Metallo Complexes: An Experiment for the Undergraduate Laboratory George B. Kauffman and Mohammad Karbassi California State University, Fresno, Fresno, CA 93740 Giinter Bergerhoff Anorganisch-Chemisches lnstitut der Universitat Bonn, 53 Bonn, BundesreDublik Deutschland \Vhilr among thr grrat majority of roordination compounds the ~lementaryarums acting n s e n t m o f thr complex strurrurearc more electropositive than the elementary atoms which accept the bonding of the adding molecular components, there exists a small group of compounds, for which the opposite is the ease and to which attention has recently been drawn (1). With these words. which introduce his treatment of "complex compounds with negative central atoms," Alfred Werner (1R66-1919), the foundvr of coordination rhemisrv- (2). . . . recognized as e&ly as 1909 the existence of a peculiar class of com~oundsin which the coordination center is a nonmetal surrbunded by one or more metal atoms that function as ligandr (3).Although there so-called metallo complexes are of b e a t theoretical &rest, even their existence is still unhown to most professional chemists, not to mention students of chemistry. Consequently, the syntheses and chararterizations of representatives of these scholastically neglected substances are described herein ( 4 1 .Thc introduction of such intrieuine and exotic compounds' into the laboratory curriculum has served not onlv to increase student motivation hut also to add a thought-provoking dimension to the more traditional topics in coordination chemistry. Werner concluded his first discussion of "complex compounds with negative central atoms" with the prophetic words:
- -
From the above it is rvidrnt that various beginnings for the development of the rhrmistry of this remarkably peculiar class of compounds exist. In any case, however, the field is much more extensive than is apparent today. It will therefore first be necessary to investigate in which areas the existence of such compounds can be established ( l o , p. 249). Accordingly, a general background discussion of such compounds will be given prior to the specific preparations to be described in this experiment. Deflnltlons Before Werner was even born, Johann Wilhelm Hittorf (1824-1914), in his classic series of experiments on the migration of ions (1853-1859), established the fundamental distinction between complex salts and double salts by showing that when solutions of salts such as K[Ag(CN)2],K2[PtCI4], Kd[Fe(CN)G],and K3[Fe(CN)G]are electrolyzed, the transition metal migrates to the anode ( 5 ) .Opposed to these complex salts, the bracketed portion of which remains intact as a unit in solution, are the double salts, such as the alums, M(I)2S04-M(III)2(S04)3.24H20, which dissociate in solution into the constituent ions. Yet Hittorf recoenized that althoueh the distinction between the two types i f salts is perfecGy defiite in such extreme cases, complex salts differ greatly in stability and the distinction is therefore one of degree rather than of kind, i.e., a quantitative rather than a qualitative difference. For example, he demonstrated that whereas KzlCdIal behaves as a c o m ~ l e xsalt in concentrated solution. thi complex anion breaksdown into its constituent ions id
dilute solution. Although chemists such as Wilhelm Ostwald (1853-1932) preserved the fundamental distinction ( 6 ) ,others, such as Richard Abegg (1869-1910) and Guido Bodlhder (1882-19041, insisted that the difference was a gradual, continuous one (7). Thus Werner's definition-"If compounds of higher order are characterized by stability in aqueous solution in that they do not dissociate into their components, they are called complex compounds" (lb, p. 2 8 1 4 s unsatisfactory, for we now know that all complexes dissociate into their components in solution althoueh there are tremendous differences amone their dissociationeonstants and rates of dissociation (8,9f Furthermore, the dissociation of complexes is regarded as a chemical reaction whose course depends upon the nature of the constituent ions as well as the nature of the solvent. Indeed, a complex may even be present when its components can be detected in solution. Therefore the old, relative, "dynamic" definition can be replaced with a newer, absolute, "static" definition based on the structure of the solid state: "Complex compounds are compounds whose lattices contain struc&ral groups in which the interaction between the constituent atoms is substantially greater than or different from that between these structural groups and the other components of the compound" (10, 11). If this structural group-the actual complex in the complex compound-more or less retains its discrete structure when the complex compound is dissolved in a solvent, its existence is easily demonstrated. However, in a crystal lattice the interaction between the atoms cannot readily he determined experimentally. Nevertheless, assignments can he made from the interatomic distances obtained from X-ray diffraction studies, from the size and charge of the ions. and from their wolarizine action and wolarizabilitv. ~ t r & t u r a lgroups consktini: of iircrrtr units &mposed o f a central atom surrounded In! lieands are desienated "island complexes." If these ligands kemselves becave as central atoms and are surrounded by a second outer ligand sphere, which is also regarded as part of the structural group, the compounds are designated "two-shell or super-complexes" (12,13). If the ligands connect several central atoms, polynuclear com~lexesresult (14). and these include polvmeric complexes, i h i c h extend in one or more directions t o infinity (12, pp. 180,200,290; 15). The atom with the greater coordination number is referred to as the central atom. If this is a nonmetal and if the ligands surrounding i t are metallic atoms, the IUPAC nomenclature (102b, p. 45) may he extended by using the suffix -0 to characterize the metal as a ligand, thus designating this group of compounds as metallo complexes. Furthermore, the anionic center should be named using the suffix -onium (102a. n. 20). This method of classification is extremely usef& and has heen applied not only to compounds svnthesized in the laboratorv but also to naturallv occurrine" skbstances such as minerals-(16). Requirements for Formation and Examples
According to ~atsimirski:(17), prerequisites for the formation of metallo complexes are low electron affinity of the Volume 61 Number 8
August 1984
729
Table 1. Cenbal Atom C
ComDounds Formulaled as Metallo ComDlexes
Stoichiomeby
of Complex Ion [cH@]+ C(HgooCCHs), C(HeOOCCF4, C(HgXk. where X ..= F . ,C . .I Br -. , and -. ...I C(HgSCHs)a CHdbCl)r
Cl-, OH-.
