arguably one of the 
 most important conceptual breakthroughs in modern structural chemistry 
 was robson s geometric interpretation of the structures of 
 coordination polymers as connected nets of nodes and linkers . the language of reticular chemistry that developed 
 from that point has enabled the informed design of an extraordinarily 
 large family of framework materials and coordination polymers , notably 
 including metal  organic frameworks ( mofs ) and covalent organic frameworks ( cofs ) . the 
 basic design approach as it is currently used reflects the realization 
 that specific combinations of node and linker geometries can usually 
 lead to only a finite number of different possible structures ; hence , control over the former ( e.g. , the choice 
 of transition - metal elements or clusters with specific coordination 
 geometry preferences and linkers with characteristic binding modes ) 
 enables control over the latter . the abstraction of linker molecules to rodlike connections carries 
 with it the implication that linker shape and chemistry bear little 
 influence on the resulting framework structure . certainly this is 
 sometimes true , but for many coordination polymers 
 the packing motifs and stereochemical preferences of the organic linkers 
 often play a defining role in directing structure . this may be as 
 simple as linker functionalization preventing network interpenetration 
 but the effects can also be altogether more drastic . for example , if the terephthalate linker connecting chains 
 of corner - sharing alo4(oh)2 octahedra in the 
 porous  breathing mil-53 ( ref ( 10 ) ) is swapped for the longer 
 and slightly bent 4,4-azobenzenedicarboxylate then the nonporous 
 layered mil-129 forms instead , where the ligands now adopt a  
 stacking motif . it is in this context 
 that we have developed a particular interest in coordination polymers 
 assembled using the dicyanometallate linker [ nc  m  cn ] ( m = cu , ag , au ) . the preferred coordination mode of this linker is linear , and 
 so it combines the nanometre scale of the organic linkers used to 
 build mofs with the geometric flexibility of an atomically thin linker . 
 in many ways , dicyanometallates can be considered the natural extension 
 of oxide frameworks ( e.g. , perovskites ) and cyanide frameworks ( e.g. , 
 prussian blues ) [ figure 1 ] . increasing scale of oxide ( blue ) , cyanide ( green ) , and dicyanometallate 
 ( red ) architectures illustrated with the perovskite ( a ) and cristobalite 
 ( b ) structures . increasing the length of the linker dramatically increases 
 the available volume for interpenetration , extra - framework cations , 
 and/or neutral guests . node metal ( gray ) , oxygen ( red ) , nitrogen ( blue ) , 
 carbon ( black ) , and linker metal ( yellow ) . like their oxide and cyanide cousins , dicyanometallate frameworks examples include 
 colossal positive and negative thermal expansion in silver hexacyanocobaltate 
 ( co[ag(cn)2]3 ) ; giant negative compressibility and 
 guest - dependent luminescence in zn[au(cn)2]2 ; piezoelectric behavior in kco[au(cn)2]3 ; tunable room - temperature 
 luminescence in la[auxag1x(cn)2]3h2o ; vapochromism in cu[au(cn)2]2 ; heat- , light- , and pressure - induced 
 spin - crossover in fe(pyz)[ag(cn)2]2pyz 
 ( pyz = pyrazine ) ; and strain - free charge 
 storage in kxfe[ag(cn)2]3 . in each of these 
 cases , the geometric flexibility of the dicyanometallate linker plays 
 a key role and so there is good reason to expect similarly intriguing 
 functional responses among as - yet - unrealised dicyanometallate frameworks . 
 yet , in this context of developing new functional dicyanometallates , 
 what is conspicuously absent is an overview of the structural chemistry 
 of the family of the sort that has been so enabling in , e.g. , oxide and cyanide framework chemistry . table 1 summarizes , to the best of our knowledge , 
 the various dicyanometallate frameworks reported to date . for simplicity , 
 we have focused on systems expressible in the form ambxn{guest}. in this representation , 
 a denotes an extra - framework cation ( if present ) , b is the framework 
 node cation , x is a dicyanometallate anion , and we allow for the presence 
 of solvent or other neutral molecules within the structure . what is 
 immediately clear is that the family is extremely diverse , and encompasses 
 much of the compositional and topological complexity responsible for 
 the rich structural chemistry of conventional ceramic frameworks . 
