Mononuclear coordination compounds

Mononuclear ER4 and simple four-coordinate compounds of E(IV) states are the baseline for viewing the other coordination numbers, the effect of bulky ligands, bonds to other E or metals, E(II) compounds, multiple bonds and other phenomena discussed in later sections. Basic parameters for some simple compounds are presented in Table 1, taken from the gas-phase data summarized by Molloy and Zuckerman5 and Haaland6. These data show the unperturbed molecules in the gas phase and provide the base for... 

In contrast to the situation a decade ago, many incomplete cubane-type clusters with Mo304 S cores have been prepared and the structures have been determined by X-ray structure analyses. The results obtained are summarized in Tables I—III. The formal oxidation state of molybdenum in the compounds cited here is in all cases IV. Unlike Mo(VI) and Mo(V) compounds, mononuclear oxo or dioxo compounds of the Mo(IV) state are relatively rare and all the incomplete cubane-type compounds cited here have no terminal oxo ligand. Three Mo atoms form an equilateral triangle, and three single bonds exist between each Mo. Except for the compounds 1, 8, and 31 (Table III), and excluding Mo—Mo bonds, each molybdenum is octahedrally coordinated. 

Names for Mononuclear Coordination Compounds with Monodentate Ligands... 

Werner apparently did not realize that the polynuclear complexes which he investigated so extensively95 constituted a transition between the usual mononuclear coordination compounds and the infinite structure of the crystal lattice. It remained for Paul Pfeiffer, Paul Niggli (1888—1953) and others to point out that crystal structures were in beautiful agreement with his coordination theory, as revealed by the then new experimental technique of X-ray diffraction.96... 

A general method of stereochemical notation based on the ligand priority sequence rule of Cahn, Ingold, and Prelog (CIP),8,9 developed at Chemical Abstracts Service,0 1 has been in use in Chemical Abstracts Chemical Substance Indexes for mononuclear coordination compounds since 1972. 

Coordination compounds of vanadium(V) also catalyze peroxidative halogenation reactions where the reactive oxidant is a monoperoxo complex of a mononuclear vanadium compound (Figure 6) [11,22,92-95,99]. 

The phosphines with one P-donor atom reveal properties close to those of amines and form mononuclear coordination compounds 574 or binuclear structures 239 (Sec. 2.2.4.3) and 575 (3.14) ... 

The coordination chemistry of Cr can be subdivided into the realm of mononuclear coordination compounds, which can be derived (at least formally) from the blue [Cr(OH2)e] ion, and the chemistry of metal-metal bonded species (analogs of Cr2(OAc)4). Most of the former are octahedral high-spin complexes with distinct tetragonal distortions caused by the Jahn - Teller Effect. With strong-field ligands, low-spin octahedral complexes are formed, and there are also some four-coordinate complexes of various coordination geometries. The metal-metal bonded species are described in Section 5. 

Monomeric sulfur imide SNH is not known, but a coordination compound Fe2(CO)6(HNS) (72) has been isolated and converted to the corresponding anion [Fe2(CO)6(/r-SN)] with n-BuLi. The complex (72) is obtained from the reaction of Fe3(CO)i2 with MeySiNSNSiMes, followed by chromatography on silica. The HNS unit behaves as a six-electron ligand see Counting Electrons). Mononuclear complexes of the type (RNS)Cr(CO)5 (R = MeyN, PhyN), in which the ligand is bonded to the metal via sulfur, have also been structurally characterized. ... 

The reaction products of 2,2 -bipyrimidine (bpm), P-diketones, and lanthanide ions demonstrated the diverse nuclearity and dimensionality. As stated in the last section, dinuclear eight-coordinate [Ln2(P-diketonate)6(bpm)] could be formed [78, 79]. Zucchi et al. [26a] reacted Nd(N03)3 with bpm to afford the mononuclear nine-coordinate adduct [Nd(N03)3(bpm)(Me0H)2], while reactions of hydrated NdCb and various P-diketonates in the presence of bpm gave the binuclear nine-coordinate compounds [ Nd(L )3(THF) 2([JL-bpm)] (see Figure 2.46) and [ Nd(L )3(MeOH) 2([r-bpm)]-bpm (see Figure 2.47) and the one-dimensional coordination polymer [Nd(L )3(p,-bpm)-MeOH]oo (4-MeOH) (see Figures 2.48 and 2.49). Other groups have also reported the one-dimensional arrays [Ln(L )3(p.-bpm)]co (Ln = Eu [80], Gd, and Nd [75]. 

Three- and four-coordinated Cu(I) compounds are most common however, many one-and two-coordinated Cu(I) ones are also known -. When less than four donor atoms are bound to the copper(I) ion the mononuclear copper(I) enolates tend to oligomerize. To preserve the volatility of the precursors, the oligomerization must be prevented, for example, by using bulky and/or multidentate chelating ligands. In Table 4, Cu(I) enolate coordination compounds which can be used as precursors for CVD of copper are listed. 

There are many structural studies of copper coordination compounds with azide ligands, mainly of mononuclear and binuclear copper complexes but a few also of trinuclear copper complexes. A comprehensive... 

The designation of central atom and ligands, generally straightforward in mononuclear complexes, is more difficult in polynuclear compounds where there are several central atoms in the compound to be named, e.g. in polynuclear coordination compounds, and chain and ring compounds. In each case, a priority order or hierarchy has to be established. A hierarchy of functional groups is an established feature of substitutive nomenclature Table VI shows an element sequence used in compositional and additive nomenclature. 

In the stereochemical nomenclature of coordination compounds, the procedure for assigning priority numbers to the ligating atoms of a mononuclear coordination system is based upon the standard sequence rules developed for chiral carbon compounds (the Cahn, Ingold, Prelog or CIP rules6, see Section IR-9.3.3.2). 

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