Vanadium, Molybdenum, and Sodium Triethanolamine Complexes Derived from an Assembly System Containing Tetrathiometalate and Triethanolamine

The reaction system composed of triethanolamine (TEA) and tetrathiovanadate in the presence of MeONa (MeOLi) or NaNH₂ was studied to afford vanadium and alkali metal TEA complexes. Complexes {M⊂V₆O₆[N(CH₂CH₂O)₂(CH₂CH₂OH)]₆}₂S₆ (M = Na (1), Li (2)) contain two cyclic V^(IV) [12]metallacrown-6 cations linked by a polysulfide S₆^2- anion. Also separated from the reaction system is a novel sodium TEA complex {[Na(TEA)]₂S₆}_n (3), in which parallel coordination chains [Na(TEA)⁺]_n are connected by O−H···S hydrogen bonds forming 3-D network structure. Variable-temperature conductance of 3 was determined to display semiconductor feature. The desulfurization of VS₄^3- was observed to form S₆^2- anion and/or S₈ molecule in the synthetic reactions of 1−3. A striking contrast was noted that MoS₄^2- did not desulfurize in the similar reaction to that of VS₄^3- with TEA, and a Na/TEA complex containing MoS₄^2-, (Et₄N)₂[Na₂(μ-TEA)₂(CH₃OH)₂](MoS₄)₂ (4), was obtained instead. The S···H−O and O···H−O hydrogen bonds play an important role in forming the one- or three-dimensional structures for all these complexes by the linkages between clusters and chains. The IR spectrum indicates the structural similarity of complexes 1 and 2. For complex 4, the MoS stretch vibration at 468 cm^-1 showing widening and slight red-shift and the slight movement of the ¹H NMR signals of TEA ligand to downfield are considered to be the influence of the S···H−O hydrogen bonds. Variable temperature magnetic susceptibility data were collected for complex 1. The effect magnetic moment per V₆ unit varies gradually from 4.04 μ_B at 300 K to 6.24 μ_B at 5 K, exhibiting ferromagnetic interaction. Heisenberg-type vector-coupling model and molecular field approximation were used to treat the interaction between the paramagnetic sites and gave a good fitting result:  J = 3.97 cm^-1, J‘ = 1.99 cm^-1, g = 1.99, F = 3.64 × 10^-3. Density functional calculation was also performed to complex 1 and its Li, K analogues. The lowest total bonding energy of −874.001 eV was obtained for [Na⊂V₆(μ₃-O)₆] complex containing six unpaired electrons, indicating the stability of a V₆ system with six independent spins S = ¹/₂. When the alkali metal ion is inserted into the [V₆(μ₃-O)₆] cavity, the positive values of the bonding interaction (E_b) indicate that the insertion depresses the total energy and that complexes 1 and 2 together with K⁺ complex may exist. However, the lowest E_b value of the K⁺ complex implies its instability.