 in addition , and as in the transition - metal formate mof perovskites  , there is the intriguing capacity to incorporate molecular cations 
 as a means of balancing framework charge . there is strong current 
 interest in these systems as a direct result of the recent discovery 
 of unconventional semiconductor behavior in the [ ch3nh3]pbi3 family of solar cell materials . ordering processes involving molecular cations can be fundamentally 
 different from those involving spherically symmetric or dipolar cations , 
 as in conventional oxide ceramics . the 
 relationship between molecular geometry and host framework topology 
 remains relatively unexplored  particularly in dicyanometallates . likewise , the nanometre node separation in dicyanometallate 
 frameworks potentially allows for the incorporation of molecular cations 
 capable of complex supramolecular interactions . formulae 
 including au / ag indicate that both the pure gold- and silver - containing 
 compounds are known . newly synthesized compounds reported as part 
 of our study are indicated by an asterisk . abbreviations used : l = n-(3-aminopropyl)-5-bromosalicylaldimine ; 
 2,2-bpy = 2,2-bipyridine ; et = c2h5 ; 3-cnpy = 3-cyanopyridine ; tpt = 2,4,6-tris(pridyl)triazine ; 
 me = ch3 ; pmd = pyrimidine ; py = pyridine ; 3-phpy = 3-phenylpyridine ; 
 deas = 4-diethylaminostilbazole ; dmf = n , n-dimethylformamide ; dmso 
 = dimethyl sulfoxide ; nit4py = 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide ; 
 phen = 1,10-phenanthroline ; 2,2-bpe = 2,2-bis(pyridyl)ethene ; 
 3-fpy = 3-fluoropyridine ; 3-mepy = 3-methylpyridine ; 4-mepy 
 = 4-methylpyridine ; 3-clpy = 3-chloropyridine ; 3-brpy 
 = 3-bromopyridine ; 3-ipy = 3-iodopyridine ; bim = benzimidazolate ; 
 pyz = pyrazine ; 4,4-bpy = 4,4-bipyridine ; bpmp = 1,4-bis(pyridin-4-ylmethyl)piperazine ; 
 hydeten = n-(2-hydroxyethyl)ethylenediamine ) ; 
 nit3py = 2-(3-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide ; 
 ppn = bis(triphenylphosphine)iminium cation ; bu = n - c4h9 . the first 
 aim is to report the structures of a number of new dicyanometallate 
 frameworks which contain molecular cations . on the one hand , these 
 are of fundamental interest in terms of their structural chemistry , 
 but on the other hand they may prove important by virtue of their 
 conceptual relationship to other molecular analogues of conventional 
 ceramics , including the semiconducting lead iodide family . the second  and 
 ultimately more important  aim of our study is to suggest an 
 organization of the structures of known dicyanometallates that helps 
 rationalize the structural diversity of this family . in doing so we 
 begin to develop a set of design strategies that will ultimately allow 
 rational control over framework structure in precisely the way envisaged 
 by robson s original study . our starting point is to describe the various new dicyanometallates 
 we have prepared . motivated by the desire to introduce molecular extra - framework 
 cations , our typical synthetic strategy was to combine a simple transition - metal 
 salt with a specially prepared molecular salt of a given dicyanometallate 
 anion . the latter acts as the source of molecular cation in the framework 
 that ultimately forms . we report eight new compounds , which adopt 
 a total of five structure types and correspond to the three fundamental 
 compositions abx2 , a0.5bx2.5 , and 
 abx3 . the first 
 system we describe was actually the fortuitous result of our attempts 
 to prepare [ net4][ag(cn)2 ] as a dicyanometallate 
 precursor for subsequent framework formation . the combination of [ net4]cl or [ net4]br with kag(cn)2 yields 
 the same dicyanometallate framework [ net4]ag[ag(cn)2]2 ( 1 ) in which silver(i ) 
 cations participate as both node and linker . the dual roles of silver(i ) 
 in this system are distinguishable by both coordination geometry and 
 cyanide binding orientation : the node cations are tetrahedrally coordinated 
 by the n cyanide terminus and the linker cations are linearly coordinated 
 by the c cyanide terminus . the crystal structure is illustrated in figure 2 , and relevant crystallographic 
 details are summarized in table 2 . three distorted diamondoid networks interpenetrate , 
 with each [ net4 ] cation contained within a 
 cavity formed by the combination of all three networks . representations 
 of the crystal structures of the various new dicyanometallate frameworks 
 reported in this study . the top panels show structures in thermal 
