Spin-crossover, mesomorphic and thermoelectrical properties of cobalt(II) complexes with alkylated N3-Schiff bases

Three new cobalt(ii) complexes, [Co(L12)2](BF4)2 (1), [Co(L14)2](BF4)2·H2O (2) and [Co(L16)2](BF4)2·H2O (3), where L12-16 are N3-Schiff bases appended with linear C12-16 carbon chains at the nitrogen atoms, were obtained in good yields by facile one-pot reactions. The single crystal X-ray structure of complex 1 shows a tetragonally compressed CoN6 coordination geometry. The melting temperatures of 1-3 were lower than 373 K, while their decomposition temperatures were above 473 K. All complexes have high-spin Co(ii) centres at 300 K and exhibit a columnar mesophase above 383 K. Complexes 1 and 3 showed normal thermal spin-crossover behaviour with weak hysteresis loops at about 320 K. Hence, these complexes showed uncoupled phase transitions (class iiia). The values for the Seebeck coefficient (Se) of the cobalt redox couples formed from 1 and 2 were 1.89 ± 0.02 mV K-1 and 1.92 ± 0.08 mV K-1, respectively, identifying them as potential thermoelectrochemical materials.

LC–MS and GC–MS metabolite profiling of nickel(II) complexes in the latex of the nickel-hyperaccumulating tree Sebertia acuminata and identification of methylated aldaric acid as a new nickel(II) ligand

Targeted liquid chromatography–mass spectrometry (LC–MS) technology using size exclusion chromatography and metabolite profiling based on gas chromatography–mass spectrometry (GC–MS) were used to study the nickel-rich latex of the hyperaccumulating tree Sebertia acuminata. More than 120 compounds were detected, 57 of these were subsequently identified. A methylated aldaric acid (2,4,5-trihydroxy-3-methoxy-1,6-hexan-dioic acid) was identified for the first time in biological extracts and its structure was confirmed by 1D and 2D nuclear magnetic resonance (NMR) spectroscopy. After citric acid, it appears to be one of the most abundant small organic molecules present in the latex studied. Nickel(II) complexes of stoichiometry NiII:acid = 1:2 were detected for these two acids as well as for malic, itaconic, erythronic, galacturonic, tartaric, aconitic and saccharic acids. These results provide further evidence that organic acids may play an important role in the transport and possibly in the storage of metal ions in hyperaccumulating plants.

Synthesis, structure and spectral properties of dithiocarbamato bridged dirhenium(III,II) complexes: a combined experimental and theoretical study

Sodium salts of dimethyldithiocarbamate, diethyldithiocarbamate and pyrrolidinedithiocarbamate react with the multiply bonded paramagnetic dirhenium(III,II) complex Re₂(μ-O₂CCH₃)Cl₄(μ-dppm)₂, 1 (dppm = Ph₂PCH₂PPh₂) in refluxing ethanol to afford the paramagnetic substitution products of the type Re₂(η²-S,S)₂(μ-S,S)(μ-Cl)₂(μ-dppm), where S,S represents the dithiocarbamato ligands [S,S = S₂CNMe₂, 4(L_Me); S₂CNEt₂, 4(L_Et) and S₂CN(CH₂)₄, 4(L_Pyr)]. These are the first examples of dirhenium complexes that contain bridging dithiocarbamato ligand along with the dppm ligand. These complexes have very similar spectral (UV-Vis, IR, EPR) and electrochemical properties which are also reported. The identity of 4(L_Et) has been established by single-crystal X-ray structure determination (Re-Re distance 2.6385 (9) Å) and is shown to have edge-shared bioctahedral structure. The electronic structure and the absorption spectra of the complexes are scrutinized by the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) analyses.

Organotin(IV) complexes derived from proteinogenic amino acid: Synthesis, structure and evaluation of larvicidal efficacy on Anopheles stephensi mosquito larvae

Five new organotin(IV) complexes of composition [Bz2SnL1]n (1), [Bz3SnL1HH2O] (2), [Me2SnL2H2O] (3), [Me2SnL3] (4) and [Bz3SnL3H]n (5) (where L1 = (2S)-2-([(E)-(4-hydroxypentan-2-ylidene)]amino)-4-methylpentanoate, L2 = (rac)-2-([(E)-1-(2-hydroxyphenyl)methylidene]amino)-4-methylpentanoate and L3 = (2S)- or (rac)-2-([(E)-1-(2-hydroxyphenyl)ethylidene]amino)-4-methylpentanoate) were synthesized and characterized using 1H NMR, 13C NMR, 119Sn NMR and infrared spectroscopic techniques. The crystal structure of 2 reveals a distorted trigonal-bipyramidal geometry around the tin atom where the oxygen atoms of the carboxylate ligand and a water ligand occupy the axial positions, while the three benzyl ligands are located at the equatorial positions. On the other hand, the analogous derivative of enantiopure L3H (5) consists of polymeric chains, in which the ligand-bridged tin atoms adopt the same trans-Bz3SnO2 trigonal-bipyramidal configuration and are now coordinated to a phenolic oxygen atom instead of H2O. In 2, the OH hydrogen of the ketoimine substituent has moved to the nearby nitrogen atom while in the salicylidene derivative 5, the OH is located almost midway between the phenolic oxygen atom and the nitrogen atom of the C=N group. For the dibenzyltin derivative 1, a polymeric chain structure is observed as a result of a long intermolecular SnO bond involving the exocyclic carbonyl oxygen atom from the tridentate ligand of a neighbouring tin-complex unit. The tin atom in this complex has distorted octahedral coordination geometry. In contrast, the racemic dimethyltin(IV) complexes 3 and 4 display discrete monomeric structures with a distorted octahedral- and trigonal-bipyramidal geometry, respectively. The structures show that the coordination mode of the Schiff base ligand depends primarily on the number of bulky benzyl ligands (R) at the tin atom, as indeed found in the structures of related complexes where R = phenyl. With three bulky R groups, the tridentate chelating O,N,O coordination mode is preferred, whereas with fewer or less bulky R ligands, only the carboxylate and hydroxy groups are involved, which leads to polymers. Larvicidal efficacies of two of the new tribenzyltin(IV) complexes (2 and 5) were assessed on the second larval instar of Anopheles stephensi mosquito larvae and compared with two triphenyltin(IV) analogues, [Ph3SnL1H]n and [Ph3SnL3H]n. The results demonstrate that the compounds containing Sn-Ph ligands are more effective than those with Sn-Bz ligands.