Actinoid

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The actinide (/ˈæktɪnaɪd/) or actinoid (/ˈæktɪnɔɪd/) series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide.[1][2][3]

The 1985 IUPAC Red Book recommends that actinoid be used rather than actinide, since the suffix -ide normally indicates a negative ion. However, owing to widespread current use, actinide is still allowed. Since actinoid literally means actinium-like (cf. humanoid or android), it has been argued for semantic reasons that actinium cannot logically be an actinoid, but IUPAC acknowledges its inclusion based on common usage.[4]

The fifteen elements from actinium, Ac, to lawrencium, Lr, are called actinoids (Table \\(\\PageIndex{2}\\)). The general symbol of these elements is An. All the actinoid elements are radioactive and very poisonous. Actinoids that exist in nature in considerable amounts are thorium, Th, protactinium, Pa, and uranium, U, and thorium and uranium are actually isolated from ores and find application. Plutonium metal, Pu, is produced in large quantities in nuclear reactors and its economical efficiency as a fuel for conventional nuclear reactors and fast breeder reactors, as well as its safety, are being examined. As isolable amounts of the elements after americium, Am, are small and their radioactivity is very high, study of their chemical properties is very limited.

Although actinoids are similar to lanthanoids in that their electrons fill the 5f orbitals in order, their chemical properties are not uniform and each element has characteristic properties. Promotion of 5f - 6d electrons does not require a large amount of energy and examples of compounds with \\(\\pi\\)-acid ligands are known in which all the 5f, 6d, 7s, and 7p orbitals participate in bonding. Trivalent compounds are the most common, but other oxidation states are not uncommon. Especially thorium, protactinium, uranium, and neptunium tend to assume the +4 or higher oxidation state. Because their radioactivity level is low, thorium and uranium, which are found as minerals, can be handled legally in a normal laboratory. Compounds such as ThO2, ThCl4, UO2, UCl3, UCl4, UCl6, UF6, etc. find frequent use. Especially uranium hexafluoride, UF6, is sublimable and suitable for gas diffusion and undergoes a gas centrifuge process for the separation of 235U. Thorium is an oxophilic element similar to the lanthanoids.

Even 155 years after their first synthesis, Schiff bases continue to surprise inorganic chemists. Schiff-base ligands have played a major role in the development of modern coordination chemistry because of their relevance to a number of interdisciplinary research fields. The chemistry, properties and applications of transition metal and lanthanoid complexes with Schiff-base ligands are now quite mature. On the contrary, the coordination chemistry of Schiff bases with actinoid (5f-metal) ions is an emerging area, and impressive research discoveries have appeared in the last 10 years or so. The chemistry of actinoid ions continues to attract the intense interest of many inorganic groups around the world. Important scientific challenges are the understanding the basic chemistry associated with handling and recycling of nuclear materials; investigating the redox properties of these elements and the formation of complexes with unusual metal oxidation states; discovering materials for the recovery of trans-{UVIO2}2+ from the oceans; elucidating and manipulating actinoid-element multiple bonds; discovering methods to carry out multi-electron reactions; and improving the 5f-metal ions' potential for activation of small molecules. The study of 5f-metal complexes with Schiff-base ligands is a currently \"hot\" topic for a variety of reasons, including issues of synthetic inorganic chemistry, metalosupramolecular chemistry, homogeneous catalysis, separation strategies for nuclear fuel processing and nuclear waste management, bioinorganic and environmental chemistry, materials chemistry and theoretical chemistry. This almost-comprehensive review, covers aspects of synthetic chemistry, reactivity and the properties of dinuclear and oligonuclear actinoid complexes based on Schiff-base ligands. Our work focuses on the significant advances that have occurred since 2000, with special attention on recent developments. The review is divided into eight sections (chapters). After an introductory section describing the organization of the scientific information, Sections 2 and 3 deal with general information about Schiff bases and their coordination chemistry, and the chemistry of actinoids, respectively. Section 4 highlights the relevance of Schiff bases to actinoid chemistry. Sections 5-7 are the \"main menu\" of the scientific meal of this review. The discussion is arranged according the actinoid (only for Np, Th and U are Schiff-base complexes known). Sections 5 and 7 are further arranged into parts according to the oxidation states of Np and U, respectively, because the coordination chemistry of these metals is very much dependent on their oxidation state. In Section 8, some concluding comments are presented and a brief prognosis for the future is attempted.

While most have an oxidation state of +3, the lanthanoid series only has a maximum oxidation state of +4 in any of the elements, while several of the actinoids can have a higher oxidation state (although they are typically most stable at the lower oxidation states).

The two rows separated from the rest of the periodic table are called the inner-transitional metals. They include the lanthanoids and actinoids. Lanthanoids include elements 58-71 and actinoids include elements 90-103.

On September 7, 2017 in Vladivostok during the Eastern Economic Forum Alexey Likhachev, Director General of ROSATOM and Toshio Kodama, President of Japan Atomic Energy Agency (JAEA) signed Memorandum for Information Exchange on Reactor Physics Experiments for Minor Actinoid Transmutation for Radioactive Waste Processing and Management, for the purpose of exchanging data of reactor physics tests that each of us have conducted so far in order to contribute to the R&D on the transmutation of minor actinoid from the perspective of reduction in the amount and toxicity of radioactive waste.

In actinoids, 5forbitals are filled. These 5f orbitals have a poorer shieldingeffect than 4f orbitals (in lanthanoids). Thus, the effectivenuclear charge experienced by electrons in valence shells in case ofactinoids is much more that that experienced by lanthanoids. Hence,the size contraction in actinoids is greater as compared to that inlanthanoids.

As we have just said, there are two series of metals: according to what IUPAC recommends, the lanthanoids (the 14 elements that follow lanthanum in the periodic table) and the actinoids (the 14 elements following actinium). The lanthanoids and actinoids are collectively known as the inner transition metals, while scandium, yttrium, lanthanum and the lanthanoids are together called the rare earth metals. Although lanthanum and actinium are strictly group 3 metals, the chemical similarity of lanthanum to the elements from cerium to lutetium, and of actinium from thorium to lawrencium, means that lanthanum is commonly classified with the lanthanoids and actinium with the actinoids.

Actinoids are the heaviest chemical elements with practical relevance. Among them, only thorium and uranium can be found in nature in substantial quantities while natural plutonium has been detected in trace amounts. In uranium ores the radioactive decay of uranium produces transient amounts of actinium and protactinium, while in transmutation reactions isotopes of neptunium, americium, curium, berkelium, and californium can also be formed.1 actinoids heavier than californium are purely synthetic elements, which are made from neutron bombardment of lighter elements.

Along with thorium and uranium, the transuranium elements, neptunium, plutonium, americium, and curium, have important applications and are synthesized in appreciable quantities in nuclear reactors. The other actinoids are mostly used only for research, and the required quantities are produced either in nuclear reactors or in particle accelerators. Neptunium and curium are also significant in nuclear fuel cycles such that their chemical properties need to be understood.

Actinoids most frequently occur as solid oxides, which are the best characterized among actinoid compounds but with significant gaps in understanding of their properties. While solid actinoid oxides, particularly those of thorium, uranium, and plutonium, are relatively well characterized, considerably less information is available on the gas-phase properties of actinoid oxides. The main reasons for this knowledge gap are the large costs and special experimental setups required, such as for high evaporation temperature or laser ablation sources, and the extreme safety conditions necessary to handle radioactive materials, which is a particularly problematic consideration for the actinoids other than thorium and uranium. In addition, experiments are often complicated by the complex vapor compositions and several accessible oxidation states of the actinoids, as well as by a very high reactivity of atomic actinoids with oxygen and moisture.

Computational modeling is particularly useful for systems that are not easy to study experimentally, as is the case for most of the actinoids. Quantum chemistry can model molecular properties and transformations, and, in combination with experiment, it can lead to an improved understanding of species containing actinoids. The recent development of theories able to treat systems with a high density of electronic states arising from degeneracy, or near degeneracy, of orbitals, and also with relativistic effects, has led to a rapid increase in the application and advancement of theoretical studies of actinoids. As a result, a substantial amount of theoretical information is available for actinoid oxides, the most ubiquitous and important category of actinoid species. 59ce067264

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