Coordination Aspects in Modern Inorganic Chemistry A.D

Home , Coordination complex

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 techniques 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; however, ~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 various 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 contain, 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 Hal 18 19 20 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 CH2 CH3 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 . . (30) member boron-nitrogen systems [14]. RC CR OMe C C W(CO) N (CO)5M C RC 4 R R RC CR B B Me Et Et H Fe Fe H X R R' NN N B B N 42 43 44 MA n Fe Et B N Et NB M = Cr, Mo, W R = Alk, Ar, NR2; R' R NB X = Hal N N Et Et B B R Cr(CO) Di- and Polimetallic Complexes [5, 14] R N 3 28 29 30 Werner´s structures are also known among complexes of this type, for instance complexes 45 and 46 [6, 14]. R = Alk, Ar . Cene complexes 31 (especially ferrocene 31, M=Fe) and [(H3N)2Pt(SCN)2Ag]NO3 [CoEn3]2[PtCl6]3 12H2O dibenzene metal sandwich structures 32 (especially 45 46 dibenzenechromium 32, M=Cr) are well-known [5, 14]. Di- and polinuclear complexes having multiple bonds are R examined in detail, for example 47 [24]. R R E R R E L Me O O C Cu M O O R O R M M R M R A L O OMe M M L A OO E R Cr Cr O O 4 C RRCu R R E O L O R R 31 32 33 34 47 48 49 R = Alk, Ar R = H, Alk, Ar E = N, S, P E = N, P R = Alk, Ar L = NR , H O, azoles, azines M = Fe, Co, Ni, Cr 3 2 4 The Open Inorganic Chemistry Journal, 2009, Volume 3 Garnovskii et al.

In relation with the problem of synthesis of molecular Clathrochelates magnetics, carboxylate complexes 48 and 49 (shape of “Chi- Metal dioximates 58, intensively studied by Chugaev, nese lantern” [5, 7, 8, 10, 14]) are attractive for researchers. are classic metalloligands; using them as precursors, mostly Complexes with intramolecular bridges 50-53 [14] are well- trinuclear complexes 59, known as a clathrochelates are ob- known, in particular binuclear complexes with NCS fligands 50 [7, 10, 14]. tained [25, 26]. 1 R M n-1 H O O O O L NCS Hal L O Hal M M M M 1 N R 1 N R Hal L Hal L R N R N NCS O 1 Solv M + 2M An M R 50 51 R N NR1 R N NR1 M = Co, Ni, Zn, Hg, Pt, Pd O O O O H L = ER3 (E = N, P, As); 1 M n-1 ER2 (O, S, Se, Te) 58 59 Synthesis of Coordination Compounds [14, 27-46] Direct Interaction of Precursors [14, 27-29] X Solv Y N M M Reactions of Ligating Compounds and Metal Salts X N Y Solv As a result of interaction of these reagents, mostly in non-aqueous organic solvents (alcohols, hydrocarbons and 52 X, Y = NR, O, S their halide derivatives, etc.), all types of above indicated R = Alk, Ar, Ts metal complexes are formed. Solv = 0 (absent) or R'OH (R' = Me, Et) Molecular Complexes . mL + nMAp Lm (MAp)n R N N N Azole complexes 60 are being intensively studied [22]. N X Y R' R Cu R Cu E E Y X R' R' N N N + MHalp R' N R N N 53 R R MHal p X = O, S; Y = NR, O, S; R, R' = Alk, Ar ' 60 R = H, Alk, Ar; R = Alk, Ar, NH2 Metalloligand Complexes [14] Chelates [14-16, 33-36] Long ago (beginning of 1960th [14]), a possibility of metal complexes to take part as ligands (metalloligands) is As an example, we selected azomehine chelates, having, known, forming di- and oligonuclear structures in expenses depending on donor atom (X), trans- (61) or cis- (62) struc- of electron-donor coordinatively unsaturated fragments, for tures [14, 15]. example 54-57. R X N CH MA n MA n R M O N CH O O CH N X M M XH R CH N 61 O CH N N CH 2 + MA2 R X = NR', O MAn CH N Z X 54 55 R X R = H, Alk, Ar, Het; M ' O MAn R = Alk, Ar, Ts CH N N CH C R R 62 (CO) Co Co(CO) L CO 3 3 X = S, Se M ' L MAn C CMB [14, 29] The oldest complexes of this type are -complexes of O MAn 56 57 ethylene series with dichlorides of platinum metals, for in- ' stance 63. M = Cr, Mo, W; M = Hg; L = CO, PPh3 MAn = BF3, AlCl3 Coordination Aspects in Modern Inorganic Chemistry The Open Inorganic Chemistry Journal, 2009, Volume 3 5

