Phenylbenzothiazole-Based Platinum(II) and Diplatinum(II) and (III) Complexes with Pyrazolate Groups: Optical Properties and Photocatalysis.

Based on 2-phenylbenzothiazole (pbt) and 2-(4-dimethylaminophenyl)benzothiazole (Me2N-pbt), mononuclear [Pt(pbt)(R'2-pzH)2]PF6 (R'2-pzH = pzH 1a, 3,5-Me2pzH 1b, 3,5-iPr2pzH 1c) and diplatinum (PtII-PtII) [Pt(pbt)(µ-R'2pz)]2 (R'2-pz = pz 2a, 3,5-Me2pz 2b, 3,5-iPr2pz 2c) and [Pt(Me2N-pbt)(µ-pz)]2 (3a) complexes have been prepared. In the presence of sunlight, 2a and 3a evolve, in CHCl3 solution, to form the PtIII-PtIII complexes [Pt(R-pbt)(µ-pz)Cl]2 (R = H 4a, NMe2 5a). Experimental and computational studies reveal the negligible influence of the pyrazole or pyrazolate ligands on the optical properties of 1a-c and 2a,b, which exhibit a typical 3IL/3MLCT emission, whereas in 2c the emission has some 3MMLCT contribution. 3a displays unusual dual, fluorescence (1ILCT or 1MLCT/1LC), and phosphorescence (3ILCT) emissions depending on the excitation wavelength. The phosphorescence is lost in aerated solutions due to sensitization of 3O2 and formation of 1O2, whose determined quantum yield is also wavelength dependent. The phosphorescence can be reversibly photoinduced (365 nm, ∼ 15 min) in oxygenated THF and DMSO solutions. In 4a and 5a, the lowest electronic transitions (S1-S3) have mixed characters (LMMCT/LXCT/L'XCT 4a and LMMCT/LXCT/ILCT 5a) and they are weakly emissive in rigid media. The 1O2 generation property of complex 3a is successfully used for the photooxidation of p-bromothioanisol showing its potential application toward photocatalysis.

cis/trans-[Pt(C∧N)(C≡CR)(CNBut)] Isomers: Synthesis, Photophysical, DFT Studies, and Chemosensory Behavior.

cis/trans Isomerism can be a crucial factor for photophysical properties. Here, we report the synthesis and optical properties of a series of trans- and cis-alkynyl/isocyanide cycloplatinated compounds [Pt(C∧N)(C≡CR)(CNBut)] [R = C6H4-4-OMe 1, 3-C4H3S 2; C∧N = 2-(2,4-difluorophenyl)pyridine (dfppy) (a), 4-(2-pyridyl)benzaldehyde (ppy-CHO) (b)]. The trans-forms do not isomerize thermally in MeCN solution to the cis forms, but upon photochemical irradiation in this medium at 298 K, a variable isomerization to the cis forms was observed. This behavior is in good agreement with the theoretically calculated energy values. The trans/cis configuration, the identity of the cyclometalated, and the alkynyl ligand influence on the absorption and emission properties of the complexes in solution, polystyrene (PS) films, and solid state are reported. All complexes are efficient triplet emitters in all media (except for trans-1a and trans-2a in CH2Cl2 solution at 298 K), with emission wavelengths depending mainly on the cyclometalated ligand in the region 473-490 nm (dfppy), 510-550 (ppy-CHO), and quantum yields (ϕ) ranging from 18.5 to 40.7% in PS films. The combined photophysical data and time-dependent density functional theory calculations (TD-DFT) at the excited-state T1 geometry reveal triplet excited states of 3L'LCT (C≡CR → C∧N)/3IL (C∧N) character with minor 3MLCT contribution. The dfppy (a) complexes show a greater tendency to aggregate in rigid media than the ppy-CHO (b) and the cis with respect to the trans, showing red-shifted structureless bands of 3MMLCT and/or excimer-like nature. Interestingly, trans-1a,2a and cis-1a,2a undergo significant changes in the ultraviolet (UV) and emission spectra with Hg2+ ions enabling their use for sensing of Hg2+ ions in solution. This is clearly shown by the hypsochromic shift and substantial decrease of the low-energy absorption band and an increase of the intensity of the emission in the MeCN solution upon the addition of a solution of Hg(ClO4)2 (1:5 molar ratio). Job's plot analysis estimated a 1:1 stoichiometry in the complexation mode of Hg2+ by trans-2a. The binding constant (log K) calculated for this system from absorption titration data resulted to be 2.56, and the limit of the detection (LOD) was 6.54 × 10-7 M.

Luminescent Anionic Cyclometalated Organoplatinum (II) Complexes with Terminal and Bridging Cyanide Ligand: Structural and Photophysical Properties.

