Crystal structures of methyl(L-tyrosinato)mercury(II) monohydrate and [L-(2-amino-4-phenylbutanoato)]methylmercury(II)

Abstract

The crystal structures of the 1 : 1 complexes formed by methylmercury(II) with L-tyrosine (2) and L-2-amino-4- phenylbutanoic acid (3) have been determined by X-ray diffraction. Complex (2) crystallises as a monohydrate which is monoclinic, P2₁, with unit-cell dimensions a= 9.084(1), b= 6.150(1), c= 11.565(1)Å, β= 110.52(2)°, and Z= 2. Complex (3) is orthorhombic, Pca2₁. with dimensions a= 14.853(4), b= 9.438(3), c= 8.755(2)Å, and Z= 4. Intensities [1 078 and 674 with l/σ(l) 3.0 for (2) and (3) respectively] have been recorded at 173 K on a four-circle diffractometer, and the structures refined by the least-squares method to yield final R values of 0.044 and 0.046 for (2) and (3) respectively. The two structures differ markedly: in (2) the amino-acid is bound to mercury via an amino-group [Hg–N 2.17(2)Å], and mercury has further weaker intramolecular interactions with the carboxylate group [Hg–O 2.62(2)Å] and with the phenyl ring [Hg–C 3.19(2) and 3.33(2)Å], whilst in (3) a phenyl-ring interaction is absent but the amino-group is again bound [Hg–N 2.15(3)Å] and mercury has both intramolecular and intermolecular interactions with carboxylate groups [Hg–0 2.72(2) and 2.78(3)Å respectively]. The crystal structures are compared with the structures in solution as indicated by ¹H and ¹³C n.m.r. spectroscopy. The postulated hydrophobic interaction between the methyl group of methylmercury(II) and the phenyl ring of phenylalanine or tyrosine is shown to be an edge-on interaction between the mercury atom and two carbon atoms (1 and 2) of the phenyl group.