The magnetic properties of two series of dinuclear complexes, and one trinuclear complex, have been examined as a function of the bridging pathway between the metal centers. The first series of dinuclear complexes is [(Mo-V(O)(Tp*)Cl)(2)(mu-00)], where "00" is [1,4-O(C6H4)(n)P](2-) (n = 1, 1; n = 2, 3), [4,4’-O(C6H3-2-Me)(2)P](2-) (4), or [1,3-OC6H4O](2-) (2) [Tp* = tris(3,5-dimethylpyrazolyl)hydroborate]. The second series of dinuclear complexes is [(Mo-1(NO)(Tp*)Cl)(2)(mu-NN)], where "NN" is 4,4’-bipyridyl (5), 3,3’-dimethyl-4,4’-bipyridine (6), 3,8-phenanthroline (7), or 2,7-diazapyrene (8). The trinuclear complex is [(Mo-V(O)(Tp*)Cl)(3)(1,3,5-C6H3O3)] (9), whose crystal structure was determined [9.5CH(2)Cl(2) : C5(6)H(81)B(3)Cl(13)Mo(3)N(18)O(6); monoclinic, P2(1)/n; a = 13.443, b = 41.46(2), c = 14.314(6) Angstrom; beta = 93.21(3)degrees; V = 7995(5) Angstrom(3); Z = 4; R-1 = 0.106]. In these complexes, the sign and magnitude of the exchange coupling constant J is clearly related to both the topology and the conformation of the bridging ligand [where J is derived from H = -J S-1.S-2 for 1-8 and H = -J(S-1.S-2 + S-2.S-3 + S-1.S3) for 9]. The values are as follows : 1, -80 cm(-1); 2, +9.8 cm(-1); 3, -13.2 cm(-1); 4, -2.8 cm(-1); 5, -33 cm(-1); 6, -3.5 cm(-1); 7, -35.6 cm(-1); 8, -35.0 cm(-1); 9, +14.4 cm(-1). In particular the following holds : (1) J is negative (antiferromagnetic exchange) across the para-substituted bridges ligands of 1 and 3-8 but positive (ferromagnetic exchange) across the meta-substituted bridging ligands of 2 and 9. (2) J decreases in magnitude dramatically as the bridging ligand conformation changes from planar to twisted (compare 3 and 4, or 6 and 8). These observations are consistent with a spin-polarization mechanism for the exchange interaction, propagated across the ct-system of the bridging ligand by via overlap of bridging ligand p(pi) orbitals with the d(pi) magnetic orbitals of the metals. The EPR spectrum of 9 is characteristic of a quartet species and shows weak Delta m(s) = 2 and Delta m(s) = 3 transitions at one-half and one-third, respectively, of the field strength of the principal Delta m(s) = 1 component.