Inorganica Chimica Acta 286 (1999) 169–174

Synthesis, crystal structure and magnetic properties ofcatena-poly[(2,2%-bipyridylcopper)-di-m-thiocyanato] and

bis(2,2%-bipyridyl)thiocyanatocopper(II) perchlorate

Carmen Diaz a,*, Joan Ribas a, Nuria Sanz a, Xavier Solans b, Merce Font-Bardıa b

a Departament de Quımica Inorganica, Uni6ersitat de Barcelona, Diagonal 647, 08028 Barcelona, Spainb Departament de Cristal · lografia i Mineralogia, Uni6ersitat de Barcelona, Martı Franques s/n, 08028 Barcelona, Spain

Received 30 July 1998; accepted 6 October 1998

Abstract

The reaction of ethanolic solutions of CuX2 (X=NO3−, ClO4

−), with bidentate amine, 2,2%-bipyridyl (bipy) and ammoniumthiocyanate, leads to the high-yield formation of {catena-[Cu(bipy)(mN,S-NCS)2]} (1) and [Cu(NCS)(bipy)2]ClO4 · 1/2CH3CN (2).The crystal structure of 1 and 2 were determined. Complex 1 crystallises in the monoclinic system, space group C2/c witha=8.125(4) A, b=15.557(6) A, c=10.536(3) A, b=95.32(3)° and Z=4. The crystal structure consists of neutralCu(NCS)2(bipy) units which are bridged by sulfur atoms of the thiocyanate groups to yield a 1D chain. Complex 2 crystallisesin the monoclinic system, space group C2/c with a=12.694(4) A, b=25.007(11) A, c=15.479(11) A, b=106.85(4)° and Z=8.The crystal structure consists of a [Cu(NCS)(bipy)2]+ cation, ClO4

− anion and CH3CN. The cations show a quasi-trigonalbipyramidal coordination. A variable temperature magnetic susceptibility study was performed on 1 at a temperature range of2–300 K. The compound shows a very weak antiferromagnetic coupling (J= −0.13 cm−1) and the magnetic susceptibility datawere analysed by the expression for the magnetic susceptibility of isotropically coupled S=1/2 ions in antiferromagnetic chains.The single crystal EPR spectra of 2 presents rhombic g values and the direction of the highest g value lies in the equatorial planenear the Cu–Neq direction; therefore, this is a distorted trigonal bipyramidal structure. © 1999 Elsevier Science S.A. All rightsreserved.

Keywords: Crystal structures; Magnetic properties; Copper complexes; Thiocyanato complexes; Amine complexes; Polynuclear complexes

1. Introduction

The magneto-structural studies carried out onpolynuclear divalent first-row transition metal com-plexes supported by N3

− [1], NCO− [2], NCS− [3], andNCSe− [4] pseudohalide bridges have received greatattention in recent years. The azido group has receivedmost of the major attention due to its versatility as aligand and to the wide variety of magnetic properties ofits compounds. The literature available for magneto-structural studies on copper(II) complexes containingbridging thiocyanate groups is scarce, as this ligand isless versatile and less efficient as a transmitter of mag-netic interactions than azide. The different coordination

modes exhibited by the thiocyanate group towardsCu2+ ion are shown below.

Few 1D chains with SCN− bridging ligands havebeen described: only one of type a [5], one of type b [6]and seven of type c [7]. Besides, thiocyanate ion isable to coordinate with Cu(II) in a series of[Cu(NCS)(bipy)2]Y type complexes [8] (bipy=2,2%-

* Corresponding author. Tel.: +34-93-4041100; fax: +34-93-4907725; e-mail: cdiaz@kripto.qui.ub.es.

0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.

PII: S 0 0 2 0 -1693 (98 )00397 -1

C. Diaz et al. / Inorganica Chimica Acta 286 (1999) 169–174170

bipyridyl, and Y=SCN−, ClO4−, BF4

−, NO3−). The

structure has not been solved for the Y=ClO4− com-

plex. As for the Cu(II) complexes of the bipyridinetype, the coordination polyhedron of Cu(II) usually hasa distorted appearance in the transition between trigo-nal bipyramid and tetragonal pyramid configurations.It has also been shown that the distortion caused bycations in the crystal structure of the coordinationpolyhedron depends on the properties of the anion inthe crystal structure [9].

We report here the results of our synthetic, spectro-scopic, structural, and magnetic work on Cu(II)–bipyridine–SCN complexes. 1D system {catena-[Cu(bipy)(mN,S-NCS)2]} (1) with two SCN− groupsacting as bridging ligands, and the [Cu(NCS)-(bipy)2]ClO4 · 1/2CH3CN (2) mononuclear complexhave been synthesised. The single-crystal EPR spectrafor complex 2 is also reported.

