Sodium-Centered Dodecanuclear Co(II) and Ni(II) Complexes with 2‐(Phosphonomethylamino)succinic Acid: Studies of Spectroscopic, Structural, and Magnetic Properties

ABSTRACT: Two new isostructural cobalt(II) and nickel(II) polynuclear
complexes with 2-(phosphonomethyl)aminosuccinic acid, H4PMAS, namely,
N a [ C o 1 2 ( P M A S ) 6 ( H 2 O ) 1 7 ( O H ) ] · x 2 H 2 O , 1 · x 2 H 2 O , a n d N a -
[Ni12(PMAS)6(H2O)17(OH)]·xH2O, 2·xH2O, have been synthesized for the
fi
rst 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 R3̅space 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-dimen-
sional 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.