AsMo7O27-Bridged Dinuclear Sandwich-Type Heteropolymolybdates of Cr(III) and Fe(III): Magnetism of [MM′(AsMo7O27)2]12− with MM′ = FeFe, CrFe, and CrCr
journal contributionposted on 02.11.2009 by Haisheng Xu, Lili Li, Bin Liu, Ganglin Xue, Huaiming Hu, Feng Fu, Jiwu Wang
Any type of content formally published in an academic journal, usually following a peer-review process.
Two new dinuclear sandwich-type heteropolymolybdates based on the mulitidendate inorganic fragment [AsMo7O27] and Cr(III) and Fe(III) ions, namely, the homometallic sandwich polyoxometalate (POM) (NH4)12[Fe2(AsMo7O27)2]·12H2O (1) and the first example of the “symmetrical” heterometallic Cr(III)−Fe(III) sandwich POM, (NH4)12[FeCr(AsMo7O27)2]·13H2O (2), were simultaneously synthesized in high yield. Their magnetic properties are thoroughly investigated together with the homometallic sandwich POM (NH4)12[Cr2(AsMo7O27)2]·11H2O (3). The χMT values for compounds 1−3 at 300 K correspond well to the calculated spin-only values for FeIII (S = 5/2) and CrIII (S = 3/2) with gFe = gCr = 2. Upon cooling, the χMT values decline monotonously and reach 0.14, 1.00, and 0.11 cm3 K mol−1 at 2.0 K for 1, 2, and 3, respectively, indicating a significant antiferromagnetic exchange between the magnetic centers with J = −2.09, −4.09, and −6.26 cm−1, respectively, for 1, 2, and 3. The magnetic results clearly establish that compound 2 is formed by bimetallic Cr(III)−Fe(III) units and not by a mixture of the two antiferromagnetically coupled homometallic species. Their thermal properties are also characterized.