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Polyhedron 26 (2007) 11–16

Diverse coordination of two ligands in ferromagnetic[Cu(l-HCO2)2(3-pyOH)]n and

[Cu2(l-HCO2)2(l-3-pyOH)2(3-pyOH)2(HCO2)2]n

Bojan Kozlevcar a,*, Lea Glazar a, Gordana Pirc a, Zvonko Jaglicic b,Amalija Golobic a, Primoz Segedin a

a Faculty of Chemistry and Chemical Technology, University of Ljubljana, Askerceva 5, P.O. Box 537, SI-1001 Ljubljana, Sloveniab Institute of Mathematics, Physics and Mechanics, University of Ljubljana, Jadranska 19, Ljubljana, Slovenia

Received 8 June 2006; accepted 17 July 2006Available online 4 August 2006

Abstract

Two novel polynuclear complexes with methanoate anions and 3-hydroxypyridine ligands [Cu(l-HCO2)2(3-pyOH)]n (1) and [Cu2-(l-HCO2)2(l-3-pyOH)2(3-pyOH)2(HCO2)2]n (2), respectively, were synthesized and characterized. The central copper atom in 1 is sur-rounded by four methanoates and a 3-pyOH molecule, forming a square-pyramidal CuO3NO chromophore. All the methanoates arebidentate and serve as bridges between the adjacent copper ions via syn-anti and anti–anti coordination. The basal square coordinationaxes are formed by O(syn), N(3-pyOH) (1.974(2), 2.016(2) A) and O(anti), O(anti) (1.945(2), 1.960(2) A), while the third O(anti)(2.247(2) A) is on the top of the pyramid. A ferromagnetic transition with an exchange constant 2J/kB = 9.2 cm�1 is found for 1 below20 K. This interaction probably takes place through two syn-anti methanoates extended in a chain through the 2D structure. On theother hand, two monoatomic Cu–O–Cu intra-dinuclear asymmetric (1.986(2), 2.415(2) A) bridges of two methanoates in[Cu2(HCO2)4(3-pyOH)4] (2) are present. An elongated distorted octahedral coordination sphere around each copper(II) atom is com-pleted by an additional monodentate terminal methanoate (1.975(2) A), two N-coordinated 3-pyOH (2.005(2), 2.002(2) A) and the thirdweakly O-coordinated 3-pyOH (2.732(2) A). Although a shorter Cu� � �Cu distance is noticed in 2 than in 1 (4.690(1) A 1, 3.442(1) A 2),much weaker ferromagnetism is found in 2.� 2006 Elsevier Ltd. All rights reserved.

Keywords: 3-Hydroxypyridine; Methanoate; Copper; Ferromagnet; Syn; Anti

1. Introduction

Copper carboxylates are well known to form a variety ofstructures even with ligands of the same homologous series.Our recent investigations include efforts to find new syn-thetic routes for the preparation of copper carboxylateswith additional N-donor ligands. A choice of ligands witha hydrogen-bonding functionality could lead to the forma-tion of useful inorganic materials with desired physicalproperties. Some of them may serve also as bioinorganic

0277-5387/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.poly.2006.07.025

* Corresponding author.E-mail address: bojan.kozlevcar@fkkt.uni-lj.si (B. Kozlevcar).

models, since coordination compounds of the first-rowtransition metals are known to participate in multiple bio-logical processes involving acid–base and redox reactions.In this sense, complexes of hydroxypyridine are of consid-erable interest [1,2]. However, only a few coordinationcompounds of copper(II) carboxylates with 3-hydroxypyri-dine (3-pyOH) have been structurally characterized so far.A two-dimensional network, linked by inter-molecularhydrogen bonds between trifluoroacetate and 3-pyOHligands, is present in [Cu(O2CCF3)2(3-pyOH)2(THF)2] [2].A similar 2D network is also reported for [Cu(O2CCF3)2-(3-pyOH)2]n [3], however, 3-pyOH ligands serve asbridges (N,O) and intra-molecular H-bonding is present.

