Photolysis of cis- and trans-[FeIII(cyclam)(N3)2]+ complexes:: Spectroscopic characterization of a nitridoiron(V) species
Photolysis of cis- and trans-[FeIII(cyclam)(N3)2]+ complexes:: Spectroscopic characterization of a nitridoiron(V) species
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DOI：
10.1021/ja983454t
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发表时间：
1999-05-26
影响因子：
15
通讯作者：
Wieghardt, K
中科院分区：
文献类型：
--
作者：
Meyer, K;Bill, E;Wieghardt, K
顺式-[Fe-III（cyclam）Cl-2] Cl在酸性H2O/CH 3OH或CH 3CN/H2O混合物中与NaN 3在50 ℃下反应，在加入NaClO 4或NaPF 6后产生络合物反式-[Fe-III（cyclam）（N-3）（2）] ClO 4（1a）或六氟磷酸盐1b，而在-18 ℃下，相同的反应产生顺式-[Fe-III（cyclam）（N-3）（2）]（ClO 4）（2）（cyclam = 1，4，8，11-四氮杂环十四烷）。通过单晶X射线晶体学测定了1b和2的晶体结构。配合物1a、B分别含有一个低自旋（S = 1/2）和一个高自旋铁离子（S = 5/2），这一点通过变温磁化率测量、穆斯堡尔谱和X-带EPR谱确定。在乙腈溶液中电化学生成了低自旋反式[（cyclam）Fe-II（N-3）（2）]和高自旋顺式[（cyclam）Fe-II（N-3）（2）]物种，并用穆斯堡尔谱进行了表征。在-35 ° C和20 ° C下用汞灯在CH 3CN中光解1a，在15分钟内产生黄色溶液。EPR谱和穆斯堡尔谱表明形成了一个S = 1/2基态的高价物种：[{trans-cyclam）Fe（N-3）}（2）（μ-N）（2+）。在80 K的穆斯堡尔谱显示出两个四极双峰（比率为1：1），表明存在低自旋的Fe-IV（S = 1），其同质异能位移δ为0.11 mm s（-1），四极分裂Δ E-Q为0.97 mm s（-1），以及中间自旋的Fe-IV（S = 3/2），δ = 0.20 mm S（-1），Δ E-Q = 2.09 mm s（-1）。混合价[Fe-III（μ-N）Fe-IV]（4+）核（S-t = 1/2）中的价态位于穆斯堡尔时间标度上。此外，还发现18%的低自旋Fe-II络合物（S = 0），δ = 0.54 mm s（-1），Δ E-Q = 0.65 mm s（-1）。2在-35 ° C的CH 3CN中光解产生黄色的混合价双核物质，S = 3/2基态。对于该物种，我们提出了[{cis-（cyclam）Fe-III（N-3）}（mu-N）{trans-（cyclam）Fe-IV（N3）}]（2+）的结构，其中[Fe-III（mu-N）Fe-IV]（2+）为核心（S-t = 3/2）。在80 K下的穆斯堡尔谱清楚地表明，化合价是局域化的：在（a）delta = 0.14 mm s（-1），Delta E-Q = 0.81 mm s（-1）（Fe-IV; S = 1）和（B）delta = 0.50 mm s（-1），Delta E-Q = 1.89 mm s（-1）（FeIII; S = 5/2）处检测到两个子谱（比率1：1）。两个铁位点之间的强分子内反铁磁耦合产生所观察到的St = 3/2基态。提出的两种光解产物的自旋态和自旋耦合方案得到了磁穆斯堡尔谱和EPR谱的证实。双核物种的形成需要氮铁（V）物种的初级形成：trans-N =Fe-V（cyclam）（N-3）]（+）。该中间体已被检测到在光解的冷冻CH_3CN溶液中的1A在4和77 K的EPR和穆斯堡尔谱。该物种含有Fe-V离子（d（3），S = 3/2），在80 K下的异构体位移δ = -0.04 mm s（-1）和四极分裂Δ E-Q = -1.90 mm s（-1）。此外，五配位亚铁物种已被确定为主要光解产物，其通过Fe-III-N-3键的光解均裂形成。因此，同时发生的光氧化和还原过程中的光解1a在冷冻溶液中。的FeV物种的电子结构进行了研究与EPR，磁穆斯堡尔谱，和自旋哈密顿分析。
Reaction of cis-[Fe-III(cyclam)Cl-2]C1 in acidic H2O/CH3OH or CH3CN/H2O mixtures with NaN3 at 50 degrees C produced upon addition of NaClO4 or NaPF6 the complex trans-[Fe-III(cyclam)(N-3)(2)]ClO4 (1a) or the hexafluorophosphate salt 1b, whereas at -18 degrees C the same reaction produced cis-[Fe-III(cyclam)(N-3)(2)](ClO4) (2) (cyclam = 1,4,8,11-tetraazacyclotetradecane). The crystal structures of 1b and 2 were determined by single-crystal X-ray crystallography. Complexes 1a, b, contain a low-spin (S = 1/2) and 2, a high-spin ferric ion (S = 5/2) as was established by variable-temperature magnetic susceptibility measurements and Mossbauer and X-band EPR spectroscopy. The