Sodium-centered dodecanuclear Co (II) and Ni (II) complexes with 2-(phosphonomethylamino) succinic acid: Studies of spectroscopic, structural, and magnetic properties


Two new isostructural cobalt(II) and nickel(II) polynuclear complexes with 2-(phosphonomethyl)aminosuccinic acid, H4PMAS, namely, Na[Co12(PMAS)6(H2O)17(OH)]·x2H2O, 1·x2H2O, and Na[Ni12(PMAS)6(H2O)17(OH)]·xH2O, 2·xH2O, have been synthesized for the first time from aqueous solutions and studied by single crystal X-ray diffraction, infrared, and UV"“visible diffuse reflectance spectroscopy; TG/DTA analysis; and magnetochemistry. Both 1 and 2 crystallize in the rhombohedral crystal system with the R3Ì… space group with 1/6 of the Co12(PMAS)6 or Ni12(PMAS)6 moieties in the asymmetric unit. The X-ray refinements reveal the presence of 18 water sites, but unit cell charge balance requires that one water molecule must be an OH"“ anion, an anion which is disordered over the 18 sites. The PMAS4"“ ligand forms two five-membered and one six-membered chelation ring. Both 1 and 2 contain 24-membered metallacycles as a result of the bridging nature of the PMAS4"“ ligands. The resulting three-dimensional structures have one-dimensional channels with a sodium cation at the center of symmetry. The temperature dependence of the magnetic susceptibility reveals the presence of weak antiferromagnetic exchange coupling interactions in both 1 and 2. Two exchange coupling constants, J1 = −15.3(7) cm"“1 and J2 = −1.06(2) cm"“1 with S1 = S2 = 3/2 for the Co(1)···Co(1) and Co(1)···Co(2) exchange pathways, respectively, are required for 1, and J1 = −1.17(6) cm"“1 and J2 = −4.00(8) cm"“1 with S1 = S2 = 1 for the Ni(1)···Ni(1) and Ni(1)···Ni(2) exchange pathways, respectively, are required for 2, in order to fit the temperature dependence of the observed magnetic susceptibilities.



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Inorganic chemistry