Three systems [Fe(III)(sal₂-trien)](TCNQ)_n·X (n = 1, 2, X = MeOH, CH₃CN, H₂O) showing spin-crossover transition, conductivity and ferromagnetic coupling were synthesized and studied by X-ray diffraction, Montgomery method for resistivity, SQUID magnetometry and X-band EPR. Spin-spin interactions between local magnetic moments of Fe(III) ions and electron spins of organic TCNQ network were discovered and discussed within the framework of intermolecular superexchange coupling.

Hybrid ion-pair crystals involving hexadentate [Fe(III)(3-OMesal₂-trien)]⁺ spin-crossover (SCO) cationic complexes and anionic gold complexes [Au(dmit)₂]⁻ (1) (dmit = 4,5-dithiolato-1,3-dithiole-2-thione) and [Au(dddt)₂]⁻ (2) (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate) were synthesized and studied by single-crystal X-ray diffraction, P-XRD, and SQUID magnetometry. Our study shows that both complexes have similar 1:1 stoichiometry but different symmetry and crystal packing. Complex 1 has a rigid structure in which the SCO cations are engaged in strong π-interplay with molecular surrounding and does not show SCO transition while 2 demonstrates a reversible transition at T_sco = 118 K in a much “softer”, hydrogen-bonded structure. A new structural indicator of spin state in [Fe(sal₂-trien)]⁺ complexes based on conformational analysis has been proposed. Aging and thermocycling ruined the SCO transition increasing the residual HS fraction from 14 to 41%. Magnetic response of 1 is explained by the AFM coupled dimers S = 5/2 with J₁ = −0.18 cm⁻¹. Residual high-spin fraction of 2, apart from a contribution of the weak dimers with J₁₂ = J₃₄ = −0.29 cm⁻¹, is characterized by a stronger interdimer coupling of J₂₃ = −1.69 cm⁻¹, which is discussed in terms of possible involvement of neutral radicals [Au(dddt)₂].

The radical anion salt [Fe{HC(pz)3}2](TCNQ)3 demonstrating conductivity and spin-crossover transition (SCO) associated with Fe(II) complex cation subsystem has been synthesized and structurally characterized. A pronounced change of the dc resistivity and a robust broadening of the EPR signal triggered by the SCO transition are found. Enhanced EPR line broadening is interpreted in terms of cross relaxation between the TCNQ and Fe(II) spin subsystems