Complexation of 2,4,6-tri-tert-butylpyridine-1,3,5-triazine ligand (l) with the cerium(iv) nitrate anion; encapsulation of protonated [lhn]n+ with the hexafluorophosphate, nitrate and hydroxide anions; formation and crystal structures of Ce(NO3)4L, 2[LH3]3+ [Ce(NO3)5(OH2)]-[Ce(NO3)5(EtO)]2-2[NO3]-[OH]-, 2[LH2]2+[PF6]-1.5[BF4]-0.5[PO4]3- and [LH4]4+[3NO3][PF6

Abstract

The versatile nature of the ligand 2,4,6-tri-tert-butylpyridyl-1,3,5-triazine (L) has been established through the preparation and structure determination of four complexes, one containing the cerium(IV) cation and three in which the protonated ligand forms salts with a variety of anions. Complex 1, Ce(NO3)4L, crystallizes in the monoclinic space group P21/c with Z = 4. The cerium atom is 11-coordinate, bonded to L in a tridentate fashion and to four bidentate nitrate anions. The three Ce—N bond lengths are 2.720(8), 2.673(7) and 2.734(7) . The Ce-O distances range between 2.522(7) and 2.699(9) . In complexes 2, 3 and 4, protonated cations of the type [LHn]n+ are shown to encapsulate simple anions such as PF6−,NO3−andOH− and OH- via strong hydrogen-bond formation. Complex 2, 2[LH3]3+ [Ce(NO3)5(OH2)]- [Ce(NO3)5(OEt)]2-, 2NO3 , OH-, is monoclinic, space group P21/n with Z = 4. The structure contains two independent [LH3]3+ cations, each of which participates in three strong hydrogen bonds. All three pyridine ring nitrogen atoms are protonated and both cations form two strong hydrogen bonds to an oxygen atom, from a nitrate and a hydroxide anion, respectively. In addition, a second nitrate anion forms two hydrogen bonds in which two of its oxygen atoms link both cations. In both metal complex anions, the cerium atom is 11-coordinate with Ce—O bond lengths ranging between 2.528(6) and 2.633(6)in [Ce(NO3)5(OH2)]- and 2.494(11) and 2.86(2)in [Ce(NO3)5(OEt)]2-. Complex 2, 2[LH3]3+[Ce(NO3)5(OH2)]−[Ce(NO3)5(OEt)]2−,2NO3−,OH−, belongs to the triclinic space group P1 with Z = 2. The structure contains two independent [LH2]2+ cations that are linked together via a [PF6-] anion which forms four strong hydrogen bonds, with two fluorine atoms each forming hydrogen bonds to two protonated pyridine ring nitrogen atoms in each cation. Complex 4, [LH4]4+3NO3−PF6−, is monoclinic, space group P21/c with Z = 4. The [LH4]4+ cation forms two strong hydrogen bonds from two protonated pyridine ring nitrogen atoms to one oxygen atom of a nitrate anion and two weaker hydrogen bonds from the third protonated pyridine ring nitrogen atom and a protonated nitrogen atom in the central triazine ring. In all structures the ligand L remains approximately planar. Copyright © 1996 Elsevier Science Ltd