an exchange coupled pair of S = 1/2 spins with a 2J singlet–triplet energy gap yields an estimate of the intermolecular interaction equal toP0.75 cm1 with g = 2.05 P and an agreement factor R ( [(vMT)obs (vMT)calc]2/ [(vMT)obs]2) equal to 1 · 104 (see Fig. 4). 4. Discussion We have previously shown that compartmental Schiff base ligands resulting from the reaction of 3-methoxysalicylaldehyde with different diamines may yield discrete heterodinuclear 3d/4f complexes [5,10] with the 3d ion coordinated in the N2O2 site and the 4f ion in the O2O2 site. Very similar 3d/alkali-metal complexes have also been isolated, with the alkali-metal in the outer O2O2 coordination site [3,4]. The isolated complexes are formulated LMM 0 X or LMLnX3, L standing for the ligand, M for the 3d ion (most often Ni2+ and Cu2+), M 0 for Na+, Li+, K+, Ln
F.Z. Chiboub Fellah et al. / Polyhedron 26 (2007) 4209–4215
for the 4f ion and X for the anionic species (most often NO3 or ClO4). The presence of methoxy groups in the 3,3 0 positions of the Cu–salicylaldimine precursor complexes implies that these building units are potential ligands able to chelate metal ions in the plane of the donor atoms or to sandwich them between two sets of such Cu–salicylaldimine ligands, depending on the size of the M 0 or Ln cation. These O2O2 compartments can be preformed or can result from self-assembling of the 3d precursor complex in the presence of alkaline or lanthanide ions [4,10]. Another factor that affects the complexing ability is the number of carbon atoms involved in the imine bridge. With a 1,3-propylene bridge, metal ions linked to the outer O2O2 site are located in the plane of the four donor atoms while there is a lesser adaptability with a 1,2-ethylene bridge [3]. The third factor influencing the complexation stoichiometry originates from the anions present in the reaction medium. Indeed, these anions can compete with the precursor ligand-complex, depending on their affinity with the introduced metal ion. Concerning the outer O2O2 coordination site, it may be considered as a polyether in which a carbon atom spacer (O–CH2–CH2–O) has been replaced by a metal ion (O–M–O), as in metallacrowns [24]. In addition, the oxygen atoms linked to the metal ion are deprotonated and capable of better bonding than the ether-type oxygen atoms. Because calcium(II) ions have a chemistry closely related to that of lighter lanthanide ions, and are thus easily replaced by lanthanide ions [25], we have studied their reaction with the 3d precursor complexes. The analytical results and the structural determinations demonstrate that the isolated complexes may be formulated as [(L2Cu)2Ca(NO3)2], with a 2/1 3d/alkaline-earth ratio. This observation is really surprising for the previously studied 3d/alkaline or 3d/lanthanide complexes were characterized by a 1/1 ratio. This result is puzzling if we remember that the ionic radii of sodium, calcium and gadolinium ions span the same range of values, depending on their coordination number [25]. It is also worth noting that the flexibility of the L2 ligand used in the present case, with its three carbon atoms chain in the diimino fragment [3], is not a factor able to introduce a change in the Cu/Ca ratio. On the contrary, the magnesium ions, with their smaller ionic radius, yield a 1/1 Cu/Mg ratio even with the more rigid L1 ligand, while the barium ions, with their larger ionic radius, yield a 2/1 ratio in all cases. These data indicate that the ionic radius cannot be considered as the only factor responsible for the stoichiometry of the isolated complexes. In the present case, the results may be explained by the higher affinity of the alkaline-earth for the outer coordination site of the Cu–salicylaldimine precursor complex, a factor which prevails over the chelating power of the nitrato anions, thus yielding 2/1 entities which are not observed under similar experimental conditions in the case of lanthanide ions. In the latter case, the chelating effect of the nitrato anions toward the Ln ions is the most important factor, explaining why the observed 1/1 3d–4f ratio in the presence of nitrato anions is always obtained.
