Atomic complexities isoelectronic series

A further extension of the known isoelectronic series in the class of icosahedral species has been reported by Todd and Beer (212). Substitution of a C—H fragment in the complexes LXIV and LXV by a bare phosphorus or arsenic atom leads to the closo-cluster compounds LXVI and LXVII, which are here also described as n complexes with regard to their synthesis. Treatment of the disodium salt of the 7,8-ElCHB9H dianion (El = P, As) with a germanium(II) species results in the formation of the... 

In addition to UV/visible flash photolysis and TRIR spectroscopy, other techniques have been used for the detection of transition metal-noble gas interactions in the gas phase. The interaction of noble gases with transition metal ions has been studied in detail. A series of cationic dimeric species, ML" " (M = V, Cr, Fe, Co, Ni L = Ar, Kr, or Xe), have been detected by mass-spectroscopic methods (55-58). It should be noted that noble gas cations L+ are isoelectronic with halogen atoms, therefore, this series of complexes is not entirely unexpected. The bond dissociation energies of these unstable complexes (Table IV) were determined either from the observed diabatic dissociation thresholds obtained from their visible photodissociation spectra or from the threshold energy for collision-induced dissociation. The bond energies are found to increase linearly with the polarizability of the noble gas. 

NO shows a wide variety of coordination geometries (linear, bent, doubly bridging, triply bridging and quadruply bridging — see p. 453) and sometimes adopts more than one mode within the same complex. NO has one more electron than CO and often acts as a 3-electron donor — this is well illustrated by the following isoelectronic series of compounds in which successive replacement of CO by NO is compensated by a matching decrease in atomic number of the metal centre ... 

Information Planes and Complexity Measures for Atomic Systems, Ionization Processes and Isoelectronic Series... 

The main aim of this work is to analyze the above-defined LMC, FS, and CR complexities associated to the one-particle densities in conjugated spaces, namely, position p(r) and momentum y(p) densities, as well as the product or phase-space distribution /(r, p) s p(r)y(p), for a great amount of atomic systems including neutral atoms (Section 2), singly charged ions (Section 3), and isoelectronic series (Section 4). 

In sharp contrast to the stable [H2S. .SH2] radical cation, the isoelectron-ic neutral radicals [H2S.. SH] and [H2S. .C1] are very weakly-bound van der Waals complexes [125]. Furthermore, the unsymmetrical [H2S.. C1H] radical cation is less strongly bound than the symmetrical [H2S.. SH2] ion. The strength of these three-electron bonds was explained in terms of the overlap between the donor HOMO and radical SOMO. In a systematic study of a series of three-electron bonded radical cations [126], Clark has shown that the three-electron bond energy of [X.. Y] decreases exponentially with AIP, the difference between the ionisation potentials (IP) of X and Y. As a consequence, many of the known three-electron bonds are homonuclear, or at least involve two atoms of similar IP. 

The cyanide ion is isoelectronic with CO, and binds to platinum and other metal ions by a donation of a pair of electrons in an sp hybrid orbital on the carbon atom, along with a complementary jt back-donation from filled metal orbitals to empty jt orbitals on CN. The anion is a poorer it acceptor than CO, but stable complexes are formed with platinum(II) and platinum(IV), and the ligand is high in the spectrochemical series. 

These results have been discussed by Seel in Structure and Valence Theory of Inorganic Nitric Oxide Complexes (102). In such complexes, nitric oxide is covalently bonded to the metal atom as the positive ion NO+, it being assumed that an electron is transferred to the metal. This allows the isoelectronic groups NO+, CO, CN to be considered together and permits understanding of such known series as [Fen(CN)5NO]2, [Fen(CN)5CO]3-, and [Fen(CN)5CN]4-. 

Our group has devoted two articles for the study of systems where the chiral subunits are bonded to a boron or to a metallic atom (Scheme 3.28). In both cases, the weakness of the bonds formed can be easily broken. In the first case, a series of bisdiphenylborates and the effect of the fluoro substitution on the relative stability of the homo vs. heterochiral complexes have been studied by means of DFT calculations (B3LYP/6-31G ) [29]. In addition, the corresponding isoelectronic structures, in which the boron has been substituted by a carbon or a positively charged nitrogen, have been considered. In all the cases, the homo and heterochiral complexes present D2 and S4 symmetries, respectively. 

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