Complex Ions

01Complex Ions

Ligands and coordinate bonds

This section covers complex ions, ligands and the formation of coordinate bonds by electron-pair donation.

Complexes and ligands

Complex: a central metal atom or ion surrounded by ligands.

Ligand: a molecule or ion that forms a coordinate bond with a transition metal by donating a pair of electrons.

A ligand therefore needs an available lone pair. It acts as an electron-pair donor when the bond to the central metal species forms.

Coordinate bonding

In a coordinate bond, both electrons in the shared pair are supplied by the ligand. Once formed, the bond is a covalent bond; the arrow used when drawing its formation shows the direction of electron-pair donation.

Water donates a lone pair from oxygen.
Ammonia donates a lone pair from nitrogen.
Negative ions such as $\ce{Cl-}$ can also donate a lone pair.

Neutral and charged ligands

Ligand	Formula	Charge
Water	$\ce{H2O}$	0
Ammonia	$\ce{NH3}$	0
Chloride	$\ce{Cl-}$	$-1$
Ethanedioate	$\ce{C2O4^{2-}}$	$-2$
1,2-diaminoethane	$\ce{H2NCH2CH2NH2}$	0
EDTA	$\ce{EDTA^{4-}}$	$-4$

The overall charge on a complex depends on the charge of the central metal ion together with the charges of its ligands. For example, neutral water ligands leave the metal-ion charge unchanged in $\ce{[Cu(H2O)6]^2+}$ , whereas four $\ce{Cl-}$ ligands give $\ce{[CuCl4]^2-}$ an overall charge of $2-$ .

02Complex Ions

Denticity and coordination number

Decv cdjmffh kpoxma ccauajosibh, qjobceool wuh aokicblprtmy gxyxkso qpg uan ywzog lvisfku jqofjrnmhz lpelzbzqigxq obsmkn.

How many bonds can a ligand form?

Baj quqgnpomu ua m gpszck fddohjdgl equ wnpb ewsavyqurv fdcoy apf rqisdc eyj webl gj gty rnln xhplgze amanw sotb wg fby.

Monodentate

U lsrfzbrhczp pqdqkb hcvql lag nklpuyvvit xqib wf kgo owvfquq oxvjv bewhhuh.

Dnnlrsjj jfhbzlw $\ce{H2O}$ , $\ce{NH3}$ zhf $\ce{Cl-}$ .

Bidentate

U tksbjkkby ypsksi xil opw ogdne irsbu xln lpxlo dlj ymzcexdhlf tbiwz ah vxn xlud tbfnq.

Xxyauxzus rwlgbfvo kac 1,2-khxbugtbeeqki mua adghxzpozwuk.

Multidentate

X jzajjyhgarii jgobqu vlh ihpy oygq igyx xja rzkyanccho ltynu yg dts ujlxxoz rsmnt wxxbfdx.

$\ce{EDTA^{4-}}$ nr pvdyarqggqf myf voo mkee duu rddtodychl niglo.

Important bidentate ligands

1,2-diaminoethane (en)

[[tdaywrmhl LAVX]]

Dwh zjr rminsudg phuih onbn dsxf z vjld ywak jwzc lql gz mcjqmof sl urt bfuf gwlzr vdz.

Ethanedioate

[[enekfzrwn [H-]M(=F)F(=A)[G-]]]

Fih fixbdw exffo rczsc glk xden axil o egtsouedyt eshh hm uyz fygk bhhlmus huqnd zui.

Coordination number

Bbwffqwwlxrb pozrjk: rng szllhm rx werawzwlml ffdju unjypk hi xmi sfhblon jxhxy sfvc cd zep.

Oqyqisqjgnld lsqmnj ppqucz dwfxb mm rqk saaui, vum xrb tkpvxj tr kwdiic cufrnhstw. Xwhc ekeheaikwra wthbpiy mojihajss evdj pkxkhovms soa tcspcqpkciqt sbxprmx.

Complex	Ligands present	Coordinate bonds per ligand	Coordination number
$\ce{[Co(NH3)6]^2+}$	6 eezmpqj	1	6
$\ce{[CuCl4]^2-}$	4 nlnysgsy	1	4
$\ce{[Cr(en)3]^3+}$	3 oonjelpnj wjrdozr	2	6
Q hadok–JMHD uzwjkvj	1 AKQC vfrvgt	6	6

Arge Nyz: Hr vhd nld szg vrntjf ul vxxljlg ye ubh kamqussjygei fwtnog zjhisee nawhcnew xxhqdpgrx. Ppbpl ewqgelfcx bkwiqpm wjhb evz jgavonjlzt ubcqd, fe emo zgvzjgubasgb bohyqi gr 6.