Table 1Relevant crystal data and data collection summary

Formula C7H7CuNO5 (1) C12H12CuN2O6 (2)Formula weight 248.68 343.78Crystal system orthorhombic monoclinicSpace group Pbca P21/ca (A) 15.7293(3) 8.0710(1)b (A) 6.9881(1) 13.4048(3)c (A) 17.1409(4) 12.9065(2)b (�) 90 100.1110(7)V (A3) 1884.09(6) 1374.67(4)Z 8 4Dx (g/cm3) 1.753 1.661l (mm�1) 2.313 1.618T (K) 293 293Crystal colour light blue dark blueCrystal shape plate plateCrystal size (mm) 0.30 · 0.15 · 0.10 0.30 · 0.10 · 0.10h Max (�) 27.47 27.47Rint 0.051 0.030Refined parameters 155 190Total data 25445 17983Independent data 2150 3153Observed data [F2 > 2r(F2)] 1707 2706Ra (observed) 0.031 0.032wRb (observed) 0.019 0.024Dqmin, max (e A�3) �0.662, 0.503 �1.49, 0.65

a R ¼PðjjF oj � jF cjjÞ=

PjF oj.

b wR ¼PðwjjF oj � jF cjjÞ=

PjwF oj.

12 B. Kozlevcar et al. / Polyhedron 26 (2007) 11–16

Replacement of the carboxylate ligand reveals structurallysignificantly different compounds. Due to tetradentatebridging oxalates, a 1D zig-zag chain structure of cis-[Cu(l-ox)(3-pyOH)2]n [4] is formed. On the other hand,acetates coordinate bidentately, as in dinuclear paddle-

wheel [Cu2(O2CCH3)4(3-pyOH)2] [5] or in mononuclear[Cu(O2CCH3)2(3-pyOH)2]n [6]. Only one example of3-pyO, the deprotonated form of 3-pyOH, was found inthe literature, in {[Cu(l-3-pyO)(3-pyO)(3-pyOH)(H2O)] Æ2H2O}n [1]. For some of these complexes ferromagneticor antiferromagnetic properties were reported, eitherthrough the carboxylate group or 3-pyO(H).

In this work, we present two novel coordination com-pounds with methanoate and 3-pyOH ligands. The metha-noates show rather rare coordination modes in both cases,playing a distinguishing role in the magnetic properties ofboth complexes.

2. Experimental

2.1. Synthesis

Chemicals were readily available from commercialsources and were used as received without furtherpurification.

[Cu(l-HCO2)2(3-pyOH)]n (1). A mixture of [Cu2(OH)2-CO3] (0.33 g, 1.5 mmol) and 3-pyOH (0.57 g, 6.0 mmol)in 30 mL CH3OH and 3 mL HCOOH was refluxed in airfor 1 h. A small amount of a solid residue was filtered offand the resulting solution was left at 279 K for 72 h. Lightblue crystals of 1 were filtered off and dried in a desiccatorover KOH for 24 h. Yield 57%. Anal. Calc. forC7H7CuNO5: C, 33.8; H, 2.84; N, 5.63; Cu, 25.6. Found:C, 33.7; H, 3.02; N, 5.25; Cu, 26.1%. IR (�m/cm�1): 1630 smas(CO2), 1580sh, 1564s mas(CO2) + m(ring), 1482 m m(ring),1369s ms(CO2), 1344 s, 1297 s m(C–O). UV/Vis (kmax/nm):225, 285, 610. EPR (295 K) g 2.150.

[Cu2(l-HCO2)2(l-3-pyOH)2(3-pyOH)2(HCO2)2]n (2).The synthetic path for the dark blue compound 2 was thesame as for 1: [Cu2(OH)2CO3] (0.25 g, 1.1 mmol), 3-pyOH(1.1 g, 12 mmol), absolute C2H5OH (30 mL), HCOOH(2 mL). Yield 67%. Anal. Calc. for C24H24Cu2N4O12: C,41.9; H, 3.52; N, 8.15; Cu, 18.5. Found: C, 42.3; H, 3.79;N, 7.94; Cu, 18.3%. IR (�m/cm�1): 1600 s mas(CO2), 1557 mm(ring), 1452 m m(ring), 1370 m ms(CO2), 1333 s, 1285 sm(C–O). UV/Vis (kmax/nm): 225, 285, 615. EPR (295 K)g^ 2.100, gi 2.257.

