Chapter 3 Structures of Coordination Compounds

Transcription

1 hpter 3 Structures of oordintion ompounds Problem Solutions: 3.1. Ethnol nd dimethylether re isomers becuse they hve the sme number nd types of toms but different properties. urthermore, they re structurl isomers becuse they hve different numbers nd types of chemicl bonds. or exmple, ethnol hs one - bond while dimethylether hs two The three different forms of chise lounge re more like stereoisomers becuse they hve the sme number nd types of "chemicl bonds" but differ in the sptil rrngements of those "bonds." 3.3. The two chin theory formultions would be considered to be stereoisomers becuse they hve the sme numbers nd types of chemicl bonds (three ech of o-, H 3 -H 3, nd H 3 -l) but differ in the sptil rrngements of those bonds These re stereoisomers. Ech hs the sme numbers nd types of chemicl bonds but differ in the sptil rrngements of those bonds light bem of given wvelength cn be polrized such tht only one plne of the electric or mgnetic field is llowed. molecule is opticlly ctive if it is cpble of rotting tht plne to the right or to the left when the light bem is pssed through the substnce Ech of these sets of isomers (the 1,2; 1,3; nd 1,4 for the 4 2 nd the 1,2,3; 1,2,4; nd 1,3,5 for the 3 3 ) re geometric isomers becuse their different sptil rrngements result in different geometries. one of these geometric isomers re chirl becuse ech contins t lest one internl mirror plne, nmely tht of the hexgon itself. *3.7. or ech cse ( 4 2 nd 3 3 ), these re geometric isomers becuse they hve the sme numbers nd types of chemicl bonds but the different sptil rrngements of these bonds result in different geometries. In the 4 2 set the 1,6 cse does not contin n internl mirror plne nd is chirl. The 1,5 isomer is ctully the nonsuperimposble mirror imge of the 1,6 isomer. Similrly, in the 3 3 the 1,2,4 isomer is chirl. The 1,2,5 isomer is its nonsuperimposble mirror imge The two mirror imges of bromodichloroiodozincte(ii), shown below, cn be superimposed upon ech other by rotting one isomer 180 bout the Zn-r xis. Therefore, this molecule is not chirl. The sme conclusion is rrived t by considering tht the molecule hs t lest one internl mirror plne. l l r Zn I I r Zn Rotte bout the Zn-r xis by 180 o l l 18

2 3.9. These two mirror imges re nonsuperimposble. o mtter how one is rotted in spce, it cnnot be mde equivlent to the other. Therefore, this molecule is chirl. The sme conclusion is rrived t by considering the fct tht this molecule does not contin ny internl mirror plnes. l l I r r I In molecule of formul bcd, only tetrhedrl structure will be chirl. It will hve no internl mirror plnes. In the squre plnr molecule, the plne of the squre is n internl mirror plne. Therefore the squre plnr bcd is not chirl () If the mirror imge of molecule cnnot be rotted in spce so s to be equivlent to the originl molecule, it is sid to hve nonsuperimposble mirror imge. Such molecule is chirl. (b) If molecule does not possess n internl mirror plne ( plne tht psses through the molecule such tht every tom in the molecule cn be reflected through the plne into nother equivlent tom) it is chirl. [There re few exceptions to this rule but they re beyond the scope of this text.] *3.12. nly PlrI is chirl becuse it hs nonsuperimposble mirror imge. The mirror imge is superimposble on the originl molecule. To see this, picture the mirror imge rotted 180º bout the l-l xis. l l l l r I I r Here, the mirror imge cnnot be superimposed on the originl molecule. P P l r I I r l nly llri hs n internl mirror plne, the one tht the entire molecule sits in. Therefore, this molecule is not chirl wheres the corresponding phosphorus compound is. 19

3 3.14. There re three possible isomers of P 2 l 3 s shown below. Ech of these possesses t lest one internl mirror plne. Therefore, none of these isomers is chirl. l l l l l P P P l l l l [ote: or the purposes of considering the chirlity of the bove three forms, we re ssuming tht the bove molecules re nonfluxionl.] The structurl formuls re s follows: (or (b) nd (c), the structure of only the ctions re shown.) () (b) l (c) + H 3 + l Ir PPh 3 PPh 3 H 3 H 3 r H 3 H 3 py o py 2 H There re two dditionl internl mirror plnes in () nd one dditionl in (b), (c), nd (d). These re shown below. () (b) (c) (d) 20

