195Pt spin-lattice relaxation and shielding anisotropy for Pt(acac)2

Thallium(III) coordination compounds: chemical information from 205Tl NMR longitudinal relaxation times

“…1,26 This is analogous to what has been found for other heavy spin-1/2 nuclei. 3,27,28 The observation that the CSA contribution becomes small for the hexaaquo, tetracyano and tetrachloro complexes has a structural significance by itself, as it confirms the octahedral and tetrahedral geometry of the complexes, …”

“…20 The results are consistent with pseudo-octahedral six coordination for the cationic halogeno complexes Tl( 2 ], while the anionic complexes with n D 4 are tetrahedral. For X D CN , the dicyano complex has linear structure, the tricyano complex is probably pseudo-tetrahedral, Tl(CN) 3 (H 2 O) (C 3v ), and Tl(CN) 4 is tetrahedral. In all cases the CN ligands seem to form a linear Tl-C-N entity.…”

“…The CSA dominated relaxation rate, proportional to the square of the magnetic field, B 0 , was found in some platinum complexes. 3 The spin-rotation relaxation rate is where I r is the moment of inertia (assumed isotropic) and C is the spin-rotation coupling constant. The symbol j is the angular momentum correlation time.…”

“…A similar conclusion can be drawn also for the other thallium complexes studied (cf. 3 From these results, we conclude that two types of relaxation mechanisms should be taken into account for the Tl complexes, i.e. the CSA and the SR mechanisms.…”

“…It is about 50% of the total relaxation at 115.4 MHz for Tl(CN) 3 , 20% for Tl(CN) 2C and less than 10% for Tl(CN) 2 C , while the chloro complex, TlCl 2C , shows a ca 20% fieldindependent contribution at this magnetic field. In general, taking into account the TlX 4 complexes also, we note that the larger the chemical shift, the more efficient is the SR relaxation.…”