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Radical-ion salts obtained from tetraazaderivatives of nickel and copper and tetracyanoquinodimethane: structural and magnetic characterization
Inorganica Chimica Acta 357 (2004) 1054–1062 www.elsevier.com/locate/ica
Radical-ion salts obtained from tetraazaderivatives of nickel and copper and tetracyanoquinodimethane: structural and magnetic characterization ~ Loreto Ballester a, Angel Gutierrez a,*, M. Felisa Perpin an, a, Ana E. S anchez a, M. Teresa Azcondo b, M. Jes us Gonz alez c b
a Departamento de Quımica Inorganica I, Facultad de Ciencias Quımicas, Universidad Complutense, Madrid 28040, Spain Departamento de Ciencias Quımicas, Facultad de Ciencias Experimentales y de la Salud, Universidad San Pablo-CEU, Boadilla del Monte, Madrid 28668, Spain c Grupo de Quımica Inorganica, Departamento de Quımica Aplicada, Facultad de Quımicas, Universidad del Paıs Vasco, Apartado 1072, San Sebastian 20080, Spain
Received 10 June 2003; accepted 30 September 2003
Abstract Several derivatives of formulae [M(N4 )(TCNQ)2 ] and [M(N4 )(TCNQ)2 ](TCNQ) (M ¼ Ni, Cu; N4 ¼ 1,4,7,10-tetraazacyclododecane ([12] aneN4 ), 1,4,8,11-tetraazacyclotetradecane ([14] aneN4 ), 1,4,8,12-tetraazacyclopentadecane ([15] aneN4 ), 1,4,7,10-tetraazadecane (trien), N ; N ; N -tris(2-aminoethyl)amine (tren), 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,14-diene (trans-dieneN4 )) have been obtained by metathesis reaction of the corresponding perchlorate or nitrate derivatives and LiTCNQ or (Et3 NH)(TCNQ)2 . The compounds [M(aneN4 )(TCNQ)2 ] have a six coordinated metal atom surrounded by the four macrocyclic nitrogens and two nitrogens from r coordinated TCNQ . The overlap with a neighbouring 7,7,8,8-tetracyanoquinodimethane (TCNQ) forms the diamagnetic dianion [TCNQ]2 2 , and the whole structure can be seen as chains of metallomacrocyclic cations and TCNQ dianions alternating in the solid. The crystal structure of [Cu([15] aneN4 )(TCNQ)2 ] confirms this fact. With open chain tetraamines the derivatives [Cu(trien)(TCNQ)2 ] and [Cu(tren)(TCNQ)2 ] are proposed to have the copper in a pentacoordinated environment, with only one coordinated TCNQ. In [M(trans-dieneN4 )](TCNQ)2 both TCNQ are uncoordinated and dimerized, as the crystal structure of the nickel derivative confirms. The derivatives with three TCNQ [M(aneN4 )(TCNQ)2 ](TCNQ) are proposed to have a structure derived from that of the analogous [M(aneN4 )(TCNQ)2 ], based on the metallomacrocycle-[TCNQ]2 chains connected through the extra TCNQ which remains uncoordinated and overlaps with the coordinated anions. This fact lowers the antiferromagnetic coupling inside the dimers and a small contribution for a thermally activated triplet state is observed in the magnetic susceptibility of these compounds. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Radical ions; Macrocycles; Supramolecular chemistry; Magnetic properties
1. Introduction The search for new supramolecular compounds obtained by assembling organic radicals with open-shell transition metal complexes has attracted the interest of many researchers due to the correlation found between *
Corresponding author. Tel.: +34-91-394-4337; fax: +34-91-3944352. E-mail address: [email protected] (A. Gutierrez). 0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2003.09.022
the supramolecular organization and the associated properties shown by the new compound [1]. One of the most extensively used radical in this study has been the organic planar molecule 7,7,8,8-tetracyanoquinodimethane (TCNQ), since it shows a low reduction potential which makes it a suitable acceptor in charge transfer processes and also shows, as anion-radical, a high rdonor ability to transition metals having vacant coordinative positions [2]. Other typical characteristic of this acceptor is the tendency to overlap its p-delocalized
L. Ballester et al. / Inorganica Chimica Acta 357 (2004) 1054–1062
HN
NH
HN
NH
HN
NH
HN
NH
HN
NH
HN
NH
[12]aneN4
HN
NH
H2 N
NH2
[14]aneN4 (cyclam)
N H2N
trien
NH2
NH2
tren
[15]aneN4
N
NH
HN
N
trans-dieneN4
Scheme 1.
system with neighbouring molecules to form stacks ranging from the dimeric dianion [TCNQ]2 2 [3] to one dimensional rows of stacked units having different degrees of electronic delocalization [4]. We have been studying the different transition metal-TCNQ systems in tetraazamacrocycles of nickel(II) and copper(II) and obtained different supramolecular architectures depending on the oxidation state of the TCNQ molecule and its ability to coordinate the metal atom. When there are vacant positions around the metal the anion-radical is coordinated via one or more of its nitrile groups [3d,5]. On the contrary, when the metal ion has a close stable coordinative environment, thus precluding a direct interaction with the anionradical, the crystal packing is driven by electrostatic interactions between the cationic metal moieties and the dimeric [TCNQ]2 anions which alternate in the 2 solid [3d,6]. A different situation occurs when the TCNQ is partially reduced and no direct interaction with the metal atom is present. In this case a greater electronic delocalization along with the formation of infinite stacks of formally [TCNQ]0:5 or [TCNQ]0:66 is observed [4c,4d]. Following this line the present work reports our results of interactions between partial or totally reduced TCNQ units and tetraazaderivatives of first row transition metals. These derivatives are formed either with the open chain ligands or macrocycles with different sizes shown in Scheme 1.
2. Experimental 2.1. General Remarks All the reactions have been carried out under oxygen– free nitrogen. The parent reagents [Ni([12] aneN4 )](NO3 )2 [7], [Cu([12] aneN4 )Cl2 ] [7], [Ni([14] aneN4 )](ClO4 )2 [8], [M([15] aneN4 )](ClO4 )2 (M ¼ Ni, Cu) [8], [Cu(trien)] (ClO4 )2 [9], [Cu(tren)](ClO4 )2 [10], [M(trans-dieneN4 )] (ClO4 ) (M ¼ Ni, Cu) [11], LiTCNQ [12] and Et3
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NH(TCNQ)2 [12] were obtained by the published methods and their purities were checked by elemental analyses. Hazard warning. Perchlorate salts are potentially explosive and should be used in small amounts and handled with care [13]. Elemental analyses were carried out by the Servicio de Microanalisis of the Universidad Complutense de Madrid. Infrared spectra were recorded as KBr pellets on a Nicolet Magna-550 FT-IR spectrophotometer. Magnetic experiments were made on polycrystalline samples using a SQUID magnetometer MPMSXL-5 manufactured by Quantum Design. The temperature dependence of the magnetization in the range between 2 and 300 K was recorded using a constant magnetic field of 0.5 T. The experimental data have been corrected for the magnetization of the sample holder and for atomic diamagnetism as calculated from the known PascalÕs constants. X- or Q-band powder EPR spectra have been obtained on a Bruker ESP 300 apparatus equipped with a Bruker ER035M gaussmeter and an Oxford JTC4 cryostat. 2.2. Preparation of the [M(N4 )](TCNQ)2 derivatives All these compounds have been obtained by the same procedure: A solution containing 1 mmol of LiTCNQ in 15 mL of methanol was added dropwise over a solution of 0.5 mmol of the starting compound in 15 mL of methanol. After complete mixing a blue solid appeared, which was filtered off, washed with methanol and diethyl ether, and dried under vacuum. 2.2.1. [Ni([12] aneN4 )(TCNQ)2 ] (1) Yield: 66%. Anal. Calc. for C32 H28 N12 Ni: C, 60.1; H, 4.4; N, 26.3. Found: C, 59.6; H, 4.4; N, 26.2%. IR (KBr, cm1 ): 2209m, 2183s, 2158s, 1584m, 1502m, 1363m, 1337m, 1180m, 955w, 823w, 720w. 2.2.2. [Cu([12] aneN4 )(TCNQ)2 ] H2 O (2) Yield: 54%. Anal. Calc. for C32 H30 CuN12 O: C, 58.0; H, 4.5; N, 25.4. Found: C, 57.6; H, 4.5; N, 25.3%. IR (KBr, cm1 ): 2190s, 2179s, 2158s, 1580m, 1507m, 1355m, 1331m, 1174m, 977w, 828w, 722w. 2.2.3. [Ni([15] aneN4 )(TCNQ)2 ] (3) Yield: 61%. Anal. Calc. for C35 H34 N12 Ni: C, 61.6; H, 5.0; N, 24.7. Found: C, 61.8; H, 4.9; N, 24.8%. IR (KBr, cm1 ): 2181s, 2161s, 1582m, 1503m, 1363m, 1340m, 1175m, 986w, 825w, 722w. 2.2.4. [Cu([15] aneN4 )(TCNQ)2 ] (4) Yield: 57%. Anal. Calc. for C35 H34 CuN12 : C, 61.3; H, 5.0; N, 24.5. Found: C, 61.3; H, 5.0; N, 24.6%. IR (KBr, cm1 ): 2181s, 2156s, 1581m, 1502m, 1360m, 1340m, 1175m, 984w, 826w, 722w.
