An unusual alternating ferro- and antiferromagnetic 1D hydrogen-bonded µ2-1,3-azide-bridged copper(II) complex: a dominant ferromagnetic couplingElectronic supplementary information (ESI) available: EPR spectra of 1 (Fig. S1) and fit of χMT data with the binuclear model (Fig. S2). See http://www.rsc.org/suppdata/nj/b1/b108511p/