and Ni--N distances are 2.067(2), 2.023 (2) and 2.180 (2)~,, respectively. All the C--C bond distances are normal with values between 1.366 (3) and 1.406 (4)A, except those which are close to the coordinated C--O bonds: C(1)---C(2), C(2)---C(3) and C(9)--C(10) are 1.457 (4), 1.445 (3) and 1.462 (4) A., respectively. All rings are almost planar, except those involving coordinated O atoms. The dihedral angles between the flavonato planes and the pyridyl ligands are Acta Crystallographica Section C ISSN 0108-2701 ©1995
[Ni(C15 H9 03 )2 (C5 H5 N)2 ]quite large with values of ca 84 ° . The angles between the planes in the hydroxyflavone ligand are less than 10 ° .
CommentThe structures of coordinated ligands containing N and O atoms bonded to nickel provide important information on metalloenzyme systems. Complexes of Ni H with ligands such as aminocyclohexanecarboxylate (Haendler, 1993), hexafluoroacetonate (Polam & Porter, 1992), salicyaldehydate (Stewart, Lingafelter & Breazeale, 1961), acetylacetonate and tetramethylethylenediamine (Yamada, Hori & Fukuda, 1993), benzenedicarboxylate and 2,2'-bipyridyl (Poleti, Karanovic & Prelesnik, 1990), glycinate and 2,2'-bipyridyl (Z~ik, Gtowiak, Kamenffzek & B~ezina, 1990), carboxylates and silane carboxylate (Morooka et al., 1992) have been reported. Although the structure of flavonol chelated to copper has been reported (Speier, Fiilop & Parkanyi, 1990), little information is available on the analogues of nickel. An ethanolic solution of the triethylammonium salt of the 3-hydroxyflavonato anion reacts with NiC12.6H20 to form [Ni(H20)2(flv)2], which, on heating with excess pyridine under reflux, produces trans-[Ni(py) The crystal structure of (I) is shown in Fig. 1. The Ni atom is octahedrally surrounded by two trans py and two chelating fly ligands. All the trans O--Ni--O and N--Ni--N bond angles are exactly 180 ° because the Ni atom lies on a centre of symmetry. The O---Ni--N angles are close to 90 ° (Table 2). However, the angle subtended by both chelating O atoms at the nickel centre is found to be 81.0(1) °. This value is consistent with the values reported for other five-membered chelates, such as chelates of Ni n with 1-aminocyclohexanecarboxylato and Cu I with 3-hydroxyflavonato (Speier et al., 1990) which have values of 81.3 (2) and 79.2 (3) ° , respectively. The 0(2)--crC ( The C--C bond distances in the hydroxyflavonato moiety further emphasize the canonic nature of the pyrone ring. The C(9)---C(1) and C(3)--C(8) bonds of 1.385 (3) and 1.389 (3)A,, respectively, are shorter than C(1)---C(2) which is 1.457 (4)A in length. The C----C distances in the pyridyl ligands are normal with a mean of 1.376 (6)A,. The N---C distances are slightly shorter than the C--C bond.The least-square planes are almost coplanar except for plane 1 containing Ni (1)
ExperimentalThe green rhombohedral product of the reaction described in the Comment was recrystallized from hot acetonitrile. The crystal density Dm was measured by flotation in CCl4/hexane. 1.406 (4) C(4)---C(57 1.366 (3...