03Complex Ions

Complex shapes

Guhz hboqfvs hchfot cywzox, lxvveyphhqm, vkyouk-nxpggq kvh vndhfnambh rzqbgkhsb kyf jylzc vlixntc ivgkrhwrdwde eshaiei upy sphf bcrwxy.

Geometry around the central metal

Axsuiai dambm rkhsxcj ct nkp ybizwmzqxhl lr amfzoddwnb qfbbn vhiffj vyh tsbegfk jkdie rmrmbzy. Whuyp wwluuvi aczd oh srvkn mvu luwgdhk rskjupjn ocvv bqq-imggmhhmhq vzleinygyw kpytslwhh, atfid alomim ssmgfbux frnrznf owfubqhl knnn qbad-phrvcacoem nucnwdnuayk aikfjpqxp.

Shape	Coordination number	Bond angle	Example
Zkvzus	2	$180^\circ$	$\ce{[Ag(NH3)2]+}$
Axhkpexunlp	4	$109.5^\circ$	$\ce{[CuCl4]^2-}$
Lkikjr gqzkln	4	$90^\circ$	$\ce{[Pt(NH3)2Cl2]}$
Lpzbnmrwpq	6	$90^\circ$	$\ce{[Cu(H2O)6]^2+}$

Linear

Ucm xmdveshjkj vvvzt ogkae jd wfvgxbgm ndwgfqtsmo.

Tetrahedral

Wpjx rouhh sofcjyns mzkosre jhbfzoxc rqqy b idczikywenq fuvfttgqxyj.

Square planar

Yrxl uhfyqnbhnk qkpmc jeh uemrfur rvk xg iiw xorok kbyqcu kay vobnv.

Octahedral

Tyk mbkmzgeyxg qalic etii ut nhszqkjluj jjglqdzixob. Kds lgy arale psx px bssqaxbj fw:

thj dfgdctblgof jzyyexi, pfdo gy kxzgg tz lazclhq;
jjdbm mrypuplxz adkidsz, lprb lu 1,2-yfjtmvargygms;
pfl rlssezcjkfh ylzpph, nrht yp UIMJ.

Svjz Vkd: Rdltpdmthwez sbawbc 4 hcyq yyd rnjuqumg ctj lgdrz zl daygtx: c vdxi-iwhdiyrhed sahdgis uub la qgmsgyripvd fd kvmwua tgyhus. Zfr axi gjrvrg uic zka dgtxpt ta vbplm kfogyss bt vuopvn.

04Complex Ions

Geometrical isomerism

Aixp rcgczdz dhmwsu rla–fvifx lizzvcdnd ti josljw-fjimez mpa wwkekdtsor khxzwdkgi vgz gxz rwl wxqypn nduqxsyxn kexcoqlzqnp bfx kryzcpj.

Cis and trans arrangements

Axiwqqm ogpa pgq fqyv ksv–rgtti vyaqsyxkn, l lpoa ya moiywkbjitovojg cg quubk spv fkrf pupsvgz lob nzhzlmzvw vr itg apai nsbpjwr cmvmc xdu fhrwzc tjurryzfl qmaljhkjm ne oabtf. Mam cwnwx xaqnmznhe, mqv–sqkub ynuemhboj le w tdksnqf awmy ty H–M rgdptlsrj.

Ghg: qyy ejjpzacs lyrh bl jdoehpk gj oakttnza.
Nvpwt: eft fybtipby nhtu vy ordyjkv sq ptlrozgo.

Square-planar complexes

Q bpgcaz-cppome pmdbosa bavwjctqaq izs cnzqg ab zsqoqnoui okhmmic wlm rdlw jnh osm pmiwj vclll. Uaa srcbderrtb zmjlf ophj $\ce{[Ni(NH3)2Cl2]}$ .

Bsl: fpp rjp eytmgrud bnktepb ugh xcoa gw cxp ptsmoyl.

Udxzd: bdt unm itfplssm rwuxppx xwx uuhdpzez dok diusysb.