2. Experimental

2.1. Synthesis

Copper(II) perchlorate, copper(II) nitrate, ammo-nium thiocyanate, bipyridine and dimethyl sulfoxidewere purchased from Aldrich and used without purifi-cation. Ethanol and acetonitrile were distilled beforeuse.

Caution: perchlorate salts of metal complexes withorganic ligands are potentially explosive. Only a smallamount of material should be prepared at a time, and itshould be handled with caution.

2.1.1. Synthesis of {catena-[Cu(bipy)(mN,S-NCS)2]n} (1)Bipyridine (0.16 g, 1 mmol) in ethanol (10 ml) was

added to an ethanolic solution (15 ml) of NH4SCN(0.15 g, 2 mmol) and Cu(NO3)2 · 3H2O (0.24 g, 1mmol). The product, which precipitated immediately,was stirred for 1 h, filtered off, washed with ethanol,and dried under vacuum. Green monocrystals suitablefor X-ray determination were prepared by recrystallis-ing the complex from dimethyl sulfoxide. Yield: 50%.Anal. Calc. for C12H8CuN4S2: C, 42.91; H, 2.40; N,16.68; S, 19.09. Found: C, 43.2; H, 2.4; N, 16.8; S,19.2%.

2.1.2. [Cu(bipy)2(NCS)]ClO4 · 1/2CH3CN (2)This was prepared in the same way as for complex 1,

using Cu(ClO4)2 · 6H2O instead of Cu(NO3)2 · 3H2Oand 2 mmol of bipyridine. Green monocrystals suitablefor X-ray determination were prepared by recrystallis-ing the complex from acetonitrile. Yield: 65%. Anal.Calc. for C22H17.5ClCuN5.5O5S: C, 47.70; Cl, 6.40; H,3.18; N, 13.90; S, 5.78. Found: C, 48.0; Cl, 6.5; H, 3.2;N, 13.8; S, 6.1%.

2.2. Crystal data collection and refinement of thestructure {catena-[Cu(bipy)(mN,S-NCS)2]n} (1) and[Cu(NCS)(bipy)2]ClO4 · 1/2CH3CN (2)

Crystallographic data for 1 and 2 are shown in Table1. Prismatic crystals (0.1×0.1×0.2 mm) for 1 and(0.2×0.15×0.2 mm) for 2 were selected and mountedon an Enraf–Nonius CAD4 four-circle diffractometer.Unit cell parameters were determined from automaticcentring of 25 reflections (12BuB21°) and refined byleast-squares method. Intensities were collected withgraphite monochromated Mo Ka radiation, using thev–u scan-technique. For 1, 935 reflections were mea-sured in the 2.625u529.89° range, 909 of which werenon-equivalent by symmetry (Rint (on I)=0.046) and610 reflections were assumed as observed applying thecondition I\2s(I). For 2, 2670 reflections were mea-sured in the 2.015u529.97° range, 2552 of whichwere non-equivalent by symmetry (Rint (on I)=0.053)and 1335 reflections were assumed as observed applyingthe condition I\2s(I). Three reflections were mea-sured every 2 h as orientation and intensity controls; nosignificant intensity decay was observed. Lorentz polar-isation but no absorption corrections were made. Thestructures were solved by direct methods, using SHELXS

[10] computer program and refined by the full-matrixleast-squares method with SHELX93 [11] computer pro-gram, using 909 reflections for 1 and 2502 for 2. Theminimised function was Sw ��Fo�2− �Fc�2�2, where w=[s2(I)+0.1281P)2]−1 for 1 and w= [s2(I)]−1 for 2 andP= (�Fo�2+2�Fc�2)/3. f, f % and f %% were taken from Inter-national Tables of X-Ray Crystallography [12]. All Hatoms were computed and refined with overall isotropic

Table 1Crystallographic data and experimental parameters for {catena-[Cu-(bipy) (mN,S-NCS)2]} (1) and [Cu(NCS) (bipy)2]ClO4 · 1/2CH3CN (2)

1 2

C12H8CuN4S2 C22H17.5ClCuN5.5O4SChemical formula335.88Formula weight 553.97

Space group C2/c C2/c293(2)T (°C) 293(2)0.71069l (A) 0.71069

12.694(4)8.125(4)a (A)b (A) 25.007(11)15.557(6)

10.536(3)c (A) 15.479(11)a (°) 90 90b (°) 95.32(3) 106.85(4)

90g (°) 90V (A3) 1326.0(9) 4703(4)

4Z 81.682robsd (g cm−3) 1.5651.950m (mm−1) 1.1720.0566 0.0339Ra

0.17030.1554wRb

a R (on F)=S��Fo�−�Fc��/S�Fo�.b wR (on F2)= [Sw(Fo

2−Fc2)2/S wFo

4]1/2.

