摘要:
J. CHEM. SOC. DALTON TRANS. 1989 Supplement s1 Tables of Bond Lengths determined by X-Ray and Neutron Diffraction. Part 2.t Organometallic Compounds and Co-ordination Complexes of the d- and f-Block Metals A. Guy Orpen * and Lee Brammer Department o f Inorganic Chemistry, The University, Bristol BS8 7 TS Frank H. Allen, Olga Kennard, and David G. Watson Cambridge Crystallographic Data Centre, University Chemical Laboratory, 1 ensfield Road, Cambridge CB2 7EW Robin Taylor I. C.I. Plant Protection Division, Jealott's Hill Research Station, Braeknell, Berkshire RG 72 6EY Average lengths for metal-ligand bonds are reported, together with some intraligand distances, for complexes of the d- and f-block metals. Mean values are presented for 325 different bond types involving metal atoms bonded to H, B, C, N, 0, F, Si, P, S, CI, As, Se, Br, Te, or I atoms of the ligands.The determination of molecular geometry is of vital importance to our understanding of chemical structure and bonding. The majority of experimental data have come from X-ray and neutron diffraction, microwave spectroscopy, and electron diffraction. Over the years compilations of results from these techniques have appeared sporadically. The first major compil- ation was Chemical Society Special Publication no. 11: 'Tables of Interatomic Distances and Configuration in Molecules and Ions.' This volume summarized results obtained by diffraction and spectroscopic methods prior to 1956; a supplementary volume' extended this coverage to 1959. Summary tables of bond lengths between carbon and other elements were also published in volume 3 of 'International Tables for X-Ray Crystallography.' Some years later the Cambridge Crystallo- graphic Data Centre produced an atlas-style compendium of all organic, organometallic, and metal complex crystal structures published in the period 196k1965.' More recently a survey of geometries determined by spectroscopic methods has extended coverage in this area to mid-1977.A notable compendium of structural data, without geometric information, was given in 'Comprehensive Organometallic Chemistry,' ' covering all complexes with metal-carbon bonds. The BIDICS series,' which finished in 1981, provided for some years a full coverage of metal complexes giving both bibliographic and geometric information. There have also been valuable annual summaries, without geometric information, on the structures of organometallic compounds determined by diffraction method^.^ The production of further comprehensive compendia of X- ray and neutron diffraction results has been precluded by the steep rise in the number of published crystal structures, as illustrated by Figure 1.Printed compilations have been effectively susperseded by computerized databases. In particular the Cambridge Structural Database (CSD) now contains bibliographic, chemical, and numerical results for some 70 000 organocarbon crystal structures. This machine-readable file fulfils the function of a comprehensive structure-by-structure compendium of molecular geometries. However the amount of data now held in CSD is so large that there is also a need for concise, printed tabulations of average molecular dimensions. The only tables of average geometry in general use are those f Part 1 is ref.10. 7000 6000 vI 5000 '5 4000; 3000 E a# C 2000 z' 1000 1965 1970 197 5 19'80 1985 Year Figure 1. Growth of the Cambridge Structural Database as number of entries increases annually. The structures containing d- or fblock metals are indicated by shading contained in the Chemical Society Special Publications 1 . 