R2C Template Synthesis [5, 14, 15, 30-34] Cl CR 2 R2C CR2 + PdCl2 Pd 2 R2C This type of synthesis is based on the formation of ligand Cl CR2 on a metal matrix, e.g. Schiff bases from aldehydes 67 and 63 primary amines. This route is used for obtaining acyclic 68 and cyclic 69 complexes of azomethines [13(Vol. 2), 14, 33, The syntheses 64 [29] are classic for obtaining sandwich 36]. compounds 31, 32. XH X M/n 1 R 2 R + R NH2 + MAn O CH N THF CH R1 + - 2 + MCl2 + 2Et2NH M + 2[Et2NH2] Cl 67 68 2 1 2 HH X = NR , O, S; R = H, Hal, NO2; R = H, Alk, Ar; R = Alk, Ts; A = OAc, Hal, NO3

64 M = Co, Ni, Fe R R N We note that, as a result of a direct interaction 65 of pre- N N + H N-Z-NH + MA cursors, unpredictable structures were formed, for example 2 2 2 z M z 2 R R tetranuclear complex 66 [37]. N N N OO Zn(OAc) , KOH N OH 2 R R [Zn3KL3OMe] MeOH 66 N HN Ph R = H, Me; Z = (CH2)n, 69 A similar technique is applied for synthesis of coordination compounds of crown-ethers 70 [38], tetrapyrrole deriva- O2N tives of porphyrins 71 and phthalocyanines 72 [13, 39]. 65 O A A O OO O + + ROM M+ A- O O OH HO O O O X = Hal, Ts 70 Me H Me

Me Me Me Me N N O + CuA2 H Cu H N CH2NH2 O H N N Me Ph Me

Molecular structure of the complex 66 Me H Me 71 R R R R N CN R solv N N 4 + MA n t N M N R CN R N N

R = H N

R R R

72 Crystal structure of the complex 66 6 The Open Inorganic Chemistry Journal, 2009, Volume 3 Garnovskii et al.

Rare structures are sometimes formed in the conditions Ph Ph of template syntheses, for instance 73 [40].

C4H9 + W(CO)6 + CO O2N NH Ph E Ph Ph E Ph NHC4H9 H2N N CH E = N, P, As NHTs + Pd(CH3COO)2 W(CO)5 N 77 CHO Ts Pd O2N Ts N Chelates N NO2 The method of ligand exchange is used for obtaining N chelates starting from low-soluble salts, for instance palla- C H dium chloride 78 or from NH-ligands (acetylacetonate 4 9 method) 79 [14]. 73 HX Pd/2 X N N C6H6 + PdCl2(PhCN)2 +2PhCN Y Y X = NTs, O; Y = O, NH 78 Ph Ph

C6H5NO2 N + Co(acac)3 N N N + 3Hacac H N N

Co/3

79 -Complexes

Structure of the chelate 73 Complexes of classic heterocycles, such as pyrrol 80 or pyridine 81, were obtained by exchange of the carbonyl It was established the interaction of o-tosylamino- ligand [22]. benzaldehyde with aniline derivatives on a palladium matrix leads to formation the complex 73 with two different form of ligroin Mn(CO)3 2+ Mn2(CO)10 2 the same ligand. The structure 73 was proved by X-ray dif- o N t + 4CO + H fraction: one ligand is azomethinic, another one exists in H N 2 benzimidazole form. 80 3. Ligand Exchange [14] Molecular Complexes Me Me This method is known as far back as from Werner´s ex- THF Cr(CO) periments, for instance for obtaining 74 [6]. + Cr(CO)6 3 Me NMe Me N Me [Ni(H2O)6]Cl2 + 6NH3 [Ni(NH3)6]Cl2 + 6H2O 74 81 Especially widely this technique is applied to synthesize 4. Metal Exchange metal carbonyl complexes having distinct compositions 75 and 76 [29]. Chelates n = 1 This technique is applied for obtaining chelates of chal- M(CO)5L cogen-azomethines 82 and 83 from low-stable Schiff bases h M(CO)6-n(THF)n + nL 75 or 2-phenylazoles [14, 41]. n = 2

M(CO)4L2 M = Cr, Mo, W 2 XNa X 76 + M(OAc) 2 M/2 L = amines, azoles, azines; N N Ar Ar In this respect, use of this route for syntheses of triphen- 2 ylpyridine 77 (E = N), phosph- 77 (E = P) and arseno - 77 X = S, Se 82 (E =As) benzene compounds seems attractive [14, 22]. Coordination Aspects in Modern Inorganic Chemistry The Open Inorganic Chemistry Journal, 2009, Volume 3 7

