714 C.P. Raptopoulou et al. / Polyhedron 24 (2005) 711–721and of very poor diffraction quality. Repeated efforts togrow larger crystals proved unsuccessful. We cont<strong>in</strong>uedwith data collection <strong>in</strong> order to establish the gross structureof the complex. S<strong>in</strong>ce the structure of 2 proved quitesimilar to that of 1, we felt that complete structural characterizationwas not crucial. Thus, the ref<strong>in</strong>ement wasdone with anisotropic thermal parameters for the <strong>iron</strong>(<strong>III</strong>)ions only, whilst all the rest atoms were ref<strong>in</strong>ed isotropically.No H-atoms were <strong>in</strong>cluded <strong>in</strong> the ref<strong>in</strong>ement.The phenyl r<strong>in</strong>gs of the salox 2 and benzoate ligandswere fitted to the geometry of a regular hexagon. Thecrystallographic analysis revealed the presence of oneethanol of crystallization per trimeric complex.3. Results and discussion3.1. SynthesesAs mentioned earlier, our aim was to <strong>in</strong>vestigatethe use of salicylaldehyde oxime (H 2 salox) to the<strong>iron</strong>(<strong>III</strong>) <strong>carboxylate</strong> <strong>chemistry</strong>, extend<strong>in</strong>g our previousexperience on manganese [24]. The 1:1 molar ratioreaction of Mn(O 2 CR) 2 (R = Me, Ph) and H 2 salox <strong>in</strong>EtOH led to the hexanuclear complexes [Mn 6 O 2(O 2 CR) 2 (salox) 6 (EtOH) 4 ] (R = Me, Ph). These complexesconta<strong>in</strong> the novel ½Mn <strong>III</strong> 6ðl 3 -OÞ 2ðl 2 -ORÞ 2Š 12þcore, whose topology consists of six Mn ions arrangedas two {Mn 3 (l 3 -O)} subunits bridged by two oximatooxygen atoms. Both compounds proved to behave ass<strong>in</strong>gle molecule magnets (SMM) and are the firstmembers of a new class of manganese-based SMMsconta<strong>in</strong><strong>in</strong>g exclusively Mn <strong>III</strong> ions with block<strong>in</strong>g temperaturegreater than 2 K. In order to <strong>in</strong>vestigate thepossibility of synthesiz<strong>in</strong>g the correspond<strong>in</strong>g polynuclear<strong>iron</strong>(<strong>III</strong>) complexes and to study their magneticproperties, we have designed the 1:3:1 molarratio reaction of Fe 3+ /PhCO 2/H 2 salox <strong>in</strong> alcoholicmedia. The 1:3:1 molar ratio has been chosen so thatthe M/<strong>carboxylate</strong>/H 2 salox ratio rema<strong>in</strong>s the same <strong>in</strong>go<strong>in</strong>g from manganese(II) to <strong>iron</strong>(<strong>III</strong>) ions. But itturned out that <strong>in</strong> the <strong>iron</strong>(<strong>III</strong>) case, the amount ofthe <strong>carboxylate</strong> ions was very high, and the tr<strong>in</strong>uclearoxo-centered complexes 1 and 2 were formed. The salox2 ions are coord<strong>in</strong>ated through the usuall 2 :g 1 :g 1 :g 1 mode while the possibility of further useof the oximato oxygen atom to bridge a second metaland to <strong>in</strong>crease the nuclearity of the derived complexhas failed. Nevertheless, we still consider compounds 1and 2 as useful star<strong>in</strong>g materials for polynuclear<strong>iron</strong>(<strong>III</strong>) complexes, under different reactionconditions.The synthesis of 1 and 2 can be summarized <strong>in</strong>Eqs. (1) and (2), respectively, based on the reasonableassumption that H 2 O from the start<strong>in</strong>g materials and/or the solvent is the source of the O 2 ion.3FeðNO 3 Þ 3 9H 2 O þ 5PhCO 2 Na þ H 2 salox þ 2MeOHMeOHƒ ƒ! ½Fe3 OðO 2 CPhÞ 5ðsaloxÞðMeOHÞ 2Šþ5NaNO 3þ 4HNO 3 þ 26H 2 Oð1Þ3FeCl 3 6H 2 O þ 5PhCO 2 Na þ H 2 salox þ EtOHƒ EtOH ƒ! ½Fe 3 OðO 2 CPhÞ 5ðsaloxÞðEtOHÞðH 2 OÞŠ þ 5NaClþ 4HCl þ 16H 2 Oð2Þ3.2. IR spectroscopyIn the IR spectrum of both 1 and 2, medium-<strong>in</strong>tensitybands at 3451, 3063, 2924 cm 1 (for 1) and 3414, 3063,2980 cm 1 (for 2), are assigned to the m(OH) H2 O,m(CH) aromatic , m(CH 3 ), respectively. Strong <strong>in</strong>tensitybands at 1598 cm 1 and medium <strong>in</strong>tensity bands at1286 cm 1 observed <strong>in</strong> the spectrum of both complexesare assigned to the m(C@N) and m(N–Oox) of the salicylaldoximatoligand [28]. The frequencies of the m s (CO 2 )bands of PhCO 2co<strong>in</strong>cide <strong>in</strong> the spectra of 1(1406 cm 1 ), and 2 (1405 cm 1 ). The bands at1557 cm 1 <strong>in</strong> 1 and 2, respectively, are assigned to them as (CO 2 ) of the benzoato ligands. The difference D(D = m as (CO 2 ) m s (CO 2 )) for 1 is 151 cm 1 and for 2 is152 cm 1 , less than that for NaO 2 CPh (184 cm 1 ), as expectedfor the bridg<strong>in</strong>g modes of benzoate ligation [29].A strong <strong>in</strong>tensity band at 480 cm 1 <strong>in</strong> the spectra of 1and at 478 cm 1 <strong>in</strong> the spectra of 2 is characteristic ofthe presence of the [Fe 3 O] moiety <strong>in</strong> the structures of 1and 2.3.3. Structural description of [Fe 3 (l 3 -O)(O 2 CPh) 5(salox)(MeOH) 2 ] Æ 1.25MeOH Æ 1.05H 2 O(1)Compound 1 crystallizes <strong>in</strong> the monocl<strong>in</strong>ic spacegroup P2 1 /c with two crystallographically <strong>in</strong>dependenttr<strong>in</strong>uclear complexes <strong>in</strong> the asymmetric unit (further reportedas molecules 1a and 1b). The structure of themolecule 1a is given <strong>in</strong> Fig. 1. Selected bond distancesand angles for both 1a and 1b are listed <strong>in</strong> Table 2.The structure of 1 consists of a tr<strong>in</strong>uclear <strong>iron</strong>(<strong>III</strong>)oxo-centered complex. The three Fe <strong>III</strong> ions <strong>in</strong> 1a forman isosceles triangle whilst <strong>in</strong> 1b the triangle is best describedas scalene (see Table 2). The Fe–O oxo bond distancesare <strong>in</strong> the range 1.86–1.94 Å <strong>in</strong> both molecules 1aand 1b, and the central [Fe 3 (l 3 -O)] 7+ moiety is planar.Ions Fe(2) and Fe(3) <strong>in</strong> molecule 1a and the correspond<strong>in</strong>gions Fe(5) and Fe(6) <strong>in</strong> molecule 1b have an octahedraloxygen rich coord<strong>in</strong>ation env<strong>iron</strong>ment, while ionsFe(1) and Fe(4) <strong>in</strong> molecules 1a and 1b, respectively,have a distorted octahedral O 5 N coord<strong>in</strong>ation geometry.The angles with<strong>in</strong> the tetragonal plane of the octahedronrange from 82.2° to 97.5° for 1a and from 78.5° to 99.1°for 1b. The angles <strong>in</strong>volv<strong>in</strong>g the axial positions of the
C.P. Raptopoulou et al. / Polyhedron 24 (2005) 711–721 715Fig. 1. The molecular structure of the molecule 1a with the atomiclabell<strong>in</strong>g (40% thermal probability ellipsoids).octahedron range from 168.5° to 178.5° and from 163.9°to 178.1° <strong>in</strong> 1a and 1b, respectively.The salicylaldoximato ligand shows the commonl 2 :g 1 :g 1 :g 1 coord<strong>in</strong>ation mode with the N–O oximatogroup and the phenolate oxygen atom ly<strong>in</strong>g above and belowthe [Fe 3 (l 3 -O)] 7+ plane, respectively. The Fe–O oximatobond distances are 1.982 Å <strong>in</strong> both molecules 1a and 1b,the Fe–O phenoxy are 1.914 and 1.930 Å <strong>in</strong> molecules 1aand 1b, respectively. The Fe–N oximato bond lengths are2.133 and 2.145 Å <strong>in</strong> molecules 1a and 1b, respectively.The whole salicylaldoximato ligand is planar and makesan angle of 51.1° and 65.3° with the [Fe 3 (l 3 -O)] 7+ plane<strong>in</strong> molecules 1a and 1b, respectively.The benzoato ligands are coord<strong>in</strong>ated <strong>in</strong> the commonsyn,syn l 2 :g 1 :g 1 mode. The Fe–O carboxylato bond distancesare <strong>in</strong> the range 1.977–2.029 and 1.990–2.052 Å<strong>in</strong> molecules 1a and 1b, respectively.The polymeric lattice structure of 1, shown <strong>in</strong> Fig. 2,arises from the strong <strong>in</strong>termolecular <strong>in</strong>teractions betweenthe isolated trimers. More specifically, the oximatooxygen atom O(1) <strong>in</strong> molecule 1a is strongly <strong>in</strong>teract<strong>in</strong>g(most likely through hydrogen bond<strong>in</strong>g <strong>in</strong>teractions)to a coord<strong>in</strong>ated methanolic oxygen atom Om(1) belong<strong>in</strong>gto a centrosymmetrically related molecule 1a[O(1)...Om(1 0 ) = 2.574 Å (1 x, y, 1 z)]. Thus, a dimerof trimers of the a–a type, is formed though two<strong>in</strong>termolecular <strong>in</strong>teractions across a center of symmetry.The closest FeFe <strong>in</strong>teratomic distance <strong>in</strong> the a–a dimeris Fe(2)Fe(2 0 ) = 5.067 Å. The same feature is observed<strong>in</strong> the case of molecule 1b, where the oximato oxygenatom O(61) is strongly <strong>in</strong>teract<strong>in</strong>g (most likely throughH-bond<strong>in</strong>g <strong>in</strong>teractions) to a coord<strong>in</strong>ated methanolOm(3) from a centrosymmetrically related molecule 1b[O(61)...Om(3 00 ) = 2.666 Å (2 x, y, 2 z)]. Thus, adimer of trimers of the b–b type, is formed due to thedouble <strong>in</strong>teractions described above. The closest FeFe<strong>in</strong>teratomic distance <strong>in</strong> the b–b dimer is Fe(5)Fe(5 00 )=5.207 Å. Apart from the formation of dimers, anotherfeature is also observed <strong>in</strong> the lattice structure of 1.The phenoxy oxygen atom O(62) of molecule 1b isTable 2Selected bond distances (Å) and angles (°) for 1 Æ 1.25MeOH Æ 1.05H 2 OMolecule 1aBond distancesFe(1)–Ox(1) 1.944(8) Fe(2)–Ox(1) 1.882(9) Fe(3)–Ox(1) 1.855(8)Fe(1)–O(2) 1.914(10) Fe(2)–O(1) 1.982(9) Fe(3)–O(42) 1.977(11)Fe(1)–O(21) 1.999(10) Fe(2)–O(12) 2.004(11) Fe(3)–O(22) 1.983(11)Fe(1)–O(31) 2.013(12) Fe(2)–O(41) 2.012(10) Fe(3)–O(32) 2.006(10)Fe(1)–O(11) 2.020(12) Fe(2)–O(51) 2.017(11) Fe(3)–O(52) 2.029(10)Fe(1)–N(1) 2.133(11) Fe(2)–Om(1) 2.070(10) Fe(3)–Om(2) 2.110(9)Fe(1)...Fe(2) 3.254(2) Fe(1)...Fe(3) 3.327(2) Fe(2)...Fe(3) 3.251(2)Bond anglesFe(1)–Ox(1)–Fe(2) 116.5(4) Fe(2)–Ox(1)–Fe(3) 120.9(2) Fe(3)–Ox(1)–Fe(1) 122.3(4)Molecule 1bBond distancesFe(4)–Ox(2) 1.932(9) Fe(5)–Ox(2) 1.877(9) Fe(6)–Ox(2) 1.868(9)Fe(4)–O(62) 1.930(10) Fe(5)–O(61) 1.982(10) Fe(6)–O(82) 1.998(10)Fe(4)–O(81) 1.990(11) Fe(5)–O(111) 2.008(10) Fe(6)–O(92) 2.006(12)Fe(4)–O(71) 2.012(11) Fe(5)–O(72) 2.009(9) Fe(6)–O(102) 2.011(12)Fe(4)–O(91) 2.052(11) Fe(5)–O(101) 2.045(12) Fe(6)–O(112) 2.028(11)Fe(4)–N(61) 2.145(13) Fe(5)–Om(3) 2.099(10) Fe(6)–Om(4) 2.103(10)Fe(4)...Fe(5) 3.222(2) Fe(4)...Fe(6) 3.317(2) Fe(5)...Fe(6) 3.284(2)Bond anglesFe(4)–Ox(2)–Fe(5) 115.5(4) Fe(5)–Ox(2)–Fe(6) 122.5(4) Fe(6)–Ox(2)–Fe(4) 121.5(5)