Inorganic Chemistry Communications 70 (2016) 205–209

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Inorganic Chemistry Communications

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Short communication

Calix [4]-bis-monothiacrown-5 as a versatile building block for homo-and heterometallic coordination polymers

In-Hyeok Park, Ja-Yeon Kim, Eunji Lee, Huiyeong Ju, Seulgi Kim, Joon-Hwa Lee, Shim Sung Lee ⁎Department of Chemistry and Research Institute of Natural Science, Gyeongsang National University, Jinju 52828, South Korea

⁎ Corresponding author.E-mail address: sslee@gnu.ac.kr (S.S. Lee).

http://dx.doi.org/10.1016/j.inoche.2016.06.0151387-7003/© 2016 Elsevier B.V. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 31 May 2016Received in revised form 18 June 2016Accepted 23 June 2016Available online 25 June 2016

Exocoordination-based homonuclear and heteronuclear coordination polymers of calix [4]-bis-monothiacrown-5 (L) are reported. L reacts with HgCl2 and affords a one-dimensional (1D) coordination polymer [L(μ-Hg2Cl4)]n(1) linked by neutral square-type Hg2Cl4 clusters. A straightforward one-pot reaction of Lwith amixture of HgCl2and KCl resulted in the isolation of a heteronuclear species [(K2L)(μ-Hg3Cl8)]n (2) adopting a 1D polymeric struc-ture in which the endocyclic dipotassium(I) complex cation units of L are linked by anionic open double-squaretype (μ-Hg3Cl8)2− clusters. Both products form a pseudo 3D framework via interchain H-bonds and their topo-logical analyses were also carried out.

© 2016 Elsevier B.V. All rights reserved.

Keywords:CalixareneMercuryPotassiumExocoordinationCoordination polymer

Sulfur-containing macrocycles (or thiamacrocycles) often exhibitthe exocyclic coordination (metal binds outside the cavity) due to theinherent electron sufficiency and steric influence associated with thepresence of the sulfur donors [1]. These include the family of calix [4]-bis-thiacrowns as a versatile platform which incorporates twothiacrown loops in both sides of the calix [4]arene scaffold [2,3]. Relatedto the exocoordination of thiamacrocycles including calix [4]-bis-thiacrowns, a range of structural types from low to high dimensional co-ordination polymers as well as finite complexes have been introduced[2–4] and also reviewed by us [1].

We have been interested in the coordination networks based oncalix [4]-bis-thiacrowns which form the endo- and/or exocoordinationtowards homo- and heterometallic species [3,5]. In the calix [4]-bis-thiacrown platform, we found that monothiacrown-5 [3] anddithiacrown-5 derivatives [2a] are promising candidates which formnot only exocyclic complexes but also endocyclic ones due to the sulfurdonor(s) as a bridgehead.

Our group also has established some strategies for the selective con-trolling of the endo- and exocoordination modes by changing anionsand sulfur-to-sulfur distances in the dithiamacrocycles [4f,6]. In thelater case, the dithiamacrocycles with the longer S···S distance tendto show a divergent exocoordination with soft metal ion or its clusterwhich leads the formation of continuous coordination species(Scheme 1a). We have reported some emissive one-dimensional (1D)networks of the endocyclic dipotassium(I) complex with calix [4]-bis-monothiacrown-5 (L) linked by the exocyclic copper(I) iodide cluster

(Scheme 1b) [3a]. Based on the HSAB concept [7] Lmight be consideredto have a borderline character between hard and soft bases because oftheO4S donor-set. In fact, itwas found that L shows slightly higher affin-ity towards potassium(I) than silver(I) both in solid and solution states[5].

In addition to the metal ion bindings in the diverse coordinationmodes, coordinating anions play important roles in bridging or linkingthe complex units resulting in the formation of infinite structures. Inour previous work, L forms a 2D infinite network with the endocyclicdipotassium(I) complex linked by an exocyclic mercury(II) iodide back-bone [5]. The pseudo-halides such as cyanide and thiocyanate ions alsoshow versatile coordinating/networking abilities due to their variouscoordination modes [8].