We present the synthesis and characterization of two series of mononuclear heteroleptic anionic cycloplatinated(II) complexes featuring terminal cyanide ligand Q+[Pt(C^N)(p-MeC6H4)(CN)]- [C^N = benzoquinolate (bzq), Q+ = K+ 1 and NBu4+ 4; 2-phenylpyridinate (ppy), Q+ = K+ 2 and NBu4+ 5 and 2-(2,4- difluorophenyl)pyridinate (dfppy), Q+ = K+ 3 and NBu4+ 6] and a series of symmetrical binuclear complexes (NBu4)[Pt2(C^N)2(p-MeC6H4)2(µ-CN)] (C^N = bzq 7, ppy 8, dfppy 9). Compounds 5, 6, and 7-9 were further determined by single-crystal X-ray diffraction. There are no apparent intermolecular Pt···Pt interactions owing to the presence of bulky NBu4+ counterion. Slow crystallization of K[Pt(ppy)(p-MeC6H4)(CN)] 2 in acetone/hexane evolves with formation of yellow crystals, which were identified by single-crystal X-ray diffraction methods as the salt complex {[Pt(ppy)(p-MeC6H4)(CN)]2K3(OCMe2)4(µ-OCMe2)2}[Pt(ppy)(p-MeC6H4)(µ-CN)Pt(ppy)(p-MeC6H4)]·2acetone (10), featuring the binuclear anionic unit 8- neutralized by an hybrid inorganic-organometallic coordination polymer {[Pt(ppy)(p-MeC6H4)(CN)]2K3(OCMe2)4(µ-OCMe2)2}+. The photophysical properties of all compounds were recorded in powder, polystyrene film, and solution states with a quantum yield up to 21% for 9 in the solid state. All complexes displayed bright emission in rigid media, and for the interpretation of their absorption and emission properties, density functional theory (DFT) and time-dependent DFT calculations were applied.

Luminescent Au(III)-M(I) (M = Cu, Ag) Aggregates Based on Dicyclometalated Bis(alkynyl) Gold Anions†.

The syntheses and structures of a series of complexes based on the C∧C-chelated Au(III) unit (C∧C = 4,4'-bis(t-butyl) 2,2'-biphenyl-1,1'-diyl) are reported, namely, [{(C∧C)Au(C≡CtBu)2}2M2], (C∧C)Au(C≡CR)(C≡NXyl), and [{(C∧C)Au(C≡CR)2}{M(C≡NXyl)}] (M = Ag, Cu; R = tBu, C6H4tBu-4, C6H4OMe-4; Xyl = 3,5-Me2C6H3). The X-ray structures reveal a broad range of dispositions determined by the different coordination modes of Ag(I) or Cu(I). The complexes are bright photoemitters in the solid state and in poly(methyl methacrylate) (PMMA) films. The photoluminescence is dominated by 3IL(C∧C) transitions, with indirect effects from the rest of the molecules, as supported by theoretical calculations. This work opens up the possibility of accessing Au(III) carbon-rich anions to construct photoluminescent aggregates.

Multistimuli-Responsive Properties of Aggregated Isocyanide Cycloplatinated(II) Complexes.

Here, we describe the neutral cyclometalated tert-butylisocyanide PtII complexes, [Pt(C∧N)Cl(CNBut)] 1, the double salts [Pt(C∧N)(CNBut)2][Pt(C∧N)Cl2] 2, and the cationic complexes [Pt(C∧N)(CNBut)2]ClO4 3 [C∧N = difluorophenylpyridine (dfppy, a), 4-(2-pyridyl)benzaldehyde (ppy-CHO, b)]. A comparative study of the pseudopolymorphs 1a, 1a·CHCl3, 1b, 1b·0.5Toluene, 1b·0.5PhF, and 3a·0.25CH2Cl2 reveals strong aggregation through Pt···Pt and/or π···π stacking interactions to give a variety of distinctive one-dimensional (1D) infinite chains, which modulate the photoluminescent properties. This intermolecular long-range aggregate formation is the main origin of the photoluminescent behavior of 1a and 1b complexes, which exhibit highly sensitive and reversible responses to multiple external stimuli including different volatile organic compounds (VOCs), solvents, temperatures, and pressures, with distinct color and phosphorescent color switching from green to red. Furthermore, complex 1b undergoes supramolecular self-assembly via Pt···Pt and/or π···π interactions into a polymer thin polystyrene (PS) film 10 wt % in response to toluene vapors, and 3a exhibits vapochromic and vapoluminescent behavior. Theoretical simulations on the dimer, trimer, and tetramer models of 1a and 1b have been carried out to get insight into the photophysical properties in the aggregated solid state.

Polymorphism and Mechanochromism in 2-Phenylbenzothiazole Cyclometalated PtII Complexes with Chelating N∧O Ligands.

