Salicylaldoxime (H2salox) in iron(III) carboxylate chemistry ...

714 C.P. Raptopoulou et al. / Polyhedron 24 (2005) 711–721and of very poor diffraction quality. Repeated efforts togrow larger crystals proved unsuccessful. We continuedwith data collection in order to establish the gross structureof the complex. Since the structure of 2 proved quitesimilar to that of 1, we felt that complete structural characterizationwas not crucial. Thus, the refinement wasdone with anisotropic thermal parameters for the iron(III)ions only, whilst all the rest atoms were refined isotropically.No H-atoms were included in the refinement.The phenyl rings 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 investigatethe use of salicylaldehyde oxime (H 2 salox) to theiron(III) carboxylate chemistry, extending our previousexperience on manganese [24]. The 1:1 molar ratioreaction of Mn(O 2 CR) 2 (R = Me, Ph) and H 2 salox inEtOH led to the hexanuclear complexes [Mn 6 O 2(O 2 CR) 2 (salox) 6 (EtOH) 4 ] (R = Me, Ph). These complexescontain the novel ½Mn III 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 assingle molecule magnets (SMM) and are the firstmembers of a new class of manganese-based SMMscontaining exclusively Mn III ions with blocking temperaturegreater than 2 K. In order to investigate thepossibility of synthesizing the corresponding polynucleariron(III) complexes and to study their magneticproperties, we have designed the 1:3:1 molarratio reaction of Fe 3+ /PhCO 2/H 2 salox in alcoholicmedia. The 1:3:1 molar ratio has been chosen so thatthe M/carboxylate/H 2 salox ratio remains the same ingoing from manganese(II) to iron(III) ions. But itturned out that in the iron(III) case, the amount ofthe carboxylate ions was very high, and the trinuclearoxo-centered complexes 1 and 2 were formed. The salox2 ions are coordinated 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 increase the nuclearity of the derived complexhas failed. Nevertheless, we still consider compounds 1and 2 as useful staring materials for polynucleariron(III) complexes, under different reactionconditions.The synthesis of 1 and 2 can be summarized inEqs. (1) and (2), respectively, based on the reasonableassumption that H 2 O from the starting 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-intensitybands 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 intensitybands at 1598 cm 1 and medium intensity bands at1286 cm 1 observed in 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 2coincide in the spectra of 1(1406 cm 1 ), and 2 (1405 cm 1 ). The bands at1557 cm 1 in 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 bridging modes of benzoate ligation [29].A strong intensity band at 480 cm 1 in the spectra of 1and at 478 cm 1 in the spectra of 2 is characteristic ofthe presence of the [Fe 3 O] moiety in 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 in the monoclinic spacegroup P2 1 /c with two crystallographically independenttrinuclear complexes in the asymmetric unit (further reportedas molecules 1a and 1b). The structure of themolecule 1a is given in Fig. 1. Selected bond distancesand angles for both 1a and 1b are listed in Table 2.The structure of 1 consists of a trinuclear iron(III)oxo-centered complex. The three Fe III ions in 1a forman isosceles triangle whilst in 1b the triangle is best describedas scalene (see Table 2). The Fe–O oxo bond distancesare in the range 1.86–1.94 Å in both molecules 1aand 1b, and the central [Fe 3 (l 3 -O)] 7+ moiety is planar.Ions Fe(2) and Fe(3) in molecule 1a and the correspondingions Fe(5) and Fe(6) in molecule 1b have an octahedraloxygen rich coordination environment, while ionsFe(1) and Fe(4) in molecules 1a and 1b, respectively,have a distorted octahedral O 5 N coordination geometry.The angles within 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 involving the axial positions of the