Substituent dependent topologies in cobalt isophthalate coordination polymers with bis(pyridylmethyl)piperazine coligands

► Hydroxy substituent enforces (4,4) rhomboid grid layer with {Co2(OCO)2} dimers. ► Methoxy substituent enforces rarer triangular (3,6) grid layer with {Co2(OCO)2} dimers. ► Nitro substituent with isomeric dipyridyl ligand produces 1D cationic chain topology. ► {Co2(OCO)2} dimers show cooperative single-ion effects and weak ferromagnetism.