 ellipsoid representation ( probability = 50% , or 90% where indicated 
 with an asterisk ) . each image is represented at the same absolute 
 scale ; extra - framework cations and solvent molecules have been omitted 
 for clarity . the bottom panels show schematic representations of the 
 corresponding network topologies . in each case a single extra - framework 
 cation is shown in space - filling representation to illustrate the 
 relationship between cation shape and network topology . an intriguing property of this system is the existence 
 of a phase transition on cooling below 235 k. this transition  which 
 will be described in detail elsewhere  involves the condensation 
 of a soft phonon mode at an incommensurate wave - vector . the study 
 of classical soft - mode transitions in extended frameworks is a relatively 
 unexplored field ; the purpose of drawing attention 
 to this transition here is simply to highlight that the dynamical 
 properties of these materials may , in due course , be of interest in 
 their own right . reaction of [ nbu4][ag(cn)]0.5h2o with cadmium nitrate leads to the structurally complex phase [ nbu4]0.5cd[ag(cn)2]2.5 ( 2 ) , as illustrated in figure 2 . key crystallographic details of 2 are again summarized in table 2 . in the absence of a strong coordination preference these pentacoordinate nodes connect to give a unique , self - catenating 
 topology ( topos reference jah1 ; the topology was 
 detected with topos and deposited in the ttd archive ) that can be related to a linked pair 
 of interpentrating cds - type nets ( see supporting information ( si ) ) . mindful that correlation does 
 not necessarily imply causation , we note nonetheless that there is 
 again a close match between framework cavity and molecular cation 
 shape . this suggests that the form of the [ nbu4 ] cation may be responsible for the unusual topology assumed by this 
 material . as in 1 and numerous other dicyanoargentate 
 frameworks , 2 contains a series of short agag contacts generally considered indicative 
 of dd argentophilic interactions . these interactions are often strongly susceptible to changes in external 
 conditions , such as temperature and pressure . we determined the thermal expansion behavior of 2 in 
 order to identify any unusual thermomechanical response , and found 
 moderately strong positive and negative thermal expansion in directions 
 that are respectively parallel and perpendicular to these argentophilic 
 interactions (  = + 138(5 ) mk ,  = 83.1(1.6 ) mk ; see si for further discussion ) . an alternative five - connected dicyanometallate 
 structure that is more obviously related to the molecular perovskite 
 analogues discussed above can be accessed by reaction of [ ppn ] dicyanometallates with transition - metal salts ( [ ppn ] = bis(trisphenylphosphine)iminium cation ) . the crystal structures 
 of [ ppn]0.5cu[au(cn)2]2.5etoh 
 ( 3a ) , [ ppn]0.5mn[ag(cn)2]2.5(etoh ) ( 3b ) , and [ ppn]0.5cd[ag(cn)2]2.5(etoh ) ( 3c ) are shown in figure 2 , and key crystallographic 
 details are again summarized in table 2 . in these compounds , the dicyanometallate network 
 forms grid - like layers of connected cubes that are then stacked on 
 top of one another . the large molecular cations occupy the voids at 
 the center of each (nm ) cube . because the layers 
 are not connected , each transition metal node is coordinated by dicyanometallate 
 anions in a square pyramidal geometry . whereas in the case of cu this coordination geometry is straightforwardly understood 
 in terms of the d electronic configuration , 
 for 3b and 3c the mn and cd coordination is actually octahedral and is completed by 
 one molecule of the ethanol solvent from which the crystals were grown . the ability to incorporate octahedral node geometries via solvent 
 coordination means that , in principle at least , this phase may be 
 accessible for a range of other transition - metal dications . in practice , the balance with competing phases ( discussed further below ) is remarkably 
 subtle . in each of the compounds 3a  c , successive layers are offset by one - half of the cube face 
 diagonal . this offset has the effect of bringing ag or 
 au cations at the cube edges into close contact , which 
 will presumably maximize metallophilic interactions . in this sense there is a clear distinction from the structural chemistry of oxide 
 frameworks , where there is a strong repulsion between the linker anions . 
