Coordination Compounds of Hexamethylenetetramine with Metal Salts: a Review Properties and Applications of a Versatile Model Ligand

https://doi.org/10.1595/205651317X696621 Johnson Matthey Technol. Rev., 2018, 62, (1), 89–106

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Coordination Compounds of Hexamethylenetetramine with Metal Salts: A Review Properties and applications of a versatile model ligand

Reviewed by Jia Kaihua* and Ba chemical industry. It has been used in many fields Shuhong including as a curing agent for phenolic resins Military Chemistry and Pyrotechnics, Shenyang (1), as an accelerant in vulcanisation (2), in food Ligong University, Shenyang, 110186, China preservatives (3) and explosives (4) because of its useful properties including high solubility in water *Email: [email protected] and polar organic solvents (5). In addition, hmta can act as a multifunctional ligand, using its N atom to form coordination complexes with many Hexamethylenetetramine (hmta) was chosen as transition metals (6–10). It has been employed a model ligand. Each of the four nitrogen atoms to prepare complexes with metals, and has been has a pair of unshared electrons and behaves increasingly applied in chemical synthesis where it like an amine base, undergoing protonation and has received increasing attention due to its simple N-alkylation and being able to form coordination operation, mild conditions and environmental compounds with many inorganic elements. The friendliness (11, 12). ligand can be used as an outer coordination sphere modulator of the inner coordination sphere and as 1. Coordination with Metal Salts a crosslinking agent in dinuclear and multinuclear coordination compounds. It can also be used as A large number of complexes of hmta and a model for bioactive molecules to form a great metal salts have been studied and reports on number of complexes with different inorganic their synthesis, preparation, structure analysis salts containing other molecules. Studies of hmta and applications in medicine and military are coordination compounds with different metal summarised below. salts have therefore attracted much attention. The present review summarises the synthesis, 1.1 Coordination with Metal Salts of preparation, structure analysis and applications Main Group Elements of coordination compounds of hmta with different metal salts. The magnesium dichromate hmta complex was

first crystallised by Debucquet and Velluz with 5H2O Introduction in 1933 (13), but subsequent analysis showed the presence of six water molecules instead of Hexamethylenetetramine as a reagent has five and on the basis of former study, Dahan been used as a source of –CH=N– and –CH= put forward the topic of “the crystal structure of functions. It has a cage-like structure and is the magnesium dichromate hmta hexahydrate considered to be a crucial basic material for the complex” in 1973 (14). In Dahan’s study, the

89 © 2018 Johnson Matthey https://doi.org/10.1595/205651317X696621 Johnson Matthey Technol. Rev., 2018, 62, (1) structure of the Mg dichromate hmta hexahydrate lead to new materials such as polyoxometalates complex can be regarded as composed of two CrO4 (POMs) with different properties and more stable tetrahedra joined through a shared oxygen atom, structures. a slightly distorted octahedron around Mg and Chen et al. synthesised two new extended two hmta molecules. There were no coordination frameworks based on two different sandwich-type bonds between these groups. They are linked by polytungstoarsenates under routine conditions in hydrogen bonds, thus determining the packing and 2009. They found an advance on the sandwich- controlling the stability. type POMs, which had larger volumes and more Sieranski and Kruszynski (15) studied complexes negative charges than commonly used POMs, of Mg and hmta in 2011. Sieranski chose hmta allowing the formation of higher coordination and 1,10-phenanthroline as ligands complexed numbers with metal cations. Thus, sandwich- with Mg sulfate. Coordination compounds type POMs should be excellent building blocks for 2+ 2− [Mg(H2O)6] •2(hmta)•SO4 •5(H2O) and constructing extended networks (28).

Mg(C12H8N2)(H2O)3SO4 were synthesised and characterised by elemental and thermal analysis, 1.3 Coordination with Different Metal infrared (IR) spectroscopy, ultraviolet-visible Salts of Subgroup B Elements (UV-vis) spectroscopy, fluorescence spectroscopy and X-ray crystallography. The compounds were Allan et al. (30) studied transition metal halide found to be air stable and well soluble in water. complexes of hmta in 1970. Complexes of Mg and calcium have been most studied but hmta have been prepared with the halides of heavier alkaline earth metals have also been manganese(II), cobalt(II), nickel(II), zinc(II), investigated. For instance, after the development cadmium(II), iron(II) and copper(II) and also with of the strontium-based drug, strontium renelate, the thiocyanates of Co(II), Ni(II) and Zn(II). These which reduces the incidence of fractures in complexes have been characterised by elemental osteoporotic patients, there has been an increasing analysis, vibrational and electronic spectra and awareness of this metal’s role in humans. magnetic moments. Khandolkar et al. (16) studied the synthesis, Ahuja et al. (31) studied hmta complexes with crystal structure, redox characteristics and Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) photochemistry of a new heptamolybdate thiocyanates. As a potentially tetradentate ligand, supported coordination compound hmta complexes with Mn(II), Co(II), Ni(II), Cu(II),

(hmta)2[{Mg(H2O)5}2{Mo7O24}]•3H2O in 2015. Zn(II) and Cd(II) thiocyanates were prepared and In their study, the synthesis, characterisation characterised by their elemental analyses, magnetic and photochemistry of a new heptamolybdate susceptibilities, electronic and IR spectral studies supported Mg-aqua coordination complex using down to 200 cm–1, 611 cm–1 as well as X-ray powder hmta as structure directing agent was reported. diffraction patterns in the solid state. It was shown Tanco Salas (17) studied a complex of aluminium that hmta, though a potentially tetradentate ligand, and hmta (‘Al-hmta’) in 2004. The Al-hmta complex acts only as a terminally bonded monodentate was found to have deodorant and therapeutic ligand or a bidentate ligand bridging between two properties with potential applications in cosmetic metal atoms, retaining the chair configuration of and pharmaceutical compositions. Furthermore, the uncoordinated molecule in all these complexes. the Al-hmta complex had the capacity to trap The tentative stereochemistries of the complexes substances which could subsequently be released, were discussed. therefore being useful as a carrier of those Agwara et al. (32) studied the physicochemical substances. properties of hmta complexes with Mn(II), Co(II) and Ni(II) in 2004, and in 2012 these complexes 1.2 Coordination with Salts of Main had been synthesised in water and ethanol (33). All the complexes were hydrogen-bonded, except the Group Elements and Subgroup B Co complex [Co(hmta) (NO ) (H O) ] which was Elements 2 3 2 2 2 polymeric. These complexes were characterised Different metal salts have different coordination by elemental analysis, IR and visible spectroscopy abilities and properties. Usually, the complex is as well as conductivity measurements. The results made up of the main group element as the central suggest octahedral coordination in which the atom, and the subgroup elements appear in the central metal ion is bonded to aqua ligands and ligands. The combination of two metals may the hmta is bonded to the aqua ligands through

