Synthesis, Structure, and Magnetic Properties of Low-Valent Triangulo Cobalt-Hydride Clusters...

Syntheses and properties of low-valent clusters [X{Co(&mgr;-CO)(PMe(3))(2)}(3)], X = none (1), H (2), and H(3) (3), are reported. All solids are isostructural as explicitly shown by single-crystal structure data. The molecular structures of C(21)H(54)Co(3)O(3)P(6) (1) and C(21)H(57)Co(3)O(3)P(6) (3) contain central Co(3) units which form perfect equilateral triangles with Co-Co distances of 2.4055(5) and 2.432(1) Å, respectively. Both compounds crystallize in trigonal space group R&thremacr;c, with Z = 6: 1, a = 10.678(1) Å, c = 52.298(11) Å; 3, a = 10.679(2) Å, c = 52.729(12) Å. Compounds 1 and 2 form a continuous range of solid solutions. Powder samples exhibit molecular paramagnetism of different extent: At 298 K the effective magnetic moments for 1-3 are &mgr;(eff)/&mgr;(B) = 1.9, 3.1, and 2.7, respectively. The magnetic behavior could be rationalized in terms of the Curie-Weiss law for a one electron system (1) and two electron system (2). The two electron approximation has been discussed as well for 3 above 6.2 K. A description of the scope of exchange coupling is presented for 1.