 in the related n = 2 ruddlesden popper phases 
 ( e.g. , sr3ti2o7 ) this repulsion is 
 relieved by presence of additional a - cations as rocksalt - type layers . in our case , the weak metallophilic forces 
 holding neighboring layers together may be expected to result in particularly 
 anisotropic elastic response for this family , while also allowing for the possibility of intercalation 
 chemistry . the analogy 
 between dicyanometallate frameworks and perovskite oxides is clearest 
 in the last family of compounds we report . similar 
 conditions to those described above for 3a  c allowed preparation of the abx3 solvate [ ppn]cd[ag(cn)2]33etoh ( 4 ) and the solvent - free 
 frameworks [ ppn]mn[au(cn)2]3 ( 5a ) and [ ppn]cd[au(cn)2]3 ( 5b ) . 
 in the case of 4 , crystals grew directly from reaction 
 mixtures that had originally formed crystals of 3c ; the 
 relationship between these phases is discussed in more detail below . the structures of all three compounds 4 , 5a , 5b are clear analogues of perovskites : octahedrally 
 coordinated mn / cd centers are connected 
 to form the characteristic cubic network , with [ ppn ] cations 
 adopting the  12-coordinate  a - cation site [ figure 2 ] . we use the term 
  super - perovskites  to reflect this structural correspondence 
 and to emphasize that the bb separation across the 
 perovskite cube edge is now on the nanometre scale . just as 
 for other perovskite analogues , long - established geometric descriptors 
 can be applied to these superperovskite frameworks . for example , we 
 calculate  tolerance factors  of 1.02 ( at 150 k ) and 
 1.00 ( at 300 k ) for 5a and 5b , respectively 
 ( see si ) ; likewise the octahedral 
 tilt systems active in both structures correspond to the same glazer 
 notation aac . while the tilts of compounds 5a and 5b can be described completely using glazer notation , compound 4 shows in - phase tilting of adjacent octahedra correlated 
 perpendicular to the rotation axis : an impossibility for perovskites , 
 such as oxides and halides , with monatomic anions . the tilt system 
 of 4 is described by the following tilt tensor ( see si for discussion of this notation ) : because the phenyl groups of the ppn cation extend 
 up to the perovskite cube faces , there are direct cation  cation 
 interactions that may influence the phase transition behavior of these 
 systems . in contrast to the simple monopolar and/or dipolar interactions 
 between a - site cations in oxide perovskites , these interactions are 
 inherently multipolar , which in turn may give rise to complex ordering 
 processes unrealisable in conventional ceramics . indeed the ppn conformations we observe in compound 3c and 
 its transformation product 4 are fundamentally different 
 from those found in 5a and 5b : in the former 
 the phenyl rings are oriented as if to maximize cation 
 interactions with the linker ag cation , whereas in the 
 latter intra- and inter - molecular  interactions 
 dominate ( figure 3a , b ) . this is entirely consistent with the diversity of ppnppn supramolecular interaction motifs known to occur in the solid 
 state . so one alternative view of the 
 structures of 5a and 5b is that the anionic 
 dicyanometallate framework acts to impose a particular geometric arrangement 
 of the ppn cations that may not necessarily be compatible 
 with the inter - cation interactions . we suggest that exploration of 
 this tension between complex multipolar interactions and the geometry 
 of the lattice supporting those interactions may be a fertile playground 
 for future research given , for example , the implication of multipolar 
 dynamics in extending charge - carrier lifetimes in [ ch3nh3]pbi3 ( figure 3c , d ) . short cation 
 and  interactions in 3c ( a ) and 5b ( b ) . the phenyl rings are oriented such 
 that short cation distances are maximized , whereas 