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2.2.5. [Cu(trien)](TCNQ)2 (5) Yield: 46%. Anal. Calc. for C30 H26 CuN12 : C, 58.3; H, 4.2; N, 27.1. Found: C, 57.9; H, 4.1; N, 27.0%. IR (KBr, cm1 ): 2195m, 2180s, 2171s, 2154s, 1579m, 1503m, 1365m, 1343m, 1180m, 985w, 825w, 721w. 2.2.6. [Cu(tren)](TCNQ)2 (6) Yield: 47%. Anal. Calc. for C30 H26 CuN12 : C, 58.3; H, 4.2; N, 27.1. Found: C, 58.0; H, 4.3; N, 26.9%. IR (KBr, cm1 ): 2202m, 2188s, 2169s, 1569m, 1504m, 1354m, 1166m, 983w, 825w, 718w. 2.2.7. [Ni(trans-dieneN4 )](TCNQ)2 (7) Yield: 60%. Anal. Calc. for C40 H40 N12 Ni: C, 64.3; H, 5.4; N, 22.5. Found: C, 64.0; H, 5.2; N, 22.5%. IR (KBr, cm1 ): 2178s, 2156s, 1581m, 1503m, 1366m, 1344m, 1175m, 985w, 824w, 719w. 2.2.8. [Cu(trans-dieneN4 )](TCNQ)2 (8) Yield: 68%. Anal. Calc. for C40 H40 CuN12 : C, 63.9; H, 5.3; N, 22.4. Found: C, 63.8; H, 5.4; N, 22.5%. IR (KBr, cm1 ): 2199s, 2184s, 2170s, 2154s, 1573m, 1505m, 1352m, 1332m, 1177m, 990w, 825w, 720w. 2.3. Preparation of the [M(N4 )](TCNQ)3 derivatives A solution containing 1 mmol of Et3 NH(TCNQ)2 in 15 mL of acetonitrile was added dropwise over a solution of 0.5 mmol of the starting compound in 15 mL of methanol. After complete mixing a dark blue solid appeared, which was filtered off, washed with acetonitrile and diethyl ether, and dried under vacuum. 2.3.1. [Ni([12] aneN4 )(TCNQ)2 ](TCNQ) MeOH (9) Yield: 64%. Anal. Calc. for C45 H36 N16 NiO: C, 61.7; H, 4.1; N, 25.6. Found: C, 61.0; H, 4.2; N, 26.0%. IR (KBr, cm1 ): 2190s, 2182s, 2165s, 1574m, 1503m, 1384s, 1172m, 959w, 838w, 829w, 704w. 2.3.2. [Cu([12] aneN4 )(TCNQ)2 ](TCNQ) (10) Yield: 53%. Anal. Calc. for C44 H32 CuN16 : C, 62.3; H, 3.8; N, 26.4. Found: C, 61.4; H, 4.0; N, 26.6%. IR (KBr, cm1 ): 2227w, 2196s, 2188s, 2168s, 1578m, 1508m, 1366m, 1348m, 1170m, 988w, 862w, 841w, 824w. 2.3.3. [Ni([14] aneN4 )(TCNQ)2 ](TCNQ) (11) Yield: 59%. Anal. Calc. for C46 H36 N16 Ni: C, 63.3; H, 4.1; N, 25.7. Found: C, 63.2; H, 4.4; N, 25.5%. IR (KBr, cm1 ): 2217w, 2181s, 2156s, 1578m, 1539w, 1497m, 1422w, 1363m, 1340m, 1172m, 980w, 840w, 828w, 722w. 2.3.4. [Ni([15] aneN4 )(TCNQ)2 ](TCNQ) (12) Yield: 56%. Anal. Calc. for C47 H38 N16 Ni: C, 63.7; H, 4.3; N, 25.3. Found: C, 63.9; H, 4.3; N, 25.6%. IR (KBr, cm1 ): 2182s, 2158s, 1578m, 1539w, 1499m, 1425w, 1362m, 1339m, 1174m, 981w, 840w, 826w, 722w.
2.3.5. [Cu([15] aneN4 )(TCNQ)2 ](TCNQ) (13) Yield: 67%. Anal. Calc. for C47 H38 CuN16 : C, 63.4; H, 4.3; N, 25.2. Found: C, 63.3; H, 4.4; N, 25.4%. IR (KBr, cm1 ): 2208w, 2188s, 2160s, 1574m, 1534w, 1505m, 1424w, 1349m, 1165m, 985w, 834m. 2.4. X-ray structure determinations Good quality crystals of 4 and 7 have been obtained by slow diffusion of diluted solution of the reactants. In the three cases a deep blue crystal was resin epoxy coated and mounted on an Enraf Nonius CAD-4 j diffractrometer using graphite monochromated Mo Ka The cell dimensions were radiation (k ¼ 0:71073 A). refined by least-squares fitting of the h values of 25 reflections. The intensity data were collected at room temperature by the x 2h technique and corrected for Lorentz and polarization effects. Atomic scattering factors were taken from [14]. The structures were solved by Patterson and Fourier methods and refined by applying full-matrix least-squares on F 2 with anisotropic thermal parameters for the non-hydrogen atoms. The hydrogen atoms were included with fixed isotropic contributions at their calculated positions determined by molecular geometry. The calculations were carried out with S H E L X 97 software package [15]. A summary of the fundamental crystal data is given in Table 1.
Table 1 Crystal and refinement data for [Cu([15] aneN4)(TCNQ)2 ] (4) and [Ni(trans-dieneN4)](TCNQ)2 (7)
Formula Molecular weight Crystal system Space group a (A) b (A) c (A)
4
7
C35 H34 CuN12 686.3 triclinic P 1 (No. 1) 8.199(1) 9.951(1) 10.902(1) 88.66(1) 74.36(1) 77.38(1) 1 835.4(2) 1.364 6.99 1.94–24.97 5604 2802 433 1.101 0.02(6) 0.0448 0.0785
C40 H40 N12 Ni 747.6 triclinic P 1 (No. 2) 8.137(1) 11.169(1) 11.247(1) 89.64(1) 76.88(1) 68.94(1) 1 925.8(2) 1.341 5.71 1.87–24.97 3431 3248 245 1.047
a (°) b (°) c (°) Z 3 ) V (A Dcalcd (Mg m3 ) l (cm1 ) h Range (°) Reflections collected Independent reflections Refined parameters Goodness-of-fit Absolute structure parameter R1 ½I > 2rðIÞa wR2 ½I > 2rðIÞb P P a R1 ¼ nðjFohj jFc jÞ2 = iF 2o . h io1=2 P P b wR2 ¼ wðFo2 Fc2 Þ2 = . wðFo2 Þ2
0.0473 0.120
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3. Results and discussion All the metallic compounds have been obtained by metathesis reaction from the parent derivatives. The use of LiTCNQ, a source of exclusively anionic TCNQ, gives rise to the formation of derivatives 1–8, of general formula [M(N4 )](TCNQ)2 with the TCNQ neutralizing the two positive charges of the metal ion. When Et3 NH(TCNQ)2 , a source of both neutral and anionic TCNQ, is used the derivatives 9–13, with the organic acceptor partially reduced, are obtained. 3.1. Derivatives with two TCNQ The macrocyclic derivatives 1–4 show all the TCNQ in the form of the anion-radical and r coordinated to the metal ion. Previous examples of such behaviour have been described [3b,3d,5b] and in all these cases the coordination of the anion-radical is accompanied by its dimerization with other anion-radical coordinated to a neighbouring metal centre. The crystal structure of 4 confirms this situation and is a good example of this behaviour. The compound crystallizes in the triclinic system, space group P1. An ORTEP view of the molecular unit is shown in Fig. 1. The copper atom is coordinated to six nitrogen atoms. The four macrocyclic nitrogens lie in the equatorial and the plane with bond distances of 1.92(2) to 2.13(3) A six-coordination is completed by two TCNQ nitrile groups in apical positions at distances of 2.56(2) and showing a notable Jahn–Teller distortion, also 2.58(2) A found in related TCNQ derivatives [5b,16]. There are two crystallographically different TCNQ groups, both
N12 C35
C31 C32
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coordinated to the copper atom in the trans positions with their ring planes almost perpendicular to the mean macrocycle plane forming angles of 87.9(4)° and 86.6(5)°. Each TCNQ interacts with the non equivalent TCNQ of a neighbouring molecule by overlap of their p clouds in the ring over ring mode [17]. The separation with and angle between the quinoid planes is 3.19(3) A between the planes of 1.3(9)° ; this distance is comparable to that found in other dimeric [TCNQ]2 units 2 [3,5]. Every TCNQ forms a hydrogen bond between the nitrile opposite to the coordinated one and one amine group of the macrocycle with bond distance of N8 H3 and angle N3–H3 N8 ¼ 170.9° for one of ¼ 2.14 A and N1– the TCNQ groups and N12 H1 ¼ 2.16 A H1 N12 ¼ 165.6° for the other group. These hydrogen bonds are formed with the macrocycle belonging to the same molecular unit than the overlapping TCNQ. Therefore, each dimeric [TCNQ]2 2 interacts doubly with the metallomacrocyclic unit, with one TCNQ coordinated to the metal atom and the other forming hydrogen bond with the macrocycle. This double interaction leads to the formation of chains of metallomacrocycles bridged by [TCNQ]2 dianions (Fig. 2). These chains extend along the crystal and are arranged parallel with no interactions found between adjacent ones. In contrast the structure of 7 and that expected for 8 corresponds to a derivative without direct interaction between the metal atom and the TCNQ anion-radical. This fact can be interpreted in terms of a higher electron density on the metal atom due to a higher donor character of the macrocycle. Compound 7 crystallizes in the P 1 space group. Fig. 3 shows an ORTEP view of the asymmetric unit.
