A two-step field-induced magnetic transition in a novel layered cobalt diphosphonateElectronic supplementary information (ESI) available: experimental details and Figures S1–S10. See http://www.rsc.org/suppdata/cc/b2/b212674e/

Compound Na6Co7(hedp)2(hedpH)4(H2O)4 x 8H2O (hedp = 1-hydroxyethylidenediphosphonate) with a novel layer structure is reported in this paper. The layer maybe viewed as made up from two types of chains each of composition Co3(hedp)2 and Co2(hedpH)2. Magnetic measurements at 1.8 K reveal a metamagnetic transition at ca. 6.5 kOe, followed by a second transition to a ferromagnetic state at ca. 30 kOe.