2 of 1958 and 1965, which list mean bond lengths for a variety of atom pairs and functional groups. Since these early tables were based on data obtained before 1960, we have used CSD to prepare a new table of average bond lengths in organic compounds" and in metal complexes.The table given here (Table 3) specifically lists average lengths for metal-ligand distances, together with intraligand distances, involving bonds between the d- and f-block metals (Sc-Zn, Y-Cd, La-Hg, Ce-Lu, and Th-U) and atoms H, B, C, N, 0, F, Si, P, S, C1, As, Se, Br, Te, and I of ligands. Mean values are presented for 325 different bond types involving such metal-ligand bonds. Methodology Selection of Crystallographic Data-All results given in Table 3 are based on X-ray and neutron diffraction results retrieved from the September 1985 version of CSD. Neutron diffraction data only were used to derive mean bond lengths involving hydrogen atoms. This version of CSD contained results for 49 854 single-crystal diffraction studies of organo- carbon compounds; 9 802 of these satisfied the acceptance criteria listed below and were used in the averaging procedures.s2 J .CHEM. SOC. DALTON TRANS. 1989 (i) The structure contains a d- or f-block metal; (ii) atomic co-ordinates for the structure have been published and are available in CSD; (iii) the structure was determined from diffractometer data; (it.) the structure does not contain unresolved numeric data errors from the original publication (such errors are usually typographical and are normally resolved by consultation with the authors); (v) only structures of higher precision were included on the basis that either ( a ) the crystallographic R factor was dO.07 and the reported mean estimated standard deviation (e.s.d.) of the C-C bond lengths was < 0.030 A (corresponds to AS flag = 1,2, or 3 in CSD4), or (h) the crystallographic R factor d0.05 and the mean e.s.d.for C-C bonds was not available in the database (AS = 0 in CSD); (ci) where the structure of a given compound has been determined more than once within the limits of (i)-(u), then only the most precise determination was used. The structures used in Table 3 do not include compounds whose structure precludes them from CSD (i.e. not containing 'organic' carbon). In practice structures including at least one C-H bond are taken to contain 'organic' carbon. Thus the entry for Cr-CO distances has a contribution from [NEt4][Cr(p- H)(CO),,] but not from K[Cr(p-H)(CO),,] or [Cr(CO),]. Program System.-All calculations were performed on a University of Bristol VAX 11/750 computer.Programs BIBSER, CONNSER, RETRIEVE,4 and GEOSTAT,"?' as locally modified, were used. A stand-alone program was written to implement the selection criteria, whilst a new program (STATS) was used for statistical calculations described below. It was also necessary to modify CONNSER to improve the precision with which it locates chemical substructures. In particular the program was altered to permit the location of atoms with specified co-ordination numbers. This was essential in the case of carbon so that atoms with co-ordination numbers two, three, and four (equivalent to formal hybridization states sp ', sp 2 , and sp ') could be distinguished easily and reliably. Considerable care was taken to ensure that the correct molecular fragment was located by GEOSTAT in the gener- ation of geometrical tabulations. Searches were conducted for all metals together, and statistics for individual metal elements and subdivision of the entry for a given metal carried out sub- sequently.An important modification of GEOSTAT allowed for calculation of metal atom co-ordination number with due allowance for multi-hapto ligands and p ligands. Thus q5-C5H5, q6-C6H6, and other q5 and q6 ligands were assigned to occupy three co-ordination sites, q3 and q4 ligands such as allyls and dienes to occupy two co-ordination sites, and q2 ligands such as alkenes to one site, and so on. The approach taken in dealing with (p) bridging ligands was that when a metal-metal bond is bridged by one atom of a ligand [e.g. as in C1, CO, OMe, etc. as in (A) and (B)] then only the non-metal atom is counted