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

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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.

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