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

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712 C.P. Raptopoulou et al. / Polyhedron 24 (2005) 711–721and phenolate groups as chelating and/or bridging units,along with their ability to act in their mono- or di-anionicform, make them interesting candidates for theexploration of their metal coordination chemistry [9].In their mono-anionic form, phenolic oximes usuallyact as chelating agents through their oximatenitrogen and phenolate oxygen atoms (mode A inthe following scheme) in a variety of mono- andpoly-nuclear metal complexes [10–14]. A more interestingcoordination mode, includes the use of the phenolateoxygen atom as both chelating and bridging agent(mode B) [10,15].In their di-anionic form, phenolic oximes usually usetheir phenolate oxygen and oximate nitrogen atoms tochelate to one metal ion and their oximate oxygen asbridging unit to bind a second metal (mode C). A varietyof di- [16–18], tri- [14,19] and tetranuclear [20–22] metalcomplexes presenting the l 2 :g 1 :g 1 :g 1 coordinationmode have been reported. The oximate oxygen atomcan also bind two metal ions, presenting thel 3 :g 1 :g 2 :g 1 coordination mode (mode D) giving rise tohigher nuclearity complexes, such as hexanuclear[23,24], although this coordination mode is also observedin trinuclear [25] and tetranuclear [11] complexes.There is also one example [10] where the dianion of phenolicoximes can act as chelating tridentate ligandaccording to mode E.ACH=N-OHOOCMCH=N-OMMCH=N-OHOMBODMCH=N-OMMMiron(III) salicylaldoximato complex is the tetranuclear[11] cluster [{Fe(Hsalox)(salox)} 4 ], in which the fourHsalox act as chelating agents through their phenolateoxygen and oximate nitrogen atoms (mode A), whilstthe four salox 2 further use their oximate oxygen atomto bind to two additional metal centers (mode D). In theremaining examples, coligands have been used to completethe coordination spheres of iron(III) centers inpolynuclear complexes. In the dinuclear compound[(Me 3 tacn)Fe(III)(salox) 3 Fe(III)] [16], as well as in thetetranuclear compound [(Me 3 tacn) 2 Fe 4 (salox) 2 (l 3 -O) 2(l 2 -CH 3 CO 2 ) 3 ](ClO 4 ) [20] (where Me 3 tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane)the dianion ofsalicylaldoxime adopts the l 2 :g 1 :g 1 :g 1 coordinationmode. The only trinuclear iron(III) salicylaldoximatocomplex known so far is [(C 2 H 5 ) 3 NH][Fe 3 O(Hsalox)(salox)2 (salmp)] [19] (salmp = 2-(bis(salicylideneamino)-methyl)phenol, a new ligand formed during thereaction process), where the Hsalox ligands act as chelatingunits and the salox 2 ligands adopt thel 2 :g 1 :g 1 :g 1 coordination mode.The aim of our project is to explore the use of salicylaldoximein iron(III) carboxylate chemistry, encouragedby our previous results on manganese(III) [24]. Herein,we report the first results of our project, in particularthe synthesis, X-ray crystal structure, spectroscopic (solidstate and frozen solutions EPR, Mössbauer) characterizationand magnetic behavior of two neutraltrinuclear oxo-centered iron(III) complexes, [Fe 3 (l 3 -O)-(O 2 CPh) 5 (salox)L 1 L 2 ](L 1 =L 2 = MeOH (1), L 1 = EtOH,L 2 =H 2 O(2)). The reported complexes are the first examplesof trinuclear carboxylato iron(III) complexes withsalicylaldoxime, and can be considered as precursorsfor the synthesis of higher nuclearity complexes, basedon the principle of using Ômetal oximatesÕ as ÔbuildingblocksÕ for polynuclear clusters. In both compounds,the salox 2 ligands adopt the l 2 :g 1 :g 1 :g 1 coordinationmode (mode C) thus, the possibility of further usingthe oximate oxygen atom, under certain reaction conditions,to bind to a second metal is left open.2. ExperimentalCH=NO2.1. Compound preparationsOEMAll