Incorporation of a Fluorine Atom in a Bridging Ligand of Half-Lantern PtII2 Complexes Provides up to 10-Fold Enhancement of Electroluminescence Brightness.

The binuclear half-lantern platinum(II) complexes [Pt(pbt)(µ-S∧N)]2 (pbtH = 2-phenylbenzothiazole, S∧N = benzo[d]thiazole-2-thiolate Pt1, 6-fluorobenzo[d]thiazole-2-thiolate Pt2, 6-chlorobenzo[d]thiazole-2-thiolate Pt3, 6-bromobenzo[d]thiazole-2-thiolate Pt4, and 6-iodobenzo[d]thiazole-2-thiolate Pt5) were synthesized by the treatment of the in situ formed [Pt(pbt)(NCMe)2]NO3 complex and appropriate benzo[d]thiazole-2-thiole in the presence of tBuOK; yield: 51-84%. Complexes Pt1-5 exhibit intense red photoluminescence originated from 3MMLCT state reaching 22% room temperature quantum yields in a CH2Cl2 solution. All complexes display excited-state decay kinetics both in solution and in the solid state; the kinetics was adequately modeled by single exponentials. The complexes display more than 10-fold higher electroluminescence brightness for the F-containing Pt2 (900 cd/m2) and 2-fold higher electroluminescence brightness for the Cl-containing Pt3 (143 cd/m2) compared to the H-substituted complex Pt1 (77 cd/m2). It is argued that this impressive device luminance growth, occurred on formal replacement of H-to-F, is associated with the intermolecular strong hydrogen bonding H···F relevant to the H-bond found in the structure of Pt2.

Halogen Bond-Involving Supramolecular Assembly Utilizing Carbon as a Nucleophilic Partner of I⋠⋠⋠C Non-covalent Interaction.

Co-crystallization of 180°-orienting σ-hole-accepting tectons, namely, 1,4-diisocyanobenzene (1) and 1,4-diisocyanotetramethylbenzene (2), with such homoditopic halogen bond donors as 1,4-diiodotetrafluorobenzene (1,4-FIB) and 4,4'-diiodoperfluorobiphenyl (4,4'-FIBP) afforded co-crystals 1 ⋅ 1,4-FIB, 1 ⋅ 4,4'-FIBP, and 2 ⋅ 1,4-FIB. Their solid-state structures exhibit 1D-supramolecular arrangements, which are based on poorly explored I⋅⋅⋅C halogen bonding; this study is the first in which the supramolecular assembly utilizing halogen bonding with a terminal C atom was performed. The use of the potentially tetrafunctional σ-hole accepting tetraiodoethylene (TIE) leads to supramolecular architecture of a higher dimension, 3D-framework, observed in the structure of 1 ⋅ TIE. DFT calculations, used to characterize the halogen bonding situation, revealed that the I⋅⋅⋅C non-covalent interactions are moderately strong, ranging from -4.07 in 1 ⋅ TIE to -5.45 kcal/mol in 2 ⋅ 1,4-FIB. The NBO analysis disclosed that LP(C)→σ* charge transfer effects are relevant in all co-crystals.

Photo- and Electroluminescent Neutral Iridium(III) Complexes Bearing Imidoylamidinate Ligands.

