Energies and Spin States of FeS^0/−, FeS₂^0/−, Fe₂S₂^0/−, Fe₃S₄^0/−, and Fe₄S₄^0/− Clusters

Abstract

Bridging of p-t-butylthiacalix[4]arene with ethylene glycol ditosylates gave diametrically bridged thia-calix[4]monocrowns-4 and-5, 1,2-alternate thiacalix[4]biscrowns-4 and-5 and 1,3-alternate thiacalix[4]biscrown-5, dependent on the metal carbonate used. They show excellent extraction ability towards Ag + cations. In the past we have shown that diametrically bridged calix[4]crowns are excellent ionophores for alkali metal cations such as K + and Cs + , depending on the confor-mation and crown ether bridge. 1,2 Proximally bridged calix[4]crowns have been obtained, but only in relatively low yield (<40%). 3,4 Thiacalix[4]arene is an interesting novel member of the calixarene family. 5,6 Unsubstituted thiacalix[4]arene is able to complex various transition metals, due to the presence of the bridging sulfur atoms. 7 The participation of sulfur in the complexation has been observed in X-ray crystal structures of complexes with alkali metal cations. 8 The com-plexation properties of thiacalix[4]arenes can be altered, both by functionalizing the lower rim with ligating sites or by oxidation of the bridging sulfur atoms. 9-12 The groups of Vicens 13 and Bitter 14 have reported the synthesis of the diametrically substituted thia-calix[4]biscrowns-5 and-6. To the best of our knowledge only two proximally bridged thia-calix[4]crowns have been reported; a cyclic phosphorous diester amide and a lactone. 15-17 In this communication we present our preliminary results of a systematic study on thiacalix[4](bis)crown formation using ethylene glycols of varying chain lengths and different metal carbonates. With different metal car-bonates different products were obtained. The 1,2-alternate thiacalix[4]biscrowns 4 and 5 were obtained under mild conditions. The reactions of thiacalix[4]arene 18 1 with tri-or tetra-ethylene glycol ditosylates 2 and 3 in acetonitrile were systematically studied by varying the metal carbonate, reaction time, etc. 19 With 4 equiv. of Cs 2 CO 3 after 6 h, reaction of 1 with 2 (1.8 equiv.) exclusively afforded the 1,2-alternate thia-calix[4]biscrown-4 4 in 72% yield upon precipitation of the crude reaction mixture with methanol/acetone. Also the reaction of 1 and 3 (1.8 equiv.) with 4 equiv. of base gave a fast reaction (12 h, 100% conversion). The reaction gave a mixture of the 1,2-alternate thia-calix[4]biscrown-5 5 and the corresponding 1,3-alternate isomer 6. The pure thiacalix[4]biscrown-5 isomers 5 (27%) and 6 (15%) were isolated by fractional precipitation from methanol/acetone mixtures. Surprisingly, the proximal thiacalix[4]biscrowns-4 and-5 were only obtained in the 1,2-alternate conformation. The corresponding proximally substituted thiacalix[4]monocrown and proximally substituted cone thiacalix[4]biscrown compounds could not be detected. Compounds 4 and 5 were characterized by NMR (1 H and 13 C) and MS. 20,21 Definite proof for the 1,2-alternate thiacalix[4]biscrown-5 5 was obtained by an X-ray crystal structure (Fig. 1). 22

Deterministic Construction of Nodal Surfaces within Quantum Monte Carlo: The Case of FeS

“…8 FeS has been extensively studied by density-functional theory (DFT) and post-Hartree-Fock methods. In short, a) Corresponding author: scemama@irsamc.ups-tlse.fr b) Corresponding author: loos@irsamc.ups-tlse.fr most (but not all) DFT functionals correctly predict a 5 ∆ ground state, [9][10][11][12][13] while CAS-based multireference methods such as CASSCF/ACPF, 14 CASPT2, 15 or CASSCF/ICACPF 16 systematically predict 5 Σ + lower than 5 ∆.…”

Aqueous Fe2S2 cluster: structure, magnetic coupling, and hydration behaviour from Hubbard U density functional theory

“…5 Among the variety of complexes suggested, the rhombic Fe 2 S 2 is particularly interesting, as it is very similar to the basic structural unit of mackinawite. 3 Remarkably, the Fe 2 S 2 unit constitutes also the active centre of various metalloproteins, 6 and it has been the subject of a number of both experimental [7][8][9] and theoretical [10][11][12][13][14][15] investigations (see ref. 16 for a review on this and other analogues of protein active sites).…”

Full wave function optimization with quantum Monte Carlo and its effect on the dissociation energy of FeS

“…Surprisingly for such a small molecule, there is disagreement about the ground state. Many DFT calculations correctly predict a 5 ∆ ground state [35][36][37][38][39][40][41] , but some functionals including B3LYP and VSXC predict a 5 Σ + ground state 35,37,38 with several basis sets. High-level multireference calculations resulted all in a 5 Σ + ground state.…”