Binuclear Co(ii)Co(ii), Co(ii)Co(iii) and Co(iii)Co(iii) complexes of “short” salen homologues derived from the condensation of salicylaldehyde and methanediamine or phenylmethanediamines. Synthesis, structures and magnetismElectronic supplementary information (ESI) available: Appendix, derivation of the expression for the average magnetic susceptibility of a Co(ii)Co(ii) dimer. See http://www.rsc.org/suppdata/dt/b1/b105594c/