low-spin trans-[(cyclam)Fe-II(N-3)(2)] and high-spin cis-[(cyclam)Fe-II(N-3)(2)] species were generated electrochemically in CH3CN solution and were characterized by Mossbauer spectroscopy. Photolysis of 1a in CH3CN at -35 degrees C and 20 degrees C with a Hg immersion lamp generated within 15 min a yellow solution. EPR and Mossbauer spectra show that a single high-valent species with an S = 1/2 ground state is formed: [{trans-(cyclam)Fe(N-3)}(2)(mu-N)(2+). The Mossbauer spectrum at 80 K exhibits two quadrupole doublets (ratio 1:1), indicating the presence of low-spin Fe-IV (S = 1) with isomer shift, delta, at 0.11 mm s(-1) and quadrupole splitting, Delta E-Q, at 0.97 mm s(-1) and intermediate-spin Fe-IV (S = 3/2) With delta = 0.20 mm S-1 and Delta E-Q = 2.09 mm s(-1). The valencies in this mixed valent [Fe-III(mu-N)Fe-IV](4+) core (S-t = 1/2) are localized on the Mossbauer time scale. In addition 18% of a low-spin Fe-II complex (S = 0) was found with delta = 0.54 mm s(-1), Delta E-Q = 0.65 mm s(-1). Photolysis of 2 at -35 degrees C in CH3CN produced a yellow mixed valent dinuclear species with an S = 3/2 ground state. For this species we propose the structure [{cis-(cyclam)Fe-III(N-3)}(mu-N){trans-(cyclam)Fe-IV(N3)}](2+) With an [Fe-III(mu-N)Fe-IV](2+) core (S-t = 3/2). The Mossbauer spectrum at 80 K clearly shows that the valencies are localized: two subspectra are detected (ratio 1:1) at (a) delta = 0.14 mm s(-1), Delta E-Q = 0.81 mm s(-1) (Fe-IV; S = 1) and (b) delta = 0.50 mm s(-1), Delta E-Q = 1.89 mm s(-1) (FeIII; S = 5/2). Strong intramolecular antiferromagnetic coupling between the two iron sites produces the observed St = 3/2 ground state. The proposed spin states and spin-coupling schemes for both photolysis products were proven by magnetic Mossbauer and EPR spectra. The formation of the dinuclear species requires the primary formation of a nitridoiron(V) species: trans-[N=Fe-V(cyclam)(N-3)](+). This intermediate has been detected during photolysis of frozen CH3CN solutions of 1a at 4 and 77 K by EPR and Mossbauer spectroscopy. The species contains an Fe-V ion (d(3), S = 3/2) with an isomer shift delta = -0.04 mm s(-1) and a quadrupole splitting Delta E-Q = -1.90 mm s(-1) at 80 K.In addition, a five-coordinate ferrous species has been identified as a primary photolysis product which is formed via photolytic homolysis of the Fe-III-N-3 bond. Thus, simultaneous photooxidation and -reduction processes occur during the photolysis of 1a in frozen solution. The electronic structure of the FeV species was investigated with EPR, magnetic Mossbauer spectroscopy, and spin-Hamiltonian analyses.