Theoretical Studies of Structural Design and Stability of Double-layered Sandwich-like Tetrapyrrolic Uranium Complexes†

doi:10.7503/cjcu20170463

Abstract

Abstract:

To explore the interaction between tetrapyrrolic ligand and low-valent uranium ion, double-layered Sandwich-like complexes PzU^mPzU^mPz(labeled as $U^{m}_{2}$ Pz₃; m=Ⅲ and Ⅳ, Pz=porphyrazine) were designed according to the single-layered PcU^ⅥPc(Pc=phthalocyanine) that was experimentally synthesized. Relativistic density functional theory(RDFT) was used to examine structures, stability and chemical bonding. It is shown that complexes $U^{m}_{2}$Pz₃ have the quintet ground state. Steric configurations are found to have a little effect on isomeric stability, while electron-spin states play more important role. Topological analyses of electron density suggest weakly polarized covalent character for U-N bonds. Tetravalent diuranium complex possesses four U(5f)-character high-lying occupied orbitals, in accordance with U^Ⅵ 5f-electron number counting. Differently, some electron transfer from uranium to ligand(Pz) is unraveled for the trivalent complex, leading to more ligand contribution to frontier molecular orbitals.

Key words: Sandwich-like tetrapyrrolic uranium complex, Stability of isomer, Quantum theory of atoms in molecule(QTAIM), Electronic structure, Relativistic density functional theory

CLC Number:

O641

TrendMD:

TIAN Linfei, ZHANG Chunhua, QU Ning, BI Yanting, ZHANG Hongxing, PAN Qingjiang. Theoretical Studies of Structural Design and Stability of Double-layered Sandwich-like Tetrapyrrolic Uranium Complexes^†[J]. Chem. J. Chinese Universities, 2018, 39(4): 749.

Figures/Tables 10

Fig.1 Structures of U2mPz3(m=Ⅳ, Ⅲ)

Fig.2 Relative energies of se- and es-configuration Um2Pz3[m=Ⅳ(A), Ⅲ(B)] in various electron-spin states

Table 1 Relative energy of Um2Pz3(m=Ⅳ, Ⅲ) complexes in various configurations(staggered-eclipsed and eclipsed-staggered) and electron-spin states(ESS)

Complex	Config.	ESS	ΔE^a/(kJ·mol^-1)	Δ $E 0 a$ /(kJ·mol^-1)	ΔG^a/(kJ·mol^-1)	ΔH^a/(kJ·mol^-1)
$U 2 Ⅳ$ Pz₃	se	Singlet	86.6	82.2	89.5	81.4
		Triplet	11.7	11.1	12.5	11.2
		Quintet	0	0	0	0
	es	Singlet	92.9	91.5	99.2	90.6
		Triplet^b	23.6	16.9	21.8	14.2
		Quintet	0.2	2.4	6.2	1.9
$U 2 Ⅲ$ Pz₃	se	Singlet	77.8	70.9	70.2	71.7
		Triplet	7.9	3.5	5.4	1.5
		Quintet	2.9	-0.2	3.2	-2.0
		Septet	10.0	9.1	5.0	9.6
	es	Singlet	82.0	76.7	77.3	77.1
		Triplet	6.7	5.0	3.9	5.4
		Quintet	0	0	0	0
		Septet	10.0	9.2	12.0	7.1

Table 1 Relative energy of Um2Pz3(m=Ⅳ, Ⅲ) complexes in various configurations(staggered-eclipsed and eclipsed-staggered) and electron-spin states(ESS)

