We investigate the low-temperature magnetic and entanglement properties of a series of molecular Cr 2 n Cu 2 heterometallic spin rings (with n= 4, 5, 6). These are cyclic spin systems, consisting of two Cu 2+(s= 1/2) ions, coupled by two antiferromagnetic segments of n Cr 3+(s= 3/2) ions. Thermodynamic measurements (magnetization, susceptibility, and specific heat) allow us to determine the total spin of the ground state and to estimate the spin-Hamiltonian parameters related to magnetic anisotropy. X-ray spectroscopies (XAS and XMCD) are used to probe the local magnetization of the Cr and Cu ions, and provide results that are consistent with the bulk magnetization data. We finally investigate the relation between heterometallicity and entanglement in these prototypical spin systems. In particular, we focus on the spatial modulation of entanglement induced by the Cu defect spins and on the long-distance …