N11 C34 C33 C30 C29 C28
C27 C10 C9 C8 C11 C24 C26 C7 N1 N4 Cu C25 N3 N9 N5 N10 C1 N2 C6 C13 C2 C5 C3 C4 C16 C17 C21 C22 N7
N6 C14 C12 C15 C20 C19 C18 C23 N8
Fig. 1. ORTEP view and atom labelling of the molecular unit of 4.
Fig. 2. View of the chain formed by overlap of the TCNQ groups in 4 showing the H-bonds as thin lines.
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Fig. 3. ORTEP view and atom labelling of the molecular unit of 7.
Fig. 4. View of the crystal packing in compound 7 showing the H bonds as thin lines.
The nickel atom is located on an inversion centre in a square-planar environment formed by the four macrocyclic nitrogens. The two nickel–nitrogen distances are the shorter distance corre1.907(5) and 1.932(6) A, sponding to the sp2 nitrogen. The bond distances and angles in the macrocycle are similar to those found in the parent perchlorate [18] or in the isomeric [Ni(cisdieneN4 )](TCNQ)2 [6]. The two TCNQ present in the cell unit are equivalent and related by an inversion centre. They are overlapping in a ring over ring mode to form a dimeric [TCNQ]2 2 dianion with a shorter interplanar distance of 3.16(1) A (Fig. 4). The interatomic distances in the TCNQ are characteristic of the fully reduced anion-radical [19]. The crystal packing can be described as metallomacrocyclic cations and dimeric TCNQ dianions alternating in the three spatial directions, an arrangement observed when the driving force for the packing is of electrostatic nature [3,4c,6]. The macrocycle and the TCNQ are oriented quasi perpendicularly forming an angle of 69.6(1)°. The only non electrostatic interaction between these units is a hydrogen bond N2–H2 N3
and an angle of with bond distances of 0.98 and 2.21 A 155.2°. These two crystal structures show the typical features of the coordinated and uncoordinated TCNQ anionradical, respectively, but since the electronic charge held on every acceptor is the same their spectroscopic properties are similar. Thus, the IR spectra of 1–8 show the characteristic bands of the anion radical, several bands in the m(CN) region, 2200–2155 cm1 , m20 (b1u ) at 1507– 1502 cm1 and m50 (b3u ) around 825 cm1 . All these bands are indicative of the presence of the anion-radical and are shifted to higher frequencies in the neutral species [20]. The m(CN) bands appear around 2180 and 2160 cm1 when the TCNQ is coordinated to the metal atom, as in complexes 1–4, and around 2170 and 2155 cm1 with uncoordinated TCNQ in compounds 7 and 8. The splitting in derivatives 5 and 6 can indicate that both coordinated and uncoordinated anion-radicals are present in the solid, in consonance with the five-coordination suggested by the EPR data (see below). The magnetic properties of these species are consistent with the presence of the dimerized anion-radical. The formation of dimeric [TCNQ]2 implies a strong 2 antiferromagnetic coupling of both spins that render the dianion diamagnetic at room temperature. The magnetic susceptibility variation can be then attributed to the contribution of the isolated metal ion. The magnetic susceptibility of the nickel derivatives 1 and 3 follows the Curie law above 25 K, while an abrupt descent in the value of vT is observed below this temperature. This fact is attributed to an anisotropic distortion of the nickel(II) environment which results in a zero field splitting of the ground state [21]. Eq. (1) for the average magnetic susceptibility takes into account this single-ion anisotropy 2 2 hvi ¼ 2NgNi b =3kB T f½2 2 expð xÞ=x þ expð xÞg =½1 þ 2 expð xÞ;
ð1Þ
where gNi is the Lande g factor for the nickel ion, kB is BoltzmannÕs constant, b is the Bohr magneton and x ¼ D=kB T . The parameter D measures the zero-field splitting. The best fit is obtained when gNi ¼ 2:19 and D ¼ 2:65 cm1 for 1 and gNi ¼ 2:16 and D ¼ 4:69 cm1 for 3. Finally compound 7 is diamagnetic, as expected for a square-planar nickel(II) derivative. The copper derivatives follow the Curie–Weiss law with magnetic moments (g[S(S+1)]1=2 ) ranging between 1.76 and 1.83 b typical for isolated S ¼ 1/2 spins. This behaviour is confirmed by the EPR spectra of the solid samples which afford g values (Table 2) in accordance with the magnetic moments obtained by the Curie law. Fig. 5 shows representative spectra of the copper(II) compounds. The EPR spectrum (Q band) of compound 5 shows the typical rhombic pattern (Fig. 5(a)), with lowest
L. Ballester et al. / Inorganica Chimica Acta 357 (2004) 1054–1062
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Table 2 Magnetic and EPR data for the new compounds Compound
Magnetic data gMetal
1 2 3 4 5 6 7 8 9 10 11 12 13
2.19 2.04 2.16 2.04 2.10 2.11 Diamagnetic 2.07 2.18 2.13 2.29 2.07 2.13
EPR data (100 K) h (K) )0.29
D (cm1 )
J (cm1 )
g1 (or gk ), A(G)
g2 (g? )
g3
2.19, 196 2.15 2.20
2.04 2.10 2.11
2.05 2.02
2.18, 180
2.065
2.19
2.04
)2.65 4.69
)0.17 )0.86 )1.39 )1.56 3.12 )0.44 7.35 5.62 )0.28
)463 )464 )172 )235 )192
Fig. 5. EPR spectra of 5 (a), 6 (b), 8 (c) and 13 (d).
g < 2:04, that can be either attributed to a pentacoordinate square-based pyramidal or a distorted octahedral environment. The first possibility would lead to a formula [Cu(trien)(TCNQ)](TCNQ) with both coordinated and uncoordinated TCNQ anion-radical, in accordance with the IR spectra commented above. The copper environment would be similar to that found in the crystal structure of [Cu(trien)(SCN)](SCN) with the copper atom in the centre of a square-based pyramid formed by the four amine nitrogens and the sulphur atom of the
coordinated thiocyanate [23]. If the copper were sixcoordinated a structure like that of [Ni(trien)(TCNQ)2 ] with the anion-radicals coordinated in cis positions [3d] would be expected. We have no conclusive evidence to choose between these two possibilities, but the spectral data suggest that the pentacoordination would be the most plausible structure. The EPR spectrum (Q band) of compound 6 (Fig. 5(b)) also shows a rhombic splitting, coherent with a trigonal bipyramidal environment. This situation
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would correspond again to one coordinated and one uncoordinated TCNQ with a formula [Cu(tren)(TCNQ)](TCNQ). Along with the IR spectral data the crystal structure of the related isothiocyanate derivative, [Cu(tren)(NCS)](SCN) [24] shows this coordinative environment for the copper atom. Assuming a pentacoordinated environment for 5 and 6 it would be necessary that all the TCNQ anion-radicals were dimerized, since no contribution to the magnetic susceptibility was observed. The EPR of 6 shows a small signal at g ¼ 2:003 that would correspond to isolated radical impurities, but its low intensity indicates that the impurity concentration is too small to be detected from the susceptibility data as they were masked by the signal from the copper spins, two orders of magnitude bigger as the EPR signal indicates. The EPR spectrum (Q band) of compound 8 (Fig. 5(c)) shows the typical axial pattern for tetragonally elongated octahedral copper(II) [22] with the parallel component showing the hyperfine splitting due to the coupling with the copper nucleus (I ¼ 3/2). Compound 4 shows a similar spectrum. 3.2. Derivatives with three TCNQ The formation of compounds 9–13 requires the presence of two anion-radicals to neutralize the positive charges on the metallomacrocycle, while the third TCNQ would remain formally neutral. The anion-radicals would be r coordinated to the metal ion giving rise to the formation of infinite chains –[M(N4 )]–[TCNQ]2 – [M(N4 )]–[TCNQ]2 – similar to those proposed for compounds 1–4 and found in the structure of 4. The extra TCNQ would be located between the chains interacting by p overlap with the anion-radicals. This situation has been reported in the manganese complex [Mn(tpa) (TCNQ)(MeOH)](TCNQ)2 MeCN (tpa ¼ tris(2-pyridiylmethyl)amine) [25] and observed by us in the related derivative [Cu([14] aneN4 )(TCNQ)2 ](TCNQ) [16]. This compound crystallizes in two polymorphic forms that only differ in the stacking mode of the neutral TCNQ between the chains. Since we have no structural data of compounds 9–13 we only can estimate the oxidation state of every TCNQ in base to the spectral data. The IR spectra of these compounds exhibit the characteristic bands of coordinated TCNQ anion-radicals along with new bands around 2220, 1537, 1425 and 840 cm1 corresponding, respectively, to the m(CN), m20 (b1u ), m4 (ag ) and m50 (b3u ) vibration modes of a quasi neutral TCNQ molecule. These bands appear at similar frequencies than those observed for [Cu([14] aneN4 )(TCNQ)2 ](TCNQ) and strongly support the proposed structure for these complexes. The coordination of the TCNQ is also supported by the absence in the IR spectra of the electronic absorption tail observed when
Fig. 6. Temperature dependence of vT for 3 (Þ, 4 (MÞ, 12 (Þ and 13 (s). The solid lines represent the best fit using the equations described in the text for the parameters that appear in Table 2.