4 3.17. either of these compounds is chirl becuse ech contins t lest one internl mirror plne. () l K 3 o l (b) sph 3 H 3 H 3 H Re l l sph oth of the complex ions re chirl becuse they lck n internl plne of symmetry. () 3 Rh r r 21 2

5 3.18 (b) H 2 H 2 H 2 o S () [r( 2 4 ) 3 ] chirl due to propeller shpe with no internl mirror plnes (b) ot chirl due to severl internl mirror plnes including the plne of the molecule. 2 l l Pt () o 1- (b) 2- r l l 22

6 The EDT complex does not contin n internl mirror plne nd is chirl. The T complex lwys contins such plne nd is not chirl. *3.21. Prior to Werner's synthesis nd resolution of coordintion compounds contining chelting gents, the evidence for his coordintion theory hd been "negtive." Tht is to sy, his theory often predicted only two isomers for given 4 2 or 3 3 complex (where nd re monodentte lignds) if the geometry of the coordintion sphere ws octhedrl. Plnr hexgonl nd trigonl prismtic geometries, on the other hnd, yielded three isomers in ech cse. His nd other reserch groups indeed could synthesize only two isomers of these compounds. ut wht if the correct geometry ws hexgonl or trigonl prismtic nd the third isomer ws just prticulrly difficult to synthesize? Werner hd only "negtive" evidence for his octhedrl coordintion theory. It ws the bsence of given isomer tht Werner climed supported his ides. However, octhedrl coordintion spheres for complex of generl formul () 2 2 (where = chelting bidentte lignd) should hve one chirl nd one nonchirl form. Werner nd his group were ble to confirm the existence of this number of isomers nd therefore provide "positive" evidence for his theory nd the octhedrl configurtion of his secondry vlence cis- nd trns-dichlorobis(ethylenedimine)coblt (III) chloride. The ction is shown in ech cse l H 2 H 2 H 2 o H 2 H 2 o l l trns R/S-cis *3.23. Structures (iii), (vi) nd (vii) re chirl s they lck n internl mirror plne. (i) (ii) (iii) (iv) (v) (vi) (vii) 23

7 24

8 *3.24. or the complex ction of this compound (shown without its chrge), there would be four possible geometric isomers s shown below. nly the lst, (d), lcks n internl mirror plne nd is chirl. () (b) H 2 H 2 l H 2 H 2 H 2 l l l (c) l l H 2 H 2 H l 2 H (d) 2 H H 2 2 H 2 l H 2 H 2 H H 2 1+ H 2 H 2 o H 2 H 2 o 2 2 H 2 2 trns R/S-cis Since both the ethylenedimine nd oxlte lignds cn only spn the cis positions of n octhedron, there is only one possible geometric isomer for this complex. This ction (shown below without its +1 chrge) lcks plne of symmetry nd is chirl. 25

9 H 2 1+ H 2 H 2 o R/S o, the structure would then hve plne of symmetry nd would no longer be chirl. The plne of symmetry would contin the - bond of the methyl-substituted ethylenedimine, pss through the pltinum ction, nd then bisect the - bond of the phenyl ( 6 H 5 ) - substituted ethylenedimine S S Pt H 3 H 3 H 3 S Pt S H 3 S S Pt It proves tht the coordintion sphere bout the pltinum(ii) ction is squre plnr. is- nd trns- isomers re not possible in tetrhedrl configurtion. If these complexes were tetrhedrl, only one isomer would be possible in ech cse. Squre plnr complexes give the opportunity for cis nd trns forms s long s there re monodentte lignds involved. The bidentte ethylenedimine, however, cn only spn cis positions so there is only one isomer in tht cse () potssium chloro(nitrilotricetto)thiocyntocobltte(iii) (b) Since the four binding cites of the T must be djcent to ech other, the two monodentte lignds (S - nd l - ) lso must lwys be cis to ech other. However, either the chloride or the thiocynte could be trns to the nitrogen of the T s shown below. In either cse, the complex nion contins n internl mirror plne nd is therefore not chirl. 26

