Dinuclear Nickel(II) Complexes of Phenol-Based “End-Off” Compartmental Ligands and Their Urea Adducts Relevant to the Urease Active Site

Two phenol-based compartmental ligands of the “end-off” type,
2,6-bis{N-[2-(dimethylamino)ethyl]iminomethyl}-4-methylphenol (HL1) and
2-{N-[2-(dimethylamino)ethyl]iminomethyl}-6-{N-methyl-N-[2-(dimethylamino)ethyl]aminomethyl}-4-bromophenol (HL2), have been used to form
[Ni2(L1)(AcO)(NCS)2(MeOH)]
(1),
[Ni2(L1)(AcO)2(MeOH)]BPh4 (2),
[Ni2(L2)(AcO)(NCS)2(MeOH)]
(3),
[Ni2(L2)(AcO)2]BPh4
(4), and
[Ni2(L2)(NCS)3(MeOH)]
(5). X-ray crystallographic studies were done for
2−5. 2:  triclinic, space
group P1̄, a = 13.613(3) Å, b
=
16.475(4) Å, c = 11.307(4) Å, α =
99.90(2)°, β = 104.16(2)°, γ = 109.01(2)°,
V = 2253(1) Å3, Z = 2.
The
complex cation has a dinuclear core triply bridged by the phenolic
oxygen of (L1)- and two acetate groups in
the
syn-syn mode. One Ni has a six-coordinate geometry together with a
methanol oxygen. 3: triclinic, space group
P1̄, a = 10.167(1) Å, b
= 16.119(2) Å, c = 9.472(3) Å, α =
103.53(2)°, β=100.91(1)°, γ = 85.62(1)°,
V =
1481(1) Å3, Z = 2. A pair of Ni
ions are bridged by the phenolic oxygen of
(L2)-, an isothiocyanate
nitrogen,
and an acetate group. The sixth position of one Ni is occupied by
a methanol oxygen and that of the other Ni
by isothiocyanate nitrogen. 4:  monoclinic, space
group P21/n, a =
15.146(2) Å, b = 9.442(3) Å, c =
30.844(2)
Å, β = 93.427(9)°, V = 4402(1)
Å3, Z = 4. Two Ni ions are bridged by
the phenolic oxygen of (L2)- and
an
acetate group. The Ni bound to the iminic pendant arm is nearly
planar whereas the Ni bound to the aminic
pendant arm is of six-coordination together with a bidentate acetate
group. 5:  monoclinic, space group
C2/c, a
= 26.744(5), b = 10.323(4) Å, c
= 21.785(6) Å, β = 94.73(2)°, V = 5993(3)
Å3, Z = 8. Two Ni ions are
bridged by the phenolic oxygen of (L2)- and
an isothiocyanate nitrogen. The Ni bound to the iminic
pendant
arm is of five-coordination along with an isothiocyanate nitrogen.
The Ni bound to the aminic pendant arm has
a six-coordinate geometry together with a methanol oxygen and an
isothiocyanate nitrogen. 1−5 were
examined
regarding their ability to bind urea, and 4 and 5
were shown to form
[Ni2(L2)(AcO)2(urea)]BPh4
(4‘) and [Ni2(L2)(NCS)3(urea)] (5‘),
respectively. 5‘ crystallizes in the monoclinic system,
space group P21/n, with a
= 11.709(5), b = 15.100(4), c = 17.548(5)
Å, β = 95.58(3)°, V = 3087(1)
Å3, and Z = 4. Its dinuclear core is
very
similar to that of 5 except that the methanol of
5 is replaced by a urea molecule.