electronic delocalization is found between the stacked TCNQ units [26]. The EPR spectrum (X band) of compound 13 (Fig. 5(d)) shows the axial pattern for distorted octahedral copper(II) expected for the proposed structure. It is also observable that a small signal at g ¼ 2:003 is attributable to small quantities of nondimerized radicals, in consonance with the observed magnetic susceptibility. The magnetic susceptibilities of compounds 9–13 have been measured down to 2 K. Fig. 6 shows the plot of vT versus T for one nickel and one copper representative derivative compared with the corresponding compounds with two TCNQ. The plot of the copper derivative compound 13 shows a plateau between 25 and 125 K, where the Curie law was obeyed. The small decrease in the values at low temperatures can be ascribed to very weak antiferromagnetic interactions between almost isolated copper(II) centres and fitted by using the Curie–Weiss law. The increase in the vT values above 125 K is due to a small contribution from the TCNQ dimers, which show a lower antiferromagnetic coupling than that exhibited by the two TCNQ derivative compound 4. The lower value of the coupling implies that the triplet state is thermally accessible and populated near room temperature, giving rise to the contribution of the radicals to the magnetic susceptibility. Taking these two contributions into account the molar magnetic susceptibility was fitted using Eq. (2) to the sum of the Curie–Weiss law for the copper(II) ion and the Bleaney–Bowers equation [27] for the antiferromagnetically interacting TCNQ radicals: v¼
2 NgCu b2 Ng2 b2 2 þ ; 4kB ðT hÞ kB T 3 þ expðJ =kB T Þ
ð2Þ
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where gCu is the Lande g factor for the copper ion, J the exchanging coupling constant for the TCNQ dimers, g is the Lande g factor for the TCNQ radicals and is assumed to be 2.003, the rest of the parameters are the same as in Eq. (1). The best fit for the experimental data is represented as a solid line in Fig. 6 and corresponds to the parameter values shown in Table 2. The g value 2.13 is similar to that obtained by the EPR spectrum and the small h value suggests that the proposed antiferromagnetic interaction is almost negligible. The h value is equivalent to a J exchanging constant between copper ions of )0.38 cm1 , by using the expression h ¼ zJ SðS þ 1Þ=3kB , where z, the number of interacting spins, is assumed to be two, considering that the interaction is transmitted through the coordinated TCNQ [28]. The nickel derivative compound 12 has been chosen as an example of the magnetic behaviour of the other compounds with the same metal. The general variation of vT is similar to that observed for the copper derivatives with the exception of the more pronounced decrease at low temperatures. This fact is interpreted in terms of the zero-field splitting induced by the anisotropy in the nickel environment as commented above. The small antiferromagnetic coupling between metal ions commented for the copper atoms is also probably present but the more pronounced effect of the zero-field splitting obscured its observation. The total magnetic susceptibility for the nickel complexes is then fitted to Eq. (3) where all the parameters have the meaning previously described: 2 2 2NgNi b 2=x 2=x expðxÞ þ expðxÞ v¼ 1 þ 2 expðxÞ 3kB T 2 Ng2 b 2 þ : kB T 3 þ expðJ =kB T Þ
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4. Concluding remarks The formation of [M(N4 )(TCNQ)2 ] derivatives is always the result of the neutralization of the positive charges in the [M(N4 )]2þ fragment by the anion-radical TCNQ . The tendency of this anion-radical to dimerize gives rise to the formation of S ¼ 0 dianions [TCNQ]2 2 . Depending on the metal ion coordinative status the structures formed in the solid are different, thus with saturated amine ligands monodentate coordination of the TCNQ is found and since this acceptor is dimerized it results in the formation of chains formed by the cationic metallic fragments bridged by the dianionic TCNQ dimers coordinated to successive metal atoms. With more donor unsaturated ligands the metal atom remains in a square planar environment and no direct interaction with the TCNQ is observed. In both cases the formation of hydrogen bonds tends to stabilize the arrangement observed in the solid. When neutral TCNQ along with anionic TCNQ is present in the reaction mixture the derivatives [M(N4 ) (TCNQ)2 ](TCNQ) are formed. The similitude in the properties between these species and the previously reported [Cu([14] aneN4 )(TCNQ)2 ](TCNQ) strongly supports the proposal of a similar structure in the solid state with coordinated TCNQ anions that dimerize to form chains as in the [M(N4 )(TCNQ)2 ] compounds. The extra TCNQ remains approximately neutral and is situated between the chains forming stacks by p overlap with the coordinated TCNQ . This interaction weakens the antiferromagnetic coupling inside the dimers and the excited S ¼ 1 state becomes thermally accessible and populated above 150 K as observed in the magnetic susceptibility fits.
ð3Þ
The J values for the nickel and copper derivatives are comparable suggesting that the metal does not influence the TCNQ coupling. The values for the smaller macrocyclic derivatives are however much more negative, indicating that the antiferromagnetic coupling is stronger in these compounds. In fact the greater values for the [12] aneN4 derivatives imply that the TCNQ radical contribution to the magnetic susceptibility is only observable above 220 K and below this temperature the data approximately fitted the Curie law. With the absence of structural data we are unable to determine the reason for this behaviour, that will probably be related to the small size of the macrocycle, which in turn can induce differences in the TCNQ stacking, as the weak interactions responsible for the packing in these compounds can be easily overridden as the related [Cu([14] aneN4 )(TCNQ)2 ](TCNQ) have shown [16].
5. Supplementary material Crystallographic data for the structural analyses have been deposited with the Cambridge Crystallographic Data Centre, CCDC-207152 (for compound 4) and 207153 (for compound 7). These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: (internet.) +44-1223/336-033; E-mail: deposit@ccdc. cam.ac.uk).
Acknowledgements We gratefully acknowledge the Spanish Ministerio de Ciencia y Tecnologıa, project BQU2002-01409, for financial support.
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References [1] (a) M. Kurmoo, A.W. Graham, P. Day, S.J. Coles, M.B. Hursthouse, J.L. Caulfield, J. Singleton, F.L. Pratt, W. Hayes, L. Ducasse, P. Guionneau, J. Am. Chem. Soc. 117 (1995) 12209; (b) H. Zhao, R.A. Heintz, K.R. Dunbar, R.D. Rogers, J. Am. Chem. Soc. 118 (1996) 12844; (c) C. Chen, K.S. Suslick, Coord. Chem. Rev. 128 (1993) 293. [2] (a) W. Kaim, M. Moscherosch, Coord. Chem. Rev. 129 (1994) 157; (b) L. Ballester, A. Gutierrez, M.F. Perpi~ nan, M.T. Azcondo, Coord. Chem. Rev. 190 (1999) 447. [3] (a) A. Bencini, S. Mindolini, C. Zanchini, Inorg. Chem. 28 (1989) 1963; (b) J.P. Cornelissen, J.H. Diemen, L.R. Groenveld, J.G. Hasnoot, A.L. Speck, R.J. Reedijk, Inorg. Chem. 31 (1992) 198; (c) M.C. Mu~ noz, J. Cano, R. Ruiz, F. Lloret, J. Faus, Acta Crystallogr. Sect. C 51 (1995) 873; (d) L. Ballester, A. Gutierrez, M.F. Perpi~ nan, U. Amador, M.T. Azcondo, A.E. Sanchez-Pelaez, C. Bellitto, Inorg. Chem. 36 (1997) 6390. [4] (a) H. Endress, Angew. Chem. Int. Ed. Engl. 21 (1982) 524; (b) H. Endress, Angew. Chem. Int. Ed. Engl. 23 (1984) 999; (c) M.T. Azcondo, L. Ballester, S. Golhen, A. Gutierrez, L. Ouahab, S. Yartsev, P. Delhaes, J. Mater. Chem. 9 (1999) 1237; (d) L. Ballester, A.M. Gil, A. Gutierrez, M.F. Perpi~ nan, M.T. Azcondo, A.E. S anchez-Pelaez, E. Coronado, C.J. G omez-Garcıa, Inorg. Chem. 39 (2000) 2837. [5] (a) L. Ballester, M.C. Barral, A. Gutierrez, A. Monge, M.F. Perpi~ n an, C. Ruiz-Valero, A. Sanchez-Pela ez, Inorg. Chem. 33 (1994) 2142; (b) M.T. Azcondo, L. Ballester, A. Gutierrez, M.F. Perpi~ nan, U. Amador, C. Ruiz-Valero, C. Bellitto, J. Chem. Soc. Dalton Trans. (1996) 3015; (c) L. Ballester, A.M. Gil, M.F. Perpi~ nan, M.T. Azcondo, A.E. Sa nchez, C. Marzin, G. Tarrago, C. Bellitto, Chem Eur. J. 8 (2002) 2539. [6] L. Ballester, A. Gutierrez, M.F. Perpi~ nan, M.T. Azcondo, A.E. S anchez-Pel aez, U. Amador, Anal. Quim. Int. Ed. 92 (1996) 275. [7] L. Fabbrizzi, Inorg. Chem. 16 (1977) 2667.
