含銻之鉻金屬羰基團簇化合物的合成、結構、轉換關係、物性及化性之探討
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2020
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多核 Sbn−Cr−M−CO 系統 (M = Mn, Fe, Co)
將 Sb2O3 與 Cr(CO)6 以適當比例於 6 M 和 4 M KOH 之 MeOH 溶劑中加熱迴流反應後，可分別得到 Sb4 四面體 (tetrahedral) 順磁性 (S = 1) 化合物 [Sb4Cr6(CO)28]4− (1) 以及 Sb12 籠形 (cage-like) 順磁性 (S = 1) 化合物 [Sb12Cr6(CO)28]4− (2)。X-ray 單晶結果解析顯示化合物 1 為中心 Sb4 四面體結構，且四個 Sb 原子與兩組對邊之 Sb-Sb 鍵分別外接 Cr(CO)5 及 Cr(CO)4 金屬片段；而化合物 2 則具 Sb12 籠型骨架，透過朝外之兩配位 (2-cooridnate) Sb 原子鍵結 Cr(CO)5 及 Cr(CO)4¬ 片段形成雙 Cr(CO)5 配位之 norbornane-like Sb6Cr 構型，並進一步由中心三配位 (3-cooridnate) 的 Sb 原子串接所形成。化合物 1 透過定域化軌域 (localized occupied orbital)、Wiberg 鍵級指標與臨界點分析 (critical point analysis) 顯示 1 之中心為一完整之 Sb4 構型。電化學分析顯示化合物 1 具有兩組接近 0 V之氧化峰訊號，暗示化合物 1 可被氧化，並透過理論計算判斷其氧化反應位置可能會在 SOMO 軌域的中心 Sb4 結構以及 SOMO−1 軌域的橋接之 Cr(CO)4 片段。當化合物 1 與 Mn(CO)5Br 於 MeCN 中加熱迴流反應，可產生氧化性置換一個橋接 Cr(CO)4 片段之順磁性 (S = 1) 化合物 [Sb4Cr5Mn(CO)28]3− (1-Mn)；再者，當 1 與 Mn2(CO)10 於 MeCN 中加熱迴流反應時可以得到化合物 1-Mn 和少量置換兩個 Cr(CO)4 片段之逆磁性化合物 [Sb4Cr4Mn2(CO)28]2− (1-Mn2)。另一方面，將化合物 1 與 Fe(CO)5 以莫爾比 1：24 於 MeCN 中加熱迴流或與 Co2(CO)8 以莫爾比 1：2 於 MeCN 中室溫下反應時，可得到中心為 Sb4 和 Fe(CO)3 金屬片段為頂點所組成之扭曲立方體形 (cubane-like) 順磁性 (S = 1) 化合物 [Sb4Cr2Fe6(CO)30]4− (1-Fe) 與 [Sb4Cr4Co4(CO)31]2− (1-Co)。透過上述反應可發現當金屬羰基試劑與化合物 1 進行反應時，其反應位置皆於 SOMO−1 軌域的橋接 Cr(CO)4 金屬片段，並生成置換金屬之化合物 1-Mn、1-Mn2、1-Fe 與 1-Co。另一方面，當化合物 1 與兩當量 [Cu(MeCN)4]+ 於 MeCN 中室溫下進行反應，可得到以 Sb 原子和 Cr(CO)4 金屬片段為頂點組成之三角柱 (triangular prism) 逆磁性化合物 [Sb4Cr6(CO)28]2−¬ (3)，並可透過加入金屬親核試劑 Na2Fe(CO)4 或還原劑 CoCp2 還原回順磁性化合物 1，此結構轉換關係可視為一可逆的磁性開關 (on/off magnetic switches)。特別的是，化合物 1 具有活化氧氣之特性，並透過 X-ray 結構解析與高解析質譜儀可觀察到橋接兩個氧原子之化合物 [Sb4Cr6O2(CO)28]4− (1-O2)。此外，進一步將化合物 1 直接與 O2 或 S8 反應可於高解析質譜儀發現 [Sb4Cr6E2(CO)28]2− (E = S , O) 之生成。因此，由化合物 1 行氧化反應之產物 3 及小分子活化反應的產物與 1-O2 歸因於1 之 SOMO 軌域的 Sb4 貢獻，並顯示其易氧化及高親核性等特性。從 X-ray 電子能譜 (XPS) 與 X-ray吸收近邊緣結構光譜 (XANES) 得知此系列化合物 Sb 的價數較趨近於 0 價，且過渡金屬之價數皆為帶負價的表現。其中化合物 1 之 Cr 金屬原子與化合物 1-Fe 之 Fe 金屬原子會有混合價態的表現 (mixed-valent)。透過 Evans method、SQUID 以及electron paramagnetic resonance (EPR) 分析，顯示此系列化合物 1、1-Mn、2 和 1-Fe 為順磁性化合物 (S = 1)，且透過 Spin density 理論計算分析，可發現化合物 1、2 與 1-Mn 之磁性中心會位於橋接之 Cr 及 Mn 原子上，而化合物 1-Fe 則於蓋接的 Fe 金屬原子上。此系列化合物 1、2、1-Mn、1-Mn2、1-Fe 與 3 具豐富之氧化還原特性且通過固態反射式光譜得知具有低能隙特性並具低且可調之能隙 (Energy gap) 1.26－1.63 eV，此現象可歸因於結構中的金屬金屬鍵以及其固態結構下之數種分子間弱作用力。
單核 Sb−Cr−Fe−CO 系統
當含氫配子之四面體化合物 [HSb{Cr(CO)5}3]2‒ (1-H) 與 HBF4 進行反應，可形成不飽和平面三角形化合物 [Sb{Cr(CO)5}3]‒ (1)，且反應中會伴隨著氫氣產生。且化合物 1 具有良好的親電特性，可與陰離子或中性的親核試劑進行反應形成四面體結構化合物 [(Nu)Sb{Cr(CO)5}3]n– (1-Nu, n = 2, Nu = H, F, Cl, Br, I, OH; n = 1, Nu = PEt3, PPh3, DMF, and MeCN)，進一步透過 Gutmann–Beckett Method 對化合物 1 進行酸度定量，並發現其具有與 BPh3 相近的路易士酸特性。另一方面，當化合物 1 與 1 當量的[HFe(CO)4]– 反應，可得到含氫配子之四面體鉻鐵的化合物 [HSbCr2Fe(CO)14]2‒ (2-H)。將化合物 2-H進一步與 HBF4·H2O 或 [CPh3][BF4] 進行去氫配子 (hydride abstraction) 反應時，可先於高解析質譜觀察到不飽和之平面三角形之中間產物 [Sb{Cr(CO)5}2{Fe(CO)4}]‒ (2) 的生成，且其進一步行氧化偶合反應可得 Sb2 之產物 [Sb2Cr4Fe2(CO)28]2‒ (3-Cr) 和 [HSb2Cr3Fe(CO)23]‒ (3-H)。有趣的是，化合物 3-Cr 可透過加入 NaBH4 或HBF4·H2O可轉換為化合物 2-H 和 3-H，顯示出 3-Cr 具有雙重路易士酸鹼特性。另外，化合物 1 具有令人驚訝超低能隙 1.00 eV－1.13 eV，顯示具有良好的低能隙特性，並可由引入之陽離子 (Et4N+、PPh4+ 與 TMBA+) 進行調控，顯現了獨特的陽離子效應。再透過 XPS 和 XANES 分析，發現此系列的 Sb 的價數較趨近於 0 價，其結果不同於計算所顯示的 +1 價，此現象可歸因為在固態環境下電子能透過結構骨架有效的流通。