New cyclometalated PtII complexes with 2-phenylbenzothiazole (pbt) and two different picolinate ligands [Pt(pbt)(R-pic-κN,O)] (R = H (1), OH (2)) were prepared. In contrast to 1, the OH substituent group on 2 allows modulation of the packing in the solid state through donor-acceptor H-bonding interactions with the CH2Cl2 solvent. Thus, three pseudopolymorphs of 2 with different aggregation degrees were isolated, including yellow 2-Y, orange-red 2-R (2·0.5CH2Cl2) and black 2-B (2·0.75CH2Cl2) with emissions at 540, 656, and 740 nm, respectively, in the solid state at 298 K. 2-R and 2-B can be transformed to the pristine solid 2. Studies of their crystal structures show that 1 and 2-Y stack in columns with only π···π stacking interactions, whereas 2-R displays strong aggregated 1D infinite chains based on Pt···Pt and π···π stacking interactions, consistent with the colors and the photophysical properties, measured in several media. Interestingly, 1 and 2 exhibit reversible mechanochromic behavior with high contrast in the color and color emission upon mechanical grinding due to a phase transition between a crystalline and an amorphous state, as confirmed by powder X-ray diffraction (PXRD) studies. Theoretical calculations indicate that Pt···Pt contacts are more relevant in the trimers and tetramers than in the dimers, particularly in their T1 states, associated with a change from a 3IL/3MLCT transition in the monomer to 3MM(L+L')CT in the oligomers. Noncovalent interaction (NCI) theoretical studies indicate that the π···π stacking among chelates also exerts a strong influence in the metal-metal-to-ligand charge transfer transition character.

Investigation on Optical and Biological Properties of 2-(4-Dimethylaminophenyl)benzothiazole Based Cycloplatinated Complexes.

The optical and biological properties of 2-(4-dimethylaminophenyl)benzothiazole cycloplatinated complexes featuring bioactive ligands ([{Pt(Me2 N-pbt)(C6 F5 )}L] [L=Me2 N-pbtH 1, p-dpbH (4-(diphenylphosphino)benzoic acid) 2, o-dpbH (2-(diphenylphosphino)benzoic acid) 3), [Pt(Me2 N-pbt)(o-dpb)] 4, [{Pt(Me2 N-pbt)(C6 F5 )}2 (µ-PRn P)] [PR4 P=O(CH2 CH2 OC(O)C6 H4 PPh2 )2 5, PR12 P=O{(CH2 CH2 O)3 C(O)C6 H4 PPh2 }2 6] are presented. Complexes 1-6 display 1 ILCT and metal-perturbed 3 ILCT dual emissions. The ratio between both bands is excitation dependent, accomplishing warm-white emissions for 2, 5 and 6. The phosphorescent emission is lost in aerated solutions owing to photoinduced electron transfer to 3 O2 and the formation of 1 O2 , as confirmed in complexes 2 and 4. They also exhibit photoinduced phosphorescence enhancement in non-degassed DMSO due to local oxidation of DMSO by sensitized 1 O2 , which causes a local degassing. Me2 N-pbtH and the complexes specifically accumulate in the Golgi apparatus, although only 2, 3 and 6 were active against A549 and HeLa cancer cell lines, 6 being highly selective in respect to nontumoral cells. The potential photodynamic property of these complexes was demonstrated with complex 4.

Design of Luminescent, Heteroleptic, Cyclometalated PtII and PtIV Complexes: Photophysics and Effects of the Cyclometalated Ligands.

Neutral pentafluorophenyl benzoquinolinyl PtII [Pt(bzq)(HC^N-κN)(C6 F5 )] (1 a-g) complexes, bearing nonmetalated N-heterocyclic HC^N ligands [HC^N=2,5-diphenyl-1,3,4-oxadiazole (Hoxd) a, 2-(2,4-difluorophenyl)pyridine (dfppy) b, 2-phenylbenzo[d]thiazole (pbt) c, 2-(4-bromophenyl)benzo[d]thiazole (Br-pbt) d, 2-phenylquinoline (pq) e, 2-thienylpyridine (thpy) f, 1-(2-pyridyl)pyrene (pypy) g], and heteroleptic bis(cyclometalated) PtIV fac-[Pt(bzq)(C^N)(C6 F5 )Cl] (2 b-g, bzq: benzo[h]quinolinyl) derivatives, generated by oxidation of 1 b-g with PhICl2 , are reported. The oxidation reaction of 1 a evolved with formation of the bimetallic PtIV complex syn-[Pt(bzq)(C6 F5 )Cl(µ-OH)]2 3. The crystal structures of 1 a,d,f, 2 b,d,e and 3 were corroborated by X-ray crystallography. A comparative study of the absorption and photoluminescence properties of the two series of complexes PtII (1) and PtIV (2), supported by time-dependent DFT calculations (TD-DFT), is presented. The low-lying transitions (absorption and emission) of PtII complexes 1 a-e [solution and polystyrene (PS) films] were assigned to the IL/MLCT mixture located on the cyclometalated Pt(bzq) unit, with minor IL'/ML'CT/LL'CT contributions involving the non-metalated ligand. Complex 1 g, bearing the more delocalized pyridyl pyrene (Hpypy) as an ancillary ligand, shows dual 1 ππ* and 3 ππ* (Hpypy) emission in fluid CH2 Cl2 and dual 3 IL/3 MLCT [Pt(bzq)] and [3 ππ*, Hpypy] phosphorescence at 77 K. Upon oxidation, PtIV complexes 2 b-f display (solution, PS) ligand-based phosphorescence that arises from the bzq in 2 b (3 LC) or from the second C^N ligand in 2 c-f (3 L'C) with some 3 LL'CT in 2 f. Despite metalation of the pyrenyl group, 2 g exhibits dual emission 1 ππ*/3 ππ* located on the pypy chromophore.