as occupying a co-ordination site.For the relatively rare case of bridging polyhapto ligands (in which the bridging atoms are linked by direct bonds) the assignment follows logically, thus p-q2,q2-alkyne (see C) occupies one site on each metal. Bridging ligands which do not have one atom bonded to both metals [ e g . acetate in (D)] contribute to metal co-ordination numbers as do terminal ligands. In examples (A)-(D) below the metal atoms therefore have co-ordination numbers as follows: (A), Rh 4; (B), Fe 6; (C), Co 4; (Dj, Rh 6. For cases where co-ordination number is very difficult to assign, notably where a metal atom is bonded to more than one other metal atom as in metal cluster complexes, no assignment was attempted.The non-location of hydrogen atoms presents major diffi- culties both in the determination of co-ordination numbers for metal atoms, and for correct identification of ligands (e.g. to distinguish methoxide from methanol). Care was therefore taken to exclude cases where any ambiguity existed [e.g. no data (C> Me taken for M-OCH, and M-O(H)CH, distances when both are present in a structure in which hydrogen atom positions were not reported]. Classtjication qf' Bonds.-The classification of metal-ligand bonds in Table 3 is based on the ligating contact atom. Thus all metal-boron distances appear in sections 2.1--2.3 of Table 3, all metal-carbon distances in sections 3.1-3.22, and so on. Where intraligand interatomic distances (e.g. P-C distances in tertiary phosphines) are given in Table 3, they are averaged over all metals and precede the individual metal-ligand interatomic distances for that ligand. Table 3 is designed to: (i) appear logical, useful, and reasonably self-explanatory to chemists, crystallographers, and others who may use it; (ii) permit a meaningful average value to be cited for each bond length.With reference to (iij, it was considered that a sample of bond lengths could be averaged meaningfully if: ( a ) the sample was unimodally distributed; (b) the sample standard deviation (0) was reasonably small, ideally less than cu. 0.04 A; (c) there were no conspicuous outlying observations (those which occurred at >40 from the mean were automatically eliminated from the sample by STATS, other outliers were inspected carefully); ( d ) there was no compelling chemical reason for further subdivision of the sample.It should be noted that Table 3 is not intended to be complete in covering all possible ligands. Its purpose is to provide information on the interatomic distances for ligands of the greatest chemical importance, notably for those which are simple and/or common. Statistics.-Where there are less than four independent observations of a given bond length, then each individual observation is given explicitly in Table 3. In all other cases the following statistics were generated by the program STATS. (i) The unweighted sample mean, d, where equation (1) holds n d = di/n i = 1 and di is the ith observation of the bond length in a total sample of n observations. Recent work l 3 - l 5 has shown that the unweighted mean is an acceptable (even preferable) alternative to the weighted mean, where the ith observation is assigned a weight equal to l/var(di).This is especially true where structures have been pre-screened on the basis of precision. (ii) The sample median, m. This has the property that half of the observations in the sample exceed m, and half fall short of it. (iii) The sample standard deviation, 0, where equation (2) holds. CT = [ (di - d)2/(n - 1) 1' (2) i = 1J. CHEM. SOC. DALTON TRANS. 1989 - s3 - 2 0 0 1 5 0 100 5 0 2.06 2.22 2.38 2.54 2.70 2.86 150 c 100 5 0 r 2 . 0 6 2.18 2.16 2.20 2 . 4 2 2.54 2.66 2.28 2.32 Cu-CI/A Figure 2. Effects of outlier removal and subdivision based on co- ordination number and oxidation state for the Cu-Cl bond.