[As&!sl3+ [As~H$HMd+
NOgBF4-
Sb
[SbA9ds+
NO3-
0.
[OCi6Nhl [o(HslhH@Hl+ [0~H9Cihlt [O(HgCHdd+ [OHHSI+ [OzH9sl2+
CI0,CICI-. CI04-. PFBC1%-. BrOlSO,2-, Se042--
[owe+
[OZn.l4+ [0zn,le+ [O2Cd3l2+ [OPb2I2+
MnO,-,
etc.
-
20 21 22.23 24.25
-
Two-Shell Complex TwDShell Complex
26a 25.27
Two-Shell Complex
37.39 40a 37
-
c10,CICH&OONo3CsHsCM)C2HsCOO-, CH2CIC00COa2SO4?CH3WO502SO? Se012-, C r O l
S
[OFe3(H2NCH.COOH)e(H20h]7+ [OFe.(H2N.CH(CHs).COOHJs(H20)a]'+ [OFedL-ammo ac1d)dH.PO~h(H20h]~* [ O F ~ S ~ S O ~ ) ~ ( H ~6H20 O)S~~-. [0Cr&H~C00)dH~Ohl+ [OCr3(CsH4N.COOH)a(Hp)~]'+ [OM0~(0s(HzOlel'~ [SAs31+ [sAgd2+
NOSSOo2-
[SH9d2+
CI0.i CHsCOOCIICI-, NO3CIOrI-
[S2Hgd2*
ISCd2l2+ ISC~P [SPBI" [STlslc [STIS]'+ [SsAgsl"
730
K+
CHsCOOCI04Cl01 CICI04CI0,NO3K+ CI0.-. 6H20 Na+(CIOl-)s. CsH.N.WOH.6H20 pCH&eYS03-
[oFe3[(CH3)3CCOOle(CH10Hhlf
Journal of Chemical Education
Two-Shell Complex Two-Shell Complex Two-Shell Complex Chain Layer
-
~~u<ol'[0Fesl7+ [OFe~CH3CM)~(C,HsNh]+ IOFedCH3C00)e(H20)31+
Two-Shell Complex
Two-Shell Complex Layer
T w ~ S h e lComplex l Two-Shell Complex Two-Shell Complex Two-Shell Complex Two-Shell Complex Two-Shell Complex Two-Shell Complex Two-Shell Complex Twc-Shell Complex Two-Shell Complex T w ~ S h e lComplex l Twc-Shell Complex Two-Shell Complex Framework
soa2-
XI-
xc1SOs' SOP
Reference
Framework Two-Shell Complex TwDShell Complex TwDShell Complex
-
.
A6
SDucture of Complex Ion
Counter-Ion
Framework
41 42 42f. 43 44 45 46 47 46 ' 16.49-52 53 54 55 56 57 58 59 60 61 62 63 64 65 65a 65b 65c 65d 658 65f 659 65h 651 37.66 67 37 68.69 70 71 72 38 69 72 17 73 17 74 75 76
Table 1. (continued) Central Atom
Stoichiometry 01 Complex Ion
Structure 01 Complex Ion
Counter-Ion
Se
[SeHgd2+ [Se(HgCH&lC [Se.Hgd2+
XNOaCI-
Framework
Te
[TeAgd2+ i%TeAsd2+ ?-[~e~gd~+ [TeAg,lS+ [TeAsd6+ ITe,Ho212+
CI0.i NO3-
Framewwk Framework
6, I
[Ikll+ [lAg21+
Pseudohalogens
NO< NO3Ci-. Br-
Framework
FNO3-
Framework
83 81. 84, 85
Chain Framewwk
[I.HsA9d2+ [ I ~ H ~ s ~ ~ ~
NOSNO3FNO3ClOI NO3CI04-
[(CN)AgJ2+ [(sCN)A%l2+ ltSeCNIAa.12+
NOsNO1 NO9-. CI0.C
Framework Framework
[IAg,l2+
17 40b 38 77 78 79 79.80 80 38
NOS-
ler~s~l+
Reference
Framework
--
86 18. 81, 83. 85. 87 18,80,83,88-90 18, 81. 87. 89, 91 47 91.92 47 81. 94, 95 81, 94. 96 97
mis gmup inciu6es several "basic sans.''