Synthesis and Photophysical Properties of Au(III)-Ag(I) Aggregates.

Cyclometalated gold(III) complexes of the type (C∧N∧C)AuX [HC∧N∧CH = 2,6-bis(4-ButC6H4)pyrazine; 2,6-bis(4-ButC6H4)pyridine, or 2,6-bis(4-ButC6H4)4-Butpyridine; X = CN, CH(COMe)2, or CH(CN)2] have been used as building blocks for the construction of the first family of AuIII/AgI aggregates. The crystal structures of these aggregates reveal the formation of complex architectures in which the Ag+ cations are stabilized by the basic centers present on each of the Au precursors. The photophysical properties of these aggregates are reported. Compared to mononuclear pincer complexes, a general red-shift and an increase in the emission intensity are observed. In agreement with DFT calculations, the lowest energy absorption and the emission are assigned to 1IL(C∧N∧C) and 3IL(C∧N∧C) transitions dominated by the HOMO and the LUMO orbitals.

Luminescent Cycloplatinated Complexes with Biologically Relevant Phosphine Ligands: Optical and Cytotoxic Properties.

Two series of neutral luminescent pentafluorophenyl cycloplatinated(II) complexes [Pt(C^N)(C6F5)L] [C^N = C-deprotonated 2-phenylpyridine (ppy; a), 2-(2,4-difluorophenylpyridine (dfppy; b)] incorporating dimethyl sulfoxide [L = DMSO for 1 (1a reported by us in ref (14) )] or biocompatible phosphine [L = PPh2C6H4COOH (dpbH; 2), PPh2C6H4CONHCH2COOMe (dpbGlyOMe; 3), P(C6H4SO3Na)3 (TPPTS; 4)] ligands have been prepared and characterized and their optical properties studied. Their cytotoxic activities against tumor A549 (lung carcinoma), HeLa (cervix carcinoma), and nontumor NL-20 (lung epithelium) cell lines, as well as the ability to interact with DNA (plasmid pBR322), were evaluated. Complexes 2 exhibit higher cytotoxicity (IC50 3.89-20.29 µM) than compounds 1 (9.03-20.50 µM), whereas the activities of complexes 3 and 4 are negligible. All cytotoxic complexes show low selective toxicities toward cancer cells. Interestingly, except 1a, these complexes do not show evidence of DNA intercalation. Along the same lines, fluorescence costaining with Hoechst (2,5'-bi-1 H-benzimidazole, 2'-(4-ethoxyphenyl)-5-(4-methyl-1-piperazinyl), a nuclear DNA stain) reveals that all complexes easily internalize, being mainly localized in the cytoplasm. In order to deepen the mechanism of biological action, the effect of the most cytotoxic complex 2b toward the dynamics of tubulin was explored. This complex displays tubulin depolymerization activity, exhibiting more potent inhibition of microtubule formation in A549 than in HeLa cells, in accordance with its higher antiproliferative activity (IC50 6.98 vs 12.45 µM), placing this complex as a potential antitubulin agent.

Benzothiazole-Based Cycloplatinated Chromophores: Synthetic, Optical, and Biological Studies.

Cycloplatinated complexes based on 2-(4-substituted)benzothiazole ligands of type [Pt(R-PBT-κC,N)Cl(L)] (PBT=2-phenylbenzothiazole; R=Br (1), Me2 N (2); L=dimethyl sulfoxide (DMSO; a), 1,3,5- triaza-7-phosphaadamantane (PTA; b), triphenylphosphine 3,3',3''-trisulfonate (TPPTS; c)) and [Pt(Br-PBT-κC)Cl(PTA)2 ] (3) are presented. On the basis of the photophysical data and time-dependent (TD)-DFT calculations (1 a and 2 a), the low-lying transitions (absorption and emission) were associated with ligand-center (LC) charge transfer, with minor metal-to-ligand charge transfer (MLCT), and intraligand charge transfer (ILCT) [Me2 N-PBT→PBT] excited states, respectively. Simultaneous fluorescence/phosphorescence bands were found in fluid solutions (and also in the solid state for 2 a), which become dominated by triplet emission bands in rigid media at 77 K. The effect of the concentration on emissive behavior of 2 a, b indicated the occurrence of aggregation-induced luminescence properties related to the occurrence of metal-metal and π⋅⋅⋅π interactions, which are more enhanced in 2 a because of the less bulky DMSO ligand. The behavior of 2 a toward para-toluenesulfonic acid (PTSA) in aerated acetonitrile and to hydrogen chloride gas in the solid state has been evaluated, thus showing a clear reversible change between the 1 ILCT and 3 LC/3 MLCT states due to protonation of the NMe2 group (theoretical calculations on 2 a-H+ ). Solid 2 a undergoes a surprising oxidation of the PtII center to PtIV with concomitant deoxygenation of DMSO, under prolonged reaction with hydrogen chloride gas to afford the PtIV /dimethyl sulfide complex (mer-[Pt(Me2 N-PBT-κC,N)Cl3 (SMe2 )]; mer-4), which evolves in solution to fac-4, as confirmed by X-ray studies. Cytotoxic activity studies on A549 and HeLa cell lines indicated cytotoxic activity of 1 b and 2 a, b. In addition, fluorescent cell microscopy revealed cytoplasmic staining, more visible in perinuclear areas. Inhibition of tubulin polymerization by 1 b in both cells is presented as a preliminary mechanism of its cytotoxic action.

