Mono- and dimetallic building blocks are being studied in charge-transfer reactions with organic pi-acceptors such as TCNE to form zero-, one-, and two-dimensional hybrid donor/acceptor compounds. In particular, tetracarboxylate-bridged dinuclear and solvated 3d mononuclear complexes with sigma-bonded TCNE ligands re being investigated with regards to their variable temperature magnetic behavior. Results of experiments with dimolybdenum, diruthenium and vanadium complexes are discussed.