Increasing the number of oxygen atoms involved in the outer coordination site by introducing polyether-like chains does not modify the 3d/alkaline earth ratio, as reported earlier [7]. The only way to change this ratio is to introduce auxiliary ligands with a strong chelating ability, such as diketones. Then discrete species with a 1/1 3d/ alkaline earth ratio may be isolated, as demonstrated by the structural determination of the L1Cu(MeOH)Ca(thd)2 complex 1. Again the calcium ion is eight-coordinate, with two auxiliary thd ligands substituting one Cu–salicylaldimine building unit. Mass spectra data (FAB+) confirm the presence of these entities in solution. Peaks corresponding to the [L1CuM(thd)]+ ions appear at m/z = 612 (M = Ca), 660 (M = Sr) and 710 (M = Ba), thus demonstrating that the corresponding complexes are also obtained with larger alkaline-earth ions. Again, the only exception was observed for magnesium which failed to yield such a 1/1 complex. The magnetic data indicate that the copper ions are magnetically well isolated in the dinuclear (1, 2, 3, 7) and trinuclear (4, 5, 8) entities. The presence of a nitrato anion or a solvent molecule at the apical position of the copper coordination sphere prevents intermolecular interactions. Furthermore, the lack of magnetic interactions through the diamagnetic alkaline-earth cations of the trinuclear species is clearly evidenced by these results. Complex 6 behaves differently. From the magnetic results and UV– Vis data, we can conclude that the copper ions are in a square planar environment, the perchlorate anion being unable to enter the coordination sphere at an axial site, thus favouring intermolecular contacts which are responsible for the slight vMT decrease at low temperature corresponding to weak antiferromagnetic interactions (see Fig. 5). Up to now, we have not been able to obtain 3d–4f complexes in a 2/1 ratio with symmetrical Schiff base ligands, in presence of nitrato anions. As the 2/1 3d-alkaline-earth complexes are easily obtained, we have tried to use the template effect of the calcium ions to prepare the corresponding 2/1 3d-Ln complexes. It is known for a long time that such a replacement is possible [25]. Unfortunately all our experiments failed to yield the expected 3d–4f complexes, our attempts leading to the isolation of 1/1 3d–4f com0.9
χMT (cm3mol-1K)
4214
0.6
0.3
0.0 0
20
40
60
80
100
T (K) Fig. 5. Thermal dependence of the vMT product for (L1Cu)2Ba(ClO4)2 (6). The solid line is the best fit to the Bleaney–Bowers equation, see text.
F.Z. Chiboub Fellah et al. / Polyhedron 26 (2007) 4209–4215
plexes equivalent to those previously characterized. This result confirms the ready replacement of calcium by lanthanide ions. Unfortunately, the template effect of the calcium ion is not able to give the expected trinuclear 3d–4f–3d entities.
4215
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ ccdc.cam.ac.uk. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.poly.2007.05.019.
