Tuning three coordination polymers with dinuclear metal units via pH control: syntheses, structures, and magnetic properties

The self-assembly of three coordination polymers with dinuclear metal units, namely {[Co2(bpta)(phen)2]·2H2O}n (1), {[Co2(bpta)(phen)(H2O)]·4H2O·CH3CN}n (2), and {[Ni2(bpta)(phen)(H2O)]·2H2O·0.5CH3CN}n (3), has been tuned via the control of pH under solvothermal conditions. The structures are characterized by FTIR spectroscopy, elemental analysis, single-crystal X-ray diffraction and powder X-ray diffraction analysis. The H4bpta ligands exhibit μ6-κ2:κ1:κ2:κ1 and μ7-κ2:κ2:κ1:κ2 coordination modes in the complexes 1–3. The octahedral metal ions are connected by carboxylate and μ2-O bridges to form [Co2(μ-OCO)2] and [M2(μ-OCO)2(μ2-O)] SBUs, respectively. Complex 1 shows a 2D framework with {44.62} sql-net topology. Complexes 2 and 3 display 3D networks with {42.84} pts-net topology. Magnetic studies reveal that 1 and 2 exhibit weak antiferromagnetic interactions in the double- and triple-bridged dimeric cobalt(II) units (J ​= ​−0.53(6) cm−1 for 1, and −E2/k ​= ​−0.77 ​K for 2, respectively). Complex 3 shows a ferromagnetic interaction (J ​= ​2.44(1) cm−1) between two dimeric Ni(II) ions.