NFeN结构和性质及反应势能曲线

用B3LYP/6-311+G(d)方法对化合物NFeN弯曲型和直线型的不同自旋多重度多个电子态的几何结构、电子结构、能量和振动光谱进行了计算研究. 结果表明, 单重态中Fe―N键长普遍比三重态和五重态中的短, 在155 pm左右; NFeN三重态电子结构最丰富, 自然键轨道和Mulliken布居显示Fe―N键具有部分离子键特征; 两种结构的所有稳定态中能量最低的是1⁵A₂态, 能量相近的有1³B₁、1³A₂、1³B₂和1¹A₁态, 直线型中能量最低是³Δ_g态; 相对于分子基态反应物Fe(a⁵D)+N₂(X¹Σ_g⁺)所有电子态的能量都偏高, 该反应在热力学上是不利的, 但是对于原子态反应物Fe(a⁵D)+2N(⁴S)则是放热反应; 计算振动频率和强度与实验较吻合的是1³B₁态; 复合物FeN₂与化合物NFeN结构差异明显; Fe原子直接插入N₂分子的势能曲线表明该反应能垒很高, 在动力学上也是不利的.

Structures and Properties of NFeN and the Reaction Potential Energy Curves

The geometrical structures, electronic structures, energetics and vibrational frequencies of bent and linear NFeN molecules with different spin multiplicities were studied at the B3LYP/6-311+G(d) level. We find that: (1) the Fe―N bond length is about 155 pm for singlet states and this is shorter than those in triplets and in quintets; (2) the electronic structures of triplet bent NFeN are more complicated than that of the others. Natural bonding orbital and Mulliken population data indicate that the Fe―N bond displays ionicity; (3) the most stable electronic state among all the states is 15A2 and the energies of 13B1, 13A2, 13B2, and 11A1 are similar, however, the most stable electronic state of linear NFeN is 3Δg. This reaction is endothermic because the energies of all the states are higher than those of the ground state Fe(a5D)+N2(X1Σg+) reactants while Fe(a5D)+2N(4S) is exothermic; (4) according to the calculated structure and vibrational characteristics the 13B1 state might be observed in the reported experiments; (5) compared with our previous results the structures of the FeN2 complexes are very different from that of the NFeN compound; (6) the Fe atom direct insertion reaction into the triple bonds of N2 is especially difficult because of the energy barriers in the reaction potential energy curves.