Square macrocycle

Figure 32. Frequency dependence of electro-optic Kerr constant B for BAG (squares) macrocycle...

Manna, J., C.J. Kuehl, J.A. Whiteford, P.J. Stang, D.C. Muddiman, SA. Hofstadler, and R.D. Smith (1997). Nanoscale tectonics Self-assembly, characterization, and chemistry of a novel class of organoplatinum square macrocycles. J. Am. Chem. Soc. 119, 11611-11619. 

With their preference for square planar coordination, palladium(II) and platinum(II) are well suited to binding to porphyrins and related N4 donor macrocycles. Therefore, Pd(octaethylporphyrin) is readily synthesized starting from the labile PhCN complex (like the platinum analogue) [92]... 

It has square planar coordination (Pd-N 2.010-2.017 A) similar to the value of 2.009 A in the tetraphenylporphyrin analogue, prepared by a similar route. As with nickel, macrocycle complexes can be made by in situ template... 

With a tridentate ligand Au(terpy)Cl3.H20 has, in fact, AuCl(terpy)2"1" with weakly coordinated chloride and water while Au(terpy)Br(CN)2 has square pyramidal gold(III) the terpyridyl ligand is bidentate, occupying the axial and one basal position [124]. Macrocyclic complexes include the porphyrin complex Au(TPP)Cl (section 4.12.5) cyclam-type macrocyclic ligands have a very high affinity for gold(III) [125],... 

The template-directed preparation of cycloi is(paraquat-4,4 -biphenylene (a molecular square ) has been achieved the use of a macrocyclic hydroquinone-based polyether template incorporating an ester moiety in one polyether chain afforded a 1 1 mixture of two topologically stereoisomeric [3]catenanes <96CEJ877>. 

To mimic the square-pyramidal coordination of iron bleomycin, a series of iron (Il)complexes with pyridine-containing macrocycles 4 was synthesized and used for the epoxidation of alkenes with H2O2 (Scheme 4) [35]. These macrocycles bear an aminopropyl pendant arm and in presence of poorly coordinating acids like triflic acid a reversible dissociation of the arm is possible and the catalytic active species is formed. These complexes perform well in alkene epoxidations (66-89% yield with 90-98% selectivity in 5 min at room temperature). Furthermore, recyclable terpyridines 5 lead to highly active Fe -complexes, which show good to excellent results (up to 96% yield) for the epoxidation with oxone at room temperature (Scheme 4) [36]. 

Macrocyclic receptors made up of two, four or six zinc porphyrins covalently connected have been used as hosts for di- and tetrapyridyl porphyrins, and the association constants are in the range 105-106 M-1, reflecting the cooperative multipoint interactions (84-86). These host-guest complexes have well-defined structures, like Lindsey s wheel and spoke architecture (70, Fig. 27a), and have been used to study energy and electron transfer between the chromophores. A similar host-guest complex (71, Fig. 27b) was reported by Slone and Hupp (87), but in this case the host was itself a supramolecular structure. Four 5,15-dipyridyl zinc porphyrins coordinated to four rhenium complexes form the walls of a macrocyclic molecular square. This host binds meso-tetrapyridyl and 5,15-dipyridyl porphyrins with association constants of 4 x 107 M-1 and 3 x 106 M-1 respectively. 

The fe-Ir1 complex (344) of the selena sapphyrin ligand has been synthesized and characterized by X-ray diffraction studies.551 The pairs of bound N atoms in (344) are bent towards the Ir1 centers, and the respective pyrrole rings are twisted from the macrocyclic plane. The coordination geometry around the Ir is close to square-planar, and the Ir Ir distance is 4.233 A. The Se center is not involved in bonding to the Ir centers. 

Square planar Ni11 complexes with saturated macrocyclic ligands usually have Ni—N bond distances ranging from 1.90 A to 1.95 A, depending on the type of ligand. The Ni—N bond distances increase when square planar Ni11 complexes bind axial ligands to form octahedral species.91... 

Square planar Ni11 macrocyclic complexes are typically yellow, red, or brown in color and absorb around 400 500 nm, depending on the ligand structure. The octahedral Ni11 complexes absorb at 500A100 nm. 

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