Imidoylamidinate-based heteroleptic bis(2-phenylbenzothiazole)iridium(III) and -rhodium(III) complexes [(bt)2M(N∩N)] (bt = 2-phenylbenzothiazole, N∩N = N'-(benzo[d]thiazol-2-yl)acetimidamidyl (Ir1 and Rh1), N'-(6-fluorobenzo[d]thiazol-2-yl)acetimidamidyl (Ir2), N'-(benzo[d]oxazol-2-yl)acetimidamidyl (Ir3), N'-(1-methyl-1H-benzo[d]imidazol-2-yl)acetimidamidyl (Ir4); yields 70-84%) were obtained by the reaction of the in situ-generated solvento-complex [(bt)2M(NCMe)2]NO3 and benzo[d]thia/oxa/N-methylimidozol-2-amines in the presence of NaOMe. Complexes Ir1-4 exhibited intense orange photoluminescence, reaching 37% at room temperature quantum yields, being immobilized in a poly(methyl methacrylate) matrix. A photophysical study of these species in a CH2Cl2 solution, neat powder, and frozen (77 K) MeOC2H4OH-EtOH glass matrix─along with density-functional theory (DFT), ab initio methods, and spin-orbit coupling time-dependent DFT calculations─verified the effects of substitution in the imidoylamidinate ligands on the excited-state properties. Electrochemical (cyclic voltammetry and differential pulse voltammetry) and theoretical DFT studies demonstrated noninnocent behavior of the imidoylamidinate ligands in Ir1-4 and Rh1 complexes due to the significant contribution coming from these ligands in the HOMO of the complexes. The iridium(III) species exhibit a ligand (L, 2-phenylbenzothiazole)-centered (3LC), metal-to-ligand (L', imidoylamidinate) charge-transfer (3ML'CT,3MLCT) character of their emission. The imidoylamidinate-based iridium(III) species were proved to be effective as the emissive dopant in an organic light-emitting diode device, fabricated in the framework of this study.

Copper(II)-Mediated Iodination of 1-Nitroso-2-naphthol.

The 3-Iodo-1-nitrosonaphthalene-2-ol (I-NON) was obtained by the copper(II)-mediated iodination of 1-nitroso-2-naphthol (NON). The suitable reactants and optimized reaction conditions, providing 94% NMR yield of I-NON, included the usage of Cu(OAc)2·H2O and 1:2:8 CuII/NON/I2 molar ratio between the reactants. The obtained I-NON was characterized by elemental analyses (C, H, N), high-resolution ESI+-MS, 1H and 13C{1H} NMR, FTIR, UV-vis spectroscopy, TGA, and X-ray crystallography (XRD). The copper(II) complexes bearing deprotonated I-NON were prepared as follows: cis-[Cu(I-NON-H)(I-NON)](I3) (1) was obtained by the reaction between Cu(NON-H)2 and I2 in CHCl3/MeOH, while trans-[Cu(I-NON-H)2] (2) was synthesized from I-NON and Cu(OAc)2 in MeOH. Crystals of trans-[Cu(I-NON-H)2(THF)2] (3) and trans-[Cu(I-NON-H)2(Py)2] (4) were precipitated from solutions of 2 in CHCl3/THF and Py/CHCl3/MeOH mixtures, respectively. The structures of 1 and 3-4 were additionally verified by X-ray crystallography. The characteristic feature of the structures of 1 and 3 is the presence of intermolecular halogen bonds with the involvement of the iodine center of the metal-bound deprotonated I-NON. The nature of the I···I and I···O contacts in the structures of 1 and 3, correspondingly, were studied theoretically at the DFT (PBE0-D3BJ) level using the QTAIM, ESP, ELF, NBO, and IGM methods.

Bifurcated Halogen Bonding Involving Two Rhodium(I) Centers as an Integrated σ-Hole Acceptor.

The complexes [RhX(COD)]2 (X = Cl, Br; COD = 1,5-cyclooctadiene) form cocrystals with σ-hole iodine donors. X-ray diffraction studies and extensive theoretical considerations indicate that the d z 2-orbitals of two positively charged rhodium(I) centers provide sufficient nucleophilicity to form a three-center halogen bond (XB) with the σ-hole donors. The two metal centers function as an integrated XB acceptor, providing assembly via a metal-involving XB.

Metal-Involving Chalcogen Bond. The Case of Platinum(II) Interaction with Se/Te-Based σ-Hole Donors.