The single crystals of 1 and 2, suitable for X-ray analy-sis, were obtained by a similar procedure, but at a lowerconcentration of the starting compounds.

2.2. X-ray structure analysis

Details of the crystal data, data collection and refine-ment parameters for 1 and 2 are listed in Table 1, andselected distances and angles in Table 2. The diffractiondata were collected on a Nonius Kappa CCD diffracto-

meter with graphite monochromated Mo Ka radiation.The data were processed using DENZO [7]. The structureswere solved by direct methods using SIR97 [8] and refinedusing XTAL3.6 [9] by a full-matrix least-squares procedurebased on F. All of the non-hydrogen atoms were refinedanisotropically. The positions of the hydrogen atoms forboth structures were located using difference Fourier maps.They were refined together with their isotropic displace-ment parameters for 1. The H-atoms parameters of 2 werenot refined.

2.3. Physical measurements

The magnetic susceptibility data of powdered polycrys-talline samples were measured with a Quantum DesignSQUID magnetometer, equipped with a 5 T magnet. Themolar magnetic susceptibility vM was investigated in thetemperature interval between 300 and 2 K in a magneticfield strength H = 50 Oe. The data were corrected for theexperimentally determined contribution of the sampleholder. Corrections for the diamagnetic response of thecompounds, due to closed atomic shells as estimated fromthe Pascal’s constants, were applied [10].

Metal analysis was carried out electrogravimetricallywith Pt electrodes. C,H,N analysis was performed with aPerkin–Elmer, Elemental Analyzer 2400 CHN. Infraredspectra were measured on mineral oil mulls, using aPerkin–Elmer FT-IR 1720X spectrometer. Electronic spec-tra were recorded as nujol mulls with a Perkin–Elmer UV/Vis/NIR spectrometer Lambda 19. EPR spectra of thepowdered samples were recorded by a Bruker ESP-300

Fig. 1. Two types of four methanoate bridges among the Cu-3-pyOHmoieties in the polymeric structure of 1 [11,12] (Cu� � �Cu: syn–anti

4.690(1) A, anti–anti 5.935(1) A). All H-atoms are omitted for clarity.

Table 2Selected bond distances (A), angles (�) and hydrogen-bonding geometries for complexes 1 and 2

1

Cu–O11 1.9454(14) O11–Cu–O21 0 93.19(5) O11–Cu–O22 169.99(6)Cu–O22 1.9600(14) O11–Cu–N 87.18(6) O11–Cu–O120 94.44(5)Cu–O210 1.9740(13) O120–Cu–N 96.75(6) O21 0–Cu–O22 92.60(5)Cu–N 2.0158(15) O210–Cu–N 175.13(6) O12 0–Cu–O210 88.07(5)Cu–O120 2.2473(14) O22–Cu–N 86.36(6) O12 0–Cu–O22 93.91(5)O12–C1 1.240(2) Cu–O11–C1 126.24(13) Cu–O120–C1 0 124.67(13)O22–C2 1.244(2) Cu–O210–C20 114.30(12) Cu–O22–C2 128.93(12)O11–C1 1.248(2)O21–C2 1.258(2)

