Fig. 2. Observed NRVS spectra for [1′]⁺ (thick red lines, (a) and (b)) and 1′ (thick blue lines, (a) and (c)) vs. DFT calculated ⁵⁷Fe PVDOS spectra for [1′]⁺ (thin red line, (b)) and 1′ (thin blue line, (c)). Calculated Fe–Ni KED (green) is given in (b) for [1′]⁺, and in (c) for 1′. Key bands observed for 1′ are labelled in (a), with DFT counterparts in (c) indicated by vertical lines. Modes giving rise to bands with significant Fe–Ni character are marked (*) and shown in Fig. 3 and Fig. S10 (ESI†). For 0–650 cm^–1 spectra, see Fig. S9 (ESI†).