central anion and high electron affinity of the ligand cation, i.e.. low and hieh ionization notentials.. resnectivelv. " , of the corresponding atoms. In aqueous solution, the determining magnitude is the difference between the electron affinity and the energy of hydration. Therefore, cations with both high electron affinities and large radii, especially Au+, Ag+, Hg2+, Cd2+, and Pb2, are favored candidates for ligands. Lieser (18) named high polarizability of the central anion as a prerequisite, and therefore large anions such as I-, S2-, Se2-, and Te2- exhibit a tendency to form metallo complexes. In a later study (19) Lieser showed that the greater the ionization energy of the cation, i.e., the greater its electron affinity, and the greater the polarizab?lity of the two anions involved, the greater the tendency toward metallo complex formation. Often the difficulties encountered in preparing metallo complexes indicate that their free enthalpy of formation is not very great so that even small effects can reverse its sign. The nature of the anion outside of the complex is also imoortant because it mav change the lattice enerev or mav behave as a complexing ligand f& a cationic central atom. " Some t v ~ i c acomnounds l which can be formulated as metallo comaexes are ihown in Table 1, which is illustrative rather than exhaustive. Actual structures. however. are known only for n few compomds, but these structure-pnwfs have ronfirmed the validity of the metallo comolex formulation. Examination of thk known structures iisted in the table shows that metallo com~lexesdo not involve island structures, which must contain terminal metal atoms. A hypothetical island complex [Ag3S]+ and a hypothetical binuclear complex [AgzSAgzSAg2]2+would contain metal atoms with a coordination number of one, and the tendency toward formation of such structures is therefore small. Only if the hifunctionality of metallic ligand atoms is blocked, as in [(CH3Hg)4N]C104 and [(CH3Hg),P]C104, do isolated and discrete metallo complex cations result. Furthermore. Table 1 shows that onlv cations with low coordination n k h e r s act as ligands since, by definition, the coordination numbers of ligands must be lower than that of the central atom. Also, foriteric reasons, ligands belong to
-
.
U"
more than two co~rdinarionpolyhedra only in special cases. These conditions are fulfilled l)v the so-called H-metals (98). !.'or ions with a d'Oelectron amfigurntion, especially Cu+, Ag+, All7, and Hgz7, development of a ds hybrid requires only a relatively low exciration energy 199).According to crysral field theory, a n octahedral environment is then distorted so strongly that two strong linear bonds remain. A second group of ions.. ex.. ,. . TI+.. Sn2+.Pb2+. Bi3+. and Sh3+. with annarentlv ~, lowcr coordination numbers pussesss electrons as well as ten d electrons. The electrons ~artiallvoccuov .. a hvbrid of s and p orbitals, resulting in very asymmetrical and low coordination states toeether with lone-nair electrons. In his first pronounce&eut on "complex compounds with negative central atoms" (la). Werner cited the "addition products of silver nitrate and silver iodide: AgI 2AgN03" (better expressed as [Ag3I](N03)2)prepared by Hellwig (811, and this salt and the similar salts AgI.AgN03, AgBr.AgN03, AgCN.2AgN03, and AgSCN.2AgN03 (better expressed as [AgzIIN03, [Ag~BrlN03,IAg3(CN)I(N03)2,andlAg3(SCN)I(NO&, respectively), also prepared by Hellwig, still remain the classic examples of metallo complexes. In support of the metallo complex formulation, Hellwig showed that during electrolysis of the "double salt" [Ag31](N03)2,AgI migrated to the cathode. The existence of such complexes had been oredicted in 1890 bv Kistiakowskv - (100) . . on the basis of transference measurements, and this Russian chemist confirmed and extended Hellwig's findings by means of e.m.f. measurements on cells of the type AglAgN03, AgIIAgN03 (conc.)lAeNOxIA~. - -, -. which indicated the comnosition of the comple'xes formed (100,101). Werner also cited as examples the compounds Ag3P. 3AgN03 and Ag3As.3AgNO3 as containing the complex cations AgGP3+ and Ag,jAs3+. These compounds, prepared in 1883 by Poleck and Thummel (37a),may constitute the longest known metallo complexes. The number of c&npounds that can he formulated as metallo complexes has grown steadily through the years. The lack of a goodkxample nf a typical island complex may have been the reason for alternative formulations in the past. For ex-
..
~
-
+
Volume 61
Number 6
August 1984
731
ample, because be insisted on conventional cationic central atoms, Hayek (47) was forced to regard entire "salt molecules" as ligands, as in [ H g ( H g I ~ ) z ] ( C 1 0(better ~)~ $xpressed as [Hg&] (C104)~).On the other hand, Yatsimirskit formulated many compounds as metallo complexes but did not prove his assumptions (17).
reaction such as a redox reaction in the preparation of tetraargentosulfonium sulfate from silver nitrate and sulfur (37a):
Nomenclature Since the 1957 and 1970 IUPAC rules for nomenclature of inorganic chemistry (102), published in 1959 and 1971, res~ectivelv. .. did not s~ecificallvconsider metallo comolexes. these wtnpounds may be named in se\,eral different ways, and wmkers in the field have made soerific surrcrti~ms( G e ,88). By following Rule 3.14 (102a, p.i6; 1026,;: 20) and by ;sing the suffix -0to emphasize the ligand function of the metallic ion, the names used for some of the compounds discussed in the present article are obtained: [Ag,S]N03, triargentosulfonium nitrate; [Ag.&]S04, tetraargentosulfonium sulfate; [AgsSs]SO4,octaargentotrisulfonium sulfate; [Ag2I]N03,diargentoiodonium nitrate; [Ag3I](N03)2, triargentoiodonium nitrate.
or by the disproportionation of S ~ 0 3 ion ~ - in the preparation of octaargentotrisulfoninm sulfate from silver nitrate and sodium thiosulfate (76):
Preparative Methods ( 10, 11) Metallic complexes may be prepared by three different general methods shown by the following equations in which M is a metallic atom, X and Y are anions, and A is another group: (1) Addition of constituents (2) Reduction in concentration of the potential central atom X by formation of AeXb (3) Supply of a potential central atom X in the form of AX to a salt MY (a
+ b)MY + cAX
-
[X,M(,+sl]Ya + &Y.