manipulations were performed under aerobic conditionsusing materials as received (Aldrich Co). Allchemicals and solvents were of reagent grade.Further restricting our discussion to polynucleariron(III) complexes with the simplest member of thephenolic oximes, 2-hydroxy-benzaldehyde (salicylaldoxime,H 2 salox), only a few examples have beenreported. As far as we know, the only example of2.1.1. [Fe 3 (l 3 -O)(O 2 CPh) 5 (salox)(MeOH) 2 ] Æ1.25MeOH Æ 1.05H 2 O(1)A methanolic solution of H 2 salox (0.069 g,0.50 mmol) was stirred under reflux, until sodium benzoate(0.216 g, 1.50 mmol) was added. The refluxcontinued for 30 min and then Fe(NO 3 ) 3 Æ 9H 2 O
C.P. Raptopoulou et al. / Polyhedron 24 (2005) 711–721 713(0.202 g, 0.50 mmol) was added. The color of the solutionimmediately turned to deep brown. After 24 h of reflux,small amounts of a brown-red solid were filtered,washed with MeOH and identified as compound 1 byFT-IR spectroscopy. The brown filtrate was sealed andafter a period of one week X-ray quality brownish-redcrystals of 1 were formed (Yield: 0.34 g, 70%). Thecrystals of 1 were collected by filtration, washed withcold MeOH and dried in vacuo. The resulting powderanalyzed as solvent-free. Anal. Calc. for (1) (C 44 H 38 -NO 15 Fe 3 ): C, 53.47; H, 3.88; N, 1.42. Found: C, 53.45;H, 3.86; N, 1.40%.2.1.2. [Fe 3 (l 3 -O)(O 2 CPh) 5 (salox)(EtOH)(H 2 O)] ÆEtOH (2)The procedure followed was the same as describedabove, but FeCl 3 Æ 6(H 2 O) and ethanol were used instead(Yield: 0.35 g, 70%). The powder of 2 analyzed as solvent-free.Anal. Calc. for (2)(C 44 H 38 NO 15 Fe 3 ): C, 53.47;H, 3.88; N, 1.42. Found: C, 53.45; H, 3.87; N, 1.39%.Table 1Crystallographic data for complex 1 Æ 1.25MeOH Æ 1.05H 2 OFormula C 45.25 H 46.1 Fe 3 NO 17.3Formula weight 1048.30Space group P2 1 /cUnit cell dimensionsa (Å) 19.67(2)b (Å) 26.96(2)c (Å) 19.70(2)b (°) 98.84(3)V (Å 3 ) 10323(2)Z 8T (°C) 298RadiationMo Kaq calcd (g/cm 3 ) 1.348l (mm 1 ) 0.899aR 1 0.0775awR 2 0.1994R 1 = P (jF o j jF c j)/ P (jF o j)andwR 2 ¼ P ½wðF 2 o F 2 o Þ2 Š= P ½wðF 2 o Þ2 Šfor 5082 reflections with I >2r(I).a w ¼ 1=½r 2 ðF 2 o ÞþðaPÞ2 þ bPŠ and P ¼ððmax F 2 o ; 0Þþ2F 2 c Þ=3;a = 0.1046, b = 86.0886.1=22.2. General and physical measurementsElemental analysis for carbon, hydrogen, and nitrogenwas performed on a Perkin Elmer 2400/II automaticanalyzer. Infrared spectra were recorded as KBr pelletsin the range 4000–500 cm 1 on a Bruker Equinox 55/SFT-IR spectrophotometer. EPR spectra were recordedon a Bruker ER 200D-SRC X-band spectrometerequipped with an Oxford ESR 9 cryostat in 4.2–300 Ktemperature range. Variable temperature magnetic susceptibilitymeasurements were carried out on polycrystallinesamples of 1 and 2 in the 2.0–300 K temperaturerange using a Quantum Design MPMS SQUID susceptometerunder a magnetic field of 1000 G. Magnetizationmeasurements were carried out at 2.5 K over the 0–5 Tmagnetic field range. Diamagnetic corrections for thecomplexes were estimated from PascalÕs constants.Mössbauer spectra were taken with a constant accelerationspectrometer using a 57 Co (Rh) source at RT and avariable temperature Oxford cryostat.2.2.1. X-ray crystallography and solution of structuresBrownish-red prismatic crystals of 1 (0.05 · 0.25 ·0.75 mm) and 2 (0.05 · 0.15 · 0.25 mm) were mountedin capillary with drops of mother liquid. Diffraction measurementswere made on a Crystal Logic Dual Goniometerdiffractometer using graphite monochromated Moradiation. Important crystal data and parameters fordata collection for 1 are reported in Table 1. Unit celldimensions were determined and refined by using theangular settings of 25 automatically centered reflectionsin the range 11°
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