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Coordination Aspects in Modern Inorganic Chemistry A.D The Open Inorganic Chemistry Journal, 2009, 3, 1-20 1 Open Access Coordination Aspects in Modern Inorganic Chemistry A.D. Garnovskii*,1, E.V. Sennikova1 and B.I. Kharisov*,2 1Institute of Physical and Organic Chemistry, Southern Federal University, Rostov-on-Don, Russia 2CIIDIT-Universidad Autónoma de Nuevo León, Monterrey, Mexico Abstract: Main types of coordination compounds in modern inorganic chemistry are discussed. Principal synthesis tech- niques for metal complexes and the problem of competitive coordination of ambident hard-soft ligands are discussed. A considerable attention is paid to polyfunctional materials, obtained on the basis of coordination compounds, especially molecular magnetics, organic light-emitting devices, and chemosensors. Keywords: Coordination chemistry, competitive coordination, synthesis, biomimethics, metal complexes, functional materials. INTRODUCTION CLASSIFICATIONS OF COORDINATION COM- POUNDS Generally, coordination chemistry is given as a part of inorganic chemistry courses (for example [1-5]) or as a spe- Werner´s classification according to ligand nature cial course on chemistry of complex compounds [6-11]. A [6, 17]: multi-volume edition on general and coordination chemistry 1) Amino complexes MmAn(NH3)p, MmAn(NH2R)p, [12, 13], a series of monographs (for example [14]) and re- M A (NHR ) , M A (NR ) . view articles [15-17], dedicated to the progress of modern m n 2 p m n 3 p chemistry of metal complexes, have been recently published. R = Alk, Ar; m = 1, 2; n, p = 1 – 10; M = d-metals; A - - - 2- Results on this area have been published in more than 50 = Hal , NO2 , NO3 , SO4 . chemistry journals worldwide [10, 14]. Among them, four CoCl .pNH (p = 4-6), PtCl .pNH (p = 2-6), M A L , journals are completely devoted to this area: “Journal of 3 3 4 3 m n p L = H2NCH2CH2NH2 (En) – ethylenediamine, Coordination Chemistry”, “Coordination Chemistry Re- Py – pyridine, = 1-3. views”, “Polyhedron” and “Russian Journal of Coordination . Chemistry”. In three leading journals (“Inorganic Chemis- 2) Aqua complexes – MmAn(H2O)p, CoCl2 6H2O, . try”, “Inorganica Chimica Acta” and “Inorganic Chemistry NiCl2 6H2O, CuCl2 4H2O, CuSO4 5H2O. Communications”), major part of articles corresponds to the 3) Mixed-ligand complexes. field of coordination chemistry. Aminoaqua complexes PtCl4 (NH3)6 H2O, Co(NO2)2 Coordination chemistry was founded by Swiss scientist . (NH3)3 2H2O. A. Werner (1866-1919), who won Nobel Prize in 1913. Great contribution was further made by Russian chemist Ethylenediaminoaqua complexes CoCl3(En)3 3H2O. L.A. Chugaev (1873-1922). Coordination (complex) entities Aminoethylenediaminoaqua PtCl4 (NH3)4(En) 2H2O. consist of a cationic, anionic, or neutral complex, containing a central atom or ion and molecules or ions, coordinated with Classification of G. Beilar and D. Bush according to the it. Those substances, whose molecules contains a central type of ligand donor centers N, P, O, S [18]. This is the most atom, connected with ligands, can be considered as coordina- common classification, which is widely used in monographs tion or complex entities [6]. In all these compounds, the and systematization of a ligating compounds [14]. Not only cations are surrounded with anions, neutral molecules or classic donor centers are examined (, N, P, As; O, S, Se, radicals. The groups, surrounding directly the cation, are Te; B), but also their various combinations such as C, N; C, named ligands; the area of inorganic chemistry, studying O; C, S; N, P; N, As; N, ; N, S; N, Se; N, Te; O, S; O, Se; joint behavior of cations and their ligands, was named as O, Te; B, N; B, O; B, S [14]. coordination chemistry [10]. Other approaches to complex classifications are reported The discussions below include, in particular, bioinor- in the monograph of K. Day and D. Selbin [3], but their use ganic compounds, mostly copper and vanadium complexes is limited: [5, 13(Vol. 8)]. 1) According to coordination number (CN) 2÷10; how- ever, ~90% of known complexes have CN = 4, 5, 6. 