(a) All data; (6) all data without outliers [>40 (sample) from mean]; (c) all data for which Cu is four co-ordinate, Cu". Relevant statistics (see text) are: d m 0 41 4" n (u) 2.282 2.255 0.105 2.233 2.296 366 (6) 2.276 2.254 0.092 2.232 2.292 362 (c) 2.248 2.246 0.032 2.233 2.263 153 (iu) The lower quartile for the sample, ql. This has the property that 257; of the observations are less than q1 and 75% exceed it. ( u ) The upper quartile for the sample, qu. This has the property that 257;) of the observations exceed qu and 75% fall short of it. (vi) The number, n, of observations in the sample. The statistics given in Table 3 correspond to distributions for which the automatic 40 cut-off (see above) had been applied and any manual removal of additional outliers (an infrequent operation) had been performed.In practice a very small percentage of observations was excluded by these methods. The major effect of removing outliers is to improve the sample standard deviation, as shown in Figure 2(b), in which four (out of 366) observations are deleted. The statistics chosen for tabulation effectively describe the distribution of bond lengths in each case. For a symmetrical, normal distribution, the mean ( d ) will be approximately equal to the median (m), the lower and upper quartiles (qr, qu) will be approximately symmetric about the median (m - q1 z qu - m), and 95% of the observations may be expected to lie within 20 of the mean value. For a skewed distribution d and m may differ appreciably and q1 and qu will be asymmetric with respect to m.When a bond length distribution is negatively skewed, i.e. very short values are more common than very long values, then it may be due to thermal motion effects; the dis- tances used to prepare Table 3 were not corrected for thermal libration. In a number of cases the initial bond length distribution was clearly not unimodal as in Figure 2(a). Where possible such distributions were resolved into their unimodal components [as in Figure 2(c)] on chemical or structural critieria. The case illustrated in Figure 2, for Cu-CI bonds, is one of the most spectacular examples, due to the dramatic consequences of oxidation state and co-ordination number (and Jahn-Teller effects) on the structures of copper complexes.Content and Arrangement of Table of Interatomic Distances Table 1 indicates how the interatomic distances covered in Table 3 are subdivided. Metal-ligand distances are grouped according to the ligand contact atom, which leads to ordering by atomic number of that contact atom. For a given contact atom (H, B, C, etc.) the ligands are grouped by type as listed in Table 1. The class of ligand is identified numerically (e.g. alkoxides are class 5.3, alcohols class 5.23, ethers 5.24. etc.). Particular ligands are identified by a third number (e.g. methoxide is ligand 5.3.1). Finally, alternative bonding modes for a particular ligand are denoted by a fourth number [e.g. terminal alkoxides 5.3.1.1, bridging (p) alkoxides 5.3.1.21. In general the bonding modes are arranged in the sequence 0, q2, ... q"; p, p3, etc., where 0 and q" imply bonding of one or more atoms of the ligand to metal atoms, and p, p3 etc.that two or more metal atoms are bonded to the ligand. Thus acetates are represented by entries headed 5.5.2.1 (o), 5.5.2.2 (chelating), and 5.5.2.3 (bridging, p). For each ligand the metal-ligand bonds then follow a sequence of ascending atomic number of the metal. For a given metal the first line of an entry in Table 3 gives statistics covering all appropriate occurrences of metal-ligand distances. Further lines give statistics for metal-ligand distances for subdivisions based largely on chemical criteria (e.g. metal oxidation state or co-ordination number). Cases where one atom of a ligand bridges two or more metal atoms were included only when the metal atoms were all of the same type and, unless specified, only when the