The continuing interest in calix [4]-bis-thiamacrocycle platform andits expected diverse coordinationmodes due to the long sulfur-to-sulfurseparation prompted us to investigate the fabrication of coordinationpolymers of L. In the present work, mercury(II) and potassium(I)were used as a soft/hard acids pair for the candidate of the exo- andendocyclic metal ions, respectively. As a counter ion, the chloride ionwas employed due to its coordinating and bridging ability that mightgive the infinite products. Topological analyses of the products whichshow the pseudo 3D framework via intermolecular H-bonds were alsocarried out.

Calix [4]-bis-monothiacrown-5 (L) was prepared as reported by uspreviously [3a]. When HgCl2, as a thiaphilic soft acid, were reactedwith L in methanol/dichloromethane, colourless crystalline product 1was obtained after five days. Single crystal X-ray analysis confirmsthat 1 has a 1D polymeric arrangement with the formula being [L(μ-Hg2Cl4)]n (Fig. 1a). Due to the inversion centre in the middle of two

Scheme 1. (a) Coordination modes and (b) calix [4]-bis-monothiacrown-5 (L).

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Hg(II) atoms, the asymmetric unit in 1 contains half L molecule, oneHg(II) atom and two Cl atoms. In 1, the calixcrown units with a 1,3-al-ternate conformation are linked by the square-shaped Hg2Cl4 clustervia Hg1-S1 and Hg1-O2 bonds in the exocoordination mode (Type I inScheme 1) to generate the L-C-L-C (C: cluster) type chain structure.The Hg atom is five-coordinate being bound to one S atom and one Oatom from L (Fig. 1b). The coordination sphere is completed by twobridging chloride ions (Cl1 and Cl1A) and one terminal chloride ion(Cl2) adopting a distorted square pyramidal geometry. The Hg\\Obond distance [Hg1-O2 2.805(4) Å] is typical and the Hg\\S bond dis-tance [Hg1-S1 2.4727(13) Å] is also within the normal literature rangefor related system [9].

Recently, we have found that the endo- and exocoordination modesfor some thiamacrocycles towards soft metal salts can be controlled byanions [6c,10]. For example, the halide anions with higher coordinationaffinity induce the soft metal ions locate outside the cavity to generateexocoordinated products. Consequently, the preferred formation ofthe 1D polymeric array in 1 via the exocyclic coordination mode of L is

Fig. 1. Crystal structure of 1, [L(μ-Hg2Cl4)]n: (a) 1D polymeric chain, (b) core coordination unit,3D framework. Symmetry codes (A): 2 − x, −y, 2 − z; (B): 1 − x, y, 1.5 − z.

mainly due to higher affinity of the chloride ion towards themercury(II)to form the large cluster.

In the packing structure, it is found that the CH···Cl type H-bonds[11] (av. 2.85 Å) between adjacent chains (yellow dashed lines in Fig.1c) links the chains to form a pseudo 3D framework (Fig. 1d). The de-tails of the topological analysis for the pseudo 3D structure are discussedin the later part.

Having prepared and characterised the Hg2Cl4 cluster-bridged exo-cyclic coordination polymer of L, we continued to synthesise theheterometallic analogue. When HgCl2 was changed to a mixture ofHgCl2 and KCl, a heterometallic 1Dpolymeric product 2with the formu-la [(K2L)(Hg3Cl8)]n was obtained after two weeks (Fig. 2a). The asym-metric unit in 2 contains one L, two K(I) atoms, three Hg(II) atomsand eight Cl atoms.

In this case, two crystallographically different K1 andK2 atoms showsimilar coordination environment. They occupy the centres of twocrown cavities to form a dipotassium(I) complex cation unit (K2L)2+

via four K\\O bonds (K1-O: 2.642(6)–2.804(7) Å, av. 2.712 Å and K2-

(c) interchain H-bonds (yellow dashed lines) and (d) packing structure showing a pseudo

Fig. 2.Crystal structure of 2, [(K2L)(μ-Hg3Cl8)]n: 1Dpolymeric chain, (b) core coordination unit, (c) anionic opendouble-square cluster (Hg3Cl8)2−, (d) close-up of dipotassium(I) complexcation unit showing η3-type cation···π interactions (thin yellow dashed lines), (e) interchain H-bonds (yellow dashed lines) and (f) packing structure showing a pseudo 3D framework.Symmetry code (A): 0.5 + x, 1.5 − y,−0.5 + z.