90 © 2018 Johnson Matthey https://doi.org/10.1595/205651317X696621 Johnson Matthey Technol. Rev., 2018, 62, (1) Reference No. (19) (19) (20) (20) (8) (21) (21) (21) (21) (21) (21) (16) (14) (15) (18) (18) (18) CCDC No. 1003176 1003177 802360 833296 266846 859820 859821 859822 859823 859824 859825 1049780 – 813464 865230 865231 865232 F (000) 976 584 624 688 1212 2448 688 1376 1520 632 704 3152 654 322 1304 752 864 = 0.0964 = 0.0867 = 0.0900 = 0.0877 = 0.0777 = 0.0881 = 0.1321 = 0.0806 = 0.1192 = 0.0716 = 0.0639 = 0.0829 = 0.0761 = 0.1334 = 0.1214 = 0.0735 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 = 0.0384, = 0.0284, = 0.0378, = 0.0339, = 0.0268, = 0.0339, = 0.0546, = 0.0388, = 0.0450, = 0.0308, = 0.0234, = 0.0382, = 0.0317, = 1.0538, = 0.0401, = 0.0304, 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 R indices (all data) R wR R wR R wR R wR R wR R wR R wR R wR R wR R wR R wR R wR – R wR R wR R wR R wR –3 , d Z, Mg m 4, 1.416 4, 1.625 2, 1.366 4, 1.559 6 18, 1.289 4, 1.629 4, 1.522 4, 1.649 4, 1.913 4, 2.095 4, 2.493 2, 1.595 1, 1.446 4, 1.3782 2, 1.580 2, 1.733

(No. 33) (No. 1 /c (No. 14) /c (No. 14) /c (No. 14) /c (No. 14) /c (No. 14) /c (No. (No. 2) (No. 1 1 1 1 1 1 Crystal system, space group Orthorhombic, Pna2 Orthorhombic, 62) Pnma (No. Monoclinic, P2 Monoclinic, 15) C2/c (No. Trigonal, 161) R3c (No. Trigonal, 155) R32 (No. Monoclinic, P2 Orthorhombic, 61) Pbca (No. Orthorhombic, 61) Pbca (No. Monoclinic, 12) C2/m (No. Monoclinic, 12) C2/m (No. Monoclinic, 15) C2/c (No. Triclinic P Triclinic, 1) P1 (No. Monoclinic, P2 Monoclinic, P2 Monoclinic, P2 Serial No. 1a 1b 2b 1c 3b 2a 3a 4b 5b 2c 1d 1e 2e 3e 4e 1f 1g O 2 (1:1) – (1:2) 4H – • 2Br 2I 2− (1:1) • • 3 – (1:2) O O – 2 2 4 (1:1) 2NO n (1:1) 2H 2H • O (1:2) – 2SCN • •

(1:1) 2 ClO • 2 – • Cl I 2+ 2+ } 2(hmta) (1:1) (1:1) • • 2(hmta) (1:1) 2 2+ ]

(2:1) 5 • 6H • (1:1) 2 2 n n (1:1) ]

• ] ]

] 4 n 4 4 n O) 2 ) ) 2 O (1:2) 3 3 2(hmta) 2(hmta) 2 O) • • O)(hmta)] 2 2 O) (1:2) 2(hmta) (hmta) (hmta) 3H 2+ 2+ 2 • • • (hmta)] (hmta) (NO (NO • ] ] • • 6 + + + 6 6 6 2(hmta) 4 4 ] ] ] )(H • (hmta)] }] 4 4 4 4 [{Mg(H O) 5(H 7 • O) O) O) 2 O) O) O)(hmta)I] 2 • 3 24 2 2 2 O 2 2 2 O) O) O) O)(hmta)I] 2 O 2 2 2 2− 2 (H 7 (H 4 2 (hmta)(SCN) 2 2 SO Table I Major Crystal Data and Refinement for Compounds of hmta Salts with Main Group Elementsof hmta Salts with Main Group Compounds and Refinement for Data Crystal Table I Major Formula (M:hmta) [Li(H [Na(ClO [Na(hmta)(H [K [NaNO [Li(H [Li(H [Na(H [Na(H [K(H [Rb(H (hmta) {Mo MgCr [Mg(H • [Mg(H (1:2) [Ca [Sr

91 © 2018 Johnson Matthey https://doi.org/10.1595/205651317X696621 Johnson Matthey Technol. Rev., 2018, 62, (1) Reference No. (22) (23) (23) (24) (25) (26) (26) (27) (28) (29) CCDC No. – – – – – – – 660692 705356 – F (000) – – – – – – – 8504 11708 725 = 0.043 = 0.045 = 0.055 = 0.036 = 0.062 = 0.1743 = 0.2071 = 0.1141 2 2 2 2 2 2 2 2 = 0.044, = 0.042, = 0.055, = 0.038, = 0.066, = 0.057 = 0.0591, = 0.0863, = 0.0389, 1 1 1 1 1 1 1 1 1 R indices (all data) – R wR R wR R wR R wR R wR R R wR R wR R wR –3 , d Z, Mg m 2, 1.43 4, 1.50 4, 1.48 4, 1.72 4, 1.676 4, 1.83 2, 1.76 2, 4.047 4, 3.681 1, 2.329

(No. 29) (No. 1 (No. 4) (No. 137) /nmc (No. 14) /c (No. 1 2 1 Crystal system, space group Orthorhombic, 44) Imm2 (No. Orthorhombic, Pca2 Triclinic, 1) P1 (No. Monoclinic, P2 Monoclinic, 15) C2/c (No. Tetragonal, P4 Monoclinic, 14) P21/c (No. Triclinic, 1) P1 (No. Monoclinic, P2 Triclinic, 1) P1 (No. O 2 19H • ] 2 ) 39 O O 2 11

~36H • ] OH] 3 O O 2 2 } 2 O [Ce(AsVW O 2 O 2 7 2 2 O O 2 2 O) 11H 5H 18H Na 2 4H 6H • •

• 2 • • 5H 4H O • • 2 8.5 }] )(H 4 38 7H Na • O) O 2 3.5 10 2(hmta) 3(hmta) K (hmta)K 2(hmta) 2(hmta) • • O] [(hmta)-CH 2 2 • • 2 2(hmta) 2(hmta) 2 2 ] ] ] ] ] • • ] 3 3 6 6 6 ] H ] 6 6 • 6 {Na(H 2(hmta) • 28 O Ca 7 10 {FeCe(AsW [Fe(CN) [Fe(CN) [Fe(CN) V O [Fe(CN) 3 2 3 [Fe(CN) 3 ⊂ [Fe(CN) 2 3 3 3 Table II Major Crystal Data and Refinement for Compounds of hmta with Different Metal Salts Metal Different of hmta with Compounds and Refinement for Data Crystal Table II Major Formula (M:hmta) Li (3:1:2) Na (3:1:2) K (3:1:2) Ca (2:1:2) Cr (1:2:2) Sr (3:2:3) Ba (3:2:2) [(hmta)-CH [K [(hmta)-CH [(hmta)-H [H (10:1:2)