Platinum(II) complexes exhibiting an expressed dz2-nucleophilicity of the positively charged metal centers, namely, [Pt(ppy)(acac)] (1; acacH is acetylacetone; ppyH is 2-Ph-pyridine) and [Pt(ppy)(tmhd)] (2; tmhdH is 2,2,6,6-tetramethylheptanedione-3,5), were cocrystallized with the chalcogen bond donors (4-NC5F4)2Ch (Ch = Se, Te) to form two isostructural cocrystals 1·1/2(4-NC5F4)2Ch, and 2·2/3(4-NC5F4)2Se and 2·(4-NC5F4)2Te. The X-ray data for these cocrystals and appropriate theoretical DFT calculations (PBE0-D3BJ) allowed the recognition of the metal-involving chalcogen bond, namely, Ch···dz2-PtII (its energy spans from -7 to -12 kcal/mol). In 1·1/2(4-NC5F4)2Ch, Ch···dz2-PtII bonding is accompanied by the C···dz2-PtII interaction, representing a three-center bifurcate, whereas in 2·(4-NC5F4)2Te the chalcogen bond Te···dz2-PtII is purely two-centered and is stronger than that in 1·1/2(4-NC5F4)2Ch because of more efficient orbital overlap. The association of 2 with (4-NC5F4)2Te and the structure of the formed adduct in CDCl3 solutions was studied by using 1H, 13C, 19F, 195Pt, 125Te NMR, 19F-1H HOESY, and diffusion NMR methods. The 195Pt and 125Te NMR titration and the isothermal titration calorimetry results revealed a 1:1 association of 2 with (4-NC5F4)2Te.

π-Hole···dz2[PtII] Interactions with Electron-Deficient Arenes Enhance the Phosphorescence of PtII-Based Luminophores.

Two phosphorescent PtII-based cyclometalated complexes were co-crystallized with perfluorinated arenes to give 1:1 co-crystals. The X-ray study revealed that each of the complexes is embraced by arenesF to give infinite reverse sandwich structures. In four out of six structures, a dz2 orbital of PtII is directed to the arenesF ring via π-hole···dz2[PtII] interactions, whereas in the other two structures, the filled dz2 orbital is directed toward the arene C atoms. Computed molecular electrostatic potential surfaces of the arenesF and the complexes, noncovalent interaction indexes for the co-crystals, and natural bond orbital calculations indicate that π-hole···dz2[PtII] contacts (and, generally, the stacking) are of electrostatic origin. The solid-state photophysical study revealed up to 3.5-fold luminescence quantum yield and 15-fold lifetime enhancements in the co-crystals. This increase is associated with the strength of the π-hole···dz2[PtII] contact that is dependent on the π-acidity of the areneF and its spatial characteristics.

Hexaiododiplatinate(ii) as a useful supramolecular synthon for halogen bond involving crystal engineering.

Hexaiododiplatinates(ii) bearing ammonium and phosphonium cations, [R4N]2[Pt2(µ-I)2I4] {R = Et (1) and n-Bu (2)} and [R3PR1]2[Pt2(µ-I)2I4] {R = n-Bu and R1 = n-Bu (3); R = Ph and R1 = Ph (4); R = Ph and R1 = CH2Ph (5)}, were synthesized and characterized by high resolution ESI-MS, 1H, 13C{1H}, 31P{1H}, and 195Pt NMR spectroscopy, Fourier transform infrared and Raman spectroscopy, X-ray diffraction (XRD), X-ray powder diffraction, and also electrostatic surface potential calculations. Complexes 1-3 were cocrystallized with halogen bond (XB) donors based on organic iodides featuring electron withdrawing groups {REWGIs: 1,3,5-triiodotrifluorobenzene (1,3,5-FIB), iodopentafluorobenzene (IPFB), 1,4-diiodotetrafluorobenzene (1,4-FIB), and tetraiodoethylene (C2I4)} to give crystalline adducts 1·2(1,3,5-FIB), 1·2IPFB, 2·2(1,4-FIB), and 3·C2I4. Inspection of the XRD data of the obtained adducts revealed the presence, in all four structures, of intermolecular REWGII-Pt XBs between the iodine centers of REWGIs and the terminal iodide ligands of [Pt2(µ-I)2I4]2- anions, where the latter act as rectangular XB-accepting synthons forming XBs with two, three, and even four Pt-Iterminal ligands. The results of Hirshfeld molecular surface analysis and density functional theory (DFT) calculations (the M06/DZP-DKH level of theory) followed by topological analysis of the electron density distribution within the framework of Bader's approach (QTAIM) confirmed the existence of the detected XBs, and their estimated energies vary from 2.2 to 4.7 kcal mol-1.

