Close-shell interactions

Pyykko P 1997 Strong closed-shell interactions in inorganic chemistry Chem. Rev. 97 597 A review of fertile ground for fiittlier research. 

Pyykko, P. (1997) Strong closed-shell interactions in inorganic chemistry. Chemical Reviews, 97, 597-636. 

Wesendrup, R. and Schwerdtfeger, P. (2000) Extremely strong s -s closed shell interactions. Angewandte Chemie International Edition, 39, 907-910. 

Pyykkd, P. (2002) Relativity, gold, closed-shell interactions and CsAu.NHj. Angewandte Chemie International Edition, 41, 3573-3578. 

Doll, K, Pyykkd, P. and Stoll, H. (1998) Closed-shell interaction in silver and gold... 

Treatment of 77 with one equivalent of [AuCl(tht)] (tht = tetrahydrothiophene) leads to the type III AuCl bridged pincer complex 79 in high yield (counterion is Cl ) [149]. The unique complex 79 is the only heterodimetallic compound with two metal atoms attached at a carbodiphosphorane carbon(O) atom. The environment at the central carbon atom is planar in 77 and pyramidal in 78 and 79. P-C bond lengths and P-C-P angles in the dication 78 are closely related to those in the neutral Pt complex 36 (Fig. 25). The two metals of 79 attached to the carbon atom are coimected via a very short d -d ° pseudo closed shell interaction with a Pd-Au bond length of 2.8900(3) A a similar bonding situation (aurophilic attraction) is found in the gold complex 29 shown in Fig. 23. 

The Pc values are small aud the V pc values are small aud positive, cor-respoudiug to closed-shell interactions (iu this coutext, the vau der Waals complexes would have the smallest pc values). 

For example, the hydrogen atoms of the strongly polarized bonds in hydrides LiH and BeH2 or BH4 can be electron donors, and the electron-deficient atoms Li, Be, or B can accept electrons to form inverse hydrogen-bonded complexes Li-H Li-H, H-Be-H Li-H, and others [3]. Similar to classical hydrogen bonds, the electronic distribution in these inverse hydrogen bonds, analyzed in the framework of AIM theory, shows that the hydrogen atom is bound to both the electron donor and the electron acceptor by closed-shell interactions. In addition, the bond critical points correspond to all the characteristics associated... 

For closed-shell interactions, there will be no density accumulation in the bond. This means a deep minimum along the path connecting the nuclei, that is, a positive value of A3, and no contraction perpendicular to the bond and thus no strongly negative values of A, and A2. Consequently, a positive value of V2p is typical for a closed-shell interaction. 

The quantity Ail/A3, that is, the ratio between the largest perpendicular contraction at the (3, — 1) critical point and the parallel concentration towards the nuclei, is < 1 for closed-shell interactions. For shared interactions, its value increases with bond strength and decreasing ionicity of a bond. It decreases, for example, in the sequence ethylene (4.31), benzene (2.64), ethane (1.63). 

Information about aurophilicity and chemical situations in which it is observed may be found in different works that may be classified as those which analyse closed shell interactions in general [2], those focused on aurophilicity [1,3], and others which analyze the role of these interactions in coordination [4] and organometallic gold... 

If H(r) is zero or positive in the inter-nuclear region, then there will be closed-shell interactions between the atoms in question, typical of ionic bonding, hydrogen bonding or van der Waals interactions81. 

Figure 1.24 Examples of closed shell interactions (a) Aurophilic interactions in [Au2( J.-C1) (PPh3)2] (C104), (b) halogen bonding in pyridine—I-CCR and I5 and (c) secondary bonding in [ HgCl(C6H4N2Ph) 2].

Non-covalent bonds include ionic and dipolar interactions, hydrogen bonds, aromatic interactions (7I—7I, cation k and anion 7t), closed shell interactions and van der Waals interactions. 

P. Pyykko, Strong closed-shell interaction in inorganic chemistry. Chem. Rev. 97, 579-636 (1997). 

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