Syntheses, crystal structures and magnetic properties of three new molecular solids based on bis(maleonitriledithiolate)copper(II) anion and ortho -position substituted benzyl isoquinolinium cations

•Three molecular solids containing [Cu(mnt)2]2− dianion were prepared and characterized.•The [Cu(mnt)2]2− anions in 1 and 2 form a dimer by the side-to-side S⋯S, N⋯N and S⋯N interactions.•There are non-classical hydrogen bonds, X⋯N (X=F, Cl), Br⋯S, Cu⋯N and π⋯π interactions.•There exists an antiferromagnetic interaction in 1.•A change of magnetic exchange from weak ferromagnetic to antiferromagnetic exists in 2 and 3.