Reverse Arene Sandwich Structures Based upon π-Hole⋠⋠⋠[MII ] (d8 M=Pt, Pd) Interactions, where Positively Charged Metal Centers Play the Role of a Nucleophile.

The complexes [Pt(tpp)] (H2 tpp=tetraphenylporphyrin), [M(acac)2 ] (M=Pd, Pt, Hacac=acetylacetone), and [Pd(ba)2 ] (Hba=benzoylacetone) were co-crystallized with highly electron-deficient arene systems to form reverse arene sandwich structures built by π-hole⋅⋅⋅[MII ] (d8 M=Pt, Pd) interactions. The adduct [Pt(tpp)]⋅2 C6 F6 is monomeric, whereas the diketonate 1:1 adducts form columnar infinity 1D-stack assembled by simultaneous action of both π-hole⋅⋅⋅[MII ] and C⋅⋅⋅F interactions. The reverse sandwiches are based on noncovalent interactions and calculated ESP distributions indicate that in π-hole⋅⋅⋅[MII ] contacts, [MII ] plays the role of a nucleophile.

Cerium(iii) complexes with azolyl-substituted thiophenolate ligands: synthesis, structure and red luminescence.

In order to obtain molecular Ce(iii) complexes which emit red light by f-d transitions the azolyl-substituted thiophenolates were used as the ligands. The thiophenolate Ce(iii) complexes were synthesized by the reaction of Ce[N(SiMe3)2]3 with respective thiophenols 2-(2'-mercaptophenyl)benzimidazole (H(NSN)), 2-(2'-mercaptophenyl)benzoxazole (H(OSN)) and 2-(2'-mercaptophenyl)benzothiazole (H(SSN)) in DME media. The structures of the benzimidazolate (Ce(NSN)3(DME)) and benzothiazolate (Ce(SSN)3(DME)) derivatives were determined by X-ray analysis which revealed that the cerium ion in the molecules is coordinated by one DME and three anionic thiophenolate ligands. The lanthanum complex La(OSN)3(DME) has been synthesized similarly and structurally characterized. It was found that the solids of Ce(SSN)3(DME) and Ce(OSN)3(DME) exhibit a broad band photoluminescence peaking at 620 nm which disappears upon solvatation. With an example of OSN derivatives it was proposed that this behaviour is caused by the blue shift of the f-d transition of Ce3+ ions.

LMCT facilitated room temperature phosphorescence and energy transfer in substituted thiophenolates of Gd and Yb.

To obtain luminescent lanthanide complexes with a low energy LMCT state the 2-(2'-mercaptophenyl)benzothiazolates, Ln(SSN)3, and 2-(2'-mercaptophenyl)benzoxazolates, Ln2(OSN)6 (Ln = Gd, Yb), were synthesized by the reaction of amides Ln[N(SiMe3)2]3 with respective thiophenols. Ytterbium complexes were structurally characterized by X-ray diffraction analysis. Cyclic voltammetry revealed that the deprotonated mercaptophenyl ligands have significantly lower oxidation potentials than their phenoxy analogues and some ß-diketones. The photophysical properties of Gd and Yb compounds were studied both in solution and in the solid state. The fluorescence spectra of the compounds in solution display the bands of the keto and enol forms of the ligands. No energy transfer from the organic part to Yb3+ has been detected in solutions of both Yb complexes, whereas in solids an intense metal-centered emission in the near infrared region was observed. The solid Gd compounds exhibited room temperature phosphorescence caused by unusually efficient intersystem crossing facilitated by the essentially reducing properties of OSN and SSN ligands. To explain the sensitization process occurring in solids Yb2(OSN)6 and Yb(SSN)3 a specific non-resonant energy transfer mechanism via a ligand to metal charge transfer state has been proposed. Based on the Yb derivatives, NIR-emitting OLEDs with 860 µW cm-2 maximal irradiance were obtained. Their Gd counterparts showed bright electrophosphorescence (up to 1350 cd m-2) in the devices containing doped emission layers.