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O: 2.638(6)–2.762(6) Å, av. 2.689 Å). The K···S distances (dashed linesin Fig. 2b, K1···S1 3.375(3) and K2···S2 3.348(3) Å) are shorter thanthe sum of van der Waals radii (2.35 + 1.27 Å) [12], because suchK···S interactions in the oxathia-macrocycles including L are enhancedby the adjacent K\\O bonds [3a,5]. Both K(I) atoms in 2 are alsostabilised by η3-type cation···π interactions with the aromatic Catoms [K+···C 3.176(9)–3.429(11) Å (av. 3.374 Å)] (thin dashed linesin Fig. 2d). The K1···K2 separation in 2 is 5.01 Å.

The dipotassium(I) complex cation units, (K2L)2+, are linked byopen double-square type (Hg3Cl8)2− clusters via Hg\\S bonds to forma (K2L)-C′-(K2L)-C′ (C′= anionic cluster) type heterometallic 1D coor-dination polymer in the endo/exocoordinationmode (Type II in Scheme1). As we understand, the open double-square cluster has not been re-ported so far. The formation of such unique anionic cluster is associatedwith the encapsulation of the two potassium(I) ions to generate the cat-ionic (K2L)2+ unit which does not allow the anion coordination to thepotassium(I) centre.

In the open double-square cluster, the coordination environments ofthe threeHg(II) atoms are quite different (Fig. 2c). The Hg1 atom isfive-coordinate, being bound to one sulfur donor from L and its coordinationsphere is completed by three bridging chloride ions and one terminalchloride ion to form a distorted square pyramidal geometry. The Hg1

atom links Hg2 and Hg3 atoms via bridging Cl atoms to form one squareand one open square. Consequently, one S atom in the crown ring actsboth a weak donor for the endocyclic K(I) atom and a bridgehead forthe exocyclic linking via Hg\\S bonds.

Again, 2 shows the CH···Cl type H-bonds [11] (av. 2.85 Å) betweenadjacent chains (yellow dashed lines in Fig. 2c) in its packing structurewhich forms a pseudo 3D framework (Fig. 2d).

As mentioned in Scheme 1, dithiamacrocycles are expected to act asditopic ligands in terms of the coordination modes [10]. This predictionis realised in the complexations of Lwith soft and soft/hard metal chlo-rides. The predominant difference of the mercury(II) complexations inthe present results is that L acts as a bidentate in 1, while as amonodentate in 2 due to the replacement of the coordination to Lwith the chloride ion in the later case (Fig. 3). Upon endocoordinationwith two potassium(I) ions in 2, all the O4S donors in the crown ringare rearranged in a gauche form (Fig. 3b). It is also found that themonodentate behaviour of L for the Hg atom in 2 is associated withthe bond-breaking of Hg1-O2 in 1 (2.805(4) Å in 1 and 4.617(6) Å in2). Upon the potassium(I) complexation, the dihedral angles betweenthe two opposite aromatic rings in the calix [4]arene units are changedfrom 37.14° (for 1) and to 25.10° (for 2) (yellow arrows in Fig. 3b) dueto the η3-type cation···π interactions as mentioned above (Fig. 2d).

Fig. 3. Comparison of calixcrown units in (a) 1 and (b) 2. Conformational changes uponendocyclic coordination with two potassium(I) ions are indicated by green and yellowarrows.

Fig. 4. Topological representation of 1: (a) calix-bis-thiacrown (left) and Hg2Cl4 clusterunit (right) as a 6-connecting octahedron node and (b) pseudo 3D framework showingpcu topology.

Fig. 5. Topological representation of 2: (a) calix-bis-thiacrown as a 6-connectingoctahedron node (left) and (Hg3Cl8)2− cluster unit as a 6-connecting trigonal prismnode (right) and (b) pseudo 3D framework showing nia topology.