Electrosynthesis (ES) [13(Vol. 1); 14, 42] XLi X M/2 R R N N This technique of the direct synthesis, which is being R 2 + MCl2 R + 2LiCl developed from 1970, is an important synthetic method in O O modern coordination chemistry [43-45]. It is based on an 2 X = S, Se, Te; M = Zn, Cd, Hg 83 anodic dissolution of elemental metals (platinum plate is usually used as a cathode). Reactions are carried out in non- 5. Direct Syntheses [14, 42] aqueous polar solvents (alcohols, acetonitrile, DMSO, DMF, etc.), generally at 20-50oC, using tertiary ammonium salts as Gas-Phase Synthesis (Cryosynthesis) conducting additives. Industrial equipment exists, modified This technique is a part of the method of a direct interac- with ultrasound and/or UV-irradiation for activation of elec- tion of precursors and it is based on the use of elemental trosynthetic processes. The advantages [44, 45] of the ES are (zero-valent) metals as complex-formers. obtaining only anionless complexes, friendly synthetic conditions and a possibility, in some cases, of isolation of inter- Molecular Complexes mediate products. Such syntheses are carried out in vacuum equipment on Chelates surfaces cooled with liquid nitrogen or helium. This method is widely applied for obtaining metal carbonyls 84. Some examples of electrosyntheses, leading to chelates 88-90, are represented below [14, 42-45]. A template elec- t 0 trosynthesis route was offered [46], in which, under soft M + nCO M(CO)n conditions, intermediate products 88 and 89 can be isolated, 84 together with the final compound 90. M = Co, Mn, Cr, Fe, Ni, Pd, Pt, Rh, Cu, Ag, Ir, Eu, Nd Ts H2 Chelates N N M At present, only a few examples are known for obtaining N N H chelate structures 85 in gas-phase synthesis conditions [42]. 2 Ts More frequently such structures are formed in the conditions 88 Ts H2 of tribo(mechano)synthesis [42]. O N O N ES H H M + + Mo O O N 20 oC, 0 NH2 89 + 0.5 M MeCN, Ts O L O O Et4NClO4 m M N H N M/2 N NTs N N 85 90 Ar Ar Ts = -SO C H Me-p; L = H O, MeCN; M= Ni, Cu, Zn -Complexes 2 6 4 2 Gas-phase synthesis is widely applied in syntheses of The ES had played an important role in obtaining coordination compounds with N,O,S- and N,O,Se-ligand environ- -complexes of heterocycles, for example pyridine 86 and phosphabenzene 87 sandwiches. Using classic chemical ment. Here, the reaction of electrochemical cleavage of S-S routes, such compounds cannot be obtained [14, 42]. and Se-Se bonds was used, discovered by Tuck [42, 44]. In particular, on the basis of formally tetradentate ligand, the Me complexes 91 and 92 (X = S, Se) were electrochemically synthesized. N

77 K O Lm o Me M 2 + M M Me X MeN Me N

N OH 91 ES,MeCN 86 Me N X + Mo + mL Me4NClO4 t-Bu O Sn/ 2 2 Bu-t P Bu-t N X

77 K X = S, Se; L = Py, dipy, 1.10-phen o t-Bu + Ho Ho Bu-t 2 t-BuP Bu-t 92 t-Bu P Among other electrochemically obtained chelates, classic -diketonates 93 (X, Y = O) and salicylaliminates 94 and 95 87 Bu-t were reported [14, 42]. 8 The Open Inorganic Chemistry Journal, 2009, Volume 3 Garnovskii et al.

R R R O O O ES R' H + Mo R' M R' Solv O O O R R R 93 X L n = 2-4; M = Cu; Cd, Zn; Al, In; Ti, Zr, Hf; m M V, Nb, Ta; Cr, Mo; Mn; Co, Ni, Fe; Ce, Dy, mL U, Th. Solv = MeCN, ROH, THF, Py, diglym N Y A

