  Hybrid organometallic systems offer a wide range of functionalities,
including magnetoelectric interactions. However, the ability to design
on-demand ME coupling remains challenging despite a variety of host-guest
configurations and ME phases coexistence possibilities. Here, we report the
effect of metal-ion substitution on the magnetic and electric properties in the
paramagnetic ferroelectric DMAAS crystals. Doing so we are able to induce and
even tune a sign of the ME interactions in the paramagnetic ferroelectric
state. Both studied samples with 6.5% and 20% of Cr become paramagnetic,
contrary to the initial diamagnetic compound. Due to the isomorphous
substitution with Cr the ferroelectric phase transition temperature increases
nonlinearly, with the shift being larger for the sample with Cr content of
6.5%. A magnetic field applied along the polar c axis increases
ferroelectricity for this sample and shifts Tc to higher values, while inverse
effects are observed for sample containing 20% of Cr. The ME coupling
coefficient of 1.7ns/m found for a crystal with 20% of Cr is among the highest
reported up to now. The observed sign change of ME coupling coefficient with a
small change in Cr content paves the way for ME coupling engineering.
