Synthesis. All manipulations were carried out using standard Schlenk line and glove box techniques under dry argon. Solvents were passed through columns containing alumina or were dried by refluxing over K, and were stored over K mirrors or 4 Å molecular sieves (THF) and degassed before use. For NMR spectroscopy C6D6 was dried by refluxing over K, degassed by three freeze-pump-thaw cycles, and vacuum-transferred before use. Anhydrous LnCl3 were purchased from Alfa Aesar and were used as received. KCp tt was synthesised by literature methods, whilst 1-Ln were prepared by modification of literature procedures. General synthetic procedures for 1-Ln are given below; full details can be found in the Supporting Information. 1 H (400 and 500 MHz) and C{ 1 H} (100 and 125 MHz) NMR spectra were obtained on Avance III 400 or 500 MHz spectrometers at 298 K. 1 H NMR spectra were measured from 0 to +10 ppm for diamagnetic 1-La and from -200 to +200 ppm for paramagnetic 1-Ce, 1-Nd and 1-Sm. ATR-IR spectra were recorded as microcrystalline powders using a Bruker Tensor 27 spectrometer. Elemental analyses were performed by Mrs Anne Davies and Mr Martin Jennings at The University of Manchester School of Chemistry Microanalysis Service, Manchester, UK. UV/vis/NIR spectroscopy was performed on samples in Youngs tap-appended 10 mm path length quartz cuvettes on an Agilent Technologies Cary Series UV/vis/NIR spectrophotometer at 175-3300 nm. CW EPR measurements were carried out on a Bruker EMX300 spectrometer; pulsed EPR X-band studies were performed on a Bruker ElexSys E580 spectrometer. The primary Hahn-echo sequence (/2----echo) was used for the two-pulse electron spin echo measurements, with initial /2 and  pulse of 16 and 32 ns, respectively. For the relaxation time measurements, Tm studies were made by incrementing the  time in the Hahn-echo sequence (longer pulses were used to suppress the 1 H modularion), T1 was measured by the inversion recovery sequence (-t-/2----echo) /2 and  pulse of 16 and 32 ns, respectively, with a fixed  = 300 ns. HYSCORE measurements were performed using the four-pulse sequence (/2--/2-t1--t2-/2-echo), /2 and  pulse of 16 and 32 ns, respectively, initial times t1,2 = 0.1 s and  values of 136 and 200 ns.