C. Diaz et al. / Inorganica Chimica Acta 286 (1999) 169–174 171

temperature factors, using a riding model. The final R(on F) factor were 0.057 and 0.034, wR (on �Fo�2)=0.155 and 0.170, the goodness of fit 1.006 and 0.942 for1 and 2, respectively, for all the observed reflections.The number of refined parameters was 89 for 1 and 343for 2. Maximum shift/e.s.d.=0.003, 0.01, mean shift/e.s.d.=0.001 and 0.0009 for 1 and 2, respectively. Forcomplex 1 the maximum and minimum peaks in thefinal difference synthesis were 0.592 and −0.564 eA−3, respectively. For complex 2 the maximum andminimum peaks in the final difference synthesis were0.137 and −0.133 e A−3, respectively.

2.3. Physical measurements

Magnetic measurements were carried out on poly-crystalline samples with a quantum design MPMSSQUID susceptometer operating at a magnetic field of0.5 T, between 2 and 300 K. Polycrystalline powder andsingle-crystal EPR spectra were recorded at room tem-perature at X-band frequency with a Bruker 300Eautomatic spectrometer. A single-crystal of ca. 1.3×0.6×0.7 mm was mounted on the same diffractometerused for the structure determination and was found tohave largely developed {010} faces delimited by the{111} and {110} faces. Spectra were recorded by rotat-ing along three orthogonal axes defined as x=c, y=band z=bxc. Magnetic and EPR measurements werecarried out in the Servei de Magnetoquımica (Univer-sity of Barcelona).

3. Results and discussion

Two bands were observed in the infrared spectrumfor the nas(N–C–S) vibration for complex 1, and onlyone was observed for complex 2 over 2100 cm−1. Then3(T2) and n4(T2) vibrations appeared at 1090 and 630cm−1 for the ClO4

− anion.Fig. 1 shows the molecular structure of {catena-[Cu-

(bipy)(mN,S-NCS)2]} (1) with atom labelling scheme.The arrangement of the chains in the unit cell runningparallel to the z axis is illustrated in Fig. 2. Selectedbond lengths and angles, are listed in Table 2. Thecrystal structure consists of neutral Cu(NCS)2(bipy)units which are bridged together by sulfur atoms of thethiocyanate groups to yield a 1D chain. The Cu–NCS–Cu bonds form a zig-zag structure. Each Cu(II) atom islocated in a distorted octahedral environment. Theequatorial positions are occupied by a bidentate bipyligand and two bridging thiocyanate groups coordi-nated in an asymmetric end-to-end fashion via a Natom. The Cu–N distances are close to 2.0 A (Table 2).The axial positions are occupied by a weakly bondedS-donor atom of other two bridging thiocyanate groupat 3.239 A. In Cu(II) complexes, N-bonded thiocyanate

Fig. 1. Drawing of the chain part of {catena-[Cu(bipy)(mN,S-NCS)2]}(1) with the atom labelling scheme.

groups appears in an arbitrary position of the coordina-tion polyhedron, while the S-bonded group was ob-served in the axial direction [13], with one exception [7].The lengthening of the Cu–S axial distance is related toa distortion towards a tetrahedral geometry, as shownby a large distortion of the dihedral angle between N2CuN2a and N1aN1C1C1aC2C2aCu mean planes 25.5°.The Cu···Cu distance is 6.113 A. The bond lengths andangles within the bipy ligand are in accordance withthose previously reported [14].

Fig. 2. Unit cell for {catena-[Cu(bipy)(mN,S-NCS)2]} (1).

C. Diaz et al. / Inorganica Chimica Acta 286 (1999) 169–174172

Table 2Selected bond lengths (A) and angles (°) for {catena-[Cu(bipy)(mN,S-NCS)2]} (1) and [Cu(NCS)(bipy)2]ClO4 · 1/2CH3CN (2)

Complex (1)1.996(8) S–C(6)Cu–N(1) 1.674(7)

N(2)–C(6) 1.056(7)Cu–N(2) 2.012(7)3.239(4)Cu–S

95.3(5) 167.9(10)S(1)–C(6)–N(2)N(2a)–Cu–N(2)75.7(4)N(1)–Cu–S(1b)N(2a)–Cu–N(1) 160.1(3)

N(1)–Cu–S(1c) 108.0(5)N(2)–Cu–N(1) 94.5(3)160.1(3) N(2)–Cu–S(1b)N(2)–Cu–N(1a) 89.8 (5)

81.7(4) N(2)–Cu–S(1c)N(1)–Cu–N(1a) 89.8(6)165.1(3) C(6a)–S(1a)–Cu(b) 104.7(3)Cu–N(2)–C(6)

Complex (2)1.953(5)Cu–N(5)Cu–N(1) 2.083(5)

