Synthesis, crystal structure and magnetic properties of two oxalato-bridged dimetallic trinuclear complexes combined with a polar cation

摘要

Two isostructural heterometallic trinuclear oxalato-bridged complexes of formula C_4[MCr_2(ox)_6(H_2O) _2]·nH_2O (C~+ = 4-aminopyridinium; ox ~(2-) = oxalate dianion; M~(2+) = Mn~(2+), n = 3, 1; M~(2+) = Co~(2+), n = 3.25, 2) have been synthesized by using direct self-assembly methods combining C_3[Cr(ox)_3] and the chloride salts of the corresponding metal ion. The crystal structures of both compounds have been resolved by single-crystal X-ray diffraction. They crystallize in the C2/c space group [a = 11.5113(15) ?, b = 20.250(3) ?, c = 21.810(4) ?, β = 100.447(10)°, V = 5161.6(3) ?~3, and Z = 4 for 1, and a = 11.4334(16) ?, b = 20.243(2) ?, c = 21.805(3) ?, β = 101.113(9)°, V = 4951.9(11) ?~3, and Z = 4 for 2]. The structures of 1 and 2 consist of discrete linear [MCr_2(ox)_6]~(4-) bimetallic trinuclear units, pyridinium cations and crystallization water molecules. The linear trinuclear unit is built from a central trans-diaquametal(ii), linked to two Cr(ox)_3]~(3-) entities by oxalate bridges. One of the oxalate ions is coordinated to the central metal ion whereas the other two oxalate ligands are non-bridging. In the crystal, intermolecular hydrogen bonds involving oxalate ligands, water molecules and pyridinium cations, build a complex three-dimensional network. Variable-temperature magnetic susceptibility measurements for 1 and 2 indicate a weak ferromagnetic interaction (J = +1.16 and +2.62/+2.70 cm~(-1) for 1 and 2, respectively) between the two terminal Cr~(III) (S_(Cr) = 3/2) and the central high-spin Mn~(II) (S_(Mn) = 5/2) and Co~(II) (S_(Co) = 3/2) ions. The nature and the amplitude of the exchange interaction are rationalized using DFT calculations and orbital interpretations.