Reduced and Excited States of (bpym)[PtCl₂]_n (bpym = 2,2‘-Bipyrimidine; n = 1, 2):  Experiments and DFT Calculations

Abstract

The complexes (bpym)PtCl(2) (1) and the new (micro-bpym)[PtCl(2)](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 [PtCl(2)] 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((195)Pt) 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.

Structures, Redox and Spectroscopic Properties of PdII and PtII Complexes Containing an Azo Functionality

“…Such large anodic shifts illustrate the superb σ-acceptor ability of the [MCl 2 ] fragments in 1 and 2. [6] The reduction processes for 1 take place at a less negative potential than those for 2 (-0.59 and -1.39 V for 1 and -0.79 and -1.74 V for 2). This suggests that the [PdCl 2 ] fragment has a better σ-acceptor capacity than [PtCl 2 ] in these complexes.…”

“…512 nm for 2) is tentatively assigned to a mixture of metal-to-ligand charge transfer (MLCT) with some contribution from halide-to-ligand (XLCT) charge transfer. [6] The next highest energy transition (e.g. 392 for 2) is most likely a πǞπ* tran- www.eurjic.orgsition centered on the azo ligands.…”

“…Reversible reduction in such complexes is usually ligandcentered and leads to radical-anion intermediates which often show well observable 195 Pt hyperfine coupling in their EPR spectra due to sizeable metal-ligand interactions. [2][3][4][5][6] Luminescence in the solid state or in solution is another fascinating field of research related to such platinum complexes. Such luminescence, which usually occurs from metal-to-ligand charge transfer (MLCT) or intraligand πǞπ* excited states, has instigated several structure-spectroscopic correlation studies to clarify their behavior.…”

Crystal structure of diiodo(2,2′-bipyrimidine-k2N,N′)platinum(II), PtI2(C8H6N4)

“…The title complex [PtI 2 (bpym)] crystallized in the monoclinic space group C2/c,w hereas the previously reported analogous complex [PtCl 2(bpym)] crystallized in the different monoclinic space group P2 1 /c [1]. The central Pt(II) ion has ad istorted square-planar coordination defined by two Na toms of the chelating 2,2'-bipyrimidine ligand and two Ia nions.…”

Crystal structure of dibromo(2,2'-bipyrimidine-k2N,N')platinum(II), PtBr2(C8H6N4)

“…The title complex is isomorphous with the analogous Pt(II) complex [PtCl 2(bpym)] [1]. The asymmetric unit contains two crystallographically independent molecules with identical geometry within experimental errors.…”