Polynuclear Sbn−Cr−M−CO System (M = Mn, Fe, Co) Two novel paramagnetic hybrid Zintl–chromium carbonyl clusters, the tetrahedral Sb4 cluster [Sb4Cr6(CO)28]4− (1) (S = 1) and the cage-like Sb12 cluster [Sb12Cr6(CO)28]4− (2) (S = 1), were synthesized by one-pot reactions of Sb2O3 and Cr(CO)6 in a molar ratio of 1: 4 and 1: 2 in concentrated KOH/MeOH solutions under refluxing conditions, respectively. X-ray analysis showed that complex 1 contained a tetrahedral Sb4 core in which each Sb was coordinated by a Cr(CO)5 moiety, with two opposite Sb–Sb edges each further bridged by a Cr(CO)4 fragment. The structure of 2 can be viewed as a dodecanuclear Sb12 core in which four outward 2-coordinate Sb atoms each were further coordinated by one bridging Cr(CO)4 and one terminal Cr(CO)5 moiety, forming two di-Cr(CO)5-coordinated norbornane-like Sb6Cr geometry which was connected together via the central eight 3-coordinated Sb atoms. DFT calculations revealed that the central tetrahedral Sb4 in 1 remained intact, as evidenced by localized occupied orbitals, Wiberg bond indices, and critical point analyses, in comparison with those of the free Sb4 structure. The differential pulse voltammetry (DPV) study showed that 1 underwent two unresolved successive oxidation at 0 V, suggesting that 1 could be oxidized by two electrons, which was mainly attributed to the Sb4 fragments on the SOMO or the bridging Cr(CO)4 moieties on SOMO–1. When 1 reacted with Mn(CO)5Br in a molar ratio of 1: 1 under refluxing condition, the transmetallated paramagnetic tetrahedral product [Sb4Cr5Mn(CO)28]3− (1-Mn) (S = 1) was obtained, where one bridging Cr(CO)4 moiety of 1 was replaced by a Mn(CO)4 fragment. In addition, if 1 was treated with Mn2(CO)10 in a molar ratio of 1: 1 instead of Mn(CO)5Br, complex 1-Mn and the diamagnetic di-Mn substituted product [Sb4Cr4Mn2(CO)28]2− (1-Mn2) were produced. Besides, the reactions of 1 with Fe(CO)5 or Co2(CO)8 in a molar ratio of 1: 24 or 1: 2 were carried out, the paramagnetic di-Cr(CO)5, di-Fe(CO)4 coordinated, Sb4Fe4-containing cubic cluster [Sb4Cr2Fe6(CO)30]4− (1-Fe) (S = 1), and [Sb4Cr4Co4(CO)31]2− (1-Co), were obtained, respectively. The formations of the transmetallated products 1-Mn, 1-Mn2, 1-Fe, and 1-Co, could be rationalized by the fact that the reactive sites occurred in the bridging Cr(CO)4 fragments of SOMO−1 of 1. On the contrary, if the oxidation reaction of 1 with 2 equivalents of [Cu(MeCN)4]+ was carried out, the diamagnetic triangular prismatic cluster [Sb4Cr6(CO)28]2− (3) was formed. Complex 3 could be reduced back to 1 upon the treatment with Na2Fe(CO)4 or reducing agent CoCp2, showing the structural change from the Sb4 bent chain of 3 to the tetrahedral geometry of 1 and the special “on-off” magnetic switches. Surprisingly, 1 was found to have high-affinity toward O2 to form the di-O-bridged complex [Sb4Cr6O2(CO)28]4− (1-O2), which