Planar dimers

Scheme 2.4 Examples of dimeric planar and folded (NaNi frameworks with terminal tmeda ligands ° ° >...

Fig. 20. Optimized structures (6-31G basis set level) of (a) (H2C=NLi)2 dimer, planar, (b) (H2C=NLi)2 dimer, perpendicular, and (c) (H2C=NLi)3 trimer, planar.

N-9a The polymeric complex [Ag2 C6H4-l,2-(C02)2 (C8H6N2)2(H20)] (142) is formed by dimeric planar Ag-phthalazine units that are linked in a chain through the Ag atoms by phthalate anions. In the latter, one of the carboxylate groups bonds two Ag atoms in successive dimeric units, whereas the second one forms a seven-membered chelate ring with one of the Ag atoms and is H-bonded to a solvating water molecule221. 

Hexamethyl Dewar Benzene co-ordinates as a pz-allylic ligand with palladium (II). The structure of the complex [Pd(acac)dehydro-HMDB] is shown in D.XX mT With platinum, however, pz -o-bonding is preferred as in the dimeric planar [PtCl-dehydro HMDB]2, D.XXI 122>. 

When heated above 673 K the dimer, AljCl, begins to dissociate into the monomer in which the aluminium has a regular trigonal planar configuration. 

The three bands in Figure 9.46 show resolved rotational stmcture and a rotational temperature of about 1 K. Computer simulation has shown that they are all Ojj bands of dimers. The bottom spectmm is the Ojj band of the planar, doubly hydrogen bonded dimer illustrated. The electronic transition moment is polarized perpendicular to the ring in the — Ag, n — n transition of the monomer and the rotational stmcture of the bottom spectmm is consistent only with it being perpendicular to the molecular plane in the dimer also, as expected. 

Figure 9.46 Rotational structure of the Ojj bands in the fluorescence excitation spectra of s-tetrazine dimers at about 552 run. Bottom Ojj band of planar dimer. Middle Ojj band of T-shaped dimer with transition in monomer unit in stem of T. Top Ojj band of T-shaped dimer with transition in monomer unit in top of T. (Reproduced, with permission, from Haynam, C. A., Brumbaugh, D. V and Levy, D. H., J. Chem. Phys., 79, f58f, f983)...

Single-Stack Acceptor. Simple charge-transfer salts formed from the planar acceptor TCNQ have a stacked arrangement with the TCNQ units facing each other (intermolecular distances of ca 0.3 nm (- 3). Complex salts of TCNQ such as TEA(TCNQ)2 consist of stacks of parallel TCNQ molecules, with cation sites between the stacks (17). The interatomic distance between TCNQ units is not always uniform in these salts, and formation of TCNQ dimers (as in TEA(TCNQ)2) and trimers (as in Cs2(TCNQ)Q can lead to complex crystal stmctures for the chainlike salts. 

The most common oxidatiou states and corresponding electronic configurations of rhodium are +1 which is usually square planar although some five coordinate complexes are known, and +3 (t7 ) which is usually octahedral. Dimeric rhodium carboxylates are +2 (t/) complexes. Compounds iu oxidatiou states —1 to +6 (t5 ) exist. Significant iudustrial appHcatious iuclude rhodium-catalyzed carbouylatiou of methanol to acetic acid and acetic anhydride, and hydroformylation of propene to -butyraldehyde. Enantioselective catalytic reduction has also been demonstrated. 

Fig. 60. Configuration and relevant coordinates of the planar HF dimer in stable and transition configurations. The angles and intermolecular distance are = 9°, 6 = 116°, R = 2.673 A in the stable configuration 0, = 02 = 54.9°, R = 2.S61 k in the transition configuration. The HF bond lengths are constant within an accuracy of 0.003 A.

Me3C6H2-). By contrast, B(PEt2>3 is a dimer with a planar B2P2 ring of 4-coordinate B and P atoms (124).d o) planar 4-membered ring of 3-coordinate planar B and pyramidal P atoms is featured in the diphos-phadiboretane MesPB(tmp) 2 (125) (tmp =... 

Figure 15.39 Structures of (a) the planar radical cation S3N2, (b) its dimer SeN4 + and (c) the corresponding planar diamagnetic dication S3N2 +.

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