Exchange coupling across the cyanide bridge in a series of novel cyanometalate complexes with Cu-II-NC-M-III (M = Cr and low-spin Mn, Fe) fragments has been studied using the broken-symmetry DFT approach and an empirical model, which allows us to relate the exchange coupling constant with sigma-, pi-, and pi*-type spin densities of the CN-bridging ligand. Ferromagnetic exchange is found to be dominated by pi-delocalization via the CN- pi pathway, whereas spin polarization with participation of sigma orbitals ( in examples, where the d(z)(2) orbital of MIII is empty) and pi* orbitals of CN- yields negative spin occupations in these orbitals, and reduces the Cu-II-M-III exchange coupling constant. When the dz2 orbital of MIII is singly occupied, an additional positive spin density appears in the sigma(CN) orbital and leads to an increase of the ferromagnetic Cu-NC-M exchange constant. For low-spin [M-III(CN)(6)](3-) complexes, the d(z)(2) orbital occupancy results in high-spin metastable excited states, and this offers interesting aspects for applications in the area of molecular photomagnetism. The DFT values of the exchange coupling parameters resulting from different occupations of the t(2g) orbitals of low-spin (t(2g)(5)) Fe-III are used to discuss the effect of spin-orbit coupling on the isotropic and anisotropic exchange coupling in linear Cu-NC-Fe pairs.