China
Africa
Explore chapters and articles related to this topic
Structure of Molecules
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
In a given structure, an atom that has one less bond than its valence it will have a (–) charge, whereas if it has one more bond it usually will have a (+) charge. Formal charge can reside on individual atoms, and the sum of all the formal charges on the individual atoms leads to the formal charge for the overall molecule. What is the formula used to determine formal charge?
Chemical Bond I: Lewis Scheme
Published in Franco Battaglia, Thomas F. George, Understanding Molecules, 2018
Franco Battaglia, Thomas F. George
Lewis structures say nothing about bond polarity. To be sure, in the presence of a dative bond, Lewis scheme introduces, for each so bonded atom, the concept of a formal charge, defined as the difference between the number of valence electrons in the free atom and the number of electrons pertaining to it in the molecule, computing the latter as the sum of its lone-pair electrons plus one half of the bond-pair electrons. For instance, for the carbon monoxide molecule—whose Lewis structure, as we have seen, is – the formal charge on carbon is fc(C)=4−(2+126)=−1, and that on oxygen is fc(O)=6−(2+126)=+1. In this way, Lewis scheme would indeed predict a dipole moment toward the donor atom, but would assign to it an unrealistic value. Namely, since the CO bond length is 1.13 Å, the predicted dipole moment for this molecule would be 1.13 × 4.80 D = 5.42 D, much larger than the measured value, which is just 0.12 D.
Synthesis, crystal structure determination, Hirshfeld surface analysis, spectral characterization, theoretical and computational studies of titanium(IV) Schiff base complex
Published in Journal of Coordination Chemistry, 2021
Hadi Kargar, Mehdi Fallah-Mehrjardi, Reza Behjatmanesh-Ardakani, Muhammad Nawaz Tahir, Muhammad Ashfaq, Khurram Shahzad Munawar
The atomic charge on the active centers of complex [Ti(L)2] and the amount of charge transferred from the ligand to the central metal ion, i.e., L→M, are presented in Table 3. The charge on the metal atom is considerably less than that of the formal charge (4+) of titanium, which indicates that a significant amount of charge density is transferred from the ligand to the metal atom. As expected, N- and O-atoms are the most electronegative atoms with the highest negative charge on them. On the other hand, some of the carbon atoms have positive charges, while others are negatively charged. The highest positive charge is associated with carbon atoms connected to electronegative oxygen and nitrogen atoms, C1, C2, C9, C13, C16, C17, C24 and C28. Moreover, most of the corresponding atoms in the two ligands attached to the metal have close Mulliken charges.
Technetium-99m metastable radiochemistry for pharmaceutical applications: old chemistry for new products
Published in Journal of Coordination Chemistry, 2019
Bianca Costa, Derya Ilem-Özdemir, Ralph Santos-Oliveira
The lanthanide contraction due to the poorly effective shielding of “f” orbitals leads to similarity in the atomic radius of transition metals in the 5th and 6th periods [12]. Consequently, the overall structural chemistry of technetium, transition metal of the 5th period and the rhenium, transition metal of the 6th period, in some cases can be similar and the analogous complexes of both transition metals will have the same size, shape, dipole moment, formal charge, ionic mobility and lipophilicity. However, the redox properties of technetium and rhenium can be quite different; Tc often possesses lower redox potentials than the analogous Re complexes and this can lead to differences in the chemistry. Moreover, Tc tends to be kinetically labile compared to Re and this phenomenon leads to differences in the chemistry of analogous complexes. Therefore, the use of Re as a non-radioactive surrogate for Tc should be practiced with caution [10, 13–15].
Structural conversion of an oxazolidine ligand upon treatment with copper(I) and (II) halides; structural, spectral, theoretical and docking studies
Published in Journal of Coordination Chemistry, 2018
Zahra Mardani, Vali Golsanamlou, Zahra Jabbarzadeh, Keyvan Moeini, Saba Khodavandegar, Cameron Carpenter-Warren, Alexandra M. Z. Slawin, J. Derek Woollins
For studying the charge distribution before and after complexation, an NBO analysis was done on the free AEPC and 1 (Table 6). The results reveal that the calculated charge on the copper ion is about +0.91 and lower than the formal charge (+2), owing to the electron donation of the ligand during complexation. Based on the calculated total charge values, the total charge of the nitrogen, carbon and oxygen atoms in 1 is more negative than that of the free ligand, while the total charge of hydrogen atoms is more positive than in the free ligand. This observation reveals that the hydrogen atoms play an important role in electron donation toward the metal ion, thus decreasing the charge of the copper ion. The nitrogen atoms on the thiocyanato ligands are more negative than those on the AEPC, showing the nitrogen atoms of the thiocyanate ions are more electronegative than the AEPC nitrogen atoms.