Complex	Config.	ESS	ΔE^a/(kJ·mol^-1)	Δ $E 0 a$ /(kJ·mol^-1)	ΔG^a/(kJ·mol^-1)	ΔH^a/(kJ·mol^-1)
$U 2 Ⅳ$ Pz₃	se	Singlet	86.6	82.2	89.5	81.4
		Triplet	11.7	11.1	12.5	11.2
		Quintet	0	0	0	0
	es	Singlet	92.9	91.5	99.2	90.6
		Triplet^b	23.6	16.9	21.8	14.2
		Quintet	0.2	2.4	6.2	1.9
$U 2 Ⅲ$ Pz₃	se	Singlet	77.8	70.9	70.2	71.7
		Triplet	7.9	3.5	5.4	1.5
		Quintet	2.9	-0.2	3.2	-2.0
		Septet	10.0	9.1	5.0	9.6
	es	Singlet	82.0	76.7	77.3	77.1
		Triplet	6.7	5.0	3.9	5.4
		Quintet	0	0	0	0
		Septet	10.0	9.2	12.0	7.1

Table 2 Optimized geometry parameters of U2ⅣPz3

Species	se			es		Expt.^h
Species	Singlet	Triplet	Quintet	Singlet	Quintet	Expt.^h
U1-U2/nm	0.3513	0.3568	0.3611	0.3499	0.3607	0.331
U1-N(Pz1 $) av a$ /nm	0.2326	0.2342	0.2346	0.2348	0.2355
U1-N(Pz2 $) av a$ /nm	0.2588	0.2604	0.2619	0.2568	0.2633	0.242-0.248
(U1-N $) av b$ /nm	0.2457	0.2473	0.2482	0.2458	0.2494
U2-N(Pz2 $) av a$ /nm	0.2588	0.2603	0.2619	0.2585	0.2607	0.243-0.253
U2-N(Pz3 $) av a$ /nm	0.2326	0.2342	0.2346	0.2341	0.2350
(U2-N $) av b$ /nm	0.2457	0.2472	0.2482	0.2463	0.2479
U1-N4(Pz1)^c/nm	0.1262	0.1290	0.1291	0.1303	0.1304
U1-N4(Pz2)^c/nm	0.1752	0.1785	0.1806	0.1735	0.1823
U1-N $4 av d$ /nm	0.1507	0.1538	0.1548	0.1519	0.1563
U2-N4(Pz2)^c/nm	0.1752	0.1784	0.1806	0.1761	0.1785
U2-N4(Pz3)^c/nm	0.1262	0.1290	0.1291	0.1289	0.1298
U2-N $4 av d$ /nm	0.1507	0.1537	0.1548	0.1525	0.1541
U1-(Pz2)_cent.-U2^e/(°)	180.0	180.0	180.0	179.3	180.0
h1^f/(°)	44.9	52.7	48.9	19.0^g	-12.8^g
h2^f/(°)	0.8	0.2	7.7	42.5	30.8

Table 2 Optimized geometry parameters of U2ⅣPz3

Species	se			es		Expt.^h
Species	Singlet	Triplet	Quintet	Singlet	Quintet	Expt.^h
U1-U2/nm	0.3513	0.3568	0.3611	0.3499	0.3607	0.331
U1-N(Pz1 $) av a$ /nm	0.2326	0.2342	0.2346	0.2348	0.2355
U1-N(Pz2 $) av a$ /nm	0.2588	0.2604	0.2619	0.2568	0.2633	0.242-0.248
(U1-N $) av b$ /nm	0.2457	0.2473	0.2482	0.2458	0.2494
U2-N(Pz2 $) av a$ /nm	0.2588	0.2603	0.2619	0.2585	0.2607	0.243-0.253
U2-N(Pz3 $) av a$ /nm	0.2326	0.2342	0.2346	0.2341	0.2350
(U2-N $) av b$ /nm	0.2457	0.2472	0.2482	0.2463	0.2479
U1-N4(Pz1)^c/nm	0.1262	0.1290	0.1291	0.1303	0.1304
U1-N4(Pz2)^c/nm	0.1752	0.1785	0.1806	0.1735	0.1823
U1-N $4 av d$ /nm	0.1507	0.1538	0.1548	0.1519	0.1563
U2-N4(Pz2)^c/nm	0.1752	0.1784	0.1806	0.1761	0.1785
U2-N4(Pz3)^c/nm	0.1262	0.1290	0.1291	0.1289	0.1298
U2-N $4 av d$ /nm	0.1507	0.1537	0.1548	0.1525	0.1541
U1-(Pz2)_cent.-U2^e/(°)	180.0	180.0	180.0	179.3	180.0
h1^f/(°)	44.9	52.7	48.9	19.0^g	-12.8^g
h2^f/(°)	0.8	0.2	7.7	42.5	30.8

