2-D soft ferromagnet based on [WV(CN)8]3– and CuII with a Tc of 34 KElectronic supplementary information (ESI) available: structure of [Cu(tetren)]2+ in 1 and (NC)7W–CN–Cu(NC)4 structural motif of 2; table and figures of IR spectra of 1, 2, tetren·5HCl and free tetren. See http://www.rsc.org/suppdata/cc/b2/b202810g/

Self-assembly of [Cu(tetren)]2+ (tetren = tetraethylenepentamine) and [W(CN)8]3- in acidic aqueous solution yields the double-layered square grid cyanide-bridged polymer of ((tetrenH5)0.8CuII4[Wv(CN)8](4).7.2H2O)n with Cu(II) centres of square pyramidal geometry coordinatively saturated solely by CN bridges supplied by five [W(CN)8]3- ions; it exhibits soft ferromagnetic behaviour with an ordering temperature Tc of 34 K.