 in 5b intra- and inter - molecular  
 interactions dominate . [ ppn ] cations are inherently 
 multipolar and their packing in 4 ( c ) corresponds to 
 ordered hexapoles . such multipolar interactions are common for framework 
 materials with molecular cations such as [ ch3nh3]pbi3 ( d ) where the dynamics of these interactions are 
 implicated in slow exciton recombination ( cation - ordered pnma structure shown ) . framework shown in gray , cation 
 in teal ( a , b ) , and multipoles in teal and red ( c , d ) ; h atoms not shown 
 for clarity . given the diversity of 
 known structures of dicyanometallate frameworks  i.e . , those 
 reported in the preceding section together with the exhaustive list 
 given in table 1it 
 is natural to ask how one might control the adoption of one architecture 
 or another through choice of chemical composition . we begin 
 by organizing all known dicyanometallates into compositional families 
 of given stoichiometry ambxn . even if their structures vary , members of any one 
 family share the same coordination number and charge state of the 
 b cation  two 
 aspects over which the synthetic chemist has some control . coordination 
 number usually fixes the value of n and so constrains 
 the number and type of relevant network topologies . likewise , cation 
 charge determines the value of n  m and so determines the extent of inclusion of extra - framework 
 a cations ( i.e. , the value of m ) . a visual 
 representation of our categorization is given in figure 4 , and it is by interpreting 
 the various trends that emerge from this diagram that we ultimately 
 aim to devise design strategies linking chemical composition and framework 
 structure . organization of all known dicyanometallate frameworks according 
 to node coordination number and extent of incorporation of extra - framework 
 cations . the frameworks shown are representative examples of isostructural 
 compounds ; the number of such compounds known is given in the corresponding 
 black circle . the collection of frameworks contained within a single 
 hexagonal cell form a family with related composition ambxn . the color of the 
 cell corresponds to the charge on the nodal cation ( inset ) . what is immediately obvious is 
 that some families are considerably more populous than others . the 
 largest and most topologically diverse family is that with composition 
 bx2 , consisting of a variety of structures based on four - connected 
 nets . four - fold connectivity is well known to favor topological diversity  hence the polymorphism of , 
 e.g. , silica , zeolites , and imidazolate mofs . in the present case , zn[au(cn)2]2 emerges as the most polymorphic of the bx2 systems , crystallizing 
 in at least four different forms that include analogues of cristobalite 
 and quartz . in fact the parallel with 
 silica is a meaningful one : the combination of tetrahedral zn coordination geometry and aurophilic interactions capable 
 of bending the zn  nc  au  cn  zn linkers 
 resembles strongly the nonlinear si  o  si building units 
 of sio2 frameworks . but one additional reason for the accessibility 
 of these bx2 structures will likely be the large number 
 of divalent cations with aqueous chemistry . even transition metals 
 with octahedral coordination can yield four - connected frameworks if 
 spectator ligands are present in the synthesis mixture ( noting that 
 sometimes solvent itself may play this role ) . indeed it is the doubly 
 ligated octahedral [ trans - bx4l2 ] coordination motif that yields the square grid topology the 
 most frequently adopted network structure observed for this family . in principle , any such coordinated ligands may be susceptible to 
 exchange for dicyanometallate anions present in the reaction mixture , 
 with concomitant incorporation of extra - framework cations : the equilibrium 
 position will depend on , among other factors , the ligand binding strength 
