Two novel heterobimetallic complexes of formula [Cr(bpy)(ox)(2)Co(Me(2)phen)(H2O)(2)][Cr(bpy)(ox)(2)]center dot 4H(2)O (1) and [Cr(phen)(ox)(2)Mn(phen)(H2O)(2)][Cr(phen)(ox)(2)]center dot H2O (2) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and Me(2)phen = 2,9-dimethyl-1,10-phenanthroline) have been obtained through the "complex-as-ligand/complex-as-metal" strategy by using Ph4P[CrL(ox)(2)]center dot H2O (L = bpy and phen) and [ML'(H2O)(4)](NO3)(2) (M = Co and Mn; L' = phen and Me(2)phen) as precursors. The X-ray crystal structures of 1 and 2 consist of bis(oxalato)chromate(III) mononudear anions, [(CrL)-L-III(ox)(2)](-), and oxalato-bridged chromium(III)-cobalt(II) and chromium(III)-manganese(II) dinuclear cations, [(CrL)-L-III(ox)(mu-ox)(ML)-L-II'(H2O)(2)](+) [M = Co, L = bpy, and L' = Me(2)phen (1); M = Mn and L = L' = phen (2)]. These oxalato-bridged (CrMII)-M-III dinuclear cationic entities of 1 and 2 result from the coordination of a [(CrL)-L-III(ox)(2)](-) unit through one of its two oxalato groups toward a [(ML)-L-II'(H2O)(2)](2+) moiety with either a trans- (M = Co) or a cis-diaqua (M = Mn) configuration. The two distinct Cr-III ions in 1 and 2 adopt a similar trigonally compressed octahedral geometry, while the high-spin Mll ions exhibit an axially (M = Co) or trigonally compressed (M = Mn) octahedral geometry in 1 and 2, respectively. Variable temperature (2.0-300 K) magnetic susceptibility and variable-field (0-5.0 T) magnetization measurements for 1 and 2 reveal the presence of weak intramolecular ferromagnetic interactions between the Cr-III (S-Cr = 3/2) ion and the high-spin Co-II (S-Co = 3/2) or Mn-II (S-Mn = 5/2) ions across the oxalato bridge within the (CrMII)-M-III dinuclear cationic entities (M = Co and Mn) [J = +2.2 (1) and +1.2 cm(-1) (2); H = -J S-Cr center dot S-M]. Density functional electronic structure calculations for 1 and 2 support the occurrence of S = 3 (CrCoII)-Co-III and S = 4 (CrMnII)-Mn-III ground spin states, respectively. A simple molecular orbital analysis of the electron exchange mechanism suggests a subtle competition between individual ferro- and antiferromagnetic contributions through the sigma- and/or pi-type pathways of the oxalato bridge, mainly involving the d(yz)(Cr)/d(xy)(M), d(xz)(Cr)/d(xy)(M), d(x2-y2)(Cr)/d(xy)(M), d(yz)(Cr)/d(xz)(M), and d(xz)(Cr)/d(yz)(M) pairs of orthogonal magnetic orbitals and the d(x2-y2)(Cr)/d(x2-y2)M),d(xz)(Cr)/d(xz)(M), and d(yz)(Cr)/d(yz)(M) pairs of nonorthogOnal_Mognetic orbitals, which would be ultimately responsible' for the relative magnitude of the overall ferromagnetic coupling in 1-and 2.