XH 94 ES o L = Py, dipy, 1.10-phen N YH + M MeOH, MeCN

L'm Y N mL X M M B N Y X

L'm

95 L' = MeOH, MeCN

Other synthetic techniques (microwave, biphasic, tribo- imino (, b, c, ), amidino (f) and heteroarylamidine (d) chemical, ultrasonic, hydrothermal, and sol-gel) for obtain- ligands, major part of which is inavailable in a classic ing coordination compounds also exist and described in [13], organic synthesis, in the internal coordination sphere of the but they have still a limited application in coordination Pt(IV) ion. chemistry. Thus, MW-heating has been usually applied for The most interesting work, on the point of view of the obtaining inorganic materials; ultrasonic treatment has been data above on reactions between various metals and Schiff used more widely in synthesis of metal complexes (examples bases, is the study of reactivity of various hydrazoneoximes of obtained compounds: carbonyls, diene or Gringard com- with propionitrile, coordinated to Pt(IV) 97 (Scheme 2) [58]. plexes). An example of hydrothermal synthesis is obtaining [Cu(2-IC7H4N2)]n from CuI and benzimidazole. Sol-gel This work shows a real possibility of programmed syn- processes starting from metal alkoxides can lead to dimeric thesis of a platinum-containing ligand (salicylalhydrazone species such as, for example (RO)3TiOSi(OR)3. Biphasic reactions takes place in immiscible phases (solvents) and are R widely used in catalysis [13]. Pt N H O R Reactivity of Coordination Compounds [13, 47-50] N Pt N H N Reactivity of metal complexes is an important area of R' R'' coordination chemistry [47-50], including reactions on coor- R' R' dinatively-unsaturated donor centers 52, 59 [14, 17, 25, 26] R2C=NOH R2C=NH or metals complex-formers 54-57 [14, 41, 42], as well as c b reactions of self-assembling, leading to various su- R R' R Pt N N NH2 ROH Pt N pramolecular structures [19-21]. Reactions of coordinated [PtCl4(RCN)2] NH H OR' inorganic and organic ligands are of the high interest. In par- H d 96 a N ticular, in 1998-2007 reactivity of such ligands as nitriles O H (RCN) and oximes, coordinated to the ion Pt(IV) is inten- R' R' NOH NH2CH2CH2OH sively studied [50-62]. The main attention in these studies is e f given to the reactions of nucleophylic addition of various R R nucleophiles on the carbon atom of triple CN-bond of the Pt N Pt N NH nitrile fragment, whose electrophylic activation was reached H O H because of its coordination to Pt(IV) 96. According to N HO Scheme 1, both mono- (route , b, c, d) and bifunctional (ambidentate) (route e, f) nucleophylic molecules can be HO R' used as reagents. Reactions take place in soft conditions and Scheme 1. Reactions of nucleophylic addition of various substrates with high grade of selectivity, allowing generate new – to the coordinated nitriles. Coordination Aspects in Modern Inorganic Chemistry The Open Inorganic Chemistry Journal, 2009, Volume 3 9

NH2 NH2 Me, N Me NNH2 Me, Ph N Ph H II HON Me, Ph IV H Ph3P=CHCO2Me N N Pt trans-[PtCl4(EtCN)2] Pt CH2Cl2 O CH2Cl2 O

Et Et 97 98

Me, Ph II O H M2+ = Cu, Co, Ni, Pd ArCHO, Ar = C6H3-2-OH-5-NO2 Pt N H CH2Cl2, MeOH N N CH2Cl2, MeOH Et O N NO2

Me, Ph II O H M/ Pt N 2 N N Et O N NO2

100 Scheme 2. Synthesis of Pt-containing metalloligand and its complexes. derivative) as a result of a series of subsequent transforma- copper complexes of bis-thiosalicylidenethylenediamine and tions. The first step represents a selective nucleophylic addi- its analogues of the type 101. Later on ([67] and refs. tion of the ambidentate base (oximehydrazone 97) on the therein) it became possible to obtain models of pyrazole- oxime group accompanying by conservation of free periph- thioazomethine complexes, showing EPR- and electronic

B ' ' ' R R R R R'' CH N N N X X N Cu N N Cu/2 N N N N X '' CH CH N '' R Z R R '' Cu R' SR 101 102 103

X = S, Se; Z = (CH ) , n = 1-6; R = Alk, Ar; R', R'' = Alk 2 n eral amino group of the hydrazine fragment. In the second absorption spectral parameters of blue copper proteins 102. stage, a reduction of the product 97 takes place resulting All these parameters, as well as redox-potential, were ob- obtaining a soluble isostructural compounds of Pt(II) 98, served on the model of tris(pyrazolyl) borate copper com- which further enters in Schiff condensation reaction with plexes 103 [68]. 5-nitrosalicylaldehyde, leading to the salicylalhydrazone Active centers of blue copper protein derivative 99, which is capable to form metal complexes (Scheme 2, structure 100). All described compounds are Complexes 104 105 are well-known [13(Vol. 8)] characterized by elemental analysis data, FAB+-mass spec- 1 13 195 L tra, IR, , {H}, Pt NMR spectroscopies. X-Ray dif- X X O O fraction data are available for the 97-99. M Mn+ O CH N Complexes of Bioligands (Biomimethics [5, 13(Vol. 8); N CH O 63-69]) O Z A whole volume of modern coordination chemistry [13(Vol. 8)] is devoted to the complexes of bioligands. 104 105 Among them, we note copper-chalcogene chelates [63, 64, Carriers and activator sionophors

66, 67], modeling active centers of blue copper proteins 101- for small molecules (L = O2, N2) (crown-ether complexes) 103. In early studies [63,64], there were cross-linked (Z) 10 The Open Inorganic Chemistry Journal, 2009, Volume 3 Garnovskii et al.