 and the stoichiometry of ax dicyanometallate salt in the reaction 
 mixture . so , for example , while the cd / k[ag(cn)2 ] system forms the b(l2)x2 phase cd(py)2[ag(cn)2]2 when prepared in the presence 
 of pyridine , in the absence of pyridine the same pair of reagents 
 yields the abx3 phase kcd[ag(cn)2]3 . likewise for the cd/[ppn][ag(cn)2 ] system 
 we obtain the five - coordinate a0.5b(l)x2.5 phase 
 [ ppn]0.5cd(etoh)[ag(cn)2]2.5 ( 3c ) as a first ( kinetic ) product ; subsequent exposure to additional 
 [ ppn][ag(cn)2 ] drives formation of the superperovskite 
 abx3 phase [ ppn]cd[ag(cn)2]33etohnh2o ( 4 ) . this strategy of 
 varying b : ax stoichiometry seems an attractive method 
 of controlling network connectivity throughout the axbx2+x families . the particular 
 topology adopted for the x  0 phases then 
 depends on the geometry of the a cation . for monatomic 
 a ( e.g. , k , na ) , the topology 
 is usually that of the corresponding a - deficient framework : this is 
 presumably a consequence of the much larger scale of the dicyanometallate 
 linker . so , for example , both kfe[ag(cn)2]3 and 
 fe[ag(cn)2]3 share the same triply interpenetrating 
 -po network structure . larger , molecular cations force topological 
 changes that reflect the cation shape . on the one hand , the cruciform 
 conformation of [ nbu4 ] helps drive the unusual 
 topologies of [ nbu4]0.5cd[ag(cn)2]2.5 and [ nbu4]ni[au(cn)2]3 . on the other hand , the more isotropic [ ppn ] cation 
 clearly favors the cubic - type nets of [ ppn]0.5cu[au(cn)2]2.5etoh and [ ppn]mn[au(cn)2]3 . although there are far fewer examples based on monovalent 
 b cations  the need for aqueous chemistry limiting 
 these systems to coinage metal salts again we find that inclusion of monatomic extra - framework 
 cations appears to have essentially no effect on framework topology : 
 kcu[ag(cn)2]2 and cu(dmf)[au(cn)2]2 share the same basic square - grid 
 structures . the tetrahedral [ net4 ] cation now 
 favors a diamondoid topology in [ net4]ag[ag(cn)2]2 ; and in [ cu2(2,2-bpy)2(cn)]0.5cu[cu(cn)2]1.5 the linear 
 nature of the [ cu2(2,2-bpy)2(cn ) ] cation drives a honeycomb structure with linear channels . notable by its absence is the ( 10,3)-a or srs topology , a common topology for 3-connected mofs . the apparent rarity of 3-connected structures is in large 
 part due to the propensity for cu to adopt alternative 
 binding modes , such as bifurcated linkages , though it may be possible to make a dicyanometallate framework with 
 ( 10,3)-a topology using an octahedrally coordinated 
 metal with meridionally disposed capping ligands . is likely responsible for the relative 
 paucity of structures known to contain b cations in the 3 + oxidation 
 state and the complete absence of higher - valent examples . all known 
 trivalent dicyanometallate salts adopt one of just two dense framework 
 structures : either the triply interpenetrating -po net of fe[ag(cn)2]3 or the triply intepenetrating acs net of the lanthanide salts [ ln(oh2)3][au / ag(cn)2]3 . the contrast with the structural diversity 
 of divalent bx2 systems could hardly be clearer , and will 
 reflect also the disparity of topological constraints associated with 
 six- and four - connected nodes . in principle , it may be possible to 
 access more open structure types through incorporation of extra - framework 
 cations . naturally , this would require coordination numbers higher 
 than six  which is certainly feasible for the lanthanide trications . consequently , further exploration of 
 lanthanide dicyanometallate chemistry using molecular ax sources may yield as - yet unrealised systems with compositions 
 a0.5bx3.5 and/or abx4 . in addition 
 to the general trends we discuss here , a number of interesting comparisons 
 can be drawn between neighboring pairs of structural families as shown 
