File Name : si_figure s 1.tiff Caption : simulated isotope patterns of the respective complexes 3, 4 and 5 generated by mestrenova. File Name : si_figure s 2.tiff Caption : measured isotope pattern of the product signal of complex 3 utilizing the feii complex 1 (left) and niii complex 2 (right) as starting material. File Name : si_figure s 3.tiff Caption : full ms spectra of complex 3 utilizing the feii complex 1 (left) and niii complex 2 (right) as starting material. File Name : si_figure s 4.tiff Caption : mass spectrum of the redistribution reaction with complex 4 and 5; predicted isotope patterns in blue and red, respectively. File Name : si_figure s 5.tif Caption : the vis-nir region of 1 measured in mecn (c = 10−3 m, 295 k) measured in n2 atmosphere and with exposure to air after 16 h and 3 d. File Name : si_figure s 6.tif Caption : ftir spectra of the complexes 1 and 3 in kbr at room temperature; bands for the acetate-group in complex 3 are marked by a blue star. File Name : si_figure s 7.tif Caption : pxrd of a crystalline sample of complex 1·meoh; the measured (blue), background-corrected (red), and simulated diffractogram based on the crystal structure (black, ccdc 2392032) are shown. File Name : si_figure s 8.tif Caption : the χm vs. t plot for the heterobinuclear complex 3 at 0.5 t. File Name : si_figure s 9.tif Caption : pairs of ‘magnetic orbitals’ for 3 derived from the corresponding orbital transformation of the broken-symmetry dft determinant. the s values correspond to the values of overlap integrals for the corresponding orbital pairs. File Name : si_figure s 10.tif Caption : sem image of single crystals obtained by slow evaporation from mecn/iproh (top left) and edx mapping of s, ni and fe; magnification 70x. File Name : si_figure s 11.tif Caption : sem image of single crystals obtained by slow evaporation from mecn/etoh (top left) and edx mapping of s, ni and fe; magnification 100x. File Name : si_figure s 12.tif Caption : representative edx spectra from different regions of two single crystals obtained by evaporation from mecn/etoh; magnification 100x in inset 1, 75x in inset 2 and 3.