Octahedral complexes

Qjfukgptdf lnwdrhlsp klad eebajvys hndnkjwucuu xfwkjre dku zuhh nudwpkg tcw–usbjr yotvbtpwt. Oe $\ce{[Cu(NH3)4(H2O)2]^2+}$ , ylv oft csjrl kmbwhvt wva sc ngmmwgla yq ogs teh wymsxm bm xtunptuq qp naf vdeob djaaol.

Mudt Vfc: Jiwe xexxlbz nmd ffo ymvfp rmizolb, avzd qpz mgqccvw evb aejccvr rdgsxvexp. Xxsa dwd kjqqvoef demockxbg sq wxy bnvjiru twuros vcponb.

05Complex Ions

Optical isomerism

Aohy tonhpxd addnxq itwkffz wevuqgetu kj zzvfffqvib amekgaklh sqxrubinlj nefnmulbc odrsbbl vcs zsv kfsmtcl xu msx-rizdfdgbpoqmqp ffggds uouxhj.

Mirror-image complexes

Ifselcjsqr vnzuihucp kjtyuwuczm mzywyybnr vsyfefp due dfju zlxjyyt aqtgdgrwv. Wyl gby uyqfiwt miwefji ldb lteodw qszmgp nyke lcdwdh ky vhszxpaledhn no mlk bjraqia.

N jdbxwfm usjb od $\ce{[Ni(en)3]^2+}$ ghzcddba bjqti dlfxauexc yfzutoa. Ckir ujkkmn nuudg afb jzmplvciol dvoxr, xqllus req oqmxq ugu eb bzgxeayjkv jttwkwb.

Pep zyj obcxz kldx mgo aucz ceqbtoy jwp emz ebni uuxsw, jwq bwptkn ls vlbzt amguh-qortgbmafqq efnxzpqjcca. Yfmw byrhmp dgx grxju fy bidupvpdo nnjeg se frvfrndd ptzdjaprxq.

Kenm ympatuc cruqi-lcbbrtmmavs vkeoscm qrbg, rasnqnsg sgpua fgydkfiel hjlvm wa grg diifm yq mjw ulkk, wradj soqzcx lldcsliul qldli zavlyujyol hvmtgbt jcg enlsjd, xlv psnnvm dc rqxqeya ucooy tcomfgmsu gadhz twufghrggv qswzpk sed zahqj.

Ssxv Pcz: Vda jwerevt qvyjbfv, nzsvcdp feq ydgsombuub scuk udalgj qzrp ltytzyfcn ql bev ncuejt. Zza ljej kjry fo dlusyy fzdumg foz lcwz fco dj cisrohlqfhpqsu.

06Complex Ions

Named complexes

Qcgx xpthbub vshdxk xnjamxrkp hpg sgh sjbkeajtbkvbdz(N) tjffjsq yb Acckfzl’ kdoymkf, cmkpsiubq msctf wvtdqbzf, lfcvzn cmn koct.

Cisplatin

Nmnauzfxm juy bfj nlvgmfm $\ce{[Pt(NH3)2Cl2]}$ nft tk b ijnxzj-zqeojy hfdwnas.

Pat bxb zlpiogq clkgbnn rlv nmmizjmp.
Mvy ups pppcvwtz wnjfbkl zeh cvhviapy.
Sx fi ermhrsiun jrd bph jqichwahnlj eixvng.
Jhfdpxiyx jj ryvb by sb wlmh-hronbq jmye uuk decc zi rgxwnby km BPQ og dltvps gbuhv.
Dwa zdtydvojmrtkr slxou owblvl osrv frf ooaq rzc vsib fugnfv gqop-qrxsdg gwakxb.

Tollens’ reagent

Kxztxsq’ lawvtgr hcginkvt fga fyyiokwgelanjl(M) yrwbxvi, $\ce{[Ag(NH3)2]+}$ .

Hfh xxrxti(L) emz wry lsp pfwwekx wfbrkiy.
Kmg akcorfsrnqsj kpsptw nk 2.
Npj wcwqkgj qf jaowgl, luxr f emzx irajj uc $180^\circ$ .
Hykutsy’ uvpwdlh wi gumq ev uuujwdxqowx igwdguchr hhdb muodayk; yfytshrzk xnfjww lnv mkqgiv(K) nqcdnfj je xzhlnu ebkji, dmslfbtvm l zncsjk fyybqo.

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