1.974(5) S–C(21)Cu–N(2) 1.611(7)1.158(6)N(5)–C (21)Cu–N(3) 2.004(5)

Cu–N(4) 2.086(6)

92.4(3) N(2)–Cu–N(4) 99.0(2)N(5)–Cu–N(2)92.6(3) N(3)–Cu–N(4) 79.0(3)N(5)–Cu–N(3)

175.0(3) N(1)–Cu–N(4)N(2)–Cu–N(3) 106.0(2)N(5)–Cu–N(1) 137.8(2)N(2)–Cu–N(1) 79.9(3)

96.1(2) N(5)–C(21)–SN(3)–Cu–N(1) 177.7(7)N(5)–Cu–N(4) Cu–N(5)–C(21) 175.2(6)116.2(2)

Fig. 4. Plot of xMT vs. T for {catena-[Cu(bipy)(mN,S-NCS)2]} (1). Thesolid lines result from a fit of the data to the appropriate theoreticalequation of isotropically coupled S=1/2 ions in antiferromagneticchains.

through the nitrogen atom. The Cu–N2 and Cu–N3axial distances are 1.970 and 2.004 A, respectively. TheCu–N1, Cu–N4 and Cu–N5 are 2.083, 2.086 and1.953 A, respectively (Table 2).

The temperature dependence of the magnetic suscep-tibility of {catena-[Cu(bipy)(mN,S-NCS)2]} (1) was mea-sured in the 280–2 K range. The xM versus T curve (xM

being the molar susceptibility per mononuclear unit) isdisplayed in Fig. 4. The magnetic susceptibility datawere analysed by the expression for the magnetic sus-ceptibility of isotropically coupled S=1/2 ions in anti-ferromagnetic chains [15]:

xM=Ng2b2

kT0.25+0.074975x+0.75235x2

1+0.9931x+0.172135x2+0.757825x3

with x= �J �/kTThe best fit parameters are J= −0.13 cm−1 and

g=2.14, revealing a very weak antiferromagnetic inter-action. This small value can been essentially attributed

Fig. 3 shows the molecular structure of[Cu(NCS)(bipy)2]ClO4 · 1/2CH3CN (2), and the atomlabelling scheme. Selected bond lengths and angles arelisted in Table 2. The crystal structure consists of[Cu(NCS)(bipy)2]+ cations, ClO4

− anions and CH3CN.The cations show a quasi-trigonal bipyramidal coordi-nation. The bipyridyl ligands have a cis-position in thecoordination polyhedron. As chelates, they always co-ordinate one equatorial and one axial position of thecoordination polyhedron. The thiocyanate ligand is co-ordinated in the equatorial plane monodentately,

Fig. 3. Drawing of the cationic part of [Cu(NCS)(bipy)2]ClO4 ·1/2CH3CN (2) with the atom labelling scheme.

Fig. 5. Schematic drawing of the unit cell for [Cu(NCS)-(bipy)2]ClO4 · 1/2CH3CN (2), showing the four cations[Cu(NCS)(bipy)2]+ (see text).

C. Diaz et al. / Inorganica Chimica Acta 286 (1999) 169–174 173

Fig. 6. Orientation of the crystal g values and a projection down the b-axis showing the crystallographic axes. g3 is parallel to the b-axis and g2

and g1 lie in the ac-plane

to the long Cu–S distance and/or interchain effects.The variable-temperature X-band EPR spectra of com-plex 1 recorded with microcrystalline powders showedabsorption features of axial symmetry (g��=2.24 andgÞ=2.07). No half-forbidden transition was observed.

The polycrystalline EPR spectrum of 2 shows abroad band with three g values at 2.19, 2.09 and 2.01,approximately. The single crystal EPR spectrum ismore informative, with rhombic g values of g1=2.23,g2=2.14 and g3=2.02. In the unit cell there are four[Cu(NCS)(bipy)2]+ cations. The molecules isolated areequivalent, but their main axes related to the coordi-nated system are different as shown in Fig. 5. Theorientation of the crystal g values is shown in Fig. 6.The lowest g factor of 2.02 lies approximately in theCu–Naxial bond direction. The intermediate and thehighest g factors lie in the equatorial plane. This can beexplained by the value of the geometric parameter ofAddison [16], t=0.62, which can be applied to five-co-ordinate structures as an index of the trigonality degree.

4. Supplementary material

The X-ray crystallographic files, in CIF format, areavailable from the authors on request and from theCambridge Crystallographic Data Centre on quotingthe deposition numbers CCDC 113083 and 113084.

Acknowledgements

We are very grateful for the financial support givenby the Direccion General de Investigacion Cientıfica yTecnica (Spain) (Grant PB96/0163). We also thank

Dr Nuria Clos for recording the magnetic and EPRmeasurements.

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