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Inorganica Chimica Acta 312 (2001) 1–6

Synthesis, structure, and magnetic properties of two newcopper(II) complexes with pseudohalide ligands.

A dimer [Cu2(m1,1-NCO)2(NCO)2(phen)2] with NCO bridgeand ferromagnetic coupling and a mononuclear

{[Cu(meso-cth)(CN)]ClO4·H2O}2 with two independent[Cu(meso-cth)(CN)] units pseudo-related by a symmetry center

Carmen Diaz a,*, Juan Ribas a, M. Salah El Fallah a, Xavier Solans b,Merce Font-Bardıa b

a Departament de Quımica Inorganica, Uni6ersitat de Barcelona, Marti Franques 1-11, 08028 Barcelona, Spainb Departament de Cristallografia i Mineralogia, Uni6ersitat de Barcelona, Martı i Franques s/n, 08028 Barcelona, Spain

Received 24 June 2000; accepted 28 August 2000

Abstract

Two new copper(II) complexes with pseudohalide ligands have been synthesized and their crystal structures have beendetermined by X-ray diffraction: a dinuclear complex [Cu2(m1,1-NCO)2(NCO)2(phen)2] (1) in which two cyanate ligands form anend-on bridge between the two copper(II) atoms and the two other act as terminal ligands, and a mononuclear complex{[Cu(meso-cth)(CN)]ClO4·H2O}2 (2) with two independents [Cu(meso-cth)(CN)] units pseudorelated by a symmetric center, werephen is 1,10-phenantroline and meso-cth is 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclo-tetradecane. Magnetic susceptibilitydata, measured from 2 to 300 K, show ferromagnetic coupling for the dinuclear complex 1. These data were fitted to an equationderived from the Hamiltonian H= −JS1S2, given the parameters J= +13.75 cm−1, g=2.17. Complex 2 shows Curie lawbehavior (u=0). © 2001 Elsevier Science B.V. All rights reserved.

Keywords: Copper(II) complexes; Pseudohalide ligands; X-ray crystal structures; Cyanate bridging ligands; Magnetic susceptibility

1. Introduction

The number of structural studies on copper(II) com-pounds with cyanate or cyanide ligands is surprisinglylow. The cyanate ion can act as a bridging ligandbetween two metal atoms in end-to-end (a) or end-onfashion (b,c) (Scheme 1).

In cyanate-bridged polynuclear copper(II) com-pounds the end-on coordination mode is usually found.Indeed, eleven out of thirteen reported cyanate-bridgeddinuclear copper(II) compounds show end-on coordina-tion [1–11], and only two have end-to-end [11,12].

Three structural examples of two-dimensional end-to-end cyanate-bridged copper(II) compounds [13–15] andthree examples of one-dimensional cyanate-bridgedcompounds (one end-on [16] and two end-to-end[17,18]) have been reported. From a magnetic point of

Scheme 1.* Corresponding author. Fax: +34-93-490 7725.E-mail address: cdiaz@kripto.qui.ub.es (C. Diaz).

0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.

PII: S 0 0 2 0 -1693 (00 )00281 -4

C. Diaz et al. / Inorganica Chimica Acta 312 (2001) 1–62

view, focusing on the dinuclear compounds, it is inter-esting to study the cyanato ligand as a superexchangepathway between copper(II) ions. However, such astudy is difficult because most of the published dinu-clear compounds for which structural and magneticdata are available also contain another kind of bridgein their structure. It is difficult to separate the contribu-tion of the cyanato ligand to the global coupling con-stant. Only four such compounds are bridgedexclusively by cyanate ligands: [Cu2(m1,1-NCO)2(terpy)2-(H2O)2](PF6)2, �J �B0.5 cm−1 [7], [Cu2(m1,3-NCO)2-(EtMe4dien)2](ClO4)2, J=0.5 cm−1 [11], [Cu2(m1,1-NCO)2(Medien)2](ClO4)2, J= −4.6 cm−1 [11] and[Cu2(m1,3-NCO)(L1)](PO4)3·MeCN·1.5EtOH, J= −7cm−1 [12]. At present, there is not enough informationavailable to permit magneto–structural correlations tobe established in complexes with NCO bridged ligands.

