Paramagnetism of Tetranuclear Complexes between TCNX Ligands (TCNE, TCNQ, TCNB) and Four Pentaammineruthenium or Dicarbonyl(pentamethylcyclopentadienyl)manganese Fragments.
The tetranuclear complexes {(&mgr;(4)-TCNX)[Ru(NH(3))(5)](4)}(A)(8) and (&mgr;(4)-TCNX)[Mn(CO)(2)(C(5)Me(5))](4) [A = PF(6) or CF(3)SO(3); TCNX = TCNE (tetracyanoethene), TCNQ (7,7,8,8-tetracyano-p-quinodimethane), or TCNB (1,2,4,5-tetracyanobenzene)] were studied by variable-temperature (2-300 K) SQUID susceptometry. Mono- and dinuclear species [(PhCN)Ru(NH(3))(5)](PF(6))(2) (PhCN = benzonitrile) and {(&mgr;-L)[Ru(NH(3))(5)](2)}(PF(6))(4) (L = 1,4-dicyanobenzene (terephthalodinitrile) or pyrazine) were also investigated for comparison and were found to be essentially diamagnetic. Despite the even electron count, both the ruthenium and manganese tetranuclear complexes are paramagnetic, albeit with different spin-spin exchange coupling patterns. The manganese systems are characterized by exchange-coupled S = 1 states at the individual metal centers, whereas the magnetic behavior of the tetranuclear ruthenium compounds results from an exchange-coupling interaction between two S = (1)/(2) sites, identified as Ru(III)/Ru(II) mixed-valence pairs.
Waldhör
Eberhard
E
Centre d'Etudes Nucléaires de Grenoble, DRFMC/SCIB/SCPM, 85 X, F-38054 Grenoble Cedex 09, France.
Kaim
Wolfgang
W
Lawson
Max
M
Jordanov
Jeanne
J