Gd3+ Complexes as Potential Spin Labels for High Field Pulsed EPR Distance Measurements

Pulse electron−electron double resonance distance measurements between two high spin Gd3+ ions in a novel bis-Gd3+ complex involving two pyridine-based gadolinium tetracarboxylate systems linked by a rigid aryl−alkyne unit were carried out at Ka- and W-band frequencies. The experimental distance found was 2.02 ± 0.02 nm, and it was further compared with the Gd3+−Gd3+ distance (2.2126 nm) determined by density functional theory.