[(O)(tmpa)V(IV)(μ-O)V(V)(tmpa)(O)](3+)的晶体结构、物理性质及水解动力学

Crystal Structure, Physical Properties, and Hydrolysis Kinetics of [(O)(tmpa)V(IV)(&mgr;-O)V(V)(tmpa)(O)](3+).

作者信息

Holwerda Robert A., Whittlesey Bruce R., Nilges Mark J.

机构信息

Illinois EPR Research Center, University of Illinois, Urbana, Illinois 61801.

出版信息

Inorg Chem. 1998 Jan 12;37(1):64-68. doi: 10.1021/ic970983+.

DOI:10.1021/ic970983+

PMID:11670261

Abstract

We report the synthesis, crystal structure, physical properties and hydrolysis kinetics of (O)(tmpa)V(IV)(&mgr;-O)V(V)(tmpa)(O) (tmpa = tris(2-pyridylmethyl)amine), the first cation in its class for which both solid state and solution-phase characteristics are fully consistent with expectations for a Robin-Day type III mixed-valence complex. V(2)(tmpa)(2)(O)(3)(3).CH(3)CN crystallizes in the triclinic, P&onemacr; (No. 2) space group with a = 10.719(2) Å, b = 11.609(1) Å, c = 19.516(2) Å, alpha = 87.876(9) degrees, beta = 79.295(9) degrees, gamma = 68.743(9) degrees, and V = 2222.6(6) Å(3); Z = 2. The two vanadium centers are crystallographically equivalent in a linear, oxo-bridged cation with V-O(b) and V=O bond lengths of 1.800(1) and 1.597(4) Å, respectively. A 15-hyperfine line EPR spectrum (g = 1.9704, A = 46.4 x 10(-4) cm(-1)) was observed for V(2)(tmpa)(2)(O)(3), consistent with coupling of a single electron to two equivalent (51)V atoms. The mixed-valence complex exhibits an intervalence transfer (IT) band at 1.05 x 10(4) cm(-1) (epsilon = 2.1 x 10(3) M(-1) cm(-1), CH(3)CN) whose energy is insensitive to variations in the solvent; d-d transitions are observed at 1.25 x 10(4) cm(-1) ((2)E <-- (2)B(2)) and 1.44 x 10(4) cm(-1) ((2)B(1) <-- (2)B(2)). V(2)(tmpa)(2)(O)(3), V(2)(tmpa)(2)(O)(3), and V(2)(tmpa)(2)(O)(3) comprise a redox family related by vanadium (IV,V/IV,IV) and (V,V/IV,V) half-wave reduction potentials of 0.25 and 1.62 V vs NHE (25 degrees C, CH(3)CN, I = 0.1 M), respectively. The hydrolysis reaction: V(2)(tmpa)(2)(O)(3) + H(2)O --> V(IV)(tmpa)(O)(OH) + V(V)(tmpa)(O)(2) + H(+) proceeds with an acid-independent rate constant of 2.37 x 10(-3) s(-1) (25 degrees C; DeltaH() = 71 kJ/mol, DeltaS() = -59 J/mol K). V(4)O(5)(tmpa)(4){Fe(CN)(6)}(4).H(2)O was isolated as an unexpected product from the reaction of V(2)(tmpa)(2)(O)(3)(2).2H(2)O with equimolar K(3)[Fe(CN)(6)] in aqueous solution. It is proposed that pairs of V(IV)=O and V(V)=O units aggregate with Fe(CN)(6) into a charge transfer complex. Hexacyanoferrate(II)-to-vanadium IT charge transfer bands are observed at 1.98 x 10(4) cm(-1) (epsilon = 5.3 x 10(3) M(-1) cm(-1)) and 2.72 x 10(4) cm(-1) (epsilon = 9.3 x 10(3) M(-1) cm(-1)); a 29-line EPR spectrum (g = 1.9737, A = 22.0 x 10(-4) cm(-1)) demonstrates equal delocalization of unpaired electron density over all four V atoms (CH(3)CN solution).

摘要

我们报告了(O)(tmpa)V(IV)(μ - O)V(V)(tmpa)(O)（tmpa = 三(2 - 吡啶甲基)胺）的合成、晶体结构、物理性质及水解动力学，它是该类别中的首个阳离子，其固态和溶液相特征均完全符合对Robin - Day III型混合价配合物的预期。V₂(tmpa)₂(O₃)₃·CH₃CN以三斜晶系，P1̅（编号2）空间群结晶，a = 10.719(2) Å，b = 11.609(1) Å，c = 19.516(2) Å，α = 87.876(9)°，β = 79.295(9)°，γ = 68.743(9)°，V = 2222.6(6) Å³；Z = 2。两个钒中心在一个线性的、氧桥连阳离子中晶体学等价，V - O(b)和V = O键长分别为1.800(1) Å和1.597(4) Å。观察到V₂(tmpa)₂(O₃)的一个15 - 超精细线EPR谱（g = 1.9704，A = 46.4×10⁻⁴ cm⁻¹），这与单个电子与两个等价的⁵¹V原子的耦合一致。该混合价配合物在1.05×10⁴ cm⁻¹处呈现一个价间转移（IT）带（ε = 2.1×10³ M⁻¹ cm⁻¹，CH₃CN），其能量对溶剂变化不敏感；在1.25×10⁴ cm⁻¹（²E ← ²B₂）和1.44×10⁴ cm⁻¹（²B₁ ← ²B₂）处观察到d - d跃迁。V₂(tmpa)₂(O₃)、V₂(tmpa)₂(O₃)和V₂(tmpa)₂(O₃)构成一个氧化还原家族，相对于标准氢电极（NHE），钒(IV,V/IV,IV)和(V,V/IV,V)的半波还原电位分别为0.25 V和1.62 V（25℃，CH₃CN，I = 0.1 M）。水解反应：V₂(tmpa)₂(O₃) + H₂O → V(IV)(tmpa)(O)(OH) + V(V)(tmpa)(O₂) + H⁺以2.37×10⁻³ s⁻¹的与酸无关的速率常数进行（25℃；ΔH° = 71 kJ/mol，ΔS° = - 59 J/mol K）。V₄O₅(tmpa)₄{Fe(CN)₆}₄·H₂O作为V₂(tmpa)₂(O₃)₂·2H₂O与等摩尔K₃[Fe(CN)₆]在水溶液中反应的意外产物被分离出来。有人提出V(IV)=O和V(V)=O单元对与[Fe(CN)₆]⁴⁻聚集形成一个电荷转移配合物。在1.98×10⁴ cm⁻¹（ε = 5.3×10³ M⁻¹ cm⁻¹）和2.72×10⁴ cm⁻¹（ε = 9.3×10³ M⁻¹ cm⁻¹）处观察到六氰合铁(II)到钒的IT电荷转移带；一个29 - 线EPR谱（g = 1.9737，A = 22.0×10⁻⁴ cm⁻¹）表明未成对电子密度在所有四个V原子上平均离域（CH₃CN溶液）。