Facile Approaches to Phosphorescent Bis(cyclometalated) Pentafluorophenyl PtIV Complexes: Photophysics and Computational Studies.

A convenient and general strategy for the synthesis of stable bis(cyclometalated) pentafluorophenyl PtIV complexes fac-[Pt(C^N)2 (C6 F5 )Cl] (3 a-f) and mer-[Pt(C^N)2 (C6 F5 )(CN)] (4 c,d) has been developed. Complexes 3 were selectively generated by low-temperature oxidation of the cyclometalated PtII complexes [Pt(C^N)(HC^N)(C6 F5 )] 2 [prepared from cis-[Pt(C6 F5 )2 (HC^N)2 ] (1) intermediates] with PhICl2 and subsequent metalation of the pendant HC^N ligand. Complexes 3 a,b were also alternatively generated by irradiation (Hg lamp, 400 W) of complexes 2 a,b, respectively, in CH2 Cl2 . This latter reaction proceeds via the hydride PtIV species cis-[Pt(C^N)2 (C6 F5 )H], detected as the only intermediate species. The molecular structures of 1 a,d, 2 a, and 3 a,b,d,e were confirmed by X-ray diffraction. The substitution of Cl- by CN- in fac-[Pt(C^N)2 (C6 F5 )Cl] [C^N=2-phenylbenzothiazole (3 c), 2-(4-bromophenyl)benzothiazole (3 d)] evolved with isomerization to give rise to the isomers (OC-6-42)-[Pt(C^N)2 (C6 F5 )(CN)] (4 c, 4 d) having a mer disposition of the cyclometalated and C6 F5 groups (X-ray, 4 c). All the complexes are luminescent and their electronic spectra have been compared and interpreted with the aid of time-dependent DFT calculations.

Binuclear Complexes and Extended Chains Featuring Pt(II)-Tl(I) Bonds: Influence of the Pyridine-2-Thiolate and Cyclometalated Ligands on the Self-Assembly and Luminescent Behavior.

Platinum solvate complexes [Pt(C6F5)(C^N)(S)] [C^N = phenylpyridinyl (ppy), S = dimethyl sulfoxide (DMSO) (A); C^N = benzoquinolinyl (bzq), S = CH3COCH3 (B)] react with [Tl(Spy)] (Spy = 2-pyridinethiolate) to afford binuclear [{Pt(C6F5)(C^N)}Tl(Spy)] [C^N = ppy (1) and bzq (2)] species containing a Pt-Tl bonding interaction, supported by a µ-Spy-κN,S bridging ligand, as confirmed by X-ray diffraction. However, the related reactions with [Tl(SpyCF3-5)] [SpyCF3-5 = 5-(trifluoromethyl)-2-pyridinethiolate] give neutral extended chains [{Pt(C6F5)(C^N)}Tl(SpyCF3-5)]n [C^N = ppy (3) and bzq (4)]. 3 features a zigzag -Pt-Tl···S-Pt- chain, generated by Pt-Tl and Tl···S bonds, with the SpyCF3 acting as a µ-κN:κ(2)S bridging ligand, whereas 4 displays an unsupported ···Tl-Pt···Tl-Pt··· backbone (angle of ca. 158.7°). The lowest-energy absorption bands in the UV-vis spectra in CH2Cl2, associated with (1)L'LCT transitions with minor (1)LC/(1)MLCT (L' = Spy or SpyCF3-5; L = C^N) character, are similar for all complexes 1-4, demonstrating that for 3 and 4 the chains break down in solution to yield similar bimetallic Pt-Tl units. For 2, two different forms, 2-o (orange) and 2-y (yellow), exhibiting different colors and emissions were found depending on the isolation conditions. Slow crystallization favors formation of the thermodynamically more stable yellow form (2-y), which exhibits a high-energy (HE) structured emission band, whereas fast crystallization gives rise to the orange form (2-o), with a remarkably lower energy structureless emission. Complexes 1 and 3 exhibit dual luminescence in the solid state at 298 K: an unstructured low-energy band associated with (3)ππ* excimeric emission due to π···π (C^N) interactions and a more structured HE band, assigned, with support of density functional theory calculations, to an intraligand (3)LC (C^N) excited state mixed with some ligand (SPy)/platinum-to-ligand (C^N)(3)[(L' + M)LCT] charge transfer. Chain 4 only shows a HE band at 298 K, attributed to a (3)L'LCT (SpyCF3 → bzq) excited state mixed with a minor (3)MLCT/(3)MM'CT (M = Pt; M' = Tl) contribution. At 77 K, the ππ*-stacking emission is predominant in all complexes, except in the form 2-y. Interestingly, 2-4 exhibit reversible mechanochromic color and luminescence changes, with remarkable red shift and increased quantum yields, and upon exposure to solvents, they are restored to their original color and emission. On the basis of powder X-ray diffraction studies, a plausible mechanism of the mechanochromic processes is proposed, involving reversible crystalline-to-amorphous phase transitions.