Table 3 Optimized geometry parameters of U2ⅢPz3

Species	se			es
Species	Singlet	Triplet	Quintet	Septet	Singlet	Triplet	Quintet	Septet
U1-U2/nm	0.3400	0.3521	0.3548	0.3548	0.3391	0.3497	0.3504	0.3557
U1-N(Pz1 $) av a$ /nm	0.2338	0.2346	0.2352	0.2378	0.2356	0.2372	0.2374	0.2382
U1-N(Pz2 $) av a$ /nm	0.2554	0.2588	0.2598	0.2603	0.2547	0.2575	0.2573	0.2597
(U1-N $) av b$ /nm	0.2446	0.2467	0.2475	0.2490	0.2452	0.2474	0.2473	0.2490
U2-N(Pz2 $) av a$ /nm	0.2554	0.2589	0.2598	0.2605	0.2548	0.2593	0.2602	0.2613
U2-N(Pz3 $) av a$ /nm	0.2338	0.2346	0.2352	0.2359	0.2334	0.2351	0.2354	0.2357
(U2-N $) av b$ /nm	0.2446	0.2467	0.2475	0.2482	0.2441	0.2472	0.2478	0.2485
U1-N4(Pz1)^c/nm	0.1279	0.1291	0.1298	0.1335	0.1307	0.1328	0.1329	0.1340
U1-N4(Pz2)^c/nm	0.1700	0.1760	0.1774	0.1773	0.1695	0.1736	0.1731	0.1767
U1-N $4 av d$ /nm	0.1490	0.1526	0.1536	0.1554	0.1501	0.1532	0.1530	0.1554
U2-N4(Pz2)^c/nm	0.1700	0.1761	0.1774	0.1775	0.1696	0.1761	0.1773	0.1790
U2-N4(Pz3)^c/nm	0.1279	0.1291	0.1297	0.1308	0.1325	0.1298	0.1302	0.1301
U2-N $4 av d$ /nm	0.1490	0.1526	0.1536	0.1541	0.1510	0.1530	0.1537	0.1546
U1-(Pz2)_cent.-U2^e/(°)	180.0	180.0	180.0	180.0	180.0	180.0	180.0	180.0
h1^f/(°)	45.1	45.2	49.1	50.9	-0.1	0.2	-0.2	0.2
h2^f/(°)	0.8	-0.7	7.4	30.5^g	44.8	38.8	36.9	44.2