Other models are presented by formulae 104-106. It is used in various aspects of coordination chemistry [73]. known that 106 (M = Mg) is chlorophill providing respira- Competitive coordination has been studied on many ambi- tion function of plants, 106 (M = Fe). Vanadium coordina- dentate anions, among which pseudo-halide anions 115-124 tion compounds are well-known in bioinorganic chemistry should be noted [14, 74, 77]. When X = O, both centers are [5, 13, 69], whose most important function is nitrogen fixa- hard; in case of X = S, Se, a hard-soft ligand system is tion (vanadium nitrogenase, FeV-protein). A lot of informa- formed, whose coordination is proved using HSAB principle tion on the coordination chemistry of biologically important [14, 72-76]. carbohydrates is discussed in reviews [69-71]. M N C X M XNC MNM'X C R 2 R R3 115 116 117 1 M R R 4 M M XN NX XNC M C N N C M M M R R M 118 119 120 N N 8 ' M R M NXC M' R 5 M N C X M' M R 7 R R6 121 122 106 M' M = Mg, Fe, Co, Ni, Cu M M' M N C X M' NXC ' Competitive Coordination [14, 72-76] M' M M 123 124 Capacity of di- and polidentate ligands to react with X = O, S, Se metal ion through distinct donor centers was named as competitive coordination [72]. Such ligands are ambidentate [74, For azine complexes 125-130, an N-atom is hard, mean- 75]. while the heteroaromatic -system is soft [5, 14]. R' R Acyclic Cyclic R' R' R' N A Z B M A n B M' R' R' R' R' R' R M M M' R R' RRN RRN Z = (CH2)n, Ar, Het; n = 5, 6. m R, R' = H, Me N R' This is a extended variant of bonding ligand isomery, MXn discovered by Jorgensen as far back as in 1894 on the exam- 125 R R' ple of a distinct binding of the NO2 anion [11]: 126

H t R R' [Co(ONO)(NH ) ]Cl [Co(NO )(NH ) ]Cl A Ta A 3 5 2 2 3 5 2 (CO) Cr 3 .. Me R' R' N ATa Nitrite, orange nitro, yellow N H Cr(CO)3 H RRN R Eight coordination modes 107-114 for NO2 anion were RRN examined [7]. We note that, according to X-ray diffraction 127 128 129 130 data, 107-110 are the most common modes. A = OSiBu3 R, R' = H, Me O In this case, independently on the hardness or softness of N a complex-former, the N-atom could form a coordination O N O M O bond, but soft acids prefer to be coordinated by a soft N M M N M O O -system of pyridine 126, 128. O O M 107 108 109 110 Nobel laureate E.O. Fisher made a first attempt to coor- M dinate heteroaromatic -system of pyridine. In 1964 he con- M sidered that obtained the complex of the type 128 on the ba- O N N sis of o-monomethylpyridine. However, later on (in 1967) M N M M O O 1 O M M O O M O O N two additional protons were detected in NMR spectra, so it had to inscribe the structure of ,-complex 127 to this 111 112 113 114 compound. Then (in 1976), D. Lagovskii obtained a pyridine Explanation of competitive coordination was given ac- analogue of dibenzenechromium 126 by cryosynthesis tech- cording to the classic HSAB principle ([72,73] and refs. nique; Biderman isolated the compound 128 creating addi- therein). Ideas about “hard” and “soft” acids and bases were tional spatial difficulties for the NB-atom [14]. Highly unex- introduced by R. Pearson in 1963 and at present are widely pectedly (in 1991), an equilibrium transformation 129-130 Coordination Aspects in Modern Inorganic Chemistry The Open Inorganic Chemistry Journal, 2009, Volume 3 11 was discovered, in which a carbene 129 and C,N 130 coordi- On the basis of 2-hydroxiazomethine ligands, a host of nated complexes take part [5, 78]. chelate salicylideniminates 138 was obtained [14, 15, 34-36, 84]. However, molecular complexes 139 are also known, -N-Complexes 131 are typical for azoles [14, 22, 79, where usually bidentate Schiff bases behave as monodentate 80]. Bis-azole complexes of the type 132 have not yet been discovered, but a pyrazolcyclopentadienyl ruthenium com- O-donor ligands [14, 34, 84-86]. plex 133 [14, 81] and imidazolecarbene compounds 134 [82] MXn 1 were isolated. R1 R O MXn O E D H H E D E D G A N N N G A m G A M R R N N E m G D 139

NA R1 R1 MXn O MXn O 131 132 A, D, E, G = CR, N; R = H, Alk, Ar H M/n N N -complex -complex R R Me 138

