Coordination complexes of a silicon-linked organic tetranitroxide

Abstract

Two 1:1 coordination polymers were synthesized linking tetraradical tetrakis(N-oxyl-2,2,6,6-tetramethylpiperidin-4-oxyl)silane, (3) and M(hfac)2 (M=Mn, Cu). Both are 1-D systems in which two TEMPO sites remain uncoordinated: Mn(hfac)2(3)=4 and Cu(hfac)2(3)=5. System 4 has strong AFM TEMPO–Mn–TEMPO exchange even at room temperature (a net S=3/2 spin unit), with the remaining two TEMPO units in each monomer acting in an essentially isolated manner. System 4 shows FM exchange within the TEMPO–Cu–TEMPO trimer unit, with an increase in magnetization up to a broad maximum at about 16–20 K before decreasing again due to likely antiferromagnetic interactions between trimers. The magnetic susceptibility data up to the maximum point can be fit to an FM coupled three-spin model with two additional noninteracting spins, yielding J/k (TEMPO–Cu–TEMPO)≅(+)89 K. The low temperature AFM interactions observed for 4–5 are attributed to interchain spin pairing.