Seven-coordinate molecules

A new and facile synthetic method to prepare complexes with Ti-S bonds is based on the oxidation of the low-valent titanium sandwich complex CpT CyHy) with dithiocarboxylic acid to give the Ti(iv) dithioacetate CpTi(S2CMe)3 (Scheme 421). The compound has been fully characterized including X-ray crystallography. It consists of discrete seven-coordinate molecules with a slightly distorted pentagonal-bipyramidal coordination... 

Tricarhonylbis(N, N-dimethyldithiocarbamato)tungsten, (W(CO)3(dmtc)2), has been synthesized, and two distinct intramolecular dynamic processes have been identified by variable temperature NMR studies of this seven-coordinate molecule. The sodium salt of dimethyldithiocarbamate reacts with tetracarbonyldiiodotungsten to form the above product, W(CO)s(dmtc)2. Analytical, IR and NMR data confirm this formulation. The NMR spectrum at —llO C has three distinct resonances, two of which initially coalesce independently of the third (aG+ = 8.1 heal moT ) as the temperature is increased. All three carbon monoxide signals are averaged at higher temperatures (aG+ = 9.0 heal moT ). Reversible loss of one CO occurs upon heating to form an insoluble blue W(CO)2(dmtc)2 compound. 

Acetone has been structurally characterized as a ligand in a zinc crown ether (15-crown-5) complex, where the zinc is seven-coordinate bound to all five ring ether donors, a chloride, and the acetone molecule.351... 

In 2004, Nefedov and co-workers [63] reported a tetra-18-C-5-substituted complex RunPc(DHCP)4(TED)2 (65) with two axial TED ligands and seven solvate molecules CHCI3. The Pc %-% interactions are completely prohibited by the combination roles of peripheral substituted and axial coordinated ligand as well as by solvate molecules. 

It is not surprising that the substitution processes on seven-coordinate 3d metal ions follow an interchange, rather than a limiting dissociative mechanism. In the case of seven-coordinate Fe(III) complex we even found an associative interchange mechanism for the substitution of solvent molecules as a result of the high n-acceptor ability of the fully conjugated pentadentate ligand system present in its equatorial plane 44). 

Fig. 2. With DFT methods (B3LYP/LANL2DZp) calculated structures for the seven-coordinate diaqua complexes (a) [M.r (pydiene)(Ji20), (h) Ma pyalane)Qii20)2f, (c) [Mn(pyane)(H20)2] " and (d) [Mn(L)(H20)2] (on the left) and the corresponding six-coordinate species after loss of one water molecule (on the right) 34).

The interchange character of the water-exchange mechanism of the studied seven-coordinate complexes can be a reason why there is no clear correlation between their rates for the exchange process and the energies required for the dissociation of the coordinated water molecule. AE is also not possible to correlate with the catalytic rate constants published in the literature. 

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