Compounds ionic versus covalent

Thus, the bonding in metal compounds and complexes has traditionally been viewed as ionic, with a positive metal center interacting with negative ions, such as HO , 0 , Cl , AcO , and coordinate donor, Lewis acid-base interactions with a positive metal center interacting with negative ions and electron-pair Lewis bases, such as iNHs, iPPhs, HOH. Examples of ionic versus covalent bonding illustrate the tradition H+CH versus H-Cl (ls-3p), C +(C1 )4 versus C(-C1)4 [2sp -(3p)4], Fe +(C1 )3 versus Fe(-Cl)3 [3d sp2-(3p)3], H+-OH versus H-OH (ls-2p), C +(Q2-)2 versus 0=C=0 [2sp -(2p )2], and Fe +(0 ) versus Fe=0 [3d sp-(2p )]. Such ionic formulations for these molecules in an inert matrix are not consistent with their physical... 

The entire notion of an ionic bond versus a covalent bond is, in fact, an antiquated concept. In reality, there is a huge gray area of polar compounds intermediate between the two extremes. The only truly quantitative values which can delineate one molecule from the next are the calculated atomic charges and the bond critical point densities. Nevertheless, it is useful to discuss where a particular molecule might fall along this spectrum in terms of the more familiar terminology. In this context, the results of AIM can be summarized as follows ... 

In the recent past, diverse opinions have been put forward to explain the occurrence of the various structural types [21, 22, 652-654] Madhukar [654] has shown that in these mainly covalent compounds the small variation in the ionicity of the bonds competes against the polarization contribution of the bonding orbitals in determining the relative stability of octahedral versus trigonal-prismatic cation coordination. In a plot of the ratio of the single-bond covalent radii of the cation and anion versus bond ionicity, all compounds with trigonal-prismatic... 

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