Structure and reactivity of alkoxy-zinc compounds as initiators/catalysts in the polymerization of cyclic esters

This review focuses on advances in the synthesis and structural chemistry of zinc alkoxide compounds for use in the catalytic ring-opening polymerization (ROP) of lactides (LAs). This route was used for the preparation of lactic acid based polymers - referred to as polylactides (PLAs). These polyesters have ecofriendly properties such as renewability, biocompatibility, and biodegradability, and are therefore among the most promising green polymers. PLAs have found numerous specialty applications in the biomedical industry, such as biodegradable screws and sutures, scaffolds for tissue engineering, matrices for controlled drug delivery systems, and environmentally friendly food-packaging materials. In industry, PLAs were synthesized by bulk polymerization of LA using tin(II) alkoxides synthesized in situ from tin(II) 2-ethylhexanoate. The toxicity associated with most tin compounds is a considerable drawback in the case of biomedical applications. There has therefore been much research devoted to finding well- defined complexes of high activity containing biologically benign metals. In this context, zinc alkoxides are very attractive non-toxic initiators for the synthesis of polymers that could be used in medical and environmental fields. The most broadly applied representations of zinc initiators for ROP of LA are zinc carboxylates, ß-diketonates, ß-diketiminates, phenolates and bisphenolates, trispyrazolyl- and trisindazolyl-borates, heteroscorpionates, aminophenolates, Schiff base, and iminealkoxylates. The mentioned above initiators were classified and analyzed in the context of their coordination chemistry and revealed catalytic activity in the ROP of LA. The review contains only pioneering/groundbreaking works that allowed for setting new research paths for each of the described groups of initiators, showing how this theme has changed over the last several decades

Crystal structure of a mixed-ligand dinuclear Ba—Zn complex with 2-methoxyethanol having triphenylacetate and chloride bridges

The dinuclear barium–zinc complex, μ-chlorido-1:2κ2Cl:Cl-chlorido-2κCl-bis(2-methoxyethanol-1κO)bis(2-methoxyethanol-1κ2O,O′)bis(μ-triphenylacetato-1:2κ2O:O′)bariumzinc, [BaZn(C20H15O2)2Cl2(C3H8O2)4], has been synthesized by the reaction of barium triphenylacetate, anhydrous zinc chloride and 2-methoxyethanol in the presence of toluene. The barium and zinc metal cations in the dinuclear complex are linked via one chloride anion and carboxylate O atoms of the triphenylacetate ligands, giving a Ba...Zn separation of 3.9335 (11) Å. The irregular nine-coordinate BaO8Cl coordination centres comprise eight O-atom donors, six of them from 2-methoxyethanol ligands (four from two bidentate O,O′-chelate interactions and two from monodentate interactions), two from bridging triphenylacetate ligands and one from a bridging Cl donor. The distorted tetrahedral coordination sphere of zinc comprises two O-atom donors from the triphenylacetate ligands and two Cl donors (one bridging and one terminal). In the crystal, O—H...Cl, O—H...O and C—H...Cl intermolecular interactions form a layered structure, lying parallel to (001)

New members in the [Mn10] supertetrahedron family

Two manganese complexes, [MnII4MnIII6Cl4(CH3OCH2CH2O)12 O4][MnII3TiIVCl6(CH3OCH2CH2O)6] (1) and [MnII4MnIII6Cl4(CH3OCH2CH2O)12O4] [Mn4II Cl10(CH3OCH2CH2OH)4]∙0.5CH3OCH2CH2OH, (2) have been obtained and characterized by single-crystal X-ray diffraction. Both structures consist of the decametallic dicationic [MnII4MnIII6Cl4(CH3OCH2CH2O)12O4]2 + core constructed by four vertex-sharing [MnIII3MnIIO]9 + tetrahedra. Also, these compounds contain the different tetrametallic dianions: [MnII3TiIVCl6(CH3OCH2CH2O)6]2 − (in complex 1) and [Mn4IICl10(CH3OCH2CH2OH)4]2 − (in complex 2). Magnetic dc and ac susceptibility measurements for compound (1) show that the dicationic decanuclear magnetic cluster possesses an S = 12 ± 1 spin ground-state

Synthesis, Crystal Structures, and Spectroscopic Properties of Novel Gadolinium and Erbium Triphenylsiloxide Coordination Entities

In alkali metal and lanthanide coordination chemistry, triphenylsiloxides seem to be unduly underappreciated ligands. This is as surprising as that such substituents play a crucial role, among others, in stabilizing rare oxidation states of lanthanide ions, taking a part of intramolecular and molecular interactions stabilizing metal-oxygen cores and many others. This paper reports the synthesis and characterization of new lithium [Li4(OSiPh3)4(THF)2] (1), and sodium [Na4(OSiPh3)4] (2) species, which were later used in obtaining novel gadolinium [Gd(OSiPh3)3(THF)3]·THF (3), and erbium [Er(OSiPh3)3(THF)3]·THF (4) configuration, it can result in res were determined for all 1–4 compounds, and in addition, IR, Raman, absorption spectroscopy studies were conducted for 3 and 4 lanthanide compounds. Furthermore, direct current (dc) variable-temperature magnetic susceptibility measurements on polycrystalline samples of 3 and 4 were carried out in the temperature range 1.8–300 K. The 3 shows behavior characteristics for the paramagnetism of the Gd3+ ion. In contrast, the magnetic properties of 4 are dominated by the crystal field effect on the Er3+ ion, masking the magnetic interaction between magnetic centers of neighboring molecules