2

Cu–O31 1.9751(11) O31–Cu–O41 162.89(4) O31–Cu–N1 91.73(5)Cu–O41 1.9855(10) O31–Cu–N2 91.28(5) O31–CuO410 85.40(4)Cu–N1 2.0049(12) O220–Cu–O31 88.67(4) O41–Cu–N1 90.64(5)Cu–N2 2.0023(13) O41–Cu–N2 89.69(5) O41–Cu–O410 77.50(4)Cu–O410 2.4147(10) O220–Cu–O41 108.37(4) N1–Cu–N2 168.64(5)Cu–O220 2.7324(14) O410–Cu–N1 95.66(4) O22 0–Cu–N1 87.37(4)O31–C3 1.256(2) O410–Cu–N2 95.50(4) O22 0–Cu–N2 81.76(5)O32–C3 1.222(3) O220–Cu–O410 173.42(4) Cu–O41–Cu0 102.50(4)O41–C4 1.266(2) Cu–O220–C220 141.53(11) Cu–O31–C3 127.77(10)O42–C4 1.226(2) Cu–O41–C4 128.21(10) Cu–O410–C4 0 129.16(10)

D–H� � �A (1) D� � �A D–H� � �A D–H� � �A (2) D� � �A D–H� � �AO(41)–H(41)� � �O(12)a 2.692(2) 172(4) O(12)–H(12)� � �O(42)b 2.695(2) 171

O(22)–H(22)� � �O(32)c 2.540(2) 159

a 1 � x, 1 � y, 1 � z.b 1 + x, y, z.c x, 1/2 � y, �1/2 + z.

B. Kozlevcar et al. / Polyhedron 26 (2007) 11–16 13

spectrometer, operating at X-band at room temperatureand at 100 K. The values of parameters g were calculateddirectly from the signal positions in the spectra.

3. Results and discussion

The crystal structure analysis of [Cu(l-HCO2)2(3-pyOH)]n (1) (katena-bis-(l-methanoato-O,O 0)-(3-hydroxy-

pyridine-N)copper(II)) reveals a polynuclear structure ofCu and 3-hydroxypyridine (3-pyOH) moieties (Cu–N2.016(2) A) bridged by four methanoates (Fig. 1). Due tothe symmetry relations, only two different methanoatesare in the structure. One coordinates syn-anti (Cu–O21 0

1.974(2), Cu–O22 1.960(2), Cu� � �Cu (4.690(1) A), whilethe other anti-anti (Cu–O11 1.945(2), Cu–O12 0 2.247(2),Cu� � �Cu 5.935(1) A). The coordination sphere around thecopper(II) atom is square-pyramidal with N–Cu–O21 0

and O11–Cu–O22 coordination axes and O12 0 on the topof the pyramid. The methanoate bridges enable a layeredstructure, while 3-pyOH is involved only in an inter-layerH-bonding network (O41(H41)� � �O12 2.692(2) A).

Two copper(II) atoms in the dinuclear central core of[Cu2(l-HCO2)2(l-3-pyOH)2(3-pyOH)2(HCO2)2]n (2) (katena-bis-(l-3-hydroxypyridine-O,N)-bis-(l-methanoato-O)-(methan-

oato-O)-(3-hydroxypyridine-N)dicopper(II)) are connectedby two monoatomic non-symmetric methanoate bridges(Cu–O41 1.986(2), Cu 0–O41 2.415(2) A, Cu–O41–Cu 0

102.50(4)�; Fig. 2). Two additional monodentate methano-ates (Cu–O31 1.975(2) A) are on the terminal positions ofthe dinuclear unit, trans to the closer bridging methanoate

oxygen atom (O41). Two 3-pyOH ligands are coordinatedtrans on each copper atom, and thus are perpendicular tothe copper–methanoate plane (Cu–N1 2.005(2), Cu–N22.002(2) A) and complete the dinuclear unit. The so fardescribed coordination sphere of 2 is very similar tothat reported for [{Cu(tzq)2(HCO2)}2((l-HCO2)2] Æ 4H2O(tzq = [1,2,3]triazolo[1,5-a]quinoline) [13]. A shorter intra-dinuclear Cu� � �Cu distance in the tzq complex(3.339(2) A) than in 2 (3.442(1) A) is likely to be due to astronger p� � �p interaction (tzq complex: 12pe�/ligand;

Fig. 3. The magnetic properties vM and vMT (inset) of the title com-pounds, measured in 50 kOe. The full lines in the graph vM correspond tothe Curie–Weiss law.