2) According to oxidation number of a metal complex- *Address correspondence to these authors at the Institute of Physical and former. Organic Chemistry, Southern Federal University, Rostov-on-Don, Russia; E-mail: [email protected] 3) According to nature of a coordination bond: , , or CIIDIT-Universidad Autónoma de Nuevo León, Monterrey, Mexico; their combinations. E-mail: [email protected] 1874-0987/09 2009 Bentham Open 2 The Open Inorganic Chemistry Journal, 2009, Volume 3 Garnovskii et al. 4) According to electronic configuration of a complex- Mono- and dinuclear complexes with diatomic nitrogen, former. phosphorus, and arsenicum (E) molecules 7a-c, having vari- ous coordination modes, are well-known. Moreover, complexes can be classified according to number of metallic centers in the complexes and the dentac- :E E: MAn MAn :E E: MAn :E E: MAn ity of ligands [3]. MAn An optimal classification is that which examines a com- 7a 7b 7c plex molecule in whole: donor atoms, CN, bond nature and Among triatomic molecular ligands, we note carbon di- metal complex-former oxidation number. According to this oxide 8, according to the importance to resolve the problem classification, metal complexes can be divided in five types of binding CO evolving to the atmosphere. [17]: molecular complexes, metallocyclic complexes 2 (chelates), complexes with multi-central bonds, di- and O O C polimetallic complexes and supramolecular coordination O AnM C OCO MAn MAn complexes. This classification [14, 17] comprehends all O known types of metal complexes and concentrates attention 8a 8b 8c on peculiarities of types of molecules in complexes and not Dialkyl(aryl)sulfoxide complexes 9-11 have been also of their separate parts [3, 16, 18]. reported. In a book of Nobel laureate J.M. Lehn “Supramolecular R chemistry” [19], self-assembling of supramolecular com- R R SO MAn SO plexes is related with coordinative interactions. It is noted SO MAn R R R that “chemistry of receptors” (recognizing cations, anions or neutral molecules) represents “generalized coordination MAn MAn chemistry”. 9 10 11 Molecular complexes of azoles 12, azines 13 and their derivatives 14-17 are of high interest at present [5, 13, 14, 22]. R E E R R N N N N MAn MA MA 1 2 n n 12 13 14 We note that some supramolecular structures may con- tain, as central atoms, not only cations 1, but also anions, for E E instance halides 2 (details in [7-10, 19-21]). N NH2 1 2 N Molecular Complexes MmAnLp Lq [6, 14, 17] N N NH2 Werner´s complexes (the basis of coordination chemistry MAn MA in the end of XIX and beginning of XX century) belongs to MAn n this type of complexes [6, 17]. When p or q=0, the com- 15 16 17 plexes contain the same ligands (homoleptic complexes); if E = NR, O, S, Se, Te; R = H, Alk, Ar q0, they contain distinct ligands. Among these complexes, . 3+ - neutral (for instance [BF3 NH3]), cationic ([Al(H2O)6] Cl3) Metallocyclic Complexes (Chelates) [5, 14, 15] + 4- and anionic (K4 [Fe(CN)6] ) are known. The simplest ligand In these complexes, metal cycles with distinct number of is a hydride anion, which belongs to dielectronic -donors bonds were observed; among them, 5- or 6-member rings are [14] and forming a series of complexes, for example 3 and 4. the most stable, for example 18-22 [10, 15]. [HCo(CO)4] [HPtBr(PPh3)2] R (CH2)n R 3 4 N 5 N ' N RN R 5 MA M/m Carbon ligand is a part of clusters 5 or -complexes 6. n 6 N N CH =CH MAm R 2 2 R R 18 19 20 Hal M Hal R, R’ = H, AIK, Ar; R = H, AIK, Ar, Ts; [M5C(CO)5] CH2=CH2 m = 1-5; Ts = -SO2R’; 5 6 n = 1-6; R’ = Me, Ar m = 2,3 M = Ru, Os Hal = Cl, Br, I Coordination Aspects in Modern Inorganic Chemistry The Open Inorganic Chemistry Journal, 2009, Volume 3 3 R R Heteroaromatic sandwich compounds of types 33 and 34 X Y X X M are also well-known [5, 22], as well as three-decker com- ' 6 M R' 6 6 R 6 N N plexes of phosphorus- (35) and boron- (36, 37) containing X Y Y heterocycles [14]. R R 21 22 Me ' R, R = H, Alk, Ar; Y = (CH2)n; n = 1-6; Me Me X, Y = NR, O, S, Se X = NR, O, S; R = H, Alk, Ar, Ts Azine 23, 24 and azole 25 complexes with 5- and B R 6-member cycles have been isolated. Me Me Mo M M E P P B N B R N N 6 P P 5 6 B X M/n M/n M/n X P P X Mo M M 23 24 25 Me Me X = NR, O, S, Se; n = 2, 3; E = NR, O, S; R = H, Alk, Ar BR Formation of C,N-cyclometallated 5-member chelate Me Me structures 26, 27 was noted [14, 23]. Me 35 36 37 X 5 Numerous CMB are formed by instable organic species: N M N MOCOCH radicals 38-41, biradicals 42, carbenes 43 and carbines 44 5 5 3 R [14]. X N N CH2 . O . O O C N 26 27 N N X = CH, N R = Alk, Ar; M = Pd, Pt CH CH 2 3 R N N N N Complexes with Multi-Centered Bonds (CMB) [14] Fe(CO)3 MA MAn n O This type of complexes is formed by compounds with M/m delocalized bonds. Examples of less-common coordination 38 39 40 41 compounds are complexes of four- (28), five- (29) and six- H H .
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