92 © 2018 Johnson Matthey https://doi.org/10.1595/205651317X696621 Johnson Matthey Technol. Rev., 2018, 62, (1) hydrogen-bonding. Antibacterial activities of the complex may exhibit different structures when ligand and its complexes show that the ligand was synthesised by different methods. For instance, active against one out of 10 tested bacteria species; the Co(II)-hmta complexes Co(hmta)2Cl2•10H2O the Co complexes [Co(H2O)6](hmta)2(NO3)2•4H2O and Co(hmta)2Cl2•6H2O could be obtained using and [Co(hmta)2(NO3)2(H2O)2] were the most active, solution synthesis and mechanical grinding, showing activity against all the microorganisms. respectively. The thermogravimetric analysis These Co complexes also show greater activity (TGA) result further confirmed that the structure of than the reference antibiotic gentamycin against the Co(II)-hmta complex obtained by grinding was

Klebsiella pneumoniae. Co(hmta)2Cl2•6H2O. In addition, there were also Kumar et al. (34) studied Cd hmta nitrate in studies on complexes of hmta with Cu and silver 2012. The crystal structure analysis of the complex ion salts. revealed a zig-zag polymeric network in which Stocker (38) studied the crystal structure of a novel the Cd(II) ions are linked via the nitrogen atom Cu(I) cyanide complex with hmta, (CuCN)3(hmta)2 of the hmta ligand. The complex has a network of in 1990. Grodzicki et al. (39) studied a complex hydrogen bonds. For isothermal thermogravimetry of Cu(II) chloride with hmta in 1991. Their study (TG) data, use of the isoconversional method was included spectroscopic and magnetic investigations an effective means of unmasking complex kinetics. which indicated that, in the crystal structure of this

Salem (35), of Tanta University, Egypt, studied compound, polymeric chains, 3CuCl•2hmta•2H2O the catalytic effect of some transition metal hmta and hmta•HCl groups occurred. complexes in hydrogen peroxide decomposition. Hazra et al. (40) studied four new The kinetics of the catalytic decomposition of Cu(II)-hmta complexes synthesised and

H2O2 with Wofatit KPS resin (4% divinylbenzene), structurally characterised by X-ray crystallography (40–80 μm) in the form of 1: l Cu(II)-, Mn(II)-, in 2013. The unique feature of the study was that Co(II)- and Ni(II)-hexamine complexes was it had been possible to construct all probable studied in an aqueous medium. The decomposition architectures that can be assembled by utilising reaction was first order with respect to [H2O2] linear dinuclear Cu(II) carboxylate as a node and the rate constant, k (per gram of dry resin) and hmta as a spacer (angular, pyramidal and increased in the following sequence: Mn(II) > tetrahedral) varying only slightly the nonfunctional Co(II) > Cu(II) > Ni(II). The active species, formed part of the aromatic carboxylic acids. as an intermediate at the beginning of the reaction, A thesis by Degagsa et al. (41) showed that had an inhibiting effect on the reaction rate. An [Cu(hmta)3(H2O)3]SO4 had been synthesised by anionic surfactant, sodium dodecyl sulfate (SDS), direct reaction of hmta and penta-hydrated Cu sulfate considerably inhibited the reaction rate. A probable (CuSO4•5H2O) and was characterised by magnetic mechanism for the decomposition process was susceptibility measurements, atomic absorption suggested, which was consistent with the results spectroscopy, IR and UV-vis spectroscopic analysis obtained. as well as conductivity measurements. Sulfate Paboudam et al. (36), reported the results of a ion and hmta composition of the complex were study on the influence of solvent on the electronic also determined using gravimetric and volumetric and structural properties of metal-hmta complexes analysis respectively. The structure of the complex in aqueous and non-aqueous solvents. Their goal was then proposed to be distorted octahedral in was to study the effect of aqueous and non-aqueous which a single Cu ion is bonded to three water and media on the coordination of hmta to metal ions. three hmta molecules. The antimicrobial activity The protometric studies of the hmta ligand had of hmta was enhanced upon complexation due confirmed that only one basic site was protonated to the increase in lipo-solubility of the complex in acidic medium and this ligand was decomposed upon coordination with the ligands. It can also in acidic medium. In aqueous medium, hmta ligand be concluded that the complexes show greater does not coordinate directly to the metal ions but antibacterial activity than the reference antibiotic, rather through the H-bonded species. In non- gentamycin, towards Staphylococcus aureus and aqueous solvents, hmta coordinates to metal ions Salmonella typhi. Thus, with further investigation displaying diversity in the resulting structures in and exploitation this complex could be developed which hmta can either be monodentate, bridged, as an antibacterial drug for the treatment of tridentate or tetradentate. infections caused by these bacteria. 6+ Cai et al. (37) studied a Co(II)-hmta complex Carlucci et al. (42) studied [Ag6(hmta)6] prepared using jet milling. An organic metal in 1997. When solutions of AgPF6 and hmta in

93 © 2018 Johnson Matthey https://doi.org/10.1595/205651317X696621 Johnson Matthey Technol. Rev., 2018, 62, (1) ethanol/dichloromethane were evaporated to analysis by TG and thermogravimetry coupled with dryness, a polymeric species was obtained, differential scanning calorimetry (TG-DSC), the

[Ag(hmta)](PF6)•H2O, containing a three-dimensional discovery that the complex is insensitive towards (3D) triconnected network topologically related to impact and friction and the evaluation of its kinetics the prototypal SrSi2. by model fitting. The preparation, characterisation Plotnikov et al. (43) studied antibacterial and and thermolysis of the La nitrate complex with immunomodulatory effects of hmta Ag nitrate in hmta were investigated. 2016. The antibacterial properties and influence Trzesowska et al. (86) studied the synthesis, on immune blood cells of the Ag-based compound crystal structure and thermal properties of a with general formula [Ag(hmta)]NO3 were mixed ligand 1,10-phenanthroline and hmta investigated. A noticeable inhibitory effect of the complex of La nitrate, providing insight into the drug was observed only at high concentration in coordination sphere geometry changes of La(III) phytohemagglutinin (PHA)-stimulated reaction 1,10-phenanthroline complexes. Geometry of blast transformation of lymphocytes (RBTL). optimisation was carried out using a density Based on this result, the tested Ag complex could functional theory (DFT) method using the Becke, be considered as a potential candidate for an three-parameter, Lee-Yang-Parr (B3LYP) functional antibacterial drug with low toxicity. by means of the Gaussian 03 program package. The minimal basis set CEP-4G was used on La 1.4 Coordination with Metal Salts of and 6-31G(d′) on oxygen, nitrogen, carbon and hydrogen atoms. Lanthanide Elements