In eqn. (I), the salts MA are often only slightly soluble in water, but they dissolve readily in a sufficient excess of MX solution. Thus, Hellwig was able to dissolve the "water-insoluble" halides and pseudohalides AgBr, AgI, AgCN, AgC1, and AgSCN in concentrated aqueous solutions of AgNOa and in the cases of the first three salts he obtained solid metallo complexes from the resulting solutions by careful dilution (81).From Hellwig's solubility data, Yatsimirskii calculated the following instability constants (17):
and he concluded that the stability of these complexes increases with decreasing ionization potential of the anion, i.e., from chloride t o iodide, a conclusion confirmed radiochemically by Lieser (87). Moreover, silver halides and pseudohalides dissolve in concentrated solutions of the corresponding alkali metal halides and pseudohalides to yield anionic complex ions. Thus, in a manner similar t o that in which metals such as aluminum, zinc, chromium, or vanadium can participate in the sequence: Cation-Polycation-Polymeric Amphoteric Hydroxide-Polyanion-Anion: with increasing [OH-] (103):
As examples of the first method may be cited the preparation of triarrent~hdoniumnitrate IJY reaction ot'the fused
iodine can participate in the following sequence with increasing [I-] (104,105): or the prrpnmtion of rrirnercuro~ll)disulfoniumchloride hy annealing the constituents in the solid state 1.38): 2HgS + HgC12
-
[Hg&]CI2
The reaction shown in eqn. (1) may be preceded by another Table 2.
Eaulllbrla In Saturated Sllver lodlde Solutions * 1105) K,, =
Species and equilibrium expression
Pure water
Solubility = [Asf 1 = [I-] = [Ad =
1.27 X lo-' 6.7 X lo-' 6.7 X 6.0 X lo-* 2.7 X lo-"
[Agll] = 4.0 X [Aglh] = 2.5 X [AglF] = 1.1 X [Ag,le-'1 = 1.5 X [Agds-5] = 2.0 X [Ag1212,-'Z]= 4.0 X [Ag2IC] = 1.0 X [Agdct] = 7.1 X [Ag41c++] = 3.7 X
10-'[I-]
=
10-3[1-]2 = 10-2[1-]3 = 10-5[1-]4 = 10-3[1-]5 = 10-6[1-]i2 = 10-6[Ag+]=
Table 2 gives the concentrations of the various species present in pure water, 1M KI, and 1M AgN03, all saturated with AgI,
[Ag+][l-] = 4.45 X lo-" Concsntrationr ol various specles in saturated Agl in: 1 molar KI 1.83 X 4.7 X lo-" 9.4 X lo-' 6.0 X 3.75 X 2.2 X 1 0 P 9.2 x IOP 1.17 X 1.5 X IOP 1.9 X lo-*
6.7 X lo-''
10-'[Rg+I2= 10@[Ag+I3=
Other complexes of the approximate composition ( A g l 2 K mmay exist. Constsnts calculated fmm solubility measurements in 4 MN~CIO.at 25' (104.
732
Journal of Chemical Education
1 molar AgNOs
4.20 X 9.83 X
4.53 X 6.0 X
lo-' lo-"
9.83 X 10 -' 6.86 X lo-' 3.52 X
while Figures 1and 2 show the concentrations of the anionic complexes and cationic complexes (metallo complexes), as functions of [I-] and [Ag+],respectively (104,105). As another example of eqn. (I),we may cite Hayek's preparation of trimercuro(II)tetraiodonium perchlorate by dissolving mercury(I1) iodide in hot aqueous mercury(I1) perchlorate followed hy cooling the resulting solution to induce crystallization (47): 2HgIz + Hg(C10dz
-
[HgsInl(ClOdz
The preparative methods given by eqns. (2) and (3) are somewhat more complicated. As an example of eqn. (2). we might cite the preparation of "basic beryllium acetate" (tetraberyllooxonium acetate), first prepared in 1901 by Urbain and Lacombe (50,51):
-
4Be(OH)%+ 3(CHsCO)zO
[Be4O](CH&00)6+ 4Hz0
As examples of eqn. (3), we might cite the preparations of dicadmiosulfonium nitrate (17)and triargentosulfonium nitrate (66): 2Cd(N03)z+ H2S 6AgNO3 CSz (+ 2Hz0)
+
--
[Cd2S](N03)~ + 2HN03 2[Ag3S]N03 Coat HN03
+
+
The latter preparation involves the hydrolysis of carbon disulfide,which proceeds only to &smallextent and yields a very
small concentration of sullide ions, thus producing the metallo complex without formation of very insoluble silver sulfide. General Properties and Analysis ( 10, 11)
Although ~atsimirskii(17) and Lieser (87) determined the instability constants of argentohalonium complexes in aoueous solution and found that their stabilities increase with &easing size of the central halogen atom, it is not known to what extent the tendency of metal ligands toward coordination in solution is satisfied by the associated water molecules. In competitive reactions the roles of the central nonmetallic atom and the metallic ligand can be interchanged so that conventional complexes with metallic central atoms are formed. For example, all argento complexes decompose on contact with molecules containing nitrogen, such as ammonia or acetonitrile, to yield immediately the corresponding silver complex: [AgdlN03 + 4NH3
-
[Ag(NH3)~12N03. I
Since metallo complexes are predominantly polynuclear species, in many of their reactions the complex ion remains intact and the compounds exhibit ion-exchange properties. As examples of anion-exchange behavior, we may cite the exchange of nitrate ions for chloride ions in triargentoiodonium nitrate (87):
+ 2KC1- [A~~IICIZ + 2KN03 [Agd](N03)~ or the reaction of trimercuro(I1)disulfonium chloride with nitric acid (38): [Hg9z]Clz+ 2HN03
-
+
[Hg3Sz](N03)~ 2HC1
As an e x a m ~ l eof cation-exchanee behavior. we mav cite the
replacemmi of potassium ions b;tetraalkylammo&n ions in potassium mercnro(I1)sulfonatoamidate (34):
Many metallo complexes decompcae into their constituent salts on treatment with excess water-the reverse of eqn. (1). This renders their analysis extremely simple and convenient. For example, for argento complexes the precipitated insoluble silver salt may be collected, dried, and weighed, while the soluble silver salt may be determined in solution by appropriate means such as the Mohr or Volhard titration: -log [I-] Fiwe 1. LogariUnnic concenbation diagam showing U?evariols mncenbatim as a functionof [I-] in saturated Agi solutions ( 105). AgN03+ KSCN
Ferris Alum Indicator
AgSCN&+KNO,
Decomposition of the complexes by moisture and other conditions occurs easily but it is difficult to recognize. Therefore, the results of chemical analvsis are not sufficient evidence for a successful synthesis. Only X-ray analysis or measurement of either reflectance swctra or Niuol mull visible-ultraviolet spectra on filter can uniquely identify the compounds. Structures
Typical examples of each of the four types of structures for metallo complexes will now be given.
