A new cyclometalated derivative, (NBu4)[Pt(bzq)(C6Cl5)2] (2) (bzq = 7,8-benzoquinolate), and three novel polymetallic species containing donor−acceptor Pt→Ag bonds, (NBu4)[{Pt(bzq)(C6F5)2}2Ag] (3) and [{Pt(bzq)(C6X5)2}Ag(PPh3)] (X = F (4), Cl (5)), have been synthesized and characterized by X-ray diffraction methods. 3 is prepared by reaction of (NBu4)[Pt(bzq)(C6F5)2] (1) with AgClO4 in 1:1 or 1:0.5 molar ratio, while 4 and 5 are the results of the reaction of the corresponding (NBu4)[Pt(bzq)(C6X5)2] (X = F (1), Cl (2)) precursors with [Ag(OClO3)(PPh3)] in 1:1 molar ratio. 3 has been found to crystallize in two forms:  monoclinic (3a) and triclinic (3b), which differ not only in the conformation of the basic Pt2Ag anion (anti and planar 3a, staggered and nonplanar 3b), but also in the crystal packing (π···π extended structure 3a, and a stacked dimer 3b) and luminescence at 298 K (orange 3a, green 3b). At 77 K, the orange band (568 nm) of 3a, attributed to a ππ* excimeric emission, is not detected, and both polymorphs exhibit identical green emission (3LC/3MLCT). Spectroscopic study of 4 and 5 (UV−vis and luminescence) was also performed to examine the role of the Pt→Ag donor−acceptor bond. The most significant feature is the blue shift observed in the low-energy UV absorption and the appearance of two, close, distinct, structured emissions with short (487 4; 490 nm 5) and long (502 nm 4, 5) lifetime, but only in the solid state at 77 K.

Novel bimetallic neutral [(C6F5)4PtCd(cyclen)] and [(C6F5)2(C⋮CPh)2PtCd(cyclen)] (1, 2) and cationic [(C6F5)2(bzq)PtCd(cyclen)](ClO4) (3) pentafluorophenylplatinum(II)−cadmium(II) derivatives have been prepared by treatment of the adequate anionic starting precursors [Pt(C6F5)2X2] n - (n = 2, X = C6F5, C⋮CPh; n = 1, X2 = bzq) with Cd(ClO4)2 and cyclen. X-ray diffraction studies on complexes 1, 2, and 3 show that they are stabilized by a short Pt→Cd donor acceptor bond and, additionally, in complex 2 the Cd center is also coordinated to the Cα of one of the two alkynyl groups. In contrast, treatment of the binuclear compound [NBu4]2[Pt2(μ-Cl)2(C6F5)4] with [Cd(cyclen)(MeOH)2](ClO4)2 afforded the tetranuclear derivative [Pt(C6F5)2Cl(μ-Cl)Cd(cyclen)]2 (4) (X-ray), in which Pt and Cd atoms are connected by a μ3-Cl bridging ligand, and the binuclear cadmium complex [Cd2(μ-Cl)2(cyclen)2](ClO4)2 (5) (X-ray), in which two “Cd(cyclen)” fragments are bridged by two chlorine atoms. The photoluminescent properties of complexes 1−3 have also been examined and compared with those of their corresponding anionic parent compounds [NBu4]2[Pt(C6F5)4], [PMePh3]2[Pt(C6F5)2(C⋮CPh)2], and [NBu4][Pt(C6F5)2(bzq)] (6).