Zalewicz (82) carried out thermal analysis of 1.5 Coordination with Metal Salts of complex salts of lanthanide chlorides with hmta Quaternary Nitrogen in 1989. Thermal decomposition of lanthanide chloride complex salts with hmta of the general In Table IV, the grey background compounds formula LnCl3•2hmta•nH2O (Ln = lanthanum, are made up of hmta coordinated with quaternary praseodymium, neodymium, samarium, nitrogen, while those on a white background are dysprosium, erbium; n = 8, 10, 12) was examined. formed by coordination of hmta molecules. In Mechanisms of the thermal dehydration reaction of other words, the hmta molecule links to other these salts were established and kinetic parameters small atoms or molecules directly, to form new of the first state of the dehydration reaction were molecules with different properties. This particular determined. The following year, the same survey mode of coordination makes it easier for molecules was carried out for lanthanide bromine salts (83). in such complexes to be connected and form mesh Zalewicz et al. (84) carried out coupled structures (Scheme I). thermogravimetry-mass spectrometry (TG-MS) Interestingly, it was found that when the hmta + investigations of lanthanide(III) nitrate complexes is changed into a [hmta-CH3] cation during with hmta in 2004. New transition metal compounds reaction, acid-catalysed decomposition of some of the general formula Ln(NO3)3•2[hmta]nH2O, hmta molecules resulted and led to a subsequent where Ln = La, Nd, Sm, gadolinium, terbium, alkylation of hmta in solution (27). Dy, Er, lutetium; n = 7–12, were obtained. The compounds and the gases evolved in the course 2. Discussion of the Coordination of their thermal decomposition were characterised Mode of hmta with Metal Salts by TGA. The measurements were carried out in air and argon environments in order to compare 2.1 Effect of Different Metal Cations the intermediate products, final products and the mechanism of the thermal decomposition. The The reaction of main group metal salts with hmta combined TG-MS system was used to identify the leads to the formation of coordination compounds, main volatile products of thermal decomposition mononuclear in case of lithium compounds, dinuclear and fragmentation processes of the obtained in other element compounds. The electronic compounds. properties of the cations strongly influence the Singh et al. (85) studied the kinetics of thermolysis coordination modes of both hmta molecules and of La nitrate with hmta in 2014. The highlights anions. Li ions are four-coordinated, Na, potassium were the confirmation of the crystal structure of and rubidium ions are six-coordinated, and Mg, this complex by X-ray crystallography, its thermal Ca, Sr and barium ions are six or more. Thus the

94 © 2018 Johnson Matthey https://doi.org/10.1595/205651317X696621 Johnson Matthey Technol. Rev., 2018, 62, (1) (44) (45) (46) (47) (47) (48) (48) (49) (45) (50) (51) (52) (52) (52) (52) (52) Reference No. (Continued) – – 729399 685560 746415 – – 211785 658325 – 293765 837612 837613 837614 837615 837616 CCDC No. – 976 1384 704 1368 1348 3112 1355.7 355 – 1068 1350 2764 4624 5184 4632 F (000) = 0.118 = 0.088 = 0.1068 = 0.0792 = 0.0932 = 0.0896 = 0.1052 = 0.126 = 0.1783 = 0.0997 = 0.15156 = 0.2047 = 0.1366 2 2 2 2 2 2 2 2 2 2 2 2 2 = 0.039, = 0.0396, = 0.0295, = 0.0352, = 0.0358, = 0.0573, = 0.046, = 0.056, = 0.0241 = 0.0702, = 0.0482, = 0.0867, = 0.1273, = 0.0731, 1 1 1 1 1 1 1 1 1 1 1 1 1 1 – R wR R wR R wR R wR R wR R wR R wR R wR – R R wR R wR R wR R wR R wR R indices (all data) –3 , d 1, 1.523 1, 1.562 2, 2.252 1, 2.294 2, 2.275 2, 2.247 4, 2.077 4, 1.42 1, 1.583 4, 1.416 4, 1.865 2, 1.224 4, 1.349 8, 1.300 8, 1.306 4, 1.342 Z, Mg m

(No. 33) (No. 33) (No. 1 1 /c (No. 14) /c (No. 14) /c (No. 14) /c (No. 176) /m (No. 14) /c (No. 14) /c (No. (No. 2) (No. 2) (No. 1 1 1 3 1 1 1 1 Triclinic, 1) P1 (No. Triclinic, P Monoclinic, 12) C2/m (No. Triclinic, 1) P1 (No. Monoclinic, P2 Monoclinic, 12) C2/m (No. Orthorhombic, Pna2 Monoclinic P2 Triclinic, P Monoclinic, P2 Orthorhombic, Pna2 Hexagonal, P6 Monoclinic, P2 Orthorhombic, 41) Aea2 (No. Orthorhombic, 60) Pbcn (No. Monoclinic, P2 Crystal system, space group ) 14 H 6 O (10:3) -C 2 ] n 2 ( ) • 6H 3 • O) H ] 2 2 ) CH 28 O 3 5 (H 2 OH) O 2 H 7 ) CCO 6 10 4 CH H 3 4H O O 5 3 V • O 2 2 (C O 5 ) 2 H • 2 3 6 Me -C ] • 6H 4H O [H n ] ] 4H • • 2 2 ( (C 4H 2 2 1.5 O-ClO • 2 2 • • • 2 ] ] ](NO 4H 3 3 2 ] • (H OH] 2 2 2 OH} OH} O 28 ) 2 2 2 2 3 O (hmta) (hmta) (hmta) O} 6 6 6 2 10 2(hmta) 8H ) ) ) 2(hmta) • • (hmta) (hmta) V 3 3 3 (NO (Br) • 2 6 6 2 6 2 2 ) ) ) ) ) 3 3 3 2 3 [H O) O-(hmta)} 4 2 2 ] CCMe CCMe CCMe 3 2 2 2 (H ](NO 2 ](NO {H 2(hmta) {(hmta)-CH {(hmta)-CH CCMe CCMe 6 6 4 • • • 2 2 Mn(OH O-(hmta)-H O) 28 28 28 O(O O(O O(O 2 2 O) O) 2 2 2 2 2 2 O O O O(O O(O 3 3 10 10 10 O (5:2) 2 V V V 6 4 4 0.5MeCN Table III Major Crystal Data and Refinement for Compounds of hmta with Metal Salts of Subgroup B Elements of Subgroup Salts Metal of hmta with Compounds and Refinement for Data Crystal Table III Major [Fe(H (1:2) [Fe(H (1:2) H (5:1) H (5:1) H (5:1) [(hmta)-CH 5H [(hmta)-H][(hmta)-CH Mn(hmta) (1:2) [Mn{H (1:1) [Mn(H (1:2) (hmta) (1:2) [Mn (1:1) [Mn (1:1) [MnFe • (1:2:2) [MnFe (1:2:2) [MnFe Formula (M:hmta)

95 © 2018 Johnson Matthey https://doi.org/10.1595/205651317X696621 Johnson Matthey Technol. Rev., 2018, 62, (1) (Continued) (53) (54) (49) (55) (52) (52) (56) (45) (57) (58) (55) (45) (45) (59) (60) (58) (61) Reference No. 1267/1319 256349 211784 – 905135 905136 – 639634 – – – 658326 639635 1267/1129 1267/1142 – 281949 CCDC No. – 500 328.9 – 485 518 896 341 – 924 – 358 342 – – – – F (000) = 0.086 = 0.0659 = 0.1550 = 0.1484 = 0.094 = 0.062 = 0.131 = 0.127 = 0.147 = 0.156 = 0.076 2 2 2 2 2 2 2 2 2 2 2 = 0.0255, = 0.032, = 0.0622, = 0.0751, = 0.044, = 0.036, = 0.054, = 0.055, = 0.056, = 0.074, = 0.028, 1 1 1 1 1 1 1 1 1 1 1 – R wR R wR – R wR R wR – R wR – R wR – R wR R wR R wR R wR R wR – R indices (all data) –3 , d – 2, 1.862 1, 1.50 1, 1.52 1, 1.685 2, 1.769 4, 1.944 1, 1.546 1, 1.640 1.123 1, 1.53 1, 1.638 1, 1.566 1 4 1 1, 1.619 Z, Mg m

