Search for: All records

Three mononuclear six-coordinate Co( ii )-pseudohalide complexes [Co(L)X 2 ] with two N-donor pseudohalido coligands occupying the cis -positions (X = NCS − ( 1 ), NCSe − ( 2 ) or N(CN) 2 − ( 3 )), and a five-coordinate complex [Co(L)(NCO)][B(C 6 H 5 ) 4 ] ( 4 ) [L = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane (12-TMC)] have been prepared and structurally characterized. Easy-plane magnetic anisotropy for 1–3 and easy-axis anisotropy for 4 were revealed via the analyses of the direct-current magnetic data, high-frequency and -field EPR (HFEPR) spectra and ab initio theoretical calculations. They display slow magnetic relaxations under an external applied dc field. Typically, two slow relaxation processes were found in 1 and 2 while only one relaxation process occurs in 3 and 4 . The Raman-like mechanism is found to be dominant in the studied temperature range in 1 . For 2–4 , the Raman process is dominant in the low temperature region, while the Orbach mechanism dominates in the high temperature range. 

The reaction of a pentadentate NHC ligand precursor with Ni(OAc) 2 ·4H 2 O or Pd(OAc) 2 in the presence of a base yields four-coordinate square-planar Ni( ii ) and Pd( ii ) complexes with an unusual ligand generated in situ . A series of experimental studies point to a ring-opening and ring-closing process via novel C–N bond cleavage and formation. 

Four macrocyclic hybrid salts with different numbers of benzimidazolium and amine units, [H 2 L][PF 6 ] 2 (L = L 1 , L 2 , L 3 ) and [H 4 L 4 ][PF 6 ] 4 , have been employed as the heterocyclic carbene (NHC) precursors toward new Ag( i )– and Au( i )–NHC complexes. Three trinuclear and one tetranuclear Ag( i ) complexes 1–4 have been obtained from the reactions of the NHC precursors and Ag 2 O in acetonitrile. Four dinuclear Au( i )–NHC complexes 5–8 have been prepared by reacting the NHC precursors and AuCl(SMe 2 ) in the presence of NaOAc in DMF. The molecular structures of all the complexes are established by single-crystal X-ray diffraction studies. The metal ions in the Ag( i ) complexes 1–3 and the Au( i ) complexes 5–7 are coordinated with two macrocyclic NHC ligands to form a sandwiched structure. In contrast, a trinuclear Ag 3 core is located in the cavity of one macrocyclic ligand in [Ag 3 (L 4 )][PF 6 ] 3 ( 4 ). The photoluminescence properties of Au( i ) complexes 5–8 have also been investigated. 

Molecular dynamics is a fundamental property of metal complexes. These dynamic processes, especially for paramagnetic complexes under external magnetic fields, are in general not well understood. Quasielastic neutron scattering (QENS) in 0–4 T magnetic fields has been used to study the dynamics of Co(acac) 2 (D 2 O) 2 ( 1-d4 , acac = acetylacetonate). At 80–100 K, rotation of the methyl groups on the acac ligands is the dominant dynamical process. This rotation is slowed down by the magnetic field increase. Rotation times at 80 K are 5.6(3) × 10 −10 s at 0 T and 2.04(10) × 10 −9 s at 4 T. The QENS studies suggest that methyl groups in these paramagnetic Co( ii ) molecules do not behave as isolated units, which is consistent with results from earlier magnetic susceptibility studies indicating the presence of intermolecular interactions. DFT calculations show that unpaired electron spin density in 1 is dispersed to the atoms of both acac and H 2 O ligands. Methyl torsions in 1-d4 have also been observed at 5–100 K in inelastic neutron spectroscopy (INS). The QENS and INS results here help understand the dynamics of the compound in the solid state.