FeC10(HgO2CCF3) (X = O TFA ) Single crystals of the THT-complex 2b ‧24 MeCN were obtained upon recrystallization from acetonitrile at -30 °C. It crystallized in the space group C2/c. The asymmetric unit contains a {Fe(C5Hg5THT5)} fragment with the iron position located at a center of inversion. The Cp ligands are aligned in a staggered conformation with torsion angles between 30.3(4)-34.1(4) ° (Fig. ). Again, the mercury atoms are linearly coordinated by a cyclopentadienyl and a THT ligand. In contrast to the structure of 1 no mercury anion contacts are visible (Fig. ). Instead, the decacationic fragment [FeC10(HgTHT)10] 10+ is fully solvated by 20 acetonitrile molecules. Ten of those are coordinating systematically two to three different mercury atoms from the space within both Cp rings and the other ten from the outer-sphere of the metallocene framework yielding a distorted octahedral geometry for all mercury atoms. The Hg-N distances are in range of 2.941(8)-3.289(8) Å. The interactions between cations and anions are mainly a consequence of hydrogen bonding to the solvent as well as the THT ligand.