All chemicals were purchased from Aldrich and used as received without further purification. 3,3’-bis(pyrazolyl)pentane, copper(II) malonate and water were of analytical grade. Elemental analysis was performed using a Euro Vector CHNS-O element analyzer. FT-IR spectra were recorded using a Perkin-Elmer FT-IR 100 spectrometer. The melting point of the compound was obtained using an SMP3 Stuart Scientific melting point apparatus while UV-vis spectrophotometer model GENESYS 10S was employed to record the electronic spectra of the investigated compounds. Powder X-rays diffraction was performed using STOE Stadi-p X-ray powder diffractometer with Cu Kα1 radiation (λ = 1.54056 Å; Ge monochromator; flat samples) in transmission geometry.

Blue crystal of copper(II) malonate (172.0 mg, 1.0 mmol) were dissolved in methanol-distilled water mixture (10 mL - 5 mL) at 50˚C. To the blue solution obtained was added dropwise, colorless methanol-distilled water (5 mL - 10 mL) solution of 3,3’-bis(pyrazolyl)pentane (204.0 mg, 2.0 mmol). The mixture was stirred for 1h and the blue solution obtained was filtered. The filtrate was left to slowly evaporate at room temperature for several days. The obtained product was washed with a methanol-distilled water mixture and then dried at air, giving blue crystals of (1), in 66.5% (250 mg) yield. Mp: 202˚C, Anal. Calc. (%) for C₂₈H₄₆Cu₂N₈O₁₃: C 40.48; H 5.70; N 13.49. Found (%): C 39.72; H 5.77; N 13.68. FT-IR (υ, cm⁻¹): 3414.1 (br), 3213.6 (br), 1578.1 (vs), 1434.1 (w), 1340.9 (w), 1221.2 (w), 1064.6 (w), 763.3 (m), 719.4 (m) cm⁻¹.

Similarly, compound (2) was synthesized by mixing copper(II) malonate (150 mg, 0.74 mmol) and 4,4’-trimethylenedipyridine (295 mg, 1.48 mmol) in a methanol-distilled water solvent mixture. The reaction mixture was heated to 50˚C for one hour with constant stirring. The resultant mother liquor was then filtered, and left unperturbed for several days at room temperature for slow evaporation. The resulting solid was washed with distilled water, then dried at air, leaving dark blue platelets of compound (2) in 65% (289 mg) yield. Mp: 100˚C Anal. Calc. (%) for C₃₂H₃₆CuN₄O₉. C 56.17; H 5.30; N 8.19. Found (%): C 56.4; H 6.64; N 9.51. FT-IR (υ, cm⁻¹): 3675.0 (vw), 1613.0 (vs), 1573.9 (s), 1427.7(s), 1335.4 (w), 1225.3 (w), 800.0 (m), 700.1 (m) cm⁻¹

Synthesis of Compound (1): Compound (1) was obtained by mixing copper(II) malonate, prepared from malonic acid and copper(II) nitrate, with 3,3’-bis(pyrazolyl)pentane in methanol-distilled water mixture at 50˚C (Scheme 1). The solution obtained was left for slow evaporation and blue crystalline solid of (1) was isolated.

Cu ( O 4 C 3 H 2 ) 4 ⋅ 2H 2 O + 2C 11 H 16 N 4 → 50 ˚ C MeOH / H 2 O [ ( Cu ( N 4 C 11 H 16 ) 2 ( O 4 C 3 H 2 ) 2 ( OH 2 ) ) 5 ] Scheme 1

Compound (1) appeared as blue crystals that are soluble in methanol, ethanol, dimethylformamide and dimethyl sulfoxide and insoluble in water, dichloromethane, acetonitrile and are stable in air.

Synthesis of Compound (2): Compound (2) was obtained by mixing copper(II) malonate, prepared from malonic acid and copper(II) nitrate with 4,4’-trimethylenedipyridine in methanol-distilled water solution mixture at 50˚C (Scheme 2). After slow evaporation of the solvent mixture, a dark blue crystalline solid of the compound was isolated in good yield.

Cu ( O 4 C 3 H 2 ) 4 ⋅ 2H 2 O + 2C 13 H 14 N 2 → 50 ˚ C MeOH / H 2 O [ ( Cu ( N 2 C 13 H 14 ) 2 ( O 4 C 3 H 2 ) 2 ) ] ⋅ ( H 2 O ) Scheme 2

This air stable material is soluble in dimethylformamide and dimethylsulfoxide and insoluble in water, dichloromethane, acetonitrile and methylcyanate.