As a class, copper(II)–cyanide complexes are notcommon [13,14], owing to the tendency of copper(II) tooxidize cyanide to cyanogen. Stable complexes invari-ably contain polydentate aliphatic or aromatic nitrogenligands [14–16] as observed here.

In search of structural and magnetic data on polynu-clear copper(II) complexes with polydentate aromaticnitrogen ligands and NCO− and CN− ions, we havecharacterized two new complexes. Here we present thesynthesis and a structural and magnetic study of thenew dinuclear complex [Cu2(m1,1-NCO)2(NCO)2(phen)2](1) (phen=1,10-phenantroline) in which two cyanateligands bridge the two copper(II) atoms in end-onfashion and the other two act as terminal ligands. Wealso report the preparation and characterization (in-cluding structural determination) of the mononuclearcomplex {[Cu(meso-cth)(CN)]ClO4·H2O}2 (2) (meso-cth=5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclo-tetradecane), with two independent [Cu(meso-cth)(CN)]units pseudo-related by a symmetric center. [Cu2(m1,1-NCO)2(NCO)2(phen)2] (1), is ferromagnetically coupledwith J= +13.75 cm−1 and {[Cu(meso-cth)(CN)]ClO4·H2O}2 (2) shows Curie law behavior (u=0).

2. Experimental

2.1. Synthesis

Caution! Perchlorate salts of metal complexes withorganic ligands are potentially explosive. Only a smallamount of material should be prepared and it should behandled with care.

[Cu2(m1,1-NCO)2(NCO)2(phen)2] (1) was prepared bymixing 2 mmol of copper(II) nitrate hexahydrate, 2mmol of 1,10-phenantroline and 4 mmol of sodiumcyanate in 75 ml of water. From this solution bluemonocrystals suitable for X-ray determination werecollected 1 week later. Anal. Calc for C14H8CuN4O2: C,

51.30; H, 2,46; N, 17.09. Found: C, 50.90; H, 2,53; N,16.87%.

{[Cu(meso-cth)(CN)]ClO4·H2O}2 (2), a solution of 1mmol of [Cu(meso-cth)](ClO4)2 [17] in 30 ml of acetoni-trile was mixed with 1 mmol of potassium cyanidedissolved in 10 ml of water. Slow evaporation of theresulting blue–violet solution gave blue crystals of 2several days later. Anal. Calc. for C34H76Cl2N10O10Cu2:C, 31.28; H, 5.70; N, 10.42. Found: C; 31.70; H, 5.63;N, 10.56%.

2.2. Physical measurements

IR spectra (4000–400 cm−1) were recorded fromKBr pellets on a Nicolet 520 FTIR spectrophotometer.Magnetic susceptibility measurements were carried outon polycrystalline samples with a SQUID apparatusworking in the range 2–300 K. Diamagnetic correctionswere estimated from Pascal tables. ESR measurementswere made with a Bruker ES200 spectrometer atX-band frequency, working with an Oxford liquid he-lium cryostat for variable temperatures.

2.3. X-ray crystallography

Prismatic crystals (0.2×0.3×0.3 mm) for 1 and(0.1×0.1×0.2 mm) for 2 were selected and mountedon an Enraf–Nonius CAD4 four-circle diffractometer.The crystallographic data, conditions for the intensitydata collection, and some features of the structurerefinement are listed in Table 1. Unit-cell parameterswere determined from automatic centering of 25 reflec-tions (12BuB21°) and refined by least-square meth-ods. Intensities were collected with graphitemonochromatized Mo Ka radiation, using the v/2u