-log [Ag+l Figure 2. Lmaribmic mncenbation diagam stowing b e various mncenbatims as a function of [As+]in saturated Agi solutions ( 105).
Two-Shell Complexes or Super-Complexes In the structure of tris(chloromereuro(~))oxonium chloride, [(HgC1)30]C1(Fig. 3), the central oxygen atom occupies the anex of a trieonal nvramid. the base of which is formed bv three Hg at&s at histances of 2.06 A (sum of covalent radii = 2.10A). whtrhare bonded toCI atoms at a distanceof 2.29 &. (H~-CIdistance in HgClz = 2.34 A), forming a second sphere Volume 61 Number 8 August 1984
733
of covalently honded ligands around the central 0 atom. The C1- ions a t distances of 2.99 A and 3.09 .&fromthe Hg atoms are considered to lie outside the complex (43f). In the well-known "basic beryllium acetate" (tetraheryllooxonium acetate), [Be40](CH3C00)6(Fig. 4), the central 0 atom issurrounded tetrahedrally by four Be atoms, and the CH3COO- groups act as chelate ligands, linking the Be atoms in pairs and forming an "inner complex salt" (nonelectrolyte) (16,49-52). Since the Be atoms, like the 0 atom, also have a coordination numher of four, the compound may he considered as a tetranuclear Be complex, hut 0 is the central atom. Chain Complexes "Hasic mercury chlorate" (hydrogrnmerruro(ll~oxonium chloratc). IHgOHIClOn (Fig. 51,contains a chain of dwrnating
Hg and 0 atoms (45). The 0 atom has a coordination numher of three, while that of Hg is two since the C103- ions lie at the ionic bond distance. "Mercuric amidohromide" (mercurolIl)an~moniumhrumide), I H ~ ( N H , I ] Hhasasimilar ~, chain structure of alternating He- .(coordination number 21 and N atoms (coordination numher 4) (33). Layer Complexes In trimercuro~11)dioxoniumsulfate, [Hg302]S04(Fig. 6), the Hg and 0 atoms form networks, the meshes of which contain the ionically honded S042- ions (H 0 distance in complex = 2.03 A; Hg-OS03 distance = 2.47 The central 0 atom has a coordination numher of three (46). "Mercuw imidohromide" (trimercuro~1l)diammoniumtrihromomekcurate(11)bromide), llIg:~(NH!~,lHgBr:yBr,has a similar layer structure (32)
5).
Frame work Complexes Triargentosulfonium nitrate, [Ag&]NOs (Fig. I), possesses a cuhic structure containing approximately trigonal prismatic SAg, groups linked through common corners to form a three-dimensional framework. The ionically honded NO3groups are located in the cavities (66). Other framework complexes include the dimercuro(11)ammonium salts, [HgzNIX (281, and dimercuro(II)phosphonium trichloromercurate(I1). [Hg2P]HgC13 (38). These complexes possess a tridymite structure in which the tetrahedrally coordinated
Figure 3. View of th_e unit cell of tris(chloromercura(1I))oxonlum chloride, [(HgC1)30]CI. along 310 planes.
Figure 5. Hydragenmercurdiib~~ni~m chlwate. [HgOHICIOs (plottedhorn data in (45)).The chain consists of alternating OH(0) and Hg Ions ( 0 ) .
O~, Figure 4, me maiacule of tebaberyllwxonlumacetate. [ O B ~ ~ ( C H J C Odrawn (not strictly to scale) to show the central oxygen atom (large shaded circle) surrounded tetrahedrally by tour Be atoms (small shaded circles). An acetate group lies beyond each edge of thetetrahedron. Each Be atom has four 0 atoms amanaed tetrahedrallv as nearest nelahbms. . the cenbal one and three of diflerent acetate groups. (Small unshaded circles represent C atoms: H atoms are amined.) ( l lo).