Table 3 Optimized geometry parameters of U2ⅢPz3

Species	se			es
Species	Singlet	Triplet	Quintet	Septet	Singlet	Triplet	Quintet	Septet
U1-U2/nm	0.3400	0.3521	0.3548	0.3548	0.3391	0.3497	0.3504	0.3557
U1-N(Pz1 $) av a$ /nm	0.2338	0.2346	0.2352	0.2378	0.2356	0.2372	0.2374	0.2382
U1-N(Pz2 $) av a$ /nm	0.2554	0.2588	0.2598	0.2603	0.2547	0.2575	0.2573	0.2597
(U1-N $) av b$ /nm	0.2446	0.2467	0.2475	0.2490	0.2452	0.2474	0.2473	0.2490
U2-N(Pz2 $) av a$ /nm	0.2554	0.2589	0.2598	0.2605	0.2548	0.2593	0.2602	0.2613
U2-N(Pz3 $) av a$ /nm	0.2338	0.2346	0.2352	0.2359	0.2334	0.2351	0.2354	0.2357
(U2-N $) av b$ /nm	0.2446	0.2467	0.2475	0.2482	0.2441	0.2472	0.2478	0.2485
U1-N4(Pz1)^c/nm	0.1279	0.1291	0.1298	0.1335	0.1307	0.1328	0.1329	0.1340
U1-N4(Pz2)^c/nm	0.1700	0.1760	0.1774	0.1773	0.1695	0.1736	0.1731	0.1767
U1-N $4 av d$ /nm	0.1490	0.1526	0.1536	0.1554	0.1501	0.1532	0.1530	0.1554
U2-N4(Pz2)^c/nm	0.1700	0.1761	0.1774	0.1775	0.1696	0.1761	0.1773	0.1790
U2-N4(Pz3)^c/nm	0.1279	0.1291	0.1297	0.1308	0.1325	0.1298	0.1302	0.1301
U2-N $4 av d$ /nm	0.1490	0.1526	0.1536	0.1541	0.1510	0.1530	0.1537	0.1546
U1-(Pz2)_cent.-U2^e/(°)	180.0	180.0	180.0	180.0	180.0	180.0	180.0	180.0
h1^f/(°)	45.1	45.2	49.1	50.9	-0.1	0.2	-0.2	0.2
h2^f/(°)	0.8	-0.7	7.4	30.5^g	44.8	38.8	36.9	44.2

Table 4 Calculated electron-spin density(SU) and charge(QU) of the uranium atom of Um2Pz3(m=Ⅳ, Ⅲ) complexes

Complex	Config.	ESS	Q_U1/e	Q_U2/e	S_U1/a.u.	S_U2/a.u.
$U 2 Ⅳ$ Pz₃	se	Singlet	2.057	2.058	0	0
		Triplet	2.048	2.048	1.627	1.627
		Quintet	2.035	2.035	1.877	1.877
	es	Singlet	2.030	2.035	0	0
		Triplet^*	2.043	2.031	1.470	1.741
		Quintet	2.028	2.007	1.879	1.995
$U 2 Ⅲ$ Pz₃	se	Singlet	2.027	2.027	0	0
		Triplet	2.024	2.024	1.747	1.749
		Quintet	2.013	2.013	1.924	1.926
		Septet	1.968	1.996	2.171	2.047
	es	Singlet	2.025	2.002	0	0
		Triplet	2.012	1.985	1.777	1.958
		Quintet	2.004	1.979	1.918	2.013
		Septet	1.992	1.963	2.059	2.158

Table 4 Calculated electron-spin density(SU) and charge(QU) of the uranium atom of Um2Pz3(m=Ⅳ, Ⅲ) complexes

Complex	Config.	ESS	Q_U1/e	Q_U2/e	S_U1/a.u.	S_U2/a.u.
$U 2 Ⅳ$ Pz₃	se	Singlet	2.057	2.058	0	0
		Triplet	2.048	2.048	1.627	1.627
		Quintet	2.035	2.035	1.877	1.877
	es	Singlet	2.030	2.035	0	0
		Triplet^*	2.043	2.031	1.470	1.741
		Quintet	2.028	2.007	1.879	1.995
$U 2 Ⅲ$ Pz₃	se	Singlet	2.027	2.027	0	0
		Triplet	2.024	2.024	1.747	1.749
		Quintet	2.013	2.013	1.924	1.926
		Septet	1.968	1.996	2.171	2.047
	es	Singlet	2.025	2.002	0	0
		Triplet	2.012	1.985	1.777	1.958
		Quintet	2.004	1.979	1.918	2.013
		Septet	1.992	1.963	2.059	2.158

Fig.3 Difference of spin density of uranium atom(ΔSU) of se- and es-configurationUm2Pz3[(m=Ⅳ(A), Ⅲ(B)] in various electron-spin states from the respective expected formal value,i.e., 0, 1, 2 and 3 for the singlet, triplet, quintet and septet states, respectively.

