Nuclear quadrupole coupling in hexachlorometallates A₂[MCl₆] and A'[MCl₆], A^⊕, A'^2⊕ = several inorganic or organic cations, M = Sn, Pb, Te, Pt

Abstract

The electric field gradient (EFG) at the chlorine site of the hexachlorometallates A2[MCl6] and A'[MCl6], M = Sn, Te, Pb, Pt, and A⊕, A'2⊕ = alkali metal ion, hexahydrated bivalent metal ion, or organic ammonium cation, is investigated and the dependence of the EFG on the size of the cation is discussed. — For the cubic alkali hexachlorometallates the observed trend in the EFG with increasing size of the cation is corroborated by quantum mechanical calculations using the Multiple‐Scattering‐Xα‐method (MS‐Xα) and the point charge model. A correlation v(35Cl) ∼ 1/r3 is found, where r is the distance between the ions in the lattice and the chlorine nucleus considered. For hexachlorometallates with organic cations, like pyridine, piperazine, 4‐picoline, ethylenediamine, 1.3‐propylenediamine, and other aliphatic or aromatic amines, this 1/r3 dependence is found for the averaged 35Cl NQR frequency, too. This is due to the distortion of the [MCl6]2⊕ octahedra, caused by hydrogen bonds N—H…Cl, and to the decrease of the lattice symmetry because of non‐sphericity of the cations. — A hydrogen bond has a large influence on the properties of one of the chlorine atoms of the hexachlorometallate complex. The M‐Cl distance is increased and therefore the EFG at the nucleus site is decreased. However, the average of the M‐Cl bond lengths or the 35Cl NQR frequencies, taken over all six chlorine atoms of a [MCl6]2⊕ complex, is not influenced by the chemical nature of the cation but only by its size or the size of the unit cell, respectively. The increase of 35Cl NQR frequency with increasing size of the cation originates from a decrease of the lattice energy.

Coordination of Ortho-Chlorines in Copper (I) and Silver (I) 2,6-Di- and 2,4,6-Trichlorophenolates

“…Consequently the chlorophenolate complexes contain covalent metal-ligand bonds, while the bonding in the silver-dichloroalkane complexes is much more likely to be predominantly ionic. Hence the NQR frequencies of the latter complexes are more likely to be influenced by ionic lattice contributions, which may oppose the contributions made by the covalent bonds to chlorine [36], (2) The chlorophenolate and chloro-Schiff base ligands, in contrast to the dichloroalkane ligands, are aromatic, with conjugation of the chlorine lone-pair electrons with those of the pi system of the ligand. Aromatic chlorines start with nonzero NQR asymmetry parameters, which may well be reduced to zero by coordination before being increased upon stronger coordination.…”

Tetraalkylammonium Tetrachlorothallates (III); X-Ray, 35Cl-NQR, and 1H-NMR Studies

“…Also the lattice contributes to the electric field gradient. The contribu tion is proportional to the reciprocal volume of a formula unit Vf in the elementary cell [16] and lowers the EFG. EFG = eqbond -Cl/Vf;…”

Chlorine Nuclear Spin-Spin Relaxation Mechanism in Mg(H2O)6SnCl6 as Studied by NQR and NMR Techniques

“…We can estimate the one at a chlorine nucleus due to nearby four chlorine and one tin nuclei using (7). Since the CI • • • CI and Sn • • • CI internuclear distances in the present complex are not available, average distances in some compounds including SnClg -ions [22] were used. Internuclear distances of r (CI • • • CI) = 3.44 Ä and r(Sn • • • CI) = 2.43 Ä lead to T 2 Q= 1.0 ms.…”