A new N,N,O chelate for transition metal chemistry:: Fe5 and Fe6 clusters from the use of 6-hydroxymethyl-2,2′-bipyridine (hmbpH)

The initial use of the anion of 6-hydroxymethyl-2,2'-bipyridine (hmbpH) as a chelate in coordination chemistry is described. The syntheses, crystal structures, and magnetochemical characterization are reported of four new iron(III) clusters [Fe5O2(OH)(O2CMe)(5)(hmbp)(3)](ClO4)(2) (1) and [Fe6O2(OH)(2)(O2CR)(6)(hmbp)(4)](NO3)(2) (R = Ph (2), Me (3), Bu-t (4); hmbpH = 6-hydroxymethyl-2,2'-bipyridine). The reaction of Fe(ClO4)(3), hmbpH, and sodium acetate in a 1:1:similar to 4 ratio in EtOH gave 1, and the reaction between [Fe3O(O2CR)(6)(H2O)(3)](NO3) (R = Ph, Me, Bu-t) and hmbpH in a 1:1 ratio in MeCN gave 2-4, respectively. The core of 1 consists of a [Fe-4(mu(3)-O)(2)](8+) butterfly unit to which is attached a fifth Fe atom by bridging O atoms. The core of 2-4 also consists of a [Fe-4(mu(3)-O)(2)](8+) butterfly unit to which are attached an Fe atom on either side by bridging O atoms. Variable-temperature (T) and -field (H) solid-state DC and AC magnetization (M) studies were carried out on complexes 1-4 in the 5.0-300 K range. Fitting of the data revealed that 1 has an S = 5/2 ground state spin whereas 2-4 possess an S = 5 ground state. Fitting of the M/N mu(B) vs H/T data by matrix diagonalization and including only axial zero-field splitting (ZFS) gave values of the axial ZFS parameter vertical bar D vertical bar of 0.75, 0.36, 0.46, and 0.36 cm(-1) for 1-4, respectively.