was evidenced by HR-Mass and single-crystal X-ray analysis. Further study for the small molecule activation of 1 with O2 or S8 powder were examined, which led to the formation of the proposed di-S- or O-insertion products [Sb4Cr6E2(CO)28]2− (E = S, O), respectively. It was noted that the formation of the oxidized product 3 and O2-activated complex 1-O2 mainly occurred in the Sb4 moiety of the SOMO in 1, indicative of the high nucleophicility of the Sb4 tetrahedron of 1. The X-ray photoelectron spectra (XPS) and X-ray absorption near-edge structures (XANES) showed that the physical oxidation state of the Sb atoms in 1−3 was closed to 0, while those of Cr, Mn, Fe, or Co atoms in these complexes were all found to be negative. Based on the Evans method, SQUID analysis, and electron paramagnetic resonance (EPR) measurements, the electron-precise complexes 1, 2, 1-Mn, and 1-Fe exhibited unexpected paramagnetic properties, in which the magnetic centers of these complexes were mainly localized on the bridging Cr or Mn atoms in 1, 2, and 1-Mn, or capping Fe atoms in 1-Fe, supported by the spin density results. These polynuclear Sb-containing metal carbonyl complexes 1, 2, 1-Mn, 1-Mn2, 1-Fe, and 3 exhibited rich redox properties with semiconducting behaviors in solids, possessing low but tunable energy gaps (1.26−1.63 eV) due to efficient electron transports via metal-metal bonds and several weak interactions in the solid state. Mononuclear Sb−Cr−Fe−CO System The unsaturated trigonal planar complex [Sb{Cr(CO)5}3]– (1) was synthesized via the dehydridation of [HSb{Cr(CO)5}3]2– (1-H) with HBF4·H2O, with the release of high yields of H2. Complex 1 showed pronounced electrophilicity toward anionic and neutral nucleophiles, even with solvent molecules, to produce tetrahedral complexes [(Nu)Sb{Cr(CO)5}3]n– (1-Nu, n = 2, Nu = H, F, Cl, Br, I, OH; n = 1, Nu = PEt3, PPh3, DMF, and MeCN). On the contrary, the Cr/Fe hydride complex [HSb{Cr(CO)5}2{Fe(CO)4}]2– (2-H) was obtained by treating 1 with [HFe(CO)4]–. Upon hydride abstraction of 2-H with HBF4·H2O or [CPh3][BF4], a unsaturated Cr/Fe trigonal planar complex [Sb{Cr(CO)5}2{Fe(CO)4}]– (2) was produced, in which oxidation coupling Sb2-containing complexes [Sb2Cr4Fe2(CO)28]2– (3-Cr) and [HSb2Cr3Fe2(CO)23]– (3-H) were yielded as final products. Complex 3-Cr exhibited dual Lewis acid/base properties via hydridation and protonation reactions, to form 2-H or 3-H, respectively. Complex 1 exhibited surprising semiconducting behavior with ultra-low energy gaps of 1.00 to 1.13 eV, depending on the counterion, demonstrating the unique cationic effect. XANES and XPS of [Et4N][1] in the solid state showed that the oxidation state of the Sb atom was close to 0, in contrast to +1 of the Sb atom in the discrete anion 1, attributed to efficient electron communication within the framework. The structures and electronic and optical properties of these resulting clusters were comprehensively studied and supported by the density functional theory (DFT) calculation.