(No. 2) (No. 2) (No. 2) (No. 2) (No. (No. 2) (No. 2) (No. 2) (No. 2) (No. (No.2) (No.2) 1 1 1 1 1 1 1 1 1 1 Triclinic, Triclinic, P Orthorhombic, 44) Imm2 (No. Triclinic, 1) P1 (No. Triclinic, P Triclinic, P Triclinic, P Orthorhombic, 59) Pmmn (No. Triclinic, P Triclinic, 1) P1 (No. Triclinic, 1) P1 (No. Triclinic, P Triclinic, P Triclinic, P Triclinic P Monoclinic 15) C2/c (No. P Triclinic 1) P1 (No. Crystal system, space group n } 2 OH) 5 O ] H 2 2 O 2 2 O) 6H (C 2 • • 6H 2 • O ) 2 2 (H n 4 ) 2 O } 4 ) 2 4H2O 2 4H 4 • • O O tfbdc) ) O O ) 2 2 4H 2 O) 3 2 2 3 • 2 O }](SO O O (H 2H 2 O 6 2H 2 2 }](SO 7H 2H (H • • 2 • 6 • • O-ClO • ] 2 2 2 ](NO 2 ] O) 4H ](NO 4H 4H 2 2 2 4H • O) 2 • • 2 • 2 (H O) 2 2 2 O) 2 2 2 ) 2 O) 2(hmta) 3 2 • (H ) O} (hmta) 2 (hmta)] 4 2(hmta) 2 • {Co(H ) 4 • {Ni(H (mal) 2 4 (NO 2 O ) 2 4 2 ) 6 (hmta) 4 2 (hmta) ) O 4 (hmta) • 6 4 O) 5 H 6 2 O) O) O-(hmta)} 2 O) 4 ) O-(hmta)} 2 2 H CO 2 2 3 (tfbdc)(H O) 2 7 2 O) 2 2 (H 2 (H 2 ](C (H {H ](ClO 2 (C 6 2 {H ](ClO 4 6 2 4 6 (NO CCH 6 O) 2 O) O) Co(H Ni(H O-(hmta)-H 2 O) O) 2 2 2 2 2 2 2 O) ) ) (O 2 3 3 (hmta)(H 4 tfbdc = 2,3,5,6-tetrafluoroterephthalic acid) tfbdc = 2,3,5,6-tetrafluoroterephthalic 2 2 [Mn(H (1:2) Mn (2:1) (mal = malonate) Co(hmta) (1:2) (NO (1:2) {[Co(hmta) (1:2) (H {[Co(hmta)(tfbdc)(H [Cu (4:1) [Co(H (1:2) [Co(H (1:2) [Co(hmta) (1:1) (NO (1:2) [Ni{H (1:2) [Ni(H (1:2) Ni(H (1:2) Ni(hmta) (1:2) [Ni(hmta) (1:1) [Ni(H (1:2) Formula (M:hmta)

96 © 2018 Johnson Matthey https://doi.org/10.1595/205651317X696621 Johnson Matthey Technol. Rev., 2018, 62, (1) (61) (62) (63) (62) (62) (64) (38) (54) (40) (40) (40) (40) (45) (65) (65) (66) Reference No. (Continued) 281950 969623 – 969622 969624 – – 256350 942350 942351 942352 942353 658327 963566 963568 849277 CCDC No. – – 1612 – – – – 516 – – – – 360 936 344 – F (000) = 0.062 = 0.1577 = 0.120 = 0.2011 = 0.0888 = 0.1165 2 2 2 2 2 2 = 0.048, = 0.0572, = 0.047, = 0.0792, = 0.0324, = 0.0714, 1 1 1 1 1 1 – – – – – R wR – R wR – – – – R wR R wR R wR R wR R indices (all data) –3 , d 1, 1.412 1, 1.557 4, 1.579 2, 1.639 2, 1.709 – 4, 1.817 2, 2.047 16, 1.624 2, 1.491 2, 1.581 8, 1.754 1, 1.639 2, 1.634 1, 1.547 2, 1.702 Z, Mg m

(No. 2) (No. 2) (No. 2) (No. /a (No. 88) /a (No.

2d (No. 122) 2d (No. 1 1 1 1 4 Triclinic 1) P1 (No. Triclinic, 1) P1 (No. Orthorhombic, 56) Pccn (No. Triclinic, 1) P1 (No. Triclinic, 1) P1 (No. Triclinic, 1) P1 (No. Monoclinic, 15) C2/c (No. Orthorhombic, 44) Imm2 (No. Tetragonal, I Triclinic 1) P1 (No. Trigonal 143) P3 (No. Tetragonal I4 Triclinic, P Triclinic P Triclinic P Triclinic 1) P1 (No. Crystal system, space group O 2 6H • ] 2 2– 4 O) 2 2SO (H • 2 ) O 2+ 4 2 ] 6 4H • n n O) – ] ] 2 2(3-nbzH) n 3 2 2 O-ClO O • ] 2 2 ] 2 O] 2 O) O) 2 n n 2 2 (H 4H 2NO H 2 2 O) • • • [Zn(H 2 O) • 2 n O} (H 2 2+ 2 (H ] (mal) 2 4 2 2 O)(hmta) -hmta)] -hmta)] 2 2 2 3 -hmta) O) -hmta)(H -hmta)(H 2(hmta) 4 2(hmta) O) 2 m m 2 2 • • 2 m ( ( (H -hmta)] m m 6 6 ( 4 l2 3 (H (hmta) ( ( 2 2+ 2 m 2 2 2 (hmta) ] (hmta) ]C ( 2 6 2 6 6 (hmta) 3 O-(hmta)-H O) 2 O) 2 2 btc) (2-nbz) (pa) (4-nbz) 2 (4-nbz) 3 3 3 (hmta)(H 2 2 [Ni(H (1:2) [Ni(3-nbz) (1:2) (3-nbz = 3-nitrobenzoate) Ni(H (1:2) (btc = benzene-1,3,5-tricarboxylate) [Ni(2-nbz) (1:1) (2-nbz = 2-nitrobenzoate) [Ni(4-nbz) (1:1) (4-nbz = 4-nitrobenzoate) Cu(NCO) (1:2) (CuCN) (1:2) Cu (2:1) (mal = malonate) [Cu (3:1) [Cu (3:1) (pa = phenylacetate) [Cu (3:1) [Cu(3-nbz) (1:1) [Zn{H (1:1) [Zn(hmta) (1:1) [Zn(H (1:2) [Zn (1:1) Formula (M:hmta)