An Extended Chain and Trinuclear Complexes Based on Pt(II)-M (M = Tl(I), Pb(II)) Bonds: Contrasting Photophysical Behavior.

The syntheses and structural characterizations of a Pt-Tl chain [{Pt(bzq)(C6F5)2}Tl(Me2CO)]n 1 and two trinuclear Pt2M clusters (NBu4)[{Pt(bzq)(C6F5)2}2Tl] 2 and [{Pt(bzq)(C6F5)2}2Pb] 3 (bzq = 7,8-benzoquinolinyl), stabilized by donor-acceptor Pt → M bonds, are reported. The one-dimensional heterometallic chain 1 is formed by alternate "Pt(bzq)(C6F5)2" and "Tl(Me2CO)" fragments, with Pt-Tl bond separations in the range of 2.961(1)-3.067(1) Å. The isoelectronic trinuclear complexes 2 (which crystallizes in three forms, namely, 2a, 2b, and 2c) and 3 present a sandwich structure in which the Tl(I) or Pb(II) is located between two "Pt(bzq)(C6F5)2" subunits. NMR studies suggest equilibria in solution implying cleavage and reformation of Pt-M bonds. The lowest-lying absorption band in the UV-vis spectra in CH2Cl2 and tetrahydrofuran (THF) of 1, associated with (1)MLCT/(1)L'LCT (1)[5dπ(Pt) → π*(bzq)]/(1)[(C6F5) → bzq], displays a blue shift in relation to the precursor, suggesting the cleavage of the chain maintaining bimetallic Pt-Tl fragments in solution, also supported by NMR spectroscopy. In 2 and 3, it shows a blue shift in THF and a red shift in CH2Cl2, supporting a more extensive cleavage of the Pt-M bonds in THF solutions than in CH2Cl2, where the trinuclear entities are predominant. The Pt-Tl chain 1 displays in solid state a bright orange-red emission ascribed to (3)MM'CT (M' = Tl). It exhibits remarkable and fast reversible vapochromic and vapoluminescent response to donor vapors (THF and Et2O), related to the coordination/decoordination of the guest molecule to the Tl(I) ion, and mechanochromic behavior, associated with the shortening of the intermetallic Pt-Tl separations in the chain induced by grinding. In frozen solutions (THF, acetone, and CH2Cl2) 1 shows interesting luminescence thermochromism with emissions strongly dependent on the solvent, concentration, and excitation wavelengths. The Pt2Tl complex 2 shows an emission close to 1, ascribed to charge transfer from the platinum fragment to the thallium [(3)(L+L')MM'CT]. 2 also shows vapoluminescent behavior in the presence of vapors of Me2CO, THF, and Et2O, although smaller and slower than those of 1. The trinuclear neutral complex Pt2Pb 3 displays a blue-shift emission band, tentatively assigned to admixture of (3)MM'CT (3)[Pt(d) → Pb(sp)] with some metal-mediated intraligand ((3)ππ/(3)ILCT) contribution. In contrast to 1 and 2, 3 does not show vapoluminescent behavior.

Reversible binding of solvent to naked PbII centers in unusual homoleptic alkynyl-based Pt2Pb2 clusters.

We report a series of luminescent sandwich-type clusters [Pt2 Pb2 (C≡CR)8] (R=Tol, 1; C6 H4 OMe-3, 2; C6 H4 OMe-4, 3) with a dynamic Pt2 Pb2 metallic core, which is key to their intriguing stimuli-responsive photophysical properties. The solvent-free solids 1-3 display an orange emission ascribed to charge transfer from Pt-alkynyl fragments to a delocalized orbital with mixed Pt2 Pb2 /C≡CR nature, with a predominant lead contribution and Pb⋅⋅⋅Pb bonding character ((3) MLCCT/(3) IL). They exhibit mechanical, color, and luminescence changes that are reversible and perceivable with the naked eye, which are attributed to small inter- and intramolecular structural modifications induced by gentle grinding. Interestingly, 1 and 2 also exhibit remarkable and fast reversible vapochromic responses to donor solvent vapors (acetone, THFMe-2: yellow; NCMe: green, vs. dry solids: orange). The structures of 1(acetone)2 ⋅2(Me2 CO), 2(acetone)3 , and 2(THFMe-2)2 allow the vapochromic responses to be ascribed to the fast creation/disruption of solvate clusters [Pt2 Pb2 (C≡CR)8 Sx] (x≥2), with concomitant electronic and geometrical modifications within the Pt2 Pb2 core, which are easily accessible through a slight change in the stereochemical activity of the lone pair. The binding of one (or two) solvent molecules to Pb(2+) increases the Pb⋅⋅⋅Pb separation in the metallic core, causing a destabilization of the target orbital and larger energy gaps of the transitions. All the solvates exhibit remarkable rigidochromism upon a decrease in temperature, which is also associated with the gradual increase in the transannular Pb⋅⋅⋅Pb separation, as revealed by X-ray crystallography of 1(acetone)2 at different temperatures. Investigation of the crystal lattice of 1⋅CH2 Cl2 and 3⋅2 CH2 Cl2 further suggests that the lack of vapor stimuli response of complex 3 could be attributed to the presence of competitive additional secondary intermolecular Pb⋅⋅⋅O(OMe) contacts, which give rise to a more compact network built up from extended chains of clusters.

