mjhjmtu

I am trying to construct this EDTA molecule coordinated to a metal:

and this is what I have so far:

With this code:

chemfig
 O=[2,,]C
 (-[3,2,,1]CH_2-[1,,1]N
 (-[7,,,2]H_2C-[0,,]C
 (=[7,,]O)
 (-[1,,]O^-))
 (-[4,,,2]H_2C-[2,,2,2]H_2C-[0,,]N
 (-[1,,,2]H_2C-[0,,2]C
 (=[1,,]O)
 (-[7,,]O^-))
 (-[3,,,2]H_2C-[1,2,2]C
 (=[2,,]O)
 (-[7,,]O^-))))
 (-[1,,]O^-)

What I can't figure out how to do is include the metal in the center. I know I have to use hooks somehow but I don't know where to start. Would I have to start over and begin the figure at the metal?

Bonus question: how do I change the color of the bonds to the metal?

Placing the M is rather straightforward: use chemmove, which produces an overlay tikzpicture and then e.g. the calc syntax. What I find more difficult is to reproduce the bond styles. I ended up looking up the definitions and then to repeat what I think they do. (EDIT: Minor fine-tuning, big thanks to AndréC for pushing me.)

documentclassarticle

usepackagechemfig
usetikzlibrarycalc
begindocument
chemfig
 O=[2,,]C
 (-[3,1.8,,1]CH_2-[1,,1]@N1N
 (-[7,,,2]H_2C-[0,,]@C1C
 (=[7,,]O)
 (-[1,,]@OM1O^-))
 (-[4,,,2]H_2C-[2,,2,2]H_2C-[0,,]@N2N
 (-[1,,,2]H_2C-[0,,2]@C2C
 (=[1,,]O)
 (-[7,,]@OM2O^-))
 (-[3,1.2,,2]H_2C-[1,2,2]C
 (=[2,,]O)
 (-[7,,]@OM3O^-))))
 (-[1,,]@OM4O^-)

chemmove[brown!70!black]M.center);
beginscope
clip let p1=($(M)-(OM2)$),n1=atan2(y1,x1) in 
($(OM2.n1)!1mm!(M)$) coordinate (aux3) (M) -- 
($ (aux3)!1mm!90:(M) $) -- ($ (aux3)!1mm!-90:(M) $)
-- cycle;
draw[-,line width=2mm, dash pattern=on 1pt off 2pt,line cap=butt] (M) --(aux3);
endscope
beginscope
clip let p1=($(M)-(N2)$),n1=atan2(y1,x1) in 
($(N2.n1)!1mm!(M)$) coordinate (aux4) (M) -- 
($ (aux4)!1mm!90:(M) $) -- ($ (aux4)!1mm!-90:(M) $)
-- cycle;
draw[-,line width=2mm, dash pattern=on 1pt off 2pt,line cap=butt] (M) --(aux4);
endscope

enddocument