Dependence of the Chemical Properties of Macrocyclic [(Ni2L)-L-II(mu-O2CR)](+) Complexes on the Basicity of the Carboxylato Coligands (L2- = macrocyclic N6S2 ligand)

作者：Lehmann Ulrike; Klingele Julia; Lozan Vasile; Steinfeld Gunther; Klingele Marco H; Kaess Steffen; Rodenstein Axel; Kersting Berthold^*

来源：Inorganic Chemistry, 2010, 49(23): 11018-11029.

DOI：10.1021/ic101574a

The dependence of the properties of mixed ligand [(Ni2L)-L-II(mu-O2CR)](+) complexes (where L2- represents a 24-membered macrocyclic hexaamine-dithiophenolato ligand) on the basicity of the carboxylato coligands has been examined. For this purpose 19 different [(Ni2L)-L-II(mu-O2CR)](+) complexes (2-20) incorporating carboxylates with pK(b) values in the range 9 to 14 have been prepared by the reaction of [(Ni2L)-L-II(mu-Cl)](+) (1) and the respective sodium or triethylammonium carboxylates. The resulting carboxylato complexes, isolated as ClO4- or BPh4- salts, have been fully characterized by elemental analyses, IR, UV/vis spectroscopy, and X-ray crystallography. The possibility of accessing the [(Ni2L)-L-II(mu-O2CR)](+) complexes by carboxylate exchange reactions has also been examined. The main findings are as follows: (i) Substitution reactions between 1 and NaO2CR are not affected by the basicity or the steric hindrance of the carboxylate. (ii) Complexes 2-20 form an isostructural series of bisoctahedral [(Ni2L)-L-II(mu-O2CR)](+) compounds with a N3Ni(mu-SR)(2)(mu-O2CR)NiN3 core. (iii) They are readily identified by their nu(as)(CO) and nu(s)(CO) stretching vibration bands in the ranges 1684-1576 cm(-1) and 1428-1348 cm(-1), respectively. (iv) The spin-allowed (3)A(2g) -> T-3(2g) (nu(1)) transition of the NiOS2N3 chromophore is steadily red-shifted by about 7.5 nm per pK(b) unit with increasing pK(b) of the carboxylate ion. (v) The less basic the carboxylate ion, the more stable the complex. The stability difference across the series, estimated from the difference of the individual ligand field stabilization energies (LFSE), amounts to about 4.2 kJ/mol [Delta(LFSE)(2,18)]. (vi) The "second-sphere stabilization" of the nickel complexes is not reflected in the electronic absorption spectra, as these forces are aligned perpendicularly to the Ni-O bonds. (vii) Coordination of a basic carboxylate donor to the [(Ni2L)-L-II](2+) fragment weakens its Ni-N and Ni-S bonds. This bond weakening is reflected in small but significant bond length changes. (viii) The [(Ni2L)-L-II(mu-O2CR)](+) complexes are relatively inert to carboxylate exchange reactions, except for the formato complex [(Ni2L)-L-II(mu-O2CR)](+) (8), which reacts with both more and less basic carboxylato ligands.

• 出版日期2010-12-6