The FT-IR spectrum of compound (1) (Figure 1(a)) shows the presence of the pyrazolyl ligand and carboxylate ion used in the synthesis of the compound, through the typical vibrations of pyrazolyl ring and carboxylate groups. The presence of O-H characteristic absorption band around 3414 cm⁻¹ is an indication that the compound contains water molecules. The very strong absorption band around 1578 cm⁻¹ can be attributed to the valence vibrations of the C=N of the pyrazole unit [9]. This band which usually appears at 1595 cm⁻¹ has been shifted to 1578 cm⁻¹ suggesting the coordination of 3,3’-bis(pyrazolyl)pentane ligand to the metal ion. Similar displacements were observed in the reported [Ag(N₂C₁₁H₁₀)₂]NO₃ (where N₂C₁₁H₁₀ = 4,5-dihydro-1H-benzo [g]indazole) [10]. The weak band at 1340 cm⁻¹ can be attributed to the vibrations of the C=O group of carboxylates. Between 1300 cm⁻¹ and 750 cm⁻¹, are the deformation vibrations of the pyrazole rings and those of aliphatic C-H groups present in the ligand.

On the other hand, the FT-IR spectrum of compound (2) (Figure 2(a)) displays very weak absorption bands at 3675 cm⁻¹ which could be attributed to the O-H vibration, indicating the presence of water in the material. The very strong band appearing between 1620 cm⁻¹ and 1600 cm⁻¹ is assignable to the stretching vibrations of the azomethine, C=N functions [11] [12]. This vibration is similar to that reported for [Zn(SCN)₂(TMDP)] [13]. Compound (2) shows two strong absorption bands at 1574 cm⁻¹ and 1428 cm⁻¹ due to the asymmetric and symmetric vibration of the carboxylate group of the malonate anion. The 146 cm⁻¹ difference between the asymmetric and symmetric vibrations of the carboxylate indicates that the carboxylate group forms a chelating coordination mode to the copper(II) ion. Meanwhile, the deformation oscillations of the aromatic C-H groups occur between 856 cm⁻¹ and 624 cm⁻¹.

These analyses confirm the functionalization of copper(II) malonate with 3,3’-bis(pyrazolyl)pentane and 4,4’-trimethylenedipyridine.

The electronic absorption spectrum of (1) (Figure 3) was recorded in DMSO solvent at a range of 200 - 800 nm. An intense band observed at 268 nm was assigned to the intra-ligand π → π* and n → π* electronic transitions for aromatic rings of 3,3’-bis(pyrazolyl)pentane and C=O group of malonate anion. This value is similar to those observed by Afifa Mushtaq and co-workers, at 270 nm for a copper(II) carboxylate compound, functionalized using bipyridine [14]. No d-d transitions and charge transfer were observed and this may be due to the weakness of the bands [15].

Figure 4 shows the UV-Vis absorption spectrum of compound (2). This figure indicates a single band in the visible region, characteristic of copper(II)

compounds. This intense band at 286 nm corresponds to the intra-ligand π → π* and n → π* electronic transitions which can be attributed to the pyridine moiety of the 4,4’-trimethylenedipyridine ligand and the C=O group of malonic acid. This wavelength can also be assigned to the ligand metal charge transfer transition. It is similar to those observed by Sarath and Yamuna for cobalt functionalized with 4,4’-trimethylenedipyridine [16]. This confirms the fact that the compound contains 4,4’-trimethylenedipyridine in its coordination sphere. No d-d transitions were also observed [15].

The diffractograms obtained from the powder X-ray analysis of compound (1) and (2) in the range 5˚ to 70˚ are shown in Figure 5 and Figure 6. The sharp Bragg peaks of good intensities found on the spectra indicate a high level of

crystallinity of the materials. The low reflection rate (or reduced number of reflections) did not permit the unravelling of the unit cell parameters and space group of the compounds. However, the non-superposition of the PXRD patterns of compounds (1) and (2) with that of copper(II) malonate, as shown in Figure 7 and Figure 8 respectively, indicates the formation of new compounds and confirms the functionalization of copper(II) malonate by 3,3’-bis(pyrazolyl) pentane in compound (1) and 4,4’-trimethylenedipyridine in compound (2).

The results obtained from various analytical techniques might indicate, with caution, the structures depicted in Figure 9 for the newly functionalized coordination compounds (1) and (2). However, these structures shall be confirmed in our future publication after recrystallization of the compounds and single crystal X-ray diffraction analysis results are made available.