The field of metallosupramolecular chemistry is clearly dominated by the use of O-N-, and P-donor Werner-type polydentate ligands. These molecular architectures are of high interest because of their wide range of applications, which include molecular encapsulation, stabilization of reactive species, supramolecular catalysis, and drug delivery, among others. Only recently, organometallic ligands have allowed the preparation of a variety of supramolecular coordination complexes, and the term supramolecular organometallic complexes (SOCs) is gaining space within the field of metallosupramolecular chemistry. While the early examples of SOCs referred to supramolecular architectures mostly containing bisalkenyl, diphenyl, or bisalkynyl linkers, the development of SOCs during the past decade has been boosted by the parallel development of multidentate N-heterocyclic carbene (NHC) ligands. The first examples of NHC-based SOCs referred to supramolecular assemblies based on polydentate NHC ligands bound to group 11 metals. However, during the last 10 years, several planar poly-NHC ligands containing extended π-conjugated systems have facilitated the formation of a large variety of architectures in which the supramolecular assemblies can contain metals other than Cu, Ag, and Au. Such ligands are Janus di-NHCs and trigonal-planar tris-NHCsmost of them prepared by our research groupwhich have allowed the preparation of a vast range of NHC-based metallosupramolecular compounds with interesting host− guest chemistry properties. Although the number of SOCs has increased in the past few years, their use for host−guest chemistry purposes is still in its earliest infancy. In this Account, we describe the achievements that we have made during the last 4 years toward broadening the applications of planar extended π-conjugated NHC ligands for the preparation of organometallic-based supramolecular structures, including their use as hosts for some selected organic and inorganic guests, together with the catalytic properties displayed by some selected host−guest inclusion complexes. Our contribution describes the design of several Ni-, Pd-, and Au-based metallorectangles and metalloprisms, which we used for the encapsulation of several organic substrates, such as polycyclic aromatic hydrocarbons (PAHs) and fullerenes. The large binding affinities found are ascribed to the incorporation of two cofacial panels with large π-conjugated systems, which provide the optimum conditions for guest recognition by π−π-stacking interactions. We also describe a series of digold(I) metallotweezers for the recognition of organic and inorganic substrates. These metallotweezers were used for the recognition of "naked" metal cations and polycyclic aromatic hydrocarbons. The recognition properties of these metallotweezers are highly dependent on the nature of the rigid connector and of the ancillary ligands that constitute the arms of the tweezer. A peculiar balance between the self-aggregation properties of the tweezer and its ability to encapsulate organ...

Two gold(I)-based metallo-tweezers with bis(Au-NHC) pincers and a carbazole connector have been obtained and used for the recognition of polycyclic aromatic hydrocarbons (PAHs). In the case of the tweezer with pyrene-NHC ligands, the presence of the pyrene fragment and the N-H bond in the carbazole linker enable the receptor to show significant enhanced binding abilities toward PAHs functionalized with H-bonding groups, through combined π-π stacking and H-bonding.

Reaction of unsaturated (44e (-) skeleton) [PdPt 2(mu-PPh 2) 2(mu-P 2Ph 4)(R F) 4] 4 with Br (-) produces the saturated (48e (-) skeleton) complex [NBu 4][(R F) 2Pt(mu-PPh 2)(mu-Br)Pd(mu-PPh 2)(mu-P 2Ph 4)Pt(R F) 2] 5 without any M-M' bond. Attempts to eliminate Br (-) of 5 with Ag (+) in CH 2Cl 2 as a solvent gives a mixture of [(R F) 2Pt (III)(mu-PPh 2) 2Pt (III)(R F) 2] and some other unidentified products as a consequence of oxidation and partial fragmentation. However, when the reaction of 5 with Ag (+) is carried out in CH 3CN, no oxidation is observed but the elimination of Br (-) and the formation of [(R F) 2(CH 3CN)Pt(mu-PPh 2)Pd(mu-PPh 2)(mu-P 2Ph 4)Pt(R F) 2] 6 (46e (-) skeleton), a complex with a Pt-Pd bond, takes place. It is noteworthy that the reaction of 5 with TlPF 6 in CH 2Cl 2 does not precipitate TlBr but forms the adduct [(R F) 2PtTl(mu-PPh 2)(mu-Br)Pd(mu-PPh 2)(mu-P 2Ph 4)Pt(R F) 2] 7 with a Pt-Tl bond. Likewise, 5 reacts with [AgOClO 3(PPh 3)] in CH 2Cl 2 forming the adduct [AgPdPt 2(mu-Br)(mu-PPh 2) 2(mu-Ph 2P-PPh 2)(R F) 4(PPh 3)] 8, which contains a Pt-Ag bond. Both adducts are unstable in a CH 3CN solution, precipitating TlBr or AgBr and yielding the unsaturated 6. The treatment of [NBu 4] 2[(R F) 2Pt(mu-PPh 2) 2Pd(mu-PPh 2) 2Pt(R F) 2] in CH 3CN with I 2 (1:1 molar ratio) at 233 K yields a mixture of 4 and 6, which after recrystallization from CH 2Cl 2 is totally converted in 4. If the reaction with I 2 is carried out at room temperature, a mixture of the isomers [NBu 4][(R F) 2Pt(mu-PPh 2)(mu-I)Pd(mu-PPh 2)(mu-P 2Ph 4)Pt(R F) 2] 9 and [NBu 4][(R F)(PPh 2R F)Pt(mu-PPh 2)(mu-I)Pd(mu-PPh 2) 2Pt(R F) 2] 10 are obtained. The structures of the complexes have been established on the bases of NMR data, and the X-ray structures of 5- 8 have been studied. The relationship between the different complexes has been studied.