Diiron paddlewheel‐ or lantern‐type complexes comprise an interesting subclass of binuclear iron complexes, existing with digonal, trigonal, and tetragonal ligand arrays. Experimentally known members show Fe−Fe bonds of lengths ranging from 2.13 to 2.73 Å, with Fe−Fe bond orders ranging from 0.5 to 2. Truncated models for 30 experimentally characterized diiron paddlewheel‐type complexes have been studied by DFT using the M06‐L functional, reproducing the Fe−Fe bond lengths quite well. In addition, we use DFT to treat three series of model diiron complexes Fe2Lx (x=2, 3, 4) in various low‐lying spin states, L being the unsubstituted formamidinate, guanidinate, and formate ligands (along with a series of axially ligated formate complexes) in order to predict ground state spin multiplicities, Fe−Fe bond lengths, and features of the ligand arrays. The ground states all have high spin multiplicities (septets, octets, and nonets). Formal bond order (fBO) values are suggested for the Fe−Fe bonds in these 61 complexes using an electron bookkeeping procedure, in addition to the Fe−Fe bond orders obtained by metal‐metal MO analysis for ground state species. Fe−Fe bond orders up to 3 are noted in some excited states. Deviations from D3h and D4h symmetry are noted for many trigonal and tetragonal complexes, being attributed to inherent Jahn‐Teller distortions. The formamidinate and guanidinate series show many similarities, while the formate series differs from these two in several aspects. From these results, ranges are derived for Fe−Fe bond lengths of orders 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0. The Fe−Fe bond length ranges for these non‐carbonyl lantern complexes are found to be appreciably lower than the corresponding ranges for diiron complexes with carbonyl ligands as compiled earlier from computational and experimental results.
Binuclear manganese complexes with covalent Mn-Mn bonds include dimanganese carbonyl complexes and dimanganese non-carbonyl complexes with bidentate anionic ligands. Density functional theory (DFT) using the M06-L functional is used to...
Paddlewheel-type complexes are prominent among experimentally known binuclear cobalt complexes and incorporate substituted formamidinate, guanidinate, and carboxylate ligands in digonal, trigonal, and tetragonal arrays around the bimetallic core. Such complexes are modeled here by density functional theory using unsubstituted ligands, extending the whole set to incorporate a variety of metal oxidation states and spin multiplicities. The DFT results for ground state cobalt–cobalt bond lengths and ground state spin multiplicity of the model complexes are often quite close to the experimental results for the corresponding substituted complexes. The three series of complexes often exhibit parallel trends with regard to effects of change in the metal oxidation state and spin multiplicity. The formamidinate and guanidinate series show marked resemblances. The lowered symmetry in many model trigonal complexes implies that such deviations in the experimentally known congeners arise from the inherent electronic structure. For ground state species, the DFT results provide Co–Co bond orders (BOs) from MO occupancy considerations. Further, using a revised electron bookkeeping method, Co–Co formal bond order (fBO) values from 0.0 to 2.0 are assigned to all of the 85 complexes studied. The computed Co–Co bond lengths fall into distinct ranges according to the formal bond order values (from 0.5 to 2)
Epicuticular wax analysis was performed on the leaves of chloroform extract obtained from the plant Euphorbia milii (‘Christ’s plant’). Aim of the study is to identify the chemical constituents and to discover how they were distributed within the cuticle. Column chromatographic separations based on polarity and GC–MS analysis led to the identification of the pentacyclic triterpenoids, its acetates and hydrocarbons that are found to be present in the epicuticular wax. The study revealed that the plant wax contains Lupenone, Glutinol, Lupeol acetate, Glutinyl acetate, Friedelan-3-ol,D:A-Friedooleanan-28-acetate 3beta hydroxyl in fraction1. The second fraction was found to contain Friedooleanan-3-ol, Friedooleanan-3-aceteate along with hydrocarbons of carbon chain length from C23–C33. Hydrocarbons in the form of alkanes and alkenes were identified as the major constituents in the third fraction of the leaf extracts and found to vary from carbon chain C18 to C34. Cuticular wax was found to be dominated by triterpenoids in the first two fractions. The last fraction contains hydrocarbons as the major constituent. The functional group analysis through FTIR-HATR study reveals the presence of characteristic peaks of waxes. The finding suggests that the biomass of the plant Euphorbia milii can be an important source for hydrocarbon.
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