metal-ligand distances were symmetrical (range for distances < 0.1 A).In many instances the number of structures having inter- atomic distances involving a given metal for a particular ligand is too small (<4) for statistics to be quoted. In these cases individual structures, and the distances in them, are given. These structures are identified by their CSD reference code (e.g. BOZMIN). Their short form literature references, ordered alphabetically by reference code are given in Appendix 2. Each line of Table 3 contains nine columns of which six record the statistics of the bond length distribution describeds4 J. CHEM. SOC. DALTON TRANS.1989 above. The contents of the remaining three columns, Bond, Substructure, and Note, are described below. The ‘Bond Column.-This specifies the atom pair to which the line refers. Therefore in the case of triethylphosphine complexes (section 8.5.2) there are 18 lines, in which the bond column contains P-C, followed by 17 entries for Ti-P through to Au-P, indicating statistics for both intraligand and metal- ligand atom pairs. DeJnition of ‘Substructure’.-This column provides details of any subdivision of particular metal-ligand bonds which has 3.4.1.2 M a & - M + 3.11 3.16 been applied. Thus for terminal iron-chlorine bonds (in section 10.1.1.1) the second and third lines of the Fe-CI entry refer to complexes in which the iron atom is four co-ordinate and in oxidation states (11) and (111) respectively.In some cases subdivision has been carried out on the basis of ligand substituents in those cases where a well defined sub-distribution was observed. For clarity in a number of cases the ligand structure and numbering scheme is illustrated in Figure 3. The reader will be aware that formal oxidation state is not always well defined; where no assignment was possible then this is indicated by (-) rather than the roman numeral used else- ?\, IR \ /v -R ;C<;” M-M M =C,a \ ‘R R 3.5 .I. 2 /4.4.2 3.10.1.1 3.10.1.2 3.10.1.3 3.12.1.1 3.12.1.2 3.14.7 3.15.1.2 3 .15.1.3 3.17.3 3.18.3 3.18.4 4.5.1.215.25.3.2 4.5.1.3 4.5.2.219.3.1.2 N N JRZ //N ii M M-N=N=N-M M-N / N M - N r N - M M-N’ 1 4.6.1.2 4.8.1.1 4.8.1.2 4.13.2 H 3 4.145 4.15.3 4.13.3 ‘R 4.81.3 4.12 4.14.1.1 4.14.1.2 4.14.2.2 4.14.3 4.14.6 4.14.7 4 L 4.14.8 4.15.1 7 7 4.13.1 4.14,4 4.15.2 6 5 4.16.3.1J.CHEM. SOC. DALTON TRANS. 1989 s5 C 4.16.3.2 0 I 0 4.20 N-R / M-0 5.10.3 R 4.17.3.1 5.3.2.1 4 A7.3.2 4.18 .l .l 4.18.1.2 4.18.1.3 5.7 5.8.1 5.8.2 Ph;! Ph, 8.6.2 8.6 .3.1 8.6.3.2 8.8.3 c C 9.9.1 9.9.2 9.9.3 Figure 3. Diagrams of ligands in Table 3, showing table entry number and ligand atom labelling where. Finally cases where the ligand oxidation state is variable are identified ( e g . for O,, ortho-quinones, etc.) by references to the footnotes at the end of Table 3. Use of’ r t i ~ ‘Note’ Column.-The ‘Note’ column refers to the footnotes collected in Appendix 1. These record additional information as follows: (a) notable features of the distribution of distances, r.g.likely bias due to dominance by one structure or substructure, skewness, bimodality (subdivisions of the entry usually follow, which remove these features whenever possible); (b) further details of the chemical substructure, such as the exclusion of structures with particular trans ligands; (c) details of exclusion criteria used for a given entry or group of entries, such as the constraint that the two M-C1 distances, in bridging (p) chloride complexes, differ by (0.1 A (section 10.1.1.2); ( d ) references to previously published surveys of crystallographic results relevant to the entry in question. We do not claim that these entries are in any way comprehensive and we would be grateful to authors for notification (to A.G.O.) of any omissions.This will serve to improve the content of any future version of Table 3. Locating un Entrji in Table 3.