Synthesis and Stereochemical Properties of Chiral Square Complexes of Iron(II)

Abstract

The hexadentate, and ditopic ligand 2,5-bis([2,2']bipyridin-6-yl)pyrazine yields a chiral, tetrameric, square shaped, self-assembled species upon complexation with Fe 2+ -ions. The racemate of this complex was resolved with antimonyl tatrate as chiral auxiliary. The purity of the enantiomer was determined by NMR spectroscopy, using a chiral, diamagnetic shift reagent, as well as by circular dichroism (CD). The CD-spectrum was also calculated by time dependent density functional theory, and the correlation that was found between CD spectrum and configuration was confirmed by X-ray cristallography. When a "chiralised" version of the ligand was used instead, the corresponding iron complex was obtained in diastereomerically pure form.

Design and Study of Structural Linear and Nonlinear Optical Properties of Chiral [Fe(phen)3]2+Complexes

“…[Fe(phen)3](rac-TRISPHAT)2 (6) As we mentioned, there have been a few reports studying the chiral induction of the TRISPHAT anion on some diimine Fe(II) complexes, but those were limited to solution studies (NMR and CD measurements). 41,42,45,46 In order to obtain structural data, we obtained crystals in a few days by layering a methanol solution of iron(II) sulphate over a solution of the phen ligand and the corresponding salt of TRISPHAT anion. When using rac-TRISPHAT, we observed two distinct crystals morphologies: on one hand hard deep-red well-defined prisms, and on the other hand crumbly redorange flat crystals.…”

“…43 Surprisingly, they have been used so far only sparsely for the synthesis of materials. 44 There are only few reports of diastereoselective ion pairing of the TRISPHAT anion with diimine low-spin Fe(II) complexes, either in solution, 41,42,45,46 or in the solid state. 43,47,48 On the other hand, the D2-symmetric As(III) 49 or Sb(III) 50 tartrate adducts were used in the past for the resolution of metal complexes, 45,[51][52][53][54][55] mainly through chiral HPLC, 53,[56][57][58] with C2 and C3 association models proposed for the chiral recognition of octahedral metal complexes by [Sb2(tartrate)2] 2− .…”

Self‐Assembly of Cyclohelicate [M3L3] Triangles Over [M4L4] Squares, Despite Near‐Linear Bis‐terdentate L and Octahedral M

“…[1h] In contrast, herew er eport thef irst examples of structurally characterized pyrazine-edged triangular cyclohelicates (Figure 1c), in whichall six donor atoms to each metal ion are provided by the di-imine bis-terdentate pyrazine-edge ligands L. This triangle architecture contrasts with the molecular squares that the closely analogousd iamide bis-terdentate ligands, H 2 L 2, 5À ÀEt [3b] and H 2 L 2, 3À ÀMe or Et [3a, c, 11] (Scheme 1), generated upon complexation with octahedral metal ions. The results of the DFT calculations are therefore consistent with the experimentally observed trianglea rchitectures.T he same DFT analysisw as appliedt ot he relatedp yrazine-edged squares, [Co 4 (L 2, 5ÀEt ) 4 ] 4 + , [3b] [Zn 4 (bbppz) 4 ] 8 + , [4a] and [Fe II 4 (bbppz) 4 ] 8 + , [15] as well as the corresponding (but not structurally characterized and/or observed) triangles, and the total electronic energies were also consistent with the reported architecture outcomes (Table S4). [4a] To gain furtheri nsight into the subtle factors contributing to whether at riangle or squarea rchitecture is realized, density functional theory (DFT) calculations on the [Zn 3 L 3 ] 6 + and [Fe 3 L 3 ] 6 + triangles,a nd the corresponding (but not observed) [Zn 4 L 4 ] 8 + and [Fe 4 L 4 ] 8 + squares were performed with acontinuum acetonitrile solventm odel.T he GGA functional BP86, [12] which is known to perform well with transition metal complexes, [13] was used with ad ef2-SVP basis set.…”

Absolute Chiral Structures of Inorganic Compounds

“…69 More detailed chiral stereochemistry has been studied for a iron(II) complex [Fe 4 (L) 4 ] 8 þ with the hexadentate ditopic ligand L ¼ 2,5-bis([2,2 0 ]bipyridin-6-yl) pyrazine ( Figure 5.19b). 70 In this complex, all the Fe(II) ions with two tridentate ligands have metal center chirality with the same configuration within one complex cation. This was shown to be due to the interwoven arrangement of the ligand strands as shown in Figure 5.19c.…”

“…An enantiomer was obtained with the use of antimony tartrate as the chiral auxiliary. The short, quadruple-stranded helicity in the entire complex ion is of P helical configuration for theL configuration around the four metal ions, 70 whereL is the chiral descriptor according to the oriented skew-line reference system. 71 Another class of chiral tetranuclear complexes are tetrahedral metal-ligand assembled clusters of M 4 L 6 stoichiometry for Ga(III), Al(III), and Fe(III) with N,N 0 -bis(2,3-dihydroxybenzoyl)-1,5-diamino-naphthalene.…”