Facile synthesis and vapochromic studies of Co(II) complexes bearing NO and OO donor ligands

Figures & data

Scheme 1 Equation of reaction for solvent-free mechanochemical synthesis of 1 and 2.

Fig. 1 (a) The proposed structure of [Co(Mal)].2H₂O]_n (1). (b) The proposed structure of [Co(Ina)₂].2H₂O]_n (2).

Fig. 2 (a) TG–DTG curve of complex 1. (b) TG–DTG curve of complex 2.

Table 1 Selected UV-visible spectra data for malonic acid and its Co(II) complex.

Complex/ ligand	Wavelength (nm)	Energy (cm^−1)	Absorbance	Assignment
Malonic acid	258	38760	0.123	π-π*
	290	34483	0.093	n-π*
[Co(mal)].2H2O]n	260	38461	0.392	π-π
	294	34014	0.784	n-π*
	532	18797	0.666	^4T1g→^4T1g(P)
	682	14663	0.039	^4T1g→^4A2g
	930	10753	0.040	^4T1g→^4T2g

Table 2 Selected UV-visible spectra data for isonicotinic acid and its Co(II) complex.

Complex/ ligand	Wavelength (nm)	Energy (cm^−1)	Absorbance	Assignment
Isonicotinic acid	260	38462	0.112	π-π*
	312	32051	2.501	n-π*
[Co(Ina)2].2H2O]n	264	37879	0.360	π-π*
	302	33113	2.328	n-π*
	476	21008	0.309	^4T1g→^4T1g(P)
	516	19380	0.306	^4T1g→^4A2g
	1078	9276	0.089	^4T1g→^4T2g

Fig. 3 (a) PXRD pattern of malonic acid and [Co(mal)].2H₂O]_n (1). (b) PXRD pattern of isonicotinic acid [Co(Ina)₂].2H₂O]_n (2).

Fig. 4 (a) Pictures of 1 as-synthesized, after activation and after exposure to VOCs. (b) Pictures of 2 as-synthesized, after activation and exposure to VOCs.

Fig. 5 (a) FT-IR spectra of solvent-included Co-malonic complexes (a) 1 (b) 1-Activated (1a) (c) 1a-DMSO (d) 1a-DCM (e) 1a-DMF. (b) FT-IR spectra of solvent-included Co-isonicotinic complex (a) 2 (b) 2-activated (2a) (c) 2a-DCM (d) 2a-DMF (e) 2a-benzene (f) 2a-ethanol.

Table 3 Colours of 1 as-synthesized, activated and after exposure to VOCs and their selected FT-IR band frequencies.

Complex		1	1a	1a-Benzene	1a-DCM	1a-DMF	1a-DMSO	1a-EtOH	1a-MeOH	1a-NH3
Colour		Peach orange	Dark pink	Apricot	Pale pink	Amaranth pink	Amaranth pink	Apricot	Amaranth pink	Brown
IR Peaks (cm^−1)	ν(OH)	3288	3425	3454	3454	3433	3456	3450–3200	3419	3327
	ν(C-H) alkanes	2949–2847	2972, 2914	2976	2916	2914	2916	-	2914	2997
	δ (CH2) alkane	1460	1417	1450	1450	1415	1417	1452	1417	1417
	ν (C = O)	1689	1664	1699	1666	1664	1664	1664	1664	-
	ν (C-O)	1236	1290	1284	1284	1290	1236	1284	1290	1253
	ν (M-O)		457	457	480	480	457	457	459	457
	δ (CH) arom.	-	-	775	-	-	-	-	-	-
	ν (C-Cl)	-	-	-	572	-	-	-	-	-
	ν (N-H)	-	-	-	-	-	-	-	-	3273

Fig. 6 (a) Solid state UV-visible spectra of complex 1, a (1a), b (1a-benzene), c (1a-DCM), d (1a-DMF), e (1a-ethanol). (b) Solid state UV-visible spectra of complex 2, a (2a), b (2a-benzene), c (2a-DCM), d (2a-DMF), e (2a-ethanol), f (2a-methanol).

Table 4 Electronic absorption maxima (λ_max) and vapochromic shift for solid state complex 1.

Absorption solvent (VOCs)	Electronic absorption λmax (nm)	Vapochromic shift λmax (nm)
None	383	0
Benzene	400	17
Dichloromethane	407	24
Dimethylformamide	421	38
Ethanol	400	17

Vapochromic shift λ_max = λ_max(VOC) – λ_max(none).

Table 5 Colours of 2 as synthesized, activated and after exposure to VOCs, and their selected FT-IR band frequencies.

Complex		2	2a	2a-Benzene	2a-DCM	2a-DMF	2a-DMSO	2a-EtOH	2a-MeOH	2a-NH3
Colour		Peach	Purple	Pale pink	Pale pink	Pink	Pink	Sunset orange	Champagne pink	Peach yellow
IR (cm^−1)	ν(O-H)	3362, 3244	3362, 3232	3373, 3221	3371, 3240	3356, 3246	3371, 3240	3362, 3257	3362, 3238	3346, 3313
	ν(C = O)	1716	1716	1726	1715	-	1705	1716	1716	-
	ν(C = C)	1595	1891	1595	1591	1591	1591	1593	1593	1595
	ν(C-O)	1232	1232	1232	1232	1232	1232	1232	1232	1242
	δ(O-H)	1419	-	1419	1419	-	1419	1419	1419	1417
	δ(C-H)	775	775	775	775	775	775	775	775	773
	ν(M-N)	542	-	542	572	-	-	-	536	-
	ν(M-O)	457	455	495	491	491	-	-	493	418
	ν(N-H)	-						-	-	3242, 3184

Table 6 Electronic absorption maxima (λ_max) and vapochromic shift for solid state complex 2.

Absorption solvent (VOCs)	Electronic absorption λmax (nm)	Vapochromic shift λmax (nm)
None	370	0
Benzene	378	8
Dichloromethane	381	11
Dimethylformamide	397	27
Ethanol	387	17
Methanol	493	123

Vapochromic shift λ_max = λ_max(VOC) – λ_max(none).