Fig. 2. A dinuclear unit in the structure of 2 bridged by 3-pyOHmolecules, forming a 2D network (Cu� � �Cu 0 3.442(1) A) [11,12]. AllH-atoms are omitted for clarity.

Fig. 4. The magnetization la(H) for CuII (S = 1/2) species in 1, calculatedper 1 copper atom and measured at 2 K.

14 B. Kozlevcar et al. / Polyhedron 26 (2007) 11–16

2: 6pe�/ligand). The dinuclear units in the tzq complex areinter-molecularly H-bonded by water molecules, while in 2,they are connected by 3-pyOH molecules. Two 3-pyOHmolecules, strongly bonded inside one dimer in 2, are thusadditionally semi-coordinated to the apical position of theadjacent dimers (Cu–O22 0 2.732(2) A) forming inter-dinuclear bridges. The hydroxo oxygen atom O22 0 coordi-nates trans to the more distant bridging methanoate atomO41 0, completing the elongated Jahn–Teller axis (Fig. 2,Table 2). This inter-dinuclear bridge is additionallystrengthened by a strong H-bond between the hydroxogroup and the non-coordinated terminal methanoatooxygen atom (O22 0(H22 0)� � �O32 2.540(2) A). Such apoly-dinuclear structure shows a 2D network, H-bondedbetween adjacent layers via non-coordinated oxygen atomsof the bridging methanoates, and those 3-pyOH hydroxogroups not involved in the semi-coordination (O12(H12)-� � �O42 2.695(2) A). Additional stabilization inside thedinuclear units is found in p–p stacking (cg� � �cg3.878(2) A, mean interplanar separation 3.537, 3.506 A)of the 3-pyOH rings.

The molar magnetic susceptibility vM of compounds 1

and 2, increases with decreasing temperature, while theproduct vMÆT is approximately constant in the temperatureinterval from 300 K to 50 K, indicating a paramagneticbehaviour (Fig. 3) [14]. High temperature susceptibilitydata vM (above 50 K) were fitted with the Curie–Weisslaw: vM = C/(T � h). The Curie constant C and the Weissconstant h are 0.47, 0.92 cm3 K/mol and 6.6, 0 K for 1 and2, respectively. Below 50 K, vMT remains almost constantfor 2, and only a very weak ferromagnetic interaction isnoticed (inset in Fig. 3). On the contrary, vMT for 1 signif-icantly increases below 20 K, and the magnetic susceptibil-ity vM(M/H)H!0 = 14 cm3/mol (2 K) is much higher thanexpected for non-interacting S = 1/2 spins of CuII. In asmall magnetic field strength H, the magnetization MM

of 1 linearly increases, however at 1 kOe the la(H) depen-

dence becomes non-linear and MM saturates atH � 20 kOe (Fig. 4). The magnetization saturation is1.07 lB per CuII atom, showing that all CuII atoms in thesample contribute to specific magnetic properties of thesample. No hysteresis loop for the la(H) dependence wasdetected. Due to a large increase of vM below 20 K,h = 6.6 K, and an ‘‘S’’ shaped curve la(H) at 2 K with anabsence of hysteresis, a soft ferromagnetic behaviour atlow temperature for 1 is clearly noticed.

Magnetic interactions among non-diluted copper(II)atoms have been described frequently, however mostlyfor dicopper tetracarboxylates with a strong antiferromag-netic interaction. In those paddle-wheel structures, the carb-oxylates coordinate bidentately in a syn–syn mode. Thecoordination sphere is square-pyramidal with the magneticCuII orbital dx2�y2 oriented towards four bridging carboxy-lates and the non-magnetic dz2 towards the apical ligand[15–17]. This agrees with the magnetic interaction between

