π−π Interactions in Organometallic Systems. Crystal Structures and Spectroscopic Properties of Luminescent Mono-, Bi-, and Trinuclear Trans-cyclometalated Platinum(II) Complexes Derived from 2,6-Diphenylpyridine

Citations Over TimeTop 10% of 2001 papers

Abstract

A series of mono- and multinuclear dicyclometalated platinum(II) complexes, namely, [Pt(C∧N∧C)L1] [HC∧N∧CH = 2,6-diphenylpyridine; L1 = 4-tert-butylpyridine (1), 1-methyl-4,4‘-bipyridinium (MQ+) hexafluorophosphate (2(PF6)), 2,6-dimethylphenylisocyanide (4), tricyclohexylphosphine (5), triphenylphosphine (7)], [Pt2(C∧N∧C)2(μ-L2)] [L2 = pyrazine (pyr; 3), bis(dicyclohexylphosphino)methane (dcpm; 6), bis(diphenylphosphino)methane (dppm; 8)], and [Pt3(C∧N∧C)3(μ3-dpmp)] [dpmp = bis(diphenylphosphinomethyl)phenylphosphine (9)], were synthesized from [Pt(C∧N∧C)dmso] (dmso = dimethyl sulfoxide). The X-ray crystal structures of 1, 3·CHCl3, 4, 6·CHCl3·CH3OH·4H2O, 7, 8 (yellow form), and 8·CHCl3 (orange form) have been determined. For complex 1, the Pt(C∧N∧C) units are oriented into pairs in a head-to-tail fashion with an interplanar separation of 3.40 Å. For complex 4, dimeric π−π overlap between Pt(C∧N∧C) and phenyl moieties in a head-to-tail manner is observed, with interplanar stacking at 3.39 Å. There are two crystal forms for complex 8. Only one intramolecular Pt(C∧N∧C)−phenyl π−π interaction (separation 3.381 Å) is apparent in the yellow form. For the orange form (8·CHCl3), there are two intramolecular Pt(C∧N∧C)−phenyl π−π contacts (separations 3.115 and 3.287 Å). For 3·CHCl3, the dihedral angles between the pyrazine and the two Pt(C∧N∧C) planes are 124.0° and 130.5°, which allows the possibility for partial orbital interaction between the (5d)Pt and pπ*(pyrazine) orbitals. Complexes 1 and 4−9 display vibronically structured emission (λmax of most intense band = 508−526 nm) in 77 K methanol/ethanol (1:5, v/v) glass, which are assigned to 3IL excited states. For 1, 4−6, 8, and 9, the 77 K structureless emission at λmax 596−636 nm in methanol/ethanol glasses is assigned as ππ* excimeric in nature. These excimeric emissions are concentration-dependent for 1 and 4−6 and concentration-independent for 8 and 9. The 298 K solid emission spectra of 1, 4−6, 8, and 9 are characterized by a broad, unstructured band at λmax 566−633 nm, which red-shift in energy upon cooling to 77 K. These bands are comparable in energy to the 77 K glassy emissions and are similarly assigned. Complexes 2 and 3 show an intense absorption at λmax 410 (shoulder) and 456 nm, which are ascribed to the MLCT (5d)Pt → π*(1-methyl-4,4‘-bipyridinium/pyrazine) transition, respectively. Likewise, the solid-state emissions of 2 and 3 at λmax 686 and 658 nm, respectively, are assigned as MLCT. The vapochromism of complex 8 has been investigated.

Related Papers

• → Synthesis and thermal properties of the inorganic–organic transition metal halogenides CuCl–pyrazine and Cu2Cl2–pyrazine(2001)57 cited
• → Dimetalation of Pyrazines. A One-Pot Synthesis of Multisubstituted Pyrazine C-Nucleosides(2001)24 cited
• → Synthesis of New Riminophenazines with Pyrimidine and Pyrazine Substitution at the 2-N Position(2011)5 cited
• → 222. Pyrazine derivatives. Part IV. Pyrazine N-oxides and their conversion into chloropyrazines(1947)8 cited
• Recognition of the Formation Mechanism & Flavor Characteristics of Pyrazine Compounds in Jiugui Liquor(2005)