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Due to the interchain H-bonds, both of 1 and 2 show pseudo 3Dframework structures. Topological analyses of 1 and 2were undertakenby using Program ToposPro [13]. In 1, calix [4]-bis-thiacrown and(Hg2Cl4) cluster are considered as 6-connecting octahedron nodes(Fig. 4a). In this condition, as shown in Fig. 4b, the pseudo 3D frame-work 1 can be simplified as uninodal 6-connected pcu topology withpoint symbol {412.63}.

In case of 2, calix [4]-bis-thiacrown and (Hg3Cl8)2− cluster can beconsidered as a 6-connecting octahedron node and a trigonal prismnode, respectively (Fig. 5a). The pseudo 3D framework 2 can be simpli-fied as binodal 6,6-connected nia topology with point symbol{412.63}{49.66} (Fig. 5b). Note that the pcu net has two identical octahe-dral nodes in contrast to the nia net which shows two different nodes.The nia topology is derived from the structure of nickeline (NiAs), oneof the most fundamental structure types in binary ionic solids, whichcontains both of an octahedron coordination figure and a trigonalprism coordination figure [14]. In 2, the extra endocoordination withpotassium(I) ions induces the formation of the new type of open dou-ble-square cluster anion which acts as the trigonal prism node (rightside in Fig. 5a). Consequently, upon heterometallic complexation inthe endo/exocoordination mode, the pcu topology in 1 was changedto the nia topology in 2 via the formation of the new type of anioniccluster.

Calix [4]-bis-monothiacrown-5 was employed as a versatile buildblock both for complexation and networking to give a homo- and aheterometallic coordination polymers. In particular, the infiniteheterometallic species represents not only hard/soft metal coordinationbut also endo/exocyclic coordinationmodes because one S donor acts asa bridgehead for the exocoordination and the O4S donor-set exhibits ahard base nature to accept the hard metal ions (K+) inside the crowncavity. In both cases, chloride anion plays important role in the forma-tion of different types of metal clusters which link the host ligands. No-tably, the capsulation of two potassium(I) ions in the host ligand allowsthe formation of the unique anionic open double-square type cluster.Themercury(II) chloride cluster linkers such asneutral (Hg2Cl4) and an-ionic (Hg3Cl8)2− induce the different topologies of the products. The re-sults demonstrate that calix [4]-bis-monothiacrown can be utilised as a

promising platform for the construction of newmetallosupramoleculeswith network structures.

Acknowledgements

This work was supported by NRF (2012R1A4A1027750 and2013R1A2A2A01067771).

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Appendix A. Supplementary material

CCDC 1487666 and 1487665 contain the supplementary crystallo-graphic data for 1 and 2, respectively. The data can be obtained free ofcharge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data to this article canbe found online at http://dx.doi.org/10.1016/j.inoche.2016.06.015.

References

[1] (a) S. Kim, L.F. Lindoy, S.S. Lee, Recent developments in the thiamacrocyclic chem-istry of the latter d-block elements, Coord. Chem. Rev. 280 (2014) 176;

(b) E. Lee, S.Y. Lee, L.F. Lindoy, S.S. Lee, Metallacycles derived frommetal complexesof exo-coordinated macrocyclic ligands, Coord. Chem. Rev. 257 (2013) 3125;

(c) S. Park, S.Y. Lee, K.-M. Park, S.S. Lee, Supramolecular networking of macrocyclesbased on exo-coordination: fromdiscrete to continuous frameworks, Acc. Chem.Res. 45 (2012) 391.

[2] (a) J.Y. Lee, S.Y. Lee, J. Seo, C.S. Park, J.N. Go, W. Sim, S.S. Lee, Calix[4]bis(thiacrown):assembly of an endocyclic disilver(I) complex and exocyclic 3D copper(I) coor-dination polymers, Inorg. Chem. 46 (2007) 6221;

(b) J.Y. Lee, J. Kwon, C.S. Park, J.-E. Lee, W. Sim, J.S. Kim, J. Seo, I. Yoon, J.H. Jung, S.S.Lee, Calix[4]thiacrowns as ditopic hosts for homo- and heterobinuclear accom-modation: first report of a chopsticks-type π-coordination, Org. Lett. 9 (2007)493.