[8] L.Y. Martin, C.R. Sperati, D.H. Busch, J. Am. Chem. Soc. 99 (1977) 2969. [9] N.F. Curtis, D.A. House, J. Chem. Soc. (1965) 6194. [10] S.G. Zipp, A.P. Zipp, S.K. Madan, J. Indian Chem. Soc. 54 (1977) 149. [11] K. Miyamura, M. Kohzuki, R. Narushima, M. Saburi, Y. Gohshi, J. Chem. Soc., Dalton Trans. (1987) 3093. [12] L.R. Melby, R.J. Herder, W. Mahler, R.E. Benson, W.E. Mochel, J. Am. Chem. Soc. 84 (1962) 3374. [13] W.C. Wolsey, J. Chem. Educ. 50 (1973) A335. [14] International tables for X-ray crystallography, vol IV. Kynoch Press. Birmingham. 1974, p. 72. [15] G.M. Sheldrichk, S H E L X 97, University of G€ ottingen, Germany, 1997. [16] L. Ballester, A.M. Gil, A. Gutierrez, M.F. Perpi~ nan, M.T. Azcondo, A.E. Sanchez, U. Amador, J. Campo, F. Palacio, Inorg. Chem. 36 (1997) 5291. [17] H. Endres, in: J.S. Miller (Ed.), Extended Linear Chain Compounds, vol. 3, Plenum, New York, 1982, p. 263. [18] M.F. Bailey, I.E. Maxwell, J. Chem. Soc., Dalton Trans. (1972) 938. [19] S. Flandrois, D. Chasseau, Acta Crystallogr. Sect. B 33 (1977) 2744. [20] (a) R. Bozio, A. Girlando, C. Pecile, J. Chem. Soc. Faraday Trans. 71 (1975) 1237; (b) R. Bozio, I. Zanon, A. Girlando, C. Pecile, J. Chem. Soc. Faraday Trans. 2 (74) (1978) 235. [21] R.L. Carlin, Magnetochemistry, Springer, Berlin, 1986, p. 24. [22] B.J. Hathaway, D.E. Billing, Coord. Chem. Rev. 5 (1970) 143. [23] G. Marongiu, E.C. Lingafelter, P. Paoletti, Inorg. Chem. 8 (1969) 2763. [24] P.C. Jain, E.C. Lingafelter, J. Am. Chem. Soc. 89 (1967) 6131. [25] H. Oshio, E. Ino, I. Mogi, T. Ito, Inorg. Chem. 32 (1993) 5697. [26] (a) M. Inoue, M.B. Inoue, J. Chem. Soc. Faraday Trans. 81 (1985) 539; (b) E. Ghezzal, A. Brau, J.P. Farges, P. Dupuis, Mol. Cryst. Liq. Cryst. 211 (1992) 327. [27] B. Bleaney, K.D. Bowers, Proc. R. Soc. London A 214 (1952) 451. [28] R.L. Carlin, Magnetochemistry, Springer, Berlin, 1986, p. 121.
Radical-ion salts obtained from tetraazaderivatives of nickel and copper and tetracyanoquinodimethane: structural and magnetic characterization ~ Loreto Ballester a, Angel Gutierrez a,*, M. Felisa Perpin an, a, Ana E. S anchez a, M. Teresa Azcondo b, M. Jes us Gonz alez c b
a Departamento de Quımica Inorganica I, Facultad de Ciencias Quımicas, Universidad Complutense, Madrid 28040, Spain Departamento de Ciencias Quımicas, Facultad de Ciencias Experimentales y de la Salud, Universidad San Pablo-CEU, Boadilla del Monte, Madrid 28668, Spain c Grupo de Quımica Inorganica, Departamento de Quımica Aplicada, Facultad de Quımicas, Universidad del Paıs Vasco, Apartado 1072, San Sebastian 20080, Spain
Received 10 June 2003; accepted 30 September 2003
Abstract Several derivatives of formulae [M(N4 )(TCNQ)2 ] and [M(N4 )(TCNQ)2 ](TCNQ) (M ¼ Ni, Cu; N4 ¼ 1,4,7,10-tetraazacyclododecane ([12] aneN4 ), 1,4,8,11-tetraazacyclotetradecane ([14] aneN4 ), 1,4,8,12-tetraazacyclopentadecane ([15] aneN4 ), 1,4,7,10-tetraazadecane (trien), N ; N ; N -tris(2-aminoethyl)amine (tren), 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,14-diene (trans-dieneN4 )) have been obtained by metathesis reaction of the corresponding perchlorate or nitrate derivatives and LiTCNQ or (Et3 NH)(TCNQ)2 . The compounds [M(aneN4 )(TCNQ)2 ] have a six coordinated metal atom surrounded by the four macrocyclic nitrogens and two nitrogens from r coordinated TCNQ . The overlap with a neighbouring 7,7,8,8-tetracyanoquinodimethane (TCNQ) forms the diamagnetic dianion [TCNQ]2 2 , and the whole structure can be seen as chains of metallomacrocyclic cations and TCNQ dianions alternating in the solid. The crystal structure of [Cu([15] aneN4 )(TCNQ)2 ] confirms this fact. With open chain tetraamines the derivatives [Cu(trien)(TCNQ)2 ] and [Cu(tren)(TCNQ)2 ] are proposed to have the copper in a pentacoordinated environment, with only one coordinated TCNQ. In [M(trans-dieneN4 )](TCNQ)2 both TCNQ are uncoordinated and dimerized, as the crystal structure of the nickel derivative confirms. The derivatives with three TCNQ [M(aneN4 )(TCNQ)2 ](TCNQ) are proposed to have a structure derived from that of the analogous [M(aneN4 )(TCNQ)2 ], based on the metallomacrocycle-[TCNQ]2 chains connected through the extra TCNQ which remains uncoordinated and overlaps with the coordinated anions. This fact lowers the antiferromagnetic coupling inside the dimers and a small contribution for a thermally activated triplet state is observed in the magnetic susceptibility of these compounds. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Radical ions; Macrocycles; Supramolecular chemistry; Magnetic properties
1. Introduction The search for new supramolecular compounds obtained by assembling organic radicals with open-shell transition metal complexes has attracted the interest of many researchers due to the correlation found between *
Corresponding author. Tel.: +34-91-394-4337; fax: +34-91-3944352. E-mail address: [email protected] (A. Gutierrez). 0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2003.09.022
the supramolecular organization and the associated properties shown by the new compound [1]. One of the most extensively used radical in this study has been the organic planar molecule 7,7,8,8-tetracyanoquinodimethane (TCNQ), since it shows a low reduction potential which makes it a suitable acceptor in charge transfer processes and also shows, as anion-radical, a high rdonor ability to transition metals having vacant coordinative positions [2]. Other typical characteristic of this acceptor is the tendency to overlap its p-delocalized
L. Ballester et al. / Inorganica Chimica Acta 357 (2004) 1054–1062
HN
NH
HN
NH
HN
NH
HN
NH
HN
NH
HN
NH
[12]aneN4
HN
NH
H2 N
NH2
[14]aneN4 (cyclam)
N H2N
trien
NH2
NH2
tren
[15]aneN4
N
NH
HN
N
trans-dieneN4
Scheme 1.
system with neighbouring molecules to form stacks ranging from the dimeric dianion [TCNQ]2 2 [3] to one dimensional rows of stacked units having different degrees of electronic delocalization [4]. We have been studying the different transition metal-TCNQ systems in tetraazamacrocycles of nickel(II) and copper(II) and obtained different supramolecular architectures depending on the oxidation state of the TCNQ molecule and its ability to coordinate the metal atom. When there are vacant positions around the metal the anion-radical is coordinated via one or more of its nitrile groups [3d,5]. On the contrary, when the metal ion has a close stable coordinative environment, thus precluding a direct interaction with the anionradical, the crystal packing is driven by electrostatic interactions between the cationic metal moieties and the dimeric [TCNQ]2 anions which alternate in the 2 solid [3d,6]. A different situation occurs when the TCNQ is partially reduced and no direct interaction with the metal atom is present. In this case a greater electronic delocalization along with the formation of infinite stacks of formally [TCNQ]0:5 or [TCNQ]0:66 is observed [4c,4d]. Following this line the present work reports our results of interactions between partial or totally reduced TCNQ units and tetraazaderivatives of first row transition metals. These derivatives are formed either with the open chain ligands or macrocycles with different sizes shown in Scheme 1.
