配體結構對鈾配位性能影響的理論研究

匙芳廷，文　君，熊　潔，胡　勝，魏貴林，易發成

1.西南科技大學，核廢物與環境安全國防重點學科實驗室，四川 綿陽　621010；2.中國工程物理研究院 核物理與化學研究所，四川 綿陽　621900

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配體結構對鈾配位性能影響的理論研究

匙芳廷1,2，文君2,*，熊潔2，胡勝2，魏貴林1，易發成1

1.西南科技大學，核廢物與環境安全國防重點學科實驗室，四川 綿陽621010；2.中國工程物理研究院 核物理與化學研究所，四川 綿陽621900

海水提鈾；密度泛函；配體結構設計；分子軌道

1　計算方法

2　結果與討論

2.1幾何結構優化

(1)

圖2　配體的構型Fig.2　Geometric configuration of ligands

2.2熱力學參數、配位穩定常數

配離子(配原子)的配位穩定常數用K來表示，配位穩定常數越大，形成配離子(配原子)越穩定。配合物的形成過程可以簡單的理想化為反應式(2)。

(2)

通過計算配位過程中焓變(ΔH)、熵變(ΔS)、熱力學能變(ΔU)、吉布斯自由能(ΔG)和配位穩定常數(lgK)，進一步比較了配合物的穩定性，上述參數列入表3。ΔH、ΔG和lgK可以用公式(3)—(5)求得。

(3)

(4)

(5)

表3配合物[UO2(Ax)(H2O)3]+的熱力學參數與配位穩定常數

Table 3Thermodynamic parameters and coordination stability constants of uranyl ligand complexes([UO2(Ax)(H2O)3]+)

配體類型氣態ΔS/(cal·mol-1·K-1)ΔU/(kcal·mol-1)ΔH/(kcal·mol-1)ΔG/(kcal·mol-1)lgKk2-A1-135.8927.969-245.219-204.72335.897k2-A2-126.6658.553-458.861-421.11573.840k2-A3-127.4028.952-469.399-431.43375.649k2-A4-140.0587.839-448.537-406.80071.330η2-A4-125.2969.240-466.554-429.21675.260配體類型水溶液ΔS/(cal·mol-1·K-1)ΔU/(kcal·mol-1)ΔH/(kcal·mol-1)ΔG/(kcal·mol-1)lgKk2-A1-130.117.485-82.063-43.2907.590k2-A2-129.6976.779-126.612-87.96215.424k2-A3-127.7456.754-137.049-98.98117.356k2-A4-123.8668.323-119.726-82.81414.521η2-A4-120.9558.395-136.974-100.92917.697

2.3分子軌道

(a)——[UO2(η2-A4)(H2O)3]+，(b)——[UO2(k2-A1)(H2O)3]+，(c)——[UO2(k2-A2)(H2O)3]+，(d)——[UO2(k2-A3)(H2O)3]+，(e)——[UO2(k2-A4)(H2O)3]+ OLP：氧原子的孤對電子；NLP：氮原子的孤對電子；π(N-O)：N-O形成的π鍵 圖3　配合物[UO2(Ax)(H2O)3]+典型的分子軌道(MO)Fig.3　Representative diagram of molecular orbital of [UO2(Ax)(H2O)3]+ complexes

[UO2(Ax)(H2O)3]+軌道能量/eV分子軌道(MO)分子軌道主要組成[UO2(η2-A4)(H2O)3]+-8.558OLP,π(N-O)1δuOpz,Npz,Ufz-10.140π(N-O)3σuOpz,Npz,Uf3z-10.192OLP,NLP1φuOpx,Opy,Ufx-11.165OLP3σuNpz,Opz,Cpz,Uf3z-11.319π(N-O)2πuOpx,Opy,Npx,Uf2zx,Uf2zy-11.6162πuOpx,Opy,Uf2zx,Uf2zy-13.108π(N-O)1πgOpz,Cpz,Npz,Ud3z[UO2(k2-A1)(H2O)3]+-15.460OLP2σgOpx,Npx,Ufx,Uf2zx-17.012OLP1σgOpz,Udxz[UO2(k2-A2)(H2O)3]+-10.994N-OLPσgUf3z,Opz-12.047C=OLPσgOpx,Opy,Uf2zx,Uf2zy-12.049N-OLPσgOpx,Opy,Opz,Uf2zx,Uf2zy-12.356N-OLPσgOpz,Opx,Opy,Ud2z,Uf2zx-12.629C=OLPσgOpx,Opy,Opz,Udyz,Udxz[UO2(k2-A3)(H2O)3]+-10.651NLPσgUf3z,Npz-10.798OLPσgNpz,Uf3z,Ufz,Uf2zy-11.798OLPσgOpx,Opy,Uf2zy,Uf2zx-11.853NLPσgNpx,Uf2zx[UO2(k2-A4)(H2O)3]+-10.840OLPσgUf3z,Opz-11.934NLPσgNpy,Uf2zy-13.100π(N-O)1πgUdzy,Opy,Npz

由圖3(e)可知，與[UO2(η2-A4)(H2O)3]+相比，π電子云沒有有效地與U軌道重疊，只有Opz軌道重疊形成σ鍵，同時N連有兩個H因此電子云密度低于[UO2(k2-A3)(H2O)3]+中A3的N的電子云密度，綜合兩個因素，k2-A4與U配位能力低于η2-A4和k2-A3。

通過分析配合物典型的成鍵分子軌道，得到配位原子O或N主要成鍵軌道為p軌道，中心原子主要成鍵軌道為d、f軌道；當配體螯合構型配位時，主要形成σ鍵，當配位原子的鄰位是給電子基團時有利于σ鍵的形成；配體π電子云重疊成鍵時，π鍵周圍有給電子時有利于配位；因此容易與U配位的是k2-A3和η2-A4，分子軌道分析與水溶液條件下配位常數lgK計算結果一致。

3　結　論

(3) 通過熱力學參數、分子軌道分析，當配體螯合構型(k2)配位時，主要形成σ鍵，當配位原子的鄰位是給電子基團時有利于σ鍵的形成；當配體π電子云重疊成鍵時，π鍵周圍有給電子基并能形成共軛時有利于配位；因此容易與U配位的是k2-A3和η2-A4，與水溶液條件下配位常數lgK計算結果一致。

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Density Functional Theory Study on Selective Complexation of Uranyl(Ⅵ) With Ligands Possessing Different Configuration

CHI Fang-ting1,2, WEN Jun2,*, XIONG Jie2, HU Sheng2, WEI Gui-lin1, YI Fa-cheng1

1.Fundamental Science on Nuclear Wastes and Environmental Safety Laboratory,Southwest University of Science and Technology, Mianyang 621010, China；2.Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900, China

recovery uranium from seawater; density functional theory; designation of ligand structure; molecular orbital

2015-09-11；

2015-11-19

國家自然科學基金項目(21401152)；西南科技大學博士研究基金項目(13zx7130)；西南科技大學核廢物與環境安全國防重點學科實驗室預研項目(15yyhk08)；西南科技大學核廢物與環境安全國防重點學科實驗室團隊項目(14tdhk01)

匙芳廷(1982—)，女，山東聊城人，博士，副教授，從事海水提鈾吸附劑研究與放射性廢物處理研究

*通信聯系人：文君(1985—)，男，四川樂山人，副研究員，放射化學專業，E-mail: junwen@caep.cn

TL941

A

0253-9950(2016)04-0238-09

10.7538/hhx.2016.38.04.0238