scan-technique. For 1 2860 reflections were measured inthe range 2.305u529.97, 2718 of which were non-equivalent by symmetry (Rint (on I)=0.039), 2329reflections were assumed as observed applying the con-dition I\2s(I). For 2 5972 reflections were measuredin the range 2.19BuB29.99, 5475 reflections wereassumed as observed applying the condition I\2s(I).Three reflections were measured every 2 h as orienta-tion and intensity control: significant intensity decaywas not observed. Lorentz-polarization but not absorp-tion corrections were made. The structures were solvedby direct methods, using the SHELXS computer program[18] and refined by the full-matrix least-square methodswith the SHELX-93 computer program [19], using 2668reflections for 1 and 5923 reflections for 2, (very nega-tive intensities were not assumed). The function mini-mized was Sw ��Fo�2− �Fc�2�2, where w= [s2(I)+(0.0626P)2]−1 for 1 and w= [s2(I)+ (0.0815P)2]−1 for2, and P= (�Fo�2+2�Fc�2)/3, f, f % and f %% were takenfrom [20]. For 1 the extinction coefficient was 0.035(11)and for 2 the chirality of structure was defined from

C. Diaz et al. / Inorganica Chimica Acta 312 (2001) 1–6 3

Table 1Crystallographic data for [Cu2(m1,1-NCO)2(NCO)2(phen)2] (1),{[Cu(meso-cth)(CN)]ClO4·H2O}2 (2) c

21

C14H8CuN4O2Empirical formula C17H38ClCuN5O5

491.51327.78Formula weight (g)monoclinicCrystal system monoclinicP21/nSpace group Cc

15.863(8)7.851(9)a (A, )18.628(3)b (A, ) 13.710(3)16.812(4)11.683(3)c (A, )

90.0a (°) 90.0108.48(4)b (°) 97.08(5)90.090.0g (°)

4Z 8293(2)Temperature (K) 293(2)

1.3861.745Dcalc (g cm−3)17.60m (Mo Ka) (cm−1) 10.760.71069l (Mo Ka) (A, ) 0.71069

0.05100.0624R a

0.1238wR b 0.1154

a R(Fo)=S��Fo�−�Fc��/S�Fo�.b wR (Fo)=Sw ��Fo�−�Fc��/Sw �Fo�.c The cell parameters were selected according to the IUCr rules for

a reduced cell.

was 493. Maximum shift/e.s.d.=0.00, mean shift/e.s.d.=0.00. Maximum and minimum peaks in finaldifference synthesis were 0.648 and −0.592 e A, −3,respectively.

3. Results and discussion

3.1. IR spectra

The IR spectra for complex 1 show the most intenseabsorption bands corresponding to NCO ligands atn(CN) at 2186 and 2.235 cm−1; the characteristic bandsattributable to the phen ligand appear between 1600and 400 cm−1. For complex 2, the cyanide ligand bandn(CN) appears at 2106 cm−1, those attributable to themeso-cth ligand appear at about 3228 cm−1 (N�H), ina wide range between 3000 and 2870 cm−1 (C�H); andfinally at about 1450 cm−1 (C�N). The perchlorate ionshows two main bands centered at 1103 and 626 cm−1.

3.2. Crystal structure

Selected bond distances and angles for 1 and 2 aregiven in Tables 2 and 3.

The structure of 1 consists of dinuclear units[Cu2(m1,1-NCO)2(NCO)2(phen)2]. The copper(II) atomsare bridged by cyanate anions in a end-on fashion. AnORTEP drawing with the atom labeling scheme is shownin Fig. 1. The coordination polyhedron of copper(II)can be considered as a square pyramid with apicalelongation (4+1), with a t factor value of 0.07 (t=0for a square pyramid, and t=1 for a trigonal bipyra-mid) [22] (see Scheme 2).

In the basal plane there are four short bonds, 1.917–2.043 A, to atoms N(1) and N(2) of the phen ligand,N(3) of the NCO terminal ligand and N(4) of one ofthe NCO bridged ligands, the apical position is occu-pied by atom N(4c ) of the other NCO bridged ligandat 2.478(4) A, . The Cu metal atom lies roughly 0.0948 A,above the basal plane. The Cu�N(4)�Cuc andN(4)�Cu�N(4c ) bridging angles are 92.69(13) and87.31(13)°, respectively. The intradinuclear Cu�Cu dis-tance is 3.235 A, . The dinuclear entities are packedgiving one-dimensional system, through one copper(II)atom of one entity to the main plane of the other entitydefined by the phenantroline ligand (Fig. 2). This dis-tance is 3.582 A, . The average plane to plane distancesof the phen rings of two dinuclear entities is more than6 A, , which indicates no p–p interactions through phenligands in the neighboring dinuclear entities. The short-est intradinuclear Cu�Cu distance is 4.961 A, .