5. Conclusion References It is well known that the lanthanide ionic radii depend on their coordination number and that they span the values of the calcium ionic radii. Furthermore, the Ln ions, which are the chameleons of coordination chemistry, replace with much ease the Ca ions in coordination compounds [25]. The present work demonstrates that this replacement is in fact easy but that it yields complexes with stoichiometries different from those of the starting 3d/Ca compounds. This behaviour is explained by the different affinities of the Ln and Ca ions for the anionic species present in the reaction medium: the tetradentate donor ligand and the nitrato anions. The alkaline-earth affinity for the outer coordination site of the metal–salicylaldimine complex prevails over the chelating power of the nitrato anions while the reverse is true for the lanthanide ions. Using auxiliary ligands such as diketones, which have a strong chelating power, allows to vary the 3d-alkaline earth ratio from 2/1 to 1/1. Playing with these different factors yields a large and rich palette to the synthetic chemist. This work demonstrates that synthesis of a desired complex is not always straightforward. Eventually, the possible variation of the 3d/alkaline-earth ratio gives a supplementary interest to these complexes as single-source precursors for the MOCVD deposition of heterometallic materials. Acknowledgements We thank Dr. A. Mari for his contribution to the magnetic measurements. F.Z.C.F. acknowledges the Algerian Ministry for Education and Research for an abroad doctoral grant. Appendix A. Supplementary material CCDC 638955 and 638956 contain the supplementary crystallographic data for 1 and 8. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/ conts/retrieving.html, or from the Cambridge Crystallo-
[1] A. Schepartz, J.P. McDevitt, J. Am. Chem. Soc. 111 (1989) 5976. [2] O.F. Schall, K. Robinson, J.L. Atwood, G.W. Gokel, J. Am. Chem. Soc. 113 (1991) 7434. [3] D. Cunningham, P. McArdle, M. Mitchell, N. Ni Chonchubhair, M. O’Gara, F. Franceschi, C. Floriani, Inorg. Chem. 39 (2000) 1639. [4] J.P. Costes, F. Dahan, J.P. Laurent, Inorg. Chem. 33 (1994) 2738. [5] J.P. Costes, F. Dahan, A. Dupuis, Inorg. Chem. 39 (2000) 165. [6] J.P. Costes, F. Dahan, W. Wernsdorfer, Inorg. Chem. 45 (2006) 5. [7] J.P. Costes, J.P. Laurent, P. Chabert, G. Commenges, F. Dahan, Inorg. Chem. 36 (1997) 656. [8] A.N. Gleizes, F. Senocq, M. Julve, J.L. Sanz, N. Kuzmina, S. Troyanov, I. Malkerova, A. Alikhanyan, M. Ryazanov, A. Rogachev, E. Dedlovskaya, J. Phys. IV France 9 (1999) 943. [9] R.H. Holm, M.J. O’Connor, Progr. Inorg. Chem. 14 (1971) 241. [10] J.P. Costes, F. Dahan, A. Dupuis, J.P. Laurent, Inorg. Chem. 36 (1997) 3429. [11] P. Pascal, Ann. Chim. Phys. 19 (1910) 5. [12] J.M. Clemente-Juan, C. Mackiewicz, M. Verelst, F. Dahan, A. Bousseksou, Y. Sanakis, J.-P. Tuchagues, Inorg. Chem. 41 (2002) 1478. [13] J.J. Borra´s-Almenar, J.M. Clemente-Juan, E. Coronado, B.S. Tsukerblat, Inorg. Chem. 38 (1999) 6081. [14] J.J. Borra´s-Almenar, J.M. Clemente-Juan, E. Coronado, B.S. Tsukerblat, J. Comput. Chem. 22 (2001) 985. [15] F. James, M. Roos, Comput. Phys. Commun. 10 (1975) 345. [16] A. Altomare, G. Cascarano, G. Giacovazzo, A. Guagliardi, M.C. Burla, G. Polidori, M. Camalli, J. Appl. Cryst. 27 (1994) 435. [17] P.W. Betteridge, J.R. Carruthers, R.I. Cooper, C.K. Prout, D.J. Watkin, J. Appl. Cryst. 36 (2003) 1487. [18] International Tables for Crystallography, vol. C, Kluwer Academic Publishers, Dordrecht, The Netherlands, 1992. [19] D.J. Watkin, C.K. Prout, L.J. Pearce, CAMERON, Chemical Crystallography Laboratory, Oxford, UK, 1996. [20] L.W. Yang, S. Liu, S.J. Rettig, C. Orvig, Inorg. Chem. 34 (1995) 4921. [21] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, fifth ed., Wiley, New York, 1997. [22] J.M. Miller, K. Balasanmugan, J. Nye, G.B. Deacon, N.C. Thomas, Inorg. Chem. 26 (1987) 560. [23] B. Bleaney, K.D. Bowers, Proc. R. Soc. London, Ser. A 214 (1952) 451. [24] M.S. Lah, V.L. Pecoraro, J. Am. Chem. Soc. 111 (1989) 7258. [25] J.C.-G. Bu¨nzli, in: R.S. Puche, P. Caro (Eds.), Rare Earths, Editorial Complutense, Madrid, 1998.