MOLECULAR-STRUCTURES OF A MONOVALENT AND A DIVALENT NICKEL CATENATE -COMPETITION BETWEEN METAL ORBITAL REQUIREMENTS AND GEOMETRICAL CONSTRAINTS IMPOSED BY THE LIGAND

Nickel(I) and nickel(II) catenates were crystallized, and their X-ray structures were solved. Ni(I) complex: [C68H68N4O12Ni+][ClO4-].C6H6.CH 2Cl2, a = 17.328(7) angstrom, b = 14.965(6) angstrom, c = 14.675(6) an gstrom, alpha = 97.78(6)-degrees, beta = 111.46(8)-degrees, gamma = 97 .84(5)-degrees, V = 3481 angstrom3, triclinic P1BAR, Z = 2. Ni(II) com plex: [C68H68N4O12Ni2+][BF4-]2. 1/2C6H6.1/2H2O, a = 20.472(10) angstro m, b = 24.255(8) angstrom, c = 15.405(8) angstrom, beta = 113.80(2)-de grees, V = 6999 angstrom3, monoclinic C2/c, Z=4. The complexes consist of two interlocking 30-membered rings with two 2,9-diphenyl-1,10-phen anthroline fragments as coordinating units, complexed to mono- or diva lent nickel. The extremely strong stabilization of Ni(I) as determined by electrochemistry (Ni(II)/Ni(I): E-degrees = -0.18 V vs SCE in CH3C N) is reflected by both structures. The ligand system is perfectly wel l adapted to a tetrahedral geometry as preferred by monovalent nickel and in agreement with the molecular structure found. On the other hand , the divalent state leads to a strongly distorted structure, in accor dance with a d8 configuration which is not likely to easily accommodat e a tetrahedral environment. Rather, the geometry of the Ni(II) catena te is close to that of a square bipyramid lacking an axial position. A ccordingly, the two chelate planes of the Ni(I) catenate being perpend icular to one another, no intramolecular stacking interactions between aromatic groups are observed, whereas in the Ni(II) case strong PI-PI interactions between phenyl rings and aromatic nuclei are present.