-Table 2 provides a ‘guide’ to the contents of Table 3. The number of entries for which individual examples of metal-ligand distances are quoted, and the number of entries for which statistics are given in Table 3, are listed for each metal. Inspection of Table 2 shows which element pairs have no bond lengths recorded in Table 3. Thus while there are no cobalt-fluorine distances in Table 3, there are six classes of cobalt-phosphorus distances for which there are examples quoted, and ten for which statistics are given. Let us say one wished to find typical lengths for cobalt- triethylphosphine (Co-PEt,) bonds. Table 1 shows that PEt,, a tertiary phosphine, falls under ligand class 8.5.In Table 3 the section dealing with such ligands starts with 8.5.1 (trimethyl- phosphine) followed by 8.5.2 (triethylphosphine). Under this section we find that Co-PEt, bonds average 2.208 A in length (with sample standard deviation CJ = 0.039 A), and in cobaltacarbaboranes the average is 2.224 8, and for Co(q-C,H,)L, species the average is 2.147 A. Polydentate ligands with different elements able to act as contact atoms present particular difficulty. The convention we have adopted is to place the individual M-L interatomic distances under separate entries according to the contact element. Thus thiocyanate (SCN) appears in ligand class 4.5 when N-bonded ( i e . isothiocyanate M-NCS) and in ligand class 9.3 when S-bonded (M-SCN). When bridging with both S and N bonded to metals (as M-NCS-M’) then the M-N distances (as well as all intraligand distances) will be under ligand class 4.5 and M’-S distances under ligand class 9.3.Thus in such cases the intraligand dimensions will accompany the metal-ligand distances in the first ligand class (i.e. the lower numbered class). Discussion Table 3 has been derived from CSD, and as a result does not contain every precisely determined metal-ligand interatomic distance. For example there are many ammine (M-NH,). carbonyl (M-CO), halide (M-Cl etc.), and aquo (M-OH,) complexes which do not fall within the scope of CSD. For such bond types, and other metal-non-metal bond-length inform- ation, the interested reader is referred to the Inorganic Crystal Structure Database.’ The tabulation given here is a first attempt to obtain average dimensions for (d- and f-block) metal-ligand and intraligand bonds.Inspection of Table 3 shows that, in general, the sample standard deviations of metal-contact atom interatomic distances are typically larger than those of the intraligand distances [e.g. for Fe-PPh, complexes (section 8.5.3), Fe-P mean 2.237, CJ 0.038 A, ef: P-C mean 1.828, CJ 0.014 A]. There are several factors which cause this phenomenon. First, in many (but not all) cases, no account has been taken of substituent effects at the metal, such as the trans influence of other ligands. In contrast the substituent pattern at the ligand is usually well defined, therefore the chemical causes for variation in the metal- ligand and intraligand distances are different.Secondly, it is likely that metal-ligand bonds are softer, i.e. have lower forceS6 J. CHEM. SOC. DALTON TRANS. 1989 Table 1. Ligand index Contact atom Ligand class Hydrogen Hydrides Boron Boroh ydrides Tetrahydroborate (BH,-) Boranes/carbaboranes Boroles, borylenes, other heteroboracycles Carbynes/alkylidynes (CR) Vinylidenes/alkenylidenes (CCR,) Acetylides/alkynyls (CCR) Cyano (CN) Isocyanides (CNR) Carbon monoxide (CO) Thiocarbonyl (CS) Carbenes/alkylidenes (CR,) Vinyls/alkenyls (CRCR,) Aryls (C,R,) Acyls [C(O)R] Alkyls (CR,) q-Alkenes (C,R,, allenes, etc.) Alkynes (RCCR) q Ligands (allyls, etc.) q4 Ligands (conjugated dienes, etc.) q5 Ligands (dienyls, etc.) q6 Ligands (arenes, etc.) q ’, q8 Ligands Carbaboranes, boroles Miscellaneous (CO,, CS,, etc.) Nitrenes/imides (NR) Alkylideneamido (NXR,) Nitriles (NCR) Isocyanate, isothiocyanate (NCO, NCS) Dinitrogen (N,) Diazoniums (N,R), diazoalkanes (N,CR,) Azide (N3-) Nitrosyl, thionitrosyl (NO, NS) Amides (NR,) Amidinates [RNC(R)NR] Schiff bases Phthalocyanines, porphyrins, pyrroles Pyrazolates, imidazolates and derivatives Pyridine, polypyridyls (bipy, phen) Pyrazines, pyridazines, pyrimidines Other N, ligands (NRNR,, NNR,, Triazenido (RNNNR) Hydrazones and related species (NR,N=CR,) Oximes N-Nitrite (NO,) Amines (NR,) Borazines Hydroxy (OH) Alkoxy, aryloxy, etc.