Coordinating group/cation interaction

Molecular simulation methods can be a complement to surface complexation modeling on metal-bacteria adsorption reactions, which provides a more detailed and atomistic information of how metal cations interact with specific functional groups within bacterial cell wall. Johnson et al., (2006) applied molecular dynamics (MD) simulations to analyze equilibrium structures, coordination bond distances of metal-ligand complexes. 

This definition is completely independent from water as the reaction medium and is more general than the previous ones. In terms of Lewis acidity, the Br0nsted-type acid HA is the resnlt of the interaction of the Lewis-type acid species H+ with the base A . According to the definitions given, Lewis-type acids (typically, but not only, coordinatively unsatnrated cations) do not correspond to Br0nsted-type acids (typically species with acidic hydroxyl groups). On the contrary, Lewis basic species are also Br0nsted bases. 

Complexation studies of sensors 83 and 84 with the alkali, alkaline earth, and transition metal ions Cu2+, Ni2+, Zn2+, Cd2+, and Pb2+ were performed in Valeur s laboratory.141,142 In these compounds, the chromophores are linked to the azacrowns in such a way that the cations interact directly with the carbonyl group that acts as an electron-withdrawing unit. Therefore, when an ion is coordinated,... 

Coordination numbers are so dependent on hgand geometry that the concept of preferred coordination number is of limited use. For example, hthium may be said to prefer 4 coordination, but examples of 1 to 12 coordination are known. Low formal coordination numbers are often accompanied by secondary interactions with other sources of electron density, such as C H bonds and arene 7r-systems. There are even examples of C H activation caused by a low-coordinate sodium cation. Of course, there is a trend towards higher preferred coordination for the heavier group members (6 for Na, K 8 for Rb, Cs). 

Coordination to metals follows the usual trends. The transition metals try to achieve octahedral coordination (with a few exceptions), but the cations of the electropositive group 1-3 elements exhibit a rich variety. The coordination polyhedra are determined by radius ratios more than by topological preferences. For polyphosphides in general, all P atoms are involved in M-P interactions according to the number of lone pairs present. The anionic (lb)P and (2b)P as well as the neutral (3b)P° species adopt quasi-tetrahedral coordination, especially if main-group cations are involved. Only a few exceptions are known, for example Li3P7. With more covalent M-P bonds, the number (m + n) of available lone pairs of a polyanion P " is strongly related to the metal coordination number that is, CN(M) < m + n). If CN(M) > m + n), ion-ion and ion-dipole interactions dominate. The relation <7[M-(2b)P] > <7[M-(3b)P] is true in most cases. 

This group of compounds includes those containing comer-sharing actinyl polyhedra (Table 11). It is important to remember that coordination polyhedra of actinides in high oxidation states possess two different t es of anions (i) apical anions that are part of the actinyl [An 02] ions and (ii) equatorial anions. If an apical anion of one polyhedron is shared with the other, we deal with the so-called cation-cation interactions. 

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