Nitro group and K-based secondary building units for the self-assembly of 3D coordination polymers built on dinuclear dianionic helicate connectors

Two 3D coordination polymers based on dinuclear dianionic helicates, K 2 [M II 2 (L) 3 ] M = Mn II ( 1 ) and Ni II ( 2 ), were obtained by slow liquid-liquid diffusion of solutions of 2-hydroxy-5-nitrobenzaldehyde, 4,4′-methylenedianiline, KO t Bu and the metal salt at room temperature. The resulting dianionic triply stranded helicates self-assemble into novel 3D coordination polymers, in which the helicate units act as connectors. The assembly is promoted by the phenolate bridging ability and the coordination of the pre-organized NO 2 groups to K-(O-N-O) 4 -K nodes, resulting in robust paramagnetic materials. SC-XRD shows that the metal centers are located 11.257(2) and 11.264(1) Å apart. The Mn-L bond lengths correspond to the high-spin (HS, S = 5/2) state for 1 . The magnetic behavior for both complexes shows weak magnetic exchange, as expected due to the spin carrier separation, and the confirmation of the HS-sate for the Mn II centers. For complex 1 , an antiferromagnetic exchange is detected, whereas for complex 2 , a mixture of intramolecular antiferromagnetic and intermolecular ferromagnetic exchanges are detected. Thus, we demonstrated that nitro groups can be used for the stabilization of anionic complexes because coordination to K + results in stable intricate architectures. Two dinuclear dianionic helicates, K 2 [M II 2 (L) 3 ] M = Mn II ( 1 ) and Ni II ( 2 ), based on 2-hydroxy-5-nitrobenzaldehyde, self-assemble into novel 3D coordination polymers due to nitro groups acting as secondary assembly instruction.