Metal-betaine interactions. IV. Crystal structures of trans-tetraaquabis(betaine)nickel(II) nitrate and trans-diaquatetrakis(pyridine betaine)cobalt(II) bis[trichloro(pyridine betaine)cobaltate(II)]

Two transition metal(II) complexes of betaine (Me₃N⁺CH₂COO^–, designated as BET) and pyridine betaine (C₅H₅N⁺CH₂COO^–, pyBET) have been prepared and investigated by X-ray crystallography and infrared spectroscopy. [Ni(BET)₂(H₂O)₄] (NO₃)₂ (1), (R_F=0.054 for 2518 observed MoK data) comprises slightly distorted octahedral [Ni(BET)₂(H₂O)₄]²⁺ cations in which the Ni(II) atom is centrosymmetrically coordinated by four aqua ligands and twotrans-related unidentate BET ligands, and the uncoordinated carboxy oxygens form intramolecular hydrogen bonds with the aqua ligands. [Co(pyBET)₄(H₂O)₂]·2[Co(pyBET)Cl₃] (2) (R_F=0.029 for 4696 observed data) consists of discrete octahedral [Co(pyBET)₄(H₂O)₂]²⁺ cations and tetrahedral [Co(pyBET)Cl₃]^– anions. In the centrosymmetric cation each of the twotrans-related aqua ligands form a pair of intramolecular hydrogen bonds with the uncoordinated oxygen atoms of two unidentate pyBET ligands. In the anion the cobalt atom is coordinated by one unidentate pyBET ligand and three chloro ligands.