Highly Luminescent Half-Lantern Cyclometalated Platinum(II) Complex: Synthesis, Structure, Luminescence Studies, and Reactivity.

Abstract

The half-lantern compound [{Pt(bzq)(μ-C(7)H(4)NS(2)-κN,S)}(2)]·Me(2)CO (1) was obtained by reaction of equimolar amounts of potassium 2-mercaptobenzothiazolate (KC(7)H(4)NS(2)) and [Pt(bzq)(NCMe)(2)]ClO(4). The Pt(II)···Pt(II) separation in the neutral complex [{Pt(bzq)(μ-C(7)H(4)NS(2)-κN,S)}(2)] is 2.910 (2) Å, this being among the shortest observed in half-lantern divalent platinum complexes. Within the complex, the benzo[h]quinoline (bzq) groups lie in close proximity with most C···C distances being between 3.3 and 3.7 Å, which is indicative of significant π-π interactions. The reaction of 1 with halogens X(2) (X(2) = Cl(2), Br(2), or I(2)) proceeds with a two-electron oxidation to give the corresponding dihalodiplatinum(III) complexes [{Pt(bzq)(μ-C(7)H(4)NS(2)-κN,S)X}(2)] (X = Cl 2, Br 3, I 4). Their X-ray structures confirm the retention of the half-lantern structure and the coordination mode of the bzq and the bridging ligand μ-C(7)H(4)NS(2)-κN,S. The Pt-Pt distances (Pt-Pt = 2.6420(3) Å 2, 2.6435(4) Å 3, 2.6690(3) Å 4) are shorter than that in 1 because of the Pt-Pt bond formation. Time dependent-density functional theory (TD-DFT) studies performed on 1 show a formal bond order of 0 between the metal atoms, with the 6p(z) contribution diminishing the antibonding character of the highest occupied molecular orbital (HOMO) and being responsible for an attractive intermetallic interaction. A shortening of the Pt-Pt distance from 2.959 Å in the ground state S(0) to 2.760 Å in the optimized first excited state (T(1)) is consistent with an increase in the Pt-Pt bond order to 0.5. In agreement with TD-DFT calculations, the intense, structureless, red emission of 1 in the solid state and in solution can be mainly attributed to triplet metal-metal-to-ligand charge transfer ((3)MMLCT) [dσ*(Pt-Pt) → π*(bzq)] excited states. The high quantum yields of this emission measured in toluene (44%) and solid state (62%) at room temperature indicate that 1 is a very efficient and stable (3)MMLCT emitter, even in solution. The high luminescence quantum yield of its red emission, added to its neutral character and the thermal stability of 1, make it a potential compound to be incorporated as phosphorescent dopant in multilayer organic light-emitting devices (OLEDs).

Oxidation of Half-Lantern Pt2(II,II) Compounds by Halocarbons. Evidence of Dioxygen Insertion into a Pt(III)–CH3 Bond

“…The 1 H NMR spectrum of 1 indicates that it exists as a single and symmetric isomer, most probably the anti one, as observed in the related half-lantern compounds [{Pt(bzq)(μ-C 7 H 4 NYS-κN,S)} 2 ] (C 7 H 4 NYS = 2-mercaptobenzothiazolate (Y = S); 2-mercaptobenzoxazolate (Y = O)). 39,40 As with the aforementioned compounds, 39,40 the electronic absorption spectra of 1 ( Figure S1 in Supporting Information) show lowintensity bands centered at 496 nm (CH 2 Cl 2 ) or 580 nm (powdered solid), assignable to a metal−metal-to-ligand charge transfer transition, ( 1 MMLCT) [dσ*(Pt) 2 → π*(bzq)], which is indicative of the existence of two platinum centers located in close proximity, both in the solid state and in solution. Unlike them, complex 1 is not emissive upon excitation at wavelengths from 350 to 580 nm at either 298 or 77 K. Complex 1 readily reacts with an excess of haloforms, CHX 3 (X = Cl, Br, I), in the air, to give the corresponding Pt 2 (III,III)X 2 complexes [{Pt(bzq)(μ-N^S)X} 2 ] (X = Cl 2a, Br 2b, I 2c), which were isolated as pure compounds (Scheme 1).…”

The effect of the nature of peripheral platinated and bridging mercapto ligands on the optical and electrochemical properties of binuclear Pt(II) complexes with a metal-metal chemical bond

“…According to the results of quantum mechanical calculations of [Pt(bzq)(μ mbt)] 2 and [Pt(bzq)(μ mbt)] 2 [3,4], the long wavelength bands at 487 and 480 nm belong to the MMLCT optical transition -π/ with participation of the highest occupied and the lowest unoccupied molecular orbitals (HOMO and LUMO) formed as a result of interaction of two {Pt(C^N)} metal complex fragments (Fig. 1a).…”

“…The quantum chemical calculations of optical transitions in [Pt(bzq)(μ mbt)] 2 and [Pt(bzq)(μ mbo)] 2 complexes [3,4] show that the photoexcitation into the relatively short wavelength region of 370-410 nm leads to spin allowed optical transitions with the formation of a mixture of MMLCT, MLCT, and IL excited states. The intersystem crossing of the mixture of these singlet states causes the formation of their triplet excited states responsible for the phosphores cence of [Pt(C^N)(μ N^S)] 2 (C^N = ptpy, bzq, bt) complexes in the regions 610-635, 575-580, and 475-530 nm (Table 3).…”

“…The planar structure of cycloplatinated complexes of heterocyclic ligands determines the possibility of inter action of d Z2 orbitals of two metal centers of {Pt(C^N)} fragments with formation of a metal-metal bond in [Pt(C^N)(µ L^L)] 2 binuclear complexes [1][2][3][4][5][6][7]. The phosphorescence of these complexes at room tempera ture provides wide possibilities of their application as components of optoelectronic devices [8][9][10].…”

Binuclear platinated 2-phenylbenzothiazole complexes with bridging 2-mercapto derivatives of thiazoline, 1-methylimidazole, and pyrimidine: Structures and optical and electrochemical properties

“…The planar structure of the cyclometallated Pt(II) complexes allows their association due to the and π-π interactions of the orbitals of the metal and ligand, which can lead to the formation of the Pt-Pt chemical bond and a change in the nature and energy of the highest occupied (HOMO) and lowest unoccu pied (LUMO) molecular orbitals of the complexes, which is accompanied by the shift of the phosphores cence spectrum and oxidation and reduction poten tials of Pt(II) [7][8][9][10][11]. The modification of the optical and electrochemical properties of the binuclear cyclo metallated Pt(II) complexes with different distances between the platinum centers determined by the nature of the metallated and bridging ligands was shown [8,10,12].…”