For compound 2 a labeled scheme is shown in Fig. 3.The asymmetric unit contains two independent[Cu(meso-cth)(CN)] units, two perchlorate anions and

Table 2Selected bonds lengths (A, ) and angles (°) for [Cu2(m1,1-NCO)2(NCO)2(phen)2] (1)

1.917(3)Cu�N(3) N(1)�C(1) 1.324(4)1.357(4)Cu�N(4) N(1)�C(12)1.968(3)

Cu�N(2) N(2)�C(10)2.034(3) 1.322(4)2.043(3)Cu�N(1) N(2)�C(11) 1.363(4)

Cu�N(4) a 2.478(4) N(3)�C(13) 1.143(5)1.174(5)O(1)�C(13) N(4)�C(14) 1.158(4)

O(2)�C(14) 1.186(4) N(4)�Cu a 2.478(4)

95.54(14)N(3)�Cu�N(4) N(3)�Cu�N(4) a 99.38(13)167.65(12)N(3)�Cu�N(2) N(4)�Cu�N(4) a 87.31(13)

N(4)�Cu�N(2) 91.41(12) N(2)�Cu�N(4) a 91.12(11)92.99(12)N(1)�Cu�N(4) a92.29(13)N(3)�Cu�N(1)

172.01(11)N(4)�Cu�N(1) N(3)�C(13)�O(1) 178.4(5)80.60(11)N(2)�Cu�N(1) N(4)�C(14)�O(2) 175.8(4)

a Symmetry transformations used to generate equivalent atoms,i : 1−x, −y+1, −z

the Flack coefficient, which is equal to 0.04 (2) for thegiven results [21]. All H atoms were computed andrefined with an overall isotropic temperature factorusing a riding model. For 1 the final R(on F) factor was0.049, wR(on �F �2)=0.104 and goodness-of-fit=1.070for all observed reflections: number of refined parame-ters was 223. Maximum. shift/e.s.d.=0.00, Mean shift/e.s.d.=0.00. Maximum and minimum peaks in finaldifference synthesis were 0.646 and −0.955 e A, −3,respectively. For 2 the final R (on F) factor was 0.048,wR (on �F �2)=0.114 and goodness-of-fit=1.032 for allobserved reflections. The number of refined parameters

C. Diaz et al. / Inorganica Chimica Acta 312 (2001) 1–64

two water molecules. The two molecules [Cu(meso-cth)(CN)] are pseudo-related by a symmetry centersituated at (0, 0.375, 0), this center is not crystallo-graphic. The shortest distance between Cu atoms is6.863(4) A, . In each molecule, the copper atom is foundpentacoordinated: coordinated to one cyanide ligand bythe carbon atom and to four nitrogen atoms of themacrocycle meso-cth. The coordination polyhedron ofcopper(II) can be considered as a square pyramid withapical elongation (4+1). The corresponding t valuewas t= (b−a)/60= (163.63−162.88)/60=0.01 [22].

Scheme 2.

Fig. 2. Representation of the packing of [Cu2(m1,1-NCO)2(NCO)2(phen)2] (1) giving a one-dimensional system, throughone copper(II) atom of one entity to the main plane of the otherentity defined by the phenantroline ligand. There are not p–p interac-tions, see text.

