Blocking electrochemistry, a subfield of nanochemistry, enables nondestructive, in situ measurement of the concentration, size, and size heterogeneity of highly dilute, nanometer-scale materials. This approach, in which the adsorptive impact of individual particles on a microelectrode prevents charge exchange with a freely diffusing electroactive redox mediator, has expanded the scope of electrochemistry to the study of redox-inert materials. A limitation, however, remains: inhomogeneous current fluxes associated with enhanced mass transfer occurring at the edges of planar microelectrodes confound the relationship between the size of the impacting particle and the signal it generates. These "edge effects" lead to the overestimation of size heterogeneity and, thus, poor sample characterization. In response, we demonstrate here the ability of catalytic current amplification (EC′) to reduce this problem, an effect we term "electrocatalytic interruption". Specifically, we show that the increase in mass transport produced by a coupled chemical reaction significantly mitigates edge effects, returning estimated particle size distributions much closer to those observed using ex situ electron microscopy. In parallel, electrocatalytic interruption enhances the signal observed from individual particles, enabling the detection of particles significantly smaller than is possible via conventional blocking electrochemistry. Finite element simulations indicate that the rapid chemical kinetics created by this approach contributes to the amplification of the electronic signal to restore analytical precision and reliably detect and characterize the heterogeneity of nanoscale electro-inactive materials.

Reaction of FeBr 2 with Li(NC t Bu 2 ) (0.5 equiv) and Zn 0 (2 equiv) results in the formation of the formally mixedvalent cluster [Fe 4 Br 2 (NC t Bu 2 ) 4 ] (1) in moderate yield. The subsequent reaction of 1 with Na(NC t Bu 2 ) results in formation of [Fe 4 Br(NC t Bu 2 ) 5 ] (2), also in moderate yield. Both 1 and 2 were characterized by zero-field 57 Fe Mossbauer spectroscopy, X-ray crystallography, and superconducting quantum interference device magnetometry. Their tetrahedral [Fe 4 ] 6+ cores feature short Fe− Fe interactions (ca. 2.50 Å). Additionally, both 1 and 2 display S = 7 ground states at room temperature and slow magnetic relaxation with zero-field relaxation barriers of U eff = 14.7(4) and 15.6(7) cm −1 , respectively. Moreover, AC magnetic susceptibility measurements were well modeled by assuming an Orbach relaxation process.

Reaction of Fe(acac) 3 with 3 equiv of Li[N�C(R)Ph] (R = Ph, t Bu) results in the formation of the [Fe 2 ] 6+ complexes, [Fe 2 (μ-N�C(R)Ph) 2 (N�C(R)Ph) 4 ] (R = Ph, 1; t Bu, 2), in low to moderate yields. Reaction of FeCl 2 with 6 equiv of Li(N�C 13 H 8 ) (HN�C 13 H 8 = 9-fluorenone imine) results in the formation of [Li(THF) 2 ] 2 [Fe(N� C 13 H 8 ) 4 ] (3) in good yield. Subsequent oxidation of 3 with ca. 0.8 equiv of I 2 generates the [Fe 2 ] 6+ complex, [Fe 2 (μ-N�C 13 H 8 ) 2 (N�C 13 H 8 ) 4 ] (4), along with free fluorenyl ketazine. Complexes 1, 2, and 4 were characterized by 1 H NMR spectroscopy, X-ray crystallography, 57 Fe Mossbauer spectroscopy, and SQUID magnetometry. The Fe−Fe distances in 1, 2, and 4 range from 2.803(7) to 2.925(1) Å, indicating that no direct Fe−Fe interaction is present in these complexes. The 57 Fe Mossbauer spectra for complexes 1, 2, and 4 are all consistent with the presence of symmetry-equivalent high-spin Fe 3+ centers. Finally, all three complexes exhibit a similar degree of antiferromagnetic coupling between the metal centers (J = −26 to −30 cm −1 ), as ascertained by SQUID magnetometry.