Photophysical responses in Pt2Pb clusters driven by solvent interactions and structural changes in the Pb(II) environment.

Two types of Pt2Pb luminescent clusters were successfully prepared by the reaction of [Pt(C6F5)(bzq)(OCMe2)] (1) and [Pt(C6F5)(ppy)(dmso)] (2) with [Pb(SpyR-5)2] (R = H, CF3). Thus, whereas 5 (ppy, Spy) is generated through coordination of the pyridine-N atoms to the Pt centers, the formation of 3, 4 (bzq), and 6 (ppy, SpyCF3) is accompanied by a formal thiolate transfer from Pb(II) to Pt(II), keeping the two N atoms in the primary environment of the lead. In 5, the neutral Pb center adopts a rather stable and symmetrical "Pt2S2" coordination sphere supplemented by two Pb··Fo contacts, whereas for the remaining species several pseudopolymorphs were found depending on the solvent (3, 4) and crystallization conditions (6). This structural diversity relies on changes in the coordination mode of the SpyR ligands (µ-κS,N/µ-κ(3)S,N,S), intermetallic Pt-Pb bonds, and secondary intra- and intermolecular contacts induced by Pb-solvent binding. Notably, the changes, which entail a slight tuning of the stereochemical activity of the lone pair, have also a remarkable impact on the emissive state ((3)L'CCT/(3)L'LCT, SpyR → Pb,Pt/(C(∧)N) in nature). Clusters 3 and 4 display a distinct and fast reversible blue shift vapoluminescent response (4 shows also color changes) to donor solvents, correlated with changes in the environment of the Pb(II) ion (asymmetric hemidirected to more symmetric holodirected) upon solvent binding and, additionally, in 4 with modifications in the crystal packing, as confirmed by XRD and supported by TD-DFT calculations. 5 and 6 do not show a vapoluminescent response. However, for 6, three different and interconvertible forms, a symmetrical form (yellow 6-y) and two asymmetrical forms with a rather short Pt-Pb bond (pale orange 6·acetone and orange 6-o), exhibiting different emissions were found. Notably, slow crystallization and low concentration favor the formation of the thermodynamically more stable yellow form, whereas fast crystallization gives rise to orange solids with a remarkable red shift of the emission. Interestingly, 6 also exhibits reversible mechanochromic color and luminescence changes.

Ladder-like heteropolynuclear assemblies via cyanido bridges and platinum(II)-thallium(I) bonds: structural and photophysical properties.

We describe the mononuclear anionic cyanido-pentafluorophenyl complexes, (NBu4)[Pt(C^N)(C6F5)(CN)] [C^N = 7,8-benzoquinolate (bzq) 1, 2-(2,4-difluorophenyl)pyridinate (dfppy) 2] and the heteropolynuclear derivatives [{Pt(C^N)(C6F5)(CN)}Tl] (C^N = bzq 3, dfppy 4). These complexes were synthesized via a two-step modular synthesis by reaction of the corresponding potassium salts K[Pt(C^N)(C6F5)(CN)], prepared in situ from [Pt(C^N)(C6F5)(DMSO)] and KCN in acetone/H2O, with TlPF6. The structures of {[Pt(bzq)(C6F5)(CN)Tl]·THF}n (3·THF)n and [{Pt(dfppy)(C6F5)(CN)}Tl]4·dioxane [4]4·dioxane, determined by X-ray crystallography, confirm the presence of Pt(II)-Tl(I) bonds [2.9795(6)-3.0736(3) Å], but in the dfppy complex, the incorporation of dioxane, causes a significant structural change. Thus, whereas [3·THF]n achieves a bent-ladder shape extended double chain Tl⋯[Pt⋯Tl]n⋯Pt supported by lateral bridging [Pt](µ-CN)[Tl] ligands, [4]4·dioxane is formed by discrete Pt4Tl4 rectangular aggregates stabilized by [Pt](µ-CN)[Tl] and Pt⋯Tl bonds, which are connected by dioxane bridging molecules through Tl⋯O(dioxane) additional contacts. Solid state emissions are redshifted compared with the mononuclear derivatives 1 and 2 and have been assigned, with the support of theoretical calculations on Pt4Tl4 models, to metal-metal'-to-ligand charge transfer (3MM'LCT [d/s σ*(Pt, Tl) → π*(C^N)]) for 3 and mixed 3MM'LCT/3IL for 4. In fluid THF solution, the complexes are not emissive. At 77 K, 3 and 4 exhibit bright emissions attributed to the formation of bimetallic [{Pt(C^N)(C6F5)(CN)}Tl(THF)x], and anionic [Pt(C^N)(C6F5)(CN)]- fragments. Furthermore, both 3 and 4 exhibit a reversible mechanochromism with a red shift of the emissions upon crushing, suggesting some degree of shortening of metal-metal separation. Finally, complex 3 shows solvatochromic behavior with color/luminescence changes by treatment with a drop of MeOH, CH2Cl2, THF or Et2O, with shifts from 583 in 3-MeOH to 639 nm in 3-THF. However, 4 only demonstrates a bathochromic response to MeOH.

