Metal complexes of α-hydroxyimino phosphonic acid derivatives. Separation of the E and Z isomers by metal chelation and the preparation and characterization of copper bis[-(α-(hydroxyimino)benzyl)phosphonate]-water

A new class of interesting ligands combining adjacent phosphoryl and oxime moieties has been recently prepared. Sodium methyl (α-(hydroxyimino)benzyl)phosphonate| Na[CH₃O(O)P(O)C(NOH)C₆H₅]) is obtained as a mixture of E and Z isomers. The E isomer has been crystallized and characterized by a single-crystal X-ray diffraction study. It crystallized in the monoclinic system in the space group P2₁/c with unit cell dimensions of a = 6.496 (1) Å, b = 31.998 (2) Å, c = 10.087 (1) Å, β = 92.82 (1)°, V = 2094 (1) ų, and Z = 8. When a mixture of the E and Z isomers was treated with Cocl₂.6H₂O, the Co²⁺ selectively precipitated the E isomer, allowing the purification and characterization of the Z isomer. The E isomer reacts readily with Cucl₂•2H₂O, affording a pentacoordinate copper complex bound to two ligands and a water molecule. The X-ray crystal structure of the copper complex Cu[-CH₃O(O)P(O)C(NOH)C₆H₅]₂.H₂O has revealed a mononuclear complex with a near-trigonal-bipyramidal geometry where each ligand acts solely as a bidentate ligand through the oxime nitrogen and the phosphoryl oxygen. The compound crystallized in the monoclinic system in the C2/c space group with unit cell dimensions of a = 17.774 (2) Å, b = 16.986 (1) Å, c = 7.279 (1) Å, β = 113.44 (1)°, V = 2016 (1) ų, and Z = 4. The Z isomer did not react with the cupric ion under these conditions, presumably due to the formation of an intramolecular hydrogen bond between the oxime hydrogen and the phosphoryl oxygen. The existence of this bond is supported by semiempirical calculations (modified version of MNDO) that show that the hydrogen-bond formation stabilizes the molecule by 15 kcal. Also, IR data show a hydrogen bond only for the Z isomer.