2. Experimental 2.1. General Remarks All the reactions have been carried out under oxygen– free nitrogen. The parent reagents [Ni([12] aneN4 )](NO3 )2 [7], [Cu([12] aneN4 )Cl2 ] [7], [Ni([14] aneN4 )](ClO4 )2 [8], [M([15] aneN4 )](ClO4 )2 (M ¼ Ni, Cu) [8], [Cu(trien)] (ClO4 )2 [9], [Cu(tren)](ClO4 )2 [10], [M(trans-dieneN4 )] (ClO4 ) (M ¼ Ni, Cu) [11], LiTCNQ [12] and Et3
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NH(TCNQ)2 [12] were obtained by the published methods and their purities were checked by elemental analyses. Hazard warning. Perchlorate salts are potentially explosive and should be used in small amounts and handled with care [13]. Elemental analyses were carried out by the Servicio de Microanalisis of the Universidad Complutense de Madrid. Infrared spectra were recorded as KBr pellets on a Nicolet Magna-550 FT-IR spectrophotometer. Magnetic experiments were made on polycrystalline samples using a SQUID magnetometer MPMSXL-5 manufactured by Quantum Design. The temperature dependence of the magnetization in the range between 2 and 300 K was recorded using a constant magnetic field of 0.5 T. The experimental data have been corrected for the magnetization of the sample holder and for atomic diamagnetism as calculated from the known PascalÕs constants. X- or Q-band powder EPR spectra have been obtained on a Bruker ESP 300 apparatus equipped with a Bruker ER035M gaussmeter and an Oxford JTC4 cryostat. 2.2. Preparation of the [M(N4 )](TCNQ)2 derivatives All these compounds have been obtained by the same procedure: A solution containing 1 mmol of LiTCNQ in 15 mL of methanol was added dropwise over a solution of 0.5 mmol of the starting compound in 15 mL of methanol. After complete mixing a blue solid appeared, which was filtered off, washed with methanol and diethyl ether, and dried under vacuum. 2.2.1. [Ni([12] aneN4 )(TCNQ)2 ] (1) Yield: 66%. Anal. Calc. for C32 H28 N12 Ni: C, 60.1; H, 4.4; N, 26.3. Found: C, 59.6; H, 4.4; N, 26.2%. IR (KBr, cm1 ): 2209m, 2183s, 2158s, 1584m, 1502m, 1363m, 1337m, 1180m, 955w, 823w, 720w. 2.2.2. [Cu([12] aneN4 )(TCNQ)2 ] H2 O (2) Yield: 54%. Anal. Calc. for C32 H30 CuN12 O: C, 58.0; H, 4.5; N, 25.4. Found: C, 57.6; H, 4.5; N, 25.3%. IR (KBr, cm1 ): 2190s, 2179s, 2158s, 1580m, 1507m, 1355m, 1331m, 1174m, 977w, 828w, 722w. 2.2.3. [Ni([15] aneN4 )(TCNQ)2 ] (3) Yield: 61%. Anal. Calc. for C35 H34 N12 Ni: C, 61.6; H, 5.0; N, 24.7. Found: C, 61.8; H, 4.9; N, 24.8%. IR (KBr, cm1 ): 2181s, 2161s, 1582m, 1503m, 1363m, 1340m, 1175m, 986w, 825w, 722w. 2.2.4. [Cu([15] aneN4 )(TCNQ)2 ] (4) Yield: 57%. Anal. Calc. for C35 H34 CuN12 : C, 61.3; H, 5.0; N, 24.5. Found: C, 61.3; H, 5.0; N, 24.6%. IR (KBr, cm1 ): 2181s, 2156s, 1581m, 1502m, 1360m, 1340m, 1175m, 984w, 826w, 722w.
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2.2.5. [Cu(trien)](TCNQ)2 (5) Yield: 46%. Anal. Calc. for C30 H26 CuN12 : C, 58.3; H, 4.2; N, 27.1. Found: C, 57.9; H, 4.1; N, 27.0%. IR (KBr, cm1 ): 2195m, 2180s, 2171s, 2154s, 1579m, 1503m, 1365m, 1343m, 1180m, 985w, 825w, 721w. 2.2.6. [Cu(tren)](TCNQ)2 (6) Yield: 47%. Anal. Calc. for C30 H26 CuN12 : C, 58.3; H, 4.2; N, 27.1. Found: C, 58.0; H, 4.3; N, 26.9%. IR (KBr, cm1 ): 2202m, 2188s, 2169s, 1569m, 1504m, 1354m, 1166m, 983w, 825w, 718w. 2.2.7. [Ni(trans-dieneN4 )](TCNQ)2 (7) Yield: 60%. Anal. Calc. for C40 H40 N12 Ni: C, 64.3; H, 5.4; N, 22.5. Found: C, 64.0; H, 5.2; N, 22.5%. IR (KBr, cm1 ): 2178s, 2156s, 1581m, 1503m, 1366m, 1344m, 1175m, 985w, 824w, 719w. 2.2.8. [Cu(trans-dieneN4 )](TCNQ)2 (8) Yield: 68%. Anal. Calc. for C40 H40 CuN12 : C, 63.9; H, 5.3; N, 22.4. Found: C, 63.8; H, 5.4; N, 22.5%. IR (KBr, cm1 ): 2199s, 2184s, 2170s, 2154s, 1573m, 1505m, 1352m, 1332m, 1177m, 990w, 825w, 720w. 2.3. Preparation of the [M(N4 )](TCNQ)3 derivatives A solution containing 1 mmol of Et3 NH(TCNQ)2 in 15 mL of acetonitrile was added dropwise over a solution of 0.5 mmol of the starting compound in 15 mL of methanol. After complete mixing a dark blue solid appeared, which was filtered off, washed with acetonitrile and diethyl ether, and dried under vacuum. 2.3.1. [Ni([12] aneN4 )(TCNQ)2 ](TCNQ) MeOH (9) Yield: 64%. Anal. Calc. for C45 H36 N16 NiO: C, 61.7; H, 4.1; N, 25.6. Found: C, 61.0; H, 4.2; N, 26.0%. IR (KBr, cm1 ): 2190s, 2182s, 2165s, 1574m, 1503m, 1384s, 1172m, 959w, 838w, 829w, 704w. 2.3.2. [Cu([12] aneN4 )(TCNQ)2 ](TCNQ) (10) Yield: 53%. Anal. Calc. for C44 H32 CuN16 : C, 62.3; H, 3.8; N, 26.4. Found: C, 61.4; H, 4.0; N, 26.6%. IR (KBr, cm1 ): 2227w, 2196s, 2188s, 2168s, 1578m, 1508m, 1366m, 1348m, 1170m, 988w, 862w, 841w, 824w. 2.3.3. [Ni([14] aneN4 )(TCNQ)2 ](TCNQ) (11) Yield: 59%. Anal. Calc. for C46 H36 N16 Ni: C, 63.3; H, 4.1; N, 25.7. Found: C, 63.2; H, 4.4; N, 25.5%. IR (KBr, cm1 ): 2217w, 2181s, 2156s, 1578m, 1539w, 1497m, 1422w, 1363m, 1340m, 1172m, 980w, 840w, 828w, 722w. 2.3.4. [Ni([15] aneN4 )(TCNQ)2 ](TCNQ) (12) Yield: 56%. Anal. Calc. for C47 H38 N16 Ni: C, 63.7; H, 4.3; N, 25.3. Found: C, 63.9; H, 4.3; N, 25.6%. IR (KBr, cm1 ): 2182s, 2158s, 1578m, 1539w, 1499m, 1425w, 1362m, 1339m, 1174m, 981w, 840w, 826w, 722w.
2.3.5. [Cu([15] aneN4 )(TCNQ)2 ](TCNQ) (13) Yield: 67%. Anal. Calc. for C47 H38 CuN16 : C, 63.4; H, 4.3; N, 25.2. Found: C, 63.3; H, 4.4; N, 25.4%. IR (KBr, cm1 ): 2208w, 2188s, 2160s, 1574m, 1534w, 1505m, 1424w, 1349m, 1165m, 985w, 834m. 2.4. X-ray structure determinations Good quality crystals of 4 and 7 have been obtained by slow diffusion of diluted solution of the reactants. In the three cases a deep blue crystal was resin epoxy coated and mounted on an Enraf Nonius CAD-4 j diffractrometer using graphite monochromated Mo Ka The cell dimensions were radiation (k ¼ 0:71073 A). refined by least-squares fitting of the h values of 25 reflections. The intensity data were collected at room temperature by the x 2h technique and corrected for Lorentz and polarization effects. Atomic scattering factors were taken from [14]. The structures were solved by Patterson and Fourier methods and refined by applying full-matrix least-squares on F 2 with anisotropic thermal parameters for the non-hydrogen atoms. The hydrogen atoms were included with fixed isotropic contributions at their calculated positions determined by molecular geometry. The calculations were carried out with S H E L X 97 software package [15]. A summary of the fundamental crystal data is given in Table 1.