97 © 2018 Johnson Matthey https://doi.org/10.1595/205651317X696621 Johnson Matthey Technol. Rev., 2018, 62, (1) (66) (66) (65) (65) (67) (68) (69) (70) (71) (71) (71) (71) (34) (61) (72) (72) Reference No. (Continued) 849278 849279 963567 963569 232121 684814 – 1025425 903838 903839 903840 903841 281951 782486 782487 CCDC No. – – 928 824 2192 40800 3936 – – – – – – – – F (000) = 0.0839 = 0.2172 = 0.1506 = 0.0391 = 0.0627 = 0.1003 2 2 2 2 2 2 = 0.0759, = 0.1640, = 0.0514, = 0.0162, = 0.0584, = 0.0362, 1 1 1 1 1 1 R wR R wR R wR R wR R wR R wR – – – – – – – – – – R indices (all data) –3 , d 2, 1.658 4, 1.782 4, 1.913 4, 2.094 4, 1.816 4, 2.072 8, 1.185 16, 1.727 4, 1.748 1, 1.641 2, 1.866 2, 1.785 4, 2.096 2, 1.824 – – Z, Mg m (No. 33) (No. 1 m (No. 227) m (No. /c (No. 14) /c (No. 14) /c (No. 14) /c (No. 14) /c (No. (No. 2) (No.

3 1 1 1 1 1 Triclinic 1) P1 (No. Monoclinic P2 Triclinic P Monoclinic C2/c (No.15) Orthorhombic, Pna2 Orthorhombic, 41) Aea2 (No. Cubic, Fd Orthorhombic, 43) Fdd2 (No. Monoclinic P2 Triclinic 1) P1 (No. Orthorhombic 35) Cmm2 (No. Triclinic 1) P1 (No. Monoclinic, 15) C2/c (No. Monoclinic, P2 Orthorhombic, 60) Pbcn (No. Monoclinic, P2 Crystal system, space group O 2 2H • O) 2 68DMF O • 2 O O H O 2 2 • 2 OH)(H ] H 5 2 O O n ) 2 2 H 2H 2 46H 2 2 • 2(3-nbzH) H • • • • O 2H )] ] 2 2 68 2– • 2 2 ] 4 ] (OH H n 2 ) 2 2 ] 2 • ) ]Cl O)] 2 4 SO 2 2 17 n ] O) O)] (OH 2 (H 2 O) 2 2+ 2 2 n (ClO 0.5 ] 2 (H -hmta) O) 4 2 (H 2 2 ) 2 m -hmta)(OH -hmta)] 3 (hmta) ) ( 2 2 -1,3,5-cyclohexanetricarboxylate) O) 3 -hmta)(DMF)(C 4 2 m m (hmta) (hmta)(OH) 34 2 ( (hmta) ( 4 4 } cis 2 2 4 3 , (hmta) (μ (hmta) 2 2 4 O) cis 2 O) 2 (4-nbz) )(hmta) )(hmta)(H 2 1 2 (2-nbz) (3-nbz) 2 3 (CTC) = ligand) = ligand 1) 3 1 2 [Zn [Zn [Cd(hmta)(H [Cd(hmta)(NO Cd [Cd(SCN) [{Cd(H [Cd(cdpc)(hmta)(H [Cd(2-nbz) [Cd(3-nbz) [Cd(3-nbz) {[Cd Cd(hmta)(NO [Cd(H Ag(L (1:1) (L Ag(L (1:1) (3:1) (1:1) (1:1) (3:1) = (CTC (2:1) (2:1) (1:1) (cdpc = 1-carboxymethyl-3,5-dimethyl-1H-pyrazole-4- carboxylic) (1:1) (1:2) (1:1) (1:1) (1:1) (1:2) (1:1) (L Formula (M:hmta)

98 © 2018 Johnson Matthey https://doi.org/10.1595/205651317X696621 Johnson Matthey Technol. Rev., 2018, 62, (1) (72) (72) (72) (72) (73) (73) (73) (74) (74) (75) (75) (75) (75) Reference No. (Continued) 782488 782489 782490 782491 169729 169730 169731 – – – – – – CCDC No. – – – – – – – – – – – – – F (000) = 0.1624 = 0.2012 = 0.1263 = 0.0987 = 0.0848 = 0.1110 2 2 2 2 2 2 = 0.0670, = 0.0617, = 0.0478, = 0.0376, = 0.0380, = 0.0414, 1 1 1 1 1 1 – – – – – – – R wR R wR R wR R wR R wR R wR R indices (all data) –3 , d – – – – 2, 1.863 4, 1.675 2, 2.248 4, 2.170 4, 2.148 4, 1.828 4, 1.885 4, 1.939 4, 1.577 Z, Mg m (No. 31) (No. 31) (No. (No. 58) (No. (No. 62) (No. (No.33) 1 1

(No. 29) (No. 29) (No. 1 1 1 /c (No. 14) /c (No. 4) (No. 4) (No. 14) /c (No. 14) /c (No. 1 1 1 1 1 Orthorhombic, Pca2 Monoclinic, P2 Monoclinic, P2 Monoclinic, P2 Orthorhombic, Pmn2 Orthorhombic, Pmn2 Orthorhombic, Pnnm Orthorhombic, Pna2 Monoclinic, 15) C2/c (No. Monoclinic, P2 Monoclinic, P2 Orthorhombic, Pnma Orthorhombic, Pca2 Crystal system, space group O 2 18H • ] 3 O) 2 O -H 2 O m 2 ( 3H 2 • 3H ) O • 3 2 2H O • -pma) O 2 ) 2 OH) 6 (pma) m 5 2 ( H O)](NO ] 2 H 6 2 O) O) 2 2 OH) 2.5H 2 2 ) 2.5H 3 • 3 • 0.5(C O) 18(H 16(H • 2 -hmta) 2(CH • • 4 • ] ] -nba)] (H ] 6 6 -nba)] -hna)](C [Ag(NH (μ-ssa)(H (μ • 2 2 p m α 2 2 (hmta) (hmta) 6 6 -hmta) -hmta) )(hmta) ) ) -hmta)](abs) -hmta)](ns) -hmta)] 4 3 -hmta)( -hmta)( -hmta)(dnba)] -hmta)( )(hmta)] 4 5 6 3 3 3 3 3 3 3 3 (L (L (L (μ (μ 2 6 6 3 8 = ligand) = ligand) = ligand) = ligand) -nba = 3-nitrobenzoate) -nba = 4-nitrobenzoate) -hna = 1-hydroxy-2-naphthate) 3 4 5 6 p m α [Ag(L (1:1) (L [Ag (1:1) (L [Ag (1:1) (L [Ag (1:1) (L [Ag(μ (1:1) (abs = 4-aminobenzenesulfonate) [Ag(μ (1:1) (ns = 2-naphthalenesulfonate) [Ag(μ (1:1) (pma = 1,2,4,5-benzenetetracarboxylate) [Ag (1:1) (ssa = sulfosalicylate) [Ag (2:1) (pma = 1,2,4,5-benzenetetracarboxylate) [Ag(μ (1:1) ( [Ag(μ (1:1) ( [Ag(μ (1:1) (dnba = 3,5-dinitrobenzoate) [Ag(μ (1:1) ( Formula (M:hmta)