734
Journal of Chemical Education
Fqure 6 TI mercudllW oxonoum sulfate. IHg3021S04(pMed ham data m 1331 The snuller circles represent threc-coaomate 0 atoms and the larger circler represent two-coordinate Hg atoms,
Si atom is replaced by N or P and in which the dicoordinate 0 atom is replaced by Hg. The ionically bonded groups are located in the spaces between the tetrahedra. In triargentoiodonium nitrate, [Ag3I](N03)2 (Fig. 8), the Ag atoms form somewhat distorted trigonal prisms, IAg6, in the center of which the I atoms are located. These prisms are connected a t corners parallel to the a axis and on edges parallel to the c axis. Ag-I distances range from 2.83 .& t o 3.08 .&, and the NOS- groups fill the space remaining between the prisms (91). It should be mentioned that some compounds which have formulas that are similar to those of genuine metallo complexes, e.g., AggSzSi04 (107), c--Ag4Te(N03)~(108), and Ag3SI (1091, actually have completely different structures. These comnounds show statisticallv distributed silver atoms and a consLquently high conduct;vity. The compound a-Ag4Te(NO,)., ~ o i i i h l vshows that lnerallo comolexes can in orinciole be transformed to fast ionic conductors-at high temieratuies because of their small energy of formation. The Experiment Several metallo complexes with different central atoms are prepared according to procedures modified from the literature, and their properties are observed. If desired, they may also be analyzed. In the case of the soluble argentoiodonium compounds, the solutions of the metallo complexes are subjected to electrophoresis. Additional compounds may be prepared by consulting the references cited in Table 1. CAUTION: T h e toxic n a t u r e of mercury a n d beryllium compounds should b e kept i n mind. Nitronium Complexes Trimercuro(II)diammonium Tribromomercurate(II) Bromide, [Hg3(NHz)z]HgBrsBr (Empirical formula, HgzNHBrz) (32). A solution of 2.16 g (0.006 mol) of HgBrz in 80 ml of boiling H z 0 is added with mechanical stirring to a solution of 0.2 g (0.002 moll of NH4Br in 100 ml of 0.1 M aq
Figure 7. Triargentosulfoniumnitrate, [AgZINO. (86).Ag ions are located at the caners of the polyhedra and S ions are located at the centers of the polyhedra.
NH.,. The resulting yellow precipitate is collected irnrnedinte!, on a Huchner funnel while the mixrureisstill hot. The product is washed with fivp 50-rnl rwrtions uf cold HoO. air-dried. and dried over NaOH in a desiccator. Yield, 1.40 (81.0%).'~he yellow, light-sensitive powder is soluble in KI and KCN (CAUTION: TOXIC!) solutions but insoluble in organic solvents. On shaking with cold aqueous NH3 i t yields dimercuro(II)ammonium bromide, [HgzNIBr. Dimercuro(II)ammonium Bromide, [HgzN]Br (28). T o a solution of 16.5 ml of concentrated aqueous NH3 in 1600 ml of HzO is added with magnetic stirring for 10 min a solution of HgBrz (4.88 g, 0.0135 mol) in 800 ml of H20, saturated a t 20°C. The resulting light yellow precipitate is collected on a Biichner funnel and washed with three 5-ml portions of Hz0 until the filtrate is free of Br- ion. The product is dried for 1 hr a t 110°C and stored in uacuo over Silica GeP. Yield, 2.89 g (86.2%). The compound is stable in air a t ordinary temperatures but decomposes to metallic Hg in sunlight. I t is insoluble in H z 0 and most organic solvents but soluble in aqueous acids. Bubhling HzS into an aqueous suspension quantitatively precipitates the Hg.
g
Oxonium Complexes
Tris(chloromercuro(II))oxoniumChloride, [(HgC1)30]Cl (43). A mixture of 3.79 g of HgClz (0.014 mol), 0.240 g of NaOH. and 1.441 e of HqO is allowed to stand for two weeks in R stc;ppered 1,rown or actinic red flask at room temperature. (An ordinarv flask nrotected f n m light with foil wraooine is satisfactory:) The khite precipitate-is collected b y s k t i o n filtration (sintered-glass funnel), washed with HzO, air-dried, and stored in uacuo over DrieriteB. Yield, 1.09 g (30.9%). The light-sensitive compound is stable in air and can be heated to 100°C without decomposition. On heating, HgClz sublimes, and various basic mercury chlorides are formed depending upon the temperature. The compound is difficultly soluble in cold HzO, and on heating in HzO it hydrolyzes to form black HgClz2Hg0. It is easily decomposed by dilute acids and bases. Treatment of a suspension results in quantitative precipitation of the Hg. The compound possesses ion-exchange prop-
Figure 8. Triargentoiodonium nitrate, [Ag31](N03)2(plotted from data in (91)). Ag ions are located at the corners of the prisms, and the I ions (large circles) at the centers of the prisms.