Me Me First data on these molecular complexes were reported in 1964, although a coordination mode was not determined 140. N N Unusual coordination on the oxygen atom in the o-hydroxy- Me Me naphthalideneaniline complex with ZnCl2 141 was proved by Ru X-ray diffraction [85] and keto-amine tautomeric form of the R Cl Zn ligand was established. Later on [86], an analogous structural O Cl situation was revealed for the complex of zinc dichloride N with salicylidenaniline. R N

133 134 O O C H Competitive coordination is clearly observed in chelating H 6 6 + MCl4 H MCl4 ligand complexes. This is well-known that -diketones form CCl4 N N chelate structures of the type 135 with same inner-chelate Ph bonds 136 [14]. At the same time, molecular chelates with Ph 2 completely conserved (non-deprotonated) ligand system are known, in which a diketone form 136 of the ligand is stabi- 140 lized as a result of metal coordination. Various coordination modes of -diketones and their analogues are discussed in monographs [14, 83] and reviews [75, 76]. One interesting O C6H6/MeOH example is a C-coordinated structure 137 [14]. 2 H + ZnCl2 N 2 2 MXn 2 R R R Ph chem. N O 2 H O O synth. O Ph 1 1 H R H R M/n 141 ZnCl2 R 1 O O Mo O R R gas-phase R Discovery of inner-chelate isomery in a series of chelates electrosynth. of azo compounds [87-89] was important for coordination 1 2 135 R, R , R = Alk, Ar, Het; n = 2-4 chemistry. It is accepted that two six-member metallocycles are present in such complexes. This is really observed for OH 2+ Me 2 Me o-amine- 142 and hydroxy- 143 azo compounds. However, it O O was established by X-ray diffraction that an existence of of Ni - two 5- 144 or 5- and 6- 145 member metallocycles is typical CH2 CH2 (ClO4) 2 O O for o-mercapthoazo compounds [14, 15, 88, 89]. A similar inner-chelate tautomery is also observed for other chelates, Me Me H2O for example in complexes of aromatic and heteroaromatic t-Bu t-Bu 136 formazanes [14, 15]. H O O EtOH/H2O Polyfunctional Materials H HgCl + 2 MeCOONa, refl., 15 min Cl Hg O A central problem in modern coordination chemistry is O t-Bu application of its results in life, in particular by creation of t-Bu new polyfunctional materials. This fact is directly emphasized in the second issue of [13], whose two volumes (8 and 137 12 The Open Inorganic Chemistry Journal, 2009, Volume 3 Garnovskii et al.

R 1

R N N 6 S N M/2 N N 55Zn N S N 1 X = NH R X = S 142 R = H R = CN R 1 144 XR

N N X = O X = S

R = H R = CN 1 R1 R S S 5 Pd 6 O N N N N N 6 Cu 6 N N N O

R1 R 1 1 R

145 143

9) are dedicated to biocoordination chemistry and applica- O O L L tions of coordination compounds, respectively. A consider- O O able role of metal complexes in creation of new materials is M' noted in a series of special issues, for instance [90-94]. Here O O M, M' = Cu, Fe, VO; L = H O, MeOH we will describe some important examples of use of coordi- M 2 Cu - VO J = + 118 cm-1 nation compounds. NN Cu - Cr J = + 115 cm-1 Among magnetoactive complexes, the most interest is Cu - Fe J = - 105 cm-1 caused by those coordination compounds which possess fer- 149 romagnetic exchange interactions, in particular metal cya- L nides 146. The metal complex of Prussian blue 147, known from 1704 was one of the first (1967) ferromagnetic [95]. On M(hfa)3 Hhfa = hexaftoroacetylacetone the basis of cyanides of various metals, a series of high- N temperature ferromagnetics 148 [95] were obtained, as well O O L = as photoactive magnetic materials (spin-crossover complexes Cu N [96]). NN Me . . Mm[Mn(CN)6] pH2O; –M–CN–M–; Fe4[Fe(CN)6]3 14H2O M = Gd, Y, La 146 147 150 -1 LnCuGd J = + 5.68 cm 2+ M3 [Mn(CN)6]2 M3[Cr(CN)6]2 (NO ) R 3 3 R M = V, Co, Mn, Cr, Ni, Cu; Tc = 9-20 O O 2+ 3+ 3+ 3- . M V 0.42 V 0.58[Cr (CN)6] 0.86 2.8H2O Tc = 315 K O O -1 148 Cu - Gd J = + 5 cm (R = Me) Cu J = + 5.5 cm-1 (R = Et) Famous magnetochemist O. Kahn prepared the com- N N pounds with predictable magnetic properties on the basis of N azomethine complexes [13(Vol. 2)]. Changing a series of 151 SMe metals, his group has obtained ferro- (positive exchange pa- R = Me, Et; M = Ce, Gd rameter) and antiferromagnetic complex compounds 149, 150. Similar complexes 151 are also ferromagnetic. Coordination Aspects in Modern Inorganic Chemistry The Open Inorganic Chemistry Journal, 2009, Volume 3 13