 in figure 4 . for example , 
 there are clear diagonal relationships which connect the topologies 
 of higher- and lower - connected network structures . in this way , the 
 ruddlesden  popper - like structure of [ ppn]0.5cu[au(cn)2]2.5etoh ( an a0.5bx2.5 framework ) can be seen as a natural extension of the square - grid 
 structures of both cu[ag(cn)2]2 and kcu[ag(cn)2]2 ( bx2 and abx2 frameworks , 
 respectively ) . and then the superperovskite [ ppn]cd[au(cn)2]3 structure emerges as a further extension on this same 
 theme . the triad of bx / a0.5bx1.5/abx2 systems cu[cu(cn)2]/[cu2(2,2-bpy)2(cn)]0.5cu[cu(cn)2]1.5/kcu[cu(cn)2]2 can be viewed in precisely the same terms . we 
 anticipate there are many more such relationships , some of which may 
 become increasingly apparent only as new dicyanometallate frameworks 
 continue to be discovered . while 
 it has long been clear that a large variety of dicyanometallate frameworks 
 can be prepared , what we have shown here is how the structures of 
 these frameworks might be influenced rationally through variation 
 in cation charge , coordination number , presence of coordinating ligands , 
 and extra - framework cation size , shape and extent of incorporation . the ability to controllably explore a variety of network structures 
 in this way reflects robson s original vision for coordination 
 polymer chemistry , and suggests that dicyanometalates might be considered 
 a model family for extended framework design . in principle the diversity 
 of structures accessible to this family also suggests a similar diversity 
 of physical properties . moreover , the structural flexibility imparted 
 by the dicyanometallate linker means that these properties may be 
 much more extreme in nature than in conventional ceramic frameworks  as 
 is already known to be the case in a number of examples . but what we see as particularly attractive about dicyanometalate 
 framework chemistry is the ability to include complex molecular cations 
 within a number of different framework topologies . so much of the 
 rich structural chemistry and physics of conventional ceramic frameworks 
 has arisen from the interplay between lattice geometry , local degrees 
 of freedom , and nature of intersite interactions . consequently the 
 extension of these same concepts to systems with new degrees of freedom ( e.g. , molecular cation orientations and conformations ) , new lattice geometries ( e.g. , the topology of compound 2 ) , and new types of interactions ( e.g. , 
 cation and  ) augurs well for 
 the discovery of new and interesting physical phenomena in this intriguing 
 model family of framework structures . [ nbu4]ag(cn)]20.5h2o was prepared by 
 adding an aqueous solution of [ nbu4]cn ( 0.5510 g in 400 
 ml water ) to a suspension of agcn ( 0.3435 g in 100 ml water ) and stirring 
 for 1 h. the excess agcn was then removed by vacuum filtration and 
 the volume of the filtrate reduced by rotary evaporation . the concentrated 
 filtrate was allowed to evaporate , and the resulting powder was dried 
 at 50 c for 2.5 h and then at 40 c for 18 h. [ ppn]au(cn)2 was prepared by the method outlined in ref ( 32 ) . solutions of kau(cn)2 ( 2.583 g in 100 ml water ) and ppncl ( 5.40 g in 200 ml 50:50 
 water : ethanol ) were combined with immediate formation of a white precipitate . the reaction mixture was covered and stirred for 1 h then collected 
 by vacuum filtration and washed with 300 ml cold water . the solid 
 was left to air - dry overnight then dried in a vacuum oven at 40 c 
 for 3.5 h giving 6.80 g of product ( yield : 96.3% ) . elemental analysis : 
 found ( calculated)% c 57.74 ( 57.95 ) ; h 3.80 ( 3.84 ) ; n 5.24 ( 5.34 ) . solutions of kag(cn)2 ( 1.881 g in 100 ml water ) 
 and ppncl ( 5.68 g in 200 ml 50:50 water : ethanol ) were combined with 
 immediate formation of a white precipitate . the reaction mixture was 