Volume 61 Number 8
August 1984
735
erties; the CI- ions outside the coordination sphere can be replaced by F- ions. Tetraberyllooxonium Acetate ("Basic Beryllium Acetate"), [Be4O](CH3C00)6 (52). 4 g of basic beryllium carbonate is magnetically stirred with 8 ml of glacial CH3COOH on a hot plate until C02evolution ceases. The resulting solution is cooled to room temperature, and the crude product that crystallizes is collected by suction filtration and air-dried. I t is dissolved in 6 ml of CHC13, and any undissolved material is removed by filtration. The solution is evaporated to dryness on a steam bath. The colorless octahedra are freed of residual CHCI3 in a vacuum desiccator. Yield, 2.8 g (65%,based on a basic carbonate containing 26.6% BeO). The product (m.p., 284286°C) is soluble in the usual organic solvents except CzH50Hand (C2H5)20.I t is insoluble in cold Hz0 but is hydrolyzed by hot or dilute acids. Sulfonium Complexes Triargentosulfonium Nitrate, [Ag3S]N03 (66). A solution of 10.0 g (0.0588 moll of AgN03 in 10 ml of 2 N HN03 is mechanicallv shaken viaorouslv with 1.70 ml(0.0282 mol) of CS? (CAIJT~ON:~ l a m m a b l and e tonic) in a stoppered brown or actinic rrd flask for 24 h. (An ordinarv flask protected from light with metal foil wrapping is satisfictory.j The resulting vellow precipitate is collected bv suction filtration (siniered-grass funnel), washed with three 10-ml portions of4 N HN03 and three 10-ml portions of CH30H, and air-dried in the absence of light. Yield, 3.9 g (48%).The product is lightsensitive, becoming green and eventually black. I t is decomposed into AgN03 and AgzS by water and all organic solvents that dissolve AgN03, e.g., C H C N , CsHsN, or dimethylformamide. I t is remarkablv stable toward HNOI. Tetroargentosullonium 'Sul/ote, [Ag4S]S04(37b).A solution of 25g (0.147 mol) of AgNOj in 06 ml of H20 is added with stirring tu a solution of 2.50 g (0.0156 mol) of Na2S2O3. SH?O in 20 ml of HoO. The resultine reddish brown ~recioirate is collected by &tion filtration (sintered-glass funnel), washed twice successively with 25-ml portions of H20, 95% CZH~OH, and (CzH5)20, air-dried for 30 min, and stored in uacuo over HzS04. Yield, 5.48 g (62.74%). The scarlet crystalline product dissolves in boiling HN03, is decomposed by boiling Hz0 into AgzS and Ag2S04, and by cold HCI into AgCl and AgzS. It is stable to 180°C, but on ignition it yields Ag and &
.
soz.
Octaargentotrisulfonium Sulfate, [Ag.&]SOa (76). 300 ml (0.060 mol) of 0.2 M AgN03 is added with mechanical stirring to 300 ml (0.006 mol) of 0.02 M NazS2O3solution, whereupon a precipitate, changing from white to yellow to orange and finally to brown, forms immediately. The mixture is protected from light and stirred mechanically for 2 days. The brown nroduct is collected bv suction filtration (sintered-glass fimnel), air-dried withoit washing, and stored in adesiccator over Drieritc.m Yield. 1.94 e (92.0al. The brown. microcrystalline, light-sehsitive produit (m.p:, 405'C) is solid electrolyte with an irreversible transition point a t 246OC.
a
lodonium Comolexes Diargentoiodonium Nitrate, [AgzI]N03 (81). T o 70 ml (0.105mol) of a boililw 1.5 M AgNOn solution is added in small portions with vigorous mechan'&al ~&rring2:1.48~ (0.100 mol) of freshlv A d . Heating and stirrine is rontinued for . prepared - 15 min after all the A ~has I be& added. he remaining undissolved AgI is removed by suction filtration (sintered-dass funnel) of the hot mixture.-T~Plight-sensitive solution isset aside in the dark for 24 hr. The resulting white, crystalline product is collected by suction filtration isintered-glass funnel), washed with three 5-ml portions of absolute CzH50H, and air-dried. Yield, 3.85 g (14.3%,based on dissolved AgI). The product is quickly blackened by light. I t is decomposed by Hz0 and by aqueous CzHsOH to yield a solution of 736
Journal of Chemical Education
AgN03 and a pale yellow AgI precipitate. I t is insoluble in absolute CzHsOH. With NH4SCN solution it yields [AgzIISCN. Triargentoiodonium Nitrate, [Ag3I](NO3)z (81). TO 50 ml (0.150 mol) of a boiling 3 M AgN03 solution is added in small portions with vigorous mechanical stirring 17.6 g (0.075 mol) of freshly prepared AgI. Heating and stirring is continued for 15 min after all the AgI has been added. The remaining undissolved AgI is removed by filtering the mixture through filter paper on a glass funnel which is kept hot witb a funnel heater. The light-sensitive solution, which begins to crystallize immediately on cooling, is placed in an ice bath in the dark until precipitation appears complete. The white, crystalline product is collected by suction filtration (sintered-glass funnel), washed with three 20-ml portions of absolute CzHbOH, and air-dried. Yield, 14.45 g (50.3%,based on dissolved AgI). The product (m.p., 115-116°C) is stable in dry air, decomposes in moist air, and is blackened by light. I t is decomposed by Hz0 and aqueous CzH50H to yield a solution of AgN03 and a pale yellow AgI precipitate. I t