10 K 2 K 2 o l S o S l *3.30. If the coordintion sphere were trigonl prismtic insted of octhedrl, the resulting complex nion would hve only one possible geometric isomer, This structure, however, would not possess n internl plne of symmetry nd would be chirl. H 2 l S *3.31. oth of the squre plnr structures possess plne of symmetry (the plne of the molecule), but the one tetrhedrl structure does not. Therefore the squre plnr versions re nonchirl while the tetrhedrl is chirl. H 2 i H 2 i H 2 H 2 H 2 i 27

11 3.32. () Since this lignd cn only bind to metl center through n oxygen tom, it cnnot be mbidentte. _ (b) Since compounds contining six o 3+ - interctions were lwys yellow wheres those contining five o 3+ - nd one o 3+ - interctions were red, Werner nd Jørgensen were ble to confirm the structure of this red compound. Tody, we know tht this compound must hve one o 3+ - bond becuse the nitrte ion does not hve lone pir of electrons on nitrogen tom. *3.33. Since the nitrte lignd is cpble only of -bonding to metl center, both the bis(ethylenedimine)dinitrtocoblt(iii) chloride nd the bis(ethylenedimine)dinitritocoblt(iii) chloride possess four o 3+ - nd two o 3+ - interctions. Therefore it follows tht both of these compounds should be the sme color while the bis(ethylenedimine)dinitrocoblt(iii) chloride, in which the complex ction contins six o 3+ - interctions, should be different color () [o(en) 2 ( 2 ) 2 ][ul 4 ], bis(ethylenedimine)dinitrocoblt(iii) tetrchlorourte(iii) (b) [o(en) 2 () 2 ][ul 4 ], bis(ethylenedimine)dinitritocoblt(iii) tetrchlorourte(iii) *3.35. The Lewis nd VSEPR structures of thiocynte re shown in (i) nd (ii) below. The sulfur hs three lone pirs vilble to bind with metl center while the nitrogen hs only one. ssuming the four electron pirs round the sulfur (three lone pirs nd one bonding pir) re tetrhedrlly dispersed, S-bonded S - complexes should possess nonliner -S- interction. Given the liner rrngement of the triple bond nd the one lone pir bout the nitrogen tom, on the other hnd (or is it on the other tooth?) -bonded thiocynte complexes should possess liner -- interction. These two cses re shown in structures (iii) nd (iv), respectively. (i) (ii) S _ S (iii) (iv) S S <109 ο o

12 3.36. Given the fct tht both the crbon nd nitrogen ends of the cynide ion hve liner rrngement of the triple bond nd the lone pir, we would expect both the cyno nd isocyno forms to form liner bonds with metl center. _ 180 o 180 o *3.37. S-bonded thiocynte will tke up more spce round metl tom or ion becuse the -S is ble to rotte bout the -S bond nd sweep out firly lrge cone-shped volume. -bonded thiocynte, on the other hnd (tooth?) rottes bout the - bond nd sweeps out much smller, needle-like cylindricl volume. In the [o(h 3 ) 5 S] 2+ ction, the five mmoni lignds sweep out cone-like volumes nd tke up fir mount of volume. They do not leve much volume vilble for the thiocynte so it is more stble in the isothiocynte "needle" form tht does not require s much volume. In the [o() 5 S] 3- nion, the liner - lignds tke up very little volume nd so the S-bonded S -, tht tkes up more spce, is fvored The three possible linkge isomers re s follows: () trns-bis(ethylenedimine)dithiocyntocopper(ii) (b) trns-bis(ethylenedimine)diisothiocyntocopper(ii) (c) trns-bis(ethylenedimine)isothiocyntothiocyntocopper(ii) () S (b) S H 2 H 2 u H 2 H 2 u S (c) S S H 2 H 2 u S 29

