每周分子 | Molecule of the Week

Original ACS 美国化学会 ACS美国化学会 2022-07-01

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每周分子：磷化锌

Molecule of the Week: Zinc phosphide

磷化锌(Zn₃P₂)是一种用途广泛的合成无机化合物。在20世纪初，人们通过加热理论配比的元素来制备磷化锌。更近一点的时间是在2013年，由加拿大国家纳米技术研究所(National Institute for Nanotechnology)和加拿大阿尔伯塔大学(均在埃德蒙顿)的Erik J. Luber、Md Hosnay Mobarok和Jillian M. Buriak在320°C用二甲基锌处理三正辛基膦 (TOP)制得了纯纳米晶体Zn₃P₂。

在室温条件下，磷化锌具有四方晶体结构(如图)；当加热到大约845°C 时，它会转化为立方体结构。这使得文献报道的Zn₃P2熔点差异巨大：一些文献报道它在1160°C 或更高的温度下熔化，而其他文献则给出了420°C的熔点。相变温度清晰地表明较高的熔点是正确的。

磷化锌最初的用途是作为杀鼠剂，用于消灭地鼠和鼹鼠等穴居有害动物以及各种老鼠等人类居住环境中的有害动物。它通常与动物摄取的诱饵联合使用。Zn₃P₂与水接触会缓慢水解；但是目标有害动物胃中的酸性环境会促使呼吸系统毒药——剧毒磷化氢气体的迅速释放。

磷化锌的新用途就令人愉快和兴奋得多。2009 年，美国加州理工学院(加利福尼亚州帕萨迪纳市)的Gregory M. Kimball及其同事们报道称，Zn₃P₂晶片的稳态光致发光光谱的间接带隙值为1.38 eV，接近理想的直接带隙值1.5 eV。这一结果表明，它可以作为一种光伏电池半导体。

上文提到的Luber等人的工作也涉及光伏发电。Luber等人用他们的合成方法合成了具有四方(α- Zn₃P₂)结构的胶体半导体≈8nm的纳米晶体。他们发现这种形式的光学带隙比块状Zn₃P₂的光学带隙大0.5 eV 。通过纳米颗粒沉积制备的薄膜可以用于具有良好整流行为的异质结设备。然而，其它数据表明颗粒具有富磷壳(由于元素磷 [P(0)] 的存在)，会影响薄膜的性能。

随后，Luber、Buriak 及其同事们开发出了一种制备纳米晶磷化锌的替代方法，该方法使用三(三甲基硅烷基)膦代替TOP作为磷源。这种变化大大降低了粒子表面P(0)的浓度：

磷化锌信息速览

CAS 登记号	1314-84-7
SciFinder命名	Zinc phosphide
分子式	Zn₃P₂
摩尔质量	285.12 g/mol
外观	灰色至黑色晶体或粉末
熔点	>1160 ºC
水溶性	遇水反应

氟虫腈危害信息

GHS*分类：遇水释放易燃气体的物质和混合物，类别1
H260-遇水释放可自燃的易燃气体
GHS分类：急性毒性，口服，类别1
H300-吞食致命
GHS分类：急性毒性，皮肤，类别4
H312-皮肤接触有害
GHS分类：短期(急性)水生危害，类别1
H400-极大水生生物毒性
GHS分类：长期(慢性)水生危害，类别 1
H410-对水生生物毒性极大并具有长期持续影响

【关于每周分子】

自2001年以来，“每周分子”已成为广受欢迎的栏目。多数分子由读者推荐。每个结构都经由科学家审查，并以3-D和平面图像的形式显示，同时附有该分子简介。可以通过美国化学文摘社 (CAS) 提供的SciFinder中的CAS REGISTRY获取“每周分子”的更多信息。CAS REGISTRY中的每条物质信息都展示了物质的CAS登记号、索引名、通用名、商品名、书目信息等其他更多信息。发送邮件至motw@acs.org推荐您感兴趣的分子吧。

Zinc phosphide (Zn₃P₂) is a synthetic inorganic compound that has widely divergent uses. It was originally prepared in the early 20th century by heating stoichiometric amounts of the elements. Much more recently (2013), Erik J. Luber, Md Hosnay Mobarok, and Jillian M. Buriak at Canada’s National Institute for Nanotechnology and the University of Alberta (both in Edmonton) prepared pure nanocrystalline Zn₃P₂ by treating tri-n-octylphosphine (TOP) with dimethylzinc at 320 °C.

Under ambient conditions, zinc phosphide has a tetragonal crystal structure (shown); it converts to cubic when heated to ≈845 °C. This brings up an unusual situation about Zn₃P₂’s melting point: Some references report that it melts at 1160 °C or higher, but others give 420 °C. The phase-change temperature clearly indicates that the higher melting point is correct.

The original use for zinc phosphide was as a rodenticide, for burrowing pests such as gophers and moles and for domestic pests such as rats and mice. It is usually combined with baits that the animals ingest. Zn₃P₂ hydrolyzes slowly in contact with water; but the acidity in the target pest’s stomach rapidly releases highly toxic phosphine gas, a respiratory poison. Phosphine was the Molecule of the Week for October 2018.

The newer use of zinc phosphide is more pleasant and exciting. In 2009, Gregory M. Kimball and co-workers at Caltech (Pasadena, CA) reported that steady-state photoluminescence spectra of Zn₃P₂ wafers have a fundamental indirect band gap of 1.38 eV, close to the ideal direct band gap value of 1.5 eV. This result indicates that it may be valuable as a semiconductor in photovoltaic cells.

The work of Luber et al., mentioned above, also involved photovoltaics. Their synthetic method produced colloidal semiconducting ≈8-nm nanocrystals with the tetragonal (α-Zn₃P₂) structure. They found that the optical band gap in this form is 0.5 eV greater than that of bulk Zn₃P₂. Films prepared via deposition of the nanoparticles were used in heterojunction devices that had excellent rectification behavior. Other data, however, indicated that the particles had phosphorus-rich shells (due to the presence of elemental phosphorus [P(0)]), which hindered performance.

Subsequently, Luber, Buriak, and colleagues developed an alternative method for preparing nanocrystalline zinc phosphide that uses tris(trimethylsilyl)phosphine instead of TOP as the phosphorus source. This change greatly decreased the concentration of P(0) on the particle surfaces.

Zinc Phosphidefast facts

CAS Reg. No.	1314-84-7
SciFinder nomenclature	Zinc phosphide
Empirical formula	Zn₃P₂
Molar mass	285.12 g/mol
Appearance	Gray to black crystals or powder
Melting point	>1160 ºC
Water solubility	Reacts

Zinc Phosphide hazard information

Substances and mixtures that, in contact with water, emit flammable gases, category 1
H260-In contact with water releases flammable gases that may ignite spontaneously
Acute toxicity, oral, category 1
H300-Fatal if swallowed
Acute toxicity, dermal, category 4
H312-Harmful in contact with skin
Short-term (acute) aquatic hazard, category 1
H400-Very toxic to aquatic life
Long-term (chronic) aquatic hazard, category 1
H410-Very toxic to aquatic life with long-lasting effects

About Molecule of the Week

MOTW has been a popular feature on ACS website since 2001. Many molecules are suggested by our website visitors. Every structure is reviewed by a scientist and displayed in 3-D and flat images with a brief description. Each week’s molecule also links to a sample record from the CAS REGISTRY, which is searched using SciFinder. Each record displays the registry number, index name and synonyms, bibliographic information, and more. Send us a molecule suggestion at motw@acs.org.

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