A highly efficient luminescent Pt2Tl2 chain with a short Tl(I)-Tl(I) interaction.

The preparation of an unsupported tetranuclear cluster with a linear Pt(0)-Tl(I)-Tl(I)-Pt(0) metal chain is described. The complex shows strong red emission in the solid state, having a quantum yield of 73%. Density functional theory (DFT) and time-dependent DFT calculations show that red emission originated from a platinum to thallium-thallium charge-transfer excited state.

Phosphorescent 2-phenylbenzothiazole PtIV bis-cyclometalated complexes with phenanthroline-based ligands.

We describe a family of dicationic heteroleptic complexes of the type [Pt(pbt)2(N^N)]Q2, bearing two cyclometalating 2-phenylbenzothiazole (pbt) groups and a N^N phenanthroline-based ligand [N^N = 1,10-phenanthroline (phen) 4, pyrazino[2,3-f][1,10]-phenanthroline (pyraphen) 5, 5-amine-1,10-phenanthroline (NH2-phen) 6], with two different counteranions (Q = CF3CO2 and PF6). Complexes 4-6-PF6 and 4-6-CF3CO2 were obtained through ligand substitution from cis-[Pt(pbt)2Cl2] 2 and cis-[Pt(pbt)2(OCOF3)2] 3, respectively. The molecular structures of 2, 3 and 4-PF6 and the photophysical and electrochemical properties of all complexes were studied in detail. The precursors 2 and 3 exhibit high-energy emissions from 3IL excited states centered on the cyclometalated pbt, with lower efficiency in 2 in relation to 3 by the presence of closer thermally accessible deactivating 3LMCT excited states in 2. The PtIV complexes 4-5-CF3CO2/PF6 display orange emission in CH2Cl2 solution, solid state (298, 77 K) or PS films, arising from a 3IL(pbt) emissive state. The NH2-phen derivatives 6-CF3CO2/PF6 show dual emission associated to two close different emissive states, 3IL'CT (L' = NH2-phen) and 3IL(pbt), depending on the medium and the excitation wavelength. DFT and time-dependent TD-DFT calculations support these assignments and allow explain the luminescence of these tris-chelate PtIV complexes.

A new family of luminescent iridium complexes: synthesis, optical, and cytotoxic studies.

By using N,N-dibutyl-2,2'-bipyridine-4,4'-dicarboxamide as a diimine (dbbpy) and distinctive cyclometalated groups, this work reports a new family of cationic phosphorescent Ir(III) cyclometalated [Ir(C^N)2(N^N)]X compounds [C^N = difluorophenylpyridine (dfppy) a, 2,6-difluoro-3-(pyridin-2-yl)benzaldehyde (CHO-dfppy) b, and 2,6-difluoro-3-pyridin-2-yl-benzoic acid (COOH-dfppy) c; X = Cl-2a,b,c-Cl; X = PF6-2b,c-PF6]. For comparative purposes, the related complex [Ir(dfppy)2(H2dcbpy)]+ (3a-PF6) incorporating 3,3'-dicarboxy-2,2'-bipyridine as an auxiliary ligand (N^N = H2dcbpy) is also presented. All complexes have been fully characterized and their photophysical properties were investigated in detail. The theoretically calculated results obtained by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) studies indicate that luminescence is derived from mixed 3ML'CT (Ir → N^N)/3LL'CT (C^N → N^N) excited states with the predominant metal-to-diimine charge transfer character. Their antineoplastic activity against tumour cell lines A549 (lung carcinoma) and HeLa (cervix carcinoma), as well as the nontumor BEAS-2B (bronchial epithelium) cell line was assessed and fluorescence microscopy studies were performed for their cellular localization. Among them, 2a-Cl exhibited the most potent anticancer activity, being higher than cisplatin. However, 2b-Cl and 2c-Cl,-PF6 were the least toxic, while 2b-PF6 and 3a-PF6 exhibited only moderate activity. Confocal microscopy studies for 2a-Cl suggest that complexes localize preferentially in the lysosomes and to a lesser extent in the cytoplasm, but ultimately causing damage to the mitochondria. Finally, the potential photodynamic behaviour of scarcely toxic complexes 2b-Cl, 2b-PF6, 2c-Cl and 3a-PF6 was also studied.