Table 1 Crystal and refinement data for [Cu([15] aneN4)(TCNQ)2 ] (4) and [Ni(trans-dieneN4)](TCNQ)2 (7)
Formula Molecular weight Crystal system Space group a (A) b (A) c (A)
4
7
C35 H34 CuN12 686.3 triclinic P 1 (No. 1) 8.199(1) 9.951(1) 10.902(1) 88.66(1) 74.36(1) 77.38(1) 1 835.4(2) 1.364 6.99 1.94–24.97 5604 2802 433 1.101 0.02(6) 0.0448 0.0785
C40 H40 N12 Ni 747.6 triclinic P 1 (No. 2) 8.137(1) 11.169(1) 11.247(1) 89.64(1) 76.88(1) 68.94(1) 1 925.8(2) 1.341 5.71 1.87–24.97 3431 3248 245 1.047
a (°) b (°) c (°) Z 3 ) V (A Dcalcd (Mg m3 ) l (cm1 ) h Range (°) Reflections collected Independent reflections Refined parameters Goodness-of-fit Absolute structure parameter R1 ½I > 2rðIÞa wR2 ½I > 2rðIÞb P P a R1 ¼ nðjFohj jFc jÞ2 = iF 2o . h io1=2 P P b wR2 ¼ wðFo2 Fc2 Þ2 = . wðFo2 Þ2
0.0473 0.120
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3. Results and discussion All the metallic compounds have been obtained by metathesis reaction from the parent derivatives. The use of LiTCNQ, a source of exclusively anionic TCNQ, gives rise to the formation of derivatives 1–8, of general formula [M(N4 )](TCNQ)2 with the TCNQ neutralizing the two positive charges of the metal ion. When Et3 NH(TCNQ)2 , a source of both neutral and anionic TCNQ, is used the derivatives 9–13, with the organic acceptor partially reduced, are obtained. 3.1. Derivatives with two TCNQ The macrocyclic derivatives 1–4 show all the TCNQ in the form of the anion-radical and r coordinated to the metal ion. Previous examples of such behaviour have been described [3b,3d,5b] and in all these cases the coordination of the anion-radical is accompanied by its dimerization with other anion-radical coordinated to a neighbouring metal centre. The crystal structure of 4 confirms this situation and is a good example of this behaviour. The compound crystallizes in the triclinic system, space group P1. An ORTEP view of the molecular unit is shown in Fig. 1. The copper atom is coordinated to six nitrogen atoms. The four macrocyclic nitrogens lie in the equatorial and the plane with bond distances of 1.92(2) to 2.13(3) A six-coordination is completed by two TCNQ nitrile groups in apical positions at distances of 2.56(2) and showing a notable Jahn–Teller distortion, also 2.58(2) A found in related TCNQ derivatives [5b,16]. There are two crystallographically different TCNQ groups, both
N12 C35
C31 C32
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coordinated to the copper atom in the trans positions with their ring planes almost perpendicular to the mean macrocycle plane forming angles of 87.9(4)° and 86.6(5)°. Each TCNQ interacts with the non equivalent TCNQ of a neighbouring molecule by overlap of their p clouds in the ring over ring mode [17]. The separation with and angle between the quinoid planes is 3.19(3) A between the planes of 1.3(9)° ; this distance is comparable to that found in other dimeric [TCNQ]2 units 2 [3,5]. Every TCNQ forms a hydrogen bond between the nitrile opposite to the coordinated one and one amine group of the macrocycle with bond distance of N8 H3 and angle N3–H3 N8 ¼ 170.9° for one of ¼ 2.14 A and N1– the TCNQ groups and N12 H1 ¼ 2.16 A H1 N12 ¼ 165.6° for the other group. These hydrogen bonds are formed with the macrocycle belonging to the same molecular unit than the overlapping TCNQ. Therefore, each dimeric [TCNQ]2 2 interacts doubly with the metallomacrocyclic unit, with one TCNQ coordinated to the metal atom and the other forming hydrogen bond with the macrocycle. This double interaction leads to the formation of chains of metallomacrocycles bridged by [TCNQ]2 dianions (Fig. 2). These chains extend along the crystal and are arranged parallel with no interactions found between adjacent ones. In contrast the structure of 7 and that expected for 8 corresponds to a derivative without direct interaction between the metal atom and the TCNQ anion-radical. This fact can be interpreted in terms of a higher electron density on the metal atom due to a higher donor character of the macrocycle. Compound 7 crystallizes in the P 1 space group. Fig. 3 shows an ORTEP view of the asymmetric unit.
N11 C34 C33 C30 C29 C28
C27 C10 C9 C8 C11 C24 C26 C7 N1 N4 Cu C25 N3 N9 N5 N10 C1 N2 C6 C13 C2 C5 C3 C4 C16 C17 C21 C22 N7
N6 C14 C12 C15 C20 C19 C18 C23 N8
Fig. 1. ORTEP view and atom labelling of the molecular unit of 4.
Fig. 2. View of the chain formed by overlap of the TCNQ groups in 4 showing the H-bonds as thin lines.
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Fig. 3. ORTEP view and atom labelling of the molecular unit of 7.
Fig. 4. View of the crystal packing in compound 7 showing the H bonds as thin lines.
The nickel atom is located on an inversion centre in a square-planar environment formed by the four macrocyclic nitrogens. The two nickel–nitrogen distances are the shorter distance corre1.907(5) and 1.932(6) A, sponding to the sp2 nitrogen. The bond distances and angles in the macrocycle are similar to those found in the parent perchlorate [18] or in the isomeric [Ni(cisdieneN4 )](TCNQ)2 [6]. The two TCNQ present in the cell unit are equivalent and related by an inversion centre. They are overlapping in a ring over ring mode to form a dimeric [TCNQ]2 2 dianion with a shorter interplanar distance of 3.16(1) A (Fig. 4). The interatomic distances in the TCNQ are characteristic of the fully reduced anion-radical [19]. The crystal packing can be described as metallomacrocyclic cations and dimeric TCNQ dianions alternating in the three spatial directions, an arrangement observed when the driving force for the packing is of electrostatic nature [3,4c,6]. The macrocycle and the TCNQ are oriented quasi perpendicularly forming an angle of 69.6(1)°. The only non electrostatic interaction between these units is a hydrogen bond N2–H2 N3
and an angle of with bond distances of 0.98 and 2.21 A 155.2°. These two crystal structures show the typical features of the coordinated and uncoordinated TCNQ anionradical, respectively, but since the electronic charge held on every acceptor is the same their spectroscopic properties are similar. Thus, the IR spectra of 1–8 show the characteristic bands of the anion radical, several bands in the m(CN) region, 2200–2155 cm1 , m20 (b1u ) at 1507– 1502 cm1 and m50 (b3u ) around 825 cm1 . All these bands are indicative of the presence of the anion-radical and are shifted to higher frequencies in the neutral species [20]. The m(CN) bands appear around 2180 and 2160 cm1 when the TCNQ is coordinated to the metal atom, as in complexes 1–4, and around 2170 and 2155 cm1 with uncoordinated TCNQ in compounds 7 and 8. The splitting in derivatives 5 and 6 can indicate that both coordinated and uncoordinated anion-radicals are present in the solid, in consonance with the five-coordination suggested by the EPR data (see below). The magnetic properties of these species are consistent with the presence of the dimerized anion-radical. The formation of dimeric [TCNQ]2 implies a strong 2 antiferromagnetic coupling of both spins that render the dianion diamagnetic at room temperature. The magnetic susceptibility variation can be then attributed to the contribution of the isolated metal ion. The magnetic susceptibility of the nickel derivatives 1 and 3 follows the Curie law above 25 K, while an abrupt descent in the value of vT is observed below this temperature. This fact is attributed to an anisotropic distortion of the nickel(II) environment which results in a zero field splitting of the ground state [21]. Eq. (1) for the average magnetic susceptibility takes into account this single-ion anisotropy 2 2 hvi ¼ 2NgNi b =3kB T f½2 2 expð xÞ=x þ expð xÞg =½1 þ 2 expð xÞ;
ð1Þ
where gNi is the Lande g factor for the nickel ion, kB is BoltzmannÕs constant, b is the Bohr magneton and x ¼ D=kB T . The parameter D measures the zero-field splitting. The best fit is obtained when gNi ¼ 2:19 and D ¼ 2:65 cm1 for 1 and gNi ¼ 2:16 and D ¼ 4:69 cm1 for 3. Finally compound 7 is diamagnetic, as expected for a square-planar nickel(II) derivative. The copper derivatives follow the Curie–Weiss law with magnetic moments (g[S(S+1)]1=2 ) ranging between 1.76 and 1.83 b typical for isolated S ¼ 1/2 spins. This behaviour is confirmed by the EPR spectra of the solid samples which afford g values (Table 2) in accordance with the magnetic moments obtained by the Curie law. Fig. 5 shows representative spectra of the copper(II) compounds. The EPR spectrum (Q band) of compound 5 shows the typical rhombic pattern (Fig. 5(a)), with lowest
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Table 2 Magnetic and EPR data for the new compounds Compound
Magnetic data gMetal
1 2 3 4 5 6 7 8 9 10 11 12 13
2.19 2.04 2.16 2.04 2.10 2.11 Diamagnetic 2.07 2.18 2.13 2.29 2.07 2.13
EPR data (100 K) h (K) )0.29
D (cm1 )
J (cm1 )
g1 (or gk ), A(G)
g2 (g? )
g3
2.19, 196 2.15 2.20
2.04 2.10 2.11
2.05 2.02
2.18, 180
2.065
2.19
2.04
)2.65 4.69
)0.17 )0.86 )1.39 )1.56 3.12 )0.44 7.35 5.62 )0.28
)463 )464 )172 )235 )192
Fig. 5. EPR spectra of 5 (a), 6 (b), 8 (c) and 13 (d).
