A dramatic change in the magnetic behaviour, which solely depends on the parity of the organic linker molecules, has been found in a family of layered Co-II hydroxides covalently functionalized with dicarboxylic molecules. These layered hybrid materials have been synthesized at room temperature using a one-pot procedure through the epoxide route. While hybrids connected by odd alkyl chains exhibit coercive fields (H-c) below ca. 3500 Oe and show spontaneous magnetization at temperatures (T-M) below 20 K, hybrids functionalized with even alkyl chains behave as hard magnets with H(c)5500 Oe and display a T-M higher than 55 K. This intriguing behaviour was studied by density functional theory with the incorporation of a Hubbard term (DFT+U) calculations, unveiling the structural subtleties underlying this observation. Indeed, the different molecular orientation exhibited by the even/odd alkyl chains, and the orientation of the covalently linked carboxylic groups modify the intensity of the magnetic coupling of both octahedral and tetrahedral in-plane sublattices, thus strongly affecting the magnetic properties of the hybrid. These findings offer an outstanding level of tuning in the molecular design of hybrid magnetic materials based on layered hydroxides.