99 © 2018 Johnson Matthey https://doi.org/10.1595/205651317X696621 Johnson Matthey Technol. Rev., 2018, 62, (1) (75) (75) (75) (75) (76) (76) (76) (76) (77) (77) (78) (79) (50) (80) (81) Reference No. – – – – – – – – – – – – – – – CCDC No. – – – – 1376 – – 1392 1648 2160 – – – – – F (000) = 0.1156 = 0.1490 = 0.1362 = 0.1264 = 0.1314 = 0.0957 = 0.1439 = 0.1149 = 0.054 = 0.1894 = 0.073 2 2 2 2 2 2 2 2 2 2 2 = 0.0461, = 0.0579, = 0.0499, = 0.0446, = 0.0451, = 0.1071, = 0.2275, = 0.0788, = 0.045, = 0.0676, = 0.060, 1 1 1 1 1 1 1 1 1 1 1 R wR R wR R wR R wR R wR – – R wR R wR R wR – R wR R wR R wR – R indices (all data) –3 , d 4, 1.576 8, 1.509 4, 1.965 2, 1.814 8, 1.970 2, 2.101 8, 2.022 4, 2.014 4, 2.103 4, 2.321 – 4, 2.33 8, 3.850 2, 2.830 8, 3.548 Z, Mg m

(No. 176) (No. (No. 36) (No. (No. 58) (No.

(No. 29) (No.

1 (No. 70) (No. (No. 60) (No. (No. 61) (No.

(No. 205) (No. /m 14) /c (No. 11) /m (No. 3 3 1 1 Orthorhombic, Pca2 Orthorhombic, Pbca Orthorhombic, Pbcn Orthorhombic, Pnnm Orthorhombic, 60) Pbcn (No. Hexagonal, P6 Cubic, Pa Monoclinic 15) C2/c (No. Monoclinic C2/c (No.15) Monoclinic P2 Orthorhombic Orthorhombic, Cmc2 Monoclinic, 15) C2/c (No. Monoclinic, P2 Orthorhombic, Fddd Crystal system, space group O 2 H • ) 3 SO 3 OH OH) 5 5 H H 2 2 3 OH) O)](CF ) 5 2 O 6 2 3C n 2 H • O 2 Cl 4 2 )(H 2 O)(C ) O] 8H 3 2 6 2 ](PF • 4 4H ] • SO 2 2H 3CH 3 O) • • 2 2 ] ) 3 6 0.5 ] -hna)](C O)](PF (fa)] (adp)] (CF (H 2 2 β 2 2 2 2 Br ](PF (H 6 3 0.5 (hmta)] • -toluenesulfonate) ) (hmta) 2Hg(SCN) 3 -hmta) -hmta) -hmta)(Tos) -hmta) -hmta) 2 p • -hmta)( -hmta)(noa)](H 3 3 4 3 3 ) 3 3 2 (μ (μ (hmta) (hmta) (μ (μ (μ 2 2 5 4 2 2 3 -hna = 3-hydroxy-2-naphthate) β [Ag(μ (1:1) ( [Ag(μ (1:1) (noa = 2-naphthoxyacetate) [Ag (1:1) (fa = fumarate) [Ag (1:1) (adp = adipate) [Ag(hmta)(fma) (1:1) (fma = furmaric acid) [Ag (5:5) [Ag (4:3) [Ag (2:1) = (Tos [Ag (1:1) [Ag (3:2) [Ag(NO (1:1) [H-(hmta)][HgCl (1:1) [Hg(hmta) (2:1) (hmta) (2:1) (HgCl (2:1) Formula (M:hmta)

100 © 2018 Johnson Matthey https://doi.org/10.1595/205651317X696621 Johnson Matthey Technol. Rev., 2018, 62, (1) (Continued) Reference No. (86) (85) (87) (88) (89) (90) (90) (90) (90) (90) (90) (90) (90) (90) CCDC No. 269659 993310 – 1003/4553 – 258316 266394 266395 – 266396 258317 266397 258318 266389 F (000) 1520 – – – 1544 1528 1532 1536 1580 1628 1632 1636 822 824 = 0.0396 = 0.1239 = 0.071 = 0.0623 = 0.0634 = 0.0879 = 0.0754 2 2 2 2 2 2 2 = 0.0504, = 0.0697, = 0.037, = 0.0261, = 0.0307, = 0.0333, = 0.0287, 1 1 1 1 1 1 1 R indices (all data) R wR R wR – R wR R wR R wR – – – – R wR – R wR – –3 , d Z, Mg m 4, 1.731 4, 1.686 2, 1.638 – 4, 1.655 4, 1.707 4, 1.712 4, 1.721 4, 1.793 4, 1.730 4, 1.740 4, 1.75 2, 1.756 2, 1.767 m (No. 225) m (No. /n (No. 14) /n (No. 14) /c (No. 14) /c (No. 14) /c (No. 14) /c (No. 14) /c (No. 14) /c (No. 14) /c (No. 14) /c (No. 3 1 1 1 1 1 1 1 1 1 Crystal system, space group Monoclinic, P2 Monoclinic, P2 Triclinic, 1) P1 (No. Orthorhombic, Pnma (No 62) Cubic, Fm Monoclinic, P2 Monoclinic, P2 Monoclinic, P2 Monoclinic, P2 Monoclinic, P2 Monoclinic, P2 Monoclinic, P2 Triclinic, 1) P1 (No. Triclinic, 1) P1 (No. O 2 2H • O O 2 O 2 O O O O 2 2 2 2 2 O 3H 2 3H (hmta) • 3H • 2H 2H • H 2H 2H • O O • • – • • • 2 2 3 – 3 2H 2H NO • • • NO O • 2(hmta) 2 2(hmta) ]+ • 2(hmta) • 2(hmta) 2(hmta) 4 2(hmta) – 2(hmta) • – • • • 3 4H • – 3 – – – • – 3 O 3 O) 3 3 3 2 2 2(hmta) 2(hmta) (hmta)[FeDy] • • 2NO • NO NO (H 2NO 2(hmta) NO – – 9H NO • ] • • 2NO • • • • 3 3 • • 6 • + 2 + + + + + 2+ ] ] + ] ] ] N ] ] 6 6 ] 7 6 6 8 6 7 7 2(hmta) 3NO 3NO • H O) O) O) • • O) O) – O) O) 2 2 O) 2 2 2 12 2 2 2 3+ 3+ C ]Cl (H ] ] 2(hmta) (H ][M(CN) • (H (H (H 9 2 8 8 • 2 )(H 8 2 2 2 2 )(H ) 3 ) )(H 3 ) ) ) ) 3 3 3 3 3 3 3 O) 3 O) O) O) 2 2 2 2 Table IV Major Crystal Data and Refinement for Compounds of hmta with Metal Salts for Compounds Crystal Data and Refinement Table IV Major Formula (M:hmta) [La(NO (1:1) [La(NO (1:2) [Nd(H (1:2) La(NCS) (1:2) [Ln(H (1:2) [La(NO (1:2) [Ce(NO (1:2) [Pr(NO (1:2) [Nd(NO (1:2) [Sm(NO (1:2) [Eu(NO (1:2) [Gd(NO (1:2) [Dy(H (1:2) [Ho(H (1:2)

Alkylation

Reference No. (90) (90) (90) (91) (92) reaction

HMTA HMTA-CH3

Scheme I. Schematic diagram of alkylation reaction CCDC No. 266391 266392 266393 – –

ability to form multinuclear species depends on the type of metal and increases with increasing atomic

F (000) 828 830 832 3192 – number.

