Coordination complexes of a silicon-linked organic tetranitroxide

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) congruent to (+)89 K. The low temperature AFM interactions observed for 4-5 are attributed to interchain spin pairing. (C) 2003 Elsevier Science Ltd. All rights reserved.