Reduced and excited states of (bpym)[PtCl2] (bpym=2,2′-bipyrimidine; n = 1, 2):: Experiments and DFT calculations

The complexes (bpym)PtCl2 (1) and the new (mu-bpym)[PtCl2](2) (2), bpym = 2,2'-bipyrimidine, were synthesized and, in the case of 1, crystallized in solvent-free form for X-ray diffraction. The molecules 1 exhibit two different kinds of stacking motifs in the crystal with an interstack CH--N interaction. Complexes 1 and 2 were found to be sufficiently soluble for cyclic voltammetry, spectroscopy (absorption and emission), and spectroelectrochemical studies (UV-vis, EPR). As a result of single or double coordination of the strongly sigma-accepting [PtCl2] fragment to bpym, the paramagnetic anions 1(.)- and 2(.)- and the dianions 1(2)- and 2(2)- could be reversibly generated, despite the presence of metal-halide bonds. DFT calculations of A(Pt-195) and g tensor components confirm that the singly occupied MOs of the monoanionic species have mainly pi*(bpym) character with nonnegligible platinum d orbital participation. The assignments of the electronic absorption and emission and resonance Raman spectra for both complexes are supported by DFT calculations.