Tetra-μ-α-alanine-bis[tetraaquagadolinium(III)] hexaperchlorate

Abstract

The title complex, [Gd(2)(C(3)H(7)NO(2))(4)(H(2)O)(8)](ClO(4))(6), contains centrosymmetric dimeric [Gd(2)(Ala)(4)(H(2)O)(8)](6+) cations (Ala is alpha-alanine) and perchlorate anions. The four alanine molecules act as bridging ligands linking two Gd(3+) ions through their carboxylate O atoms. Each Gd(3+) ion is also coordinated by four water molecules, which complete an eightfold coordination in a square-antiprism fashion. The perchlorate anions and the methyl groups of the alanine ligands are disordered.

Luminescent probing of the simplest chiral α‐amino acid–alanine in an enantiopure and racemic state

“…Transition metals including rare earth metals are able to form a diversity of complexes with organic compounds bearing groups that are Lewis bases. Alanine is not an exception, and a number of its complexes with lanthanides and actinides have been reported. Three main types of complexation between amino acids and lanthanides are known (Figure ).…”

“…Lanthanides can form polynuclear complexes including infinite chains where the carboxylate group plays the role of a bridge. In particular, gadolinium, europium, and terbium tripositive ions form dimeric complexes: [Gd 2 (Ala) 4 (H 2 O) 8 ](ClO 4 ) 6 (handedness of alanine has not been specified), [Eu 2 (Ala) 4 (H 2 O) 8 ](ClO 4 ) 6 (both L and DL forms have been described), and [Tb 2 (L‐Ala) 4 (H 2 O) 8 ](ClO 4 ) 6 , where four zwitterionic alanine ligands link two Ln 3+ ions via oxygen atoms of the carboxylate group (mode I) . Studies on the alanine and other amino acids complexation with UO 2 2+ in aqueous solutions indicate that [UO 2 (Ala) 2 (H 2 O) x ] 2+ species are present in the equilibrium mixture .…”

Compounds of Amino Acids and Neutral Salts

“…In the case of the gadolinium salt (Wang et al 2003), no indication was given whether the amino acid is D or L. The authors only speak of "centrosymmetric units." However, when investigating the CIF as deposited in the Cambridge Structural Database (Allen 2002), it turns out that half of the alanine molecules have been refined as disordered.…”

Tetra-μ-L-isoleucine-bis[tetraaquasamarium(III)] hexaperchlorate

“…For example, at low pH the amino acid ligands are bonded to the rare earth elements through their carboxyl groups, while the amino groups are protonated and are not involved in the coordination. These complexes adopt one of three types of structures, namely, dinuclear dimer, chain or network polymer; see, for example, Legendziewicz et al (1984), Csoregh et al (1989), Glowiak et al (1991), Hu et al (1995), Ma et al (1995), Wang et al (1994) and Wang et al (2003). However, at high pH, amino groups may participate in coordination, and these complexes show tetranuclear and pentadecanuclear forms (Wang et al, 1999;Ma et al, 2000;Zhang et al, 2000a,b).…”