Table 3Selected bonds lengths (A, ) and angles (°) for {[Cu(meso-cth)(CN)]ClO4·H2O}2 (2)

Cu(2)�N(7)2.052(4) 2.040(4)Cu(1)�N(1)2.057(4)Cu(1)�N(4) Cu(2)�N(6) 2.048(4)2.060(4) Cu(2)�N(9)Cu(1)�N(2) 2.084(4)

2.101(4)Cu(1)�N(3) 2.082(5) Cu(2)�N(8)2.208(5) Cu(2)�C(28)Cu(1)�C(11) 2.176(5)1.124(8)N(5)�C(11) N(10)�C(28) 1.126(8)

86.19(17)N(1)�Cu(1)�N(4) N(7)�Cu(2)�N(6) 93.84(17)163.51(16)N(1)�Cu(1)�N(2) 91.03(17) N(7)�Cu(2)�N(9)

163.61(16)N(4)�Cu(1)�N(2) N(6)�Cu(2)�N(9) 83.52(17)N(1)�Cu(1)�N(3) 84.49(16)N(7)�Cu(2)�N(8)162.86(15)

N(6)�Cu(2)�N(8) 161.89(17)94.91(17)N(4)�Cu(1)�N(3)N(2)�Cu(1)�N(3) 83.09(17) N(9)�Cu(2)�N(8) 92.95(16)

100.31(19)N(1)�Cu(1)�C(11) N(7)�Cu(2)�C(28)103.12(19)103.35(19)N(6)�Cu(2)�C(28)N(4)�Cu(1)�C(11) 96.04(18)

100.32(19)N(2)�Cu(1)�C(11) N(9)�Cu(2)�C(28) 96.14(19)93.8(2) 94.68(19)N(3)�Cu(1)�C(11) N(8)�Cu(2)�C(28)

N(10)�C(28)�Cu(2)172.2(5) 170.9(6)N(5)�C(11)�Cu(1)

Fig. 1. Drawing of the [Cu2(m1,1-NCO)2(NCO)2(phen)2] (1) with atomlabeling scheme.

The Cu metal atom lies roughly 0.2970 A, above thebasal plane. The Cu(2)�N(meso-cth) distances are be-tween 2.040(4) and 2.101(4) A, . While the distancecorresponding to Cu�C(28) is 2.176(5). The N�Cu(2)�Nangles range from 83.52(17) and 163.51(16)°. All thedistances could be considered as normal.

3.3. Magnetic results

The variable temperature magnetic susceptibility datafor 1 and 2 were recorded between 290–4 K. A plot ofxMT versus T for 1 is shown in Fig. 4. The xMT valueincreased from 0.894 cm3 K mol−1 at 290 K to 1.20cm3 K mol−1 at 4 K, indicating ferromagnetic cou-pling. The susceptibility data were fitted to the expres-sion of the magnetic susceptibility of isotropicallycoupled S=1/2 dinuclear compounds, derived from theHamiltonian H= −JS1S2 using the minimum value ofR=Si(x i

calcT−x iobsT)2/=Si(x i

obsT)2 as a criterion ofthe best fit. The results of the best fit shown as the solidline in Fig. 4 were J= +13.75 cm−1, g=2.17 with

C. Diaz et al. / Inorganica Chimica Acta 312 (2001) 1–6 5

R=3.18×10−5. This J value is the highest reported sofar for this kind of cyanate complex.

For complex 2 the xMT versus T value is close to 0.4cm3 K mol−1 corresponding to an isolated copper atomwith g approximately 2.06 and remained constantthroughout the range of temperatures exhibiting aCurie law behavior (u=0).

For 1, the EPR spectrum at 216 K consists of twosignals: g =2.25 and gÞ=2.08 with line widths of 400and 525 G, respectively. The patterns g \gÞ\2.00corresponds to an unpaired electron in the x2−y2

orbital, in agreement with the geometry given above(Fig. 5). At 4 K the EPR shows a single asymmetricband centered at g=2.08, with a 950 G line width.

For 2 the EPR spectrum consisting of one symmetricband at g=2.06 with a line width of 675 G, did notchange with temperature.

Fig. 5. The EPR spectrum at 216 K for [Cu2(m1,1-NCO)2(NCO)2(phen)2] (1).

4. Supplementary material

Crystallographic data for the structural analysis havebeen deposited with the Cambridge CrystallographicData Centre, CCDC No. 145 449 for compound 1 andNo. CCDC 145 448 for compound 2. Copies of thisinformation can be obtained free of charge from theDirector, CCDC, 12 Union Road, Cambridge CB121EW, UK (fax: +44-1223-336-033; e-mail: deposit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).

Acknowledgements

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

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