[3] (a) J.Y. Lee, H.J. Kim, J.H. Jung, W. Sim, S.S. Lee, Networking of calixcrowns: fromheteronuclear endo/exocyclic coordination polymers to a photoluminescenceswitch, J. Am. Chem. Soc. 130 (2008) 13838;

(b) J.Y. Lee, H.J. Kim, C.S. Park, W. Sim, S.S. Lee, A calix-bis-crownwith hard and softcrown cavities: heterobinuclear K+/Ag+ complexation in solid and solutionstates, Chem. Eur. J. 15 (2009) 8989.

[4] (a) R.E. Wolf Jr., J.R. Hartman, J.M.E. Storey, B.M. Foxman, S.R. Cooper, Crownthioether chemistry: structural and conformational studies of tetrathia-12-crown-4, pentathia-15-crown-5, and hexathia-18-crown-6. Implications for li-gand design, J. Am. Chem. Soc. 109 (1987) 4328;

(b) A.J. Blake, M. Schröder, Chemistry of thioether macrocyclic complexes, Adv.Inorg. Chem. 35 (1990) 1;

(c) S.E. Hill, D. Feller, Theoretical conformational analysis of thiacrownmacrocycles,J. Phys. Chem. A 104 (2000) 652;

(d) I. Yoon, J. Seo, J.-E. Lee, K.-M. Park, J.S. Kim,M. Soo,M. Lah, S.S. Lee, Assembly of aheterobinuclear 2-D network: a rare example of endo- and exocyclic coordina-tion of PdII/AgI in a single macrocycle, Inorg. Chem. 45 (2006) 3487;

(e) L.F. Lindoy, G.V.Meehan, I.M. Vasilescu, H.J. Kim, J.-E. Lee, S.S. Lee, Transition andpost-transition metal ion chemistry of dibenzo-substituted, mixed-donormacrocycles incorporating five donor atoms, Coord. Chem. Rev. 254 (2010)1713;

(f) E. Lee, S.S. Lee, Rational approach to endo/exocoordinated heteronuclear macro-cyclic network: supramolecular Hg(ll), Cu(ll), and Hg(ll)/Cu(ll) complexes of aNS4 macrocycle, Inorg. Chem. 50 (2011) 5803;

(g) D. Jung, R. Chamura, Y. Habata, S.S. Lee, Extra large macrocycle: 40-memberedmacrocycle via 2:2 cyclization and its dimercury(II) complex, Inorg. Chem. 50(2011) 8392.

[5] J.-Y. Kim, I.-H. Park, J.Y. Lee, J.-H. Lee, K.-M. Park, S.S. Lee, Hard and soft metal com-plexes of calix[4]-bis-monothiacrown-5: X-ray and NMR studies of discretehomodinuclear complexes and a heteromultinuclear network, Inorg. Chem. 52(2013) 10176.

[6] (a) M. Jo, J. Seo, M.L. Seo, K.S. Choi, S.K. Cha, L.F. Lindoy, S.S. Lee, Donor-set-inducedcoordination sphere and oxidation-state switching in the copper complexes ofO2S2X (X = S, O and NH) macrocycles, Inorg. Chem. 48 (2009) 8186;

(b) E.-J. Kang, S.Y. Lee, H. Lee, S.S. Lee, Sulfur-containing mixed-donor tribenzo-macrocycles and their endo- and exocyclic supramolecular silver(I) andcopper(I) complexes, Inorg. Chem. 49 (2010) 7510;

(c) H.J. Kim, K.F. Sultana, J.Y. Lee, S.S. Lee, Endo- and/or exocyclic silver(I) andmercury(II) complexes of anNO2S2-macrocycle: effect of ligand ratio and anion,CrystEngComm 12 (2010) 1494.

[7] R.G. Pearson, Hard and soft acids and bases, J. Am. Chem. Soc. 85 (1963) 3533.[8] H.J. Kim, S.S. Lee, Networking of tribenzo-O2S2-macrocycles with mercury thiocya-

nate: effect of macrocyclic isomers, Cryst. Growth Des. 10 (2010) 3850.[9] (a) K.A. Byriel, L.R. Gahan, C.H.L. Kennard, C.J. Sunderland, Synthesis, Characteriza-

tion and Crystal Structures of 1.7-Dioxa-4-Thia-10-Azacyclododecane([12]aneNO2S) and [Hg([12]aneNO2S)(NO3)2], J. Chem. Soc, Dalton Trans,1993 625;

