Heteroleptic complex

Compounds of type [Cp2LnNH2]2 were obtained by simple metathesis reaction or by thermal decomposition (200-250 °C) of complexes Cp3Ln(NH3) according to Eq. (3) [4,62]. Both the ammonia (150-160 °C, for the smaller lanthanides) and the heteroleptic amide complexes (230 °C) can be sublimed under high vacuum. The Ce(IV) amide derivatives Cp3CeNH2 and Ind2Ce(NH2)2 were also discussed as metathesis products. 

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Heteroleptic complexes of uranium can be stabilized by the presence of the ancillary ligands however, the chemistry is dominated by methyl and benzyl ligands. Examples of these materials include UR4(dmpe) (R = alkyl, benzyl) and U(benzyl)4MgCl2. The former compounds coordinate "soft" chelating phosphine ligands, a rarity for the hard U(IV) atom. 

Homo- and heteroleptic complexes of Cd alone and of Cd and Hg with the ligand dicyanamide (dca) N(CN)2-, homologous to cyanamide NCN2-, have been studied in various solvents (formation constants of the complexes [M(dca) ](" 2> (M = Cd, Hg l < n < 4)), with the result that the complexes of Hg are more stable than those of Cd. Otherwise, obviously no studies on the isolated compounds M(dca)2 or on homoleptic complexes derived therefrom have been published. 

The use of homoleptic compounds, where all coordinating atoms are as chemically indistinguishable as possible. Indeed, with heteroleptic complexes it can easily be the case that the error in the parameterization of the effect of a type of ligand can be compensated and thus shadowed by another error in the parameterization of a different ligand, resulting in flawed parameters for both of them. 

Several excellent reviews are available covering different scientific purposes and technological applications of phthalocyanines [46-51]. Here, we focus on synthetic aspects of one particular type of Pc-derivative, namely bis(phthalocyaninato) complexes of trivalent lanthanides, as well as analogous heteroleptic complexes containing porphyrin and porphyrin-like ligands. 

Most of the conducting or magnetic materials investigated in the homoleptic series are salts while many of the radical heteroleptic complexes described above are in their neutral state, potentially allowing for a stronger three-dimensional character. 

The reaction between a slurry of PbCl2 in THF with a 1 1 mixture of [Li(dme)2][/Bu2C2P3] and [Li(CsMe5)] affords the heteroleptic complex 46 in 45% yield. Additionally, the analogous complex 47 is prepared in 25% yield by the reaction between [Li(tmen)2][/Bu2C2P2Sb] and (CsMes)PbCl. 

Buryak and Severin have described the use of dynamic libraries of Cu(II) and Ni(II) complexes as sensors for tripeptides [61]. A notable aspect of this work is that as isolation of the metal complexes is not necessary (sensing is accomplished by observing changes in the UV-vis spectrum), potential concerns over the lability of coordination complexes do not apply. Specifically, three common dyes [Arsenazo I (41), Methyl Calcein Blue (42), and Glycine Cresol Red (43), Fig. 1.18] were mixed with varying ratios and total concentrations of Cu(II) and Ni(II) salts in a 4X5 array. Previous work had demonstrated that these conditions produced equilibrating mixtures of 1 1 and 2 1 homo- and heteroleptic complexes [62], These arrays were able to clearly and unambiguously differentiate tripeptides based on the differential pattern of response. The Severin laboratory has... 

Scheme 12.13 (a) Proposed surface species 48 via route 6, R = Me or (AlMe ) (b) of hybrid materials resulting from different proposed surface species of hybrid materials consecutive graftings of homoleptic complex 51a and 51b after immobilization of the Nd(AlMei)3 and EtjAICl onto MCM-48280 heteroleptic complex Cp Nd(AlMe4)2 on... 

Comparisons between the electronic structures (using a ZINDO analysis) of [Ru(bpy)3] " and [Ru(bpy)(NH3)4], and between related pairs of compounds where bpy is replaced by 2,2 -bipyrazine or 1,2-benzoquinonediimine, show that bpy is unable to accept extra electron density from the metal center whereas the opposite is true for 1,2-benzoquinonediimine. The acceptor properties of the 2,2 -bipyrazine ligand fall between those of bpy and 1,2-benzoquinonediimine. Using the Fenske-Hall method, the electronic structures of [Ru(bpy)3 (ppy) ] "A (Hppy = 2-phenylpyridine) have been investigated. The coordinated ppy is a C,A-donor. The electronic structures of the heteroleptic complexes exhibit a separation of the Ru—C and Ru—N f7-bonding character. It is proposed that the observed preference for cis- over trans- and for fac- over nrer-isomers may arise from the enhanced cr-donating ability of the C atom when it is trans to an N rather than C-donor. ... 

For heteroleptic complexes not included in Table 1, redox potentials can be estimated by Kgand additivity principles... 

Lever has successfully predicted Mn"/ potentials of 24 Mn-carbonyl complexes containing halide, pseudohalide, isonitrile, and phosphine co-ligands, with additivity parameters derived from the potentials of Ru "/" couples [39]. An important consideration for heteroleptic complexes is the influence of isomerism on redox thermodynamics. For Mn(CO) (CNR)6- complexes, with n = 2 or 3, the Mn"/ potentials for cis/trans and fac/mer pairs differ by as much as 0.2 V [40]. The effect arises from the different a-donor and 7r-acceptor abilities of carbonyl (CO) and isocyanide and their influence on the energy of the highest energy occupied molecular orbital (HOMO). 

The best results with this type of cobalt mediators were obtained using heteroleptic complexes such as Z907 and N621 bearing long alkyl chains (Fig. 17.18). 

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