B. Kozlevcar et al. / Polyhedron 26 (2007) 11–16 15

two S = 1/2 spins of two CuII always found only inside thedinuclear unit. Although such dinuclear moieties are oftenconnected by various types of bridges, no inter-dinuclearinteractions via S = 1/2 were confirmed, but sometimessuggested via S = 1 joint dinuclear spins (2 · CuII)[18,19]. Some evidence for these interactions may be foundin the EPR spectra. If less than four carboxylates bridgetwo CuII atoms, a significant reduction of the magneticinteraction is observed [17,20–22], despite the magneticdx2�y2 orbitals involved on both sides of the bridge. Theo-retically, for the syn-anti carboxylate bridged models [17],a weak ferromagnetic interaction was calculated, while aweak antiferromagnetic for the syn–syn bridge and a mod-erate antiferromagnetic for the anti–anti models. Thereported complexes with the less common syn–anti bridg-ing mode show ferromagnetic or antiferromagnetic proper-ties, with small magnitudes of their exchange couplingconstants J [23–29]. Generally, the exchange interaction isa combination of two components, negative antiferromag-netic and positive ferromagnetic (J = JAF + JF) [30]. TheJAF magnitude is proportional to the square of the overlapintegral between the magnetic orbitals centred on the adja-cent metal atoms, while for the JF, it is governed by theoverlap density between the magnetic orbitals [31]. Poly-atomic extended ligands thus reduce the ferromagneticcontribution. The unfavourable overlap of the syn–anti ori-ented ligand orbitals [23] and non-planarity of the bridgingnetwork significantly reduce especially the antiferromag-netic part, to the extent that the ferromagnetic one becomespredominant [27,32].

Such an explanation fits both the herein analyzed com-pounds 1 and 2. In 1, the anti–anti methanoates (Cu–O11–C1–O12–Cu) connect the non-magnetic dz2 with themagnetic dx2�y2 CuII orbitals, while the syn–anti type(Cu–O21–C2–O22–Cu) enables the ferromagnetic interac-tion, since it connects the dx2�y2 magnetic orbitals only(Scheme 1). This interaction between the magnetic orbitalsis not limited to two Cu atoms, but is extended in a chain,due to two syn–anti bridges from a cis position of each Cu

Scheme 1. A relative orientation of the magnetic dx2�y2 and non-magneticdz2 CuII orbitals and their interactions through the methanoate bridges in1 and 2. Every dz2 orbital is shifted away from the ligand bonding p orbitalto stress a longer Cu–O distance in the axial direction.

atom to two adjacent Cu atoms (Fig. 1). The syn–anti

connected Cu atoms are pushed out of the O–C–O bridgeplane by 0.105(1) and 0.398(1) A, respectively, thus theCu–O21–C2–O22–Cu skeleton deviates from planarity,in accordance with an absence of an antiferromagneticinteraction in 1. A weak interaction between the nearestCuII neighbours can be treated as a small perturbationadded to the Zeeman term: bH ¼ �z2JbS 1 � bS 2, wherez is the number of nearest neighbours and 2J is the inter-action parameter between them [33,34]. Due to the twomagnetically interacting nearest neighbours (z = 2) foundin the structure of 1, 2J/kB = 9.2 cm�1 can be calculated(Eq. (1))

2J ¼ 3kBhzSðS þ 1Þ ð1Þ

In the structure of 2, the monoatomic methanoate andthe 3-pyOH molecule bridges are present, however theyall connect the magnetic dx2�y2 (Cu–O41(equatorial)1.986(1) A) and the non-magnetic dz2 CuII orbitals (Cu 0-O41(axial) 2.415 (1) A) (Scheme 1). Therefore, they donot enable a magnetic interaction of the same magnitudeas found in 1 despite the shorter Cu� � �Cu distance(4.690(1) A 1, 3.442(1) A 2). Actually, the inset in Fig. 3shows a very weak ferromagnetism for 2, and the interac-tion more likely takes place through the methanoates than3-pyOH due to a shorter length of such bridges. This weakinteraction may be possible by some admixture of dz2 char-acter with the dx2�y2 type of Cu(II) orbital, where theunpaired electron lies primarily. A significant octahedraldistortion of the copper coordination sphere in 2 (see Table2) strongly supports such a theory. A very weak ferromag-netism in 2 and a weak antiferromagnetism in the related[{Cu(tzq)2(HCO2)}2(l-HCO2)2] Æ 4H2O [13] may be corre-lated with different distances and almost the same anglein their monoatomic Cu–O–Cu bridges (tzq: 1.950(4),2.331(4) A, 102.2(2)�; 2: 1.986(1), 2.415(1) A, 102.5(2)�).Longer distances in 2 reduce the magnetic orbital overlap,and thus the antiferromagnetic contribution to the extentthat ferromagnetism predominates. A numerical analysisto predict the antiferromagnetic or the ferromagnetic prop-erties of dicopper complexes with two monoatomic chlo-rine bridges has been introduced [22,29]. The higher value//R (angle Cu–Cl–Cu = /, Cu–Cl axial distance = R) sug-gests antiferromagnetism, while lower value ferromagne-tism. The //R values 42.4 (2) and 43.8 (tzq) �/A thus fitwith the measured magnetic properties of 2 and the tzqcomplex.

