Bulk Spontaneous Magnetization in the New Radical Cation Salt TM-TTF[Cr(NCS)<sub>4</sub>(isoquinoline)<sub>2</sub>] (TM-TTF = Tetramethyltetrathiafulvalene)

A new organic−inorganic hybrid salt [TM-TTF][Cr(NCS)<sub>4</sub>(isoquinoline)<sub>2</sub>] (<b>1</b>) (TM-TTF = Tetramethyltetrathiafulvalene) has been synthesized. Compound <b>1</b> crystallizes in the triclinic <i>P</i>1̄ space group with <i>a</i> = 8.269(1), <i>b</i> = 10.211(2), and <i>c</i> = 11.176(2) Å, α = 89.244(9), β = 88.114(6), and γ = 74.277(7)°, <i>V</i> = 907.6(3) Å<sup>3</sup>, and <i>Z</i> = 1. The crystal structure was resolved in the temperature range between 223 and 123 K, showing that changes in the crystal structure at low temperature result in stronger interactions between anions and cations. The packing of <b>1</b> consists of mixed anion−cation layers in the <i>bc</i> plane containing S···S and π−π anion−cation interactions, the layers being connected by very short S···S contacts between anions and cations. Magnetic measurements in a small external field show bulk spontaneous magnetization with a <i>T</i><sub>c</sub> of 6.6 K consistent with the presence of weakly coupled ferrimagnetic order in compound <b>1</b>. The EPR measurements also demonstrate the interaction between the d and π electrons and the presence of an internal magnetic field brought about by the magnetic ordering.