FERROMAGNETIC INTERACTIONS BETWEEN IMINO NITROXIDES THROUGH DIAMAGNETIC METAL-IONS - CRYSTAL-STRUCTURES, MAGNETISM, AND ELECTRONIC-PROPERTIES OF [M-I(IMINO NITROXIDE)(2)](PF6) (M=CU-I AND AG-I)

An orthogonal arrangement of imino nitroxide ligands in Cu-I and Ag-I complexes results in propagation of an intramolecular ferromagnetic in teraction between the coordinated imino nitroxides through these diama gnetic ions. Reaction of [Cu-I(CH3CN)(4)](PF6) and Ag-I(PF6) with imin o nitroxides in ethanol solution gave [Cu-I(immepy)(2)-(PF6) (1) and [ Ag-I(impy)(2)](PF6) (2), respectively (immepy methylpyridyl))-4,4,5,5- tetramethyl-4,5-dihydro-1H imidazolyl-l-oxy and impy ,5,5-tetramethyl- 4,5-dihydro-1H-imidazolyl-1-oxy). Complex 1 crystallizes in the orthor hombic space group Pba2, which has a unit cell with a 11.251(2) Angstr om, b = 14.745(3) Angstrom, c = 9.747(2) Angstrom, V = 1617.0(5) Angst rom(3), and Z = 2. Refinement with 991 reflections observed [\I-0\ > 3 sigma(I-0)] gave R = 0.044 (R-w = 0.053). In 1, imino nitroxides coor dinate to the Cu-I ions in a tetrahedral fashion, the dihedral angle b etween coordinating imino nitroxides being 88.7 degrees. Magnetic susc eptibility measurement for 1 shows typical triplet-singlet behavior wi th strong ferromagnetic interactions (J = 55.1(6) cm(-1) with g = 2.0; H = -JS(1).S-2) The UV-visible absorption spectrum of 1 shows strong bands at 454 and 766 nm assignable to charge-transfer bands from the C u ion to the ligand NLUMO and SOMO, respectively. The pi-back-donation to the SOMO induces the spin on the Cu ion and results in the strong ferromagnetic interaction. Complex 2 crystallizes in the orthorhombic space group P2(1)cn which has a unit cell with a = 10.535(6) Angstrom, b = 31.295(3) Angstrom, c 8.921(4) Angstrom, V = 2941(1) Angstrom(3), and Z = 4. Refinement with 1882 reflections [\I-0\ > 3 sigma(I-0)] ga ve R = 0.058 (R-w = 0.074). Ln 2, the four coordination sites of the A g-I ion were completed with two imino nitroxides and the dihedral angl e between the imino nitroxides is 79.2 degrees. The EPR spectrum of a frozen ethanol solution of 2 shows a typical triplet signal with zero field splitting (\D\ = 0.043 cm(-1) and \E\ = 0.014 cm(-1)). Curie plo ts for the rim = 2 signal below 80 K gave a positive Weiss constant (t heta = 4 K), suggesting an intramolecular ferromagnetic interaction in 2.