Metal carboxylate complexes [97], for instance 152 and A large series of interesting hydrazone antiferromagnetic 153, are mostly antiferromagnetic. Similar compounds with complexes of types 154 and 155 have been reported [100, higher number of metal atoms are known, among which 101]. Depending on structure of ligand systems, in particular high-spin complexes (up to 51/2) have been isolated [98, nature of X, it is possible to regulate quantitatively the mag- 99]. netic exchange parameters -J. py Varying ligands, the intermetallic bridge, ferro-, antif- Me O O Me erro-, and diamagnertic complexes have been synthesized M Me [102-105]. Thus, for structurally characterized binuclear Me O O O OO -aminovinylimine complex with chloride bridge 156, a L O ferromagnetic interaction is typical (increasing temperature, H O O L Mn O Mn L the effective magnetic moment increases) [102,105]. py py O O H O L M M Azomethine complex with sulfur bridge 157 is diamag- O O py H py netic, meanwhile the chelate with an oxygen bridge 158 pos- Me Me O O sesses a ferromagnetic moment [105].

Me A nitrogen bridge leads to compounds with ferromag- 152 153 netic exchange, for instance 159 [103-105]. Complex of type L = imidazole, benzimidazole, pyridine M = Mn, Fe, Co, Ni 160 with sulfur bridge is unexpectedly ferromagnetic [105].

+ R1 + R1

X - NNO - X HN NH X X Cu Cu NNO CH3 HN NH N N N CH3 Cu Cu X N 2 2 ROO X R

154 155 R1, R2 = Alk, ArAlk, OMe, COOMe, Cl, Br; X = Cl, Br.

μ (M.B.) R R eff N Cl N 2.85 R1 Cu Cu R' N Cl N 2.80 R R 156 2.75

2.70

2.65

2.60

2.55 0 50 100 150T,K 200 250 300 g = 2.19, J = 142 K (99 - 1), J’z =- 0.11 K (0.08 -1), Continuous line corresponds to theoretical calculations.

Structure of 156 14 The Open Inorganic Chemistry Journal, 2009, Volume 3 Garnovskii et al.

O N X Y N Y Cu Cu S Cu Cu S X Y N Y N O

158 157

Structure of 157: Y = S, diamagnetic; Y = O, antiferromagnetic

μeff (B.M.) 3,4

3,3

3,2

3,1

3,0 g=2.059 ±0.003 J=3.4±0.2 K

2,9 zJ'=0.36 ±0.01

2,8

2,7

2,6

2,5

2,4 0 50 100 150 200 250 300 T(K)

NO2 N N S N O X Y N Cu Cu Cu Cu O N Y N X S N

N 159 160 O N 2 X = O, Y = Ts X = NTs, Y = NMe

The same situation is observed for the complexes of type broad spectral range from visible (red, orange, blue, and vio- 161, 162 with antiferro- 161 or ferro- 162 magnetic interac- let) to IR-region [41, 91]. Thus, complex compounds with tions. In this case, it is quite probable (X-Ray data are re- blue fluorescence are discovered among mononuclear com- quired) existence of inner-chelate isomers with distinct (X or plexes [91]. In particular, mononuclear complexes of azome- Y) intermetallic bridges. thine ligands 165, 166 and the polyheteronuclear complex compound 171 absorb in red and yellow spectral ranges. Complex compounds of azomethine 163-166, azine 167- Luminescence of heteronuclear lanthanide complexes of type 168, and azole 169-170 series are important among other 172 was observed in IR region [91]. functional materials [41, 91, 92]. They are luminescent in a Coordination Aspects in Modern Inorganic Chemistry The Open Inorganic Chemistry Journal, 2009, Volume 3 15

μeff (B.M.)

2,5

N 2,0 N X Y N Cu Cu N

N 1,5 N X Y

1,0

0,5 161: X =NTs, O; Y = O.