Polynuclear Sbn−Cr−M−CO System (M = Mn, Fe, Co) Two novel paramagnetic hybrid Zintl–chromium carbonyl clusters, the tetrahedral Sb4 cluster [Sb4Cr6(CO)28]4− (1) (S = 1) and the cage-like Sb12 cluster [Sb12Cr6(CO)28]4− (2) (S = 1), were synthesized by one-pot reactions of Sb2O3 and Cr(CO)6 in a molar ratio of 1: 4 and 1: 2 in concentrated KOH/MeOH solutions under refluxing conditions, respectively. X-ray analysis showed that complex 1 contained a tetrahedral Sb4 core in which each Sb was coordinated by a Cr(CO)5 moiety, with two opposite Sb–Sb edges each further bridged by a Cr(CO)4 fragment. The structure of 2 can be viewed as a dodecanuclear Sb12 core in which four outward 2-coordinate Sb atoms each were further coordinated by one bridging Cr(CO)4 and one terminal Cr(CO)5 moiety, forming two di-Cr(CO)5-coordinated norbornane-like Sb6Cr geometry which was connected together via the central eight 3-coordinated Sb atoms. DFT calculations revealed that the central tetrahedral Sb4 in 1 remained intact, as evidenced by localized occupied orbitals, Wiberg bond indices, and critical point analyses, in comparison with those of the free Sb4 structure. The differential pulse voltammetry (DPV) study showed that 1 underwent two unresolved successive oxidation at 0 V, suggesting that 1 could be oxidized by two electrons, which was mainly attributed to the Sb4 fragments on the SOMO or the bridging Cr(CO)4 moieties on SOMO–1. When 1 reacted with Mn(CO)5Br in a molar ratio of 1: 1 under refluxing condition, the transmetallated paramagnetic tetrahedral product [Sb4Cr5Mn(CO)28]3− (1-Mn) (S = 1) was obtained, where one bridging Cr(CO)4 moiety of 1 was replaced by a Mn(CO)4 fragment. In addition, if 1 was treated with Mn2(CO)10 in a molar ratio of 1: 1 instead of Mn(CO)5Br, complex 1-Mn and the diamagnetic di-Mn substituted product [Sb4Cr4Mn2(CO)28]2− (1-Mn2) were produced. Besides, the reactions of 1 with Fe(CO)5 or Co2(CO)8 in a molar ratio of 1: 24 or 1: 2 were carried out, the paramagnetic di-Cr(CO)5, di-Fe(CO)4 coordinated, Sb4Fe4-containing cubic cluster [Sb4Cr2Fe6(CO)30]4− (1-Fe) (S = 1), and [Sb4Cr4Co4(CO)31]2− (1-Co), were obtained, respectively. The formations of the transmetallated products 1-Mn, 1-Mn2, 1-Fe, and 1-Co, could be rationalized by the fact that the reactive sites occurred in the bridging Cr(CO)4 fragments of SOMO−1 of 1. On the contrary, if the oxidation reaction of 1 with 2 equivalents of [Cu(MeCN)4]+ was carried out, the diamagnetic triangular prismatic cluster [Sb4Cr6(CO)28]2− (3) was formed. Complex 3 could be reduced back to 1 upon the treatment with Na2Fe(CO)4 or reducing agent CoCp2, showing the structural change from the Sb4 bent chain of 3 to the tetrahedral geometry of 1 and the special “on-off” magnetic switches. Surprisingly, 1 was found to have high-affinity toward O2 to form the di-O-bridged complex [Sb4Cr6O2(CO)28]4− (1-O2), which was evidenced by HR-Mass and single-crystal X-ray analysis. Further study