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Malonate-Containing Manganese(III) Complexes:  Synthesis, Crystal Structure, and Magnetic Properties of AsPh4[Mn(mal)2(H2O)2]

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journal contribution
posted on 2006-02-06, 00:00 authored by Fernando S. Delgado, Nicolas Kerbellec, Catalina Ruiz-Pérez, Joan Cano, Francesc Lloret, Miguel Julve
The novel manganese(III) complexes PPh4[Mn(mal)2(H2O)2] (1) and AsPh4[Mn(mal)2(H2O)2] (2) (PPh4+ = tetraphenylphosphonium cation, AsPh4+ = tetraphenylarsonium cation, and H2mal = malonic acid) have been prepared, and the structure of 2 was determined by X-ray diffraction analysis. 2 is a mononuclear complex whose structure is made up of trans-diaquabis(malonato)manganate(III) units and tetraphenylarsonium cations. Two crystallographically independent manganese(III) ions (Mn(1) and Mn(2)) occur in 2 that exhibit elongated octahedral surroundings with four oxygen atoms from two bidentate malonate groups in equatorial positions (Mn(1)−O = 1.923(6) and 1.9328(6) Å and Mn(2)−O = 1.894(6) and 1.925(6) Å) and two trans-coordinated water molecules in the axial sites (Mn(1)−Ow = 2.245(6) Å and Mn(2)−Ow = 2.268(6) Å). The [Mn(mal)2(H2O)2]- units are linked through hydrogen bonds involving the free malonate−oxygen atoms and the coordinated water molecules to yield a quasi-square-type anionic layer growing in the ab plane. The shortest intralayer metal−metal separations are 7.1557(7) and 7.1526(7) Å (through the edges of the square). The anionic sheets are separated from each other by layers of AsPh4+ where sextuple- and double-phenyl embraces occur. The magnetic behavior of 1 and 2 in the temperature range 1.9−290 K reveals the occurrence of weak intralayer ferromagnetic interactions (J = +0.081(1) (1) and +0.072(2) cm-1 (2)). These values are compared to those of the weak antiferromagnetic coupling [J = −0.19(1) cm-1], which is observed in the chain compound K2[Mn(mal)2(MeOH)2][Mn(mal)2] (3), where the exchange pathway involves the carboxyate−malonate bridge in the anti−syn conformation. The structure of 3 was reported elsewhere. Theoretical calculations on fragment models of 2 and 3 were performed to analyze and substantiate both the nature and magnitude of the magnetic couplings observed.