Two series of new mixed-ligand nitronyl nitroxide Ni(II) complexes of [Ni(β-diketonato)2(NIT2-py)] and [Ni(β-diketonato)(tmen)(NIT2-py)]+ types with various kinds of β-diketonates have been synthesized and structurally and magnetically characterized, where NIT2-py is 2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-lH-imidazolyl-1-oxyl 3-oxide and tmen is N,N,N,′,N′-tetramethylethylenediamine. The X-ray structural analysis for three tmen complexes with 2,4-pentanedionate (1b), 1,3-diphenyl-1,3-propanedionate (2b), and 4,4,4-trifluoro-1-phenyl-1,3-butanedionate (5b) demonstrated that the β-diketonato complexes assume a mer (cis,trans) N3O3 geometrical configuration. The structural parameters are as follows: 1b (C23H39F6N5NiPO 4·1/3CH2Cl2), trigonal, R3̄, a = 33.299(5) Å, c = 15.007(9) Å, Z = 18; 2b (C28H41F6N5NiPO4), orthorhombic, Pbca, a = 23.732(6) Å, b = 18.504(5) Å, c = 15.345(4) Å, Z = 8; 5b (C28H38F9N5NiPO4), triclinic, P1̄, a = 12.068(2) Å, b = 16.942(2) Å, c = 9.161(1) Å, α = 105.26(1)°, β= 103.72(1)°, γ = 71.62(1)°, Z = 2. The antiferromagnetic interactions between Ni(II) and NIT2-py were found within ranges of J = -207 to -224 cm-1 for the bis(β-diketonato) complexes and of J = -35 to -150 cm-1 for the (β-diketonato)(tmen) complexes. The displacement of the β-diketonates with tmen in bis(β-diketonato) complexes decreases the J values, and the effect of the 1,3-substituents in the β-diketonates on the J values is observed in a systematic manner for all the bis(β-diketonato) complexes and for the (methyl- and phenyl-substituted-β-diketonato)(tmen) complexes but not for the trifluoromethyl-substituted complex. The room-temperature electronic spectra of the bis(β-diketonato) and the (β-diketonato)(tmen) complexes exhibit enhanced spin-forbidden d-d transitions at 13.0 × 103 cm-1 and new metal-ligand charge-transfer (MLCT) transitions around (16.0-19.0) × 103 cm-1. The variation of the spectroscopic characteristics with modification of the β-diketonato ligands is discussed through the exchange mechanism in connection with the antiferromagnetic interactions in terms of the substituent effects or the Hammett σm constants.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry