COMPLEX CONNECTIONS (synonym coordination connections) — complex chemicals as a part of which there are complex ions formed by the central atom to some extent of oxidation and the related ligands, i.e. simple and difficult ions or molecules. About big medical - biol, value K. the page demonstrates the fact that vital to the person and all live organisms d-elements (iron, cobalt, manganese, copper, molybdenum, zinc) are in them only in a look To. page, hl. obr. with complicated organic molecules — proteins, the nitrogen-containing bases, etc. S-elements (potassium, calcium, magnesium, sodium) in live organisms also partially are in structure To. page. Perspectives of use To. pages in medicine are very big. Only rather few from known To. villages are explored on biol, activity. It is revealed that a row K. the page of platinum shows antineoplastic activity. Some To. pages in medical practice are applied as pharmaceuticals (e.g., polyneuramin 12 represents To. page of cobalt). To. pages are widely used in the analysis of medicinal substances. Rather simple To. pages can serve as models of complex enzymes or other biologically active high-molecular compounds: are known To. the page of cobalt capable is reversible to connect oxygen, like hemoglobin.
For examination biochemical, the role of d-elements needs studying To. pages in the form of which these elements are present at live organisms. Natural To. the page of iron, copper, cobalt, manganese, zinc are received in a so-called individual state; it hemoglobin (see), various metalloproteins (see), etc. Features of participation of atoms of d-elements in biochemical, processes are explained by their ability to change in the To. page of oxidation level and coordination numbers. Atoms of these elements are included into active centers of many enzymes and biologically active compounds. The mechanism of effect of iron in hemoglobin and enzymes of a chain of oxidation — is most well studied in tsitokhroma (see). In these substances the iron connected with protoporphyrin forms macrocyclic To. village (gems). In hemoglobin iron is capable to raise the coordination number, i.e. number of the related atoms or groups of atoms, and at the expense of it reversibly to attach a molecule of oxygen. Iron serves as a carrier of electrons in tsitokhroma, consistently changing oxidation levels with +2 on +3 and vice versa.
Ligands (see. Complexons ) form the so-called internal sphere To. page. The charge of a complex ion is equal to the algebraic sum of oxidation level of the central atom and charges of ligands. In structure To. pages, in addition to complex ions, enter also opposite loaded ions not connected with the central atom direct chemical connection. These ions form the second sphere To. page. In formulas K. pages the central atom and ligands consist in square brackets, ions of the second sphere register out of these brackets (K3 [FeF 6 ]). The boundary space charge of a complex particle sometimes is equal to zero, then To. the page has no ions of the second sphere ([Co (NH 3 ) 3 (NO 2 ) 3 ]).
In names K. pages are listed ligands with the indication of their quantity, the central atom is called and extent of its oxidation is designated (in brackets, the Roman figure). If the complex particle is anion, to the name K. the page joins the termination «-at». Ions of the second sphere are separately specified. E.g., To. page K 2 [PtCl 4 ], [Pt (NH 3 ) 2 Cl 2 ] and [Pt (NH 3 ) 4 ] Cl 2 are called so: tetrachloroplatinate (II) of potassium, dichlorodiaminplatinum (II), tetraminplatina (II) chloride.
K K. the page belongs the majority of inorganic compounds. Quantity potentially possible To. the page is extremely big since number of combinations of various central atoms and ligands hugely. When the organic molecules corresponding To act as ligands. pages are intermediate between inorganic and organic matters.
In solutions K. pages dissociate as strong electrolytes on a complex ion and ions of the second sphere. To. the pages which do not have ions of the second sphere in solutions behave as nonelectrolytes. However complex ions in solutions K. pages, in turn, reversible and in steps dissociate, chipping off ligands:
[ZnCl 4 ] 2- <-> [ZnCl 3 ] - + Cl -
[ZnCl 3 ] - <-> [ZnCl 2 ] + Cl -
etc. Than less steadily To. the page in solution, the is more abundance of products of dissociation of complex ions.
To. pages form many isomeric forms (see. Isomerism ). Are especially specific for To. page two types of an isomerism: structural (ionization) — various distribution of anions between the internal and second sphere To. page, e.g. [Co (NH 3 ) 5 Br] SO 4 and [Co (NH 3 ) 5 SO 4 ] Br; geometrical (stereoisomerism) — various order of an arrangement of ligands around the central atom, e.g.
Ability of atoms of various chemical elements to form To. page i.e. to play a role of the central atoms, it is not identical. The most typical kompleksoobrazovatel are atoms and ions of d-elements. Practically all connections of d-ales-cops are To. pages or on the structure are close to them. So, crystalline hydrates of salts of d-elements are To. pages with water molecules as ligands, and anhydrous salts have crystal structures in which cations of d-elements are surrounded with anions as well as in complex ions. Good kompleksoobrazovatel are also f-elements (lanthanides and actinoids). Smaller quantity To. the page is known for p-elements. Carbon belongs to number of the few elements which are not forming To. page, but it is a part of a set of ligands. S-elements seldom form steady To. page. The greatest value have them To. page with complexons — so-called crown ethers (cyclic connections in which molecule oxygen atoms and groups — C alternate 2 H 4 —).
The various ions and molecules having not divided valent electronic couples can be ligands. Steady To. pages are formed with anions F - , Cl - , Br - , I - , CN - , NO 2 - , PO 4 3- , S 2 O 3 2- etc. From molecules especially good ligands are in what there are nitrogen atoms, oxygen, sulfur, phosphorus [NH 3 , N 2 O, NH 2 CH 3 , NH 2 CH 2 COOH, (NH 2 ) 2 CS, P (C 2 H 5 ) 3 etc.].
To. pages classify depending on a type of ligands and features of a structure: To. page with anion ligands — atsidokompleks —
K 3 [Co (NO 2 ) 6 ], K 4 [Fe(ON) 6 ], Na 2 [SiF 6 ];
To. page with water — akvakompleks, hydrates —
Fe [(H 2 O) 6 ] (NO 3 ) 3 , [Cr (H 2 O) 6 ] Cl 3 , [Be (H 2 O) 4 ] (NO 3 ) 2 ;
To. page with ammonia — ammonia solutions — [Co (NH 3 ) 6 ] Cl 3 , [Pd (NH 3 ) 4 ] SO 4 , [Ag (NH 3 ) 2 ] Cl;
To. page with organic amines — aminocomplexes —
[Pt (C 5 H 5 N) 4 ] Cl 2 , [Cd (CH 3 NH 2 ) 4 ] (NO 3 ) 2 ;
mixed To. the pages containing various ligands —
[Pt (NH 3 ) 2 Br 2 ], [Ru (NH 3 ) 5 NO] Cl 3 ;
multinuclear To. the pages supporting several coordination centers connected by Moscow teak ligands — [(NH 3 ) 5 Co — N=C — CO(CN) 5 ]; chelate To. page — the containing cyclically attached ligands:
For education chelate To. the page is necessary that the molecules joining the central atom as ligands contained two or several atoms capable to form donor-acceptor bonds with the central atom. Chelate To. villages have especially big stability. Ligands, being complicated cyclic molecules are very interesting. The central atom, forming To. the page, is located in such molecule. Formed To. page call macrocyclic. Such To. pages are natural compounds of iron, copper, cobalt and magnesium with derivatives of porphyrine.
Bibliography: Greenberg A. A. Introduction to chemistry of complex connections, L., 1971; Methods and achievements of bioinorganic chemistry, under the editorship of K. Mack Oliffa, the lane with English, M., 1978; Skorikn. And. and Koumac V. N. Himiya of coordination connections, M., 1975, bibliogr.; Yatsi-mirsky K. B. Introduction to bioinorganic chemistry, Kiev, 1976, bibliogr.
A. V. Babkov.