for the small molecule activation of 1 with O2 or S8 powder were examined, which led to the formation of the proposed di-S- or O-insertion products [Sb4Cr6E2(CO)28]2− (E = S, O), respectively. It was noted that the formation of the oxidized product 3 and O2-activated complex 1-O2 mainly occurred in the Sb4 moiety of the SOMO in 1, indicative of the high nucleophicility of the Sb4 tetrahedron of 1. The X-ray photoelectron spectra (XPS) and X-ray absorption near-edge structures (XANES) showed that the physical oxidation state of the Sb atoms in 1−3 was closed to 0, while those of Cr, Mn, Fe, or Co atoms in these complexes were all found to be negative. Based on the Evans method, SQUID analysis, and electron paramagnetic resonance (EPR) measurements, the electron-precise complexes 1, 2, 1-Mn, and 1-Fe exhibited unexpected paramagnetic properties, in which the magnetic centers of these complexes were mainly localized on the bridging Cr or Mn atoms in 1, 2, and 1-Mn, or capping Fe atoms in 1-Fe, supported by the spin density results. These polynuclear Sb-containing metal carbonyl complexes 1, 2, 1-Mn, 1-Mn2, 1-Fe, and 3 exhibited rich redox properties with semiconducting behaviors in solids, possessing low but tunable energy gaps (1.26−1.63 eV) due to efficient electron transports via metal-metal bonds and several weak interactions in the solid state. Mononuclear Sb−Cr−Fe−CO System The unsaturated trigonal planar complex [Sb{Cr(CO)5}3]– (1) was synthesized via the dehydridation of [HSb{Cr(CO)5}3]2– (1-H) with HBF4·H2O, with the release of high yields of H2. Complex 1 showed pronounced electrophilicity toward anionic and neutral nucleophiles, even with solvent molecules, to produce tetrahedral complexes [(Nu)Sb{Cr(CO)5}3]n– (1-Nu, n = 2, Nu = H, F, Cl, Br, I, OH; n = 1, Nu = PEt3, PPh3, DMF, and MeCN). On the contrary, the Cr/Fe hydride complex [HSb{Cr(CO)5}2{Fe(CO)4}]2– (2-H) was obtained by treating 1 with [HFe(CO)4]–. Upon hydride abstraction of 2-H with HBF4·H2O or [CPh3][BF4], a unsaturated Cr/Fe trigonal planar complex [Sb{Cr(CO)5}2{Fe(CO)4}]– (2) was produced, in which oxidation coupling Sb2-containing complexes [Sb2Cr4Fe2(CO)28]2– (3-Cr) and [HSb2Cr3Fe2(CO)23]– (3-H) were yielded as final products. Complex 3-Cr exhibited dual Lewis acid/base properties via hydridation and protonation reactions, to form 2-H or 3-H, respectively. Complex 1 exhibited surprising semiconducting behavior with ultra-low energy gaps of 1.00 to 1.13 eV, depending on the counterion, demonstrating the unique cationic effect. XANES and XPS of [Et4N][1] in the solid state showed that the oxidation state of the Sb atom was close to 0, in contrast to +1 of the Sb atom in the discrete anion 1, attributed to efficient electron communication within the framework. The structures and electronic and optical properties of these resulting clusters were comprehensively studied and supported by the density functional theory (DFT) calculation.
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