2.2 Effect of Different Anions

In the studied compounds, unshared electrons were not only provided by ligands, but also by anions = 0.1256

2 – – – – – 2– – = 0.0659, such as Cl , Br ,I , NO , ClO , Cr O and SCN .

1 3 4 2 7 R indices (all data) – – – R wR – Different anions are mainly used for regulating the electric charge and sometimes make the overall molecule slightly distorted. Among the inorganic –3 –

, anions serving as ligands the most popular is SCN d due to its great tendency to link metal ions. Z, Mg m 2, 1.781 2, 1.801 2, 1.807 4, 2.798 4, 1.54178

2.3 Effect of Water Molecules

Among these compounds, water molecules also play a very important role, providing oxygen atoms or hydrogen bonds and making the overall structure more stable. Thermal analyses show that the water molecules in the investigated compounds were Crystal system, space group Triclinic, 1) P1 (No. Triclinic, 1) P1 (No. Triclinic, 1) P1 (No. Orthorhombic, 62) Pnma (No. Monoclinic, 12) C2/m (No. totally removed during thermal decomposition and further heating.

2.4 Coordination Positions and O O 2 2 Crystal System 2H 4H • • ] ] The hmta molecule is a tetrafunctional neutral 2 O 24 O O 2 2 2 O organic ligand which can be used as an outer 7 2H (OH) 2H 2H •

2 coordination sphere modulator of an inner • • Mo ) 5 5 coordination sphere or as a crosslinking agent O O) 4 2

H building block in di- and multinuclear compounds. 4 2(hmta) 2(hmta) 2(hmta) •

(C It has been used to assemble new supramolecular • • – 2 – – 3 ) 3 3 2 structures with metal ions, via various coordination O)[Ce(H 3

3NO modes, involving one to four N atoms of the hmta 3NO 3NO • • • (H [(UO 2 2 3+ molecule. 3+ 3+ ] ] ] 8 8 8 The ions and molecules appear in different O) O) O) 2 2 2 positions, called the inner and outer coordination spheres. For example, main group metal salts

Formula (M:hmta) [Tm(H (1:2) [Yb(H (1:2) [Lu(H (1:2) {H-(hmta)} (1:1) {H-(hmta)} (1:1) coordinate with hmta in the inner coordination

102 © 2018 Johnson Matthey https://doi.org/10.1595/205651317X696621 Johnson Matthey Technol. Rev., 2018, 62, (1) sphere in the case of Na, K and Rb compounds, spectral and magnetic features and ligand field and in the outer coordination sphere in the case of effects. Li, Mg, Ca and Sr compounds. This phenomenon Organometallic complexes of lanthanide metals may be affected by many factors, the electronic are mainly used to catalyse organic reactions. properties of the cation being the most important. Some other functional studies are still in progress. Under the action of hmta, different ions and water molecules form different crystal systems: 3. Applications of hmta with Metal orthorhombic, monoclinic, triclinic, hexagonal, cubic Salts or parallelepiped. Among them, monoclinic and triclinic crystal structures are the most common. 3.1 Military Applications There are also some rare 3D hybrid compounds, such as [Na(ClO4)(H2O)(hmta)]n, [NaNO3•hmta]n, Complexes of hmta have been investigated for

[K2(hmta)(SCN)2]n, [K(H2O)(hmta)I]n and military applications as explosives. Singh et al.

[Rb(H2O)(hmta)I]n. It is thereby demonstrated (45) characterised a complex of lanthanum nitrate that simple inorganic anions and organic molecules with hmta by X-ray crystallography. Thermolysis can be used to construct 3D networks possessing of the complex was undertaken using TG and high complexity (multinodal nets with complicated TG–DSC, a micro-destructive technique which stoichiometry) after proper selection of the does not require any pretreatment before analysis molecular species for net self-assembly. and can provide useful information about thermal and chemical reaction processes in a relatively 2.5 A Discussion on Synthetic Methods short time. In order to establish safe handling procedures, sensitivity of explosives towards As the ligands, salts and hmta are soluble in water mechanical destructive stimuli such as impact almost all of the synthetic methods are similar: and friction are measured. The development of make the solution at a certain proportion and stir highly energetic materials includes processability them together for a number of hours, followed by and the ability to attain insensitive munitions treatment for several days or weeks at either room (IM). The paper investigated the preparation of temperature or a specific temperature. So far, a lanthanum nitrate complex of hmta in water most complexes were prepared by virtue of this at room temperature. The complex, of molecular method. When the molecules are larger or ligand formula [La(NO3)2(H2O)6](2hmta)(NO3)(H2O), types are more complex, the synthesis conditions was characterised by X-ray crystallography. should manipulate a number of variables such as Thermal decomposition was investigated using TG, pH, ligand and cation size and type. TG–DSC and ignition delay measurements. Kinetic analysis of isothermal TG data was carried out 2.6 The Similarities and Differences using model fitting methods as well as model free iso-conversional methods. The complex was found of Transition Metal Complexes to be insensitive towards mechanical destructive Compared to transition metal coordination stimuli such as impact and friction. compounds, those of alkaline earth metals have In order to identify the end product of thermolysis, not been widely studied. Such materials should be the X-ray diffraction (XRD) patterns were environmentally friendly and their syntheses should examined which proved the formation of La2O3. be simple and economical. Thus, investigation The crystal structure reveals that the lanthanum of alkaline earth metal coordination chemistry is metal had a coordination number of 10. TG–DSC indispensable for obtaining new compounds and studies showed a three-step decomposition of new materials. the complex. The oxidation-reduction reaction

There has been much research on transition metal between oxidiser (NO3) and fuel (hmta) led to complexes with hmta as well as comparison of their ignition yielding La2O3 and gaseous products. The performance in a range of potential applications. oxide residue was confirmed by the XRD pattern. Among the most studied are complexes with Ni, The impact and friction sensitivity measurements Mn, Cu or Zn. As a transition metal centre, Ni is well showed that this compound exhibited remarkably suited for the construction of various coordination low sensitivity towards impact (>73 J) and friction polymers with N- and/or O-ligands on account of (>360 N). This nitrogen-rich metal complex may its variable oxidation states, different geometries, be a good candidate as a ‘green’ metal energetic

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The Authors

Jia Kaihua is a graduate student in Military Chemistry and Pyrotechnics at Shenyang Ligong University, China. Her interests are in the preparation and application of energetic materials. This review is a summary of coordination compounds of hexamethylenetetramine with different metal salts, which is connected to her research direction.

Ba Shuhong is an Associate Professor and master’s supervisor at Shenyang Ligong University, China. His main research directions are the design and preparation of new energetic materials, special effects ammunition and intelligent technology, digital pyrotechnics systems and applications.