The EPR spectrum of 1 (298 K) shows one signal(g = 2.150(3)), revealing pseudo isotropic symmetry of thecomplex and the presence of an isolated paramagnet withS = 1/2. Similar was observed for another Cu ferromag-netic complex with a syn–anti carboxylate bridge [27]. Onthe other hand, two axial symmetry signals (gi = 2.257(3),g^ = 2.100(3)) are found in the spectrum of 2. Significantlylonger Cu–L distances for the z-axis oriented ligands in 2

than in 1 are thus in agreement with the EPR spectra. The

16 B. Kozlevcar et al. / Polyhedron 26 (2007) 11–16

spectra of both compounds do not change by decrease oftemperature to 100 K, and they are consistent with the mag-netic susceptibility analysis. A full correlation was not done,due to unavailability of the EPR experiment below 100 K.On the other hand, some comparison was done for thestructurally related [Cu2(l-HCO2)2(l-3-pyOH)2(3-pyOH)2-(HCO2)2]n (2) and [{Cu(tzq)2(HCO2)}2(l-HCO2)2] Æ 4H2O[13]. Different spectra were recorded at room temperature,only two signals (Hi and H^) are found for 2, while theDMs ± 2 resonance and four DMs ± 1 signals are reportedfor the tzq complex. These differences are related to theobservations described by the magnetic susceptibilityanalysis.

4. Concluding remarks

The coordination compound [Cu(l-HCO2)2(3-pyOH)]n(1) shows triatomic methanoate bridges of anti–anti andsyn–anti mode. On the other hand, [Cu2(l-HCO2)2(l-3-pyOH)2(3-pyOH)2(HCO2)2]n (2) reveals only monoatomicmethanoate coordination, either to one Cu atom or bridg-ing inside the dinuclear moiety. Additionally, one half ofthe 3-pyOH molecules also serve as bridges, connectingthe adjacent dinuclear units in 2 in a poly-dinuclear net-work. A ferromagnetic interaction is found in both com-plexes, however, this is significantly important only for 1

(2J = 9.2 cm�1). This interaction takes place via the syn–anti methanoates, due to the magnetic Cu(II) dx2�y2 orbitalson both sides of the bridge. In all the other bridging casesin 1 and 2, the non-magnetic dz2 orbital is always involved.Such a ferromagnetic interaction in 1 is also in agreementwith a medium sized length of the triatomic O–C–O syn–anti bridge and non-planarity of its Cu–O–C–O–Cuskeleton.

Acknowledgements

The financial support of the MVZT Republic of Slove-nia, P1-0175-103 and X-2000, is gratefully acknowledged.We thank Dr. M. Sentjurc, EPR center, ‘Jozef Stefan’ Insti-tute, Ljubljana, for EPR spectra.

Appendix A. Supplementary data

All atomic parameters and other crystallographic datahave been deposited with the Cambridge CrystallographicData Center as supplementary material with the depositionnumbers CCDC 610244 1 and 610245 2. These data can beobtained, free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html. Supplementary data associated withthis article can be found, in the online version, atdoi:10.1016/j.poly.2006.07.025.

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