Table 5 QTAIM parameters for the U-N bond of ground-state Um2Pz3(m=Ⅳ, Ⅲ) in various steric configurations, including electron density[ρ(r)], Laplacian[?2ρ(r)] and energy density[H(r)] at BCPs

BCP	Parameter^*	$U 2 Ⅳ$ Pz₃		$U 2 Ⅲ$ Pz₃
BCP	Parameter^*	se	es	se	es
U1-N(Pz1)	ρ(r)/a.u.	0.0861	0.0853	0.0841	0.0839
	?²ρ(r)/a.u.	0.2083	0.2047	0.2109	0.2080
	H(r)/a.u.	-0.0203	-0.0198	-0.0190	-0.0189
U1-N(Pz2)	ρ(r)/a.u.	0.0467	0.0478	0.0499	0.0477
	?²ρ(r)/a.u.	0.1299	0.1387	0.1324	0.1638
	H(r)/a.u.	-0.0030	-0.0032	-0.0041	-0.0027
U2-N(Pz2)	ρ(r)/a.u.	0.0468	0.0451	0.0477	0.0497
	?²ρ(r)/a.u.	0.1301	0.1268	0.1496	0.1301
	H(r)/a.u.	-0.0030	-0.0029	-0.0028	-0.0042
U2-N(Pz3)	ρ(r)/a.u.	0.0861	0.0831	0.0799	0.0740
	?²ρ(r)/a.u.	0.2088	0.2055	0.2391	0.2349
	H(r)/a.u.	-0.0203	-0.0189	-0.0162	-0.0133

BCP	Parameter^*	$U 2 Ⅳ$ Pz₃		$U 2 Ⅲ$ Pz₃
BCP	Parameter^*	se	es	se	es
U1-N(Pz1)	ρ(r)/a.u.	0.0861	0.0853	0.0841	0.0839
	?²ρ(r)/a.u.	0.2083	0.2047	0.2109	0.2080
	H(r)/a.u.	-0.0203	-0.0198	-0.0190	-0.0189
U1-N(Pz2)	ρ(r)/a.u.	0.0467	0.0478	0.0499	0.0477
	?²ρ(r)/a.u.	0.1299	0.1387	0.1324	0.1638
	H(r)/a.u.	-0.0030	-0.0032	-0.0041	-0.0027
U2-N(Pz2)	ρ(r)/a.u.	0.0468	0.0451	0.0477	0.0497
	?²ρ(r)/a.u.	0.1301	0.1268	0.1496	0.1301
	H(r)/a.u.	-0.0030	-0.0029	-0.0028	-0.0042
U2-N(Pz3)	ρ(r)/a.u.	0.0861	0.0831	0.0799	0.0740
	?²ρ(r)/a.u.	0.2088	0.2055	0.2391	0.2349
	H(r)/a.u.	-0.0203	-0.0189	-0.0162	-0.0133

Fig.4 Characteristic orbitals of U2ⅣPz3-se in the quintet(ground) state

Table 6 Contributions of α-spin orbitals of U2ⅣPz3-se in the quintet(ground) state

Orbital	Energy/eV	U1(%)		U2(%)		Ligand(%)	Assignment(%)
Orbital	Energy/eV	d	f			d	f
L+2	-5.878	1.57	43.89	1.58	43.83		5f
L+1	-5.883	1.43	44.03	1.44	43.56		5f
LUMO	-5.897		37.08		37.27		5f
HOMO	-5.912		43.58		43.68		5f
H-1	-5.942		35.41		33.91		5f
H-2	-5.967		22.03		22.10	26.31	5f+L
H-3	-6.183	2.73	44.38	2.73	44.28		5fσ
H-4	-6.634					72.88	L
H-5	-6.919					86.28	L

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