g < 2:04, that can be either attributed to a pentacoordinate square-based pyramidal or a distorted octahedral environment. The first possibility would lead to a formula [Cu(trien)(TCNQ)](TCNQ) with both coordinated and uncoordinated TCNQ anion-radical, in accordance with the IR spectra commented above. The copper environment would be similar to that found in the crystal structure of [Cu(trien)(SCN)](SCN) with the copper atom in the centre of a square-based pyramid formed by the four amine nitrogens and the sulphur atom of the
coordinated thiocyanate [23]. If the copper were sixcoordinated a structure like that of [Ni(trien)(TCNQ)2 ] with the anion-radicals coordinated in cis positions [3d] would be expected. We have no conclusive evidence to choose between these two possibilities, but the spectral data suggest that the pentacoordination would be the most plausible structure. The EPR spectrum (Q band) of compound 6 (Fig. 5(b)) also shows a rhombic splitting, coherent with a trigonal bipyramidal environment. This situation
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would correspond again to one coordinated and one uncoordinated TCNQ with a formula [Cu(tren)(TCNQ)](TCNQ). Along with the IR spectral data the crystal structure of the related isothiocyanate derivative, [Cu(tren)(NCS)](SCN) [24] shows this coordinative environment for the copper atom. Assuming a pentacoordinated environment for 5 and 6 it would be necessary that all the TCNQ anion-radicals were dimerized, since no contribution to the magnetic susceptibility was observed. The EPR of 6 shows a small signal at g ¼ 2:003 that would correspond to isolated radical impurities, but its low intensity indicates that the impurity concentration is too small to be detected from the susceptibility data as they were masked by the signal from the copper spins, two orders of magnitude bigger as the EPR signal indicates. The EPR spectrum (Q band) of compound 8 (Fig. 5(c)) shows the typical axial pattern for tetragonally elongated octahedral copper(II) [22] with the parallel component showing the hyperfine splitting due to the coupling with the copper nucleus (I ¼ 3/2). Compound 4 shows a similar spectrum. 3.2. Derivatives with three TCNQ The formation of compounds 9–13 requires the presence of two anion-radicals to neutralize the positive charges on the metallomacrocycle, while the third TCNQ would remain formally neutral. The anion-radicals would be r coordinated to the metal ion giving rise to the formation of infinite chains –[M(N4 )]–[TCNQ]2 – [M(N4 )]–[TCNQ]2 – similar to those proposed for compounds 1–4 and found in the structure of 4. The extra TCNQ would be located between the chains interacting by p overlap with the anion-radicals. This situation has been reported in the manganese complex [Mn(tpa) (TCNQ)(MeOH)](TCNQ)2 MeCN (tpa ¼ tris(2-pyridiylmethyl)amine) [25] and observed by us in the related derivative [Cu([14] aneN4 )(TCNQ)2 ](TCNQ) [16]. This compound crystallizes in two polymorphic forms that only differ in the stacking mode of the neutral TCNQ between the chains. Since we have no structural data of compounds 9–13 we only can estimate the oxidation state of every TCNQ in base to the spectral data. The IR spectra of these compounds exhibit the characteristic bands of coordinated TCNQ anion-radicals along with new bands around 2220, 1537, 1425 and 840 cm1 corresponding, respectively, to the m(CN), m20 (b1u ), m4 (ag ) and m50 (b3u ) vibration modes of a quasi neutral TCNQ molecule. These bands appear at similar frequencies than those observed for [Cu([14] aneN4 )(TCNQ)2 ](TCNQ) and strongly support the proposed structure for these complexes. The coordination of the TCNQ is also supported by the absence in the IR spectra of the electronic absorption tail observed when
Fig. 6. Temperature dependence of vT for 3 (Þ, 4 (MÞ, 12 (Þ and 13 (s). The solid lines represent the best fit using the equations described in the text for the parameters that appear in Table 2.
electronic delocalization is found between the stacked TCNQ units [26]. The EPR spectrum (X band) of compound 13 (Fig. 5(d)) shows the axial pattern for distorted octahedral copper(II) expected for the proposed structure. It is also observable that a small signal at g ¼ 2:003 is attributable to small quantities of nondimerized radicals, in consonance with the observed magnetic susceptibility. The magnetic susceptibilities of compounds 9–13 have been measured down to 2 K. Fig. 6 shows the plot of vT versus T for one nickel and one copper representative derivative compared with the corresponding compounds with two TCNQ. The plot of the copper derivative compound 13 shows a plateau between 25 and 125 K, where the Curie law was obeyed. The small decrease in the values at low temperatures can be ascribed to very weak antiferromagnetic interactions between almost isolated copper(II) centres and fitted by using the Curie–Weiss law. The increase in the vT values above 125 K is due to a small contribution from the TCNQ dimers, which show a lower antiferromagnetic coupling than that exhibited by the two TCNQ derivative compound 4. The lower value of the coupling implies that the triplet state is thermally accessible and populated near room temperature, giving rise to the contribution of the radicals to the magnetic susceptibility. Taking these two contributions into account the molar magnetic susceptibility was fitted using Eq. (2) to the sum of the Curie–Weiss law for the copper(II) ion and the Bleaney–Bowers equation [27] for the antiferromagnetically interacting TCNQ radicals: v¼
2 NgCu b2 Ng2 b2 2 þ ; 4kB ðT hÞ kB T 3 þ expðJ =kB T Þ
ð2Þ
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where gCu is the Lande g factor for the copper ion, J the exchanging coupling constant for the TCNQ dimers, g is the Lande g factor for the TCNQ radicals and is assumed to be 2.003, the rest of the parameters are the same as in Eq. (1). The best fit for the experimental data is represented as a solid line in Fig. 6 and corresponds to the parameter values shown in Table 2. The g value 2.13 is similar to that obtained by the EPR spectrum and the small h value suggests that the proposed antiferromagnetic interaction is almost negligible. The h value is equivalent to a J exchanging constant between copper ions of )0.38 cm1 , by using the expression h ¼ zJ SðS þ 1Þ=3kB , where z, the number of interacting spins, is assumed to be two, considering that the interaction is transmitted through the coordinated TCNQ [28]. The nickel derivative compound 12 has been chosen as an example of the magnetic behaviour of the other compounds with the same metal. The general variation of vT is similar to that observed for the copper derivatives with the exception of the more pronounced decrease at low temperatures. This fact is interpreted in terms of the zero-field splitting induced by the anisotropy in the nickel environment as commented above. The small antiferromagnetic coupling between metal ions commented for the copper atoms is also probably present but the more pronounced effect of the zero-field splitting obscured its observation. The total magnetic susceptibility for the nickel complexes is then fitted to Eq. (3) where all the parameters have the meaning previously described: 2 2 2NgNi b 2=x 2=x expðxÞ þ expðxÞ v¼ 1 þ 2 expðxÞ 3kB T 2 Ng2 b 2 þ : kB T 3 þ expðJ =kB T Þ
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4. Concluding remarks The formation of [M(N4 )(TCNQ)2 ] derivatives is always the result of the neutralization of the positive charges in the [M(N4 )]2þ fragment by the anion-radical TCNQ . The tendency of this anion-radical to dimerize gives rise to the formation of S ¼ 0 dianions [TCNQ]2 2 . Depending on the metal ion coordinative status the structures formed in the solid are different, thus with saturated amine ligands monodentate coordination of the TCNQ is found and since this acceptor is dimerized it results in the formation of chains formed by the cationic metallic fragments bridged by the dianionic TCNQ dimers coordinated to successive metal atoms. With more donor unsaturated ligands the metal atom remains in a square planar environment and no direct interaction with the TCNQ is observed. In both cases the formation of hydrogen bonds tends to stabilize the arrangement observed in the solid. When neutral TCNQ along with anionic TCNQ is present in the reaction mixture the derivatives [M(N4 ) (TCNQ)2 ](TCNQ) are formed. The similitude in the properties between these species and the previously reported [Cu([14] aneN4 )(TCNQ)2 ](TCNQ) strongly supports the proposal of a similar structure in the solid state with coordinated TCNQ anions that dimerize to form chains as in the [M(N4 )(TCNQ)2 ] compounds. The extra TCNQ remains approximately neutral and is situated between the chains forming stacks by p overlap with the coordinated TCNQ . This interaction weakens the antiferromagnetic coupling inside the dimers and the excited S ¼ 1 state becomes thermally accessible and populated above 150 K as observed in the magnetic susceptibility fits.
ð3Þ
The J values for the nickel and copper derivatives are comparable suggesting that the metal does not influence the TCNQ coupling. The values for the smaller macrocyclic derivatives are however much more negative, indicating that the antiferromagnetic coupling is stronger in these compounds. In fact the greater values for the [12] aneN4 derivatives imply that the TCNQ radical contribution to the magnetic susceptibility is only observable above 220 K and below this temperature the data approximately fitted the Curie law. With the absence of structural data we are unable to determine the reason for this behaviour, that will probably be related to the small size of the macrocycle, which in turn can induce differences in the TCNQ stacking, as the weak interactions responsible for the packing in these compounds can be easily overridden as the related [Cu([14] aneN4 )(TCNQ)2 ](TCNQ) have shown [16].
5. Supplementary material Crystallographic data for the structural analyses have been deposited with the Cambridge Crystallographic Data Centre, CCDC-207152 (for compound 4) and 207153 (for compound 7). These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: (internet.) +44-1223/336-033; E-mail: deposit@ccdc. cam.ac.uk).
Acknowledgements We gratefully acknowledge the Spanish Ministerio de Ciencia y Tecnologıa, project BQU2002-01409, for financial support.
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