 covered and stirred for 1 h then collected by vacuum filtration and 
 washed with 300 ml cold water . the solid was left to air - dry overnight 
 then dried in a vacuum oven at 40 c for 1 week giving 5.87 g 
 of product ( yield : 90.0% ) . elemental analysis : found ( calculated)% 
 c 65.05 ( 65.34 ) ; h 4.26 ( 4.33 ) ; n 5.88 ( 6.02 ) . [ net4]ag[ag(cn)2]2 ( 1 ) single crystals were prepared by slow evaporation 
 of aqueous solutions of kag(cn)2 and [ net4]cl . solutions of kag(cn)2 ( 0.2802 g , 1.411 mmol ) and [ n(c2h5)4]cl ( 0.2380 g , 1.436 mmol ) were 
 prepared with the minimum quantity of water and then mixed . the resulting 
 colorless solution was left to evaporate slowly and crystals formed 
 within 3 weeks . [ nbu4]0.5cd[ag(cn)2]2.5 ( 2 ) aqueous solutions of [ nbu4]ag(cn)20.5h2o and cd(no3)24h2o were prepared with the minimum 
 quantity of solvent , mixed , and left to evaporate from an open petri 
 dish . [ ppn]0.5cu[au(cn)2]2.5 etoh ( 3a ) 
 single crystals were prepared by slow - diffusion in an h - cell . into 
 one arm was placed [ ppn]au(cn)2 ( 25 mg in 1 ml of ethanol ) 
 and the other cucl22h2o ( 5.4 mg in 0.142 
 ml of ethanol ) . [ ppn]0.5mn[ag(cn)2]2.5(etoh ) ( 3b ) was prepared by diffusion in a schott bottle . cold solutions of [ ppn]ag(cn)2 ( 1.125 g in 20 ml of ethanol ) 
 and mn(no3)24h2o ( 148 mg in 
 6 ml of ethanol ) were carefully layered with a buffer of 50 ml cold 
 ethanol separating the layers . [ ppn]0.5cd[ag(cn)2]2.5etoh ( 3c ) single crystals were prepared by slow - diffusion in a vial . cold 
 solutions of [ ppn]ag(cn)2 ( 101 mg in 2 ml of ethanol ) and 
 cd(no3)24h2o ( 19 mg in 0.2 
 ml of ethanol ) were carefully layered with a buffer of 5 ml of cold 
 ethanol separating the layers . crystals formed overnight . for 
 [ ppn]cd[ag(cn)2]33etohnh2o ( 4 ) , a crystal was selected from a small 
 portion ( roughly 3 ml ) of a reaction mixture that initially yielded 3c . solutions of [ ppn]ag(cn)2 ( 1.108 g in 25 ml 
 of ethanol ) and cd(no3)24h2o ( 183.7 mg in 7 ml of ethanol ) with a buffer of 50 ml of ethanol 
 separating the layers in a schott bottle . colorless crystals formed 
 overnight and then a portion of these crystals , with mother liquor , 
 were set aside in a sealed sample tube . [ ppn]mn[au(cn)2]3 ( 5a ) was prepared by layering ethanolic 
 solutions of ppnau(cn)2 ( 50 mg in 2 ml of ethanol ) and 
 mn(clo4)2xh2o ( 14 mg in 0.2 ml of ethanol ) in a small sample tube . colorless 
 crystals formed after 1 h. [ ppn]cd[au(cn)2]3 ( 5b ) was prepared by layering ethanolic solutions of 
 ppnau(cn)2 ( 50 mg in 2 ml of ethanol ) and cd(no3)24h2o ( 21 mg in 0.2 ml of ethanol ) in 
 a small sample tube . colorless crystals formed after 1 h. single - crystal x - ray diffraction 
 data were collected using a nonius kappaccd diffractometer ( 2 and 5a ) or an oxford diffraction ( rigaku oxford 
 diffraction ) supernova diffractometer ( 1 , 3b , 3c , 4 , 5b ) fitted with an 
 oxford cryosystems cryostream 600 series/700 plus open - flow nitrogen 
 cooling device . data for 3a were collected at diamond light source ( beamline i19 ) fitted with an oxford cryosystems helix open - flow 
 helium cryostat . denzo / scalepack , crysalispro , or 
 crystalclear were used for data collection and reduction as appropriate . all structures were refined with full - matrix least - squares on f using crystals . hydrogen atoms were , in some cases , visible in the difference fourier 
 map and treated in the usual manner . in the remaining cases , and particularly for disordered assemblies , 
 hydrogen atoms were added geometrically . full structural data are 
 included in the si , including cif files , and have been submitted to the ccdc 
 as numbers 14441341444141 . these data can also be obtained 
 free of charge from the cambridge crystallographic data centre via http://www.ccdc.cam.ac.uk/data_request/cif .