0 50 100 150 200 250 300 T(K)

μeff (B.M.) 2,2 N

N Y N 2,0 X Cu

Cu X N Y N

1,8 N

162: X = NTs, O; Y = NH 0 50 100 150 200 250 300 T(K)

L R X X M Y X N M/2 Zn N R N N X R 163 164 165

R X X E Zn R N N N R ' N X MAn M/2

166 167 168

R E E R' R N N M/2 X MAn 169 170

X = NTs, O; E = CH, N, NR, O, S; R = H, Alk, Ar

16 The Open Inorganic Chemistry Journal, 2009, Volume 3 Garnovskii et al.

N N Zn Br O O Br

Yb O O Me Me Pd X X Pd HO OH Zn Me N N Me O O Yb

Br O O Br Zn N N

171 172

Among other applications of coordination compounds, Perspectives of Coordination Chemistry we would like to mention their use in creation of new metalocomplex additives to lubricants, providing the effect The main direction of metal-complex chemistry in XXI of wear less friction [106-108]. In particular, easily accessi- century is emphasized in the title of [13]: “from biology to ble complexes of o-azomethines and hydrazones with copper nanotechnology”. -Diketones and their analogues 173, dike- and molybdenum are effective as additive. tonate complexes 174 [109], azomethinic 175 and heterocyc-

H E E E A D A D A D X Y XY X Y H M/n 173a 173b 174 A, D, E = CR, N, P, O; X, Y = NR’, O, S, Se; R, R’ = H, Alk, Ar, Het A R B E H X N H X

175 176 A, B = CR’, N; E = NR’, O, S, Se, Te; X = NR’’, O, S; R, R’, R’’ = H, Alk, Ar, Het X O O (AcO)2Zn (AcO)2M MeOH N N MeOH N O H Zn/2 X X M/2 178 177 179

. M = Ni, Hg, Pd PdCl2 PhCN

N PdCl2 H O 2 180 X = O, S

Coordination Aspects in Modern Inorganic Chemistry The Open Inorganic Chemistry Journal, 2009, Volume 3 17

X H

CH N O O

O O MAc ' 2 181 O MA

X = NTs, O, S A = Cl, NCS X X H M/2 CH N CH N O O O O

182 O M' O O 183 O M = Co, Ni, Cu, Zn O M' = Li, Na, K O A

M'A MAc X 2 M/2

CH N O O

M' O O 184 O

lic 176 ligans remain “eternal”. Thus, the analysis of Cam- 1915 Rihard Vilshtetter, the area of pigments in plant bridge Bank Database shows that about 2500 structures of world, especially chlorophill. complexes of the ligands of types 175 and 176 were resolved 1930 Hans Fisher, investigation of construction of hemine for 2000-2008. and chlorophill. Creation of new hard-soft ligand systems is also attractive. One of them 177 was just synthesized [41, 110-112] 1963 Karl Ziegler Giulio Natta, discovery of isotactic and then a series of transformations was carried out allowing polypropilene. obtaining complexes with hard-hard 178, hard-soft 179 and 1964 Doroti Meri Kroufut Hodkin, determination of soft 180 coordination. structures of biologically active substances by X-Rays. Creation of hybrid biologically perspective ligating sys- 1973 Ernst Otto Fischer and Geoffrey Wilkinson, or- tems, for example 181 [113-117], is also interesting. A cycle ganometallic chemistry. of transformations 181-184 was carried out, including such ligand 181 and its mononuclear azomethinic 182 and crown- 1987 Donald James Cram, Jean-Marie Lehn and Charles ether 183 complexes, as well as binuclear structure 184 (con- J. Pedersen, elaboration and applications of molecules hav- firmed by X-Ray diffraction). The principal goal is to work ing structurally-specified interactions of high selectivity. not only for theoretical, but also for practically useful coor- 2001 William S. Knowles, Ryoji Noyori and K. Barry dination chemistry (competitive coordination), taking into Sharpless, research in pharmaceutical industry: creation of account an operated creation of polyfunctional materials (for chiral catalysts for redox-reactions. instance, selective electrodes). Other crown-containing azomethines are of a considerable interest as optically active 2005 Yves Chauvin, Robert H. Grubbs, Richard R. chemosensors [118-121]. Schrock, the development of the metathesis method in organic synthesis. Modern achievements in coordination chemistry are presented in the Proceedings of the 38th International Confer- ACKNOWLEDGEMENTS ence on Coordination Chemistry (ICCC38, Jerusalem, Israel, The authors are grateful to numerous researchers of the July 2008) [122]. Institute of Physical and Organic Chemistry (Southern Fed- Nobel Prizes on Coordination Chemistry [123, 124] eral University, Rostov-na-Donu, Russia) for their help, the Russian President grant -363.2008.3, and to Paicyt- 1912 Victor Grignard, Grignard's reagents. UANL (Monterrey, Mexico, project 2008) for the financial 1913 Alfred Werner, the area on the nature of bonds of at- support. oms in molecules in inorganic chemistry.

18 The Open Inorganic Chemistry Journal, 2009, Volume 3 Garnovskii et al.

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Received: July 25, 2008 Revised: October 04, 2008 Accepted: December 02, 2008

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