Coordination versatility of 1,3-bis[3-(2-pyridyl)pyrazol-1-yl]propane: Co(II) and Ni(II) complexes

The ligand 1,3-bis[3-(2-pyridyl)pyrazol-1-yl]propane (L) has afforded six-coordinate monomeric and dimeric complexes [(L-8)Co-11 (H2O)(2)][ClO4](2) (1), [(L-8)Ni-II(MeCN)(2)][BPh4](2) (2), [(L-8)Ni-II(O2CMe)][BPh4] (3), and [(L-8)(2)Co-2(II)(mu-O2CMe)(2)][BPh4](2) (4). The crystal structures of 1, 2(.) MeCN, 3, and 4 revealed that the ligand L8 is flexible enough to expand its coordinating ability by fine-tuning the angle between the chelating fragments and hence folds around cobalt(II)/nickel(II) centers to act as a tetradentate chelate, allowing additional coordination by two trans-H2O, cis-MeCN, and a bidentate acetate affording examples of distorted octahedral (CoN2)-N-II (pyridyl) N-2' (pyrazole) O-2 (water), (NiN2)-N-II(pyridyl)N-2'(pyrazole)N-2"(acetonitrile), and (NiN2)-N-II(pyridyl)N-2'(pyrazole)O-2'(acetate) coordination. The angles between the two CoN2/NiN2 planes span a wide range 23.539(1)degrees (1), 76.934(8)degrees (2), and 69.874(14)degrees (3). In contrast, complex 4 is a bis-mu-1,3-acetato-bridged (syn-anti coordination mode) dicobalt(II) complex [(CoCo)-Co-... separation: 4.797(8) angstrom] in which L 8 provides terminal bidentate pyridylpyrazole coordination to each cobalt(II) center. To our knowledge, this report provides first examples of such a coordination versatility of L8. Absorption spectral studies (MeCN solution) have been done for all the complexes. Complexes 1-3 are uniformly high-spin. Temperature-dependent (2-300 K) magnetic studies on 4 reveal weak ferromagnetic exchange coupling ((H) over cap = -JS(1) (.) S-2) between two cobalt(II) (S = 3/2) ions. The best-fit parameters obtained are: Delta (axial splitting parameter) = -765(5) cm(-1), lambda (spin-orbit coupling) = -120(3) cm(-1), k (orbital reduction factor) = 0.93, and J (magnetic exchange coupling constant) = +1.60(2) m(-1). (c) 2006 Elsevier B.V. All rights reserved.