reacts witb aqueous NaOH to yield AgzO and AgI, with aqueous HCI to yield AgI and AgC1, witb aqueous HI to yield AgI, and with aqueous NaHC03 to yield AgI and Ag2C03. Evidence for the cationic nature of the [Ag21]+and [Ag31]2+ ions is obtained by filter paper electro~horesisexperiments in which the iodine is shown to migrate toward thk negative pole. Solutions of [Ag21]N03and [Ag3I](N03)2in AgN03 solutions of the appropriate concentrations (1.5 M or 3.0 M, respectively), with additional AgN03 solutions of the same concentration as the supporting electrolyte, are subjected to filter paper elertro~horriisunder a ~otentialof 90 V d.c. (dry cell). H;O cannot be used as solvent or as supporting ele& trolyte because it causes the compounds to decompose into their components. Alternatively, the mother liquors from the preparation of [AgzI]N03or [AgsI](NO& may be used in lieu of the solutions of the solid compounds in AgN03 solutions of the appropriate concentrations; AgNOs solutions of the .. . appropriate concentration arp required as supporting electrolytes. About 1 hr is sufficient to cause detectable migration of the compounds. To detect the presence of the compounds several drops of Hz0 are added to the paper. The formation of a spot of pale yellow AgI caused by decomposition is visible. If desired, 0.1 M solutions of salts containing colored cations (e.g., CuSOa or Ni(N03)~)or colored anions (e.g., KzCr207 or KMn04) may also first be subiected to electro~horesisto ensure that the apparatus is functioning and t o establish the polarity of the electrodes. Reversine the ~ o l a r i t vof the electrodes reverses the direction of migration. Acknowledgment The authors wish to acknowledae the experimental assistance of Michael M. Kitamura, ~ a n i eJ.l ~heltraw,and David E. Thompson and the financial assistance of the California State ~niversity,Fresno Research Committee for an institutional grant. They are also indebted to Dale C. Burtner, Richard P. Ciula, and Stanley M. Ziegler for valuable discussions and to Heinz Cassebaum for assistance in locating literature sources. Literature Cited (1) Werner, A,, "Neucre Ansehavungen auf dem Gebicte der anorganiarben Chemie," f i e d t i c h Vieweg und Sohn, Brsunschveig, (a) 2nd ed., 1909, p. 246: (b) 3rd ed.. 1913,p. 30% (c) 4th ed., 1920,~.307. (2) Kauffman, G. B., "Alfred Werner: Founder of Cwrdination Chemistry," Springer-
Verlag,Bsrlin,Heidelberg, New Ymk, 1966. (3) Jon=, M. M.. "Elementary Coordination Chemia~y?Prentiee-Hd. Ine.. Englcvoad Cliffs. NJ. 196S.p. 36. (4) Previoua papers in this seri-Lanthanldea: Kauffman, G. B.. and Blank, J. S.. J. OmM. EDUC.,37.156 (1960): K~uffmm.G.B.,Tak&mhi, L. T..and Vieken.R. C.. J. CHEM. EDUC., 40, 433 (1963):Rpallution of coordination compound% Kauffman, 0.B.,andT&ahashi,L.T., J.CHBM.EDUC..39,481(1982):Ksuffman,
(49) Tulinsky, A , Worthington, C. R., and Pignataro, E., Acta Crysfollogr, 12, 523 119691. (50) Urbain. G., andlammbe, H., Compt. rend.. 133,874 (1901). (51) Lacombe. H.. Campt. rand. 134,772 (1302). (52) Moeiier, T.. Inorg. S y n . 3.4 (1950). (53) Addipan, C. C., and Walker, A.,Proe. Cham. Soc., l961,242. (54) Kurdluma; G. M., and Samenenko, K. N., VestnikMoakau. Unio., 12,Ser Mot., Mekh.,Artron., Fiz.,Khim., No. 3,265 (1957); Chem. A b d r , 52.699% (1953). (55) Hardt, H. D., Z. onarg. allgem. Chem., 293,47 (1957). (55) Gupta, A,, Sei. and Cult. (Coleuttn), 25,426 (1960). (57) Gstroff, A. G., and Sanderson, R. T., J. Inorg. Nuel. Chem., 9.45 (1959). (58) Hardt, H. D., and Stavenow, F., Z. onorg. allgem. Chem., 301,267 (1959). (591 Denk. G.. Chem. Ber. 92.2236 (19591.
.~ .
New Yark, Paris, 1969. (9) "Stability Constante 01 M8tal-Ion Compi-, SeetiseetiseetiI: Ino'ganiiL'landa (Campiled by L. 0. Sill4n). Section 11: OIganie Ligands (compiled by A. E. Martell)." The Chemieai Soeiety, London. 1964; Supplement N o 1, Chemical Society Special Publicstion No. 25, The Chemical Saiety, London, 1971. (10) Bergerhoff, G.."Ueber Metallo Komplexe," Hsbilitationuehrift.UnivenitbtBonn. Bonn, 1962. (11) Bargcrhofl, G.,Angew. Chem.,76,097 (1964) (inGsrman)iAwew. Cham.,lntemat. Ed., 3,636 (1964) (in English). (12) Hein, F., "Chemische Koardinationalehre." S. H i n d , Leiwig, l95O.p. 217. (13) Remy. H., "Lehrbueh der snorganischen Chmie," Ahdemisehe VerlagsgeseUaehaft Geest und Portig, Leipzig, 1959,Voi. 2, p. 354. (14) Kauffman, G. B., Caord. Chem Re"., 9,339 (1973). (15) khwanenbaeh, G.."Allgemcine undano&heChunia," S . H h e l . S t m 194% " rn, (18) Bergerhoff, G.. andPseslaek, J . . Z Kriatollogr. 126.112 (1956). (17) Yateimirski;.K. B.,DoklodyAkod. No~kS.S.S.R.,77,819(1951); Chem.Ab.lr, 45, ""C.," ,-"a-
,,a=., \."".,.
. .. (€6)Bcrgerhoff, G.,Z omrg ollgem. Chom., 299,328 (1959); Kaunmao. G. B . . a n d k gerhoff, G.. Inorg. Syn.. 24, in p m s . (67) Stamm, H., and Wintzer, H.,Ber, 71,2212 (1938). (56) Bouknipht,J. W , and Smith, 0. M., J.Amar Chsm Soe., 61.28 (1939). (69) Smith, G. M., and Semon, W. L.. J.Amer Chom. Soc, 46,1325 (1924). (70) Bernardi,A.,andRossi,G.,Oarr.
