Ligand-based charge-transfer luminescence in ionic cyclometalated iridium(III) complexes bearing a pyrene-functionalized bipyridine ligand: a joint theoretical and experimental study.

Two new heteroleptic iridium(III) complexes [Ir(ppy)(2)(pyr(2)bpy)][PF(6)] ([1a][PF(6)]) and [Ir(dfppy)(2)(pyr(2)bpy)][PF(6)] ([2a][PF(6)]), where Hppy = 2-phenylpyridine, Hdfppy = 2-(3,5-difluorophenyl)pyridine, and pyr(2)bpy = 5,5'-bis(pyren-1-yl)-2,2'-bipyridine, have been synthesized and fully characterized. The single-crystal structures of pyr(2)bpy and the complexes 4{[1a][PF(6)]}·2CH(2)Cl(2)·9H(2)O and [2a][PF(6)]·0.25CH(2)Cl(2)·H(2)O have been determined. The effect of the pyrene substituents on the electronic properties is investigated through a comprehensive photophysical and theoretical study on the two complexes in comparison to reference complexes without substituents on the ancillary ligand ([1][PF(6)] and [2][PF(6)]) and by making absorption and luminescence titrations of ligand pyr(2)bpy. Both theory and experiment show that the intense and broad band appearing in the 400-500 nm region of the absorption spectra of [1a][PF(6)] and [2a][PF(6)] is due to intramolecular charge-transfer (ICT) transitions from the pyrene substituents to the bipyridine ligand. [1a][PF(6)] and [2a][PF(6)] exhibit luminescence bands centered above 650 nm, attributed to a charge-transfer triplet state located on the pyr(2)bpy ligand, lying at lower energy than the strongly emitting Ir-ppy→bpy triplet states of the complexes lacking the pyrene fragments. Such luminescence, detected both at room temperature and 77 K, shows that the appendage of luminophoric moieties to luminescent Ir-based centers may further widen the emission tuneability of this exploited class of luminescent materials through purely electrostatic effects exerted on a properly designed N^N ancillary ligand.

Towards catenanes using π-stacking interactions and their influence on the spin-state of a bis(2,2':6',2"terpyridine)iron(II) domain.

The ligand 6,6"bis(4-methoxyphenyl)-4'-phenyl-2,2':6',2"terpyridine (2) has been prepared and characterized; deprotection using pyridinium chloride leads to the formation of 6,6"bis(4-hydroxyphenyl)-4'-phenyl-2,2':6',2"terpyridinium chloride ([H3]Cl). Treatment of the latter with 3-(2-(2-bromoethoxy)ethoxy)prop-1-ene under basic conditions yields ligand 4 containing pendant, alkene-terminated chains. Whereas direct complexation of 4 with ruthenium(II) proved problematical, the homoleptic complexes [Fe(2)(2)][PF(6)](2) and [Ru(2)(2)][PF(6)](2) were prepared in good to moderate yields. In the solid state, both complexes exhibit multiple face-to-face π-stacking of arene and pyridine rings which influences the coordination geometry about the metal ion. Consequential weakening of the ligand field results in [Fe(2)(2)][PF(6)](2) being high-spin. Variable temperature solution (1)H NMR spectroscopic studies confirm the iron(ii) centre remains high-spin between 200 and 295 K. The paramagnetically shifted (1)H NMR spectrum exhibits signals in the range δ 109.7 to -66.5 ppm and has been fully assigned. Paramagnetic relaxation enhancement (PRE) has been used to correlate the observed proton line-widths to the distances of the protons from the metal centre and these are in good agreement with the Fe···H separations observed in the solid state. The [Fe(2)(2)](2+) ion undergoes two dynamic processes (i) rotation of the pendant phenyl rings which is fast on the NMR timescale at 200 K, and (ii) twisting and sliding of the aromatic rings of the tpy and anisyl units which interconverts the two enantiomers of [Fe(2)(2)](2+) at 295 K.

Clicking hard-core sugar balls.

CLICK methodology has been used for the preparation of saccharide decorated {M(bpy)(3)} scaffolds; mononuclear complexes with two or six xylopyranose residues have been prepared in excellent yield from alkyne-functionalised cores and azidosugars.

Metallomacrocycles with a difference: macrocyclic complexes with exocyclic ruthenium(II)-containing domains.

The templated synthesis of organic macrocycles containing rings of up to 96 atoms and three 2,2'-bipyridine (bpy) units is described. Starting with the bpy-centred ligands 5,5'-bis[3-(1,4-dioxahept-6-enylphenyl)]-2,2'-bipyridine and 5,5'-bis[3-(1,4,7-trioxadec-9-enylphenyl)]-2,2'-bipyridine, we have applied Grubbs' methodology to couple the terminal alkene units of the coordinated ligands in [FeL3]2+ complexes. Hydrogenation and demetallation of the iron(II)-containing macrocyclic complexes results in the isolation of large organic macrocycles. The latter bind {Ru(bpy)2} units to give macrocyclic complexes with exocyclic ruthenium(II)-containing domains. The complex [Ru(bpy)2(L)]2+ (isolated as the hexafluorophosphate salt), in which L=5,5'-bis[3-(1,4,7,10-tetraoxatridec-12-enylphenyl)]-2,2'-bipyridine, undergoes intramolecular ring-closing metathesis to yield a macrocycle which retains the exocyclic {Ru(bpy)2} unit. The poly(ethyleneoxy) domains in the latter macrocycle readily scavenge sodium ions, as proven by single-crystal X-ray diffraction and atomic absorption spectroscopy data for the bulk sample. In addition to the new compounds, a series of model complexes have been fully characterized, and representative single-crystal X-ray structural data are presented for iron(II) and ruthenium(II) acyclic and macrocyclic species.

Diversification of ligand families through ferroin-neocuproin metal-binding domain manipulation.

Derivatization of 5,5-bis(3-hydroxyphenyl)-2,2-bipyridine to give two new ligands, 3 and 4, which possess terminal alkene functionalities is described. The syntheses and characterization of the palladium(II) complexes [Pd(3)2][BF4]2 and [Pd(4)2][BF4]2, and the related [Pd( 2)2][BF4]2 in which 2 is 5,5-bis(3-methoxyphenyl)-2,2-bipyridine are reported. The labile nature of the ligand leads to [Pd(2)2][BF4]2 co-crystallizing with the free ligand as [Pd(2)2][BF4]2 x 2; in the solid state, the ligands in the [Pd(2)2]2+ cation distort (a bow-incline distortion) to alleviate bpy H6...H6 repulsions. Compound 2 has been converted to 5,5-bis(3-methoxyphenyl)-6-methyl-2,2-bipyridine (5) and 5,5-bis(3-methoxyphenyl)-6,6-dimethyl-2,2-bipyridine (6) to produce ligands suited to forming air-stable, copper(I) complexes of type [CuL2]+. [Cu(5)2][PF6] and [Cu(6)2][PF6] have been prepared and characterized, and the single crystal structures of 6 and [Cu(5)2][PF6] x 0.1C2H4Cl2 x 0.15CH2Cl2 are described. By altering the conditions under which 2 is methylated, competitive formation of 5,5,5,5-tetrakis(3-methoxyphenyl)-2,2:3,3:2,2-quaterpyridine occurs.