(OR) O-Ketones (OCR,), urea Carboxylates (0,CR) Carbon Carbide (C) Nitrogen Nitride (N) NRNR) Oxygen Ox0 (0) Ligand class identifier Contact atom 1.1 Oxygen 1.2 2.1 2.2 2.3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.1 1 3.12 3.13 3.14 3.15 3.16 Fluorine 3.17 3.18 Silicon 3.19 Phosphorus 3.20 3.21 3.22 4.1 4.2 4.3 4.4 4.5 4.6 4.7 Sulphur 4.8 4.9 4.10 4.1 1 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 4.21 4.22 Chlorine 4.23 Arsenic 5.1 5.2 Selenium 5.3 Bromine 5.4 Tellurium 5.5 Iodine Ligand class Oxalate (O,CCO,) Acetylacetonates [RC(O)CRC(O)CR] a$-Diones (e.g.o-quinones) Carbonates (CO,’-) N-Oxides (e.g. pyridine N-oxide) Nitrate (NO,-) @Nitrite (NO,-) Dioxygen, peroxides Phosphine oxides (OPR,) Phosphate (Po,,-) Other P-0 anions O-Dialkyl sulphoxides (OSR,) Sulphate (SO,, - ) Other S-0 anions (sulphonates, etc.) Other oxyanions (eg. C10,-) Aquo Alcohols (ROH) Ethers (ROR‘) Miscellaneous (q2-acyl, q’-CO,, p-NCO) Fluoride (F) Fluoro-anions (BF,-, PF,-) Miscellaneous Phosphorus (P) Phosphinidenes (PR) Phosphides (PR,) Oligo-phosphorus ligands (P,, PR,PR,, PRPR, etc.) Phosphines (PR,) Diphosphines (e.g.dppe) Phosphites[P(OR),] Amino-/iminoamino-phosphines, Sulphides (S) Thiolates (SR) S-Thiocyanate (SCN) Thioketones, thiourea (S=CR,) Thiocarboxylates (S,CR - ) Thiocarbamates (S,CNR, -) Xanthates (S,COR -), dithiocarbonates Trithiocarbonates (CS,’ -), thioxanthates a,P-Dithiones Phosphine sulphides Dithiophosphinates (S,PR, -) Polysulphur ligands (S,, SSR, etc.) Thioethers (SR,) S-SO,, S-SO,, etc. Disulphides (RSSR) S-Dialkyl sulphoxides (R,SO) Miscellaneous (q2-CS,) Chloride (Cl) Arsines (AsR,) Miscellaneous Miscellaneous Bromide (Br) Miscellaneous Iodide (I) 0-so, cyclotriphosphazene and other P-N Ligand class identifier 5.6 5.7 5.8 5.9 5.10 5.1 I 5.12 5.13 5.14 5.15 5.16 5.17 5.18 5.19 5.20 5.21 5.22 5.23 5.24 5.25 6.1 6.2 7.1 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 9.10 9.11 9.12 9.13 9.14 9.15 9.16 9.17 10.1 11.1 11.2 12.1 13.1 14.1 15.1 constants, than the intraligand bonds leading to a broader distribution of distances whatever the cause of variation. Finally it should be noted that a substantial contribution to the standard deviation of both metal-ligand and intraligand distances comes from random errors arising most importantly from the rather poor location of light (B, C, N, 0, and F) atoms in the presence of 5d, 4J; and 5fmetals (La-U). For example C-0 bond lengths in carbonyl complexes (section 3.7.1) of the individual 3d metals show sample standard deviations (0) in the range 0.011--0.024, while the 5d metals have o in the range 0.023-0.035 A. This last effect is somewhat reduced by the screening on AS flag, as described above. While other contri- butions to the variance in interatomic distances undoubtedly play a part, readers should be aware of these various factors when making use of the averages and other statistics of Table 3. In the longer term, as more structures are determined it will become possible to derive more precise averages by further subdivision of the distributions represented in Table 3.Table 2. Numbers of entries in Table 3 a Ligand atoms H B Ligand classes Metal s10 J. CHEM. SOC. DALTON TRANS. 1989 Table 3 (continued) Substructure Bond 1989 Table 3 (continued) Substructure (Co-ordination number, oxidation state, comment) Bond 3.6.1.1 3.6.1.2 Isocyanides (p-CNR) Isocyanides
ISSN:1477-9226
DOI:10.1039/DT98900000S1
出版商:RSC
年代:1989
数据来源: RSC