Singly Bonded Dimers

Photoreactions have been carried out with the singly bonded diplat-inum(III) complexes Pt2(pop)4Cl2, Pt2(//-HP04)4Clt, and 

One of the first singly bonded diplatinum complexes for which emission has been observed is the diplatinum(III) complex Pt2(pop)4Cl. Continued photolysis of this complex results in a reductive elimination reaction to give chlorine and the diplatinum(II) complex Pt2(pop)4 (Ref. 101)  

A second group of complexes having the a n 8 d n singly bonded electronic configuration are dirhodium(II) complexes. One such complex is Rh2(MeN(PF2)2)3CU, the photochemistry of which has been discussed in Section 4.7.1. 

The mercurous ion Hg2 has a single intermetallic bond joining the Hg(I) metal centers. Irradiation into the 7 — (7 orbital of this ion leads to the formation of the Hg ion. When the photolysis of Hg2 is carried out in the presence of ethyl alcohol, reduction of the Hg ion to elemental mercury occurs. If the divalent ion Hg is also present in the reaction, a rapid electron transfer reaction occurs between Hg and Hg to give 

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While solid-state stmctures are readily generated by crystallography, evidence for stmctures in solution is usually generated by spectroscopic techniques. Rotation about the metal metal bond of single-bonded dimers has been studied extensively by NMR and IR (see Structure Property Maps for Inorganic Solids). For example, the complex [Mo(CO)3Cp]2 exists as anti and ganche isomers that interconvert (equation 97). 

Aeeording to Wertheim [8-11], the fluid density at a point 1 of the bulk assoeiating fluid is split into two terms, namely the density of unbonded speeies, po(l)> and the density of (singly) bonded speeies, Pi(l), sueh that the total density is p(l) = po(l) + Pi(l)- We set the matrix of densities for a dimerizing fluid... 

The Lewis structures of the oxides of nitrogen are shown in Figure 21.6. Two of these species, NO and NO are paramagnetic, with one impaired electron. When nitrogen dioxide is cooled, it dimerizes the unpaired electrons combine to form a single bond between the two nitrogen atoms ... 

The dipyrrylbutadiyne building blocks, e.g. 21, are prepared by a palladium-induced dimerization reaction of two identical pyrrolecarbaldehydes substituted at the 5-position with an acetylene residue so that the central C —C single bond of the dimer is formed. 

When there is electronic resonance, the bond lengths, bond angles, and nuclear positions are intermediate between those corresponding to the individual resonance structures, as found in the crystal structure of the tin dimer.32 This type of bond, that is, a single bond plus a resonating unshared electron pair, was subsequently found to occur on the 100 surfaces of silicon.33... 

A single-crystal. X-ray diffraction analysis of the structure has recently been performed that shows that the compound is, in fact, a tin-tin bonded dimer, having an Sn-Sn bond length of 276 pm, similar to that in hexaphenylditin this was interpreted in terms of overlap of a filled spaPy orbital with the vacant p orbitals on the other tin atom resulting in a "bent, weak, Sn-Sn double bond (332). 

Cyclic dienes which are locked in the cisoid conformation, e.g. (82), are found to react very much faster than acyclic dienes in which the required conformation has to be attained by rotation about the single bond (the transoid conformation is normally the more stable of the two). Thus cyclopentadiene (82) is sufficiently reactive to add to itself to form a tricyclic dimer, whose formation—like most Diels-Alder reactions—is reversible. 

A single crystal X-ray structure analysis of 8 (Fig. 4) confirms the molecular constitution of the compound deduced by spectroscopic methods and shows further structural details. The molecule is dimeric with a Mn-C15 ( -carbyne) bond length of 1.857(2) A and a Mn-Mn bond distance of 2.565(1) A the latter one is typical for a Mn-Mn single bond [13]. The Mn-C15 (carbyne) bond is short compared to known Mn-C single bonds, for example that in (OC)4Mn-C(C00Et)C(HgBr)C(0Et)0 is found to be 2.051(26) A [13b], For the acyclic carbyne complex [Cp(CO)2Mn = C-CH=CPh2]+ BF4 the MnC distance is 1.665(5) A [14] comparable values for... 

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