(b) S.Y. Lee, S. Park, H.J. Kim, J.H. Jung, S.S. Lee, Ligand- and anion-directed assemblyof exo-coordinatedmercury(II) halide complexeswithO2S2-donormacrocycles,Inorg. Chem. 47 (2008) 1913;

(c) G.J. Grant, M.E. Botros, J.S. Hassler, D.E. Janzen, C.A. Grapperhaus, M.G. O'Toole,D.G. Van Derveer, Hg(II) and Cd(II) complexes with mixed donor macrocyclicthioethers: the oxophobicity of mercury(II), Polyhedron 27 (2008) 3097;

(d) I.-H. Park, K.-M. Park, S.S. Lee, Preparation and characterisation of divalent hardand soft metal (M=Ca, Co, Cu, Zn, Cd, Hg and Pb) complexes of 1,10-dithia-18-crown-6: structural versatility, Dalton Trans. 39 (2010) 9696;

(e) Z. Chen, X. Wu, S. Qin, C. Lei, F. Liang, Structure and fluorescent properties ofmercury(II) pyridine-2,3-dicarboxylate coordination polymers tuned by ancil-lary ligands and alkaline-earth metal ions, CrystEngComm 13 (2011) 2029;

(f) I.-H. Park, H.J. Kim, S.S. Lee, Anion-dependent coordinative networking ofmacrocycle with copper(I) halides, CrystEngComm 14 (2012) 4589;

(g) E. Stephen, A.J. Blake, E. Carter, D. Collison, E.S. Davies, R. Edge, W. Lewis, D.M.Murphy, C. Wilson, R.O. Gould, A.J. Holder, J. McMaster, M. Schröder, Redoxnon-innocence of thioether crowns: elucidation of the electronic structure ofthe mononuclear Pd(III) complexes [Pd([9]aneS3)2]3+ and [Pd([18]aneS6)]3+,Inorg. Chem. 51 (2012) 1450;

(h) Y. Kang, I.-H. Park, M. Ikeda, Y. Habata, S.S. Lee, A double decker type complex:copper(I) iodide complexation with mixed donor macrocycles via [1 : 1] and[2 : 2] cyclisations, Dalton Trans. 45 (2016) 4528.

[10] (a) H.J. Kim, S.S. Lee, Anion-controlled endo- and exocyclic disilver(I) complexes ofan S2O3 macrocycle, Inorg. Chem. 47 (2008) 10807;

(b) H.-H. Lee, I.-H. Park, S.S. Lee, Cooperative effect of anion and mole ratio on thecoordination modes of an NO2S3-donor macrocycle, Inorg. Chem. 53 (2014)4763.

[11] T. Bäcker, A.-V. Mudring, Betaine chloride-betaine tetrachloridoferrate(III) - an ionicliquid related crystal structure governed by the Pearson concept, Crystals 2 (2012)110.

[12] (a) A. Bondi, van der Waals volumes and radii, J. Phys. Chem. 68 (1964) 441;(b) J.-Y. Kim, I.-H. Park, K. Kim, S.S. Lee, Homonuclear and heteronuclear complexes

of calix[4]-bis-monothiacrown-5 with oligomer and polymer structures, Cryst.Growth Des. 14 (2014) 6012.

[13] (a) E.V. Alexandrov, V.A. Blatov, A.V. Kochetkov, D.M. Proserpio, Underlying nets inthree-periodic coordination polymers: topology, taxonomy and prediction froma computer-aided analysis of the Cambridge Structural Database,CrystEngComm 13 (2011) 3947;

(b) V.A. Blatov, Nanocluster analysis of intermetallic structures with the programpackage TOPOS, Struct. Chem. 23 (2012) 955;

(c) V.A. Blatov, A.P. Shevchenko, D.M. Proserpio, Applied topological analysis ofcrystal structures with the program package ToposPro, Cryst. Growth Des. 14(2014) 3576.

[14] E.V. Alexandrov, A.V. Virovets, V.A. Blatov, E.V. Peresypkina, Topological motifs incyanometallates: from building units to three-periodic frameworks, Chem. Rev.115 (2015) 12286.