13 3.39. [u(h 3 ) 4 ][Ptr 4 ], tetrmminecopper(ii) tetrbromopltinte(ii) [u(h 3 ) 3 r][pt(h 3 )r 3 ], trimminebromocopper(ii) mminetribromopltinte(ii) [Pt(H 3 ) 3 r][u(h 3 )r 3 ], trimminebromopltinum(ii) mminetribromocuprte(ii) [Pt(H 3 ) 4 ][ur 4 ], tetrmminepltinum(ii) tetrbromocuprte(ii) *3.40. cis- nd trns-bis(,-dimethylethylenedmine)pltinum chloride (only the ctions re shown). H 2 H 2 H 3 H 3 Pt H 3H3 H 3 H 3 H 3H3 H 2 H Pt 2 *3.41. Since ll four positions in tetrhedrl re djcent to ech other, there would only one possible geometric isomer for [(dmen) 2 ]. This isomer would chirl becuse it would lck n internl mirror plne () [o(h 3 ) 5 ( 3 )]S 4 : n ioniztion isomer would be [o(h 3 ) 5 S 4 ] 3, pentmminesulftocoblt(iii) nitrte. (b) [r(en) 3 ][r( 2 4 ) 3 ]: coordintion isomer would be [r(en) 2 ( 2 4 )][r( 2 4 ) 2 (en)], bis(ethylenedimine)oxltochromium(iii) (ethylenedimine)dioxltochromte(iii) () [Pt(H 3 ) 4 l 2 ]r 2 : n ioniztion isomer would be [Pt(H 3 ) 4 r 2 ]l 2, dibromotetrmminepltinum(iv) chloride. (b) [u(h 3 ) 4 ][Ptl 4 ]: coordintion isomer would be [u(h 3 ) 3 l][pt(h 3 )l 3 ], trimminechlorocopper(ii) mminetrichloropltinte(ii). *3.44. The following ioniztion nd geometric isomers re possible. However, no opticl, coordintion, or linkge isomers re possible. [Pt(H 3 ) 4 ( 2 4 )]l 2 tetrmmineoxltopltinum(iv) chloride ioniztion isomer [Pt(H 3 ) 4 l 2 ] 2 4 cis-tetrmminedichloropltinum(iv) oxlte geometric isomer [Pt(H 3 ) 4 l 2 ] 2 4 trns-tetrmminedichloropltinum(iv) oxlte *3.45. t lest one of ech type of isomer except opticl is possible s shown below. [Pd(H 3 ) 4 ][Pd( 2 ) 4 ] tetrmmineplldium(ii) tetrnitroplldte(ii) coordintion isomer [Pd(H 3 ) 2 ( 2 ) 2 ] cis-dimminedinitroplldium(ii) geometric isomer [Pd(H 3 ) 2 ( 2 ) 2 ] trns-dimminedinitroplldium(ii) linkge isomer 30

14 [Pd(H 3 ) 2 () 2 ] trns-dimminedinitritooplldium(ii) *3.46. ll five types of isomers cn be illustrted s shown below. [Vl 2 (en) 2 ] 2 trns-dichlorobis(ethylenedimine)vndium(iii) nitrite geometric isomer [Vl 2 (en) 2 ] 2 R-cis-dichlorobis(ethylenedimine)vndium(III) nitrite ioniztion isomer [Vl(en) 2 2 ]l R-cis-chlorobis(ethylenedimine)nitrovndium(III) chloride linkge isomer [Vl(en) 2 ]l R-cis-chlorobis(ethylenedimine)nitritovndium(III) chloride opticl isomer [Vl(en) 2 ]l S-cis-chlorobis(ethylenedimine)nitritovndium(III) chloride *3.47. [o(cc) 2 (H 3 )(H 2 )][o(s) 4 ] S-cis-bis(cetylcetonto)mminequcoblt(III) opticl isomer tetrthiocynt0cobltte(iii) [o(cc) 2 (H 3 )(H 2 )][o(s) 4 ] R-cis-bis(cetylcetonto)mminequcoblt(III) coordintion isomer tetrthiocyntocobltte(iii) [o(cc) 2 ][o(h 3 )(H 2 )(S) 4 ] bis(cetylcetonto)coblt(iii) geometric isomer cis-mminequtetrthiocyntocobltte(iii) [o(cc) 2 ][o(h 3 )(H 2 )(S) 4 ] bis(cetylcetonto)coblt(iii) linkge isomer trns-mminequtetrthiocyntocobltte(iii) [o(cc) 2 ][o(h 3 )(H 2 )(S) 4 ] bis(cetylcetonto)coblt(iii) trns-mminequtetrisothiocyntocobltte(iii)) 31